| 1. |
- Nourozi, Behrouz, 1986-, et al.
(författare)
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Heat transfer model for energy-active windows – An evaluation of efficient reuse of waste heat in buildings
- 2020
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 162, s. 2318-2329
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Tidskriftsartikel (refereegranskat)abstract
- Minimizing thermal losses through windows and maintaining large glazing areas to provide adequate natural lighting in residential buildings are essential considerations for modern architecture, sustainability, and indoor comfort. In this study, a detailed heat transfer model for a novel energy-active window (EAW) is developed and validated to rate its thermal performance. An EAW utilizes low-grade heat to reduce building heat losses during the winter season. A thorough literature review was conducted to select the correct heat-transfer correlations for the investigated configuration. A two-dimensional finite differencing scheme was applied to approximate the vertical and horizontal temperature distribution across the EAW. Detailed temperature gradients, across the height and width of the window, were obtained. Thorough sensitivity analyses of the governing parameters were conducted to evaluate the windows' thermal performance. The results indicate that EAWs have the potential to reduce heating power demand by approximately 2.2 W/m(2) floor area and 1.3 W/m(2) floor area at outdoor temperatures of-20 degrees C and-5 degrees C, respectively, for buildings with a window-to-floor area ratio of 10%. This potential increases proportionally with the ratio. The highest thermal efficiency of EAW is achieved when the temperature of the supplied air inside the EAW is equal to or above room temperature.
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| 2. |
- Nourozi, Behrouz, 1986-, et al.
(författare)
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Integrated Energy Active Windows with Low-Temperature Heating Systems in Cold Climates
- 2020
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Konferensbidrag (refereegranskat)abstract
- This study investigated the thermal performance of energy active windows (EAW). The obtained U-values of the studied EAW were compared to state-of-the-art triple-glazing windows (TGW) during a heating season. Simulation software, Matlab, was used for analytical heat transfer modeling of the studied window- types and to illustrate temperature gradients across the windows. The main objective was to evaluate how lower U-values during the coldest winter hours can be achieved to potentially shift peak heating loads of buildings. Generally, it was shown that the EAW had lower U-values compared to conventional TGW. It is concluded that windows, which have always been considered as a heat sink in constructions, can maintain building energy requirements while improving the indoor environment quality, the aesthetics, and natural lighting in buildings if replaced by EAW.
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| 3. |
- Abdi, Amir, et al.
(författare)
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Experimental investigation of solidification and melting in a vertically finned cavity
- 2021
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- Extending the heat transfer area is a simple technique to improve the thermal performance of phase change materials with low thermal conductivity. However, as the governing mechanisms differ in solidification and melting, fins can affect the processes in different ways. This demands assessment of fin enhancement in a combined analysis on both solidification and melting, often neglected in literature. This paper presents visual-izations of solidification and melting of n-eicosane in a rectangular cavity and experimentally investigates the enhancing effect of vertical fins with varying number and length. Experiments were conducted at water inlet temperature ranges of 15-25 degrees C and 50-60 degrees C for the solidification and melting processes, respectively. The results show that the vertical fins can be more influential in solidification rather than in melting with similar losses in the storage capacity. In the solidification process, as natural convection is absent, the mean power is enhanced by a maximum of 395% with a 10% loss in the storage capacity, as compared to the benchmark. In the melting case, the mean power is increased by a maximum of 90% with a 9% loss in the storage capacity. Although increasing the surface area with vertical fins contributes to development of convective structures, it makes a modest enhancement. In overall, increasing the fin volume fraction, in exchange for the loss in the storage capacity, enhances the solidification significantly while it has relatively low enhancement effect in melting. At the end, the performed experiments could be helpful for validation of future simulation tools with complex features, particularly solidification models lacking in literature.
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| 4. |
- Abdi, Amir, et al.
(författare)
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Experimental investigation of thermo-physical properties of n-octadecane and n-eicosane
- 2020
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Ingår i: International Journal of Heat and Mass Transfer. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0017-9310 .- 1879-2189. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- Reliable knowledge of phase change materials (PCM) thermo-physical properties is essential to model and design latent thermal energy storage (LTES) systems. This study aims to conduct a methodological measurement of thermo-physical properties, including latent enthalpy, isobaric specific heat, thermal conductivity and dynamic viscosity, of two n-alkanes, n-octadecane and n-eicosane. The enthalpy and isobaric specific heat of the materials are measured via differential scanning calorimetry (DSC) technique, using a pDSC evo7 from Setaram Instrumentation with a sample mass of 628.4 mg. The influence of the scanning rates, varying from 0.5 K/min to 0.025 K/min, in dynamic continuous mode within temperature range of 10-65 degrees C is investigated. The thermal conductivity and the dynamic viscosity are measured via Hot Disk TPS-2500S instrument and Brookfield rotational viscometer, respectively, up to 70 degrees C. The thermal analysis results via the pDSC show that the isothermal condition can be approached at a very low scanning rate, however at the cost of a higher noise level. A trade-off is observed for n-octadecane, achieving the lowest deviation of 0.7% in latent heat measurement at 0.05 K/min, as compared to the American Petroleum Table values. For n-eicosane, the lowest deviation of 1.2% is seen at the lowest scanning rate of 0.025 K/min. The thermal conductivity measured values show good agreements with a number of documented literature studies in the solid phase, within deviations of 2%. Larger deviations of 5-16% are found for the measurement in the liquid phase. The viscosity values also show a good agreement with the literature values with maximum deviations of 2.9% and 6.3%, with respect to the values of American Petroleum Tables, for n-octadecane and n-eicosane, respectively. The good agreements achieved in measurements establish the reliable thermo-physical properties contributing to the future simulations and designs.
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| 5. |
- Abdi, Amir, 1987-
(författare)
-
Heat Transfer Enhancement of Latent Thermal Energy Storage in Rectangular Components
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Latent Thermal Energy Storage (LTES) is an interesting choice to storethermal energy in a sustainable energy system. The primary benefit of LTESis the relatively high latent heat of fusion of the materials, known as PhaseChange Materials (PCM), used in such a system as the storage medium.However, as the thermal conductivity of PCMs is often very low, there is aneed to enhance the rate of heat transfer within the charging/dischargingprocess and to improve the thermal performance of the LTES systems.This thesis addresses the enhancing effect of extending heat transfer area inrectangular LTES enclosures. A key contribution of this thesis is acomprehensive visualization of the phase change processes for an organicPCM, including solidification and melting, constrained as well asunconstrained, known as Close-Contact Melting (CCM), in a cavity with andwithout fins. Observations have been carried out for fins of different lengthsand numbers with a varying angle of inclination, and a comprehensive analysisin terms of phase change time and thermal power is conducted.The observations show fins are more influential in solidification than inmelting, reducing the solidification time by 80% and increasing the meanpower by 395%, at a cost of 10% loss in the extracted energy. In contrast, inmelting, fins have a modest effect in enhancing the process. The relativeenhancement effect of fin is higher in constrained melting than inunconstrained melting. In a case with maximum enhancement, a reduction by52% in the constrained melting time and a relative enhancement in the meanpower by 90% is achieved at a cost of 9% loss in the stored energy. As thevolume fraction of fin increases, the discrepancies in melting time betweenthe constrained and unconstrained melting diminishes.A numerical model for solidification and constrained melting is validatedbased on the experiments, and a more inclusive sensitivity analysis of finparameters is performed. The enhancing effect of different parameters on thephase change time and the thermal power is analyzed and the relatively moreeffective measures are identified. Analyzing the simulation data withdimensionless parameters for a cavity oriented horizontally and enhancedwith vertical fins, overall dimensionless groups for solidification and constrained melting have been obtained. The dimensionless groupscontribute in general to achieving a better understanding of fins parametersand to facilitating the LTES designs.In addition, this thesis investigates a novel idea of extending the surface areavia incorporating mini-channels into LTES enclosures, used as passages forair as a low thermal conductive Heat Transfer Fluid (HTF). The mini-scaleinternal hydraulic diameter of the mini-channels and their high external areato-volume ratios make a potential for dual enhancement on both the PCMside and the HTF side. An existing design and a conceptual one with thepossibility of adding fins on the PCM side, capable of being manufactured viaproduction methods of extrusion and Additive Manufacturing (AM),respectively, have been simulated and studied.The two mini-channel types provide considerable enhancements in the rateof heat transfer for a PCM heat exchanger working with air. The degree ofenhancement increases as the air flow rate increases, at the cost of anincreasingly higher pressure drop. Regarding this, increasing the number ofchannels is identified as a more effective enhancing measure than adding finsto the PCM side. In addition, the conceptual design with a higher internalhydraulic diameter and considerably a higher aspect ratio has a lower pressuredrop than the existing design, charging/discharging the thermal energy at asimilar rate but with a lower fan power. More optimized designs withminimization of pressure drop, contribute to paving the way in facilitation ofthe utilization of the enhanced air-PCM heat exchanger in variousapplications.
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| 6. |
- Abdi, Amir, et al.
(författare)
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Numerical Investigation of Latent Thermal Storage in a Compact Heat Exchanger Using Mini-Channels
- 2021
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:13, s. 5985-
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with d(h) = 1.6 mm and channel-2 with d(h) = 2.3 mm) are oriented vertically in a cuboid of 0.15 x 0.15 x 0.1 m(3) with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15-31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41-53% and increasing the mean UA values within melting by 19-52% for a packing factor range of 77.4-86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation.
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| 7. |
- Abdi, Amir, et al.
(författare)
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Numerical investigation of melting in a cavity with vertically oriented fins
- 2019
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Ingår i: Applied Energy. - : ELSEVIER SCI LTD. - 0306-2619 .- 1872-9118. ; 235, s. 1027-1040
-
Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the effect of vertical fins, as an enhancement technique, on the heat transfer rate and energy density of a latent heat thermal energy storage system. This contributes with knowledge on the interaction of heat transfer surface with the storage material for optimizing storage capacity (energy) and power (heat transfer rate). For the assessment, numerical modeling is employed to study the melting process in a two-dimensional rectangular cavity. The cavity is considered heated isothermally from the bottom with surface temperatures of 55 degrees C, 60 degrees C or 70 degrees C, while the other surfaces are insulated from the surrounding. Aluminum and lauric acid are considered as fin/enclosure material and phase change material, respectively. Vertical fins attached to the bottom surface are employed to enhance the charging rate, and a parametric study is carried out by varying the fin length and number of fins. Thus, a broad range of data is provided to analyze the influence of fin configurations on contributing natural convection patterns, as well as the effects on melting time, enhanced heat transfer rate and accumulated energy. The results show that in addition to increasing the heat transfer surface area, the installation of vertically oriented fins does not suppress the natural convection mechanism. This is as opposed to horizontal fins which in previous studies have shown tendencies to reduce the impact of natural convection. This paper also highlights how using longer fins offers a higher rate of heat transfer and a better overall heat transfer coefficient rather than increasing the number of fins. Also, fins do not only enhance the heat transfer performance in the corresponding melting time, but also maintain similar total amount of stored energy as compared to the no-fin case. This paper discusses how this is the result of the enhanced heat transfer allowing a larger portion of sensible heat to be recovered. For example, in the case with long fins, the relative mean power enhancement is about 200% with merely 6% capacity reduction, even though the amount of PCM in the cavity has been reduced by 12% as compared to the no-fin case. Although the basis for these results stems from the principles of thermodynamics, this paper is bringing it forward with design consideration. This is because despite its importance for making appropriate comparisons among heat transfer enhancement techniques in latent heat thermal energy storage, it has not been previously discussed in the literature. In the end, the aim is to accomplish robust storage systems in terms of power and energy density.
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| 8. |
- Abdi, Amir, et al.
(författare)
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State of the art in hydrogen liquefaction
- 2020
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Ingår i: Proceedings of the ISES Solar World Congress 2019 and IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019. - Freiburg, Germany : International Solar Energy Society. ; , s. 1311-1320
-
Konferensbidrag (refereegranskat)abstract
- Hydrogen is a potential option to replace fossil fuels considering the increasing demand of energy applications. It is naturally abundant and is regarded as a suitable energy carrier. There has been extensive research to improve the efficiency of storing hydrogen with different methods, including gas compression, liquefaction and sorption in metal hydrides or carbon nanotubes. A comparison of the storage methods shows that liquefaction of hydrogen is more beneficial than compression of hydrogen in terms of higher volumetric capacity, and it is more technologically mature than sorption technologies. This makes it more plausible for long distance distribution. On the other hand, the obstacles in full exploitation of the method are low energy efficiency of the liquefaction process and associated high cost. The recent research has been focusing on increasing the energy efficiency of the storage process. This paper provides, with regard to the conventional methods, a state of the art review of the novel and modified liquefaction process and the latest developments in increasing the efficiency of the energy intensive process. Furthermore, the developments in combining the hydrogen liquefaction plants with renewable energy sources are covered and reviewed. Finally, the ongoing development of hydrogen liquefaction is highlighted.
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| 9. |
- Castro Flores, José Fiacro
(författare)
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Low-temperature based thermal micro-grids: operation and performance assessments
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy use in the urban environment is vital for the proper functioning of our society, and in particular, comfort heating –or cooling– is a central element of our energy system often taken for granted. Within this context, district energy systems and especially, district heating (DH) systems must evolve to adapt to the upcoming decades-long transition towards a sustainable energy system. This dissertation seeks to introduce, discuss, and assess from a techno-economic perspective the concept of low-temperature (LT) based thermal micro-grids (subnets) as active distribution thermal networks. It explores the role of the subnet at the system distribution level supervised by an active agent (DH substation), performing tasks of heat supply and demand management (storage and dispatch), as well as coordinating bidirectional flows. Here, a mixed methodological approach based on analytical simulation for the assessment of alternatives to evaluate a set of technologies is developed and discussed. This approach covers: the identification of knowledge gaps through the state-of-the-art analysis; a collection of incremental technical and/or economic performance assessments; and the analysis of a measurement data set from an existing LTDH demonstration project. Key findings of this work include: an updated and improved model of aggregated heat loads; identification of differences in load and temperature patterns for certain LT subnets; analysis of benefits and drawbacks of active substations with distributed heat sources and/or storage; and the impact on the reduction of the primary network return temperature as a consequence of the increase in the share of LT subnets, leading to lower generation and operating costs. These outcomes reveal that the integrated design and operation of the active thermal micro-grid have the potential to improve both the performance of the subnet, and that of the primary network. It further enhances the capability of the overall system to integrate unconventional and distributed heat sources together with energy efficient buildings by increasing the system’s flexibility and controllability. Active thermal distribution networks will likely become a subsequent step in the technological development of DH technologies, to address the matter of providing comfort heating in an effective and cost-efficient manner. This work advances the current DH knowledge by identifying synergies and challenges that arise with these new developments, in order for DH technology to play a key role in the future smart and sustainable energy system.
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| 10. |
- Chiu, Justin NingWei, 1984-, et al.
(författare)
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Industrial Applications of Thermal Energy Storage Systems
- 2022
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Ingår i: Advances in Energy Storage. - : John Wiley & Sons.
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter provides an overview of the application of thermal energy storage in industrial scale systems, e.g. steel works, pulp mills, and also power generation and district heating and cooling utilities. The purpose is to illustrate the benefits of integrating thermal energy storage in such processes, from both a technical functional and economical perspectives. Examples of such benefits are resource efficiency, stability of operation, and lowered cost of fuel.
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| 11. |
- Fujii, S., et al.
(författare)
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Techno economic analysis of thermochemical energy storage and transport system utilizing "zeolite Boiler" : Case study in Sweden
- 2018
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Ingår i: Energy Procedia. - : Elsevier. - 1876-6102. ; , s. 102-111
-
Konferensbidrag (refereegranskat)abstract
- Thermochemical energy storage and transport system utilizing zeolite steam adsorption and desorption cycle is one of the methods to resolve the mismatch between industrial surplus heat and heat demands. To generate 60°C hot water utilizing zeolite 13X, zeolite boiler employing moving bed and indirect heat exchanger was developed. Pressurized water is heated up and flash steam is injected into the zeolite bed for adsorption. A quasi - 2D model solving heat and mass conservation equations was developed, leading to a performance characterization of this zeolite boiler. The developed simulation model was used to predict performance of a heat charging device employing moving bed as well. Based on this calculation, a case study, heat transporting between a local steel works and a hotel was examined and all corresponding cost were fixed. The Levelized Cost of Energy (LCOE) results in around 60 €/MWh which is comparable cost against conventional pellet boiler. Sensitivity analysis showed both of cheaper transportation cost and larger zeolite capacity on the one trailer give a comparable impact on the LCOE.
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| 12. |
- Gallardo, Felipe, 1989-, et al.
(författare)
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Assessing sizing optimality of OFF-GRID AC-linked solar PV-PEM systems for hydrogen production
- 2022
-
Ingår i: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487.
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Tidskriftsartikel (refereegranskat)abstract
- Herein, a novel methodology to perform optimal sizing of AC-linked solar PV-PEM systems is proposed. The novelty of this work is the proposition of the solar plant to electrolyzer capacity ratio (AC/AC ratio) as optimization variable. The impact of this AC/AC ratio on the Levelized Cost of Hydrogen (LCOH) and the deviation of the solar DC/AC ratio when optimized specifically for hydrogen production are quantified. Case studies covering a Global Horizontal Irradiation (GHI) range of 1400–2600 kWh/m2-year are assessed. The obtained LCOHs range between 5.9 and 11.3 USD/kgH2 depending on sizing and location. The AC/AC ratio is found to strongly affect cost, production and LCOH optimality while the optimal solar DC/AC ratio varies up to 54% when optimized to minimize the cost of hydrogen instead of the cost of energy only. Larger oversizing is required for low GHI locations; however, H2 production is more sensitive to sizing ratios for high GHI locations.
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| 13. |
- Gao, J. T., et al.
(författare)
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Feasibility and economic analysis of solution transportation absorption system for long-distance thermal transportation under low ambient temperature
- 2019
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Ingår i: Energy Conversion and Management. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0196-8904 .- 1879-2227. ; 196, s. 793-806
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Tidskriftsartikel (refereegranskat)abstract
- Sensible heat transportation with water is widely adopted in traditional heating network, which suffers from the low energy transportation density and inevitable heat loss for long-distance heat transportation. To address these two issues, the solution transportation absorption system has been proposed, which transports the thermal energy by stable chemical potential. However, boundary between the two technologies is not clear due to the lack of direct comparison on both technological and economic aspects. In this work, feasibility analysis of the solution transportation absorption system is performed using Aspen plus, and low ambient temperature is considered for a practical scenario. Economic contrast is performed by exergoeconomic analysis. Results show that the coefficient of performance and exergy efficiency of the solution transportation absorption system can reach 0.556 and 24.6% in optimal condition. The energy transportation density is nearly three times higher than that of traditional sensible heat transportation. Moreover, the exergoeconomic analysis indicates that the new system is more economical when the distance exceeds 6 km. It has been proved that the solution transportation absorption system is a feasible and economical way to efficiently transport thermal energy over long distance.
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| 14. |
- Gkoutzamanis, Vasilis, et al.
(författare)
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Thermal energy storage for gas turbine power augmentation
- 2019
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Ingår i: Journal of the Global Power and Propulsion Society. - : Global Power and Propulsion Society. - 2515-3080. ; 3, s. 592-608
-
Tidskriftsartikel (refereegranskat)abstract
- This work is concerned with the investigation of thermal energy storage (TES) in relation to gas turbine inlet air cooling. The utilization of such techniques in simple gas turbine or combined cycle plants leads to improvement of flexibility and overall performance. Its scope is to review the various methods used to provide gas turbine power augmentation through inlet cooling and focus on the rising opportunities when these are combined with thermal energy storage. The results show that there is great potential in such systems due to their capability to provide intake conditioning of the gas turbine, decoupled from the ambient conditions. Moreover, latent heat TES have the strongest potential (compared to sensible heat TES) towards integrated inlet conditioning systems, making them a comparable solution to the more conventional cooling methods and uniquely suitable for energy production applications where stabilization of GT air inlet temperature is a requisite. Considering the system’s thermos-physical, environmental and economic characteristics, employing TES leads to more than 10% power augmentation.
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| 15. |
- Guedez, Rafael, et al.
(författare)
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Techno-economic comparative analysis of innovative combined cycle power plant layouts integrated with heat pumps and thermal energy storage
- 2019
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Ingår i: Proceedings of the ASME Turbo Expo. - : ASME Press. - 9780791858608
-
Konferensbidrag (refereegranskat)abstract
- In the pursuit of increasing their profitability, the design and operation of combined cycle power plants needs to be optimized for new liberalized markets with large penetration of renewables. A clear consequence of such renewable integration is the need for these plants for being more flexible in terms of ramping-up periods and higher part-load efficiencies. Flexibility becomes an even clearer need for combined heat and power plants to be more competitive, particularly when simultaneously following the market hourly price dynamics and varying demands for both the heat and the electricity markets. In this paper, three new plant layouts have been investigated by integrating different storage concepts and heat-pump units in key sections of a traditional plant layout. The study analyses the influence that market has on determining the optimum layouts for maximizing profits in energy-only markets (in terms of plant configuration, sizing and operation strategies). The study is performed for a given location nearby Turin, Italy, for which hourly electricity and heat prices, as well as meteorological data, have been gathered. A multi parameter modeling approach was followed using KTH's in house teclmo-economic modeling tool, which uses time dependent market data, e.g. price and weather, to determine the trade-off curves between minimizing investment and maximizing profits when varying critical size-related power plant parameters e.g. installed power capacities and storage size, for pre-defined layouts and operating strategies. A comparative analysis between the best configurations found for each of the proposed layouts and the reference plant is presented in the discussion section of the results. For the specific case study set in northern Italy, it is shown that the integration of a pre-cooling loop into baseload-like power-oriented combined cycle plants is not justified, calling for investigating new markets and different operating strategies. Only the integration of a heat pump alone was shown to improve the profitability, but within the margin of error of the study. Alternatively, a layout where district heating supply water is preheated with a combination of a heat pump with hot thermal tank was able to increase the internal rate of return of the plant by up to 0.5%, absolute, yet within the error margin and thus not justifying the added complexity in operation and in investment costs. All in all, the analysis shows that even when considering energy-only market revenue streams (i.e. heat and electricity sells) the integration of heat pump and storage units could increase the profitability of plants by making them more flexible in terms of power output levels and load variations. The latter is shown true even when excluding other flexibilityrelated revenue streams. It is therefore conclusively suggested to further investigate the proposed layouts in markets with larger heat and power price variations, as well as to investigate the impact of additional control logics and dispatch strategies.
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| 16. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
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Binary Phase Equilibrium Study of the Polyols Blend Erythritol-Xylitol with the T-History Method for Phase Change Materials Design
- 2015
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Ingår i: The 13th International Conference on Energy Storage- Greenstock 2015.
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Konferensbidrag (refereegranskat)abstract
- Polyols are emerging PCM with attractive melting temperatures and enthalpies. The binary phase diagram of the system Erythritol-Xylitol is constructed using the Temperature-history method, and evaluated for its PCM-suitability. With blending, lowering of the melting points was expected, also verified with a recent study presenting the system as a simple eutectic. Herein, the tests covered the full compositional range, with thermal cycling around the previously reported eutectic. Some compositions exhibited possible glass transition after the first melting. For these, by seeding the starting material to the supercooled liquid, a preceding melting with heating was achieved. The results show several PCM suitable points in the phase diagram: eutectics and congruent melting compounds. This appears to be a partially isomorphous type, but not simple eutectic type. Microstructural evaluations for phase and miscibility verifications can further clarify this. For some compositions secondary phase changes were observed, indicating probable polymorphs, of solid-solid PCM interest.
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| 17. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
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Erythritol, Glycerol, their Blends, and Olive Oil, as Sustainable Phase Change Materials
- 2017
-
Ingår i: Energy Procedia. - The Netherlands : Elsevier. - 1876-6102. ; 135, s. 249-262
-
Tidskriftsartikel (refereegranskat)abstract
- In searching for new candidates to be used in latent heat storage, it is desirable to explore food-grade materials of renewable origin. Here, erythritol, glycerol, and olive oil have been characterized as PCMs. An assessment of the production process of erythritol (melting between 117-120 °C with an enthalpy around 300 kJ/kg) indicates its renewable aspects as a PCM. In addition, a simplified cost assessment of high-purity erythritol production, using glycerol, indicates a potential cost reductions up to 130-1820 times lower than the current laboratory-grade prices. Glycerol already is cost-effective. However, the glycerol-erythritol system, evaluated using the Temperature-history (T-history) method, did not exhibit phase change suitable for PCMs. Glycerol, and up to 30 mol% erythritol compositions had no phase change due to glass transition; the remainder froze but with large supercooling; and the system underwent thermally activated change. Hence, to realize glycerol or the glycerol-erythritol system as PCMs, further research is needed primarily to device fast-crystallization. Olive oil is a cost-effective food commodity, with potential for further cost reductions by mass-production. An olive oil sample, containing the fatty acids: linoleic, palmitic, oleic, margaric, and stearic was evaluated using the T-history method. This olive oil melted and froze between -4.5 to 10.4 °C and -8 to -11.9 °C respectively, with the respective enthalpies 105 and 97 kJ/kg. As the specific heat (cp) profiles of olive oil displayed two peaks, the composition adjustment of olive oil could yield a eutectic or confirm a polymorph. In either case, olive oil has a potential to be a PCM e.g. in chilling applications, while its properties such as thermal conductivity need to be determined. As a whole, this study exemplifies the potential of renewable organic materials, in pure and blend forms, as sustainable PCMs, making TES with PCMs sustainable.
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| 18. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Experimental phase diagram of the dodecane–tridecane system as phase change material in cold storage : [Diagramme de phase expérimental du système dodécane–tridécane comme matériau à changement de phase pour des applications d'entreposage frigorifique]
- 2017
-
Ingår i: International journal of refrigeration. - : Elsevier. - 0140-7007 .- 1879-2081. ; 82, s. 130-140
-
Tidskriftsartikel (refereegranskat)abstract
- Integrating thermal storage with phase change materials (PCMs) in refrigeration and air conditioningprocesses enables energy performance improvements. Herein, the experimental phase diagram of thealkanes system dodecane-tridecane (C12H26-C13H28) is evaluated to find PCMs for freezing applications.For that, the Temperature-history method was coupled with a Tammann plot analysis. The obtainedC12H26-C13H28 phase diagram indicated a congruent minimum-melting solid solution and polymorphs. Theminimum-melting liquidus and the polymorphs identified here, agree with previous literature. However,the system does not represent a eutectic, as previously was proposed. The minimum-meltingcomposition is here identified within 15-20 mol% C13H28 compositions. The 17.7 mol% C13H28 is thenarrowest minimum-melting composition among those analyzed, melting and freezing between -16 to -12 °C and -17 to -15 °C, with: the enthalpies 185 kJ kg-1 and 165 kJ kg-1; no supercooling; and only minorhysteresis. Hence, this blend has potential as a PCM in freezing refrigeration applications.
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| 19. |
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| 20. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Phase equilibrium in the design of phase change materials for thermal energy storage: State-of-the-art
- 2017
-
Ingår i: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 73, s. 558-581
-
Forskningsöversikt (refereegranskat)abstract
- This paper presents a review of phase equilibrium as a tool for accurately identifying suitable blended phasechange materials (PCMs) to be used for thermal energy storage (TES). PCM storage increases the overall energyefficiency for many applications, however, high cost and complex phase change phenomena in blends oftenundermine the benefits. The study of phase equilibrium as derived from phase diagrams is the key to solve theseissues. It enables the evaluation of PCM-suitability through indication of temperature-composition points, e.g.congruent melting compositions, eutectics and peritectics. To clearly stake out the opportunities of a phaseequilibrium-based design methodology, this paper reviews the state-of-the-art based on findings from fourdecades (1977–2016). On one hand, eutectics, salts-based systems, fatty acids, and alkanes dominate theexisting PCM literature. Here peritectics have often been erroneously praised as suitable PCMs despite the manyproblems depicted from a phase equilibrium point of view. On the other hand, the most PCM-ideal congruentmelting systems, as well as the blends of polyols, fats, metal alloys and organic-inorganic combinations lack fullattention. This work brings forward the knowledge on these insufficiently explored yet extremely suitable phaseequilibrium characteristics. In addition, comprehensive PCM-design thermal properties of these various blendsare presented, as a basis to further extensive explorations, and material category-based predictions.
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| 21. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Polyols as phase change materials for surplus thermal energy storage
- 2016
-
Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 162, s. 1439-1452
-
Tidskriftsartikel (refereegranskat)abstract
- Storing low-temperature surplus thermal energy from industries, power plants, and the like, using phasechange materials (PCM) is an effective alternative in alleviating the use of fossil based thermal energyprovision. Polyols; of some also known as sugar alcohols, are an emerging PCM category for thermalenergy storage (TES). A review on polyols as PCM for TES shows that polyols have phase change temperaturesin the range of 15 to 245 C, and considerable phase change enthalpies of 100–413 kJ/kg. However,the knowledge on the thermo-physical properties of polyols as desirable PCM for TES design is presentlysparse and rather inconsistent. Moreover, the phase change and state change behaviors of polyols need tobe better-understood in order to use these as PCM; e.g. the state change glass transition which manypolyols at pure state are found to undergo. In this work preliminary material property characterizationwith the use of Temperature-History method of some selected polyols, Erythritol, Xylitol andPolyethylene glycol (PEG) 10,000 were done. Complex behaviors were observed for some of the polyols.These are: two different melting temperatures, 118.5–120 C and 106–108 C at different cycles and anaverage subcooling 18.5 C of for Erythritol, probable glass-transition between 0 and 113 C for Xylitol,as well as a thermally activated change that is likely an oxidation, after three to five heating/coolingcycles for Xylitol and Erythritol. PEG 10,000 had negligible subcooling, no glass-transition nor thermallyactivated oxidation. However a hysteresis of around 10 C was observed for PEG 10,000. Therefore thesematerials require detailed studies to further evaluate their PCM-suitability. This study is expected to be an initiation of an upcoming extensive polyol-blends phase equilibrium evaluation.
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| 22. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
The Experimental Phase Diagram Study of the Binary Polyols System Erythritol-Xylitol
- 2017
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier. - 0927-0248 .- 1879-3398. ; 174, s. 248-262
-
Tidskriftsartikel (refereegranskat)abstract
- A comprehensive phase diagram for the binary polyols system erythritol-xylitol has been mapped with a transparent characterization approach. Here, the phase equilibrium of the system has been studied experimentally using a combination of methods: Temperature-history (T-history), X-Ray Diffraction (XRD), and Field-Emission Scanning Electron Microscopy (FESEM), and linked to Tammann plots. Existing literature has previously shown the system to be a non-isomorphous type forming a simple eutectic, by combining experimental data with theoretical modelling. The present investigation shows that the system’s phase diagram is a partially isomorphous type forming a eutectic, but not a non-isomorphous type forming a simple eutectic. Here, the eutectic was found within 25-30 mol% erythritol and at 77 °C, which differs from the previous studies identifying the eutectic respectively at 25 or 36 mol% erythritol and at 82 °C. The reasons for the differences are hard to deduce since the research approach is not presented as fully transparent from the past studies. In the present study, only the temperature-composition plot of the first melting (of the two components in a physical mix, but not of a single blend) indicated the shape of a simple eutectic in a non-isomorphous system. The cycles after the first melting in contrast started from the real blend, and displayed eutectic and solid-solid phase changes in T-history. These were verified as forming solid solutions with XRD and FESEM. This eutectic melts at a temperature suitable for low-temperature solar heating, but displayed glass transition, supercooling, and thermally activated degradation, thus affecting its practical aspects as a PCM.
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| 23. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Thermal conductivity measurement of erythritol, xylitol, and their blends for phase change material design : A methodological study
- 2019
-
Ingår i: International Journal of Energy Research. - : John Wiley & Sons. - 0363-907X .- 1099-114X. ; 43:5, s. 1785-1801
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents and discusses a detailed thermal conductivity assessment of erythritol, xylitol, and their blends: 25 mol% erythritol and 80 mol% erythritol using the transient plane source (TPS) method with a Hot Disk Thermal Constants Analyzer TPS‐2500S. Thereby, the thermal conductivities of xylitol, 25 mol% erythritol, 80 mol% erythritol, and erythritol were here found for respectively in the solid state to be 0.373, 0.394, 0.535, and 0.589 W m−1 K−1 and in the liquid state to be 0.433, 0.402, 0.363, and 0.321 W m−1 K−1. These obtained results are comprehensively and critically analyzed as compared to available literature data on the same materials, in the phase change materials (PCMs) design context. This study clearly indicates that these thermal conductivity data in literature have considerable discrepancies between the literature sources and as compared to the data obtained in the present investigation. Primary reasons for these disparities are identified here as the lack of sufficiently transparent and repeatable data and procedure reporting, and relevant standards in this context. To exemplify the significance of such transparent and repeatable data reporting in thermal conductivity evaluations in the PCM design context, here focused on the TPS method, a comprehensive measurement validation is discussed along various residual plots obtained for varying input parameters (ie, the heating power and time). Clearly, the variations in the input parameters give rise to various thermal conductivity results, where choosing the most coherent result requires a sequence of efforts per material, because there are no universally valid conditions. Transparent and repeatable data and procedure reporting are the key to achieve comparable thermal conductivity results, which are essential for the correct design of thermal energy storage systems using PCMs.
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| 24. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Thermal Conductivity Measurement of Erythritol, Xylitol and Their Blends for Phase Change Materials Design : a Methodological Study
- 2018
-
Ingår i: The 14th International Conference on Energy Storage. - Adana, Turkey : IEA ECES. - 9789754872187 ; , s. 364-378
-
Konferensbidrag (refereegranskat)abstract
- This work presents and discusses a detailed thermal conductivity assessment of erythritol, xylitol and their blends: 25 mol% erythritol and 80 mol% erythritol using the Transient Plane Source (TPS) method with a Hot Disk Thermal Constants Analyzer TPS-2500S. Their thermal conductivities were here found to be respectively: 0.59; 0.37; 0.39 and 0.54 W/(m·K) in the solid state, and to be 0.32; 0.43; 0.40 and 0.36 W/(m·K) in the liquid state. These obtained results are comprehensively and critically analyzed as compared to available literature data on the same materials, in the phase change materials (PCMs) design context. This study clearly indicates that the literature has considerable discrepancies among their presented thermal conductivities, and also as compared to the values found through the present investigation. Primary reason for these disparities are identified here as the lack of sufficiently transparent and repeatable data and procedure reporting, and relevant standards in this context. To exemplify the significance of such transparent and repeatable data reporting in thermal conductivity evaluations in the PCM design context, here focused on the TPS method, a comprehensive measurement validation is discussed along various residual plots obtained for varying input parameters (i.e., the heating power and time). Clearly, the variations in the input parameters give rise to various thermal conductivity results, where choosing the most coherent result requires a sequence of efforts per material, but there are no universally valid conditions. Transparent and repeatable data and procedure reporting is the key to achieve comparable thermal conductivity results, which are essential for the correct design of thermal energy storage systems using PCMs.
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| 25. |
- Gunasekara, Saman Nimali, Dr. 1982-, et al.
(författare)
-
Thermal Energy Storage Materials (TESMs)-What Does It Take to Make Them Fly?
- 2021
-
Ingår i: Crystals. - : MDPI AG. - 2073-4352. ; 11:11, s. 1276-
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal Energy Storage Materials (TESMs) may be the missing link to the "carbon neutral future " of our dreams. TESMs already cater to many renewable heating, cooling and thermal management applications. However, many challenges remain in finding optimal TESMs for specific requirements. Here, we combine literature, a bibliometric analysis and our experiences to elaborate on the true potential of TESMs. This starts with the evolution, fundamentals, and categorization of TESMs: phase change materials (PCMs), thermochemical heat storage materials (TCMs) and sensible thermal energy storage materials (STESMs). PCMs are the most researched, followed by STESMs and TCMs. China, the European Union (EU), the USA, India and the UK lead TESM publications globally, with Spain, France, Germany, Italy and Sweden leading in the EU. Dissemination and communication gaps on TESMs appear to hinder their deployment. Salt hydrates, alkanes, fatty acids, polyols, and esters lead amongst PCMs. Salt hydrates, hydroxides, hydrides, carbonates, ammines and composites dominate TCMs. Besides water, ceramics, rocks and molten salts lead as STESMs for large-scale applications. We discuss TESMs' trends, gaps and barriers for commercialization, plus missing links from laboratory-to-applications. In conclusion, we present research paths and tasks to make these remarkable materials fly on the market by unveiling their potential to realize a carbon neutral future.
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| 26. |
- Gunasekara, Saman Nimali, 1982-, et al.
(författare)
-
Thermodynamic Assessment of Binary Erythritol-Xylitol Phase Diagram for Phase Change Materials Design
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Here, the experimental phase equilibrium data of the erythritol-xylitol system were thermodynamically optimized, to explore compositions suitable as phase change materials (PCMs) for thermal energy storage (TES). A previous experimental study revealed that erythritol-xylitol was a partially isomorphous system with a eutectic. In the thermodynamic evaluation, the CALPHAD method was employed coupling the phase diagram and thermodynamic property information. There, both unary and binary systems’ experimental data were taken into account, and all phases were described using the substitutional solution model. Finally, a self-consistent thermodynamic description for the erythritol-xylitol system was achieved. The calculated eutectic point is at 76.7 °C and 26.8 mol% erythritol, agreeing well with the experimental data. The calculated phase diagram better-verifies the systems’ solidus and the solvus, disclosing the stable phase relations. Based on the Gibbs energy minimization, phase diagrams can be predicted for the binary and higher order systems, provided the component subsystems are thermodynamically assessed beforehand. In conclusion, to move forward beyond e.g. non-isomorphous simple eutectic systems, methods using Gibbs free energy minimization from a fundamental point-of-view such as CALPHAD are essential.
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| 27. |
- Hu, Ming-Hsuan, et al.
(författare)
-
Experimental analysis of submerged coil and encapsulated slab latent heat storage
- 2022
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 209
-
Tidskriftsartikel (refereegranskat)abstract
- Latent heat thermal energy storage (LHTES) has two primary LHTES packing methods, encapsulation and bulk PCM storage. Since there is still a lack of experimental comparison between these two methods, two types of LHTES units based on separated methods were built for direct comparison. Moreover, the impact of heat transfer fluid (HTF) flowrate on LHTES performance was evaluated. Unit one is a 0.38 m(3) tank containing slab-shaped macro-encapsulated phase change material (PCM); unit two is a 0.54 m(3) tank containing submerged spiral coil heat exchanger (SCHE) in PCM. PCM with a melting temperature of 58-60 ? was charged/discharged between 46 and 72 ?. Parametric studies on constant and time-varying HTF flowrates were conducted to test the impact on the thermal storage performance.& nbsp;The time-varying flowrate control enables the system to supply the needed power at different discharging stages. Moreover, partial charging/discharging demonstrates higher mean thermal power than full charge/discharge rendering this control strategy adequate under specific operating conditions. Finally, the comparison between the slab-encapsulated PCM storage unit and the SCHE based unit shows that the former requires a shorter completion time while the latter has a higher energy storage density.
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| 28. |
- Koide, Hiroaki, et al.
(författare)
-
Development of Novel Microencapsulated Hybrid Latent/Chemical Heat Storage Material
- 2020
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:39, s. 14700-14710
-
Tidskriftsartikel (refereegranskat)abstract
- Phase change materials (PCM) and thermochemical materials (TCM) attract increasing attention as next-generation heat storage technologies. A novel CaO-supported microencapsulated phase change material (CaO/MEPCM) has been developed by combining a latent heat storage material with a chemical heat storage material. With this novel concept, higher storage performance and improved structural benefits are obtained. Microencapsulated Al-25 wt % Si alloy as the PCM and CaO/Ca(OH)2 as the TCM are investigated in this paper. Sample preparation processes include (1) boehmite (AlOOH) treatment, (2) thermal oxidation treatment, (3) impregnation with CaO precursor, and (4) calcination. From SEM and XRD, the presence of CaO was confirmed on the microcapsules. According to the thermal analysis of CaO 30 wt %/MEPCM under a controlled H2O/N2 atmosphere, two endothermic peaks are present at around 500 and 577 °C, and the total heat storage capacity amounts to 412 kJ kg–1. Besides this, the stability in five cycles is also shown. It is also demonstrated through this work that the expansion of CaO can be successfully suppressed with the impregnation coating treatment. These results indicate that the combination of latent heat storage material and chemical heat storage material attains a synergistic effect and that the result is a novel heat storage material hybrid with high application potentials.
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| 29. |
- Koide, Hiroaki, et al.
(författare)
-
Performance analysis of packed bed latent heat storage system for high-temperature thermal energy storage using pellets composed of micro-encapsulated phase change material
- 2022
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- High temperature latent heat storage has gained increasing attention owing to its potential in the integration of renewable energy sources. This study is a novel experimental investigation on the heat storage performance of a horizontal packed bed containing composites comprising Al-Si-based microencapsulated phase change material in a high-temperature air heating system. The pellet type composites with 3 mm is tested here in a 1L scale packed bed heat exchanger at airflow rates between 75 and 150 L min−1. The composite exhibited a narrow phase change temperature range and high heat storage/release characteristics. As the airflow increased, the phase change time of the composite decreased, and the heat exchanging rate increased. The heat exchange efficiency during charging and discharging ranged from 71.0 % to 98.3 % and 69.0 %–90.2 %, respectively. In the discharging mode, although supercooling which comes from the microencapsulated phase change material, was observed, this did not noticeable effect on the heat transfer.
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| 30. |
- Konig-Haagen, Andreas, et al.
(författare)
-
Analysis of the discharging process of latent heat thermal energy storage units by means of normalized power parameters
- 2023
-
Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 72
-
Tidskriftsartikel (refereegranskat)abstract
- Many efforts are being made to mitigate the main disadvantage of most phase change materials - their low thermal conductivities - in order to deliver latent heat energy storage systems (LHESS) with adequate perfor-mance. However, the effect of applied methods is difficult to compare as they are mostly tested for different storage types and sizes and/or different boundary and initial conditions, which hinders rapid progress in the optimization of these approaches. In this work, a previously developed method for comparing the performance of LHESS is applied to experimental results of different storage systems under different conditions and subsequently analyzed and further refined. The main idea of the method is to normalize the power with the volume and a reference temperature difference and compare its mean value plotted over the normalized mean capacity flow of the heat transfer fluid (HTF). This enables the presentation of the results in a compact and easily comparative way. Attention has to be paid when it comes to the choice of the reference temperature difference, the reference volume and the method for calculating the mean value. Two variants of calculating the mean value (time-weighted and energy-weighted) and two variants of reference temperatures for determining the temperature difference to the inlet temperature of the HTF (initial temperature and melting temperature) are applied and discussed in detail. While the method significantly increases the comparability of results, none of the options listed above are without drawbacks. Approaches are shown to reduce or eliminate these drawbacks in the future. The recommendation for comparing different LHESS under different conditions is to use the method described here and clearly state the chosen reference temperature, reference volume and method for calculating the mean value.
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| 31. |
- Manyumbu, Edson, et al.
(författare)
-
Prospective PCM-Desiccant Combination with Solar-Assisted Regeneration for the Indoor Comfort Control of an Office in a Warm and Humid Climate-A Numerical Study
- 2023
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 16:14
-
Tidskriftsartikel (refereegranskat)abstract
- Favorable thermal conditions within buildings are a necessity. Mechanical air conditioning, although effective, contributes a significant percentage of the world's total energy use, which contributes to global warming. In addition, the refrigerants used in air conditioning also contribute to global warming. Passive means to provide thermal comfort have therefore been considered as alternative solutions. Phase-change materials (PCMs) have been considered as one passive cooling option. Although this option achieves a certain degree of effectiveness, especially in warm and dry climatic conditions, its effectiveness in warm humid climates is subdued due to its inability to handle humidity. In the present study, the suitability of a novel passive comfort provision strategy that combines a PCM and a desiccant is assessed. The passive system operates in a cycle of two phases: the moderating phase and the regenerating phase. For the proposed strategy, the regeneration process first involves the external desiccant bed, then night air drying using the regenerated external bed; the dried air subsequently regenerates the internal wall surface. The study involves the modeling of the proposed strategy and simulation of its performance. The simulation results indicate the significant potential for providing satisfactory comfort and health conditions through application of a combination of a desiccant and a PCM.
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| 32. |
- Reboli, Tommaso, et al.
(författare)
-
Thermal energy storage based on cold phase change materials : Charge phase assessment
- 2022
-
Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; 217
-
Tidskriftsartikel (refereegranskat)abstract
- Integration of thermal energy storage in energy systems provides flexibility in demand-supply management and in supporting novel operational schemes. In a combined heat and power cycle, it has been shown that integration of cold thermal energy storage is beneficial to fine-tune electric power and heating/cooling production profiles to better match the load demand. Latent heat storage systems have the advantage of compactness and low temperature swing, however storage performance analysis on large scale setup operating around the density inversion temperature is still limited. In this work, a shell & tube, latent heat based cold thermal energy storage was studied around the density inversion temperature of ice-water at 4 degrees C and the performance was characterized. Sensitivity analyses on heat transfer fluid flow rate, flow direction and inlet temperature were performed. The results show 27% power increase with doubled mass flow and 18% shorter charge time with 2 degrees C lower charge temperature. Contrary to general expectations during solidification, the cold thermal energy storage actually shows between 5% and 6% better thermal performance and reducing instant icing power jump of 36% due to supercooling with downwards cold heat transfer fluid flow in cooling charge cycle due to buoyancy change around density inversion temperature. This fact highlights the importance of accounting for the buoyancy effect due to density inversion when designing the operational schemes of large size cold thermal energy storage.
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| 33. |
- Reboli, Tommaso, et al.
(författare)
-
Thermal energy storage based on cold phase change materials : Discharge phase assessment
- 2023
-
Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 73, s. 108939-
-
Tidskriftsartikel (refereegranskat)abstract
- In an energy scenario characterized by strong requirements in terms of flexibility and readiness, the integration of thermal energy storage in energy systems could play an important role in demand-supply management and allows novel operational schemes. Thermal Energy Storages based on latent heat are characterized by their compactness and small temperature swing. However, there is still a lack of performance analysis on large-scale setups. This work aims to fill this gap. In this paper, a shell & tube latent heat-based cold thermal energy storage was characterized in the discharge configuration, considering different temperatures and mass flow of the heat transfer fluid, representing an opportunity to understand the behavior of a full-scale system in different operative conditions. Sensitivity analyses on heat transfer fluid flow rate, flow direction, and inlet temperature were performed. The results show that peak power increases by approximately 25 % with doubled mass flow rate, and it doubles with increased inlet temperature by 6 °C. Since the impact of the buoyancy effect occurs when the liquid phase is predominant over the solid one, there is no strong impact on the direction of the Heat Transfer Fluid, from top to bottom or viceversa. Despite no metastability phase being detected, many discontinuities in the thermal power and temperature profiles were identified and analyzed, providing new insights into full scale latent heat storage. Finally, in this work, the thermal round-trip efficiency was estimated to reach above 90 %.
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| 34. |
- Shan, Lianying, et al.
(författare)
-
Techno-Economic Analysis of Latent Heat Thermal Energy Storage Integrated Heat Pump for Indoor Heating
- 2023
-
Ingår i: 36th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2023. - : Curran Associates, Inc.. ; , s. 2265-2276
-
Konferensbidrag (refereegranskat)abstract
- Electricity prices have increased significantly in Europe and other regions due to the recent energy crisis. Latent heat thermal energy storage (LHTES) implemented in residential heating systems has attracted attention for its role in peak/load shifting to reduce heating costs. A new layout with LHTES integrated with a heat pump (HP) is proposed here to store low grade heat during off-peak demand periods, later used as heat source for the heat pump during peak demand periods. This novel layout is assessed for its heat capacity variation and levelized cost of energy (LCOE). The results show that increased amount of power input is required when a storage component is integrated into the heating system, while it can be compensated by shifting to off-peak electricity usage.
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| 35. |
- Shan, Lianying, et al.
(författare)
-
Techno-economic analysis of latent heat thermal energy storage integrated heat pump for indoor heating
- 2024
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 298
-
Tidskriftsartikel (refereegranskat)abstract
- Latent heat thermal energy storage (LHTES) implemented in residential heating systems has attracted attention for its role in peak/load shifting. A novel layout integrating LHTES with a heat pump is proposed to store low grade heat during off-peak demand period, later used as heat source for the heat pump during on-peak demand period. This novel layout is assessed according to different seasons, LHTES height-to-diameter (H/D) ratios, mass ratios of inflow water to radiator return water, and levelized cost of energy (LCOE). The results show that an overall increased amount of power input is required when utilizing LHTES, while it can shift 2.8–3.6 kW electricity from on-peak to off-peak. The case with an H/D ratio of 1.7 shows slight reductions in heating costs and LCOE as compared to a H/D ratio of 0.6. Considering heating costs, a mass ratio of 50 % performs better in December 2022 and a mass ratio of 10 % performs better in January 2023 due to different operating conditions. The heating costs of the integrated system are 1.0 %–2.1 % higher than those of the typical system due to limitations in the rated capacity of the heat pump and lower effectiveness of the shell-and-tube heat exchanger.
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| 36. |
- Shao, Xue-Feng, et al.
(författare)
-
Hydroxyl group functionalized graphene oxide nanosheets as additive for improved erythritol latent heat storage performance : A comprehensive evaluation on the benefits and challenges
- 2020
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 215
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene oxide (GO) nanosheets were employed as the additive to make composites of erythritol, a promising medium-temperature PCM candidate. GO nanosheets modified with hydroxyl groups were applied to improve the dispersion stability of the composites. A systematic characterization on the latent heat storage performance was performed for both pure and composite erythritol, in order to identify the benefits and challenges of the composites. It was found that the thermal conductivity is increased by nearly twice and the degree of supercooling was lowered from ~64 °C to ~48 °C at the loading of 1.0 wt% GO nanosheets (the maximum loading tested). The addition of GO nanosheets also leads to an increase of the retrievable latent heat during crystallization, from ~187 kJ/kg to ~225 kJ/kg at the same loading, by increasing the crystallinity. However, the introduction of GO nanosheets can also lead to a rise in the dynamic viscosity of erythritol. As a result, the crystallization rate is slowed down and accordingly, the duration of crystallization becomes 62% longer when the loading reaches 1.0 wt%. In addition, favorable dispersion stability of the erythritol composites is observed, and their melting point (~117 °C) remains almost unchanged during 50 melting-crystallization cycles. Functionalized GO nanosheets have been shown to be an efficient additive for improving the performance of erythritol, but a trade-off analysis on the loading would be required to achieve the best overall performance.
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| 37. |
- Shao, Xue-Feng, et al.
(författare)
-
Polyvinylpyrrolidone (PVP)-enabled significant suppression of supercooling of erythritol for medium-temperature thermal energy storage
- 2022
-
Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 46, s. 103915-
-
Tidskriftsartikel (refereegranskat)abstract
- The supercooling effect is deemed to be a crucial issue for thermal energy storage using phase change materials (PCMs). The exploration of promising additives plays a decisive role in effective suppression efforts for suppressing the supercooling effect of a PCM. The present work proposed a potential additive, polyvinylpyrrolidone (PVP), to reduce the supercooling of erythritol, which is the most promising polyol PCM candidate for medium temperature range. PVP with various loadings was dispersed in erythritol to make composites for the proof-of-concept tests. It was shown that the degree of supercooling of erythritol can be reduced significantly from over 64 ? to about 21 ? in the presence of only 1.0 wt.% PVP. Along with the mitigated supercooling effect, the addition of PVP also leads to an increase of the retrievable latent heat during crystallization, from ~187 J/g to ~224 J/g at the same minute PVP loading of 1.0 wt.%, by increasing the crystallinity of erythritol. The PVP-loaded erythritol composites exhibit little sacrifice in latent heat of fusion, i.e., only ~15% loss when the PVP loading reaches 6.0 wt.%. In addition, multiple tests confirmed that PVP can be dissolved in erythritol, thus desirable compatibility was obtained and the composites would have long-term reliability. This proposed additive enables an efficient and cost-effective way for improving the crystallization behaviors of erythritol (and other polyol PCMs) towards real-world applications.
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| 38. |
- Söderqvist, Minna, et al.
(författare)
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Internationalisation Of Doctoral Education Within The European University Alliance : A Multi-partner Co-tutelle Model
- 2024
-
Ingår i: Internationalization of the Doctoral Experience: Models, Opportunities and Outcomes. - : Taylor & Francis. - 9781003317555
-
Bokkapitel (refereegranskat)abstract
- This chapter describes the development by Unite! (University Network for Innovation, Technology and Engineering), an alliance of seven European universities, of a new multiple Co-tutelle model for joint doctoral education. The chapter discusses what a Co-tutelle means, the Unite! model and how it was created, different student and faculty experiences, the new multiple Co-tutelle framework, and its individual annexes and foundational principles. Features that prohibit and promote this kind of multiple Co-tutelle model are reflected on, along with lessons learned.
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| 39. |
- Xu, Tianhao, et al.
(författare)
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Design Aspects of a Latent Heat Storage Unit for Heat Production Shifting at a Cogeneration Plant
- 2019
-
Ingår i: SWC2019 Proceedings.
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Konferensbidrag (refereegranskat)abstract
- In the present study, a latent heat thermal energy storage (LHTES) unit with two different configurations (a shell-and-tube design using spiral coils as tubes and an encapsulation design using commercial capsules) are investigated and compared over their thermal performance for providing heat storage and recovery. The designed latent heat storage unit is to be implemented at an existing cogeneration plant for heat production shifting purposes. The design procedure involves several aspects of theoretical investigations: the determination of suitable melting point of the employed phase-change material (PCM); the selection of heat exchanger configuration; and the prediction of the units’ transient charging/discharging thermal behavior under operating conditions set by the cogeneration plant. Numerical approaches are used in this study to estimate the heat transfer conditions in PCMs as well as the transient charging/discharging thermal power of the entire unit. The accumulative stored/released energy throughout a charging process of three hours and a discharging process of one hour is also calculated. With the cylindrical containment tank in the same geometry, the spiral coil design exhibits a 52%-higher total heat storage capacity than the encapsulation design, and the simulation results show that it can store a higher amount of heat by 20% after first three hours of charging. For discharging, however, the encapsulation design exhibits a higher completion rate of 96% than the spiral coil design (53%) after first hour of discharging. Besides, the heat recovery capacity with the encapsulation design is 26% higher. The spiral coil design therefore shows advantage in the charging mode in terms of higher storage capacity while the encapsulation design outperforms when discharging due to is higher discharge rate within the given discharge operating duration of one hour.
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| 40. |
- Xu, Tianhao, et al.
(författare)
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Experimental and Numerical Investigation of a Latent Heat Thermal Energy Storage Unit with Ellipsoidal Macro-encapsulation
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Annan publikation (populärvet., debatt m.m.)abstract
- Experimental and Numerical Investigation of a Latent Heat Thermal Energy Storage Unit with Ellipsoidal Macro-encapsulationTianhao Xu, Emma Nyholm Humire, Silvia Trevisan, Monika Ignatowicz, Samer Sawalha, Justin NW Chiu*Department of Energy Technology, KTH Royal Institute of Technology, 100 44, Stockholm, SwedenAbstractIn this paper, a novel type of macro-encapsulated phase change material (PCM)shaped in ellipsoidis investigated on a component scale.The encapsulated PCM is a paraffin-based commercial material (ATP60); differential scanning calorimetry and transient plane source method are used to measure the thermo-physical properties of the PCM. A numerical model and a 0.382 m3latent heat thermal energy storage (LHTES) prototype have been built and experimentally characterized. The temperature measurements indicate that thermocline is retainedin the packed bed region. The charge/discharge can be accelerated by65% with20 K increase intemperature difference between the phase-change temperature and heat transfer fluid (HTF)inlet temperature. Increasing HTF inlet flowrate from 0.15 m3/h (Re=77) to 0.5 m3/h (Re=256) shortenscompletion time of charge by51%. Furthermore, a one-dimensional packed bed using source based enthalpy method was constructed and validatedwithin6.6% errorfor aReynolds numberof 90 to 922. Compared with a conventional cylindrical PCM capsule, the ellipsoidal encapsulation shows60% increase in discharge speed but 23%lower storage capacity. This work demonstrates a combined experimental and numerical characterization approach for a novel ellipsoidal PCM encapsulationgeometry.
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| 41. |
- Xu, Tianhao, et al.
(författare)
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Experimental investigation on cylindrically macro-encapsulated latent heat storage for space heating applications
- 2019
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Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 182, s. 166-177
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Tidskriftsartikel (refereegranskat)abstract
- The integration of latent heat thermal energy storage (LHTES) units with heating systems in buildings is regarded as a promising technology for heating load management; however, so far a limited number of experimental studies have been reported that focus on space heating applications on a representative scale. In this study, we develop and test a 0.38 m3 LHTES unit containing cylindrically macro-encapsulated phase change materials (PCMs) with a melting temperature range of 44–53 °C and with gross mass of 154 kg. The unit has been tested with two tank orientations, horizontal and vertical. In the horizontal orientation tests, parametric studies show that increasing the difference between heat transfer fluid (HTF) supply temperatures and phase-change temperatures of PCMs, as well as increasing HTF flowrates, can both reduce the complete melting/solidification and complete charging/discharging time. Non-linear charging/discharging rates in PCMs are observed. The vertical orientation enables the forming of either a stratified or mixed flow regime in the tank. For charging, the stratified flow provides higher charging rates in PCMs compared to the mixed flow. When discharging the unit with a stratified HTF flow at 35 °C, lower HTF flowrates prolong the discharging time during which the released heat sustains an outlet temperature above 45 °C. Finally, comparisons between horizontal and vertical orientation tests reveal that although the vertical orientation can shorten the charging/discharging time by up to 20% for the entire unit to reach an energy density of 30 kWh/m3, it leads to decrease in PCM thermal capacity by at most 8.2%. The speculated cause of this loss is phase segregation suggested by observed fluid motions in PCM cylinders. This study comprehensively characterizes an LHTES unit providing insights to optimizing its operating strategies considering its coupling with space heating systems.
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| 42. |
- Xu, Tianhao, 1992-
(författare)
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Integrating Latent Heat Storage into Residential Heating Systems : A study from material and component characterization to system analysis
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Latent heat thermal energy storage (LHTES) systems can be coupled with heat pump (HP) systems to realize heat load shifting on demand side. With phase change material (PCM), well designed LHTES components exhibit high storage energy density and thus have large potentials to be integrated in residence where a compact energy storage solution is needed. However, real installations of LHTES-HP integrated systems are still rare nowadays; feasibility of this technology in achieving technically sound and economically viable load shifting operations should be demonstrated and understood by stakeholders to promote its implementation. Therefore, this thesis presents an exemplary feasibility study for three selected off-the-shelf macro-encapsulated PCM products, encompassing in-depth experimental and numerical modelling investigations on three levels—material, component, and system. The feasibility is studied with a specific scenario where the macro-encapsulated LHTES systems are designed to integrate with HP-based heating systems in common Swedish residential buildings. On the material level, three commercial PCMs (C48, C58, and ATP60) are selected by the operating temperature levels in typical HP-based space heating systems. Differential Scanning Calorimetry and Temperature-History method are employed to measure PCM enthalpy-temperature profiles; Transient Plane Source method is used to measure the thermal conductivity of ATP60. C58 based on sodium acetate trihydrate is prioritized for in-depth feasibility analyses because of its highest volumetric heat storage capacity.On the component level, three full-scale macro-encapsulated LHTES components (Component 1: cylindrical encapsulation of C48; Component 2: cylindrical encapsulation of C58; Component 3: ellipsoidal encapsulation of ATP60) are developed for integration in single-family houses to achieve full peak load shifting. A test rig is built for characterizing the three components under possible operational conditions in practical systems. The heat transfer enhancing effects from increasing the temperature difference between heat transfer fluid (HTF) inlet temperature and phase-change temperature as well as from increasing the HTF inlet flowrate are quantified. Performance indicators, such as completion time of charge/discharge, energy storage density, and capacity enhancement factor, are evaluated at different operating temperature ranges. Overall, Component 2 is feasible in delivering around 90% of storage capacity (the capacity loss is due to phase separation). However, storage design and control improvements are still needed for realizing full peak load shifting over a three-hour discharging process. For Component 2, an improved storage solution with a reduced capsule diameter and time-increasing HTF flowrate profiles is developed through numerical simulation using an experimentally-validated two-dimensional heat transfer model. Furthermore, a one-dimensional model is developed and validated for simulating storage thermal output of Components 2 and 3. On the system level, a numerical model is developed to calculate electricity input to the LHTES-HP integrated systems for technical, economic, and environmental load shifting evaluation. Three new integration layouts are developed to charge scaled-up Component 2 with a de-superheater and/or a booster heat pump cycle. The new layouts can improve the weekly heating performance factor by 22%–26%, compared with a conventional layout using the condenser for charging. Savings in operational expenses can justify a capital expense of 25,000 Swedish Krona (about 2,500 €) for the LHTES system with a 15-yr operation. Although this justifiable capital expense is lower than the storage component cost alone estimated with the cost of Component 2, it is anticipated that similar LHTES solutions may gain more economic feasibilities with larger peak-valley electricity price differences foreseeable in the future. Through presentation of the multi-level feasibility evaluation, this thesis identifies key design and operational issues which might be neglected in single-level investigations. Furthermore, the thesis develops two new LHTES-HP integrated solutions with improved storage design/control strategies and enhanced system coupling methods from the existing solutions. This provides application-oriented insight for design and operation of the load-shift based LHTES installations in residential buildings, potentially contributing to decarbonisation of the increasingly electrified heating sector.
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| 43. |
- Xu, Tianhao, et al.
(författare)
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Latent heat storage integration into heat pump based heating systems forenergy-efficient load shifting
- 2021
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 236:114042
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Tidskriftsartikel (refereegranskat)abstract
- Integrating latent heat thermal energy storage (LHTES) units into building heating systems has been increasinglyinvestigated as a heat load management technology. A conventional LHTES integration method for heat pumpbased heating systems is to connect the heat pump’s condenser for charging the LHTES unit. This integratinglayout however usually leads to increased electricity input to the heating system. To underline this issue andprovide solutions, this paper presents three new LHTES integrating layouts where the LHTES unit is connectedwith the de-superheater of the main heat pump (Case 2), the condenser of a cascaded booster heat pump cycle(Case 3), or a combination of using both the de-superheater and the booster cycle (Case 4). In the context of amulti-family house in Stockholm, a quasi-steady state heating system model was developed to evaluate the newintegrating layouts, which were benchmarked against the baseline heating system without storage (Case 0) andthe conventional integrating layout using the main heat pump condenser (Case 1). Hourly electric power input tothe heating system was modelled for calculating the performance indicators including the heating performancefactor, the operational expense and justifiable capital expense, and the indirect CO2 emissions. Two load shiftingstrategies were simulated for an evaluation period of Week 1, 2019: 1) charge during off-peak hours (8 pm to 6am) and 2) charge during daytime hours (10 am to 7 pm). The simulation results of the off-peak charging strategyshow that, in Cases 2–4, the heating performance factor is 22%-26% higher than Case 1 and the operational expense can be reduced by 2%-5% as compared with Case 0. The savings in the operational expense can justifythe capital expense of 11 k-25 k Swedish Krona (SEK) for the LHTES systems in Cases 2–4 assuming a 15-yearoperation. Furthermore, the advantage of using the daytime charging strategy is principally the mitigation of CO2 emissions, which is up to 14% lower than the off-peak charging strategy. In summary, higher energy efficiencyfor heating is validated in the three new proposed integration layouts (Cases 2–4) against the condensercharging layout.
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| 44. |
- Xu, Tianhao, et al.
(författare)
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Performance evaluation of three latent heat storage designs for cogeneration applications
- 2021
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 225, s. 444-462
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Tidskriftsartikel (refereegranskat)abstract
- Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A onedimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46-72 degrees C and a HTF supplying flowrate range of 4.2-8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/ discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6-12% lower than the spiral coil design and by 2-3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications.
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| 45. |
- Xu, Tianhao, et al.
(författare)
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Thermal behavior of a sodium acetate trihydrate-based PCM : T-history and full-scale tests
- 2020
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 261
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Tidskriftsartikel (refereegranskat)abstract
- Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material’s (PCM’s) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance.
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