| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Li, Lifeng, et al.
(författare)
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Hydrodynamics and mass transfer of concentric-tube internal loop airlift reactors : A review
- 2022
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 359
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Forskningsöversikt (refereegranskat)abstract
- The concentric-tube internal loop airlift reactor is a typical reactor configuration which has been adopted for a myriad of chemical and biological processes. The reactor hydrodynamics (including mixing) and the mass transfer between the gas and liquid phases remarkably affect the operational conditions and thus are crucial to the overall reactor performance. Hence, this study aims at providing a thorough description of the basic concepts and a comprehensive review of the relevant reported studies on the hydrodynamics and mass transfer of the concentric-tube internal loop airlift reactors, taking microalgae cultivation as an exemplary application. In particular, the reactor characteristics, geometry, CFD modeling, experimental characterization, and scale up considerations are elucidated. The research gaps for future research and development are also identified.
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| 3. |
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| 4. |
- Li, L., et al.
(författare)
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Optical analysis of a multi-aperture solar central receiver system for high-temperature concentrating solar applications
- 2020
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Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 28:25, s. 37654-37668
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Tidskriftsartikel (refereegranskat)abstract
- A multi-aperture solar central receiver system is optically analyzed for increasing the net power to the receiver in a wide temperature range of 600-1800 K. A model system comprises a tower, a multi-aperture receiver with compound parabolic concentrators, and heliostat sub-fields. Optical modeling is performed using in-house developed Monte-Carlo ray-tracing programs. The heliostat sub-field geometrical configuration, the number of receiver apertures and optical properties of reflective surfaces are varied in the parametric study. Increasing the number of apertures from one to four increases the maximum net receiver power from 116MW to 332MW. The use of more than four apertures results in only limited further gain of the net receiver power but significantly decreases the overall optical efficiency and the solar-to-thermal efficiency. The optimal temperature for the maximized annual solar-to-exergy efficiency is found in the range of 1100-1200 K. This optimal temperature decreases slightly with an increasing number of apertures.
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| 5. |
- Liu, Qingming, et al.
(författare)
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On the dynamics and heat transfer of bubble train in micro-channel flow boiling
- 2017
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Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 87, s. 198-203
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics and heat transfer characteristics of flow boiling bubble train moving in a micro channel is studied numerically. The coupled level set and volume of fluid (CLSVOF) is utilized to track interface and a non-equilibrium phase change model is applied to calculate the interface temperature as well as heat flux jump. The working fluid is R134a and the wall material is aluminum. The fluid enters the channel with a constant mass flux (335 kg/m(2)*s), and the boundary wall is heated with constant heat flux (14 kW/m(2)). The growth of bubbles and the transition of flow regime are compared to an experimental visualization. Moreover, the bubble evaporation rate and wall heat transfer coefficient have been examined, respectively. Local heat transfer is significantly enhanced by evaporation occurring vicinity of interface of the bubbles. The local wall temperature is found to be dependent on the thickness of the liquid film between the bubble train and the wall.
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| 6. |
- Ruan, Tianqi, et al.
(författare)
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A new optimal PV installation angle model in high-latitude cold regions based on historical weather big data
- 2024
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- PV technologies are regarded as one of the most promising renewable options for the transition towards Net Zero. Despite the rapid development of PV systems in recent years, achieving the necessary goals requires more than a threefold increase in annual capacity deployment by 2030. However, current PV systems often fall short of optimal performance due to improper installation angles. In high-latitude cold regions, the actual PV generation capacity is frequently overestimated due to the omission of snow conditions. This study introduces a novel model designed for high-latitude regions to predict local optimal PV installation angle that maximizes PV power generation, utilizing historical weather big data, including snowfall and melting effects. A case study is presented within a Swedish context to demonstrate the implementation of these methods. The results highlight the crucial role snow conditions play in determining PV performance, resulting in an average reduction of 14.7% in annual PV power generation. Optimal installation angle could yield approximately a 4.8% improvement compared to common installation angles. The study also explores the application of snow removal agents, which could potentially increase PV generation by 0.1–2.3%. Additionally, the new PV installation angle successfully captures the impact of the local weather changes on PV power generation, potentially serving as a bridge between climate change adaptation and future PV power generation endeavors.
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| 7. |
- Shao, X. -F, et al.
(författare)
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Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature latent heat storage. (Ⅰ) : Non-isothermal melting and crystallization behaviors
- 2018
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Ingår i: Energy. - : Elsevier Ltd. - 0360-5442 .- 1873-6785. ; 160, s. 1078-1090
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Tidskriftsartikel (refereegranskat)abstract
- Towards latent heat storage in the low-to-medium temperature range (70–250 °C), screening of sugar alcohols and their binary eutectic mixtures as potential phase change materials was carried out by focusing on the non-isothermal melting and crystallization behaviors. A preliminary screening shortened the long list of isomers from common four-carbon to six-carbon sugar alcohols to only six affordable candidates, i.e., xylitol, d-sorbitol, erythritol, d-mannitol, d-dulcitol and inositol (ordered with increasing the melting point). Based on the six pre-screened sugar alcohols, a total of 15 binary eutectic mixtures were prepared to manipulate the melting points for more flexible match with real applications. Non-isothermal tests were then performed on a differential scanning calorimeter at various ramping/cooling rates up to 10 °C/min. In addition to determination of the melting point and latent heat of fusion, a special attention was paid to the crystallization behaviors by undertaking consecutive melting-crystallization cyclic tests. It was found that the two candidates with the lowest melting points (both below 100 °C), i.e., xylitol and d-sorbitol, as well as the nine binary eutectic mixtures containing at least one of them, are unable to crystallize from the melt during cool-down at any cooling rates tested (down to 0.5 °C/min). Four other binary eutectic mixtures, i.e., erythritol (84 mol%) + d-mannitol, erythritol (95 mol%) + d-dulcitol, erythritol (96 mol%) + inositol and d-dulcitol (69 mol%) + inositol, were also shown to be unable to crystallize upon cooling, with the crystallization occurring during the reheating process instead, referred to as cold crystallization. The rest four pure sugar alcohols with relatively high melting points (110–230 °C), i.e., erythritol, d-mannitol, d-dulcitol, inositol, and two mixtures, i.e., d-mannitol (70 mol%) + d-dulcitol and d-mannitol (82 mol%) +inositol, were found to be able to crystallize upon cooling, although they all suffer from severe supercooling (e.g., up to over 100 °C for erythritol). The affordable pure and mixture sugar alcohols were deemed to have desirably high latent heat storage density, especially for those with higher melting points. However, they all face specific issues associated with crystallization, which must be addressed before they can really be utilized in real applications. In addition, it may not worth making eutectic mixtures, although this is deemed to be an effective way of manipulating the melting points of sugar alcohols.
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| 8. |
- Shao, Xue-Feng, et al.
(författare)
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Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature thermal energy storage. (II) : Isothermal melting and crystallization behaviors
- 2019
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 180, s. 572-583
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Tidskriftsartikel (refereegranskat)abstract
- Based on the non-isothermal phase change behaviors of twenty-one pure and mixture sugar alcohols presented in our previous study (Part 1), the isothermal melting and crystallization behaviors were further tested in this supplemental work for five selected pure sugar alcohols (xylitol, erythritol, dmannitol, d-dulcitol and inositol) and their five binary eutectic mixtures to make an advanced screening of these candidates for low-to-medium temperature latent heat storage. The isothermal melting and crystallization behaviors of these ten candidates were tested at a constant degree of superheat (10 degrees C) and various degrees of subcooling up to 210 degrees C. The phase change temperatures, degrees of supercooling and durations of phase change were determined by the recorded temperature-history curves. It was found that the incrystallizable xylitol and its eutectic mixture of xylitol (75 mol%) + erythritol with low melting points under 100 degrees C are also unable to crystallize during isothermal cool-down at any degrees of subcooling (30-90 degrees C) due to the unavailability to nucleation. The rest eight crystallizable candidates all suffer from severe supercooling and are unable to crystallize at low degrees of subcooling (<20 degrees C). They undergo both one-phase supercooling due to poor nucleation performance and two-phase supercooling, which was unable to be obtained previously by non-isothermal cooling, due to slow crystallization kinetics. However, it seems difficult to find a correlation between the observed degrees of supercooling in both the liquid and solid phases and the prescribed degrees of subcooling by only three consecutive isothermal melting and crystallization cycles, as a result of the randomness of nucleation and large size of samples. The duration of crystallization was shown to decrease with increasing the degree of subcooling for both pure and mixture sugar alcohols due to the enhanced driving force for crystallization. The durations of crystallization of the mixture sugar alcohols appear to be longer than those of their pure compounds, due to the lower thermal conductivity and higher dynamic viscosity of the mixtures. Combining the present isothermal and the previous non-isothermal test results, it has been confirmed that the difficulty in crystallization and the severe supercooling are the primary issues for sugar alcohols, which must be addressed before they can be used in real-world latent heat storage systems.
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| 9. |
- Shao, Xue-Feng, et al.
(författare)
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Screening of sugar alcohols and their binary eutectic mixtures as phase change materials for low-to-medium temperature thermal energy storage. (III) : Thermal endurance
- 2020
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Ingår i: Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0360-5442 .- 1873-6785. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- The thermal endurance of four pure and three binary eutectic mixture sugar alcohols were examined as a complementary work to the previous screening efforts based on the phase change behaviors towards latent heat storage. It was shown that both the melting point and latent heat of fusion of these sugar alcohols degrade with increasing the heating duration, and that a higher degree of superheat leads to faster degradation. The melting point drift mainly attributes to the shrinking range of hydrogen bonding, whereas the decay of latent heat is likely resulted from the disruption of hydrogen bond networks and incomplete crystallization. Among the various candidates, erythritol exhibits the best thermal endurance. The infrared spectra demonstrated that sugar alcohols can be oxidized to generate aldehydes upon heating when exposed to air. It was also found that the duration for 10% degradation of the latent heat of fusion of inositol can be extended by similar to 9 times when being protected by nitrogen gas. However, although the introduction of nitrogen gas could efficiently improve the thermal endurance, other complex reactions can still occur in inert gas atmosphere at high temperatures, leaving the room for further improving the thermal endurance of sugar alcohols toward real-world applications.
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| 10. |
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| 11. |
- Wang, Wujun, 1984-, et al.
(författare)
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The effect of the cooling nozzle arrangement to the thermal performance of a solar impinging receiver
- 2016
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 131, s. 222-234
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the multi-row nozzle arrangement to the thermal performance of an impinging solar receiver is studied, and new governingequations are introduced for modifying the earlier introduced inverse design method. With the help of the modified inverse designmethod and a numerical conjugate heat transfer model, an impinging receiver based on stainless steel 253 MA material has been designedfor the combination of a micro gas turbine and the EuroDish collector system. At a DNI level of 800 W/m2, the average air temperatureat the outlet and the thermal efficiency can reach 1071.5 K and 82.7%. Furthermore, the temperature differences on the absorber can bereduced to 130 K and 149 K for two different DNI levels respectively. This represents a greatly improvement compared with other publishedcavity receiver designs.
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| 12. |
- Yang, Hanmin, 1992-, et al.
(författare)
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Carbon-negative valorization of biomass waste into affordable green hydrogen and battery anodes
- 2023
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The global Sustainable Development Goals highlight the necessity for affordable and clean energy, designated as SDG7. A sustainable and feasible biorefinery concept is proposed for the carbon-negative utilization of biomass waste for affordable H2 and battery anode material production. Specifically, an innovative tandem biocarbon + NiAlO + biocarbon catalyst strategy is constructed to realize a complete reforming of biomass pyro-vapors into H2+CO (as a mixture). The solid residues from pyrolysis are upgraded into high-quality hard carbon (HCs), demonstrating potential as sodium ion battery (SIBs) anodes. The product, HC-1600-6h, exhibited great electrochemical performance when employed as (SIBs) anodes (full cell: 263 Wh/kg with ICE of 89%). Ultimately, a comprehensive process is designed, simulated, and evaluated. The process yields 75 kg H2, 169 kg HCs, and 891 kg captured CO2 per ton of biomass achieving approx. 100% carbon and hydrogen utilization efficiencies. A life cycle assessment estimates a biomass valorization process with negative-emissions (−0.81 kg CO2/kg-biomass, reliant on Sweden wind electricity). A techno-economic assessment forecasts a notably profitable process capable of co-producing affordable H2 and hard carbon battery anodes. The payback period of the process is projected to fall within two years, assuming reference prices of 13.7 €/kg for HCs and 5 €/kg for H2. The process contributes to a novel business paradigm for sustainable and commercially viable biorefinery process, achieving carbon-negative valorization of biomass waste into affordable energy and materials.
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| 13. |
- Aichmayer, Lukas, et al.
(författare)
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Design and Analysis of a Solar Receiver for Micro Gas Turbine based Solar Dish Systems
- 2012
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Ingår i: Proceedings of the International SolarPACES Conference 2012. Marrakesh, Morocco. September 11-14, 2012.
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Konferensbidrag (refereegranskat)abstract
- The solar receiver is one of the key components of hybrid solar micro gas turbine systems which would seem to present a number of advantages when compared with Stirling engine systems. A solar receiver meeting the specific requirements for integration into the power conversion system of the solar laboratory of the Royal Institute of Technology - which will emulate a solar dish system and is currently under construction - was designed. The simulations that have been performed utilize a heat transfer and pressure drop model coupled with a multi-objective optimizer as well as a coupled-CFD/FEM tool, allowing determination of the ideal receiver design for the expected conditions. The analysis has shown that the use of volumetric solar receivers to provide heat input to micro gas turbine based solar dish systems appears to be a promising solution; with pressurized receiver configurations as the preferred choice due to significant lower pressure drops as compared to atmospheric configurations.
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| 14. |
- Aichmayer, Lukas, et al.
(författare)
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Experimental evaluation of a novel solar receiver for a micro gas-turbine based solar dish system in the KTH high-flux solar simulator
- 2018
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 159, s. 184-195
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Tidskriftsartikel (refereegranskat)abstract
- This work presents the experimental evaluation of a novel pressurized high-temperature solar air receiver for the integration into a micro gas-turbine solar dish system reaching an air outlet temperature of 800°C. The experiments are conducted in the controlled environment of the KTH high-flux solar simulator with well-defined radiative boundary conditions. Special focus is placed on providing detailed information to enable the validation of numerical models. The solar receiver performance is evaluated for a range of operating points and monitored using multiple point measurements. The porous absorber front surface temperature is measured continuously as it is one of the most critical components for the receiver performance and model validation. Additionally, pyrometer line measurements of the absorber and glass window are taken for each operating point. The experiments highlight the feasibility of volumetric solar receivers for micro gas-turbine based solar dish systems and no major hurdles were found. A receiver efficiency of 84.8% was reached for an air outlet temperature of 749°C. When using a lower mass flow, an air outlet temperature of 800°C is achieved with a receiver efficiency of 69.3%. At the same time, all material temperatures remain below permissible limits and no deterioration of the porous absorber is found.
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| 15. |
- Aichmayer, Lukas, et al.
(författare)
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Experimental Flux Measurement of a High-Flux Solar Simulator using a Lambertian Target and a Thermopile Flux Sensor
- 2016
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Ingår i: AIP Conference Proceedings 1734. - : American Institute of Physics (AIP). - 9780735413863
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Konferensbidrag (refereegranskat)abstract
- A measurement system for the experimental determination of the flux distribution at the focal plane of the KTH high-flux solar simulator was designed and implemented. It is based on a water-cooled Lambertian target and a thermopile flux sensor placed close to the focal point of the solar simulator. Correction factors to account for systematic effects were determined and an uncertainty analysis was performed. The measurement system was successfully used to evaluate the flux distribution of a single lamp/lens-arrangement with a peak flux of 675kW/m².
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| 16. |
- Choque Campero, Luis Antonio, et al.
(författare)
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Biomass-based Brayton-Stirling-AGMD polygeneration for small-scale applications in rural areas
- 2024
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 304
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Tidskriftsartikel (refereegranskat)abstract
- The lack of access to electricity and clean water still affects a substantial proportion of rural areas worldwide, in particular the global south. This paper presents a sustainable polygeneration system that can provide electricity, heat, and drinking water by using agricultural residues in remote rural areas. This polygeneration system consists of a solid biomass-fueled Brayton-Stirling combined cycle system, a boiler, and an air-gap membrane distillation unit. Four different system operation modes were designed to examine the most ideal configurations for maximizing power output, overall efficiency, and/or clean water production, considering a polygeneration system designed for a rural village with daily demands of 13450 kWh electricity and 7.5 m3 drinking water. A thermodynamic analysis are employed to analyze and compare these modes, each operating under steady state conditions. The highest electricity output, up to 160 kW, while the highest clean water is up to 0.7 m3/h. The fuel consumption can reach 0.9 kWh/kg of solid fuel and provide up to 0.0045 m3 of freshwater. In addition, nonlinear multi-objective optimization is used to meet the power demands of typical day in rural areas by varying the polygeneration operation modes and turbine inlet temperature.
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| 17. |
- Choque Campero, Luis Antonio, 1986-
(författare)
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Brayton-Stirling-Membrane Distillation systems for clean energy and water access in rural Bolivia
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Remote rural areas in developing countries face significant challenges toward securing supplies of energy and clean water. This thesis presents an investigation of an innovative concept—Brayton-Stirling-Membrane Distillation cogeneration—for the simultaneous provision of electricity and water with particular focus on small scale, decentralized applications in rural areas of Bolivia. The considered Brayton and Stirling cycles are externally fired, allowing for utilization of a locally available energy resource (waste agricultural biomass) via standard combustion processes. Both cycles can be paired thermally to make use of cascaded heat, with additional low-grade heat used to drive water purification through membrane distillation.Thermodynamic analyses of each operation mode were used to assess the system performance. The performance of the operation modes ranges from 100-200 kW of produced electricity and up to 0.7 m3/h of drinking water. Parameters such as turbine inlet temperature, pressure ratio, regenerator effectiveness, and working fluid impact cogeneration efficiency. The turbine inlet temperature had the largest effect on the production of electricity and water. This study identified trends in water production and energy and exergy efficiency, emphasizing the capability of the system to generate both electricity and drinking water from agricultural residues. Multi-objective Nonlinear Programming (MNLP) was employed for dispatch optimization, considering factors such as an externally fired gas turbine inlet temperature range of 973 to 1123 K, minimum daily water demand of 7.5 m3 and typical hourly-daily electrical demand of 13450 kWh. The results demonstrate the system’s ability to meet dual objectives, electricity and clean water demand, while minimizing excess power and deficits. Expanding the scope, this thesis delves into a hybrid cogeneration system integrating PV panels, batteries, and the Brayton-Stirling-MD system. Geographical diversity was considered, emphasizing the adaptability of the system to varying solar irradiation, temperature, and altitude. Economic indicators for three villages of around 500 people, including Levelized Cost of Electricity (LCOE) and Levelized Cost of Clean Water (LCOW), are presented. The system currently lacks economic viability, but ongoing technological development and component integration will lead to cost reduction towards to accept level in the future.
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| 18. |
- Choque Campero, Luis Antonio, et al.
(författare)
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Thermodynamic and exergetic analyses of a biomass-fired Brayton-Stirling cogeneration cycle for decentralized, rural applications
- 2023
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 292
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Tidskriftsartikel (refereegranskat)abstract
- Access to electricity in many remote rural areas of the world is wanting and often relies on decentralized concepts that are environmentally detrimental, costly, and unreliable. The purpose of this study was to examine an approach to meet this need that is based on an external biomass-fueled cogeneration system incorporating combined cycles for maximizing efficiency while ensuring robust operation. Specifically, the first and second laws of thermodynamics were analyzed in a system composed of a Brayton-Stirling cycle and a water boiler to compare efficiency, heat and electricity generation under three different power layouts of cogeneration for applications in the range of 100-200 kW electrical power output. The results show that overall efficiency is maximized at 85% with a hybrid power layout for cases where the turbine inlet temperature is 1273 K, the pressure ratio is 0.4, the regenerator effectiveness is 0.95, and the dead volume of the Stirling engine is 0.3. These findings provide a basis for implementing cogeneration systems to improve the reliability and robustness of power systems for rural electrification.
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| 19. |
- Garrido Galvez, Jorge, 1990-, et al.
(författare)
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A Detailed Radiation Heat Transfer Study of a Dish-Stirling Receiver : the Impact of Cavity Wall Radiation Properties and Cavity Shapes
- 2015
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Ingår i: SOLARPACES 2015: INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS. - : American Institute of Physics (AIP). - 9780735413863
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Konferensbidrag (refereegranskat)abstract
- A detailed 3-D radiation analysis of a dish-Stirling cavity receiver is carried out to estimate the cavity steady-state temperatures in order to assess the receiver integrity, lifetime and efficiency performance. For this purpose, a parabolic dish was modeled with 5.2 m focal length, 8.84 m aperture diameter and 2.1 mrad typical surface error. Three generic cavity shapes (cylindrical, diamond-shaped and reverse-conical) with three different emissivities (0.2, 0.4 and 0.7) are studied. Worst-case scenario heat generations (total absorbed radiation), maximum steady-state temperatures and energy balances of the cavities are calculated to evaluate the receiver performance. The results show that reverse-conical cavities can significantly reduce cavity wall peak temperatures (by 40-120 K), improve the temperature evenness and decrease the radiation losses by 4-5%. Regarding radiation properties, low reflectivities present lower steady-state temperatures even for low/moderate direct solar fluxes. Due to the lower temperatures, lower total thermal losses are also expected.
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| 20. |
- Garrido, Jorge, et al.
(författare)
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Characterization of the KTH high-flux solar simulator combining three measurement methods
- 2017
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 141, s. 2091-2099
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the characterization of the first Fresnel lens-based High-Flux Solar Simulator (HFSS) showing the evaluation of the total thermal radiative power dependent on the aperture radius at the focal plane. This result can be directly applied to calculate the thermal power input into any solar receiver tested in the KTH HFSS. Three measurement setups were implemented and their results combined to assess and verify the characterization of the solar simulator: a thermopile sensor measuring radiative flux, a CMOS camera coupled with a Lambertian target to obtain flux maps, and a calorimeter to measure the total thermal power within an area of 300×300 mm. Finally, a Monte Carlo analysis was performed to calculate the total uncertainties associated to each setup and to combine them to obtain the simulator characterization. The final result shows a peak flux of 6.8 ± 0.35 MW/m2 with a thermal power of 14.7 ± 0.75 kW within an aperture of 180 mm in diameter at the focal plane, and a thermal-electrical conversion efficiency of 25.8 ± 0.3%. It was found very good repeatability and a stable energy output from the lamps during the experiments.
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| 21. |
- Liu, Qingming, et al.
(författare)
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A numerical study of the transition from slug to annular flow in micro-channel convective boiling
- 2017
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Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 112, s. 73-81
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Tidskriftsartikel (refereegranskat)abstract
- A numerical study on the transition from slug flow (or elongated flow) to annular flow of convective boiling under high heat flux in a micro-channel with diameter of 0.4 mm is conducted. A constant velocity inlet boundary with mass flux 400 kg/m2 s, and heated wall with a constant heat flux (160, 80 kW/m2) are applied. A novel initialization method is proposed. Growth rate of the bubble and transition of the flow regime are well predicted by comparing with an experimental visualization. Effects of the transition are studied and findings are that this process disturbs thermal boundary layer which further enhances bubble evaporation.
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| 22. |
- Liu, Qingming, et al.
(författare)
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Mathmatical Modeling of the Thermal Behavior of a Long Lithium-Ion Battery
- 2023
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Ingår i: 2023 3rd International Conference on Energy, Power and Electrical Engineering, EPEE 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 460-465
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Konferensbidrag (refereegranskat)abstract
- A two-dimensional mathematical model is proposed to study the thermal behavior of a long lithium-ion battery. Bernardi's electrochemical heat generation theory is adopted and a finite element method is used to discrete the coupled electrochemical thermal equations. The potential and current density distribution in the electrodes of the batteries are presented as function of depth of discharge. Modelling results shows that the battery temperature increases as increase of discharging time. The temperature distribution in the battery electrodes are calculated and compared to experiments. It is found that the simulation has good agreement with the experimental studies.
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| 23. |
- Liu, Qingming, et al.
(författare)
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WITHDRAWN: Numerical study of the interactions and merge of multiple bubbles during convective boiling in micro channels
- 2017
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Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier. - 0735-1933 .- 1879-0178. ; 80, s. 10-17
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Tidskriftsartikel (refereegranskat)abstract
- Multi bubbles interaction and merger in a micro-channel flow boiling has been numerically studied. Effects of mass flux (56, 112, 200, and 335 kg/m2 ∗ s), wall heat flux (5, 10, and 15 kW/m2) and saturated temperature (300.15 and 303.15 K) are investigated. The coupled level set and volume of fluid (CLSVOF) method and non-equilibrium phase model are implemented to capture the two-phase interface, and the lateral merger process. It is found that the whole transition process can be divided to three sub-stages: sliding, merger, and post-merger. The evaporation rate is much higher in the first two stages due to the boundary layer effects in. Both the mass flux and heat flux affect bubble growth. Specifically, the bubble growth rate increase with the increase of heat flux, or the decrease of mass flux.
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| 24. |
- Liu, Yanyan, 1987-
(författare)
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Application of Rare-Earth Doped Ceria and Natural Minerals for Solid Oxide Fuel Cells
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although solid oxide fuel cell (SOFC) technology exhibits considerable advantages as compared to other energy conversion devices, e.g. high efficiency, low emission and fuel flexibility, its high operating temperature leads to rapid component degradation and has thus hampered commercialization. In recent years, intensive research interests have been devoted to lowering the operating temperature from the elevated temperature region (800-1,000 ℃) to intermediate or low-temperature range (<800 ℃). To achieve this goal, material selection plays a dominant role, involving improving the conductivity of existing electrolytes and developing new exploitable materials. This dissertation is focused on enhancing the ionic conductivity of rare-earth oxides (principally doped ceria) and exploring new candidate materials (e.g. natural minerals) for low temperature (LT) SOFCs.In this work, the scientific contributions can be divided into four aspects:i) To develop desirable superionic conductors, Sm3+/Pr3+/Nd3+ triple-doped ceria is designed to realize the desired doping for Sm3+ in bulk and Pr3+/Nd3+ at surface domains via a two-step wet chemical co-precipitation method. It exhibits high ionic conductivity, 0.125 S cm-1 at 600 ℃. The SOFC device using this material as electrolyte displays a high output power density of 710 mW cm-2 at 550 ℃.ii) To further clarify the individual effect of Pr3+ in the doped ceria, a single-element (Pr3+) doped ceria is studied, exhibiting a mixed electronic/ionic conduction property, capable of being employed as the core component of electrolyte-layer free solid oxide fuel cells (EFFCs).iii) To investigate various rare-earth doped-ceria materials in double- and triple-element doping solutions for LT-SOFCs, Sm3+/Ca2+ co-doped ceria and La3+/Pr3+/Nd3+ triple-doped ceria are synthesized and then further incorporated with semiconductors, e.g. La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) or Ni0.8Co0.15Al0.05Li-oxide (NCAL), to serve as a semiconducting-ionic conducting membrane in EFFCs.iv) To exploit the feasibility of natural mineral cuprospinel (CuFe2O4) as an alternative material for LT-SOFCs, three different types of fuel cell devices are fabricated and tested. The device using CuFe2O4 as cathode exhibits a maximum power density of 180 mW cm-2 with an open circuit voltage of 1.07 V at 550 °C, while the device using a homogeneous mixture membrane of CuFe2O4, Li2O-ZnO-Sm0.2Ce0.8O2 (LZSDC), and LiNi0.8Co0.15Al0.05O2 (NCAL) demonstrates an improved power output, 587 mW cm-2 under the same measurement conditions. Based on this work, a new triple-doping strategy is exploited to improve the ionic conductivity of doped ceria materials by surface- and bulk-doping methodology. Furthermore, the material developments of single-phase mixed electronic/ionic conducting doped ceria and doped ceria/semiconductor composites are realized and verify the feasibility of EFFC technology. Investigations on CuFe2O4 indicate the utility of natural minerals in developing cost-effective materials for LT-SOFCs.
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| 25. |
- Lyu, Xiaozan, et al.
(författare)
-
A bibliometric evaluation and visualization of global solar power generation research : productivity, contributors and hot topics
- 2024
-
Ingår i: Environmental Science and Pollution Research. - : Springer Nature. - 0944-1344 .- 1614-7499. ; 31:5, s. 8274-8290
-
Tidskriftsartikel (refereegranskat)abstract
- The demand for sustainable energy is increasingly urgent to mitigate global warming which has been exacerbated by the extensive use of fossil fuels. Solar energy has attracted global attention as a crucial renewable resource. This study conducted a bibliometric analysis based on publication metrics from the Web of Science database to gain insights into global solar power research. The results indicate a stable global increase in publications on solar power generation and a rise in citations, reflecting growing academic interest. Leading contributors include China, the USA, South Korea, Japan, and India, with the Chinese Academy of Sciences emerging as the most prolific institution. Multidisciplinary Materials Science, Applied Physics, Energy and Fuels, Physical Chemistry, and Nanoscience and Nanotechnology were the most used and promising subject categories. Current hot topics include the systematic analysis of photovoltaic systems, perovskite as a solar cell material, and focusing on stability and flexibility issues arising during photovoltaic-grid integration. This study facilitates a comprehensive understanding of the status and trends in solar power research for researchers, stakeholders, and policy-makers.
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| 26. |
- Martinez-Manuel, Leopoldo, et al.
(författare)
-
A comprehensive analysis of the optical and thermal performance of solar absorber coatings under concentrated flux conditions
- 2022
-
Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 239, s. 319-336
-
Tidskriftsartikel (refereegranskat)abstract
- Solar Absorber Coatings (SACs) are widely used materials for improving thermal efficiencies of solar receivers. Traditionally, these SACs are investigated using heat treatments to test their optical-thermal properties; however, tests under concentrated flux conditions are still required. In this work, the thermal efficiency of different SACs is experimentally evaluated and compared. The analyzed SACs are: (1) Pyromark®2500, (2) Solkote®, (3) Thurmalox®250, (4) Comex® and (5) a new Soot from Forest Biomass (SFB) based coating. To assess the SACs performance, a High Flux Solar Simulator along with a calorimetric test bench are implemented under a well-controlled indoor environment applying two levels of concentrated irradiance of 100 ± 3 kW/m2 and 415 ± 12 kW/m2 named low and high flux level, respectively. Results show that, for a low flux level, the analyzed coatings present thermal efficiencies in a range from 91.74% to 83.24%, exhibiting a slightly close performance in most of the cases. Correspondingly, for a high flux level, the efficiencies range from 88.69% to 72.69%, with Pyromark®2500 being the most efficient in both cases. In addition, variations in the optical properties are reported for the experimental campaign with the high flux level, observing slight changes in the spectral absorptance and emittance. From these results, Pyromark presents the highest drop in solar absorptance of 1.22%, which is attributed to microcracks observed through the Scanning Electron Microscope (SEM). Thus, the presented approach can provide valuable information about the effects that concentrated flux levels can have in the optical-thermal performance of the analyzed samples.
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| 27. |
- Martinez-Manuel, Leopoldo, et al.
(författare)
-
Numerical analysis on the optical geometrical optimization for an axial type impinging solar receiver
- 2021
-
Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 216
-
Tidskriftsartikel (refereegranskat)abstract
- Solar cavity receivers are key components in point-focus concentrating solar power technologies due to their benefits of high efficiency and operating temperature. Accordingly, the enhancement of the optical performance can yield to significant improvements in the whole thermal power system. In this study, a geometrical optimization of an axial type impinging receiver for a solar dish Brayton system was analytically accomplished through Monte Carlo ray tracing method. By modeling a reference cylindrical cavity, optical surface properties and geometrical parameters were analyzed by dividing the cavity into three zones: front wall, middle wall and back wall. Simulation results show that the light flux peaking on the cylindrical wall can be significantly reduced when the cavity front wall is modified by changing the inclination angle; the light flux distribution over the absorber surface can be flattened by increasing the cavity radius; the irradiance distribution over the absorber can be efficiently adjusted by modifying the cavity back wall. After the cavity geometry optimization, the optical efficiency of the receiver can be enhanced by 3.34%, the material volume can be reduced by 20.1% and the peak flux on the cavity wall can be reduced by 38.6%, from 30 to 18.4 kW/m(2).
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| 28. |
- Martinez-Manuel, Leopoldo, et al.
(författare)
-
Optimization of the radiative flux uniformity of a modular solar simulator to improve solar technology qualification testing
- 2021
-
Ingår i: Sustainable Energy Technologies and Assessments. - : Elsevier BV. - 2213-1388 .- 2213-1396. ; 47
-
Tidskriftsartikel (refereegranskat)abstract
- Solar simulators are key facilities for conducting solar research and certification tests under a well-controlled environment. This study presents the optical design optimization of a modular low flux solar simulator to improve solar technology qualification testing. The optical system was designed as a multi-lamp array of 26 subunits. Each subunit consists of a 575 We metal halide lamp and a parabolic reflector. The Monte Carlo ray tracing technique was used for analyzing the optical performances of the proposed design. Reflector design parameters were analyzed in detail for optimizing the uniformity of the flux distribution on the target. Results show that an average flux of 1198 W/m(2) over a target area of 2000 mm x 1000 mm, with a conversion efficiency of 25.7% and a sustained non-uniformity of only 1.4% was numerically achieved, predicting a Class A solar simulator for large target areas. A shutter curtain was modeled and introduced between the light source and the target for flux regulation, achieving average flux levels ranging from 1162 to 105 W/m(2) with a resolution of approximately 100 W/m(2). The modular nature of this design has the great advantage that it could be easily scaled according to the test requirements of potential solar systems.
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| 29. |
- Pan, Tianyao, 1994-, et al.
(författare)
-
A novel gas turbine simulator for testing hybrid solar-Brayton energy systems
- 2022
-
Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904 .- 1879-2227. ; 268
-
Tidskriftsartikel (refereegranskat)abstract
- A novel gas turbine simulator is developed to establish controllable boundaries for investigating the characteristics of key components in gas turbine based hybrid energy systems under different operating conditions. The gas turbine simulator consists of a compressed air system, an electrical heater, a mass flow controller, a proportional solenoid valve, a dual-flow choked nozzle, and a PLC-based control system. With the proposed control strategy, the fluid parameters, such as temperature, mass flow rate, and pressure, can be automatically regulated to simulate the boundary conditions of a gas turbine under various workloads. Experimental results for both cold and hot states have validated the capabilities of the gas turbine simulator to deliver convergent control results with fast response. The gas turbine simulator has demonstrated considerable performance in stabilizing system boundaries with the precision in terms of pressure control reaching +/- 0.004 bar for steady states, and +/- 0.018 bar to +/- 0.076 bar for transient states with mass flow and temperature perturbations. The gas turbine simulator can also accurately track linear and nonlinear trajectories during operating point migrations, and effectively limit deviations within +/- 0.037 bar.
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| 30. |
- Pan, Tianyao, 1994-
(författare)
-
Development of a Novel Gas Turbine Simulator for Hybrid Solar-Brayton Systems
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hybrid solar-Brayton systems utilize both solar thermal energy and supplementary renewable fuels to provide controllable and dispatchable power output, which renders them a promising way to meet the growing energy demand and reduce the carbon footprints. However, existing testing facilities for key components in such hybrid systems often fail to accomplish the testing requirements, hence impeding the improvement of the renewable energy share and the overall efficiency. A novel testing facility is urgently needed in order to thoroughly stimulate and analyze the component characteristics.This research work focuses on the development of a gas turbine simulator as an innovative testing facility for hot, pressurized components in hybrid solar-Brayton systems. The dual-flow choked nozzle based flow control has been proposed, explained, and analyzed in comparison to the single-flow layout. The basic idea of gas turbine simulator has been experimentally implemented and validated on a prototype, verifying its functionality. By incorporating a PLC-based control system, an automated gas turbine simulator has been designed and modified based on the prototype. Its performance with regard to stabilizing boundaries and tracking trajectories has been evaluated by experiments.Based on the experimental results, the gas turbine simulator prototype has proven its ability to establish controllable boundary conditions and migrate operating points for the impinging receiver. Through manual adjustments, excellent quasi-steady state performance has been obtained, with the precision for pressure control reaching ±0.005 bar at ambient temperature and ±0.015 bar at high temperature of 797.1-931.5 °C. The manual operation time has been identified at 23.1 s for establishing the receiver boundaries, and at 70 s for changing operating points.With the help of the proposed control strategy, the automated gas turbine simulator has eliminated the need for manual adjustments, and demonstrated the ability to maintain the safe and convergent operation for the receiver. The performance in boundary condition stabilization has been satisfactory, with enhanced steady-state accuracy comparing to the prototype by virtue of the PID controller. The transient-state fluctuations in pressure control have been effectively restrained within an acceptable region with deviations of ±0.018 bar to ±0.076 bar from the desired 2.400 bar operating pressure. The capability of tracking linear and nonlinear trajectories has also been testified, with the precision level between ±0.023 bar and ±0.037 bar.Finally, in view of the good stability, high precision, and rapid response manifested in the experimental studies, the gas turbine simulator has validated its ability to imitate the steady and transient characteristics of gas turbines on the boundaries of the test section. It also grants the possibilities to conduct control variable studies and wide-range transition studies. The gas turbine simulator is a suitable testing facility for the key components in hybrid solar-Brayton systems.
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| 31. |
- Ragnolo, Gianmarco, et al.
(författare)
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Technoeconomic Design of a Micro Gas-Turbine for a Solar Dish System
- 2014
-
Ingår i: Proceedings of the International SolarPACES Conference 2014. Beijing, China. September 16-19. - : Elsevier.
-
Konferensbidrag (refereegranskat)abstract
- An integrated approach for the design of a custom-tailored hybrid solar MGT with an integrated solar receiver for the use in a small-scale solar dish unit is presented in order to overcome the inherent limitations of adapting a MGT in the desired power range to solar operation. The resulting MGT-dish equipped with the ‘optimal’ MGT shows a nominal conversion efficiency of 29.6%. Then, a thermoeconomic analysis of the entire system is performed to evaluate and compare the economic and environmental performance of the MGT-dish with a Dish-Stirling system. From an economical point of view the MGT-dish outperforms the dish-Stirling with LCoEs as low as 15.3€cts/kWhel compared to 22.4€cts/kWhel.
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| 32. |
- Ruan, Tianqi, et al.
(författare)
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Potential of grid-connected decentralized rooftop PV systems in Sweden
- 2023
-
Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 9:6
-
Tidskriftsartikel (refereegranskat)abstract
- Solar power generation in Sweden is far from required capacity to help with transition towards 100% renewables in the power sector by 2040. Decentralized PV system attracts attentions given the conflicts of future increasing demands and land scarcity in the urban areas. However, it is not easy to implement it due to challenges on local conditions and lack of references. This paper aims to propose an overview of the potential of small-scale grid-connected PV systems in a Swedish context and offer an example for urban PV system planning in Sweden or high latitude areas. A model considering weather, space, infrastructures and economics is developed and implemented with a real case in the Swedish context. The findings verify the technical and economic feasibility of urban decentralized rooftop PV systems in the Swedish context. It is found that this kind of system does have considerable power potential in the Swedish context without land requirements. This kind of PV system could be a promising option for future power generation which satisfies part of demands and reduces pressure on external grids. The full potential could be only achieved with improved infrastructures, and the profitability of the system relies heavily on market and political conditions. This study can be a refence for other high latitude areas.
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| 33. |
- Stanek, Bartosz, et al.
(författare)
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A potential solution in reducing the parabolic trough based solar industrial process heat system cost by partially replacing absorbers coatings with non-selective ones in initial loop sections
- 2023
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 331
-
Tidskriftsartikel (refereegranskat)abstract
- An important step to achieve low-emission production is the integration of solar energy into industrial processes for decarbonizing the industrial sector. It is therefore necessary to attempt to minimize the cost of these solar industrial process heat systems. The article presents a strategy to reduce the investment costs and thus increase the popularity of parabolic trough collectors by partially replacing the expensive selective coating with a high absorptive, low-cost, non-selective coating in the initial sections of the solar loop where the heat transfer fluid temperature is lower. The analysis was performed for 4 case studies reflecting commercially available solutions with varying temperature ranges for different industrial applications. Calculations were performed using the twodimensional developed mathematical model that validated with experimental data. The assumed heat transfer fluid is Therminol VP-1. The results have shown the potential of partial use of the Pyromark coating for low and medium-temperature industrial process heat systems with inlet-outlet temperature ranges of 60-120 degrees C and 100-200 degrees C. The analysis also showed that all the absorbers can be covered with a low-cost coating in the first scenario. Efficiency increases from 1.5 to 5.5 percentage points have been observed. For the second scenario, 15 of the 24 absorbers can be covered with a low-cost coating, when the installation works at a solar irradiance of 800 W/m2. Since the results are depended on the solar irradiance and the chosen regulation strategy of the flow, the final number of absorbers possible to cover with non-selective coating requires a long-term analysis for each case examined.
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| 34. |
- Trevisan, Silvia, et al.
(författare)
-
A high-temperature thermal stability and optical property study of inorganic coatings on ceramic particles for potential thermal energy storage applications
- 2022
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 239
-
Tidskriftsartikel (refereegranskat)abstract
- Ceramic-based packed bed solutions are becoming more common in the energy fields as both thermal energy storage and heat exchanger. Such solutions are usually designed for the working temperature ranges above600 ◦C, thus thermal radiation becomes significant and even acts as the dominant heat transfer mechanism. Therefore, applying high-temperature coatings with different thermal properties could be an efficient way in enhancing the performance of these applications. In this work, the high-temperature long residency and cyclic thermal stability of six inorganic coatings applied on a ceramic substrate are investigated. Both qualitative and quantitative assessments are performed. The results show that HIE-Coat 840MX and Pyropaint 634 ZO exhibit excellent thermal stability performance both at high-temperature testing (1000 ◦C) and under thermal cycle testing (400 ◦C–800 ◦C). TiO2 based coatings could be a viable solution if the powder is pre-treated to avoid polymorph transition during the operation. Stainless steel 304 powder-based coating could also be a possible solution, since the adhesive curbs the oxidation and hinders the coating from deterioration. Contrarily, Pyromark2500 and MgO-based coating show different degradation problems that limit their exploitation in high-temperature applications undergoing thermal cycles. The investigated coatings show a wide range of thermal emissivity (between 0.6 and 0.9), with stable or decreasing trends with temperature. This enables a potential20% change of the effective thermal conductivity for the packing structure. This work is a stepping-stone towards further detailed experimental studies on the influence of coatings on various packed bed thermal storage systems, and thus offer a new option in improving the performances of the energy equipment with packed bed systems.
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| 35. |
- Trevisan, Silvia, et al.
(författare)
-
A study of metallic coatings on ceramic particles for thermal emissivity control and effective thermal conductivity enhancement in packed bed thermal energy storage
- 2022
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 234
-
Tidskriftsartikel (refereegranskat)abstract
- Ceramic particles-based packed bed systems are attracting the interest from various high-temperature applications such as thermal energy storage, nuclear cooling reactors, and catalytic support structures. Considering that these systems work above 600 ◦C, thermal radiation becomes significant or even the major heat transfer mechanism. The use of coatings with different thermal and optical properties could represent a way to tune and enhance the thermodynamic performances of the packed bed systems. In this study, the thermal stability of several metallic (Inconel, Nitinol, and Stainless Steel) based coatings is investigated at both high temperature and cyclic thermal conditions. Consequently, the optical properties and their temperature dependence are measured. The results show that both Nitinol and Stainless Steel coatings have excellent thermal stability at temperatures as high as 1000 ◦C and after multiple thermal cycles. Contrarily, Inconel (particularly 625) based coatings show abundant coating degradation. The investigated coatings also offer a wide range of thermal emissivity (between0.6 and 0.9 in the temperature range of 400–1000 ◦C), and variable trends against increasing temperature. This work is a stepping-stone towards further detailed experimental and modelling studies on the heat transfer enhancement in different ceramic-based packed bed applications through using metallic coatings.
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| 36. |
- Trevisan, Silvia, et al.
(författare)
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Coatings utilization to modify the effective properties of high temperature packed bed thermal energy storage
- 2021
-
Ingår i: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 185
-
Tidskriftsartikel (refereegranskat)abstract
- High-temperature thermal energy storage is becoming more and more important as a key component in concentrating solar power systems and as an economically viable large-scale energy storage solution. Ceramics and natural rocks based packed beds are one of the attracting solutions. For application temperatures above 600 ◦C, radiation heat transfer becomes the dominant heat transfer phenomenon and it greatly influences the performance of thermal storage systems. Coatings with different thermal properties (mainly thermal emissivity and thermal conductivity) could be exploited to modify the effective thermal properties of packed beds. In this work, we present a methodology to account for the thermal effect of a coating layer applied over the pebbles of a packed bed. The influences on the packed bed effective thermal conductivity of several characteristics of the coating material, packed bed arrangement, and filler material are investigated. The results show that low emissivity coatings could reduce the effective thermal conductivity of a rock based packed bed of about 58%, with respect to a similar uncoated solution, already at 800 ◦C. A low emissivity coating could also limit the increase in the thermal effective conductivity from the cold to the hot zone of the storage. Coatings would have a higher influence when applied in packed beds with large size particles, relatively high thermal conductivity of the substrate and void fraction. The application of different coatings, with various thermo-physical properties, in different parts of the storage could modify the effective thermal conductivity distribution and enable a partial control of the thermocline degradation, increasing the storage thermal efficiency.
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| 37. |
- Trevisan, Silvia, et al.
(författare)
-
Experimental Evaluation of a High-Temperature Radial-Flow Packed Bed Thermal Energy Storage under Dynamic Boundary Conditions
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- High-temperature thermal energy storage is recognized to be a key technology to ensure a future fossil-free energy scenario. Packed bed thermal energy storage is an economically viable high-temperature and large-scale energy storage solution. The present work introduces the experimental investigation of an innovative 49.7 kWhth radial-flow type high-temperature packed bed thermal energy storage under dynamic boundary conditions. Various quasi-dynamic air flow rate profiles, representative of different potential applications, have been tested during the charge process to investigate their influence on the thermodynamic performance of the storage. The outlet thermal power during the discharge has been controlled by managing the air flow rate. Short operational cycles have also been performed. The results show that dynamic boundary conditions can lead to a thermal efficiency reduction between 0.5 and 5 % with respect to static conditions. A control of the air mass flow rate could be an efficient strategy to stabilize the thermal power output during the discharge while minimizing peaks in the pressure drop. This work testifies that specific dynamic boundary conditions should be included during the thermal storage design process since they could largely affect the unit thermodynamic performance and potential scale-up. If no specific dynamic profiles are available during the packed bed storage design stage, it is suggested to consider average air mass flow rate to guarantee limited efficiency reduction.
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| 38. |
- Trevisan, Silvia, et al.
(författare)
-
Experimental evaluation of a high-temperature radial-flow packed bed thermal energy storage under dynamic mass flow rate
- 2022
-
Ingår i: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 54, s. 105236-
-
Tidskriftsartikel (refereegranskat)abstract
- High-temperature thermal energy storage is recognized to be a key technology to ensure future sustainable energy generation. Packed bed thermal energy storage is a cost-competitive large-scale energy storage solution. The present work introduces the experimental investigation of an innovative 49.7 kWh(th) radial-flow type high-temperature packed bed thermal energy storage under dynamic mass flow rates. Various dynamic air flow rate profiles, representative of different potential applications, have been tested during the charging process to investigate their influence on the thermodynamic performance of the storage. The outlet thermal power during the discharge has been controlled by managing the air flow rate. Short operational cycles have also been performed. The results show that dynamic mass flow rates can lead to a thermal efficiency reduction between 0.5 % and 5 % with respect to static conditions. Controlling the air mass flow rate could be an efficient strategy to stabilize the thermal power output during the discharge while minimizing peaks in the pressure drop. This work testifies that specific dynamic boundary conditions should be included during the thermal storage design process since they could largely affect the unit thermodynamic performance and potential scale-up. If no specific dynamic profiles are available during the packed bed storage design stage, it is suggested to consider typical dynamic profiles of the air mass flow rate to guarantee limited efficiency reduction during operation.
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| 39. |
- Trevisan, Silvia, et al.
(författare)
-
Experimental evaluation of an innovative radial-flow high-temperature packed bed thermal energy storage
- 2022
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 311
-
Tidskriftsartikel (refereegranskat)abstract
- High-temperature packed-bed thermal energy storage represents an economically viable large-scale energy storage solution for a future fossil-free energy scenario. The present work introduces first-of-a-kind experimental setup of a radial packed-bed TES, and its performance assessment based on experimental investigations. The storage performance is analyzed based on a set of dimensionless criteria and indicators. The laboratory-scale prototype has an energy capacity of 49.7 kWhth and working temperatures between 25 ◦C and 700 ◦C with anon-pressurized dry airflow. The influence of different working fluid mass flow rates and inlet temperatures during charge and discharge is assessed. The proposed storage design ensures limited pressure drop, lower than1 mbar, and thermal losses, about 1.11 % during dwell after charging at 700 ◦C until a state of charge of 55.8 %. A maximum overall thermal efficiency of 71.8 % has been recorded and trade-offs between efficiency, thermal uniformity, and thermocline thickness are highlighted. This work testifies that reduced pressure drops are the key advantage of radial-flow packed-bed designs. Thermocline degradation is shown to be the main weak point of this thermal energy storage design.
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| 40. |
- Trevisan, Silvia, et al.
(författare)
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Laboratory prototype of an innovative radial flow packed bed thermal energy storage
- 2022
-
Ingår i: SOLARPACES 2020. - : AIP Publishing.
-
Konferensbidrag (refereegranskat)abstract
- This work presents a laboratory scale 50kWhth prototype of an innovative radial flow packed bed thermal energy storage. The proposed storage has an inward radial heat transfer fluid flow during charge and a reverted fluid flow, by means of a valve arrangement, during discharge. The storage unit is equipped with differential pressure gauges, mass flow controller and 50?K-thermocouples to accurately measure the thermodynamic behavior of the unit. In order to assess the performance of the proposed thermal energy storage design two specific indicators have been introduced and defined, namely: the temperature uniformity, and the hydrodynamic uniformity. The results of preliminary CFD studies show a maximum temperature deviation of 20°C along the storage axial direction and uniformity indexes higher than 90%.
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| 41. |
- Trevisan, Silvia, 1993-
(författare)
-
Renewable Heat on Demand : High-temperature thermal energy storage: a comprehensive study from material investigation to system analysis via innovative component design
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-temperature thermal energy storage could enable widespread exploitation of renewable energy sources, providing the required energy flexibility. Technology and component development is needed to enhance the storage thermo-dynamic performance, and identify key design features. Similarly, system-level integration studies are required to fully understand the techno-economic potential of high-temperature thermal energy storage as integrated into different energy systems. This research work focuses on the development of an innovative packed bed high-temperature thermal energy storage and a multi-level investigation of the potential of this technology. The integration and techno-economic performance of a packed bed thermal energy storage have been studied focusing primarily on its application within concentrating solar power plants. Numerical studies and experimental tests have been conducted assessing the suitability of various coatings to optimize the heat transfer in high-temperature packed beds. A comprehensive design of an innovative packed bed thermal energy storage prototype and its experimental evaluation have been presented. Adapted numerical models have also been validated based on the experimental results, providing the ground for further technology development.The outcomes of this research work show that packed bed thermal energy storage could be a key component in air-driven concentrating solar powerplants, granting high capacity factor while limiting the capital costs. The designed radial flow packed bed storage showed thermal efficiency of about72 % and extremely low-pressure drops. Thermocline degradation control strategies and proper packing have been highlighted as key aspects to target for further development. This research also highlights that accurate boundary conditions should be accounted for when designing packed bed thermal energy storage. Innovative figures of merit, such as the Levelized Cost ofStorage, should be included in the design process. The outcomes of this work show also that coatings could be exploited to modify the particle surface properties while optimizing the heat transfer within packed bed units. In particular, high emissivity coatings could enhance the effective thermal conductivity, while coatings with low thermal emissivity could be exploited as a form of passive thermocline control. Finally, this work testifies that high temperature packed bed could represent a techno-economically valuable energy storage solution. Optimized packed bed designs and their system integration could enable higher renewable penetration, as well as the recovery of a large amount of waste heat from the hard-to-abate and energy-intensive industrial sector.
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| 42. |
- Trevisan, Silvia, et al.
(författare)
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Techno-economic analysis of an innovative purely solar-driven combined cycle system based on packed bed TES technology
- 2020
-
Ingår i: AIP Conference Proceedings. - : AIP Publishing.
-
Konferensbidrag (refereegranskat)abstract
- The present work performs a techno-economic analysis of a purely solar driven combined cycle composed of a solar air receiver directly connected to a topping gas turbine coupled to a bottoming packed bed thermal energy storage atthe gas turbine exhaust, which runs in parallel to a bottoming steam cycle. Capacity factor, capital expenditure, and Levelized Cost of Electricity have been considered to assess the plant performance. A sensitivity analysis has been performed in order to understand the influence of solar multiple, energy storage capacity and gas turbine expansion ratio over the plant key performance indicators. The results show that the studied solar driven combined cycle is more costly than conventional ones, and therefore it leads to higher Levelized Cost of Electricity. However, it enables a complete reduction of CO2 emissions and increased flexibility in the system with the help of the introduction of an intermediate packet bed thermal energy storage. Furthermore, large solar multiple, medium storage capacity and complete expansion ratio through the gas turbine enable enhanced system performance. Finally, further works including optimized dispatch algorithms could enable a proper evaluation of the economic profit given by the flexibility offered by the storage unit and by a potential control of the Brayton cycle recuperation level in the modified plant layouts.
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| 43. |
- Wang, Wujun, 1984-, et al.
(författare)
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A dual-flow choked nozzle based precise pressure controller for high-temperature gas systems
- 2021
-
Ingår i: Measurement. - : Elsevier BV. - 0263-2241 .- 1873-412X. ; 184
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Tidskriftsartikel (refereegranskat)abstract
- A novel dual-flow choked nozzle based pressure controller is developed to achieve high-precision pressure control. The primary air flow is mainly used for offering the required mass flow to the test section, and the secondary air flow is used for regulating the total mass flow through the choked nozzle to achieve required pressure levels. The test results show that the precision of the stabilization of the pressure can reach +/- 0.005 bar for cold-state environments with air flow at ambient temperature, and +/- 0.015 bar for hot-state environments with air flow temperature in the range of 797.1-931.5 degrees C. Besides, this pressure controller has fast response. A new pressure steady state can be reached within 23.1 s for air flow at ambient temperature and 70 s for hightemperature scenario. Since no moving component exposed to the high-temperature air flow, it is very suitable for the pressurized test rigs with extremely high-temperature gas flow.
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| 44. |
- Wang, Wujun, 1984-, et al.
(författare)
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A New High-Temperature Durable Absorber Material Solution through a Spinel-Type High Solar Absorptivity Coating on Ti2AlC MAX Phase Material
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:37, s. 45008-45017
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Tidskriftsartikel (refereegranskat)abstract
- Enhancing the operating temperature of concentrating solar power systems is a promising way to obtain higher system efficiency and thus enhance their competitiveness. One major barrier is the unavailability of suitable solar absorber materials for operation at higher temperatures. In this work, we report on a new high-temperature absorber material by combining Ti2AlC MAX phase material and iron-cobalt-chromite spinel coating/paint. This durable material solution exhibits excellent performance, passing the thermal stability test in an open-air environment at a temperature of 1250 degrees C for 400 h and at 1300 degrees C for 200 h. The results show that the black spinel coating can offer a stable high solar absorptivity in the range of 0.877-0.894 throughout the 600 h test under high temperatures. These solar absorptivity values are even 1.6-3.3% higher than that for the sintered SiC ceramic that is a widely used solar absorber material. Divergence of solar absorptivity during these relatively long testing periods is less than 1.1%, indicating remarkable stability of the absorber material. Furthermore, considering the simple application process of the coating/painting utilizing a brush followed by curing at relatively low temperatures (room temperature, 95 and 260 degrees C in sequence), this absorber material shows the potential for large-scale, high-temperature solar thermal applications.
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| 45. |
- Wang, Wujun, 1984-, et al.
(författare)
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A theoretical heat transfer analysis of different indirectly-irradiated receiver designs for high-temperature concentrating solar power applications
- 2021
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 163, s. 1983-1993
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Tidskriftsartikel (refereegranskat)abstract
- Indirectly-irradiated receivers are widely used in most of the existing commercial concentrating solar power (CSP) plants. In order to compare the performances of the potential design strategies for the future high-temperature indirectly-irradiated receivers, a theoretical study has been conducted from a thermodynamic point of view. By analyzing the thermal circuit of the absorber wall, the roles of the heat flux through the wall and the total heat resistance have been observed to become more important to the receiver performances with increasing the concentration ratio. The influences of four parameters to the receiver performances have been analyzed: the convection heat transfer coefficient of the working fluid, the cavity shape factor, the thermal conductivity and the thickness of the absorber wall. Designing the absorber in a cavity shape has been proved to be an efficient way in enhancing the receiver performances by reducing the heat flux through the absorber wall. The advantage of the cavity receivers increases with increasing the concentration ratio, especially for gaseous working fluids which have relatively low heat transfer rates. The theoretical performance maps have been obtained for different potential design strategies, which will be helpful for making decisions in the future conceptual choice of receiver designs.
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| 46. |
- Wang, Wujun, 1984-, et al.
(författare)
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An axial type impinging receiver
- 2018
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Ingår i: Energy. - : Elsevier Ltd. - 0360-5442 .- 1873-6785. ; 162, s. 318-334
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Tidskriftsartikel (refereegranskat)abstract
- An axial type impinging receiver has been developed for a solar dish-Brayton system. By using selective reflection cavity surfaces as a secondary concentrator, the solar irradiation is reflected and concentrated on a cylindrical absorber that is located in the center of the cavity. A modified inverse design method was applied for quickly finding possible cavity receiver designs, and a numerical conjugate heat transfer model combined with a ray-tracing model was utilized for studying the detailed performance of the impinging receivers. The ray-tracing results show that the flux distribution on the cavity and absorber surfaces can be efficiently adjusted to meet the design requirements by changing the absorber diameter, the cavity diameter, the cavity length and the offset length. A candidate receiver design was selected for detailed numerical studies, and the results show that the average outlet air temperature and the radiative-to-thermal efficiency can reach 801.1 °C and 82.8% at a DNI level of 800 W/m2. The temperature differences on the absorber can be controlled within 122.7 °C for DNI level of 800 W/m2, and 126.4 °C for DNI level of 1000 W/m2. Furthermore, the structure is much simpler than a typical radial impinging design.
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| 47. |
- Wang, Wujun, 1984-, et al.
(författare)
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An inverse design method for a cavity receiver used in solar dish Brayton system
- 2014
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 110, s. 745-755
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Tidskriftsartikel (refereegranskat)abstract
- An inverse design method is developed in order to quickly find possible cavity receiver designs with relative uniform cavity wall surface temperature for a solar dish cavity receiver. In this design method, a heat transfer model of the absorber wall is used for analyzing the main heat transfer process between the cavity wall outer surface, the inner surface and the working fluid. Furthermore, a ray-tracing model based on the parameters of a real dish is utilized for obtaining the solar radiative boundary conditions for the heat transfer model. Impinging jet cooling technology is introduced due to its high heat transfer coefficient in the stagnation area, which can be used for cooling the peak flux on the cavity wall. After applying a well-designed impinging system, the temperature peak on the peak flux region in traditional receiver designs can be mitigated without introducing any over pressure drop problem.
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| 48. |
- Wang, Wujun, 1984-, et al.
(författare)
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Comparison of potential control strategies for an impinging receiver based dish-Brayton system when the solar irradiation exceeds its design value
- 2018
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Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 169, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Potential control strategies for an impinging receiver based dish-Brayton system have been presented for protecting the key components from the risks of overheating when the solar irradiation exceeds its design value. Two of them are selected for a detailed study: changing the effective diameter of the shading device and changing the inlet temperature. A rope-pulley shading device is developed for controlling the shading area in the center of the dish, and the change of the inlet temperature is achieved by applying a bypass at the cold side of the recuperator for reducing the heat transfer rate. Both control strategies can manage the peak temperature on the absorber surface within 1030 °C with an outlet temperature fluctuation between −4.1 and 15.1 °C, so that the impinging receiver can work for long time at any solar direct normal irradiance value. Furthermore, the temperature differences on the absorber surface are between 137.1 °C and 163.8 °C. The cases that are achieved by changing the shield effective diameter are significantly lower (11–26 °C) than the corresponding cases that are achieved by changing the inlet temperature.
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| 49. |
- Wang, Wujun, et al.
(författare)
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Conjugate heat transfer analysis of an impinging receiver design for a dish-Brayton system
- 2015
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 119, s. 298-309
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Tidskriftsartikel (refereegranskat)abstract
- An impinging receiver design has been developed for a small scale solar dish-Brayton system. A numerical conjugate heat transfer model combined with a ray-tracing model, based on the boundary conditions of the micro gas turbine and the EuroDish system, has been used for studying the thermal performance of an impinging receiver. According to the results of the preliminary estimation by an inverse design method, four possible impinging nozzle arrangements have been studied by the numerical model based on a 240 mm diameter and 3 mm wall thickness cavity. The inverse design method has been verified to be an efficient way in reducing the calculation costs during the design procedure. Furthermore, the impacts of the cavity diameter and the wall thickness have also been studied.
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| 50. |
- Wang, Wujun, et al.
(författare)
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Design and Validation of a Low-cost High-flux Solar Simulator using Fresnel Lens Concentrators
- 2013
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Ingår i: Proceedings of the SolarPACES 2013 International Conference. - : Elsevier. ; , s. 2221-2230
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Konferensbidrag (refereegranskat)abstract
- A systematic design procedure for a high flux solar simulator is presented in this paper. The 84 kWe solar simulator is based on an array of 12 commercially available xenon-arc lamps (each 7 kWe) coupled with silicone-on-glass Fresnel lenses as the optical concentrator. A ray-tracing model of the xenon lamp has been developed based on the real emitter shape and the Fresnel lens optics; simulations performed using a non-sequential Monte Carlo technique have been validated against experimental test data. The results show that 19.7 kW of radiative power is delivered on a 20 cm diameter target with and a peak flux of 6.73 MW/m2 and an electricity to radiative power efficiency of 23.4%. This research facility will be used as an experimental platform for high flux solar receiver and thermochemical reactor research, as well as for advanced high-temperature material testing.
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