| 1. |
- Ahsan, Amimul, et al.
(författare)
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Modeling of a new triangular shape solar distillation system integrated with solar PV panel and DC water heater
- 2023
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier. - 2214-157X. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- A new triangular shape solar distillation system is fabricated using locally available materials by integrating with solar PV panel connected to DC water heater. It is designed for the first time to distill saline water or seawater using solar heat energy directly (to heat sample water) and indirectly (through water heater to heat sample water). The trough is made of Plexiglass and painted in black color which is placed inside the triangular frame made of UPVC pipe. The performance of the still is experimented in field. The diurnal variations of solar heat energy, distillate output, various temperatures and relative humidity are observed. A few linear proportional relationships are obtained between the sunlight heat energy and the productivity, between the ambient temperature and the productivity, and between the productivity and water-cover temperature difference. The production rate of the still is higher than the conventional one. An improved simulation model is proposed to estimate the productivity of the still as some previous simulation models cannot estimate the productivity of the solar still precisely. A few new factors are incorporated in the new model as these factors affect the distillate output of the solar still.
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| 2. |
- Alhajri, Ibrahim H., et al.
(författare)
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Retrofit of heat exchanger networks by graphical Pinch Analysis - A case study of a crude oil refinery in Kuwait
- 2021
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier BV. - 2214-157X. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- Energy integration of the existing chemical and petrochemical facilities is regarded as a keystone for sustainable energy systems. It is widely known that a considerable number of the petrochemical industries are not applying efficient heat exchanger network (HEN) systems to minimise the use of external utilities. In the present study, a Pinch Analysis-based graphical approach is used to retrofit an existing HEN for optimising a crude oil distillation operation. The existing HEN is represented using Thot-Tcold diagram, where the cold stream temperatures are plotted on the x-axis and the hot stream temperatures are plotted on the y-axis, for each exchanger unit. The graphical approach is applied to a real case study of a petroleum refinery plant located in Kuwait with the objective of performing energy analysis and retrofitting the existing HEN. Retrofit modifications are extracted from the graphical representation to enable scenarios for energy and emission reduction. The application of the proposed approach resulted in substantial energy savings of about 10.4 MW compared to the current operation, leading to annual operating cost savings of about MM$2 and less than one-year payback time. Overall, this study provides tools to address the energy traits in crude preheat trains of industrial feature, which can improve the overall economic-environmental sustainability of existing refineries.
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| 3. |
- Du, Z., et al.
(författare)
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Melting-solidification cycle of finned heat storage tank : Optimization of fin structure by response surface method
- 2023
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier Ltd. - 2214-157X. ; 52
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Tidskriftsartikel (refereegranskat)abstract
- The impact of the enhanced heat transfer performance of longitudinal fins on the entire process of melting and solidification in a phase change heat storage unit is investigated through experiments and numerical simulations in this paper. The position and structure of the longitudinal fins are optimized by using the response surface method while ensuring that the total volume of the heat storage medium remains unchanged. Studies have identified that some challenging zones in melting and solidification significantly impact the heat transfer of the entire heat storage cycle. Specifically, the challenging zone in melting primarily exists in the lower part of the unit during the charing process, while the challenging zone in solidification is mainly distributed around the unit during the discharging process. Through optimization, the optimized structure (fin spacing is 22.5 mm, fin width is 6.05 mm) can reduce the charging and discharging time by 16.94 % and 45.90 %, respectively. Additionally, the round trip time is significantly reduced by 39.19 %, and the mean heat absorption rate during the melting process is enhanced by 20.28 %. Moreover, the mean heat release rate during solidification is enhanced by 80.23 %.
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| 4. |
- Eboh, Francis Chinweuba, et al.
(författare)
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Evaluating improvements in a waste-to-energy combined heat and power plant
- 2019
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier. - 2214-157X.
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Tidskriftsartikel (refereegranskat)abstract
- Evaluation of different alternatives for enhancement in a waste combustion process enables adequate decisions to be made for improving its efficiency. Exergy analysis has been shown be an effective tool in assessing the overall efficiency of a system. However, the conventional exergy method does not provide information of the improvements possible in a real process. The purpose of this paper is to evaluate state-of-the art techniques applied in a municipal solid-waste fired heat and power plant. The base case plant is evaluated first; the results are then used to decide upon which technical modifications should be introduced and they are thereafter evaluated. A modified exergy-based method is used to discover the improvement potential of both the individual components and the overall base case plant. The results indicate that 64% of exergy destruction in the overall process can theoretically be improved. The various modifications selected involve changing the bed material, using a gasifier followed by a gas boiler and incorporating a more durable material into the boiler walls. In addition, changing the heating medium of the incoming air (from steam to flue gas) along with a reduction in the stack temperature and the integration of flue gas condensation were considered for utilizing the exergy in the flue gases. The modification involving gasifier, gas boiler and flue gas condensation proved to be the best option, with the highest exergy efficiency increment of 21%.
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| 5. |
- El Jery, Atef, et al.
(författare)
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Proposing empirical correlations and optimization of Nu and Sgen of nanofluids in channels and predicting them using artificial neural network
- 2023
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier. - 2214-157X. ; 45
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Tidskriftsartikel (refereegranskat)abstract
- Getting the best performance from a thermal system requires two fundamental analyses, energy and entropy generation. An ideal mechanism has the highest Nu and the lowest entropy Sgen. As part of this research, a large dataset of fluid flow via tubes has been collected experimentally. As well as the inclusion of nanoparticles, analyses are included as well. By using deep learning algorithms, the Nusselt number and total entropy generation are predicted. In both models, the mean absolute error was lower than 5%. To determine the most accurate model, hyperparameter tuning is performed. That is adjusting all the settings in the neural network to attain the best results. The results of the predictive models are compared against experimental and benchmark results. The study incorporates a massive optimization strategy to fine-tune the predictive capabilities of the models. Furthermore, the model's predictive abilities are evaluated through the use of the coefficient of determination R2. For water and nanofluids flowing through circular, square, and rectangular cross-sections, the proposed models can predict Nu and Sgen. The results showed remarkable agreement with the experimental results. The models showed an MAE of not higher than 1.33%, which is a great achievement. Also, empirical correlations are proposed for both parameters, and double factorial optimization is implemented. The results showed that to achieve the best results, the Re should be higher than 1600, and the nanoparticle concentration should be 3%. A thorough justification of selected cases is presented as well.
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| 6. |
- Gao, X., et al.
(författare)
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Thermo-economic assessments on building heating by a thermal energy storage system with metal foam
- 2023
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier Ltd. - 2214-157X. ; 49
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Tidskriftsartikel (refereegranskat)abstract
- Due to the intermittency and discontinuity of solar energy, thermal energy storage (TES) using phase change materials (PCMs) is generally required to ensure stable operation in solar heating systems (SHS) during winter. This paper presents the design of a TES unit with different horizontal metal foam filling ratios (60%–100%), and simulations of thermal characteristics, such as complete melting time and heat storage capacity by numerical method. Based on the heating demands of an office building in Xi'an, TES units are combined in parallel and economic indexes are calculated based on static evaluation method, including initial investment and investment payback period. Novelty, the contribution of gradient microstructure to the phase transition process is evaluated from thermophysical properties and economy. Results show that the TES unit with a filling ratio of 90% possesses the shortest complete melting time of 5310 s, which is 87.56% shorter than that of a TES unit with pure PCM. Finally, economic assessments of the engineering application of the partially filled metal foam structure are carried out, and it is determined that the SHS with the TES system of 90% filling ratio requires the least number of 548 TES units, with a payback period of three heating seasons.
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| 7. |
- Gao, Y., et al.
(författare)
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Cooling pitch cabinets in wind turbines using a pulsating heat pipe : A case study
- 2023
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Ingår i: Case Studies in Thermal Engineering. - : Elsevier Ltd. - 2214-157X. ; 50
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Tidskriftsartikel (refereegranskat)abstract
- As the electric capacity of wind turbine increases, heat dissipation in pitch cabinets becomes challenging owing to the limited space and rotating conditions. To cool down the pitch cabinet more effectively and allow heat dissipation, we designed and implemented a pulsating heat pipe (PHP) in this study. We designed PHP parameters and conducted performance tests to compare the cooling performance of the fabricated PHP with that of an air-based cooling system in a 1.5 MW wind turbine. The results demonstrated steady PHP operation under rotating conditions (17.3 rpm). At a heat load of 1000 W, the evaporator outlet temperature was only 76.1 °C. However, increasing the ambient temperature adversely affected PHP operation, resulting in higher temperature and thermal resistance. The heat-pipe-based cooling system lowered the insulated gate bipolar transistor (IGBT) temperature by about 20.4 °C in relation to the air-based cooling system, while being suitable under varied conditions. Additionally, the system could successfully operate when the heat load of IGBT was 2350 W, corresponding to a 7 MW electric capacity of the wind turbine. Reducing the manufacturing cost of the heat pipe would further enhance the applicability of this system for pitch cabinet IGBT cooling, such as decreasing payback period.
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| 8. |
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| 9. |
- Hu, Shih-Cheng, et al.
(författare)
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Energy savings approaches for high-tech manufacturing factories
- 2020
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Ingår i: CASE STUDIES IN THERMAL ENGINEERING. - : ELSEVIER. - 2214-157X. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- This study integrates a fab energy simulation (FES) tool and energy conversion factors to analyze energy consumption and identify energy savings opportunities of high-tech manufacturing factories. The data used is the 169,124 MW h annual energy consumption of a Taiwanese semiconductor manufacturing fab. We proposed a compressed/clean dry air (CDA) system as a two-pressure system using a heated-type dryer. The proposed method achieved 3050 MW h as the highest energy savings in the CDA system compared to the original fab data. The results also indicate that lowering the make-up air unit (MAU) operating temperature caused significant energy savings for the high-temperature water chiller system. When the outlet air temperature of the MAU system was 14 degrees C, the maximum energy savings were 3532 MW h. In addition, the process cooling water (PCW) system could potentially save energy by reducing the pumping head of water in its open system. Therefore, we suggested a closed PCW system that reached a maximum energy saving of 1541 MW h.
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| 10. |
- Ji, Xinyu, et al.
(författare)
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Two-phase flow characteristics and visualization of distributed confined array jet boiling
- 2024
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Ingår i: Case Studies in Thermal Engineering. - 2214-157X. ; 57
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Tidskriftsartikel (refereegranskat)abstract
- Confined array jet boiling can achieve high heat flux in a compact space and its flow resistance characteristics are critical to the design of cooling systems. The boiling images of distributed confined jet of HFE-7100 is recorded by a high-speed camera in this study. The effects of jet mass flux, jet height and surface structure of two-phase jet flow characteristics on micro-pin-finned surfaces are studied. A benefit from the distributed configuration of the jet array, in contrast to previous studies, is that the jet boiling pressure drop is independent of the heat flux, but only related to the jet mass flux. The effect of the surface structure on the pressure drop is negligible. Jet flow instability will be triggered by intermittently blockage of the jet inlet and outlet by large vapor masses in certain heated surfaces. Reducing the jet height can suppress two-phase flow instabilities while keeping the pressure drop almost constant and the CHF to slightly increase. The COP of distributed jet impingement boiling cooler proposed in this work can be up to 6 times higher than that of the conventional jet boiling cooler, and more than 2 times higher that of the microchannel heat sink.
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