查看更多>>摘要：Global warming has tried the world with challenges like increased cooling energy demand, heatwaves, and unbearable summers, with accentuated nuances in dense urban areas. Here heat island effects are most pronounced and heat-safe pockets are a necessity rather than a comfort. Bus stops can act as shelters for commuters with the advantage of usually being well distributed across the cities in the form of semi-enclosed spaces. Daytime radiative cooling is a novel technology that enables free cooling of a substance under direct solar radiation. In this study, radiative cooling is combined with the hydronic radiant cooling technology in the integrated design of the Cooling Station, a bus shelter capable of providing energy-free urban thermal comfort throughout the summer. The study aims at evaluating the effect of geometry, orientation, surrounding elements, and climate on the performance of the Cooling Station. It is found that humidity and surrounding buildings diminish the performance of the radiative cooling panels, but the penalty can be significantly mitigated by applying non-reciprocal asymmetric transmission windows on top of the panels. The results indicate that the optimized design of the Cooling Station is capable of decreasing the Universal Thermal Climate Index (UTCI) by up to 10 °C in the considered scenario of a mid-rise area in Tehran, the capital of Iran. Further, the performance evaluation across all K?ppen-Geiger climate classes demonstrates that in hot and semi-arid climates, the Cooling Station develops its full potential.
查看更多>>摘要：The composite air-conditioning system combined heat pipes and vapor compression, which can utilize natural cooling sources effectively, has been widely used in data centers recently. The common energy-saving strategy is to make the best use of the natural cooling sources according to outside ambient temperature. However, existing studies indicate that the cooling failure problem often occurs in the mechanical refrigeration mode due to incorrect control strategy, when the outdoor ambient temperature is lower and natural cooling capacity is insufficient. Thus, taking the multi-split backplane cooling system used in the data center as an object, the reason for the cooling failure under the condition of lower outside ambient temperature is investigated through theoretical analysis and experimental study. Results indicate that system energy consumption will decrease as condensing pressure decreases, but lower condensing pressure may cause insufficient refrigerant problems at the most unfavorable terminal. To solve the problem, a reliable operation control strategy based on variable condensing pressure is proposed and validated by experiments, and results indicate that a maximum of 12% energy consumption can be saved with the decrease of condensing pressure. Finally, the determination for condensing pressure setpoint is provided, and it is pointed out that how to determine optimal condensing pressure setpoint is worthy of further study in the consideration of energy efficiency and cooling effect meantime.
查看更多>>摘要：The importance of climate change mitigation and energy efficiency as a growing global concern has intensified the development of techniques to reach and improve thermal comfort and energy efficiency of buildings. The study of the effect of the height of the openings on the internal natural airflow in one-story buildings can be found in many studies; However, studies on the effect of this important factor on providing thermal comfort in high-rise buildings equipped with DSF are not available. This paper focuses on natural-ventilated buildings based on wind-driven and buoyancy-driven forces. The aim of this study is to use passive strategies in high-rise office buildings in hot and dry climates. In this research, two methods of field studies and numerical modeling have been used in order to provide accurate results. In order to achieve optimal patterns in the design of natural-ventilated buildings; CFD simulation and PMV thermal comfort index have been used in the evaluation of various configurations. The results of the present study show that although the cooling energy demand in high-rise buildings in hot climates is high and the use of natural ventilation systems is beneficial, but these systems alone are not able to provide thermal comfort conditions. However, the accurate and correct location of the openings is effective in improving thermal comfort by increasing the volume flow.
查看更多>>摘要：Various energy efficiency and environmental regulations around the world, such as the European Union's (EU) F-Gas regulation, are pushing refrigerator manufacturers to replace halogenated refrigerants with environmentally-friendly alternatives with low Global Warming Potential (GWP) without energy efficiency decrease. In this respect, increasing energy conversion performance by using a low GWP refrigerant in the mini thermoelectric refrigerators (MTERs) gains important for revealing sustainable and environmentally friendly refrigerators. To make this possible, the paper provides a comprehensive examination of the effect of climate-friendly refrigerant replacement in the closed-loop two-phase thermosyphon (CLTPT) on the performance of the MTER. This study treats the experimental investigation of the R600a as a low GWP substitute to R134a in the CLTPT of the MTER. Different from the other study in the literature, an extensive performance evaluation of the commercial MTER in terms of exergy as well as energy was performed and the various filling ratios (FR) of the R600a from 19% to 78% were analyzed for the best performance. The results showed that the MTER with a 46% and 32% FR of R600a had the highest exergy efficiency with 8.55% and 8.11%, respectively while reference MTER with R134a had 5.27%. It is concluded that 32% and 46% FR of the R600a enhanced the MTER energy conversion performance according to the 19% FR of the R134a, in line with the F-Gas regulation. The 32% and 46% FR of the R600a for MTER are the best refrigerant replacement, both from thermal performance and environmental points of view.
查看更多>>摘要：A CFD-based optimization process was used to design an air supply casing shape for the indoor unit (IDU) of a split-type air conditioner (SAC). The aim was to enhance the IDU performance, including the volume flow rate and total cooling capacity. To this end, the numerical results, including the pressure, velocity, temperature, and humidity ratio distribution, were used to evaluate the IDU performance. For the CFD-based optimal design, a 3D printer was used to manufacture an optimized casing in combination with four IDU geometric parameters. The optimal tongue gap, rear wall gap, and radii of curvature for the first and second segments were 2.2, 8.4, 56.7, and 98.8 mm, respectively. As a result, the measured and predicted volume flow rate and total cooling capacity of the optimized IDU increased by nearly 20% and 27%, respectively, compared with those of the original IDU. Moreover, the predicted and measured volume flow rates and total cooling capacities agreed well, with the relative errors of the IDU performance being less than 1% and 5%, respectively. In addition, the measured power consumption of the cross-flow fan of the optimized IDU was reduced by 19.4% compared with that of the original IDU.
查看更多>>摘要：Enhancing the charging rate capability is beneficial for the driving convenience of electric vehicles. However, high current rate charging causes inevitable severe heat generation, thermal inconsistency, and even thermal runaway. This study proposes a parallel liquid cooling system for a prismatic battery module to achieve the shortest charging interval and thermal safety under fast charging. Furthermore, a surrogate model with the objectives of the thermal performance and energy cost is constructed, the impact of some influential design parameters is explored through sensitivity analysis and response surface analysis. Moreover, a multi-objective optimization design is conducted for the optimal design selection. Finally, the optimal design is validated by experiments under 2.5C fast charging. Results demonstrate that mini-channel depth is the most influential design parameter on the cooling effect (70.8%), the temperature distribution uniformity (75.7%), and the energy cost (86.1%). Volume energy density, maximum temperature (Tmax), temperature standard deviation (TSD), and the energy cost (W) of the system are enhanced by 9.0%, 2.1%, 23.7% and 26.9%, respectively. Experimental validation proves that Tmax, TSD, and W of the battery module can be maintained within 33.1℃, 0.9℃, and 17.29 J, respectively. This study guides for the battery thermal management system design with enhanced efficiency and energy cost, especially during harsh operations.
查看更多>>摘要：The thermal performance index (TPI) known as the efficiency parameter evaluates the highlight of the heat transfer for the same pumping power requirement. The optimum design of a heat exchanger with minimum pressure drops and efficient heat transfer is a big challenging task from an energy-saving point of view. One way to optimize this efficiency parameter is by changing the geometric parameters of the heat exchanger. For this purpose, the multi-objective reinforcement learner non-dominated sorting genetic algorithm (NSGA-RL) is employed maximizing TPI and Nusselt number and minimizing Fanning friction factor to the optimal design of a double pipe heat exchanger, with perforated baffles in the annulus side. Its performance is compared with a non-dominated sorting genetic algorithm - version II (NSGA-II), and a chaotic non-dominated sorting genetic algorithm (CNSGA). The calculations were carried out using the turbulent shear stress transport k-ω model. The multi-objective optimization techniques presented promising results in terms of the number of nondominated solutions, Euclidean distances to the origin point (reference point), and hypervolume indicators. However, in general, the results based on mean values indicate that the NSGA-RL outperforms the NSGA-II and CNSGA concerning the three performance indicators for the two double pipe heat exchanger evaluated cases. TPI increases 78% for case 1, and 108% for case 2 compared without baffles in a double pipe heat exchanger (DPHE). Numerical results revealed that DPHE employing internal perforated baffles improved heat transfer significantly with Nusselt number increased around 7.93–8.25 times and friction factor increased by 6.5–9.75 times compared with plain DPHE.
查看更多>>摘要：Computational Fluid Dynamics has emerged as one of the major investigative tools for aerodynamics and thermal analyses of today's road vehicle design processes. This work presents the design of a new heat exchanger layout that could support the transition from thermal to electrical propulsion of an existing motor vehicle. A procedure is established to develop and assess a heat exchanger prototype. The aerodynamic performance of an electric vehicle equipped with the above-mentioned heat exchanger is assessed numerically, and results compared with its thermal counterpart. The comparison between both layouts shows a 5% reduction of the vehicle's drag and a net reduction of the overall weight with the newly designed system, introducing the proposal for a new form of heat exchanger packaging.
查看更多>>摘要：Fouling on tube surfaces degrades the heat transfer characteristics of heat exchangers. The objective of this study was to predict the distribution of deposits on the surface of heat transfer tubes and assess its influence on heat transfer characteristics. For this purpose, a comprehensive model of impurity migration and deposition, which considered deposition and removal processes under boiling conditions, was established to simulate the fouling characteristics of steam generators. A critical time step was determined to solve the problems at a large time-scale span between the fluid flow and long-term deposition time in actual operation. Then, the deposit distribution was used to propose a fouling thermal resistance model based on the Maxwell model to study the influence of fouling on the heat transfer performance of steam generators. The results showed that the corrosion products were mainly deposited on the hot side and in the U-bend region. The deposition rate on the hot side gradually decreased with time, whereas the deposition mass on the cold side linearly increased with time. Fouling had an evident effect on the overall heat transfer efficiency and distribution of steam generators. This study is relevant for the prediction of operating conditions during the life cycle of heat exchangers in industry.
查看更多>>摘要：In this study, a planar ionic wind generator with two flat electrodes was investigated numerically and experimentally to reveal its electrohydrodynamic and heat transfer characteristics. The multi-physical characteristics, including the discharge process, movement of electrons, positive ions, and negative ions, as well as the formation of ionic wind and its flow characteristics were simulated numerically. It was found that two corona discharges with different polarities were produced simultaneously when a high voltage was applied between the emitting and the ground electrodes. The intensity and direction of ionic wind produced by planar ionic wind generator was revealed. The effects of discharge gap, flat electrode thickness, and discharge polarity on the heat transfer characteristics and power consumption of the planar ionic wind generator were also investigated experimentally. The minimum discharge gap to maintain a stable corona discharge is determined. A better heat dissipation capacity of the planar ionic wind generator can be obtained with a larger electrode gap, and the optimized ionic wind generator can reduce the surface temperature of a 2.05 W powered heat source by more than 46 °C compared with natural cooling. The maximum heat transfer coefficient is 35 W?m?2?K?1. This study can provide a theoretical guidance for the application of planar ionic wind generators to highly compact electronic devices.
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Elsevier