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• Thermographic phosphor (TPs) was first used to investigate heat transfer of an impinging synthetic jet. • A link was built between the flow structure and the cooling performance. • Wall temperature's influence was reflected in the strength of the wall shear layer. • Effect of the orifice-to-wall distance was manifested in the coherence of impinging vortex rings. • Penetration of the wall shear layer played a vital role in the cooling performance of an impinging synthetic jet. This study experimentally investigated the combined effects of the wall temperature (T w 0) and the orifice-to-wall distance (H / D) on the flow and heat transfer characteristics of an impinging synthetic jet. Thermographic phosphor thermometry (TPT) was used to measure the wall surface temperature, and the quantitative flow velocity was obtained using time-resolved particle image velocimetry (PIV). A cavity-diaphragm actuator was employed to generate a round synthetic jet to impinge onto a heated wall that was coated with Mg 4 FGeO 6 :Mn (MFG) for use as a temperature sensor. Three orifice-to-wall distances (H / D = 10, 15, and 20) and three wall temperatures (T w 0 = 60 °C, 90 °C, and 120 °C) were tested for comparison, whereas the the operating conditions of the incident synthetic jet were kept constant. It was found that the maximum temperature drop at the stagnation point could reach approximately 50°C although the orifice-to-wall distance was relatively large in this study, which indicated a good cooling performance of the synthetic jet. The penetration of the wall shear layer played an important role on the cooling performance of the impinging synthetic jet. For a heated wall with high T w 0 , the enhanced buoyancy and thermal boundary layer resulted in the formation of a strong wall shear layer, which was more difficult for the impinging synthetic jet to affect or penetrate. For a large H / D , the vortex rings of the synthetic jet lose coherence completely before impacting the wall. Thus, they have no ability to penetrate the wall's shear layer to interact with it directly. As a result, the cooling performance of the impinging synthetic jet gradually decreased as both T w 0 and H / D increased. In particular, the maximum cooling effect by the synthetic jet impingement can achieve 64% of the theoretical maximum. [ABSTRACT FROM AUTHOR]

Sensible thermal energy storage has been widely used with a single water storage tank for both heat-mode and cooling-mode. However, a large water storage tank is required to avoid the inevitable limitation of low energy storage density. Although latent heat thermal energy storage has compatibly high energy storage density, it requires separate tanks for heating-mode and for cooling-mode. This study considered a single tank for both heating and cooling modes, composed of 1620 (9 × 9 × 20) capsules filled with cooling-PCM or heating-PCM. Recently our research group developed a new effective thermal conductivity model that properly reflected the increased strength of natural convection in the molten PCM, and in this study we applied the model to simulate the full scale tank. Five different mixing ratios of cooling-PCM and heating-PCM, defined as the capsule number filled with cooling-PCM or heating-PCM to the total capsules in the tank, were investigated, and the range of the ratio of cooling-PCM and heating-PCM was found to satisfy both the required energy storage densities in heating and cooling demand. For the required energy storage densities of heating mode, 25 kwh/m3, and cooling mode, 30 kwh/m3, the results suggest the combined ratio in the dual PCM tank is within a 50/50–90/10 mixing zone ratio, of the cooling-PCM/heating-PCM respectively. [ABSTRACT FROM AUTHOR]

The phase change material (PCM) based battery thermal management system (BTMS) is an effective cooling system for ensuring the reliability, safety, lifespan and performance of li-ion batteries. The kinds of PCM-based BTMS include the pure PCM, composite PCM and hybrid PCM-based BTMS. This work focuses on the review of the research progress in the PCM-based BTMS to propose its prospects and challenges. The research results show that most pure solid-liquid PCMs are of low thermal conductivity, which leads to large amounts of heat accumulation in a harsh operating environment. The addition of carbon materials and metals can significantly increase the thermal conductivity and the strength of the PCMs. The hybrid BTMS can further reduce the temperature rise and enhance the temperature uniformity of the battery compared with a single BTMS. Thus, the hybrid BTMS is more suitable to high power battery packs. This study provides a direction for future research, including screening new PCMs, improving the efficiency, reducing the energy consumption, volume and weight of the PCM-based BTMS. • Performance of passive phase change material thermal management system is compared. • Enhanced phase change material thermal management system is investigated in detail. • Advantages of hybrid thermal management system are summarized. • Development of phase change material based thermal management system is prospected. [ABSTRACT FROM AUTHOR]

Evaporative cooling can be integrated into fresh-air-handling units, to reduce cooling demand. This study considers a hybrid fresh-air-handling unit which incorporates a vapor-compression cooling cycle and indirect evaporative cooling to condition an ambient primary airstream to a desired supply air state. The cooling effects of using various modes (vapor compression only; direct expansion with mist; direct expansion with water shower; and direct expansion with mist and water shower) are compared when the fresh-air-handling unit operates in harsh (hot and humid) climatic conditions experienced in Qatar. Experimental analysis is based on actual ambient conditions measured from August 2018 to July 2019. It is found that the best-performing wet mode of operation saves more than 60% of the energy required by a conventional direct expansion cooling system operating under the same ambient conditions. In hot, dry conditions, the coefficient of performance of the fresh-air-handling unit when using the indirect evaporative mode of operation is double the coefficient of performance when operating with direct expansion mode only. [ABSTRACT FROM AUTHOR]

• A novel radiant panel with filled liquid was developed for indoor air cooling. • The cooling performance of the radiant panel was proven excellent. • The cooling performance of radiant panel was adjustable through filling with different liquids. Radiant ceiling cooling system is considered as a promising technique, which has huge potential to energy saving and suits for independent control of temperature and humidity. In this paper, a novel radiant panel was developed for cooling, which consists of top flat plate, bottom groove plate, and heat transfer liquid filling in the gap of two plates. A series of tests were conducted and results suggested that the cooling capacity of this radiant panel could reach at 93.5 W/m2 to 153.3 W/m2 in test condition, which was higher 18%～25% than that of traditional metal radiant panels. Besides, the maximum temperature difference on the surface of the novel radiant panel was <2.9 ℃ which is smaller than traditional one that is designed as cold-water tubes touching radiant plate directly without filled liquid. These advantages indicate that the radiant panel is suitable for hot and humid environment. The vertical temperature gradient of indoor air within staff activity area was 2.31–2.89 ℃ /m, meeting the requirements of ISO 7730. Moreover, the cooling performance of radiant panel can be changed when filled with different kinds of liquids, so that the radiant panel can be applied in different occasions and suitable for using in series. [ABSTRACT FROM AUTHOR]

In this study, the cooling performance of nanofluids in car radiators was investigated. A car radiator, temperature measuring instrument, and other components were used to set up the experimental device, and the temperature of nanofluids passing through the radiator was measured by this device. Three kinds of nanoparticles, γ-Al2O3, α-Al2O3, and ZnO, were added to propylene glycol to prepared nanofluids, and the effects of nanoparticle size and type, volume concentration, initial temperature, and flow rate were tested. The results indicated that the heat transfer coefficients of all nanofluids first increased and then decreased with an increase in volume concentration. The ZnO-propylene glycol nanofluid reached a maximum heat transfer coefficient at 0.3 vol%, and the coefficient decreased by 25.6% with an increase in volume concentration from 0.3 vol% to 0.5 vol%. Smaller particles provided a better cooling performance, and the 0.1 vol% γ-Al2O3-propylene glycol nanofluid had a 19.9% increase in heat transfer coefficient compared with that of α-Al2O3-propylene glycol. An increase in flow rate resulted in a 10.5% increase in the heat transfer coefficient of the 0.5 vol% α-Al2O3-propylene glycol nanofluid. In addition, the experimental temperature range of 40–60°C improved the heat transfer coefficient of the 0.2 vol% ZnO-propylene glycol nanofluid by 46.4%. [ABSTRACT FROM AUTHOR]

A passive radiative cooling method has a significant influence on thermal management applications because it can cool without any energy input. This work both experimentally and theoretically demonstrates a multilayer thin film structure with high solar reflectance, which can be applied to passive daytime radiative cooling. The combination of physical vapor deposition and spin-coating prepared the samples, which were also characterized experimentally by spectrometers. On-site measured results show that the emitter can effectively achieve daytime radiative cooling, and the cooling performance can be further improved with the increase of the ambient air temperature. When the emitter is exposed to direct solar radiation (AM1.5) of about 880 W/m2 on a rooftop under dry air conditions, it can achieve an average temperature reduction of about 12.6 °C from the ambient air temperature with nonradiative heat transfer (11 a.m.–1 p.m.). Theoretical simulations reveal that the emitter can still have a certain cooling performance in the presence of significant nonradiative heat exchange and nonideal atmospheric conditions. The influence of ambient air temperature on the cooling performance of the emitter is also theoretically analyzed. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of the cross-flow regenerative heat and mass exchanger (HMX) and the conventional cross-flow HMX for indirect evaporative cooling (IEC) with numerical methods. The objective of this study is mainly to clarify the applicability of the two HMXs. The numerical model was built and validated by existing experimental data. The difference in heat and mass transfer between the two HMXs was revealed by analyzing the change of the temperature and moisture content of the air, and the influence of the main operating parameters on the cooling performance of the HMXs was analyzed. In the typical operating conditions, when the HMXs are used alone, the cooling performance of the regenerative HMX is better than that of the conventional HMX under low supply air flow rate. When the HMXs are used in the multistage evaporative cooling systems with high supply air flow rate, the conventional HMX is more suitable as the first stage of the system to pre-cool the supply air, while the regenerative HMX is more suitable as the second stage to re-cool the supply air. [ABSTRACT FROM AUTHOR]

The cooling performance of a slice die is studied numerically and experimentally. The slice die is designed to improve the cooling performance compared to that of a conventional die that is generally used in the Hot Press Forming (HPF) process by modifying the cooling channel layout and arrangement. In order to understand the physical phenomenon of the slice die cooling performance, the cooling performance of the conventional die is also simulated and their results are compared with the slice die results. From the results of the maximum temperature of the blank and die and the temperature distribution of the blank, the slice die has considerably improved cooling performance. To validate the simulation results, the slice die is prototyped and a blank is produced by the HPF process. Blank temperatures are measured by a thermal imaging camera at several holding times. The simulation and experimental results of the blank temperatures are compared and agree with the error rate of 3%. In order to verify the quality of the produced blank, ultimate tensile stress, yield stress, and elongation tests are conducted for specimens that are extracted from the blank and are compared with existing literature results. [ABSTRACT FROM AUTHOR]