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Array jet impingement cooling is a significant technology of enhanced heat dissipation which is fit for high heat flux flow with large area. It is gradually applied to the cooling of electronic devices. However, The research on the nozzle array mode and the uniformity of the cooling surface still has deficiencies. Therefore, the influence of heat flux, inlet temperature, jet height, array mode, and diversion structure on jet impingement cooling performance and temperature distribution uniformity is analyzed through numerical calculation. The results show that the heat transfer coefficient of jet impingement cooling increases linearly with the increment of heat flux and inlet temperature. With the increment of the ratio of jet height to nozzle diameter (H/d), the heat transfer coefficient increases first and then decreases, that is, there is an optimal H/d, which makes the heat transfer performance of the array jet impact cooling best. The temperature uniformity of array jet impact cooling is greatly affected by array mode. The improvement effect of nozzle array mode on temperature uniformity is ranked as sequential >staggered >shield >elliptical array. The overall temperature uniformity and heat transfer coefficient are increased by 5.88% and 7.29% compared with the elliptical array. The heat transfer performance can be further improved by adding a flow channel to the in-line array layout, in which the heat transfer coefficient is increased by 6.53% and the overall temperature uniformity is increased by 1.45%. [ABSTRACT FROM AUTHOR]

With the rapid increase of heat flux and demand for miniaturization of electronic equipment, the traditional heat conduction and convective heat transfer methods could not meet the needs. Therefore, the spray cooling experiment was carried out to obtain the basic heat transfer and cooling process. In this experiment, the spray cooling system was set up to investigate the influence of refrigerant charge on heat transfer performance in steady-state, dynamic heating, and dissipating processes. In a steady-state, the heat transfer coefficient increased with the rise of the refrigerant charge. In the dynamic dissipating process, both heat flux and heat transfer coefficient decreased rapidly after the critical heat flux, and the surface temperature drop point of each refrigerant charge was presented. The optimum refrigerant charge was provided considering the cooling parameters and the system operating performance. When the refrigerant operating pressure was 0.5 MPa, the spray cooling process presented with the higher heat flux, heat transfer coefficient, and cooling efficiency in this experiment. Meanwhile, the suitable surface temperature drop point and more gentle heat flux curves in the nucleate boiling region were obtained. The research results will contribute to the spray cooling system design, which should be operated before departure from the nucleate boiling point for avoiding cooling failure.

In this paper, the outside cabin heat exchanger based on the porous media approach was established. The effects of altitude, viscous resistance coefficient, inertial resistance coefficient, and core thickness on the naturally captured air volume of the heat exchanger were investigated by numerical simulation. Results showed that the naturally captured air volume of the heat exchanger tends to be larger on both sides and smaller in the middle, and there is a quasi-linear increase proportional to the incoming wind velocity. With the increment of altitude, viscous resistance coefficient, and inertial resistance coefficient, the average naturally captured air volume of the heat exchangers shows a downward trend. The trend would be clear with the increment of the incoming wind velocity, nevertheless, the effect of core thickness is weak. In addition, the design values of the viscous resistance coefficient and the inertial resistance coefficient should be restricted in the order of 106 and below 500, respectively. Based on the weak effect of the naturally captured air volume of the heat exchanger, the thickness of the core can be appropriately increased to ensure the heat transfer area of the heat exchanger. [ABSTRACT FROM AUTHOR]

This paper studies the frozen pork transportation in short and long distances, the loss of cooling capacity and the energy consumption in the cold chain transportation are analyzed experimentally and numerically. It finds that the material for freezer insulation plays in important role in energy consumption and energy saving during refrigerated transportation, an optimal freezer can reduce temperature rise by 13.88% and the heat flow by 71.05% compared with the traditional ones. A fractal model is established to reveal the thermal property of the freezer. [ABSTRACT FROM AUTHOR]

Spray cooling is a promising and effective cooling method, which may be used to solve the heat dissipation problem of high-power electronic components. In this paper, the influences of flow rate, sub-cooling degree, and refrigerant charge on the spray cooling heat transfer performance with R134a as the working fluid were experimentally studied. Results showed that the enhancement effect of the increase of sub-cooling degree on the heat transfer performance is very limited in this experiment. When the sub-cooling degree rises from 5 to 8 K, the heat transfer coefficient increases by 2.6% on average at lower heat flux (45.93–72.55 W/cm2). The increase of refrigerant charge can effectively improve the heat transfer performance, especially at higher heat flux (84.02–105.25 W/cm2). However, the Jacobian number decreases with the increase of the refrigerant charge, which hinders the improvement of heat transfer performance at higher heat flux. Therefore, there is an optimal refrigerant charge of 1.05 kg in this experiment. In addition, based on the experimental data, a Nusselt number dimensionless correlation of R134a solution with higher prediction accuracy was proposed. [ABSTRACT FROM AUTHOR]

For the outside cabin heat exchanger of wind power generation, the overall numerical simulation plays an important role in its design and optimization. The periodic iterative simulation method proposed in this paper makes up for the deficiency of analogy research using the local model in the previous research of plate-fin heat exchanger so that the research conclusions can be directly applied to practical engineering. The effectiveness of this method is verified by comparing 10 groups of simulation results with experimental results. It is concluded that the maximum relative error of the periodic iterative simulation method is 0.9%, which meets the requirements of engineering calculation. The number of iterations can be reduced to two when only the outlet average temperature is involved, which is more convenient than the dozens of iterations. Furthermore, the effects of altitude, air velocity, air temperature, wave fin structure parameters, and generator power on the performance of heat exchanger are comprehensively analyzed. The results show that larger naturally captured air volume, lower ambient temperature, and lower altitude can effectively reduce the outlet temperature of ethylene glycol solution. When the amplitude and wavelength of the corrugated fin on the airside of the heat exchanger are 0.6 mm and 20 mm respectively, the naturally captured air volume is effectively increased, the overall heat exchange performance of the heat exchanger is further improved. [ABSTRACT FROM AUTHOR]

The wetting behavior of molten Zn and Zn-Sb alloy and X80 steel in a high vacuum environment was studied by the modified sessile drop method. The wetting morphology and interface structure were analyzed by scanning electron microscope and energy dispersive spectrometer. The results show when the content of Sb in Zn-Sb alloy increases from 0.0 wt. % to 1.0 wt. %, the initial contact angle between the droplet and the substrate decreases from 102.8° to 82.5°, and the equilibrium contact angle also decreases from 57.4° to 41.4°. Sb element in the Zn-Sb alloy can reduce the contact angle and improve the wettability due to its smaller surface tension. The spreading process of Zn-Sb alloys on X80 steel can be divided into rapid adsorption, reaction control, steady-state equilibrium stages, and Zn-Sb alloys with different mass fractions have the same spreading kinetics. The volatilized Zn element in the Zn-Sb alloy will reduce the oxide film on the surface of the substrate, making it easier for the Zn-Sb droplet to wet the steel plate and induce the formation of a precursor film. The formation mechanism of the precursor film is the subcutaneous penetration mechanism. [ABSTRACT FROM AUTHOR]

In this study, influence factors of liquid nitrogen spray cooling, including the parameters of the nozzle, the area of the heat sink, and the flow rate of liquid nitrogen, were investigated experimentally. On the basis of experimental data, experimental dimensionless correlations were obtained. It was shown that the error of correlation with only the Reynolds number (Re) and Prandtl number (Pr) was too low to predict the Nusselt number (Nu). With Re, Pr, the boiling number (Bg), and the Jacob number (Ja), while the error of correlation decreased, the experimental data deviated considerably from the fitting line by the correlation, which was still not suitable for prediction. The reasons for the experimental data's deviation were that the uniformity of the droplet distribution varied with the nozzle aperture, a change in the heat exchange area resulted in the formation of a local gas film, the droplet splash caused by a change in the flow rate influenced the heat exchange. The correlation obtained with Re, Pr, Bg, Ja, and the effective of spray mass flow flux η which was determined as the ratio of the liquid nitrogen mass flow rate involved in heat transfer to the uniform mass flow on the heat surface could be used to accurately predict Nu. [ABSTRACT FROM AUTHOR]