Experimental investigation on bubble confinement and elongation in microchannel flow boiling, Experimental thermal and fluid science

a b s t r a c t Bubble confinement and elongation in flow boiling were investigated experimentally in a rectangular microchannel with 0.5 mm in width and 1.0 mm in height using DI water as the working fluid. Bubble growth under various mass flux, heat flux and inlet subcooling conditions was visualized using a highspeed CCD camera, and the recorded images were analyzed to provide quantitative information of the bubble confinement and elongation in the microchannel. The flow conditions and the underlying mechanisms for bubble confinement to occur were discussed. In addition, the bubble growth characteristics, such as the bubble length and growth rate, in both free and confined growth periods were compared. It was found that the bubble growth rate in free growth period is far less than that in confined growth period, and the bubble growth rate before confinement decreases with the increase of bubble size, while the elongation rate increases with the increase of confined bubble size. What is more, it was noted that the initial shape of nucleated bubble in channel corner had significant influences on bubble confinement and elongation

Heat Transfer of Water Flow Boiling in Nanostructured Open Microchannels

In recent years, the open microchannel has drawn increasing interest, but severe local dryout limited the heat transfer capability of flow boiling. It was anticipated that nanostructures with exceptional capillary wicking abilities would overcome this problem. In this study, blade-like CuO nanostructures were created in the copper open microchannels to experimentally investigate water flow boiling. Experiments were carried out in nanostructured open microchannels (NMCs), and smooth-surface open microchannels (SMCs), as a comparison, were examined under identical operating conditions. Four main flow patterns, including bubbly flow, slug flow, and two kinds of stratified flow, dominated successively in NMCs and SMCs. Although the flow patterns were similar in NMCs and SMCs, the heat transfer coefficient (HTC) of flow boiling was greatly enhanced by nanostructures under conditions of medium and high heat flux, while the nanostructures’ influence on HTC was unnoticeable at low heat flux. At medium and high heat fluxes, the dependence of HTC on heat flux and flow rate indicated the joint contribution of nucleate boiling mechanism and convective evaporation mechanism to heat transfer. The enhanced effect of nanostructures on nucleate boiling and convective evaporation became more prominent as heat flux increased, leading to a higher HTC in NMCs than in SMCs at higher heat flux conditions

Phase-change cooling of lithium-ion battery using parallel mini-channels cold plate with varying flow rate

In this study, a liquid phase-change cooling module with mini-channels cold plate was designed. The temperature properties of a battery monomer with different cooling conditions and varying discharge rates were investigated. The heat dissipation contribution of latent heat transfer to the overall cooling performance of the mini-channels cold plate was analyzed based on the outlet vapor quality. Particularly, a cooling strategy with varying coolant flow rates was proposed and examined at 3C discharge rate. The results illustrated that the designed battery cooling module had an ideal effect on lowering the battery's surface temperature and increasing the battery's temperature uniformity. Compared to the cooling strategy with constant coolant flow rate, the proposed variable flow cooling strategy better matched the dynamic law of battery heat generation and increased the contribution of the latent heat transfer to the battery cooling, thereby efficiently reducing the coolant consumption and the pump power consumption of the BTMS (battery thermal management system) while providing the same or even superior cooling performance. The findings could assist the optimization of the BTMS and be the reference for the application of the varying flow rate cooling strategy in actual engineering