竖直互连小通道内流动沸腾传热强化机理分析

Analysis of Heat Transfer Enhancement Mechanism on Flow Boiling in Vertical Rectangular Interconnected Microchannels

为推动流动沸腾技术在燃料电池散热领域的应用,该文以R141b为工质,对不同流速下的并联直通道及互连小通道内流动沸腾情况进行三维瞬态数值模拟。利用换热系数、基底温度及综合换热因子等参数对比各结构的换热性能,并探究互连小通道的换热强化机理。研究表明:换热趋势随气泡行为呈周期性变化,气泡脱离时的换热效果最佳;由连通口引发的二次流促进热量传递与壁温升高,使通道可提前2 ms满足成核条件,且气泡在10^(-4) m/s以上的二次流速作用下率先脱离;五连通通道的换热系数较并联直通道可提升19.6%~23.3%,继续增加连通口数,换热系数的相对增长率均不足3.5%;涡结构使压降随连通口数增加而增大,且增势并不减弱,八连通通道的压降较并联直通道增加29.5%~42%。可见,二次流在影响气泡行为、强化换热的同时也带来压力损失,综合换热性能与连通口数目不成正相关。

To enhance the wide application of flow boiling technology in the field of fuel cell heat dissipation,this paper uses R141b as the working medium to conduct three-dimensional transient numerical simulation of flow boiling in parallel straight channels and interconnected small channels at different flow rates.Parameters such as heat transfer coefficient,base temperature and comprehensive heat transfer factor are used to compare the heat transfer performance of each structure,and the heat transfer strengthening mechanism of interconnect small channels is explored.The results show that the heat transfer trend changes periodically with the bubble behavior,and the heat transfer effect is the best when the bubble is separated.The secondary flow caused by the connecting port promotes the heat transfer and wall temperature rise,so that the channel can meet the nucleation conditions 2 ms in advance,and the bubble breaks away first under the action of secondary flow rate above 1×10^(-4) m/s.Compared with the parallel straight channel,the heat transfer coefficient of five-connected channel can be increased by 19.6%~23.3%,and the relative growth rate of heat transfer coefficient is less than 3.5%as the number of connected channels continues to increase.The vortex structure leads to an increase in pressure drop with the increase of the number of connected channels,and the increasing trend does not diminish.The pressure drop of eight-connected channels is increased by 29.5%~42%compared with that of parallel straight channels.It can be seen that secondary flow not only affects bubble behavior and strengthens heat transfer,but also brings pressure loss.Comprehensive heat transfer performance is not positively correlated with the number of connecting vents.