粗糙元对微通道稀薄气体流动换热影响研究

Research on the effect of the rough element on the rarefied gas flow andheat transfer in microchannels

针对壁面粗糙元对微尺度通道内稀薄气体流动和传热的影响,采用直接模拟蒙特卡洛法(DSMC)进行研究,分析了粗糙元数量、分布和高度不同时,各类型微通道内稀薄流动和传热状态及特征参数的变化情况.结果显示,当粗糙元数量增加时,微通道壁面压力和换热量分布略有波动,壁面摩阻和通道中心线上的雷诺数受流场总体速度降低的影响,变化较为明显;当粗糙元的高度增加时,微通道内流场发生了较为明显的变化,通道内平均换热量、壁面摩阻和中心线上的雷诺数均有不同程度的下降,而壁面压力和雷诺数等流动性能的波动性显著增大.由此可以说明,粗糙元对微通道内的流动换热性能产生的主要影响为压缩和阻滞效应,前者会提高局部流速的波动性,后者则会降低通道内流场的流动性,相比于增加粗糙元数量,提高粗糙元的高度所产生的影响更为明显;另外,微通道内的换热性能主要取决于流动速度,粗糙元能够增大换热面积并通过压缩效应增大局部换热量,但由于其阻滞效应的作用,通道内流速随之降低,从而导致平均换热量有所下降.

The direct simulation of Monte Carlo(DSMC)method is utilized to research the effect of rough element on rarefied gas flow and heat transfer in microchannels.When the numbers,distribution and heights are different,the changes of rarefied flow,heat transfer state and characteristic values in various types of microchannels are analyzed.The results show that when the number of rough elements increases,the wall pressure and heat transfer distribution of the microchannel fluctuate slightly,and the wall friction and Reynolds number on the centerline of the microchannel are affected by the decrease of the overall velocity of the flow field;when the height of the roughness element increases,the flow field in the microchannel changes obviously,the average heat transfer,wall friction and Reynolds number on the centerline decrease in varying degrees,while the fluctuation of wall pressure and Reynolds number increases significantly.It can be concluded that the main effects of roughness elements on the flow and heat transfer performance in microchannels are compression and retardation effects,the former can improve the fluctuation of local velocity,while the latter can reduce the fluidity of the flow field in the channel;in addition,the heat transfer performance in the microchannel mainly depends on the flow velocity,the roughness element can increase the heat transfer area and increase the local heat transfer through the compression effect.However,the flow velocity in the microchannel will decrease due to the blocking effect caused by roughness element,resulting in the decrease of the average heat transfer.