带半椭球凹坑微通道流动换热的数值模拟

Numerical Simulation of Flow and Heat Transfer of Microchannel with Semi-Ellipsoidal Dimples

采用数值模拟的方法,使用laminar模型及Reynolds Stress模型,在工质为水,雷诺数小于8000的情况下,对高0.6 mm、宽9 mm的带有半椭球凹坑的微通道(带凹坑的通道)及不带有半椭球凹坑的微通道(光滑通道)的流动换热进行深入分析。结果表明:带凹坑的通道内,流动从层流发展到充分湍流的过渡区雷诺数范围为900~3800,仅过渡区内,凹坑前方出现回流,并且产生附壁效应,造成流动换热的不对称,不对称方向随机;过渡区和湍流区内,凹坑尾部均形成三个低压回流区,掺混产生三股速度较高的流动流向下游,造成下游凹坑前方三个换热增强点;流动分离造成首排凹坑压力较小位置为中间整个区域,下游凹坑压力较小位置为中间两侧区域;带凹坑的通道与不带凹坑的通道的努塞尔数之比,在低雷诺数时,随雷诺数增大而明显增大,由105%增长至最大值265%,在较高雷诺数时,随雷诺数增大而减小且趋于平缓,趋近109%。

With working medium of water and Reynolds number of less than 8000,the flow and heat transfer of microchannels with and without semi-ellipsoidal dimples are deeply investigated via numerical simulation.The microchannel has 0.6 mm in height and 9 mm in width.The laminar model and the Reynolds Stress model are employed in this study.The result shows:In the channel with dimples,the transition Reynolds number where the flow develops from laminar to fully turbulent ranges from 900 to 3800.Only in the transition,a backflow occurs in front of the dimples,and the Coanda effect occurs,resulting in asymmetric flow and heat transfer,and the asymmetry direction is random.In the transition and turbulence,the tail of the dimples is formed into three low-pressure recirculation zones.Mixing produces three high-speed flow recirculation zones,causing three heat transfer enhancement points in front of the downstream of dimples.The flow separation leads the low pressure position of the first row of dimples to be the entire middle area,and the low pressure position of the downstream of dimples to be the two sides of the middle area.At low Reynolds numbers,the ratio of the Nusselt numbers of channels with and without dim ples increases significantly with Reynolds numbers,from 105%to a maximum of 265%.At relative high Reynolds number,the ratio increases and becomes flat as Reynolds number increases,approaching 109%.