矩形微通道流动入口段的阻力特性分析

Friction Factor Characteristics of Rectangular Microchannels in Hydrodynamic Entrance Region

运用Fluent软件对宽高比ε为0.1~1.0的矩形微通道层流流动入口段的阻力特性进行了三维数值模拟.结果表明:宽高比ε和雷诺数Re对表观摩擦因子与雷诺数乘积fappRe有一定的影响.fappRe值随着宽高比ε的增大而减小,在不同的Re数范围内呈现了不同的影响.当Re数小于300时,fappRe值随Re数的增大而减小;Re数大于300后,fappRe值随Re数变化很小.当流动达到充分发展后fappRe值保持不变,且与Re数无关.此外还研究了ε和Re数对水力进口长度的影响.发现当Re数小于和等于20时,无量纲进口长度随着ε的增大逐渐减小;当Re数大于20,无量纲进口长度随着ε的增大呈先增后减的趋势,且在宽高比为0.3~0.4时达到峰值.基于得到的结果,提出了新的层流流动进口长度关系式,该式对微型设备的设计和优化具有一定的指导意义.

The friction factor characteristics of rectangular microchannels with aspect ratio ε from 0.1 to 1.0 in hydrodynamic entrance region were investigated by using the Fluent software. The results reveal that the aspect ratio ε and Reynolds number Re have effects on the product(fappRe)of the apparent friction factor and Reynolds number. The fappRe of rectangular microchannels decreases as the aspect ratio ε increases, and different effects are presented in the different range of Re. The fappRe decreases with the increase of Re when Re is less than 300;while the fappRe varies slightly when Re is more than 300. When the flow is fully developed, the fappRe remains unchanged and becomes nearly independent of Reynolds number.The effects of ε and Re on the hydrodynamic entrance length is also studied. It is found that when Re is less than 20, the dimensionless entrance length gradually decreases with the increase of the aspect ratio ε. When Re is more than 20, the dimensionless entrance length first increases and then decreases with the increase of the aspect ratio ε, and reaches the peak value as the aspect ratio is between 0.3 to 0.4. Based on the obtained results, a new hydrodynamic entrance length correlation for laminar flow was proposed, which may provide guidance for the design and optimization of microchannels.