微通道内亲疏水壁面特性对入口段长度的影响

Influence of hydrophobic and hydrophilic surfaces characteristic to entrance region length in micro channels

针对水力直径为200μm的微尺度通道,采用数值模拟的方法研究了壁面亲疏水特性产生的速度滑移对微尺度通道入口段长度的影响,建立了包含滑移长度影响的入口段长度修正计算公式。研究表明:相同流量下,速度滑移的存在使得微尺度通道充分发展段的最大速度减小,从而缩短了入口段长度,且在低雷诺数区域,入口段的缩短效应更为显著。针对不同的雷诺数区域分别进行无量纲入口段长度计算公式的拟合,得到拟合系数随滑移长度的变化规律与对应关系,从而建立了滑移长度对入口段长度的修正计算方法和准则关系式,利用修正公式计算的结果与数值模拟结果相比,最大误差为3.7%。

Numerical simulations were conducted to investigate the influence of slip boundary condition produced by hydrophobic and hydrophilic surfaces characteristic on the hydrodynamic entrance length in micro channels with hydraulic diameter of 200 μm. A modified calculation method of entrance length was established by considering the slip length on channel walls. The results indicated that under the same flow, the velocity slip can reduce the maximum velocity in fully developed region of micro channels, which consequently shortened the entrance length. And in low Reynolds number region, the shortening effect was more significant. The calculation equation of dimensionless entrance length was fitted according to different Reynolds number regions, and cubic polynomial functions were employed to correlate the slip length and the fitting coefficients. By comparing the numerical simulation results and the results calculated by modified entrance length formula, the maximum error was 3.7%.