微通道内液-液泰勒流传热的计算流体力学模拟

CFD simulations of heat transfer of liquid-liquid Taylor flow in microchannels

微通道内的液-液两相流型在低流速时以泰勒流为主,本文使用计算流体力学方法,对微通道内液-液泰勒流的传热特性进行了研究。首先考察了分散相流速、物系和管径对微通道壁面温度的影响。结果表明:分散相流速和物系热导率增大使得微通道壁面温度降低,管径的改变对微通道壁面温度影响较小。然后针对当量直径为0.5mm的微通道内工作介质为甲苯和水的两相泰勒流模型,考察了微通道壁面剪切力、界面涡度和努塞尔数对壁面和内部温度的影响,并与文献中气-液两相泰勒流的传热性质作了比较。结果表明:壁面剪切力和界面涡度对管壁和界面温度的波动性变化有一定影响,壁面剪切力和界面涡度的波峰往往出现在温度的波峰附近,并且有一定的时间滞后性。甲苯-水两相泰勒流动下的壁面努塞尔数比气-液两相流大得多,液弹单元的平均努塞尔数是相同条件下单相流体流动的1.3倍。

Under low flow velocity, the flow pattern in a microchannel is typically the so-called Taylor flow regime. A computational fluid dynamics package FLUENT was adopted for simulation of the heat characteristics of liquid-liquid two-phase Taylor flow in a microchannel. The effects of the dispersed phase velocity, the materials and the diameter of the microchannel on the wall temperature were investigated first. The results indicated that when the velocity of the dispersed phase and the thermal conductivity of the material increased, the wall temperature decreased, and the change of diameter had little effect on the wall temperature. The effect of the wall shear stress, interfacial vorticity and the Nusselt number on the wall and internal temperature were investigated subsequently in view of toluene-water two-phase Taylor flow system in a microchannel with a diameter of 0.5mm. The heat transfer characteristics were compared with the gas-liquid two-phase flow in literature. The results showed that the wall shear stress and interface vorticity had certain effect on the fluctuating changes of wall and interface temperature. The wave crests of wall shear stress and interface vorticity often appeared near the peaks of temperature, and had a certain time lag. The wall Nusselt number of toluene-water two-phase Taylor flow was much greater than that of gas-liquid two-phase flow. The average Nusselt number of a liquid slug unit was 1.3 times of single-phase flow under the same condition.