入口流速对间断微通道内流型演变及流量分配特性影响

Effect of inlet velocity on flow pattern evolution and flow distribution characteristics in discontinuous microchannels

微通道内气液两相流动规律是影响微通道换热器换热系数和流场温度均匀性的主要因素。以N2和H2O为工质,对间断、并联矩形微通道换热器内气液两相流型的起始、发展、稳定过程的演化以及并联通道内流量分配不均匀特性进行了数值模拟研究。结果表明,不同的进口Re对微通道内流型的演变过程和流动周期有重要影响,当进口Re为450时,气相工质在均流腔内以离散的散团状形态脉动扩散至微通道中,并联通道内气相工质从弹状流型态逐渐转变为泡状流型态;当进口Re增至为1600时,气相工质在均流腔内以较连续的椭圆状型态扩散至微通道中,并联通道内气相工质从环状流型态逐渐转变为泡状流型态。通道结构还将影响并联通道间的流量分配的均匀性,间断微腔的存在使微通道内工质质量流量分布均匀性提升38.7%,通过研究通道内压力分布规律,发现通道内静压的分布不均匀是导致两相工质从均流腔进入微通道时发生不均匀分配的重要原因。

The law of gas-liquid two-phase flow in microchannel is the main factor affecting the heat transfer coefficient and flow field temperature uniformity of microchannel heat exchanger.Using N2and H2O as working fluids,the initiation,development,and stability of gas-liquid two-phase flow pattern in discontinuous and parallel rectangular microchannel heat exchangers and the uneven flow distribution in parallel channels are numerically simulated.The results show that the inlet Re of the two-phase working medium has an important influence on the evolution process and flow cycle of the flow pattern in the microchannel:when the inlet Re is 450,the gas phase working medium diffuses into the microchannel in a discrete"bulk"shape in the flow sharing cavity,and the gas phase working medium in the parallel channel gradually changes from a slug shape to a bubble shape;When the inlet Re rises to 1600,the gaseous working medium diffuses into the microchannel in a continuous"elliptical"shape in the flow sharing cavity,and the gaseous working medium in the parallel channel gradually changes from annular flow pattern to bubble flow pattern.The channel structure also affects the uniformity of flow distribution between parallel channels.The existence of discontinuous microcavity improves the uniformity of working medium mass flow distribution in the microchannel by 38.7%.By studying the pressure distribution law in the channel,it is found that the uneven distribution of static pressure in the channel is an important reason for the uneven distribution of twophase working medium when entering the microchannel from the flow sharing cavity.By changing the inlet structure to ensure the uniform distribution of static pressure in each channel,combined with the discontinuous microcavity between continuous channels,the temperature uniformity of flow field can be better guaranteed and better heat transfer performance can be obtained.