微通道内纳米流体换热与压降特性

为研究微通道换热和压降特性的影响因素,在当量直径分别为0.923 1,1.333 3和2.000 0 mm的矩形微通道内,以0.1%和0.5%(体积分数)的Al2O3-H2O纳米流体为实验工质,进行无相变以及沸腾传热与流阻特性实验研究,分析雷诺数对努塞尔数和单相流动压降的影响。研究结果表明:增加纳米粒子体积分数对摩擦压降影响较小,而努塞尔数则得到较大提高;在2.0 mm宽槽道内,纳米流体的换热系数比水的换热系数高18%;而0.6 mm宽槽道的换热系数比2.0 mm宽槽道的换热系数提高了近2倍;随着槽道尺寸的减少,摩擦压降显著增大;当雷诺数为800时,0.6 mm和1.0 mm宽槽道摩擦压降分别是2.0 mm宽槽道摩擦压降的23.3倍和4.4倍;热流密度和质量流量增大都将导致摩擦压降增大。

Heat transfer and pressure drop of Al2O3 nanofluids in microchannels

The single-phase and two-phase flow and heat transfer characteristics were experimentally investigated through the aluminum-based rectangular microchannels with different hydraulic diameter of 0.923 1,1.333 3 and 2.000 0 mm,using Al2O3-H2O nanofluids with particle of 0,0.1% and 0.5%(volume fraction) as the working fluids.The effect of the Reynolds number,the heat flux density,the size of the channel and the nanoparticle concentration on the pressure drop and convective heat transfer were investigated.The results show that the Nusselt number increases considerably as the nanoparticle volume fraction increases slightly but causes little extra pressure drop.The heat transfer coefficient of nanofluid rises by 18% than that of deionized water in 2.0 mm width channel.The heat transfer coefficient in 0.6 mm width channel is double higher than that in 2.0 mm width channel.With the decrease of the channel width,the pressure drop rises rapidly.The pressure drops of fluids in 0.6 and 1.0 mm width channels are 23.3 and 4.4 times of that in 2.0 mm width channel,respectively(Re=800).The pressure drop and flow friction of the nanofluids are also influenced by the heat flux density and mass velocity.