【摘要】 采用去离子水作为实验工质,对14条水力直径为187.5μm的平行矩形微通道内两相流动阻力特性及气泡行为进行可视化实验。研究发现,当质量流速一定时,随着热通量增大,汽相逐渐增多,平行多微通道内压降相应增加;当热通量一定时,随着质量流速减小,压降出现先减小后增大的趋势,该曲线中的最低点被认为是静态流动不稳定性起始点(OFI点)。结合可视化图像并利用气泡动力学理论对4种不同的汽相行为特征进行分析,发现汽核受限、倒流等堵塞流道现象的出现导致系统阻力增大,压降增加。通过压降实验值与Kim&Mudawar关系式在不同质量流速下进行比较发现,Kim&Mudawar关系式仅能对本实验压降变化趋势进行预估,而无法对压降数值进行有效预测。更多还原

【Abstract】 The characteristics of two-phase flow resistance and bubble behavior had been experimentally investigated in a microchannel heat sink containing 14 parallel 0.15 mm × 0.25 mm rectangular microchannels with hydraulic diameter of Dh=187.5μm by using deionized water as working fluid.The experimental results revealed that vapor phase gradually increase with the increase of heat flux under constant inlet temperature and mass flux,leading to the increase of pressure drop in parallel multiple microchannel.When keeping the heat flux and inlet temperature constant,the pressure drop exhibited a trend of first decrease and then increase with the increase of mass flux.In addition,the lowest point in the curve of pressure drop vs mass flux(Δpexpvs G)is considered to be the starting point of the static flow instability(namely,OFI point).The characteristics of four different bubble behavior are studied by basing on the help of visual image and bubble dynamics theory.It is found that due to the effects of theinteraction of buoyancy and flow inertia force,the bubble was rapidly cleared at the initial stage of bubble nucleation.When the bubble size is approximately equal to the height of the channel,the bubble enter the local confined growth phase,leading to the increase of viscous resistance between the bubble and the surface of wall.And under the influence of heat flux,the bubble continues to grow and is limited in the width direction,so that the bubble’s growth was completely confined both at height and width direction.Thereafter,the bubble gradually grew and elongated as well as flowed downstream.Moreover,when the surface tension is insufficient to maintain the liquid bridge between two adjacent bubble,the liquid bridge broke and resulted in bubbles merging.It is more interesting that due to the influence of the downstream bubble reversal flow and the flow inertia force,The upstream bubble is gradually compressed,leading to the velocity of the bubble tail lower than that of the bubble head.Finally,by using the current pressure drop data to verify the prediction accuracy of Kim & Mudawar correlation,it is found that the Kim &Mudawar correlation can only predict the variation trend of pressure drop,but can not predict the pressure drop value.更多还原