垂直矩形窄通道流动沸腾换热理论和实验研究

Theory and Experiment Research on Flow Boiling Heat Transfer in Vertical Rectangular Narrow Channel

建立单面加热垂直矩形窄通道流动沸腾换热实验装置,针对截面250 mm×5 mm的窄缝通道,对水流动沸脯换热特性进行实验研究.通过实验分析可知,1)流体处于泡状流时,主导机理为饱和核沸腾,其局部换热系数存在一个最大值;2)质量流量对通道出口顶端测点局部换热系数的影响主要体现在两个方面:流量的增大会使流动流体的紊流度增加,加强了液膜的对流换热;流动流体流速的增大会减小液膜的厚度,增强了液膜的导热和蒸发换热;3)当所取测点靠近汽化核心处时,流量增大会使过冷液体预热不充分直接进入饱和主流液体中,汽化核心产生的汽泡遇到过冷液体被冷凝而湮灭,导致换热系数的降低.

A single-side heating apparatus is set up to study flow boiling and heat transfer mech- anism in vertical narrow rectangular channel, experiment research on flow boiling and heat transfer characteristics in the channel with the section of 250 ramx5 mm is carried out. According to the experimental analysis： 1） when the fluid is in bubble flow, the dominant mechanism is saturated nucleate boiling, and the local heat transfer coefficient exists a maximum value; 2） two main influences for local heat transfer coefficient in the channel top points： Increasing mass flux will make the fluid＇s turbulence intensity increased, and strengthen liquid film＇s convective heat transfer; increasing flow velocity will reduce the thickness of the liquid film, and strengthen liquid film＇s heat conduction and evaporation heat transfer; 3） When the measurement point is close to vaporization core, increasing mass flow will make the super-cooled liquid which is not fully preheated directly into the saturated mainstream liquid, the bubbles generated by vaporization core encounter super-cooled liquid, then condensed and annihilated, at last heat transfer coefficient is reduced.