竖直矩形窄通道内水流动沸腾换热特性的研究

建立单面加热垂直矩形窄通道流动沸腾换热试验装置,针对截面250mm×3.5mm的窄缝通道,对水流动沸腾换热特性进行试验研究。通过试验分析可知:(1)随着干度的增加,局部换热系数先增加后减小,有一个最大值,此时处于饱和核沸腾区域,其蒸汽干度也接近于0,同时也接近于沸腾起始点。相应地流体从单相流-泡状-块状流-搅拌-环状流转变。(2)在流动沸腾换热中,热流密度对核态沸腾换热有明显影响,而对流动沸腾液膜蒸发的影响甚小,所以可以认为由热流密度的变化而引起的换热变化,主要表现在核态沸腾。(3)入口温度的变化对单相流动的换热系数有影响,而沸腾换热系数与流型及汽泡的产生及扰动有极大关系,入口温度对流动沸腾局部换热系数基本没有影响。

Studies on Water Flow Boiling Heat Transfer Characteristics in Vertical Narrow Rectangular Channel

A single-side heating apparatus is set up to study the flow boiling and heat transfer in vertical narrow rectangular channel,experiment research on flow boiling and heat transfer characteristics in a vertical narrow rectangular channel with the section of 250mm × 5 mm is carried out. According to the experimental analysis:( 1) With the increase of dryness,the local heat transfer coefficient firstly increases then decreases,there is a maximum,which is saturated nucleate boiling region,the steam quality is close to zero,also it is close to the onset of boiling. Accordingly flow mode of fluid is from single phase,bubble,slug, churn to annular flow.( 2) For flow boiling heat transfer,nuclear boiling heat transfer is significantly affected by heat flux,but liquid film evaporation is nearly not. So it is assumed that heat transfer is caused by the change of heat flux.( 3) The change of inlet temperature has influence on single-phase flow heat transfer coefficient,but flow boiling heat transfer coefficient has great relationship with flow pattern and generated bubbles,and not inlet temperature.