局部超亲水调控自然循环流动沸腾传热研究

Study of the Natural Circulation Flow Boiling Heat Transfer Based On Partially Superhydrophilic Surface Modification

气液分层流动沸腾现象是水平加热管道内在低热流和流量条件下常见的现象,提高和改善气液分层流动沸腾换热对于改善换热设备性能具有重要意义。本文通过建立蒸发段水平加热自然循环流动沸腾实验台,通过对加热功率为1000 W,长度为0.8 m,,内径为15.0 mm的蒸发段内典型的气液分层区域(C-D区)沸腾表面进行局部超亲水修饰,研究局部超亲水修饰对自然循环系统内气液分层流动沸腾性能的影响。实验结果表明:局部超亲水表面处理方法可以有效改善传热特性,蒸发段各截面温度均有不同程度的下降,并且各截面温度变化趋势趋于平缓;局部超亲水表面可以提高蒸发段平均传热系数159%,并且有效降低蒸发段热阻。

The phenomenon of gas-liquid stratified flow boiling is usually happened in horizontally tubes in condition of the low heat and mass flux.It is of great significant to improve thermal performance of thermal systems by enhancing and regulating the gas-liquid flow boiling heat transfer.In this work,a natural circulation flow boiling test rig of thermosyphon loop with horizontal arranged evaporator was set up.The experiment was carried out by heating a 0.8 m-long horizontal evaporator with an inner diameter of 15.0 mm under a heat load of 1000 W.Effects of partially superhydrophilic surface on the thermal characteristics of the gas-liquid stratified flow boiling in the natural circulation system were investigated.The local surface at region C-D where gas-liquid stratification often occurred was modified in this work.The results show that heat transfer performance in the evaporator was effectively improved by the partially superhydrophilic surface modification.Temperatures at each cross section of the evaporator appeared different degrees of decline.And temperature fluctuation between the cross sections tended to be more moderate.Finally,the average heat transfer coefficient was enhanced by 159%due to the modification of superhydrophilic surface.And a decrease of thermal resistance was also observed.