介质流量密度对铝合金喷射淬火界面热交换率的影响规律及机理

通过喷射淬火试验,研究了在高温铝合金表面进行水射流淬火、喷雾淬火和高速空气淬火的热交换过程,并对这3种在线淬火界面的热流密度(q)和传热系数(h)进行了反分析求解,重点探究了试样表面介质流量密度(q_(s))对界面热交换率的影响规律及其机理。结果表明,随q_(s)增大,喷射淬火界面热交换率先增大后减小,即存在一个临界q_(s),此时临界热流密度(q_(c))取得最大值。当q_(s)小于其临界值时,喷射淬火界面热交换率随q_(s)增大而增大;当q_(s)大于临界值时,随q_(s)继续增大,喷射淬火界面热交换率反而减小。喷雾淬火的单位体积冷却介质最大吸热量(Q_(max))最高,且淬火介质相同时,Q_(max)随q_(s)增大而减小。增大q_(s)对提高喷水淬火表面的热交换率效果最好。

Thermal transfer experimental research of a horizontal tube evaporative condenser

The thermal resistances distribution in different wet-bulb temperatures, air velocities and spraying water densities were achieved by the experimental test. The fluctuation of the water film convection and the water-air interfacial thermal resistance were reviewed especially. In the distribution of thermal resistance, the rank of the thermal resistance proportion （from max to min） is air flow heat transfer resistance, heat transfer resistance between refrigerant and wall, water film convection resistance and wall heat transfer resistance. When the heat flux is constant, the total resistance lowers nearly along with the increasing of air flow and water spray density. But there are a best air flow value of 2.98 m/s and a best spray water density of 0.064 kg/（m ·s） respectively, if continue to increase them, condensation performance is not significantly improved any more. The test results are available to improve the evaporative condenser performance and the designing lever.

基于反热传导法的铝合金喷水冷却界面换热系数求解

数值模拟喷水冷却过程时,界面换热系数的准确求解是保证模拟结果可靠的先决条件。本文采用反热传导法求解了6082铝合金喷水冷却界面热流密度和界面换热系数,并通过对比同一特征点的试验测量温度和计算温度,验证了反热传导法计算结果的可靠性。结果表明：铝合金喷水冷却过程中,界面换热经历了过渡沸腾阶段、核沸腾阶段和单相对流阶段,且过渡沸腾阶段冷却界面的热交换率明显高于核沸腾阶段;铝合金喷水冷却的界面热流密度随试样表面温度降低先增大后减小,其最大值约为4.4 MW/m^2;铝合金喷水冷却的界面换热系数随试样表面温度降低先近似线性增大后逐渐减小,其最大值出现在核沸腾换热阶段,约为23. 8 k W/m^2K。