R290蒸气珠状凝结传热微尺度特性的研究

通过对自然工质R290蒸气珠状凝结传热过程的微尺度特性分析得出,在一定的过冷度、液珠半径和分形维数下,液珠的导热热阻随接触角的增大而增大,促进层的热阻在接触角为90°时最小,气液界面的热阻随着接触角的增大而减小,单个液珠的总传热热阻随着接触角的增大呈现出先减小后增大的变化规律,即存在最佳接触角,在此最佳接触角下,单个液珠的总传热热阻最小,单个液珠的传热量最大,换热表面的热流密度最高。随着液珠半径的增大,最佳接触角减小。随着过冷度的增加和分形维数的增大,换热表面液珠成核中心密度增大,表面的热流密度增加。在一定的过冷度下,液珠半径增大,液珠分布密度减少,分形维数增大,液珠的分布密度增加。在一定的分形维数和过冷度下,随着液珠半径的减小,换热表面的热流密度增大。

Investigations on Microscale Characteristics of R290 Vapor Dropwise Condensation Heat Transfer

By analyzing the microscale characteristics of natural refrigerant R290 vapor dropwise condensation heat transfer,the following conclusions are obtained. At a certain subcooling degree,droplet radius and fractal dimension,the thermal resistance of single droplet conductivity increases with the increase of contact angle,the thermal resistance of promoting layer has the smallest value at the contact angle of 90°,the thermal resistance of vapor-liquid interface decreases with the increase of contact angle,the total thermal resistance of single droplet decreases first and then increases with the increase of contact angle,namely has proved the existence of the optimum contact angle,and at this optimum contact angle,the total thermal resistance of single droplet has a smallest value,the heat transfer capacity of single droplet and the heat flux of heat transfer surface have the largest value. Also,with the increase of droplet radius,the optimum contact angle decreases. Moreover,with the increase of subcooling degree and fractal dimension,the nucleation density of dropwise condensation increases on the heat transfer surface,so the heat flux enhances. At certain subcooling degree,with the increase of droplet radius,the distribution density of condensation droplet reduces,however,with the increase of fractal dimension,the distribution density of condensation droplet increases. At a certain fractal dimension and subcooling degree,with the reduceing of droplet radius,the heat flux of heat transfer surface increases.