孔隙直径对R134a管外沸腾换热影响研究

Influence of pore diameter on boiling heat transfer of R134a outside horizontal tubes

在工况温度分别为6℃和10℃,对R134a在光管和三根双侧强化管(F38,F46,F56)外进行池沸腾换热试验研究。结果表明:两种工况下,R134a在光管外沸腾表面传热系数与Cooper公式计算值相对偏差均在±15%以内,R134a在强化管外沸腾表面传热系数变化趋势与光管Cooper公式基本一致。受试验管外表面孔隙直径的影响,当热流密度小于50k W/m2(或壁面温差小于2K)时,孔隙直径越小,沸腾换热效果越好;反之,当热流密度大于50k W/m2(或壁面温差大于2K)时,孔隙直径大的强化表面沸腾换热效果要优于小孔隙直径表面。

Experimental studies on pool boiling heat transfer of R134a outside one horizontal smooth tube and three doubly - enhanced tubes（ F38, F46, F56）have been conducted with the saturation temperature of 6~C and 10~C respectively. The results indicate that the predicted boiling heat transfer coefficient of R134a on smooth tube from the Cooper formula agrees with the ex- perimental data within 15 percentage. The change tendency of boiling heat transfer on enhanced tubes is consistent with the Coop- er formula for smooth tube. It is found that the boiling heat transfer coefficients are affected by the surface pore diameter outside test tubes. While the heat flux is less than 50kW/m2 （ or wall temperature difference is less than 2K） , the effect of boiling heat transfer is better with the smaller pore diameter. On the contrary, while the heat flux is more than 50kW/m2 （ or wall temperature difference is higher than 2K） , the effect of boiling heat transfer of tube with big pore diameter enhanced surface is better than the small one.