R404A和R407C在水平强化管外的凝结换热实验研究

Experimental Investigation on Condensation Heat Transfer of R404A and R407C outside Horizontal Enhanced Tubes

实验研究了近共沸制冷工质R404A与非共沸制冷工质R407C在水平强化换热管管外的凝结换热性能。采用"Wilson图解法"对实验数据进行处理。结果表明:对于R404A和R407C,强化管外的凝结换热系数随着壁面过冷度的增加而增大,呈现出与纯工质冷凝时不同的变化趋势,这主要是近共沸或非共沸工质凝结过程中,某些组分的凝结会遇到其它组分的凝结气膜热阻所造成的;随着过冷度增加,易挥发组分开始凝结,气膜变薄,冷凝传热系数增大。R407C在强化换热管管外的凝结换热系数比R404A要小70%左右,这是由于R407C的温度滑移较R404A要大,管外形成的凝结扩散气膜造成的影响更大。R407C在高热流密度工况下的换热效果提升明显,故应尽量工作在高热流密度区域。

The condensation heat transfer performance outside horizontal enhanced tubes of near-azeotropic refrigerant R404A and zeotropic refrigerant R407 C was investigated in this study. The experimental data were analyzed using Wilson graphical method. The results show that the coefficients of condensation heat transfer outside horizontal enhanced tubes of R404A and R407C increase with the increase of supercooling degree of tube wall, which is different from pure refrigerant. For near-azeotropic or zeotropic refrigerant, some components will encounter the gas film resistance caused by the condensation of other components. With the increase of super- cooling degree of tube wall, the volatile components begin to condense and the gas film becomes thin, thus the coefficient of conden- sation heat transfer will increase. The coefficient of condensation heat transfer outside horizontal enhanced tubes of R407C is 70% lower than R404A, which is due to the fact that the temperature glide of R407C is larger than R404A, and the impact of gas film outside tubes is greater. The heat transfer coefficient of R407C is improved obviously at higer heat flux condition, which is suitable for practical application.