微小内螺纹管冷凝实验结果及关联式评价

Experimental Result of condensation in micro-fin tubes of different geometries

为了研究不同顶角的内螺纹管单相及冷凝的压降及换热性质,对具有相同外径(5mm)、相同螺旋角(18°)的内螺纹管进行实验,使用制冷剂为R22和R410A,质量流速为200～650kg/(m2.s),饱和温度为320K,进出口干度分别为0.8和0.1.结果表明,内部实际换热面积增加比Aai/Afr是和强化换热系数直接正相关的.其中R22为工质的1#管和R410A为工质的7#管具有相对高的换热系数和相对低的压降.且在计算压降时,应用了Churchill模型[27]得出的摩擦系数及一个合适的相对粗糙度来修正光管的压降关联式.对Kedzierski和Goncalves关联式[11]进行修正,用基于齿根直径的换热面积代替实际内部换热面积,使误差在20%以内.

An experimental investigation was performed with R22 and R410A for single-phase flow and condensation inside seven micro-fin tubes with the same outer diameter 5 mm and helix angle 18° to obtain pressure drop and heat transfer coefficient characteristics of tubes with different apex angle a. Data are for mass fluxes at 200-650 kg/（m^2 · s）. The nominal saturation temperature is 320 K, with inlet and outlet qualities of 0.8 and 0. 1, respectively. The results suggest a positive correlation between surface heattransfer area ratio and heat exchange enhancement ratio. When R22 is used, Tube 1 has the relatively high heat transfer coefficient and relatively low pressure drop, the same as tube 7 when R410A is used. In addition, Pressure drop correlations for plain tubes were applied to micro-fin tubes by using a friction factor calculated by the Churchill model and a suitable relative roughness. The Kedzierski and Goncalves correlationE10 has been modified to be based on the nominal heat transfer area adopting the fin root diameter instead of the actual inner surface heat transfer area, which can predict all data points within a ±20% error band.