R134a在螺旋管内的流动沸腾传热

Flow Boiling Heat Transfer of R134a in a Helical Coiled Tube

制冷剂R134a作为CFCs类工质的替代物已经投入商业应用。螺旋管具有传热效率高、结构紧凑等优点 ,在各种工业领域中被广泛使用。研究R134a在螺旋管内的流动沸腾传热性能对制冷系统中新型蒸发器的设计具有重要意义。实验测量了R134a在管内径 10mm ,螺旋直径 180mm ,螺旋节距50mm的紫铜螺旋管内的流动沸腾传热系数。实验段外缠电阻丝加热 ,热流密度q =3～ 2 1.2kW /m2 ,质量流量G =150～ 4 2 0kg/(m2 ·s)。实验表明 ,由于二次流的存在 ,螺旋管对流动沸腾传热具有一定的强化作用 ,而且在低干度区的强化效果比高干度区更好。

The helical coiled tube's high heat transfer efficiency and compact volume make it important in many engineering areas. The study of flow boiling heat transfer in helical coiled tube is essential for engineering application purposes, such as the design of evaporators using new alternatives for CFCs. This paper presents flow boiling heat transfer characteristics of an ozone friendly refrigerant R134a inside a helical coiled tube. The helical coiled tube used in the experiment is wound with 10 mm inside diameter smooth copper tube. The helical diameter and pitch are 180 mm and 50 mm, respectively. To obtain uniform heat flux boundary condition, heat is applied to the test section using electric resistance heater. Test parameters are varied as follows: heat flux, 3 to 21.2 kW/m 2; refrigerant mass flux, 150 to 420 kg/(m 2·s); and quality, 0.1 to 0.9. The correlations of Jung and Wattelet are compared with the experimental heat transfer coefficients. The results show that the intube flow boiling heat transfer of R134a has been enhanced to a certain extent for action of secondary flow by using helical coiled tube. The augmentation in lower quality region is much more significant than that in higher quality region.