Condensation of refrigerant in a multi-port channel

In the present paper, the local characteristics of pressure drop and heat transfer are investigated experimentally for the condensation of pure refrigerant R134a in four kinds of multi-port extruded aluminum tubes of about 1 mm in hydraulic diameter. Two tubes are composed of plane rectangular channels, while remaining two tubes are composed of rectangular channels with straight micro-fins. The experimental data of frictional pressure drop (FPD) and heat transfer coefficient (HTC) in plane tubes are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large diameter tube. It is confirmed that parameters such as tube diameter, surface tension, free convection in FPD and HTC correlations should be taken into account more precisely. Considering the effects of surface tension and kinematic viscosity, new correlation of FPD is developed based on the Mishima-Hibiki correlation. New correlation of HTC is also developed modifying the effect of diameter in the correlation of Haraguchi et al. Both new correlations are compared with experimental data for tubes with micro-fins. Satisfactory agreement between experimental and predicted results is obtained. This means that the micro-fin effect is taken into account by using hydraulic diameter and the heat transfer enhancement effect of micro-fins is mainly due to the enlargement of heat transfer area.