An empirical study on heat transfer characteristics of R۱۳۴a flow boiling in annular metal-foam filled tubes

The purpose of this study is to experimentally investigate the flow boiling heat transfer of R۱۳۴a refrigerant through annular metal foam for low-range mass fluxes. Three annular tubes with a length of ۳۰ cm and outer and inner diameters of ۱۴.۳ mm and ۴.۷ mm are employed. Two tubes of them are filled with copper foam pieces with pore densities of ۱۰ PPI and ۲۰ PPI, respectively and the third tube is considered plain annular for the sake of comparison. The heat transfer coefficient values are calculated and the results of the metal-foam filled tubes are then compared to those of the plain annular tube. The experiments are performed in a mass flux range of ۱۰-۶۵ kgm-۲s-۱ and the vapor quality ranging from ۰.۱۳ to ۰.۸۵. Generally, the results show that using metal foam increases the heat transfer coefficient compared to that of the plain annular tube. The enhancement rate increases with the increase of pore density in a way that the annular tube filled with ۲۰ PPI copper foam, promotes the heat transfer coefficient to a maximum of ۲.۸ times that in the annular tube without metal foam. Also, the heat transfer increases with both an increment in mass flux and a decrement in vapor quality.

Keywords:

Flow Boiling , Heat Transfer , R۱۳۴a , Metal Foam , Annular tube , Empirical