Experimental study of flow condensation heat transfer in tubes partially filled with hydrophobic annular metal foam

Abstract

The effect of metal foam surface wettability on vapor flow condensation heat transfer in tubes is experimentally studied in this paper. The hydrophobic metal foam surface is obtained by surface oxidation and chemical modification method. The annular metal foam is partially filled in the tube. The inner tube diameter is 22 mm and water is used as working fluid. The impact of steam-mass flow, the pores per inch (PPI) value of metal foam, and the metal foam surface wettability on flow condensation heat transfer characteristics are analyzed. Experimental results show that a hydrophobic metal foam tube achieves better heat transfer performance and lower pressure drop compared with those of an untreated metal foam tube. With modified surface wettability, the average heat transfer coefficient (HTC) in a 10 PPI metal foam tube is higher than that in a 15 or 20 PPI metal foam tube when the inlet steam pressure and mass flow rate are the same. The average HTC increases with the increasing of steam mass flow. The HTC can reach 30153 W m−2 K−1 for 10 PPI hydrophobic metal foam tube when the mass flow rate is 65.8 kg m−2 s−1 and average cooling water temperature is 55 °C. The comprehensive evaluation index of a hydrophobic metal foam tube is much higher than that of an untreated metal foam tube, which implies that hydrophobic metal foams have useful applications in vapor flow condensation heat transfer.