Condensation of R134a outside single horizontal titanium, cupronickel (B10 and B30), stainless steel and copper tubes

Experiments were conducted on the condensing heat transfer of eleven horizontal tubes with refrigerant R134a at saturated temperature of 40 °C (1.01 MPa). The tube materials are titanium, cupronickel (B10 and B30), stainless steel and copper, among whom the former four materials are of low thermal conductivity. The enhanced tubes include integral-fin and three dimensional geometries. The results indicate that the heat transfer coefficients of the enhanced copper tube are about 1.6–2.1 times of low thermal conductivity tubes with the same enhanced geometries. Compared with plain tube the mean enhanced ratio of tubes made from titanium, B10, B30 and stainless steel are 8.48, 8.31, 8.22 and 7.52, respectively. The reason why low thermal conductivity affects the condensation heat transfer of enhanced structure is discussed in detail.