Influence of Gravity Orientation on Downward Condensation of Refrigerants in Metal Foam-Enhanced Tubes: An Experimental Investigation

Enhancing condensation in refrigeration and air-conditioning systems can be achieved with tube inserts. This experimental study explores how combining metal foam-filled tubes and inclined tube orientation utilizes gravity effects to improve heat transfer performance. The effects of metal foam pore densities, tube inclination angle, mass flux, and vapor quality on condensation heat transfer coefficient and pressure drop of R134a flow were studied here. A total number of 240 experiments were performed over a mass flux of 54−90 kg/(m2·s), vapor quality of 0.2−0.8, using metal foams with pores per inch (PPI) of 10 and 15 and porosity of 0.85. Compared to plain tubes, the metal foam-filled tubes with PPI of 10 and 15 showed an increase in heat transfer by up to 3.21 and 2.97 times, respectively, accompanied by a pressure drop rise. The change of inclination angle from condensation downward flow (−90°) to horizontal flow (0°) nearly doubles the heat transfer rate at constant conditions, while the pressure drop remains almost unaffected. The maximum performance evaluation criterion value of 1.879, obtained for the tube with PPI of 10 at −60° inclination, vapor quality of 0.2, and mass flux of 90 kg/(m2·s), representing the optimum experimental conditions of this study.