Flow pattern visualization and heat transfer characteristics of R-134a during condensation inside a smooth tube with different tube inclinations

Experimental investigations are conducted herein to study the heat transfer and observe the condensation flow patterns of refrigerant R-134a inside a single smooth tube. The test apparatus makes the tube capable of having different inclination angles, ‘α’. The experiments are performed for seven different tube inclinations in the range of −90° to +90° and six refrigerant mass velocities between 53 and 212 kg/m2 s for each tube inclination angle. It is observed that the tube inclination noticeably influences the vapor and condensed liquid distribution, and also the condensation heat transfer coefficient. Eight different flow regimes have been observed during condensation inside a smooth tube with different tube inclinations. In the case of condensation heat transfer, the best performance is achieved by the tube with inclination angle of +30° (for all refrigerant mass velocities). The effect of inclination angle on heat transfer coefficient, h, is more prominent at low vapor quality and mass flux. Finally, an empirical correlation has also been developed to predict the heat transfer coefficient during condensation inside a smooth tube with different tube inclinations.