Experimental study of the pressure drop during condensation in an inclined smooth tube at different saturation temperatures

Several applications exist in industry where condensation does not occur in horizontal or vertical tubes but in inclined tubes. Examples are aeroplanes during take-off, landing and banking, automobiles and trucks driving over hilly terrains and large industrial A- and V- frame condensers. However, very little work has been done for condensation in tubes at different inclination angles, and most work was done for flow in horizontal tubes and vertical tubes. The few studies that were conducted for flow at different inclination angles were limited to saturation temperatures of 40 °C. Previous work showed that the saturation temperature of condensation influences the heat transfer and pressure drop results. Therefore, it was the purpose of this study to experimentally study the pressure drops during condensation in inclined tubes at different saturation temperatures. More than 700 condensation experimental data points were collected with the refrigerant R134a in a smooth copper tube of inner diameter of 8.38 mm for vapour qualities ranging between 0.1 and 0.9. The mass fluxes varied between 100 kg/m2 s and 400 kg/m2 s and measurements were taken at saturation temperatures of 30 °C, 40 °C and 50 °C. Inclination angles ranging from −90° (downward flow) to +90° (upward flow) were considered. The pressure drops were measured with a differential pressure transducer connected to the inlet and the outlet of the test section over a length of 1.704 m. The frictional pressure drops were also determined by using a recently developed void fraction drift model. It was found that the pressure drops were significantly influenced by the inclination angle and saturation temperature. The void fractions and frictional pressure drop results also showed that they were largely influenced by these parameters. While the highest and lowest measured pressure drops were obtained during the upward flow and downward flow respectively, the results obtained for the void fraction and the frictional pressure drop showed that the highest pressure drop values were obtained during the downward flow, while the lowest values were obtained during the horizontal and upward flows.