Pressure drop during reflux condensation of R134A in a small diameter tub

The pressure drop during reflux condensation of R134a in a small diameter tube is investigated. The inner diameter of the tube is 7 mm and the length is 500 mm. The test tube represents a single sub-channel of a compact condenser. Measurements are carried out with a differential pressure transducer at system pressures of 0.68 and 0.82 MPa, respectively, and at inclination angles of 30°, 45°, 60° and 90° from the horizontal. The experimental data show that the pressure drop is small up to the onset of flooding because flooding occurs already at low vapour velocities. At the flooding point the pressure drop rises sharply due to condensate bridging inside the tube. The inlination angle does not have a significant effect on the pressure drop. A calculation of the frictional, accelerational and gravitational components of the pressure drop shows that the gravitational component has the greatest magnitude due to the relatively high density of the vapour.