Condensation and pressure drop characteristics of R600a in a helical tube-in-tube heat exchanger at different inclination angles

An experimental investigation is carried out to study the condensation and pressure drop characteristics of R-600a inside a helical tube-in-tube heat exchanger. The axis of the helical condenser was located at inclination angles of zero, +30°, +60° and +90° from horizontal. The test condenser was a counter flow helical tube-in-tube heat exchanger. The diameter, pitch, height and the number of coil turns were 305 mm, 35 mm, 210 mm and 6, respectively. Experiments were also implemented in a straight tube-in-tube condenser; all tests were performed at average saturation temperatures ranging between 38.5 and 47 °C. Refrigerant mass fluxes varied in the range of 155–265.5 kg m−2 s. The average vapor quality varied between 0.11 and 0.78. The effects of inclination angle, mass flux and average vapor quality on the heat transfer coefficient and pressure drop are discussed. It is shown that the highest and lowest values of the heat transfer coefficient occur for 30° and 90° inclination angles respectively, while the pressure drop has the maximum value for the horizontal case. Compared to the horizontal straight condenser, the average heat transfer coefficient and the pressure drop of the horizontal helical condenser increase in the range of 24–165% and 33–157%, respectively. Moreover, the performance index values of horizontal helical condenser are about 15–41% higher than that of inclination angle of 90°.