Heat transfer and pressure drop characteristics during R22 evaporation in an oval microfin tube

An experimental study on R22 evaporating heat transfer in round and oval mi crofin tubes has been performed. The oval tube was an elliptic tube of axis ratio 1:1.5, which was fabricated from the round tube with an outer diamet er of 9.52 mm and 18 deg helix angle counterclockwise. The test section was a straight horizontal tube of 0.6 m in length and was heated electrically by a tape heater wound on the tube surface. Heat flux of 12 kW/m(2) was mai ntained constant and the range of refrigerant quality was 0.2-0.8. The test s were conducted for evaporation at 15 degreesC for 30-60 kg/h mass flow ra te (mass flux; based on, the oval tube: 150-300 kg/m(2)s) and the installat ion angles of the oval tube were varied between 0 and 135 deg in the circum ferential direction. The local and average heat transfer and pressure drop characteristics for the oval tube were compared to those for the baseline r ound tube. The average two-phase heat transfer coefficients for the oval tu be were 2-12 percent higher than that for the round tribe and pressure drop s for both tubes are similar. The single heat transfer coefficient and fric tion factor correlations for the round and oval microfin tubes are develope d within the rms errors of +/-5.6 percent and +/-10.0 percent, respectively .