Evaporating heat transfer of R22 and R410A in horizontal smooth and microfin tubes

An experimental investigation of evaporating heat transfer in 9.52 mm O.D. horizontal copper tubes was conducted. The refrigerants tested were R22 and the near-azeotropic mixture, R410A. The test rig had a straight, horizontal test section with an active length of 0.92 m and was heated by the heat transfer fluid (hot water) circulated in a surrounding annulus. Constant heat flux of 11.0 kW/m2 was maintained and refrigerant quality varied from 0.2 to 0.8. The results were reported for evaporation at 15 °C in a 0.92 m long test section for 30–60 kg/h mass flow rate. The local and average heat transfer coefficients for seven microfin tubes were presented compared to those for a smooth tube. The average evaporation heat transfer coefficients of R22 and R410A for the microfin tubes were 1.86–3.27 and 1.64–2.99 times higher than those for the smooth tube, respectively. When compared to R22 at the same test conditions, the evaporating heat transfer coefficients for R410A were 97–129% of R22.