Uthen Kuntha and Tanongkiat Kiatsiriroat

pp. 243 - 253

Abstract

Boiling heat transfer coefficients and pressure drop of R-22 and its alternatives, which are R32/R125a/
R134 (23%/25%/52%) and R32/R125a (50%/50%), flowing inside smooth and grooved tubes have been
determined with the conditions similar to those in small refrigerators. The range of mass flow rates examined
is between 0.0025 and 0.0125 kg/s. The data have been taken at the evaporator temperatures of -35 to -4 ^oC
and at the condenser temperatures of 40 to 50 ^oC. The boiling heat transfer coefficients of the refrigerants
in the grooved tubes are higher than those in the smooth tubes and R-22 shows the best performance for
both tubes. The heat transfer correlations have also been developed. In case of the pressure drop, the twophase friction multiplier φ_G² increases with Martinelli parameter and there is no effect of the tube
roughness and the types of the refrigerants.