This study investigates the flow resistance and surface coefficient of the heat transfer of four types of refrigerant with different tube diameters for a finned-tube heat exchanger. The optimum tube diameter for each refrigerant was studied using a developed simulation model. The simulation results show that the flow resistance characteristics of the four refrigerants followed the order of R22 > R290 > R410A > R32

and the comparison of the surface coefficient of the heat transfer followed the opposite trend. For an air conditioner

the system coefficient is known to increase with the decrease in the condenser inlet pressure (compressor exhaust pressure) under a fixed cooling capacity. According to the simulation results

the condenser inlet pressure first decreased and then increased with the increase in the tube diameter of the heat exchanger when the heat transfer capacity was set to 2 000 W. The optimum diameters of the heat exchanger for R22

R410A

R32

and R290 followed the sequences of 7–7.5 mm

6–6.5 mm

6–6.5 mm

and 6.5–7 mm.