The fluid flow and heat transfer characteristics of R-32 in a small Tube.

• The heat transfer characteristics of R-32 in a 4.0 mm diameter tube at 10 oC was studied. • The pressure drops in a 4.0 mm diameter tube was also evaluated. • We clarified the results by comparing them to the existing correlations. Due to the Global Warming effect considerations, refrigerants with lower value of the Global Warming Potential will be the next generation refrigerants which are used in the air-conditioner systems. Currently, a new developed refrigerant R-32 has proposed to substitute R-410A. Therefore, many air-conditioning manufactures have determined refrigerant R-32 in their products and some studies have been discussed in recent years. However, the information of refrigerant R-32 on saturation temperature around 10°C is still insufficient, and the heat transfer coefficient (HTC) of refrigeration system around -20°C to -40°C has not been clarified. In this study, two-phase HTC s and pressure drops of refrigerant R-32 are measured in a horizontal tube with 4.0 mm inner diameter, and at saturation temperature of 10°C. The test section is a double pipe heat exchanger, where refrigerant flows in the tube side and water flows in the annular side. Also, modified Wilson Plot method was used to calculate the single-phase HTC s and pressure drops of R-32 refrigerant. In this study, two-phase experiments were conducted at vapor qualities ranging from 0.1 to 0.9 where the range of mass fluxes was 200 to 600 kg m−2 s−1 and heat fluxes ranging from 26 to 46 kW m−2. The results showed that the two-phase test results agreed well with the correlations of Shah (Shah, 1982), Gungor and Winterton (Gungor and Winterton, 1986), and Liu and Winterton (Liu and Winterton, 1991). However, the accuracy of results at different flow conditions was different, this was attributed to the change in the enhancement factor of each flow boiling model. [ABSTRACT FROM AUTHOR]