Thermal and flow characteristics of the condensation of R404A refrigerant in pipe minichannels

This article presents the results of experimental investigations of heat exchange and pressure drop during the condensation of R404A refrigerant in stainless steel pipe minichannels with internal diameters of 1.4–3.30 mm. A review is provided of the present state of knowledge concerning the condensation of this refrigerant in conventional channels and in small-diameter channels. It is emphasized that there are few prior publications concerning this issue. The test setup is described as well as the results of the experimental tests. We discuss the dependence of the heat transfer coefficient and the pressure drop of the R404A refrigerant on both minichannel diameter and process parameters. The pressure drop during the condensation of this refrigerant is satisfactorily described by the Friedel and Garimella correlations. Based on the experimental tests, we propose a new correlation for the calculation of the local heat transfer coefficient. The values calculated from this correlation were in agreement with the experimental results to within ±20%.