A study on boiling heat transfer characteristics of refrigerant mixtures in a horizontal tube

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

In the present study the evaporating heat-transfer characteristics of mixtures of refrigerant fluids were analysed. This paper presents experimental heat transfer coefficients obtained during the evaporation of the zeotropic mixtures: R407C (R32-R125-R134a 23- 25-52% in weight) and R417A (R125-R134a-R600 46.6-50-3.4 % in weight) and of the near-azeotropic mixtures: R404A (R125/R143a/R134a 44/52/4 % by weight) and R410A (R32/R125 50/50 % by weight). The test section was a smooth, horizontal, stainless steel tube (6 mm I.D., 6 m length) uniformly heated by Joule effect. The heat transfer characteristics were measured at an evaporation pressure of about 4.00 bar varying the refrigerant mass flux within the range 200-1100 kg/m2s, with heat fluxes within the range 10-15 kW/m2. The experimental data are discussed in terms of the heat transfer coefficients as a function of the vapour quality. The experimental results clearly show that the heat transfer coefficients increase with increasing the refrigerant mass flux with a power coefficient varies in the range 0.57 – 0.86. In the experimental tests R410A shows the higher values of the heat transfer coefficients. In the paper are reported also the pressure drops values for the same experimental data.