Nucleate boiling of pure and quasi-azeotropic refrigerants from copper coated surfaces

• Experimental analysis of pool boiling on a horizontal copper coated tubes has been presented.
• Pure (R-134a and R-600a) and quasi-azeotropic (R-410A) refrigerants have been tested.
• The effect of saturation temperatures or pressures and heat flux on heat transfer coefficient are considered.
• Experimental results are compared with existing correlations and also developed a correlation for present data.

The present experimental study deals with boiling heat transfer enhancement over surfaces fabricated by gas flame spraying. The copper powder was used as a coating material applied to the outer surfaces of copper tubes of 25.4 mm diameter and an effective length of 116 mm. The surfaces having coating thickness of 42.2 µm and 95.4 µm were used. Pool boiling experiments for saturated refrigerants under pure fluid category R-134a and R-600a and, quasi-azeotropic mixture R-410A (mixture of R-32 and R-125) were carried out for heat fluxes ranging from 5 to 50 kWm−2 for their respective saturation pressure corresponding to temperature of 10 °C. A significant enhancement of boiling heat transfer coefficients due to coating were found for all three refrigerants. For R-600a, the nucleate boiling heat transfer coefficients were approximated 1.35–1.52 times and 1.09–1.2 times higher than those of R-134a and R-410A respectively. The experimental data for coated surfaces were correlated in terms of relevant parameters and also compared with the existing correlations in the literature.