Experimental study of nucleate boiling heat transfer of R-134a and R-600a on thermal spray coating surfaces

• Experimental analysis of pool boiling on a horizontal copper uncoated and coated tubes have been presented.
• Refrigerants R-134a and R-600a have been tested.
• Effect of coating parameters and heat flux on heat transfer coefficient are considered.
• Experimental results are compared with some empirical correlations and also developed a predicted correlation.

This paper presents the results of experimental investigations carried out with refrigerants R-134a and R-600a during pool boiling on horizontal coated tubes of outside diameter 25.4 mm at saturation temperature of 10 °C. The coated tubes were prepared by powder flame spraying technique. This technique using copper as a coating material was applied to the outside of the copper tube with an effective length of 116 mm. The experimental data were taken in the range of heat flux from 5000 to 50000 Wm−2 with an interval of 5000 Wm−2. The effect of coating parameters on heat transfer coefficients and boiling characteristics of both refrigerants were presented. Enhancement of heat transfer coefficients due to coating were found for both boiling refrigerants. The boiling heat transfer coefficient of copper coated tube was enhanced approximately 0.99–2.1 times that of uncoated tubes. The experimental heat transfer coefficients were also compared with the existing correlations and the results of other authors published data. Further, thermal performance of copper coated tubes were correlated in terms of coating parameters (thickness, pore size and porosity) to examine the consistency of experimental data conducted on coated tubes of different characteristics.