Significance of surface modification on nucleate pool boiling heat transfer characteristics of refrigerant R-141b

Abstract

Experimental investigations were conducted to study the significance of surface modification on the heat transport phenomena under nucleate pool boiling configuration of saturated R-141b at ambient condition over SiO2 thin film (TF) nanocoated surfaces. The experiments were conducted within the heat flux variation of 50 to 185 kW/m2 at an interval of 15 kW/m2. The diameter of the heating surface was 9 mm, and the thickness was 3 mm. Five Cu heating surfaces of circular shape having zero (Emery polished surface (S1)), 125 (S2), 250 (S3), 375 (S4), and 500 (S5) nm coating thicknesses were fabricated employing the Sol-Gel approach accompanied by spin coater and characterized by surface profilometer and field emission scanning electron microscopy (FE-SEM). The current experimental results were verified with the existing correlations proposed in the literature. It was found that the heat transfer coefficient increased with an increase in the heat flux, and it is also witnessed here that modification in the surface significantly contribute towards the improvement in the heat transfer coefficient. The maximum and the minimum heat transfer were revealed at 375 (S4) and 500 (S5) nm coating thickness, respectively. Modification of the surface leads to an increase in the heat transfer coefficient due to the existence of a large number of dynamic nucleation sites. Finally, a mathematical model to predict the optimum nucleate pool boiling heat transfer coefficients for different coating thicknesses was proposed which reflects the effects of surface thickness, coating thickness, and the imposed heat flux. The model predicts good agreement with the experiment of R-141b and other existing findings within an accuracy of ±5%.