An Experimental Investigation of Pool Boiling Heat Transfer from Cylindrical Surfaces

Abstract

The objective of the present work is to carry out experimental study on pool boiling heat transfer over micro-finned cylindrical surfaces with R 141b and R 123 at different pressure. The experiments have been conducted for heat flux ranging from 10 to 100 kW/m2 on a copper tube of outside diameter 20 mm and effective heating surface length of 44 mm. In the present work, results of the pool boiling heat transfer enhancement on three micro-finned cylindrical surfaces with different geometries are compared with plain surface at atmospheric pressure on a prevalidated test setup. It is found that surface with lower fin depth, fin spacing and fin pitch results into the better performance. It is found that BHTC increases in the range of 20 % to 318 % with a micro-finned surface over a plain surface with R 141b at atmospheric pressure. Moreover, it is observed that BHTC enhancement decreases with increase in heat flux. Also, experiments have been conducted on one of the micro-finned surface with R141b and R123 at different pressure to know the effect of pressure on pool boiling heat transfer coefficient. Results indicates that BHTC increases with increase in pressure irrespective of the fluid. BHTC is higher for R123 compared to R141b at atmospheric pressure however, its value decreases with increase in pressure. The value of bubble departure diameter decreases with increase in pressure due to decrease in surface tension of fluids. The experimental values of bubble departure diameter are compared with existing correlations and newly developed analytical model. Distribution of bubble departure diameters is similar to normal distribution curve. A new correlation to determine BHTC over a micro-finned surfaces is developed. The effect of geometrical parameters, operating pressure and thermo-physical properties of fluids are taken into consideration. The standard error of the fitted data is 0.0461.The average absolute error of the whole data is obtained as 2.56 %. All the predicted values fall within ± 10 % of the measured values of the BHTC.