NUMERICAL INVESTIGATION OF NUCLEATE BOILING HEAT TRANSFER ON THIN SUBSTRATES UNDER THE INFLUENCE OF SURFACE ROUGHNESS

The effect of surface roughness on nucleate boiling heat transfer is analytically explored over a wide range of roughness values in water and Flourinent FC - 77 ,two fluids with different thermal poperties and wetting characteristics.The test surfaces ranged from a polished surface of 0.045μm to 10.5μm.Different trends were observed in the heat transfer coefficient ,percentage of vapour and Vapour generated time with respect to surface roughness between the two fluids on the same set of surfaces.For FC - 77,the percentage of vapour developed was increased continually with increasing roughness.For water,on the other hand,surfaces of intermediate roughness and maximum roughness displayed similar values of percentage of vapour.While the roughest surface showed maxim um percentage of vapour.The heat transfer coefficients and percentage of vapour developed were more strongly influenced by Fc - 77than with water.At a very least vapour generated time of 0.4sec Fc - 77 developed maximum percentage of vapour than with water