Experimental Study of Onset of Nucleate Boiling from Submerged Ribbon Heaters of Varying Width

In a heat transfer system, the point of onset of nucleate boiling (ONB) is important as it distinguishes boiling regime from the natural convection regime. Its importance is similar to that of critical Reynolds number which demarcates laminar and turbulent flow in fluid dynamics (Frost and Dzakowic in Manual of boiling heat-transfer design correlations, 1969). This makes the study of ONB important in design and sizing of heat transfer surfaces to get the optimum performance. ONB prediction models available in the literature take into account the effects of subcooling, contact angle and wettability. However, the effect of heater size factors like the thickness and width of the heater on ONB is not considered, and such studies are scarce. The present study focuses on trying to unravel the dependence of ONB on the aforementioned parameters. Experimental investigation was undertaken to study the effect of different widths of stainless steel 316 strips on ONB during steady heating. It was found that the heat flux and wall superheat at ONB increase with decrease in width of the heater. A presence of sharp transition point was observed between 4 and 2 mm width which is under further investigation.