Boiling heat transfer enhancement with surfactant on the tip of a submerged hypodermic needle as nucleation site

Abstract

The addition of small concentration surfactant additive in pure water decreases the surface tension of aqueous solution considerably, and, critical micelle concentration (cmc) decides the limit of reduction in surface tension with increasing additive concentration. The objective of the present investigation is to study bubble growth in aqueous 2-Ethyl-1-Hexanol solution, and compare it with pure water experimentally. The bubble growth was studied at 880pmm concentration of 2-Ethyl-1-Hexanol which is critical micelle concentration (cmc). A single bubble was generated using the right angle tip of a hypodermic needle as a nucleation site. Bubble growth was studied using high speed camera operating at 1000 frames per second. The investigation was conducted at two values of heat fluxes to check the effect of heat flux on bubble growth. At low heat flux (q=20kW/m2), the bubble departure diameter was found to be almost equal for both water and aqueous surfactant solution. At high heat flux (q=100kW/m2), bubble departure diameter increases in water, but, decreases significantly in aqueous surfactant solution. The bubble release frequency was nearly equivalent for both solutions at low heat flux, but, increases for aq. surfactant solution at high heat flux, which indicates augmentation in boiling heat transfer.