Investigation of the effects of surfactant concentration on the boiling curve of water

Abstract

Boiling is a widely used heat transfer process in industry that allows for high heat transfer with a small temperature gradient. In this study the effects of two homologous series of surfactants (trimethylammonium bromide (TAB) and methylglucamine (MEGA)) on the boiling curve of water were explored. Heat transfer vs. temperature plots were obtained for five surfactants for various concentrations under the cricical micelle concentration (CMC). Plots of temperature vs concentration for specific heat fluxes showed the lowering of the superheat that improves heat transfer when surfactants were added, resulting in an overall left shift of the boiling curve. The shifting that occurs at low concentrations of surfactant seem correlated with the diffusion coefficients of the different surfactants. The large shifting that occurs at larger concentrations is correlated with the hydrophobic tail length of each of the surfactants. This supports the hypothesis that the lowering of the dynamic surface tension, which correlates with the diffusion coefficient, is responsible for part of the lowering of the superheat. The fact that the larger shifting is correlated with the hydrophobic tail length supports the hypothesis that part of the shifting occurs due to the surfactants adsorbing onto the surface, making it more hydrophobic, increasing the contact angle, and decreasing the nucleation energy. The results of this work add to the understanding of the effects surfactants have on the boiling of water and give engineers more tools to adjust heat.