Pool boiling of a dilute emulsion: Surfactant effect on heat transfer

Abstract

We report measurements of boiling heat transfer in a dilute emulsion in the presence of a surfactant on an upward facing flat surface. The emulsion comprises FC 72 droplets in water with Tween 20 as the surfactant at 0, 10, 60 and 100 ppm by volume. Boiling data for the emulsion without surfactant confirms previously observed trends, with an increase in heat transfer coefficient occurring near 80 °C. Boiling with the surfactant does not produce an enhancement of the heat transfer coefficient in both aqueous surfactant mixtures and emulsions with surfactant. Laser diffraction imaging shows that emulsions with different volume fractions of the disperse component have different particle size distributions from the same emulsification process. Mixtures with the surfactant tend to have a tighter particle size distribution with a mean diameter of 2 μm. The similarity of boiling behavior for mixtures of water with Tween 20 and the emulsion with surfactant suggests that the boiling behavior is characterized mostly by interface chemistry unique to the surfactant than to the effect of droplet size distribution.