Heat transfer enhancement of self-rewetting aqueous n-butanol solutions boiling in microchannels

Abstract

Boiling experiments of pure water, aqueous n-butanol solutions and pure butanol were conducted in arrays of parallel microchannels with a cross-section of 25 × 25 μm and 50 × 50 μm. The introduction of 2% and 6% n-butanol solutions into microchannels with the mass fluxes ranging from 83 kg/m2 s to 208 kg/m2 s demonstrated an enhanced heat transfer during boiling compared to pure water and pure butanol. Both concentrations of butanol lowered the maximum temperature measured during boiling in the microchannel test section for approximately 10 K and 30 K compared to pure water and pure butanol, respectively. High-speed visualization, measurements of the contact angles and analysis of the surface roughness indicated that enhanced heat transfer originates from the improved wettability of the butanol solutions during boiling in microchannels, which is directly related to the positive surface tension gradient and the Marangoni effect. The self-rewetting property of the butanol solutions stimulated the formation of a well pronounced annular flow, enhanced the heat transfer and substantially lowered the temperatures measured in the microchannels during boiling.