Comparison of pool boiling heat transfer performance between aqueous cationic and anionic surfactant solutions with similar ionic group

Abstract

Pool boiling in aqueous surfactant solution is found to have a better heat transfer performance than that in distilled water. The present study intends to investigate the effect of functional ionic group in cationic or anionic surfactant on pool boiling performance. Two pairs of surfactants, namely, cationic surfactants of Dodecyltrimethylammonium bromide (DTAB) / Dodecyltrimethylammonium chloride (DTAC) and anionic surfactants of Sodium dodecyl sulfonate (SD-Sulfonate) / Sodium dodecyl sulfate (SD-Sulfate), are added into distilled water with a mass concentration of 100–3200 ppm. Boiling performance and thermophysical properties of the corresponded surfactant solutions are measured and compared with water. The bubble behaviour and surface wettability are also analyzed. Results indicate that the surfactant solutions can generally increase the heat transfer coefficient (HTC) compared with water and a higher concentration solution usually owns a greater HTC. The maximum relative HTC enhancement can reach up to 2.33 times. The reduction in surface tension and an additional repulsion force due to the addition of surfactant result in a denser nucleate site, a smaller bubble departure diameter and a faster bubble departure frequency, which results in a higher HTC. The surface tension reduction caused by surfactant addition and the boiling process make the copper surface more wettable, resulting in a higher critical heat flux (CHF). However, the surfactant also makes the fresh water supply difficult at a high heat flux and subsequently results in a lower CHF. The CHF is comprehensively affected by the surface wettability of boiling surface and surfactant concentration and their relative strength determines the final magnitude of CHF. The surfactants with a same or similar functional ionic group have similar boiling heat transfer performance in aqueous solutions. The present study can provide meaningful guidance for further pool boiling studies and relevant highly efficient heat exchanger design.