On the mechanism of boiling heat transfer enhancement by surfactant addition

Abstract

In our previous study, bubble jet and bubble explosion around a heated wire were discovered in aqueous cetyltrimethyl ammonium chloride (CTAC) solutions (Wang et al., 2016), in which the bubble explosion process was explained. The bubble explosion phenomenon was proven to be a failed coalescence of unstable bubbles which caused local disturbance and enhanced boiling heat transfer. In this paper, comparative experiments of boiling around a heated wire for different types of surfactant solutions, ethanol and silicone oil were carried out in order to explore the mechanism of surfactant addition enhancing boiling heat transfer. All these fluids had lower surface tensions than that of water. Cationic surfactant of CTAC, anionic surfactant of sodium dodecylbenzenesulfonate (SDBS) and nonionic surfactant of alkyl polyglycoside (APG) were used. Bubble jet and bubble explosion phenomenon were found in all three kinds of surfactant solutions, exhibiting excellent heat transfer effect. For the pool boiling in ethanol, only bubble jet around the heated wire was found, showing better heat transfer efficiency than water. However, weaker boiling heat transfer occurred in silicone oil without bubble jet and bubble explosion. Due to the heat sensitivity characteristics, APG solution had a lower critical heat flux (CHF) than water, while CTAC and SDBS solution had higher CHF. With all phenomena and heat transfer performances, the mechanism of boiling heat transfer enhancement by surfactant addition was confirmed, i.e., the bubble jet and bubble explosion process enhanced the boiling heat transfer in surfactant solution rather than low surface tension.