Boiling heat transfer enhancement by surfactant additives

Small amounts of certain surfactant additives in water have been found to drastically change the boiling phenomena and enhance the solution's nucleate boiling heat transfer coefficient significantly. Besides being a viable enhancement technique of boiling heat transfer, the use of surfactant additives in liquids is of interest from a fundamental scientific viewpoint as well. They can be employed to gain valuable information about the boiling behavior of mixtures and as model systems to investigate interfacial properties governing two-phase flow with phase change. Boiling with surfactant additives, is generally an exceedingly complex process, and it is influenced by a larger set of variables than the phase-change process of pure water. In addition to the wall heat flux (or wall superheat), heating surface geometry, and bulk concentration of additives, the boiling behavior is also dependent upon, among others, the role played by interfacial properties (surface tension and contact angle), nucleate process, the Marangoni effects, and foaming. It appears that boiling mechanism itself is influenced by the nature of additive and its chemistry in the solution. The importance of surfactant enhanced boiling is widely recognized by the heat transfer community and research has been carried out focused in particular on nucleate boiling heat transfer. More fundamental studies have been carried out in the past and are being undertaken at present. Not all the phenomena occurring, however, are fully understood due to the great complexity of the physics involved. This paper reviews some of the investigations on this topic covering the periods from 1939 to 2004 and attempts to show the evolution of how the practice of employing surfactant additives in liquids may develop and mature into an enhancement technique for boiling heat transfer.