Mass transfer behavior at bubble surface during nucleate boiling

Interfacial mass transfer mechanisms played an essential role to the high heat transfer efficiency noted for nucleate boiling. There existed a zone around the bubble surface that exhibited zero net mass flux, termed herein as the "zero-flux zone". This work investigated analytically the interfacial vaporization and condensation processes around a boiling bubble, based on which the positional dependence of zero-flux zone was derived. For a stationary bubble the zero-flux zone shifted to the upper hemisphere with decreasing wall superheat and/or with increasing contact angle. Moreover, the bubble growth (shrinkage) largely enhanced (retarded) such a trend. At the extreme condition where the bubble grew at a very fast speed the entire bubble surface would be subject to liquid evaporation only. Experiments observed a "thermal jet" emerging from the bubble cap, which was attributed to the interfacial vapor condensation flux at the bubble cap.