The effect of radiation on film-boilng heat transfer

An analysis has been performed to determine the extent to which film-boiling heat transfer is affected by thermal radiation. Consideration is given both to the direct radiation between the heated surface and the liquid and to the emission and absorption of radiation in the vapor layer which lies between the surface and the liquid. It is found that the direct surface-to-liquid radiation can appreciably increase the film-boiling heat transfer. A quantitative criterion is deduced which states the conditions under which the effects of surface-to-liquid radiation are significant. The analysis which includes the radiatively-participating vapor involves some uncertainty in that only incomplete information is available on the radiation properties of vapors. In particular, even for steam, the vapor emissivity is not known with any certainty at pressures above 1 atm. The results of the analysis indicate that the effects of a radiatively-participating vapor on heat transfer are negligible within the parameter range investigated.