Preliminary Investigation of Boiling and Transpiration of Water in a Porous Media Cooled With an Air Flow

This paper describes a study focused on heat and mass transfer through various porous media involving both boiling and transpiration. Heat was supplied to a porous structure immersed in water. Water was boiled at the base of the porous material and in some cases advected from the porous structure by air blown over its surface. The porous media was expected to provide higher heat fluxes than those attained during pool boiling by providing additional surface area and by increasing the number of nucleation sites. The behavior was studied from just below the boiling point and into the nucleate boiling regime. The experimental apparatus consisted of a 2.5 cm square jet impinging onto a 2.5 cm square porous sample. A total of four copper foam samples and one carbon graphite foam sample were tested. The foam sample was placed in contact with a 2.5 cm square heated surface. Water was supplied through the sides of the porous sample and was able to leave the system as a vapor through the top surface of the sample, where it was advected away. It was determined that the presence of an impinging jet had no noticeable effect on heat flux. Up to 60% enhancement in heat flux was observed, compared to boiling of the plain surface. Contact resistance was significant and mitigated the affects of sample thermal conductivity.