Effects of air and water contents on the effective thermal conductivity of air-impregnated gels.

Abstract

The effective thermal conductivity of air-impregnated gels of various air and water contents was measured at 20°C by the steady heat flow method, and the applicability of the sphere dispersion heat conduction model (the Maxwell-Eucken model) was studied. The Maxwell-Eucken model gave a fairly good approximation for the effective thermal conductivity of air-impregnated gels of the lowest water content, but that of air-impregnated gels of higher water content was underestimated by the Maxwell-Eucken model. In addition to that, the effective thermal conductivity of the air-impregnated gels of the highest water content at 40°C exceeded the maximum limit expected by the parallel layers heat conduction model. These facts suggested the existence of some heat transfer mechanism other than heat conduction and the significant role of water in it. To explain the discrepancy in applicability of known heat conduction models, a model of heat transfer in air-impregnated gels, which includes heat transfer by water vapor, is presented and discussed.