The transportation characteristics of porous media at high temperature

As a functional material of the enhanced cooling, porous matrix has been widely used in the environments concerned with very high temperature. Through the pores of the porous matrix, the flowing coolant absorbs and takes away the heat inside the matrix to achieve the thermal protection of high temperature structures. In the past investigations on the permeability of porous materials, experiments and measurements were almost conducted at ambient temperature. Therefore it is necessary to discuss the effect of the temperature on the transportation properties of the fluid within the porous matrix. In this paper, a modification of the permeability equation of porous materials is presented, so that it can be applied under the circumstance with a large temperature range or a great temperature gradient. In the modified equation, three effects of temperature on the permeability are considered: 1) the natural and forced convection within the porous matrix; 2) the characteristic variations of the fluid coolant; 3) the parameters of the porous matrix. Using our experimental data, the relationship between environmental conditions and performances of the fluid coolant is validated. Through the discussions, the interaction of porous matrix, environmental conditions and fluid performances in a high temperature range is estimated.