An analysis of self-cooling with infiltrated porous composites including the effect of the melt layer

Abstract

A detailed analytical model was developed to include the effect of the melting process on a porous composite which retards its own heating rate by sacrificing its infiltrant. A transient one-dimensional heat-transfer analysis was conducted considering both the heats absorbed by melting and vaporization of the infiltrant from within the matrix. A finite-thickness liquid layer was seen to exist above the composite surface as a result of the flow of liquid coolant onto the surface induced by the expansion of the coolant on melting. There existed a period of time during which the melt layer was subject to both depletion due to vaporization and renewal by the flow of liquid coolant onto the surface. As the heating process continued the melt layer was depleted and the liquid coolant vaporized from within the tungsten matrix. The analysis was solved by finite-difference techniques and programmed for the IBM 7040/1401 Digital Computing System. An extensive search was conducted to determine the dependence of temperature on the thermophysical properties of seven different metallic coolants. Data were obtained for the various infiltrants up to that time at which the melt layer vaporizes completely from above the composite surface. A fundamental understanding of the effects of the melting process and of assuming variable properties on the early stages of the self-cooling process was obtained.