| OCR Text |
Show Critique on Heat and Vapor Transfer in Show E, LaChapelle The flow of heat through snow is a complex process. Snow, particularly at low densities, is a good thermal insulator*, Like other insulating materials, it transfers heat by a combination of molecular conduction through the solid framework, by conduction, diffusion and convection of the entrapped air, and by internal radiation exchange* Unlike other insulators, it also transfers heat by sublimation of the solids- in this case ice- and associated diffusion and convection of the vapor phase. The latent heat of sublimation of ice is high, 680 calories per gram at the freezing point; consequently water vapor can be an efficient means of heat transport within snow which introduces complicating factors in the bulk thermal conductivity,. Owing to this contribution of water vapor to heat flow, the bulk conductivity becomes dependent on absolute temperature as will be demonstrated below. Moreover, recrystallization of ice which has passed through the vapor stage rearranges the solid framework and effects a permanent time- dependent change of conductivity. In addition to thermal effects, this latter change also profoundly alters the mechanical properties of snow; the stabilizing and strengthening effects of destructive crystal metamorphism are reversed and the snow becomes mechanically weaker. Early workers [ Abels ( 1), Jansson ( 2) and Devaux ( 3) are frequently cited] obtained values for the bulk conductivity of snow, and related these simply to the snow density, Abels obtained the expression /\ « 0,0068 P2 where ^ = coefficient of thermal conductivity ( cal/ cm/° C/ sec) p = snow density ( g/ cm^) |
