A 2-D MICROSCOPIC SIMULATION OF HEAT AND MASS-TRANSPORT IN DRY SNOW

The problem of acid deposition and its effects on the environment is receiving increasing attention in North America and Europe. The interaction between seasonal snowcovers and deposited pollutants is of particular importance because a snowpack accumulates and stores pollutants which can ultimately be released in a rapid pulse with the first melt water in the springtime. As a direct result of an impurity pulse, water quality degrades with deleterious effects on the local environment and aquatic biological species. The timing and severity of an inpurity pulse is dependent upon the redistribution of pollutants in a snowpack which is attributed to a process known as temperature gradient metamorphism. This work investigates the influence of geometry, density and temperature on the coupled heat and mass transport in idealized, two dimensional ice lattice cells. Mass flux, concentration and temperature distributions, as well as effective diffusion coefficients and thermal conductivities are presented as functions of temperature, geometry, and density, A finite element model of the coupled, heat and mass transport is used to analyze the problem on a microscopic scale in two dimensions. Deforming meshes are used to simulate the growth/decay process which occurs over time in an ice lattice pore. The results of the analysis provide a microscale view of temperature gradient metamorphism which did not previously exist. The preferential growth of branch grains is verified using both static and dynamic compuier generated images of the ice lattices undergoing temperature gradient metamorphism. It is found that the specific ice crystal geometry is determined by the thermodynamics at the solid/vapor interface. An enhancement in the effective diffusion coefficients relative to the diffusion coefficient for water vapor in dry air is observed for all the two dimensional geometries studied. A communication length on the scale of several pore lengths is found for the vapor transport through the ice lattices, and it is demonstrated that the heat and mass transfer rates are highly dependent upon the local ice lattice tieometrv and the snow density. © 1990, Taylor & Francis Group, LLC. All rights reserved.