An analysis of the drying process in forest fuel material

Abstract

It is assumed that the flow of moisture in forest fuels and other woody materials is determined by the gradient of a quantity g which is a function of some property, or properties, of the moisture content. There appears to be no preferred choice for this function, hence moisture transfer equations can be based on a number of equally valid definitions of g. The physical meaning and dimensions of the mass conductivity kg will depend on the definition of g but the mass diffusivity α is independent of g. Simplified solutions to the transfer equations are expressed in terms of the ratio t/τ. The timelag τ is a measure of the drying rate. It scales as the second power of the appropriate dimension of the specimen, such as the half thickness, when the Biot number is large but scales as the first power of the characterizing dimension when the Biot number is small. Analytic solutions are not possible when properties are variable but the scaling relationships remain unchanged. The basic theory of the drying process throws considerable light on the complex interacting effects of air movement, radiation, and evaporationcooling on the drying rates of forest fuel material.

Citation

Byram, G.M.; Nelson, R.M. 2015. An analysis of the drying process in forest fuel material. e-Gen. Tech. Rep. SRS-200. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 45 p.