A laboratory study of weather effects on the drying rate of jack pine litter

Abstract

This paper describes the variation in the drying rate of jack pine (Pinusbanksiana Lamb.) litter with external conditions. Temperature, relative humidity (RH), and wind were varied separately. Drying runs were carried out in a cabinet with controlled temperature and humidity and also in the open laboratory. Most runs followed the exponential pattern, and the drying rates were measured in terms of the slope of the semilog graph of free moisture content versus time. The logarithm of this slope was found to be inversely proportional to the reciprocal of absolute temperature. The drying rate varied with 100 – RH at high RH but increased only slightly below 60% RH owing to the limiting effect of the wax and resin content on the rate of internal diffusion. Drying in wind proceeded in two stages, the first faster than the second. Wind was important at low speeds, and the drying rate increased but little above 2 km/h. These principles were used in the design of the drying equations of the Fine Fuel Moisture Code of the Canadian Forest Fire Weather Index.