Drying variables affecting drying rate and moisture content distribution in Western Hemlock

For a dry kiln to be operated in a highly productive manner it is important that the kiln operator understand the variables that can, and often do, impact drying quality. These may be kiln variables such as temperature and air velocity or they may be wood variables such as density and moisture content. To actually measure the effect of these variables would require many kiln runs. The use of a computer model which simulates kiln drying allows us to estimate these effects without actually measuring them experimentally. The purpose of this paper is to: 1) demonstrate how wood drying models can be used to benefit researchers and kiln operators, and 2) evaluate the relative effects of various wood and kiln parameters on the final outcome of the kiln schedule in an effort to understand the variability that results in kiln drying. The drying model used herein was developed within Weyerhaeuser under the direction of Kayihan. Details of the model are published elsewhere (2,3,4). Briefly, the simulation can be described as a stochastic model which employs population balances techniques. Written in Fortran, it is capable of running on IBM-PC compatibles in a matter of minutes, and provides an estimate of the drying rate curve as well as a final moisture content distribution. In order for the model to produce reasonably accurate results, it must first be "fitted" to a specific kiln and lumber type (size and species).