Non-Darcian Air Flow in Wood. Part 1. Specimen Length Effect

Abstract

The longitudinal superficial air permeability of red oak and red alder heartwood, and ponderosa pine and Douglas-fir sapwood at various specimen lengths, was measured with a specially designed apparatus. The results showed that non-Darcian behaviour due to specimen length existed in all tested wood species and types. Furthermore, there was a strong evidence of the existence of a certain specimen length above which permeability remained almost constant. These specimen lengths for the tested species were 140, 100, 60, and 40mm for red oak, red alder, ponderosa pine, and Douglas-fir. respectively. Within these specimen lengths for the respective tested species, permeability increased drastically with decreasing specimen lengths. Therefore, the specimen lengths of 140. 100, 60. and 40mm for red oak heartwood, red alder heartwood, ponderosa pine sapwood, and Douglas-fir sapwood, respectively, will be used for the evaluation of non-Darcian air flow due to other factors such as slip flow and nonlinear flow in a subsequent series of experimental tests.