Corrections for capillaries used in permeability measurements of wood

Summary Owing principally to kinetic energy losses, flow in which the flow rate is not linearly proportional to the applied pressure difference occurs to a considerable extent when the Reynolds number exeeds the length-to radius ratio of the capillary. When capillaries are used for flow or viscosity measurements corrections must be made for kinetic energy losses, end-effects and gas expansion. The results obtained for air flow through straight circular capillaries imply that non-linear flow may occur in wood and other heterogeneous porous media at Reynolds numbers in the region of 0.1 to 10.This work was carried out at the University of Aberdeen while J. F. Siau was on sabbatical leave and was partially supported by the NATO Senior Scientists Programme. The authors thank Professor J. D. Matthews for providing facilities for this work.