External heat and mass transfer coefficients for kiln drying of timber

Correlations are derived relating the heat-transfer coefficient to the mass-transfer coefficient in kiln drying of timber boards by using the Chilton-Colburn analogy. Existing experimental data for the mass-transfer coefficient of naphthalene vapour in the airstream at low temperature are converted to coefficients under commercial timber drying conditions. The calculated results from this analysis are compared with the values employed by wood drying modellers in their models and it appears that the external transfer coefficients used by the drying modellers are generally below the values calculated from the laboratory data.