Radio frequency vacuum drying of wood. I. Mathematical model

A one-dimensional mathematical model to describe the transport phenomena du ring continuous radio frequency/vacuum (RF/V) drying of thick lumber was de veloped from general conservation equations. When drying at temperatures ne ar the boiling point, as in RF/V drying, the effect of the gas phase pressu re gradient on moisture transfer within the solid can be very important. Th e controlling resistances and transport mechanisms are discussed in detail. In addition, capillary transport in RF/V drying is discussed and its effec t is compared with convective drying. The model provides a relatively fast and efficient way to simulate vacuum drying behavior assisted by dielectric heating. As an example, the governing heat and mass transfer equations, in cluding consideration of internal heat generation and the effect of gas pha se pressure gradient, are derived and solved in a one-dimensional system us ing a finite volume method. The effect of changes of the most important par ameters on the predictions of the model is also presented.