A one-dimensional mathematical model is presented that accounts for a moving evaporation interface in simulating the coupled heat and mass transfer during convective drying of wood. In the model proposed, the only mechanism considered in water transport within wood is diffusion. Additionally, the transport of moisture is dominated by the gradient of the moisture content. The controlling equations were established from Whitaker's volume averaging laws and solved numerically with the finite volume method.The simulation results for the density of vapor and the volume rate of evaporation indicate that the migrating moisture was mainly in the form of gas under conditions of lower moisture content. The evaporation interface moved at approximately constant speed and the evaporation rate of the interface decreased with time. Finally, the core temperature and average moisture content in wood were successfully simulated. Downloaded by [University of Otago] at 06:05 21 July 2015 2

A 3D numerical solution of the heat conduction equation is proposed based on the finite volume method to describe the heating of wood, where the thermal conductivity (ThC) is variable, and the convective heat transfer coefficient is constant. ThC parameters were found through an optimization process based on genetic algorithms. The objective function between measured and simulated curves is determined, and parameters with greatest correspondence between measured and estimated values were obtained. As a result, a new equation for ThC is proposed, which depends on moisture and temperature. The proposed coefficient is validated by experiments, and a good agreement was found between experimental heating curves and those obtained by simulation by means of the new heat conduction equation.

The mass and heat transfer mechanisms during radio frequency/vacuum (RF/V) drying of square-edged timber were analyzed and discussed in detail. Based on the mass and heat transfer theory of porous materials, a one-dimensional mathematical model was developed from conservation equations. Compared with conventional models, it has the following advantages: (1) Each independent variable has a separate governing equation and is solved independently by converting the partial differential equation into a difference equation with the finite volume method; and (2) The calculated data from different parts of the wood specimen are displayed in the evolution curves because the specimen is divided into several units along fiber direction. Therefore, the change law of the parameters can be better described. The software Matlab, which has the advantages of fast calculation speed and high precision, was used for programming and calculations. In addition, the square-edged timber Sugi specimen was dried in a laboratory RF/V dryer, and the total average moisture content (MC) and local temperature were monitored as a function of time. By analyzing the calculated and experimental results, it can be concluded that most of the important phenomena observed during RF/V drying can be adequately described by this model.

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