Influence mechanism of radio frequency heating on moisture transfer and drying stress in larch boxed-heart square timber

Radio frequency heating combined with convection (RF/C) drying of larch boxed-heart square timber and its influence on drying kinetics such as rate, moisture content distribution, and stresses was explored. Results revealed that RF heating increased the drying rate and in RF/C drying was twice as high as in conventional drying. Below fiber saturation point, RF heating reduced internal moisture gradients, especially around moisture content of 20%. The effect of RF heating on moisture transfer was strongly associated with moisture content. Specifically, above the fiber saturation point, RF heating played a minor role in moisture transfer however, it reached maximum around fiber saturation point and thereafter, it largely decreased with moisture content. RF heating relieved some drying stresses during RF/C drying and reduced residual stresses in the timber surface layers. Furthermore, it changed the original development pattern of drying stresses in conventional drying.