Simultaneous Heat and Moisture Diffusion During Microwave Heating of Moist Wood英文电子书.pdf

SIMULTANEOUS HEAT AND MOISTURE DIFFUSION DURING MICROWAVE HEATING OF MOIST WOOD G. Brodie ABSTRACT. The influence of simultaneous heat and moisture diffusion on moisture movement in porous materials, such as cotton, has been known since the late 1940s. Until now this theory has not been applied to the problem of microwave heating in moist materials. Derivation of the partial differential equation, which describes simultaneous heat and moisture diffusion under the influence of microwave heating, yields two independent values for the combined heat and moisture diffusion coefficient. The slower diffusion coefficient of this coupled system is always less than either of the isothermal diffusion constant for moisture or the constant vapor concentration coefficient for heat diffusion. The faster diffusion coefficient is always many times greater than either of the independent diffusion constants. Based on the earlier work with moisture movement in cotton, it was anticipated that the combined diffusion coefficient for heat and moisture during microwave heating should be approximately 7.8 times greater than the constant vapor concentration coefficient for heat diffusion for wood. An analytical solution to the derived partial differential equation was used to model the temperature distribution inside wood heated by 2.45-GHz microwaves in a wave-guide applicator. Using the default constant vapor concentration coefficient for heat diffusion in moist wood did not model the temperatures inside the wood very well; however when this value was multiplied by a factor of 7.8 there was very good agreement between theoretical and measured temperatures. Keywords. Microwave, Microwave radiation, Modeling, Lumber, Wood. ndustrial microwave heating has been used