NANO/MICRO SCALE DRYING MODEL BASED ON LIQUID-VAPOR PHASE CHANGE THEORY AND DEVELOPMENT OF NEW DRYING METHOD

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We present a novel drying method by using microwave. Microwave is irradiated in pulse or intermittently so as to keep the temperature of material at around room temperature in a reduced pressure system. Energy of microwave is supplied just for the latent heat for evaporation. Also, by introducing a small amount of external air into the system, water vapor can be effectively carried out of the drying system. The drying time was successfully shortened as compared with the warm-air drying and the drying at room-temperature results in good quality for dried materials. We also examined the internal resistance for water transport based on the porous media model. It is found that the internal channel for the water transportation can be kept during the microwave-vacuum drying and it results in the high permeability at the wide range of moisture content. In this study, molecular dynamics simulations have also been carried out to study the effect of the nanostructures on the wetting characteristics at the solid-liquid interface. The wettability of the solid-liquid interface is examined with evaluating the contact angles at the three-phase interface. A modified description of contact angle in consideration of molecules filling ratio among nanostructures was proposed. The simulations show that the evaporation rate of the ultra thin liquid film decreases when the film thickness is thinner than 4〜6 molecular layers. We have done the dropwise condensation tests to obtain reliable experimental data on the condensation coefficient of water. A high vacuum system was developed to eliminate the effect of non-condensable gases on liquid-vapor interface mass transfer. Also, a thin film thermometer made of copper and nickel was formed onto the surface of silicon wafer for a direct measurement of surface temperature. We got the values in the range of 0.5-0.6.