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

提出了一种新的微波干燥方法。在减压系统中，微波以脉冲或间歇方式照射，使物料的温度保持在室温左右。微波能量仅供蒸发潜热使用。此外，通过将少量外部空气引入系统，可以有效地将水蒸气带出干燥系统。与暖风干燥相比，缩短了干燥时间，在室温下干燥，干燥后的物料质量较好。我们还研究了基于多孔介质模型的水输运内阻。结果表明，在微波真空干燥过程中，可以保持内部的水分输送通道，从而在较宽的含水率范围内保持较高的透气性。在本研究中，还进行了分子动力学模拟，研究纳米结构对固液界面润湿特性的影响。通过评价三相界面的接触角来考察固液界面的润湿性。提出了一种考虑分子间填充比的纳米结构接触角的改进描述方法。模拟结果表明，当薄膜厚度小于4 ~ 6分子层时，超薄液膜的蒸发速率降低。我们进行了水滴凝结试验，得到了可靠的水的凝结系数的实验数据。为了消除不可冷凝气体对液-汽界面传质的影响，研制了一种高真空系统。同时，在硅片表面形成由铜和镍制成的薄膜温度计，直接测量表面温度。我们得到的值在0.5-0.6之间。

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.