Research On Heat And Mass Transfer Of Porous Media By Assisted Of Microwave Heating

Compared with the traditional heating type, microwave heating is volumetic heating which makes it has many advantage such as fast-heating, energy conservation. Therefore, microwave heating is widely used in chemical industry, materials processing, medical treatment, especially in food drying. However, non-uniformity of temperature in the heating process results in low quality and safety issues of products. These will limit the development of microwave heating technique.During microwave heating process, heat and mass transfer happened at the same time, temperature variation inside materials is complicated. Temperature distribution depends on uniformity of the, dielectric properties, shape and size of materials. Different shape of materials electromagnetic fields makes different electromagnetic distribution, so temperature distribution is different. All this will effect moisture content migrate from materials. Dielectric properties, temperature, moisture content, the penetration depth, electromagnetic fields, microwave power density, all these parameters interact and couple with each other, which makes drying process complexity. Thence, mechanism of microwave heating and heat and mass transfer become research points.This study use experiment method, select potato and white radish as materials, research the effect of shape and size of materials, cavity size, waveguide location, material species on temperature distribution. The results show:temperature distribution vary as different shape material, for cube the temperature is least uniformity and hot spot distributed along the edge and corners, for cylinder temperature is more uniformity; hot spot concentrate on center for small size and transfer to edge, hot spot appear on the edge for large size. Large cavity utilize the energy more efficient and temperature increase is more; temperature near the waveguide is higher than the symmetrical parts; material with high permittivity has lower temperature increase than low permittivity. This paper also discuss the effect of different volume and surface area on microwave power adsorption, which indicate that materials with large volume and surface area is more efficient for microwave energy absorbtion. Paper also research the drying curve of potato and white radish and get that drying rate of materials with high moisture content is faster.