Microwave drying mechanism
    Indeed , water circulation intensity equations are so complicated. But it is a direct indication of how we evaluate various factors on the drying process , as well as provide an analysis of the role of power and an effective way to strengthen them . Help us into the right half of the drying process of internal heat and moisture transfer mechanism. Similarly, the microwave heating of the drying process dynamic analysis package can make use of these equations to obtain useful inspiration .
    ( A ) microwave drying mechanism
    Microwave heating body heat makes the presence of wet material , changing the conventional heating drying process some migration potential and migration potential gradient direction, forming a unique mechanism of microwave dry operation .
    As mentioned above , for liquid water wet material loss factor greater . To significantly absorb microwave energy and convert it to heat , therefore , the heating and evaporation of wet material in the wet material in the whole volume simultaneously. The material surface for the sake of evaporative cooling , while filling material surface temperature is lower than the inner layer temperature bribery , which is its - .
    Second , the result of drying the wet water transferred to its surface to the surrounding medium , the material quality of moisture migration. Conventional drying medium theory states that the inner material moisture migration to the second layer , and ultimately through the drying medium ( such as hot air ) with a drying device outside of the system , regardless of the dryer work is intermittent or continuous , the drying medium is required flow through the material surface , then paste the material will be formed at the surface of the interface layer . Movement in the interface layer working medium parameters and status of its state of motion , necessarily dry room away from the interface with the work of the media do not ask. For example , the more distant from the interface layer is a medium flow rate is large, and in the boundary layer near the surface , since the friction material and other reasons , the more close to the surface of the medium flow rate is smaller , the interface layer is generated in the the outer surface of the flow velocity gradient point , which depends on the size and shape of the surface layer , and the viscosity of air . Then dried in a convection state, the interface layer medium flow temperature below the temperature at different distances from the surface , causing different temperatures. This temperature gradient direction and the velocity gradient in the same direction , and its presence will draw additional resistance caused by heat and humidity . Therefore, the presence of the interface layer hinders dry, but just rely on convection heat medium from drying methods are not available for free .
    However, the microwave heating temperature is higher than at the beginning when there is no material drying medium , initial energy for heating and irresolute material does not rely on wet or dry medium to pass incidentally . Therefore , the temperature around the material , i.e. a space from the material surface temperature at each point not higher than the temperature of the surface structure material . If we consider the case against humidity and air flow , the material near the surface of space will be a temperature gradient exists . But exactly with the direction of the temperature gradient, convection drying medium temperature gradient universal opposite, that is pointed by the spatial surface .
    Material during microwave heating the temperature gradient , heat and vapor pressure are consistent with the direction of migration , which holds the microwave heating , determines the heating drying process, both the material surface interface layer , or do not exist within the material from moisture barrier materials towel off of Inso . Relatively dry in terms of dielectric heating method , which greatly improves the moisture migration during drying conditions . This is what we use to analyze thermodynamics of irreversible processes to strengthen the potential for energy migration occurs when the desired situation.
    Not only are things also mindful of the fact that , due to the penetration of the microwave microwave field inside the heated material families outset be quite severe , resulting in material vapor formation rate is likely to exceed its migration speed. Therefore, the total pressure gradient in the material . There is no doubt . The total pressure gradient but also to promote the material humidity . This phenomenon has also been confirmed by the practice , when the humidity thing pre- heated in the microwave division , this rapid migration to form the total pressure gradient force , so that the material accelerated outward diffusion of water within , so that part of the water is vaporized it has not yet had to be discharge of materials outside .
    This makes microwave heating and drying of the material aspects of the internal transmission of power than conventional drying medium enhances a dynamic factor . Performance at the macro level to speed up the drying rate . Thus apparently making the situation better than conventional microwave drying humidity and dry.
    Secondly , because of the pressure of this additional term migration force , from the inside out with the microwave drying characteristics , that the whole of the material , the material will be completed first inner dehydration dry operation . In such circumstances to conventional drying process of some inner dielectric heating water before drying to form the outer crust due to compaction and difficult to continue to evaporate dry materials to bring the gospel . They can be characterized by selective microwave heating in the microwave heating of water ejected from the inner layer of the material as a whole to achieve the ultimate purpose of drying the same . For example, most dry macaroni microwave drying should be adopted as part of a hollow macaroni , difficult to discharge moisture leaving the conventional dielectric drying method is not easy to dry. Others, such as cocoon dry coal has a similar situation.
    The structure is more fibrous tissue capillary material ( such as food and grains were used in this example ) , when it is rapidly vaporized moisture within the capillary at the appropriate conditions can be advantageous OBJECTS puffing effect . According to reports, at home and abroad with a microwave puffing on tobacco stems were successfully tested . However, excessive energy dissipation of the dry, high -density , friable media processing is disadvantageous because the viscous resistance of the material impede the migration of water to the surface . In extreme cases, the material inside the high pressure vaporization material sufficient to cause rupture. Interestingly, the adverse consequences , but was used for ore crushing operations. According to reports, the U.S. Bureau under the Ministry of the Interior Minerals rapid microwave heating ore to make use of thermal stress crushing principle , heating pyrite, the iron extracted string consists of less than 10 % to 99% , and 24% energy saving . Seems appropriate to control microwave heating power directly to affect the processing conditions and consequences , resulting in different applications.