Power microwave equipment for drying effect
Usually early in the dry , high moisture content in the material , the microwave power on the drying effect of higher, continuous microwave heating can be used , then most of the microwaves can be absorbed by water migration and rapid evaporation of moisture ; dried at constant velocity and deceleration period, with the reduction of water , require less microwave energy , microwave heating can be between pulses .
Industrial production , there are many items can not be dried at high temperature processing , vacuum drying , a basic principle is based on : saturated water vapor pressure and temperature are closely related , in a vacuum state, the lower the boiling point of water , i.e. is operated under vacuum at low temperature , high temperatures can be avoided in the destruction of vitamins and other nutrients , while increasing the drying rate . Microwave equipment in addition to the vacuum system , the content per unit volume lower than the atmospheric air in an amount of oxygen in the environment for a relatively food drying can reduce or even avoid the oxidation of fat in foods opportunity to browning or other oxidative deterioration of pigments etc. Therefore, the vacuum -dried to obtain a better quality of the food .
Conventional heating methods such as steam , hot air , electric heating , etc. is the use of heat conduction , convection, radiation principle of the heat transfer within the material from the outside , from outside to inside take some time , the worse the thermal conductivity of the material the more time is required long, slow and uneven heating of the heating energy consumption is high.
Microwave drying principle is: the microwave generator microwave radiation to the dry material on the inside of the microwave injection materials , through the water and other polar molecules with microwave frequency for synchronous rotation, such as dried vegetable products using 915MHz microwave , then vegetables such as water molecules within the polar rotation 915 million times per second , water and other polar molecules as a result of such high-speed rotation of the instantaneous friction heat the material , causing the material surface and the internal temperature at the same time , a large number of water molecules escape from the material , to effect drying stacked together when they are not as many small particles , but a whole , requires special attention temperature difference between the inner and outer material layer . Generally when the material in the form of large , the need to slow down drying period the material near , the lower microwave power , thus effectively reducing the internal and external temperature , the disadvantage is to extend the drying time .
There are microwave equipment microwave selective heating of the material properties. Water is a polar molecule is very strong material , are more susceptible to microwave and heat , so the higher the moisture content of the material , the more easily absorbed microwave , heating it faster ; when the moisture content is reduced , its ability to absorb microwaves reduced accordingly .