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Material drying according to its thermal conductivity can be divided into two categories: one is relying on the surface of the material heat medium layer by layer into the material internal heating, called surface heat conduction heating method, namely the conventional drying method, the thermal medium can be hot air, steam, and far infrared radiation (heat source); Another kind of material, to rely on the microwave penetration and material interaction between polar molecules into heat energy, make the material in each part are obtained at the same instant heat and heat up, this material has the overall heating called microwave heating drying heat source heating conditions. The two heating mode and its heat transfer characteristics are very different. The study shows that the microwave electromagnetic field can produce the result of the interaction between material effect of two aspects: one for microwave energy into heat energy for heating material material heats up; Another for the bioactive component in with material (such as protein enzyme) or mixture (such as bacteria, mold, etc.) interact with each other, make their biological activity, be suppressed or incentives (depending on factors such as the frequency and intensity of microwave electromagnetic field, and the biological activity material inactivated threshold). The former is called the heating effect of microwave for material; The latter is called the nonthermal effect.
Peanut microwave frying machine, which is caused by the loss of electric field energy by the dielectric material itself, is completely different from other conventional heating methods. Traditional microwave frying machine is based on the principle of heat conduction, convection and radiation to transfer heat from the outside to the material. Heat is always transferred from the surface to the inside to heat the material. Thermal gradient inevitably exists in the material, so the material heated is not uniform, resulting in local overheating of the material. Microwave heating can raise the temperature of heated material by high frequency reciprocating motion of dipole molecule inside the heated body. Without any heat conduction process, it can make both inside and outside of the material heated at the same time. The heating speed is fast and uniform. The heating purpose can be achieved only by using a fraction or a dozen parts of the energy consumption of the traditional heating method. Theoretical analysis shows that the amount of heat generated by matter in microwave field is closely related to the type of matter and its dielectric properties, that is, microwave has selective heating characteristics for matter.
Characteristics:Penetrating heating with fast heating speed. The penetration distance is theoretically the same order of magnitude as the wavelength of electromagnetic wave. Microwave heating is to make the heated object itself become a heating object. It is called the whole heating mode. It does not need the process of heat conduction, so it can be heated in a short time. When heated by microwave, the parts of the object, regardless of their shape, can usually penetrate the electromagnetic wave evenly to generate heat, which greatly improves the inefficiency of medium material heating. Heating uniformly. When heated by microwave, all parts of an object, regardless of their shape, can usually penetrate microwave uniformly to generate heat. Therefore, the uniformity is greatly improved. It can avoid the phenomena of endogenous coke, dry coke and wet coke, and improve the quality of food products, which is conducive to the formation of the quality of food materials. Low temperature and short time sterilization. Microwave heating sterilization is a combination of thermal effect and non-thermal effect (biological effect). Compared with conventional thermal sterilization, microwave heating sterilization has the characteristics of low temperature and short time sterilization. Not only is it safe and safe, but also it can keep the nutritional components of food from being lost and destroyed. It is beneficial to maintain the original quality of the product, and less loss of color, aroma, taste and nutrients. It is also very beneficial to the maintenance of vitamin C and amino acids. Experiments show that the nutrient contents of chlorophyll and vitamin are only 3% in dried fresh vegetables, 17% in shade, 40% in hot air drying, 60%-90% in microwave drying and 97% in microwave sublimation drying.
Microwave heating technology is fast, nutritious and flavor-preserving, uniform, disinfection and sterilization, energy-saving, hygienic and safe.Non-pollution, high efficiency, convenience, controllability, small investment, conducive to improving product quality, prolonging shelf life, improving labor conditions, and realizing production automation, is an advanced technology worthy of promotion.
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