Research On The Process Of Heat And Mass Transfer Of The White Mushroom Microwave Freeze Drying

White mushroom(Agaricus bisporus) is a kind of food which has the function of health care and nutritious. Its nutrition is rich and unique, and also has the functions of detoxification eliminate heat, anti-inflammatory lungs etc. But because of its high moisture content, delicate texture, it’s not resistant to storage, so the drying method is usually adopted for preservation. At present, there are various drying methods: the natural drying, hot air drying, freeze drying etc. The first method is easy to cause gill black, and its quality is unstable, so it’s not suitable for mass production. Compared with freeze-drying, product appearance of hot-air drying is serious shrinkage, recovery rate is low, and the loss of nutrients is large. The product of freeze-drying remained the original product shape and color, but also good rehydration, and the protein and vitamin C were higher than those of hot-air dried product. But the freeze-drying is time-consuming, and energy consumption is too high which resulting in high cost of freeze-drying.Microwave freeze-drying(MFD) can make up for the above shortcomings, because the microwave energy can penetrate into the internal medium in the form of electromagnetic wave. With the temperature increasing, the ice sublimate quickly. To a certain extent, it can improve drying rate and shorten the drying time. MFD is a rapid dehydration technique that can be applied to certain foods, particularly to sea foods, and fruits and vegetables. MFD involves much less drying time and energy consumption than conventional freeze-drying methods, and also improves product quality. But the heat and mass transfer mechanism of MFD process has always been restricting the development of the technology, as well as the technique haven’t used in actual production.In this paper, the following three aspects are mainly studied in view of the above problems:(1) we are considering the dielectric properties of microwave materials factors based on drying model and the control equations established by the previous, using the Matlab for numerical simulation, further study on the mechanism of heat and mass transfer and the effects of different parameters on the drying process of law;(2) the determination of the dielectric properties of white mushrooms: the dielectric constant ε′ and dielectric loss factor ε′′, instruments used is the network analyzer.(3) the verification test of the white mushroom analysis the effect of drying pressure, material thickness and other factors on the drying rate and the change of the material temperature. Numerical simulation and verification test are compared to get the conclusion.The main conclusions:(1) the determination of white mushroom dielectric properties: we obtain the dielectric constant and the dielectric loss factors were regression equation of temperature, moisture content. And the dielectric loss factor regression equation is: y=62.4943365-124.61825910x1+0.28264244820x2-0.15420650792x1x2+89.72199675x12, the equation is highly significant.(2) In the MFD verification test of the white mushroom, we obtain the effect of white mushroom thickness, pressure of drying on drying rate, also get the temperature change law of white mushroom. White mushroom reasonable parameters of microwave freeze drying: initial pressure 120 Pa, analytic drying stage pressure for 100 Pa, the material thickness is 10 mm, the drying time is about 11 h, to give a moisture content of 7% of the products.(3) MFD compared with the verification test, it gets better effect in terms of heat and mass tranfer.