Micro Wave-Vacuum Drying Technology And The Numerical Simulation Research Of Potatoes

This thesis studied the drying characteristics and significant degree of the influencing factors under the condition of microwave-vacuum in the name of potatoes slice sheet material, the method of multivariate nonlinear regression analysis which belongs to mathematical statistics was used to establish the regression model of energy consumption and recovery ratio of water, then compared the microwave with the hot air-microwave drying method about their energy consumption and the sensory quality that the indicators of their state. Secondly, it has established the heat and mass transfer model of moisture content and temperature variation in drying process, by a good solving of the heat transfer model, it preferably explained the problem which is represented by center coking and overall aging degradation. The main research content is as follows:1. The research significance of the topic is proposed, then this thesis has given a brief analysis of the technology principle and characteristics of microwave-vacuum drying technology, finally it summarize the research methods and status of microwave-vacuum drying technology from the following three angels:theoretical research, applied research and development trendency.2. Respectively, it has researched the drying characteristics of potato slices, then established a dynamics drying model that brought in the interaction of the arbitrary two factors as following:unit mass transmission power, layer thickness and vacuum degree, it can accurately describe the potatoes water loss rate, by the comparison of experimental results and the model calculation results, it showed that the model can reflect the filtration characteristics of potatoes.3.By carrying out the quadratic orthogonal rotation combination test, it established the nonlinear regression model of potato’s drying index under the condition of microwave-vacuum, the significance test of regression model showed that the models were relativly resonable. Weighted average method is adopted to establish the comprehensive index evaluation function, then the object function was optimized by using matlab platform:when the unit mass transmission power(Xl) is 1.3182W/g;layer thickness(X2) is 2.6364mm and the vacuum degree (X3) is-64.875 lKPa,each indexes can achieve good level.4.By adopting the method of orthogonal experiment,it has studied the various factors’significance to dry index. Comparison of the different drying method shows that: ①in terms of energy consumption, energy of hot-air drying is the maximum,8775 KJ, that is two times of microwave-vacuum and microwave vacuum -hot air drying consumption of microwave drying was only about 10% of its energy consumption;② the microwave vacuum drying has a excellent appearance and high quality of flavor, a good puffing effect and organization crisp, its water capacity was close to 200%, that was 1.44 times of air-drying.③ improving the microwave power does not necessarily make water effective diffusion coefficient to increase, water effective diffusion coefficient was not correspondence with the increasing of vacuum degree;④ 50% was the best moisture content transfer-point of hot air - microwave drying.5.By the improving of traditional heat and mass transfer model under microwave drying condition, it obtained a improved heat and transfer model which can describe the moisture content and dynamic surface temperature of potatoes slice’s different position, by analyzing the result of the model, it explained the reason of degradation of potatoes which expanded outward from the core and overall aging degradation, then it put forward the principle of choosing a right drying factor levels and a feasible scheme:the heating time of speed up drying stage was 18 minutes, then tempering time was 3 minutes; the heating time of constant rate drying period was 20 minutes, the second tempering time was also 3 minutes; finally, heating for 5 minutes to the bitter end in falling-rate drying period.