Heat And Mass Transfer Analysis Of Broad Bean During Freezing And Drying

In this paper,the development and status quo of seed drying were analyzed,and the value of broad bean was briefly introduced,which revealed the important significance of dry storage of broad bean.Then the research history of freeze-drying is described,and the basic principles and application rules of freeze-drying are analyzed.On this basis,the application of porous media theory in food drying process is summarized.The researchers used a variety of models to simulate the freeze-drying process,and gradually improved the simulation accuracy of freeze-drying,but did not define the thermal properties of the simulation process.Therefore,the text directly applied the variation of thermal properties of broad bean seeds with temperature to the simulation process of freezing and drying,and optimized the simulation precision of the freeze-drying process of broad bean.In this paper,the experimental scheme and principle of thermophysical parameters and basic characteristic parameters of broad bean were introduced,and the variation of thermal property parameters of broad bean seeds with temperature was obtained.The results showed that the thermal conductivity of broad bean showed a trend of decreasing first and then increasing with the decrease of temperature;the crystallization point temperature of broad bean fluctuated when the cooling rate was lower than 20 ? /min,but overall,the crystallization point temperature The rate of cooling decreases and decreases.Among the different cooling rates,the specific heat capacity has the same trend with temperature,but there is a strong change during the frozen phase transition.Experimental study on thermophysical properties of broad bean in the freezing process provided experimental data support for heat and mass transfer analysis of lyophilized seeds.The temperature change of the broad bean freezing process was dynamically monitored by the data acquisition instrument to obtain the curve of the temperature of the broad bean with the freezing time.During the freezing process,the temperature change of the broad bean was basically divided into three stages: the initial cooling stage,the freezing stable stage,and the rapid cooling.stage.The two-dimensional finite element model of broad bean.was established by COMSOL Multiphysics software to simulate the change of temperature field of broad bean during freezing process.The simulation results of broad bean temperature and the experimental results are basically the same with time.The temperature error of the broad bean is about 500 seconds,and the temperature error does not exceed 4?.It proves the accuracy of the two-dimensional finite element model of broad bean,and the finite element model can be used.Estimate the temperature profile of the broad bean freezing process.The temperature change during the drying process of broad bean was dynamically monitored by the data acquisition system of the dryer,and the curve of the temperature of the broad bean with the drying time was obtained.The temperature field of broad bean in sublimation drying and analytical drying was simulated by COMSOL Multiphysics software.The simulation results of the broad bean temperature were basically the same as the experimental results with time,and the error between the temperatures did not exceed 3?.In the initial stage of freeze-drying,the internal temperature of broad bean showed a stable trend.As the freeze-drying process progresses,the temperature rises gradually,and the temperature of the broad beans is also higher.The accuracy of the freeze-drying model of broad bean was proved.The finite element model can be used to estimate the temperature curve of the drying process of broad bean.The use of 3D digital video microscope to observe the broad bean cells before and after freeze-drying confirmed the dehydration effect of freezedrying from the microscopic point,and showed great changes in cell structure and morphology during freeze-drying.