Numerical Simulation Of Heat And Mass Transfer In Hot Air Drying Of Mushroom Based On Pore Network Model

A large amount of moisture in shiitake mushrooms can be removed by drying to extend its shelf life in order to promote the production and marketing of shiitake mushrooms.Hot air drying is one of the most important drying methods in agricultural production practice.The heat and mass transfer during the hot air drying process affects the quality of drying directly.Numerical simulation has become an effective tool for drying process research,traditional methods obtain empirical parameters to predict the drying process,which draw on the assumption of continuum,and the moisture transfer and flow characteristics in the material porosity were ignored.In this paper,a numerical simulation study on heat and mass transfer of hot air drying was carried out to explore the influence of the material internal structure on the drying process based on the pore network.First,the porous medium hypothesis of the shiitake mushrooms was proposed,and a two-dimensional regular pore network model of the porous medium was constructed.The model was constructed by combining the two-dimensional discrete pore network and the continuity model.The results show that the material of shiitake mushrooms has a pore structure at mesoscopic scale,and the porous medium hypothesis of the shiitake mushrooms was valid.The pore network model parameters accord with the real material,which can represent the real mushroom tissue structure.Secondly,according to the moisture distribution and the dynamic characteristics of moisture transmission,the moisture transfer in different structures in the model of the mushroom material during the drying process were analyzed.Then mathematical models were established according to the mechanism of moisture transfer.Including the moisture transfer between adjacent skeleton,between the skeletons and the pores,the gas-liquid different phase transfer between the pores and so on.A dry mass and heat transfer mathematical model based on a discrete pore network was constructed.Finally,the actual shiitake mushrooms slices were dried by hot air at a temperature of 40?,and the drying curves of the samples were obtained.The experimental results were compared with the simulation results of the pore network model.And numerical simulations of the drying process were carried out by changing the transfer parameters,the number of mass transfer surfaces,temperature and humidity.The results show that the model agreed well with the experimental results and could reflect the actual drying process.And the transfer between the skeletons has an important influence on the final drying result;The drying time of two mass transfer boundary model was longer than that of four mass transfer boundary model;the drying temperature and humidity will affect the moisture diffusion in the material,which can affect the drying time and the moisture content of the material.