Study On Heat And Moisture Transfer Characteristics Of Fu Brick Tea Fermentation And Optimization Of Air Distribution In Drying Room

Fu brick tea is a special series of black tea products,its value mainly depends on the production of a beneficial bacteria-"Golden Flower fungus" in the fermentation process.Drying room is the main production place of Fu brick tea fermentation,which provides proper temperature and humidity environment for the propagation of "Golden Flower fungus".However,there is a problem of uneven distribution of indoor temperature and humidity in Fu brick tea drying room,the same batch of products can not achieve synchronous fermentation,which affects the product qualify rating and economic value.To deal with the above problem,the study mainly focus on the heat and moisture transfer characteristics in the fermentation process of single tea brick,and further propose the optimization scheme for the air distribution of an practical drying room.The main research work is as follows:Firstly,based on the characteristics of unsaturated porous media of Fu brick tea,in the fermentation process,3 kinds of heat transfer pathways,namely heat conduction,heat convection and phase change,and 3 kinds of mass transfer mechanism,namely molecular diffusion in gas phase,capillary effect in liquid phase and convection,were elucidated.The heat and mass transfer coupling model for Fu brick tea fermentation was established,and the validity of the model was verified by fermentation experiments.The fermentation characteristic curve of Fu brick tea was drawn,and the spatial distribution pattern of water saturation in liquid phase and heat and moisture load were obtained.Secondly,taking a Fu brick tea drying room in Xianyang city of Shaanxi Province as the prototype,a three-dimensional mathematical model of the flow and heat transfer of wet air in the drying room was established.The heat and moisture load of the first day of fermentation process under the condition of full storage(with 4320 pieces of Fu brick tea of the same specification)was taken as the design heat and moisture load,which were calculated to be 4.44 k W and 1.69 g/s respectively.According to the indoor temperature base and the allowable fluctuation range of the drying room,the air supply parameter between 6 ℃ and 9 ℃ are determined,and the influence of the temperature difference on the air distribution of the heat pump drying room is studied.The air distribution is evaluated by the temperature non-uniformity coefficient and air distribution performance index(ADPI).The results show that the best uniformity and rationality of air flow organization is obtained when the temperature difference of supply air is 6 ℃,and the temperature non-uniformity coefficient and ADPI are 0.057 and 53%,respectively.Finally,The test data and simulation results of temperature and humidity in the drying room,were compared and the main reasons for the unreasonable air distribution in the drying room are: the unreasonable layout of the flow equalization plate,the end effect of the air supply pipe and the insufficient heat transfer in the lower area of the shelf due to the rapid rise of hot air.To ensure the uniform flow of the hole and enhance the heat transfer in the lower area of shelves,this paper proposed to reduce the number of holes along the flow direction in the air supply pipeline with same hole radius,and put forward three optimization schemes of hole array.The results show that:,Under the three optimization schemes,the temperature non-uniformity coefficient is reduced by 0.025-0.035,and the ADPI is increased by 12%-31%,which is compared with the actual hole array scheme,can play a better optimization effect.Through theoretical and experimental research,the heat and moisture transfer mechanism of fermentation was clarified,and the heat and moisture transfer characteristics were obtained;the optimal temperature difference of air supply was determined,and put forward three optimization schemes of orifice array can effectively reduce the temperature non-uniformity coefficient and improve ADPI.This study is of great reference value to the optimization of air distribution in Fu brick tea drying room,and has certain guiding significance to the optimization design of other types of drying rooms.