Numerical Simulation Of Thermal And Humid Environment In Bulk Curing Barn With Loose Leaf Tobacco Loading

In the context of “reduction in labor,cost reduction,quality improvement,and efficiency enhancement” in the country,the bulk leaf tobacco technology significantly increases the tobacco content during the tobacco leaf curing process compared with other tobacco packaging technologies,and greatly reduces coal consumption,labor and energy consumption.Cost is in line with the development trend of modern agricultural production.However,the current use of the standard loose leaf tobacco baking process has problems such as uneven temperature and humidity distribution in the tobacco packaging room,unclear optimal tobacco content,poor coordination of chemical components of the cured tobacco leaves,and low appearance quality of the tobacco leaves,so it is promoted Cause hindrance.However,the improvement of the loose leaf baking process through experimental tests has problems such as large workload,long test period,and high cost.Therefore,the CFD technology is applied to the intensive baking of loose leaf tobacco to obtain and optimize the changes in the thermal and humid environment inside the curing barn.The improvement has good practical significance for optimizing the loose leaf baking process and improving the quality of loose leaf baking.Therefore,in view of the problems existing in the current standard bulk tobacco curing process,this paper applies the porous media theory and the UDS transmission equation moisture evaporation model to establish the dry heat and moisture transfer model of the bulk curing barn,and simulates and analyzes the standard bulk tobacco.The distribution law of temperature field,humidity field and air distribution in bulk curing barn under the leaf-loaded tobacco curing process,and using experimental data to verify the established barn CFD model.The CFD model was used to simulate the process parameters under four different working conditions: air inlet speed,smoke density,stacking spacing,and air distribution plate angle,and the optimal baking process parameters were proposed.The main conclusions obtained are as follows:(1)Numerical simulation results show that the pressure in the upper area of the rear part of the tobacco loading chamber is the largest,about 70 Pa,and the pressure is the smallest near the air outlet,which is close to 0Pa;the speed is the largest near the air outlet,about 9.5m/s,and the velocity changes more in the tobacco accumulation area.Small,about 0.2m/s ? 0.25m/s.In terms of temperature distribution,the temperature of the upper layer of tobacco leaf accumulation area is greater than that of the lower layer of tobacco leaf,the temperature of the middle and rear tobacco leaf accumulation area is greater than that of the front,and the temperature gradient in the vertical direction is greater than the horizontal direction;the overall relative humidity in the yellowing period is 85%-95% The fixation period is about 45%?70%,and the dry tendon period is about 10%?25%.The heat and humidity environment and air distribution in the tobacco chamber under the standard loose leaf baking process are unreasonable.(2)The test results show that the temperature of the upper layer of tobacco accumulation area is always higher than that of the lower layer,and the temperature of the middle and rear tobacco accumulation area is always higher than that of the front.The temperature difference between the upper and lower layers first becomes larger and then smaller;the relative humidity of the upper layer tobacco accumulation area is always lower than that of the lower layer,and The relative humidity of the upper tobacco leaves first began to decrease,and the overall relative humidity decrease showed the characteristics of first becoming larger and then smaller.At the same time,the numerical simulation results of the CFD model of the loose leaf baking in the bulk curing barn were highly positively correlated with the experimental data,and the error was kept at a reasonable level.Within range.(3)The CFD model is used to simulate and analyze the process parameters under four different working conditions: air inlet speed,smoke density,stacking spacing,and air distribution plate angle.The results show that as the air inlet wind speed increases,the wind speed between the leaves increases less.The pressure difference is rising exponentially,and the temperature distribution becomes more uniform;the smaller the density of tobacco,the linear increase of the wind speed between the leaves in the tobacco accumulation area;increasing the angle of the air divider can increase the wind speed between the leaves in the tobacco accumulation area,and at the same time increase the horizontal temperature The uniformity of distribution;the wind speed between the upper and middle layers of tobacco accumulation areas decreases with the increase of the inter-layer spacing,and the inter-leaf wind speed in the lower tobacco accumulation areas increases with the increase of the inter-layer spacing.Considering the temperature distribution in the tobacco chamber and the rationality of the wind speed between the leaves,the best loose leaf baking process has a tobacco density of80?85kg/m3,a stacking layer spacing of 250 mm,and a fan plate angle between 45° and60° At the same time,the yellowing period of the air inlet speed is 4.5m/s,the fixed color period is 5m/s,and the dry tendon period is 4m/s.