Numerical Simulation Analysis And Baking Process Research Of Heat Pump Bulk Curing Barn

After tobacco is cultivated in the field,the first process is tobacco leaf baking,and the quality of its baking directly affects a series of subsequent processing steps,and even affects the quality of the final cigarette.The air source heat pump bulk curing barn is the main tobacco baking equipment currently promoted.Its internal flow field,wind speed,temperature and humidity distribution uniformity and the supporting baking process can directly affect the tobacco baking uniformity and the quality of cured tobacco.Improving the internal flow field distribution uniformity of the heat pump bulk curing barn and optimizing the baking process are crucial to improving the tobacco baking quality.Therefore,this article applies the theory of heat and mass transfer in porous media and the discrete phase moisture evaporation model,combined with the drying characteristics of tobacco leaves and considering the shrinkage of tobacco leaf volume during the baking process,to establish a numerical model for the baking process of tobacco leaves in the heat pump bulk curing barn.It simulates and analyzes the distribution of airflow velocity,temperature,and humidity in the baking area of tobacco leaves in the heat pump curing room at different baking stages,as well as the corresponding relationships between various flow field parameters,Compare and verify the key data of the flow field with the experimental measurement results.Use the established numerical model to compare and analyze the uniformity of flow field distribution in the tobacco leaf baking area under different air inlet speeds and tobacco loading processes,and propose the optimal combination plan.Finally,the baking experiment was conducted by changing the temperature during the yellowing period and the color setting period of the conventional baking process,and a comprehensive comparison was made between the appearance quality,structural grade and average price,main chemical component content,and sensory evaluation quality of the cured tobacco leaves under different baking conditions.The main conclusions obtained are as follows.(1)According to the experimental findings,the flow field’s temperature,humidity,and wind speed vary at various points inside the baking room,and the uniformity of the flow field changes depending on the stage of baking.The uniformity of the flow field is best during the changing yellow period,followed by the dry reinforcement period,and the uniformity is worst during the fixed color period.When baking,the volume shrinkage rate of the tobacco leaves and the inlet air speed both increase the wind speed of the flow field;The temperature in the tobacco leaf region at the front of the curing chamber is greater than that in the back,and the flow field temperature in the upper tobacco leaf area is always higher than that in the lower layer;The humidity in the tobacco leaf region in the front of the curing chamber is always lower than that in the back,and the relative humidity of the flow field in the higher tobacco leaf area is always lower than that in the lower layer.(2)By analyzing the variation of tobacco leaf moisture content and leaf shrinkage rate with baking time through baking experiments,it was found that there is a significant correlation between tobacco leaf moisture content and leaf shrinkage rate,providing experimental basis for the variation of porous tobacco leaf layer porosity in numerical simulation.(3)The internal flow field characteristics at various baking stages have a remarkably modest relative error between experimental and numerical simulation results.This numerical model’s construction is dependable and efficient,and it can offer theoretical backing for enhancing the uniformity of the flow field in the baking room.By analyzing the flow field distribution in the bulk curing barn at different curing stages in the numerical model,it was found that the distribution of temperature and humidity in the tobacco curing area was mainly affected by the distribution of air flow velocity.The area with high air flow velocity had higher temperature and lower humidity;Areas with low airflow velocity have low temperature and high humidity.The inlet air velocity has a significant impact on the average airflow velocity in the tobacco leaf baking area,and the average velocity in the tobacco leaf area increases with the increase of inlet air velocity;The uniformity of air flow distribution in the tobacco leaf baking area is influenced by two factors: inlet air velocity and tobacco loading.The uniformity of air flow distribution in the tobacco leaf baking area decreases with the increase of inlet air velocity and improves with the increase of tobacco loading.When the air inlet speed is1.5m/s in yellowing period,2.7m/s in color fixing period and dry reinforcement period,and the volume of tobacco is 6t,the uniformity of air flow speed,temperature and humidity distribution in tobacco leaf area has been improved.(4)In the baking process for the central tobacco leaves of Yunyan 87 variety in Jiangchuan region,there are certain differences in the baking quality of the cured tobacco leaves under different processing techniques.When compared to the local baking methods that are frequently employed,properly raising the baking temperature during the period of yellowing and lowering the curing humidity during the period of fixed color can enhance the overall baking quality of the cured tobacco leaves.