Flow Field Simulation And Structural Optimization For New Bulk Tobacco Curing Barn Based On CFD

The tax of tobacco industry is one of the main taxes in China.Tobacco curing is the first process after picking up tobacco leaves from the field.Tobacco curing barn can directly affect the quality of tobacco curing and the choice of subsequent processing methods,and it can even affect the quality of cigarette products.The new bulk tobacco curing barn can improve the efficiency of tobacco curing process.And the quality of cured tobacco is determined by the internal environment in tobacco curing barn.CFD is applied to the new bulk tobacco curing barn to understand the internal flow field.It has a practical significance to improve the tobacco curing efficiency.In this thesis,internal flow field in the new bulk tobacco curing barn was analyzed by CFD technology.Discrete phase model was used to model water evaporation in the curing barn.And a numerical simulation was calculated for the thermal and humid environment inside the barn.The measurement of tobacco weight was used to validate the curing barn CFD model.The tobacco area was studied as porous media model.And the influence on the temperature distribution inside the barn with different porous media parameters was studied.A numerical simulation was calculated for internal airflow velocity field to study the influence on the airflow environment with different air holes,wind deflectors and outlets.And structure optimization design for the barn was implemented.The main conclusions are as follows:(1)Curing test of the new bulk tobacco curing barn was carried out to study the changes of temperature,humidity and tobacco leaves weight.The temperature of the upper zone of the tobacco leaves area was always lower than the bottom area.And the relative humidity of the upper zone was higher than the bottom area.The relative humidity in the non tobacco area was low and remained consistent.The weight loss rate during curing process was divided into four stages.(2)Water evaporation inside the barn was modeled by using discrete phase model.The tobacco moisture content was introduced into the barn from inlet boundary when the multiphase flow was used.But the water was from the tobacco leaves.And if the inlet boundary was moved to tobacco area,the airflow in the barn could be affected.Using discrete phase model to model water evaporation in the barn can introduce water droplets in from unstructured planes.The planes could be anywhere in the barn and could not affect the airflow.(3)Temperature and humidity field in the new bulk tobacco curing barn was studied by using CFD.The temperature and relative humidity predictions showed good agreement with the experimental measurements with a high coefficient of correlation.It meant that the CFD model could predict the thermal and humid environment in the barn.Temperature on the bottom of the barn was higher than the top area,and temperature inside the porous media was lower than the outside area.And the water vapor mass fraction was on the contrary.And the increase of porosity and particle average diameter increased the speed of heat conduction.During tobacco curing process,appropriate choice of loading density could improve the curing efficiency.(4)Structure optimization design was carried out on the new bulk tobacco curing barn.With the increase of the number of ventilation holes,the average velocity of air flow in the barn was increased,and the flow rate of the air flow was also increased.But the effect gradually weakened when the number of ventilation holes was increased.And wind deflector could affect the airflow non-uniform coefficient.Small angle wind deflector was appropriate.The top outlets could slightly improve the airflow velocity and the airflow uniformity in the middle and top area compared to the bottom outlets.