Experimental And Simulation Research Study On Drying Characteristics Of Comas Tower Dryer

Comas tower dryer(CTD)is a kind of full automatic dryer and a new type of air drying machine.It has the advantages of short drying time,high production efficiency and good quality.CTD has gradually been applied in domestic tobacco companies.However,in the actual application of the equipment,there are some problems of uneven material and uneven moisture content.Therefore,in this paper,experimental measurement and numerical simulation are used to study the flow and heat transfer characteristics in the comas tower dryer.And the influence of different parameters on the cut tobacco drying characteristics is analyzed and it aim to improve the quality of drying quality by improve the drying process parameters and structural parameters of the drying machine.At the same time,it has important value for engineering application.The main work and conclusions are as follows:1)Experimental platform has been designed for studying the drying characteristics of tobacco in self-building hot-air dryer.The effect of drying temperature and hot air velocity on the effective diffusion coefficient(Deff)and activation energy has been analyzed.The results showed that the values of Deff would increase with the addition of drying temperature.But with the increase of airflow velocity,the drying rate of cut tobacco decreases.Drying kinetics of cut tobacco is explained and compared using three mathematical models.The Logarithmic model is selected as the model that has best results in predicting the drying behavior of cut tobacco,while the prediction error of the model is over 20%in the late drying stage.Based on the Logarithmic model and the Two-term model,a prediction model for the drying characteristics of the cut tobacco is developed.And the maximum prediction error of the new model does not exceed 1%,which greatly improves the prediction accuracy of the drying characteristics of tobacco.2)The simulation model of the drying characteristics of tobacco in tower drying machine is established.Based on the prediction model by hot-air drying experiment,the cut tobacco drying process is simulated by Fluent.The simulation results show that the cut tobacco has obvious influence on the velocity,temperature and water concentration distribution characteristics of the tower.It is find that the air temperature ranged from 395 to 428.8K.At the same time,the water mass fraction increased by 1.1 times.For tobacco particles,the particle drying time varying from 1 to 4.635s.At the outlet of the model,the moisture content of the particles is 0.176 at the maximum,and the minimum value is 0.001.Studies show that the standard deviation of the outlet position values is 0.07,and the standard deviation of the model outlet moisture content is 0.012,which expressed the uniformity level on the drying.According to statistical analysis of the simulation results,it seems that the dry quality of CTD was relatively poor in the original conditions.3)The influence of process parameters and model structure on the drying effect of tobacco is studied.The parameters of the Comas tower dryer are optimized and its structure is improved.Through orthogonal experiments and range analysis,several factors influencing the drying effect of cut tobacco are ranked.The results show that the influence of process air temperature and tobacco flow rate on the drying quality of cut tobacco is most significant and the effect of water vapor flow is minimal.There is a combination of a set of optimal process parameters(air velocity is 23m/s,hot-air temperature is 155.55?,water vapor mass flow rate is 400kg/h,cut tobacco mass flow rate is 2300kg/h).Improvements have been made to the existing dryer structure.The curved deflector is added to the inside of the dryer when the cut tobacco enters the inside of the dryer.The plane structure at the top is turned into a hemispherical form,and the outlet of the dryer rotates 90 degrees along the positive direction of the Z axis.After the structure is improved,the standard deviation of the outlet position is 0.037 at the minimum and the standard deviation of the moisture content is 0.006.The drying effect is significantly improved.