Research On Characteristics Of Expanded Feed And Airflow Field Simulation In The Belt Cross-Flow Dryer

In this paper,physical and thermal characteristics parameters of expanded feed were measured,and then through thin layer of hot air drying testing,drying characteristics of expanded feed is presented.In addition,the condition of air distribution in the belt cross-flow dryer was numerically simulated when expanded feed is dried with computational fluid dynamics(CFD) methods,in order to understand air distribution in the belt cross-flow dryer,supply base theoretics to design dryer equipment which is used to dry expanded feed.The main research conclusions are listed:(1) Two kinds of expanded feed are the equivalent diameter 8.1mm,9.8mm of expanded feed.The average measured values of porosity of expanded feed were respectively 0.3347,0.3424.The density of expanded feed increases with the increase of moisture content.The specific heat capacity of expanded feed were measured with KD2 PRO thermal characteristics analyzer,the specific heat capacity increases with the increase of moisture content.(2) The thermal conductivity of expanded feed were measured with KD2 PRO thermal characteristics analyzer, the results indicated that the thermal conductivity of expanded feed was positively correlated with moisture content and temperature.The values of thermal conductivity of the equivalent diameter 8.1mm of expanded feed were 0.0543-0.1627Wm-1K-1,when moisture content of expanded feed was 3.69%-32.93% and temperature was 45℃. The values of thermal conductivity of the equivalent diameter 9.8mm of expanded feed were 0.0623-0.1597Wm-1K-1,when moisture content of expanded was 3.17%-31.26% and temperature was 45℃.(3) Measuring equilibrium moisture content obtained for the desorption assays of expanded feed with static balance methods.The results indicate that equilibrium moisture content increases with the increase of air relative humidities,decreases with the increase of temperature.The equilibrium moisture content of the equivalent diameter 8.1mm of expanded feed were 6.43%-31.04%(%d.b.),when relative humidities was 11.28%-92.31% and temperature was 30℃.In the range of the different relative humidities,the variation tendency of equilibrium moisture content of expanded feed was different.The equilibrium moisture content of the equivalent diameter 8.1mm of expanded feed varied not significant in 10%-65% relative humidities,but the equilibrium moisture content rapidly increased when the relative humidity was more than 65%.Modified Halsey model can be adopted to describe equilibrium moisture content of expanded feed,meanwhile the average relative error of the model P=4.46%,the standard deviaion S.E=0.0078,the determination coefficient R2=0.9834,the residual between experiment values and prediction values of equilibrium moisture content was 2.04%.(4) Studied thin layer of hot air drying testing,and plotted drying rate curves of expanded feed with GZ-1 circulating hot air drying machine.The results indicate that of hot air temperature,hot air velocity,initial moisture content of expanded feed on the drying rate affected significant.Throughout the drying process, the drying rate at the initial stage was small,drying rate increased gradually and peaked in the late stages with drying time,the drying rate gradually decreased in the last stage,the constant speed drying stage didn't appear at the drying process.Acorrding to nonlinear regression analysis of the thin layer drying experiment,Page and modified Page model can be adopted to described the drying process of expanded feed.(5)Base on the key structure parameters and technological parameters of in the belt cross-flow dryer which can produce 3000kg/h expanded feed with material balance method,the air field in the multi belt cross-flow dryer numerically simulated with Fluent software,the results showed that when the air inlet is arranged in the belt dryer width direction,the air in the drying machine of the length, height direction uniform,air flow rate is higher at the inlet and outlet,air flow rate is higher between the dryer wall and the edge of expanded feed bed than inner ari flow rate.Through the air inlet is arranged in the length direction and arranged in the bottom,the air velocity distribution is more uniform.