| Drying is the most important process of aquatic feed production.Belt dryer is a common equipment in drying feed,which is used to reduce the moisture content of feed.Appropriate drying conditions can effectively reduce the moisture content of feed.Feed moisture is an important parameter for quality evaluation of feed products.At present,the basic research on the airflow distribution and related drying conditions of the belt dryer used in industry is not clear,which leads to the nonuniform moisture content,low drying efficiency,and affects the feed quality.In view of this problem,the drying process parameters(fan frequency,feed thickness,drying temperature)of belt dryer were studied,CFD model and drying dynamic model were established,and the drying characteristics of feed was analyzed in this paper.Theoretical basis for optimizing the drying process of feed was provided.The experimental platform of belt dryer was developed.The experimental platform was consisted of frame,heater,circulating fan,double feed conveyor,exhaust fan,intelligent control system and automatic data acquisition system.It could detect the changes of air velocity at all points in the dryer in real time,and assist in the study of the actual production situation of belt dryer.Based on the Computational fluid dynamics(CFD)simulation and experimental verification,the airflow distribution in the belt dryer at four different fan frequencies(25Hz,30Hz,35Hz and 40Hz)was studied.Anemometers were placed at nine points on the feed surface to measure the airflow velocity.The results showed that the experimental and the simulation value were in the same trend.When the fan frequency increased from 25Hz to 40Hz,the average airflow velocity on the feed layer surface was range from 0.39m/s to 0.64m/s.When the frequency of fan was 30Hz,the airflow distribution on the feed layer surface was more uniform.The average values of simulated and experimental airflow velocity on the upper layer were 0.44(±0.02)and 0.46(±0.02)m/s,respectively.The average values of simulated and experimental airflow velocity on the lower layer were 0.51(±0.11)and 0.48(±0.07)m/s,respectively.The airflow distribution in the dryer at five different feed thicknesses(20mm,30mm,40mm,50mm,and 60mm)were studied,and verified by experiments.The results showed that the experimental value was consistent with the simulated value.The airflow velocity on the feed layer was range from 0.40 m/s to 0.51m/s.When the feed thickness was 40mm,the airflow distribution on the feed layer was more uniform.The average values of simulated and experimental airflow velocity on the upper layer were 0.39(±0.01)and 0.44(±0.06)m/s,respectively.The average values of simulated and experimental airflow velocity on the lower layer were 0.50(±0.14)and 0.49(±0.10)m/s,respectively.The drying characteristics of extruded feed were studied at different fan frequencies(5Hz,10Hz,15Hz),feed thicknesses(10mm,15mm,20mm),and drying temperature(70℃,90℃,110℃).At the same time,five different drying dynamic models(Newton,Henderson and Pabis,Page,Modified Page,and Weibull)were selected.The results showed that the time needed to the extruded feed moisture reach below 10%was proportional to the feed thickness,and was inversely proportional to the fan frequency and drying temperature.The drying rate of feed increased first and then decreased with time.The drying rate of feed was proportional to the fan frequency and drying temperature,and was inversely proportional to the thickness of feed layer.It was found that Weibull model was most suitable for describing the feed drying process.Compared with the fan frequency and drying temperature,the feed thickness had the greatest influence on the effective feed moisture diffusion coefficient. |
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