Research On Airflow Field Simulation In The Circulating Dryer Of Chinese Jujube

Drying of Chinese Jujube can not only reduce the loss, improve the quality, but also prolongthe shelf life of fruit, increase commodity rate and add value, so it plays an important role inincreasing farmers’ income and promote the development of red dates industry. The internal structureof drying equipment determines the distribution of hot medium in the drying chamber and energyconsumption, and has an important influence on the uniformity and efficiency of red dates’ drying.However, the general structure size of dryer is too large and the conventional test means leads tohigh cost and a long period with difficulty of measuring relevant data on site. The integration ofcomputer simulation and experimental study can visualize the airflow distribution of drying chamberdirectly. The software, Fluent, is used to simulate airflow field in the circulating dryer to improve thedistribution uniformity of heat medium drying chamber.Through testing basic physical parameters of the material, the density, porosity and averagediameter are determined. An experiment is carried out to investigate the influence of airflow rate onred dates’ drying rate and the results shows that the appropriate wind speed for red dates’ drying is0.5m/s. Through introducing the working principle and drying technology of circulating dryer, thispaper completes the design of feeding device, heating device and container structure. Throughstudying fluid mechanics theory, a steady-state model of dryer flow field, which is based on thedifferential equation and standard k-ε turbulence model, is established. In this model, we use porousmedium model instead of dates, select the SIMPLE algorithm and two order upwind schemes and useICEM to mesh.Besides, establishing monitoring points and evaluation index in each layer of red dates, fourkinds of the air flow characteristics of entrance velocity are studied. The simulation results indicatethat the field uniformity in drying chamber is worse with the increase of inlet velocity; the dryingchamber pressure has little effect on red dates’ drying rate; inlet velocity of dryer is5760m3/h, whichcan meet the requirements of the red dates drying rate. The flow distributions of two kinds of dryingchamber structure are analyzed. The results show that eddy current phenomenon formed in thedistribution chamber without baffle can lead to velocity of red dates uneven; the ladder shapedarrangement of baffle at the entrance can reduce eddy current of flow field, and the uniformity ofwhole flow field are improved. Uneven coefficient of the underlying red dates’ wind speed decreasesfrom19.13%to7.9%, and uneven coefficient of the middle red dates’ wind speed decreases from6.94%to3.15%. In addition, flow field of the heating device is simulated, and outlet temperature canreach80℃. The measured results of temperature is76.3℃, which is consistent with the simulationresults, and meets the requirements of drying red dates.The dissertation provides a method for the research of circulating dryer of Chinese Jujube basedon numerical simulation of computational fluid dynamics, strengthening the design ideas andproviding a basis for optimization of the dryer’s structure.