The Flow Field Distribution And Model Simulation Research On The Airflow Field In The Atmospheric Freeze Drying

Atmospheric Freeze Drying is a new type of drying technology; it has beenreported by many scholars at home and abroad. There are many problems include thedehumidification, device configuration, energy conservation in traditional atmosphericfreeze-drying technology. To solve these problems, the vortex tube was used as thedehumidification cold source of atmospheric freeze-drying, while the convective heattransfer fluid medium was also provided. Material sublimation of moisture wascontrolled by the vortex tube cooling air convection, and the hot air which exhaustedfrom vortex tube can be used to drying plant material in the chassis to make full use ofresources.In order to explore the effect of atmospheric freeze drying based on vortex tuberefrigeration effect, and the uniformity and stability of cold air-field arising fromvortex tube whether can meet freeze-dried process or not. This paper not only studiedthe performance of the vortex tube, and also studied the flow field distribution ofdrying chamber by use computational fluid dynamics while test the physicalparameters of carrot. The conclusions are as follows:1. The simulation theory and method of atmospheric freeze drying are determined.According to the fact of drying chamber, the mathematical model suitable fornumerical simulation of drying chamber was set up and the corresponding boundaryconditions were determined. At the same time he physical properties parameters ofmaterial were studied, which laid a foundation for further numerical simulation. Theexperiment showed that: the porosity of carrot was0.685; the equivalent diameter was7.66mm; and the true density and bulk density of the carrot are1013.2kg/m3and857.5kg/m3, under the conditions of the initial moisture.2. The properties of the vortex tube at different inlet temperature, different inletpressure and different hot valve open condition were studied. Test results show that:the temperature of inlet is lower, its refrigeration effect is better, its refrigerating capacity is higher, but its thermal effect is worse, and its energy separation effect haslittle influence; The pressure of inlet is higher, its refrigeration effect and thermaleffect is better, its refrigerating capacity is higher, energy separation effect is better;When the hot valve opens K=2, the vortex tube has the best refrigeration efficiencyand refrigerating capacity; When K=3, the vortex tube has the best thermal efficiency;When K=2and K=3, the vortex tube has a higher energy separation effect.3. Simulation of flow field within the atmospheric freeze drying chamber wasstudied. Investigate the characteristics of air-velocity field distribution of atmosphericfreeze drying chamber at different outlet position, different materials plate layers anddifferent inlet velocity. The result show that: when the outlet in the middle of the wall,the air field distribution was uniform; the number of plies of the plate has little effecton the distribution pattern, the plate layers can be appropriately increased; the inletvelocity has little effect on the distribution pattern, the velocity can be appropriatelyincreased to accelerate drying rate.The research of internal air flow field simulation on the distribution pattern,which can be used to design and optimize the atmospheric freeze drying equipmentand further experiment.