| Seed of rape (Brassica campestris L.), namely rapeseed, as one of the main source of edible vegetable oil in China, possesses high nutritional and economic values. In China, most rapeseed is of species of rape(Brassica napus L.). Rape planting areas are mainly in the Yangtze River region and the basin area of Sichuan Province. And the harvest season of the rapeseed is mainly in rainy season. The moisture content of the newly harvested rapeseed is high, and the protein content in rapeseed is high and easy to absorb moisture. Therefore, if the newly harvested rapeseed is not dried timely, it is easy to result in mildew and deterioration, which affects the oil quality and people’s health. So, newly harvested rapeseed must be dried timely.Rapeseed grain has complex porous media biomass structure characteristics and the heat and mass transfer of drying process is relatively complex, and the domestic study is less. Based on this, in the thesis, seed of rape (Brassica campestris L.) was focus on as the research object. Through the experimental study and numerical simulation, rapeseed hot air drying characteristics and the flow field in the drying box were studied, which can provide data support for optimizing the rapeseed drying technology and drying box design. The main conclusions of the study are as follows:(1)Through experiment study, the rapeseed drying characteristic curve and the change of air speed field and temperature field in the drying box curve under conditions of different hot air temperature, hot air speed, initial moisture content and thickness were obtained. The results showed that the changing trend of the moisture content under different drying conditions is almost the same. But as different factors have different effects on the drying process mechanism, with different importance of influence on moisture content. Results showed that the hot air temperature has the highest level contributed to the moisture content change, and it is followed by hot air velocity, and the thickness of rapeseed has the lowest level. Air velocity field of the drying box can reach a steady state in a short period of time. Temperature field gradually rise with the drying process. When hot air temperature is 373 K, hot air velocity is 1.000 m/s, thickness of rapeseed is 0.8 cm, and drying time is 1500 s, the air velocity values at positions of drying box center, outlet, and up-surface of rapeseed are 0.200 m/s,0.225 m/s and 1.500 m/s, respectively, and the temperature values of those positions are around 335 K,335 K,330 K, respectively.(2)Through numerical simulation, the moisture content curve and flow characteristics of rapeseed in the drying box were obtained. The results showed that the moisture content at the drying time of 300s,600s,900s,1200s and 1500s are 11.8%d.b., 8.1%d.b.,5.0%d.b.,2.9%d.b.,1.0%d.b., respectively. The relative error is less than 7% compared with the experiment results. The relative error of the air velocity field and temperature field values at the center, the outlet and up-surface of rapeseed are less than 11%. The simulation results are in good agreement with the experimental results.(3) By changing the outlet of the drying box, the structure of the box was optimized. Through the simulation of 5 drying box models, by evaluating moisture content, air velocity field and temperature field, results showed that:when the outlet is the up-semi-outlet structure of the original model (model 1), there are more decreases of moisture content, big range of air velocity change, and the temperature of the rapeseed is high. Therefore under the same conditions more rapeseed can be dried and waste of energy can be avoided, then model is better than others. |
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