Modeling and Evaluation of Heat and Mass Transfer of Rapeseed (Brassica napus L.) During Hot-air Dry

来源 :The Sixth Asian Conference on Precision Agriculture (第六届亚洲精准 | 被引量 : 0次 | 上传用户:lansu_0754
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  Rapeseed (Brassica napus L.) is an unsaturated porous medium with sorptivity and its kernel owns complex porous media structure with biomass features.The heat and mass transfer process of rapeseed hot-air drying consists of multi-phase coupling and wet-phase transition.In order to provide reference for optimization of drying technique and equipment of rapeseed hot-air drying, the drying characteristics of rapeseed thin-layer hot-air drying was experimentally investigated, the flow distributionsof air velocity and air temperature in the drying box were modeled and evaluated, and the moisture content changes, from experiment and modeling, of the rapeseed during hot-air drying were validated.For the heat and mass transfer modeling, a code incorporating the effects of heat and moisture transfer was compiled by means of User-Defined Functions (UDFs), and the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) was adopted to solve the constitutive equations governing the rapeseed hot-air drying by methodology of Computational Fluid Dynamics (CFD) within Fluent.The drying characteristics of rapeseed thin-layer hot-air drying showed that no constant rate drying stage was observed for the rapeseed, and the moisture transfer of the rapeseed was mostly occurred during the falling rate drying stage.The moisture changes of the rapeseed were also obtained through modeling of the thin-layer hot-air drying process, with moisture content of the rapeseed being 11.3 %d.b., 7.5 %d.b.,5.2 %d.b., 3.2 %d.b.and 1.2 %d.b.at process time of 300 s, 600 s, 900 s, 1200 s and 1500 s under conditions of air temperature 373 K, air velocity 1.0 m/s, initial moisture content of rapeseed 15 %d.b.and layer thickness 2 cm, and the relative error of the moisture contents between experiment and simulation was less than 7%.Furthermore, the flow distributions of air velocityand air temperaturein the drying box at different process time were obtained through the modeling, and the following observations were made: the flow distribution of air velocity reaches a stable status in quite a short period of time, the air velocities just above the rapeseed layer and at the center position of the drying box are nearly same (the velocity of the latter is small a little), and the air velocity at the outlet of the drying box is much higher than those above the rapeseed layer and at the center position;the flow distribution of air temperature gradually changes with the drying process goes on, and the air temperature above the rapeseed layer is higher than the temperatures at the center position and outlet of the drying box, whichbenefits the rapeseed thin-layer hot-air drying.The air velocity and air temperature above the rapeseed layer, at the center position and outlet of the drying box at process time of 600 s, 1200 s and 1500 s were tested as well, and the maximum relative errors of the air velocityand air temperature between experiment and simulation were less than 11% and 1.6 %, respectively.
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