Research On Drying And Hygroscopic Characteristics Of Rapeseed(Brassica Napus)

The drying and hygroscopic characteristics of rapeseed were studied to obtain the better drying process and storage data of rapeseed (Brassica napus). Rapeseed hot air drying process, Key problems, such as heat and mass transfer mechanism, dynamic behavior of the transfer process, hygroscopicity to moisture equilibrium, in the process of hot air drying of rapeseed were studied to deeply understand the hot air drying process, to optimize the drying process parameters, to improve drying quality and to reduce drying energy consumption of the rapeseed drying, and at the same time to provide a theoretical basis to them.In this paper, the Pore Network Model of rapeseed was numerically simulated and analyzed by applying FLUENT, done the numerical simulation and the simulation analysis, and the main research contents are as follows:(1) The external and internal boundary conditions of the model were set in FLUENT by using Mixture Model of the multiphase flow and defining the main phase liquid, namely, water, and the second phase gas. Iterative solution of two-phase flow model of SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm was conducted. The initial temperature of the fluid in the pore is 310K, and heat source is wall of temperature 333K. Mass source and energy source term were embedded in the FLUENT to solved the problem by means of UDF functions(2) Contours of moisture loss rate in the micro-pores, liquid velocity, the distribution of the liquid velocity at different moisture contents, liquid pressure were obtained. The effects of temperature change and moisture content on liquid velocity were analyzed. From the simulation, higher temperature and moisture content results in higher drying rate of rapeseed, and high temperature, high moisture, and high hot air speed can lead the drying efficiency to increase.(3) The drying rate curves of thin layer drying experiment were analyzed. The effects of moisture content, temperature and hot air speed on the drying rate of rapeseed were analyzed as well. Comparisons of the thin layer drying experiment and simulation reveals a good consistence. Drying parameters were selected according to practical requirements:for seeding purposes, the optimal temperature is from 40℃to 60℃, and for industrial use, the optimal temperature is from 90℃to between 150℃; the moisture content is from 12% to 21%. Since there are good consistence between experiment and simulation, and temperature has more influence on the drying rate of rapeseed than hot air velocity and moisture content, priority should be given to temperature in the practical drying process of rapeseed to prove the drying efficiency.Hygroscopic characteristics experiments of rapeseed were conducted to obtain the hygroscopicity curves of different moisture contents and temperatures. The critical relative humidity curves of rapeseed were simulated, and the moisture equilibrium curve model was established. The moisture equilibrium curve was obtained by means of MATLAB data fitting. The analysis results showed that the critical relative humidity of rapeseed is 58% at 0℃, and 68%,72%,74% at 10℃, 20℃, and 30℃, respectively. When the temperature is 20℃-30℃and relative humidity is about 50%, short time is needed to reach moisture equilibration time, and then the mass of moisture absorption to rapeseed is small, which meets the storage requirements of rapeseed.