| The newly harvested grains need to be dried to below safe moisture for long-term storage.The dynamic characteristics of transverse relaxation time(T2)of wheat was studied by performing LF NMR.The bound form and T2 of water in wheat were obtained.The change laws and migration characteristics of water with different bound form in wheat under different drying stages and drying conditions were determined.The influence of dynamic characteristics of water with different bound form on diffusion behavior during drying and the suitable drying method of wheat were analyzed.Chemically bound water in wheat was converted into evaporable water(EW),which comprised physically bound water and free water components that can evaporate and gasify directly.The drying characteristics of EW dominated by diffusion were studied.The effect of chemically bound water migration to EW on EW diffusion during wheat drying was discussed,and the feasibility of variable temperature drying was demonstrated.The activaactivation tion energy required for the removal of EW from wheat(Ea)comprises the energy of the diffusion of EW from wheat(Ea-EW*)and the activation energy of the conversion of chemically bound water to EW(Ea-c).The relationship between Ea,Ea-EW*,Ea-c and the moisture content of biomass was revealed.Swing temperature and alternating airflow were adopted.The influence of the ratio of the normal flow heating time to the reverse flow time,tempering time,tempering air velocity,tempering temperature,and air velocity throughout the drying process on drying drying uniformity in deep-bed wheat drying was studied.The optimum drying process for grain drying uniformity and economy was obtained.The energy consumption and unit area capacity of fixed bed,alternating flow fixed bed,swing temperature and alternating airflow fixed bed,spouted bed and fluidized bed were compared by the same calculation method. |
