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The characteristics of moisture diffusion during wheat drying were determined through low-field nuclear magnetic resonance. The feasibility of variable temperature drying was validated by identifying the variation in the characteristics of evaporable water (EW) and each water component in wheat. During drying, chemically bound water in wheat was converted into EW, which comprised physically bound water and free water components that can evaporate and gasify directly. EW was removed from wheat through diffusion. The analysis of the average rate of the reduction in EW and the variation in the characteristics of weakly chemically bound water ( T 22 ) at different wheat drying stages showed that EW was rapidly removed from wheat at the drying temperature was set at 80 °C during the early stage of drying. The highest average drying rate of T 22 was observed during the later stage of drying at the drying temperature of 70 °C. As inferred from the behavior of chemically bound water during conversion and the behavior of EW during diffusion in wheat, the activation energy required for the removal of EW from wheat comprises the activation energy of the diffusion of EW from wheat ( E a − EW ∗ ) and the activation energy of the conversion of chemically bound water to EW ( E a − c ). Calculations showed that E a − c and E a − EW ∗ fell within the ranges of 25.72–53.75 and 1.09–24.17 kJ/mol, respectively. The maximum value of E a − EW ∗ was less than the minimum value of E a − c . This result confirmed that the energy consumption of removal of chemically bound water is bigger than that of EW. A method for calculating the drying activation energy of wheat ( E a ) was developed in reference to the characteristics of the stable component contents of mature wheat. The relationship between E a and the moisture content of biomass was revealed. [ABSTRACT FROM AUTHOR]

A small, novel wheat drying oven was designed, and tested in order to validate the possibility of recovering diesel engine waste heat as thermal energy. Prior to experiments, the theoretical probability was conducted, and it was confirmed that the thermal energy required for drying wheat could be satisfied by reusing the diesel engine waste heat. Three different experiment parameters, including air temperature, baffle angle, and drying time, were controlled to optimize the results. Based on the experiment data, the optimum temperature for drying wheat was 55°C, and the optimum baffle angle was 23.25°. The drying efficiency decreased as the drying temperature and drying time increased. The moisture content of wheat decreased from 26.0% to 20.0% with 55°C hot air when the proposed wheat drying oven was used. The test results demonstrated that the proposed oven could be made to work. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the airflow distribution in a mixed-flow dryer (MFD) and to study the effect of different bed materials and air duct arrangements. The results were used to validate the numerical model developed in a previous work based on Computational Fluid Dynamics (CFD). A series of experiments have been conducted at a semi-technical MFD test dryer with horizontal and diagonal air duct arrangement. Wheat and rapeseed were used as bed materials. The experiments were performed under isothermal conditions. Two experimental methods were selected and adapted to the measuring problem—the measurement of the isobar distribution within the grain bed and the residence time analysis using the tracer gas pulse method. As could be shown, the isobar distributions measured for wheat and rapeseed agreed well with the model predictions. The numerical model could calculate the influence of the bed material with its different particle characteristics (e.g., particle shape, particle size, bed porosity). The results obtained from the residence time analysis confirmed the known quartering of the air stream flowing from one inlet air duct to the four surrounding outlet air ducts for the horizontal air duct arrangement; in the diagonal air duct arrangement, the air stream from one inlet air duct was nearly halved flowing to the two adjacent diagonal outlet air ducts. These results were confirmed by investigations of the air velocity distribution within the grain bulk. Further experiments are necessary to refine the model. The residence time and isobar measurements will be extended to study the influence of different air properties under real drying conditions, the effect of structural elements, and dryer designs. [ABSTRACT FROM PUBLISHER]

A mathematical model of temperature and wheat moisture content distribution inside a triangular spouted bed dryer was developed. The model is based on analysis of heat and mass transfer inside the dryer. In addition to that, an empirical bulk density model has been developed for wheat and included in the drying simulation. A laboratory-scale triangular spouted bed (TSB) dryer was used to dry wheat grain to validate the model. The dryer was divided into three sections, namely spouting, downcomer, and fountain. A series of drying runs were conducted to record moisture and temperature profile. There were two distinct regions observed during wheat drying. A constant rate period was observed during the initial drying stage and the falling rate period took place at the later drying stage. Initial moisture content and operating drying temperature governed the timing of transition from constant rate period to falling rate period. The model can be used to accurately predict the moisture content of wheat during drying. The temperature prediction inside the TSB dryer was less accurate, especially at high temperatures due to heat losses in the experimental dryer. Further studies are needed to improve the accuracy of this model, especially with regard to the temperature prediction. [ABSTRACT FROM AUTHOR]

In this study, temperature rise and non-uniformity of heating of grain with different moisture contents after microwave treatment were investigated. The temperature anomalies after microwave treatment were measured for barley and wheat at four moisture levels (12, 15, 18, and 21% wet basis) and for canola at five moisture levels (8, 12, 15, 18, and 21% wet basis). Fifty grams of grain samples were heated in a laboratory scale, continuous-type, industrial microwave dryer (2450 MHz) at five power levels (100, 200, 300, 400, and 500 W) and two exposure times (28 and 56 s). Grain samples were thermally imaged using an infrared thermal camera as soon as they came out from the microwave chamber. Average, maximum, and minimum temperatures were extracted from each thermal image and the difference between maximum and minimum temperatures (ΔT) was calculated. The grain type had significant effect on the surface temperatures after microwave treatment. The surface temperatures increased with microwave powers and exposure times but decreased with moisture content. The average surface temperatures after microwave treatment were between 72.5 and 117.5°C, 65.9 and 97.5°C, and 73.4 and 108.8°C for barley, canola and wheat, respectively, when the applied microwave power was 500 W. At the same power level, the maximum surface temperature was between 100.3 and 140.0°C, 77.8 and 117.7°C, and 98.3 and 130.9°C for barley, canola, and wheat, respectively. Non-uniform heating patterns were observed for all three grain types at all moisture contents, power levels, and exposure times. The ΔT was in the range of 7.2 to 78.9°C, 3.4 to 59.2°C, and 9.7 to 72.8°C for barley, canola, and wheat, respectively. The location of hot and cold spots may vary in different dryers based on the position of magnetron and other components, but almost similar non-uniform heating pattern is expected in all microwave dryers. Therefore, this non-uniformity must be taken into consideration while developing microwave processing systems for grains. [ABSTRACT FROM AUTHOR]