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Drying of wheat grain in thin layers Bhargava, Veerendra Kumar


The effect of drying parameters on the drying-rate constant, the diffusion coefficient, and the dynamic equilibrium moisture content was investigated using the Park variety of wheat. The initial moisture content of all the grain used in the drying tests was approximately 29 percent, dry basis. Air temperatures of 120, 100, 80 and 60 degrees Farenheit; air flow rates of 120, 80, 20 and 5 feet per minute and several relative humidities were employed as the drying conditions during the tests. A closed cycle, heated air dryer in which the air temperature and the relative humidity could be controlled to ± 2 degrees Farenheit and ± 5 percent respectively, was constructed for the investigation. It was assumed that the mechanism of internal flow of moisture within a kernel is that of diffusion. When the initial transition drying period was neglected, the drying-rate constant and the diffusion coefficient were found to be constant and the plot of log moisture ratio against time gave an excellent fit for each drying test. It was concluded that the falling-rate period in thin layer drying could be represented by a constant drying-rate constant and diffusion coefficient. The effect of air temperature on the drying-rate constant and diffusion coefficient was found to be inconsistent with an Arrhenius type equation. There was no observable effect due .to air flow rate and relative humidity of the drying air. The dynamic equilibrium moisture content increased with increased relative humidity of the air. A plot of log dynamic equilibrium moisture content versus log-log relative humidity gave a straight line relationship and satisfied Henderson's equation. The equilibrium constants were found to vary with the air temperature. The dynamic equilibrium moisture content was found to decrease with both the air temperature and air flow rate. The effect of air flow rate was quite small except at low' temperatures. When log air temperature was plotted against dynamic equilibrium moisture content, it followed a straight line, indicating that an exponential relationship between the two might exist.

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