Rough Rice Grain Cooling Using Vaporization of Temporarily Deposited Surface Water

Abstract

A method of grain cooling by vaporizing temporarily deposited surface water on rough rice was tested in this study. The surface water was deposited by ventilating rough rice grains with saturated air (humidification) for predetermined time periods (3.5 and 7 minutes). After humidification, evaporative cooling was achieved by ventilating rough rice grains with ambient air. The data were collected using a bed of rough rice (height 0.15m) in a 0.11m diameter circular bin. Temperature and the relative humidity of the ambient air during the experiment time was 30±1°C and 65±1%. The grain temperature was monitored at 0.025, 0.075 and 0.125m heights from the bottom of the rough rice column using thermocouples. The temperature and relative humidity of air at the inlet, outlet and the ambient were recorded. The enthalpy values of air and grain and the temperature drop of grains were calculated for the two humidification times of 3.5 and 7 minutes using an iterative procedure. The 7 minutes humidification led to an average temperature drop of 3.3°C compared to 3.5 minutes humidification in which the drop was 2.1 °C. The 7 minutes humidification has an advantage in bringing down the grain temperature significantly (P<0.001; 95% confidence interval of the difference was 0.57 to 1.58°C; coefficient of variance was 4.58%)