Comparison of Rice Drying Thermal Efficiency Using Hot Air Flow with Full and Half Open of Blower Throttle

摘要

This research is a part of a comprehensive study, in order to make an effective, economical dryer for agricultural products in which it has stable and homogenous room temperature. The tested dryer was an indirect contact type which has a seven-level sliding tray type, the width of each tray was 98 x 65 cm, and LPG was as fuel. The aim of this study was to compare the thermal efficiency of grain drying of 28 kg each; first, between the valve openings of full and half open blower throttle; second, the dryer without installed heating fins and without heating air recirculation.Before the drying process was carried out, 28 kg of harvested grain were spread over seven levels of the tray, randomly but evenly distributed. The drying chamber temperature was set in 50-550C, then the stove was turned on. During the drying process, the temperature of the drying chamber around the temperature sensor was relatively 50-550C, it was because the thermo controller regulates the work of the solenoid valve automatically so that the fuel rate flows normally or small in order to maintain the flame of the stove large or small and to maintain the temperature of the drying chamber as desired. The drying of 28 kg grain was done twice in which it had a heating air circulation which produced by a 2" blower, with the speed of air flow with a full and half open throttle. The grains on each tray were relocated every 30 minutes to different levels so that grain heating was evenly distributed. During the drying process, the temperature of the outside air and the drying chamber at the odd number tray level were recorded every 10 minutes interval using several digital thermometers. The drying time length was 540 minutes each.The moisture content of the grain was calculated based on the grain samples which was dried using an oven until the water content became 0%, both harvested wet grain and dry grain from the results of drying used the dryer. The data obtained from this study were then used as the basis for calculating the thermal efficiency of the grain drying. The calculation results show that the thermal efficiency of grain drying with full open blower throttle is 25.3%, while the thermal efficiency of drying grain with half-open blower throttle is 35.2%.