| บทคัดย่อ(English) |
The purpose of this thesis is to investigate the technique of in-store drying of corn under tropical climates as in Bangkok. Corn drying experiments were conducted in a dryer having a diameter of 0.75 meter and a height of 2.75 meters. Height of corn bed was set at 1.4 meters and air flow rates at ambient temperature were varied from 1.5 to 4.5 m(3)/min-m(3) of corn. The experiment was categorized into continuous and intermittent ventilations (75 % relative humidity). Experimental results indicated that in-store corn drying was technically feasible. Product quality could be well controlled (low moisture gradient and low aflatoxin concentration after drying). Air flow rate should be around 2.0-2.5 m(3)/min-m(3) of corn and initial moisture content should be limited to be not higher than 19 % wet-basis. Intermittent ventilation during the day consumed less energy compared to continuous ventilation. A mathematical near-equilibrium drying model including heat and moisture from respiration and development of aflatoxin was developed. It was found that the model gave fairly good prediction of moisture and temperature gradients especially at the bottom of corn bed. Effect of heat from respiration was significant when initial moisture content of corn was high. Simulation results under various conditions were used to construct four quadrant charts. In constructing this chart, dry matter loss, aflatoxin concentration and final moisture content were limited to 0.5 %, 50 ppb and 14 % wet-basis respectively. These charts are expected to be useful for designers to reduce calculation time and to help select appropriate design and operating parameters such as initial moisture content, height of corn bed and air flow rate, etc. |
