The modelling and potential applications of a simple solar regenerated grain cooling device
G. R. Thorpe
Postharvest Biology and Technology, Volume 13, Number 2. April 1998 , pp. 151-168.
1998
บทคัดย่อ
Cooling stored grains is an effective method of slowing the growth of populations of pest insects and maintaining desirable properties of the grains, such as seed viability. In temperate and sub-tropical climates, ventilation or aeration with ambient air at night usually results in reducing the wet-bulb temperature of the intergranular air, and this has a beneficial effect on storage. However, the relative humidity of ambient air at night is usually high, and this limits its cooling capacity. This paper describes a device that reduces the humidity of ambient air almost isothermally, and which therefore enables grain to be cooled to lower temperatures than those attainable using ambient air. The grain cooling device is simple to build using readily available materials, and requires only sheet metal working skills for its fabrication. Furthermore, the energy consumption of the device is very low and it uses solar energy to regenerate beds of desiccant. A mathematical model of the device is presented which enables the heat and mass transfer processes that occur in the device to be studied in detail. The model is validated against previously published experimental results. It is indicated that when operating in a subtropical climate the cooling device is capable of reducing the wet-bulb temperature of ambient air from about 17.3°C to about 12.3°C. Under these conditions the cooling device provides typically 50 times more cooling energy than electrical energy consumed. The model demonstrates that the degree of grain cooling that is possible decreases with increasing air flow rate, but the quantity of grain that can be cooled increases. The model is used to explore the effects of aerating grain with air conditioned by the solar cooler on insect population growth, the rate of pesticide decay and seed viability.