Exergy Evaluation in Grain Drying
In Japan, about 800,000 kl of fuel oil are consumed for drying farm products every year. Consequently, saving energy in the grain drying process has become an important agricultural problem. To reduce the energy consumed in grain drying and to establish a
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Koro Kato
Department of Agricultural Engineering, Kyoto University Kyoto, 606 JAPAN every year in agriculture, Japan is a major oilconsuming nation and most of the oil is imported. Therefore the problem of energy saving in agriculABSTRACT ture becomes important. Since the humidity is high in Japan, heated air dryers are mostly used In Japan, about 800,000 kl of fuel oil are for drying farm products, and 800,000 kl of fuel consumed for drying farm products every year. Conoil are consumed annually for this purpose. Of sequently, saving energy in the grain drying prothis amount, some 450,000 kl are used for drying cess has become an important agricultural problem. To reduce the energy consumed in grain drying and rice and wheat. In general, the measure for energy savings to establish a method of evaluating energy requireconsists of: (1) utilization and development of ment based on exergy, theoretical and experimental new energy or alternative energy sources, studies were carried out. The energy supplied for (2) improvement and development of processes, grain drying is finally converted into the energy (3) utilization of exhaust heat, and of grain moisture concentration difference, and is (4) reduction of total energy by systems analysis. stored in grain. This energy is based on the diffWith regard to energy used for drying farm erence in moisture content of grain compared with products, the following approaches have been surroundings, and is released as heat of wetting studied and applied partially in practice: when the moisture absorption occurs. In this study, (1) the utilization of rice-husks for fuel, we propose a method of exergy evaluation for grain (2) the use of solar energy, and drying, taking into account this energy of moisture (3) the use of atmospheric or exhaust heat, concentration difference. increasing the temperature with heat pump First, we measured the thermal properties such Subsequently, the improvement and development as heat of wetting and equilibrium moisture content of drying processes are necessary, and the estabof rice. The exergy of moist grain can be obtained lishment of a method of energy evaluation for the by integrating the exergy of the equilibrium vapor grain drying process becomes important. The purpressure of the grain moisture. Taking into account pose of this study is to establish a method of the moisture concentration exergy of moist grain energy evaluation for grain drying, especially a and moist air, we investigated the flow and effimethod based on exergy. ciency of energy and exergy of conventional heated For the grain drying process, the energy of air rice dryer.ยท The efficiency of converting supp grain moisture concentration difference has an lied energy to moisture concentration energy (exceimportant significance, because the energy supppting the latent heat of vapor) is 2 to 4% for the lied is finally converted into the energy of grain heated air rice dryers. The efficiency of convermoisture concentration difference and stored in ting supplied energy to moisture concentrat
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