1976 年 37 巻 4 号 p. 613-624
In order to recover the exhaust-air-enthalpy of a heated-air-drier and utilize it for heating the inlet-air, a heat-pump and the exhaust-air-reculation with this pump were used in this method. From the experimental results it was clear that most of the heat lost by the exhaust-air including the latent-heat of vaporization of the grain-moisture was recovered.
(1) Experimental models and plot are illustrated in Fig. 2 and Tab. 2. Five experiments were conducted including an experiment using a heater without heat-pump. From the change of air-state, the flow and balance of the water and energy were obtained, then the energy-efficiency of drying was discussed.
(2) In case of recovering the exhaust-enthalpy by the heat-pump only, [system (A)], it was possible to decrease the enthalpy of the exhaust-air. Tower than that of the inlet-air and discharge it. Therefore it was also possible to pump up the heat of the atmosphere into the system during the first stage of drying-period.
(3) When the recovering-heat-capacity of the heat-pump was lower than the exhaust-enthalpy, the method of using the exhaust-air-recirculation with the heat-pump, [system (C), (D)], was effective. The heat was accumulated in the system, the air-humidity and enthalpy became higher, and because the water is taken out from the system by the evaporator, then the air-humidity became lower. In case of the exhaust-air-recirculation without controlling the temperature, [system (C)], the air-temperature became high, and the drying-rate did not fall although the air-humidity was high.
In case of controlling the air-temperature at 45°C, [system (D)], because of the exhaust-air-recirculation, the drying-rate decreased but and the energy supplied from the heater to control the air-temperature was reduced.
(4) The capacity of the heat-pump used in this test was small, so that the coefficient of performance per watt-consumption was about 2. In case of the heat-pump, without heater, [system (A), (C)], the energy-efficiency of drying was about twice of that of using the heater without heat-pump.
(5) With this method, the energy can be educed, and it is possible to avoid the inconvenience of using oil and the effect of stink on grain. In case of using the exhaust-air-recirculation with the heat-pump, supposing that the condensed-water is within the system, this will be a closed system and the dust will not be scattered. A heat-pump is more expensive than an oilburner. Therefore it is necessary to apply a heat-pump for coolin-gstorage after drying in practice.
(6) In order to increase the energy-efficiency of drying, it is necessary to improve the insulation of the equipment and the performance of the heat-pump as wall as the enlargement of the scale and the usability of the multiple-effect-compression-method. From point of view of fuelcost in Japan now, the energy-efficiency required for drying by electricity will be 4-5 times that of using petroleum.