Most dryer used in farms is a method for drying the drying material with the hot air generated by the heater as the heater dryer. It makes heat loss by 40∼50% because the some of hot and humid air by the evaporation of the moisture go to outside. To solve this problem, development of the dryer exhaust heat recovery is a necessity. The heat pump dryer which has the waste heat recovery technology has a high efficiency as a dryer using the heat of the condenser and the evaporator. However, there are a system optimization and design technology is insufficient due to the lack of accumulation of technical data through a complete understanding of the experimental model of the system. So, we are going to study the factors that affect the heat pump performance.
It plans to experiment on the temperature and air flow in dryer because performance of the dryer is determined by the amount of heat input to the chamber. A heat source in the heat pump dryer is a condenser and a compressor, in order to increase the temperature of the dryer to increase the opening degree of the expansion valve. Since degree of opening of the expansion valve makes the flow rate of the refrigerant to increase, the high pressure and its saturation temperature increase. The air flow rate is controlled via a blower, the face velocity is measured to the basket in chamber
For an existing dryer electric heater dryer, the experiment was performed according to the set temperature. According to the set temperature increasing, to increase the drying amount and power consumption in a similar growth rete. The result is SMER is about 0.93kg/kWh.
In the heat pump dryer experiment, a drying amount tended to linearly increase with the increase in the opening degree. Heat generation rate increase in condenser as increasing opening of degree, it makes heating amount to increase in chamber inlet. But, power consumption is increased slightly. Because change of power consumption is not large, drying efficiency is increased.
In case of change of air velocity, a drying amount tend to linearly increase with the increase of the air velocity. Because the increase of the air velocity makes heat quantity of the chamber to increase. So, drying amount increase. It has lower growth than the expansion valve opening experiment results. Power consumption dramatically increases. The reason is that pressure loss in the air flow duct is increased substantially in proportion to the square of the air velocity. When degree of opening of expansion valve is 90% and air velocity is 0.64m/s, heat pump dryer has max efficiency. At that time, MER is 1.42kg/h, SMER is 1.57kg/kWh.
When heat pump dryer has maximum efficiency, we estimated the drying tendency which is based on measured absolute humidity change amount at the chamber inlet and outlet. While experiment about 6hours, it showed constant drying rate period. Following P-h charts, we find that power of heat pump dryer is 972W and refrigerant mass flow is 0.0297kg/s. Also, amount of heat of condenser and evaporator is 5.40kW, 4.43kW. So, COPC is 4.58 and COPH is 5.57.