Abstract
In order to further decrease the energy consumption of desiccant wheel dehumidification, the drying medium circulation characteristics of a system combining heat pump drying with desiccant wheel dehumidification were investigated. Moreover, the critical dehumidification conversion mechanism was studied. The analysis of the heat pump hot air circulation system demonstrated that the heat pump system has the best dehumidification efficiency. Through the analysis of the system combining heat pump drying with desiccant wheel dehumidification, the critical conversion point was determined. The critical dehumidification mechanism was further verified using an online temperature and humidity measurement system. To investigate the effect of the critical point on energy consumption and drying quality and develop a drying model, response surface experiments were performed based on the effects of regeneration temperature, drying temperature, and conversion point relative humidity on rehydration, color difference, and specific moisture extraction rate (SMER). The optimal conversion point humidity was determined to be about 46% RH, which was slightly different from the test optimization value of 45.6% RH. In addition, comprehensive optimization and experimental verification of the influencing factors were conducted. The results demonstrated that the R2 values of the three models were greater than 0.98, and the experimental factors had a significant effect on drying quality and energy consumption. When the regeneration temperature was 96°C, the drying temperature was 53°C, the relative humidity of the conversion point was 46%, the color difference was 46.3, the rehydration ratio was 5.75, and the SMER was 1.62 kg/kW·h.
Highlights
Drying agricultural products is an important means for reducing losses and facilitating safe storage
While heat pump drying has found relatively mature applications in the field of agricultural drying [12], the equipment related to desiccant wheel dehumidification is relatively simple. e main problems are due to unreasonable design and high energy consumption, which is associated with the regeneration technology and return air circulation
When the air is at low temperature and has high relative humidity after leaving the evaporator, it is conducive to desiccant wheel dehumidification
Summary
Drying agricultural products is an important means for reducing losses and facilitating safe storage. While heat pump drying has found relatively mature applications in the field of agricultural drying [12], the equipment related to desiccant wheel dehumidification is relatively simple. Either cycle with bypass rate can be mixed at a certain proportion of return air to achieve energy-saving drying [17]; it does not meet the low dew point dehumidification requirements of desiccant wheel dehumidification. Based on the drying requirements of agricultural products and the characteristics of the combined desiccant wheel dehumidification and heat pump drying system, a flexible dehumidification method for a constantly changing air return and fresh air system is proposed, aiming to achieve energy-saving drying of agricultural products
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