循环热风低温干燥系统湿空气冷凝特性分析

基于能量梯级利用热力系统耦合理论，集成了一种适合热敏性农副产品烘干的新型空气干燥循环系统，系统可得到热敏性干燥产品，同时回收湿空气冷凝废热用于有机朗肯循环(ORC)系统对外做功。对关键部件湿空气冷凝器建立传热传质数学模型并经实验验证，考察了关键操作参数对系统脱水速率及节能效果的影响。结果表明，湿空气湿度是影响该系统凝水和节能的最关键参数，该系统凝水及节能特性均随湿空气湿度提高而改善；当干燥箱出口湿空气含湿量温度一定时，新型空气干燥循环凝水量主要受到干燥箱出口空气流量的影响，系统的凝水量和换热量均随湿空气质量流量增加先增加后降低，在0.10~0.15 kg/s出现极大值；系统净输出功随ORC底循环蒸发温度提高显著增加。本系统下的热敏性农副产品烘干建议选择低空气流速、低烘干温度，推荐的ORC底循环蒸发温度为313~323 K。

Analysis of condensation characteristics of moist air in low temperature drying system using circulating hot air

Air drying is one of the widely used farm products process technologies. Due to the thermal-sensitivity performances of the farm products, the low operation temperature makes waste heat recovery from the drying chamber exhaust wet air become difficult, and the conventional open air-drying process is energy consumption. A novel closed air drying system is proposed through integrating the top air drying cycle and a bottom organic Rankine cycle (ORC). After verified the mathematical model of the wet air waste heat recovery through the wet air condenser, condensed water mass flow rate and the energy saving characteristics of the proposed system were investigated through analyzing the key parameter influences on the overall performance indices. The results showed that under the operation condition in this study, compared to the wet air inlet temperature and mass flow rate, increasing the relative moisture content in the wet air improved the condensed water mass flow rate and heat exchanged substantially. Also the maximal value of mass flow rate of condensed water was obtained with the optimal wet air mass flow rate at 0.10~0.15 kg/s. The overall net power output of the system increased prominently as both the dew point temperature of the drying cabin outlet wet air and the evaporation temperature of the bottom ORC increased. Therefore, for the conventional heat-sensitive farm products drying process, the low drying temperature and high dew point temperature for the wet air at drying chamber outlet, and the evaporation temperature at 313~323 K of the ORC were recommended.