闭式跨临界CO_(2)热泵烘干系统最优工况研究

Optimal Working Conditions of Closed Transcritical CO_(2) Heat Pump Drying System

目的对跨临界CO_(2)热泵驱动的闭式干燥系统展开理论研究,得到CO_(2)闭式热泵中最优工况的计算方法和原理。方法通过建立CO_(2)循环与空气循环热力学耦合的数学模型,计算干燥循环中空气的温度、焓值、相对湿度、含湿量,以及跨临界CO_(2)热泵系统中工质的温度、压力、焓值等参数。通过调整冷凝干燥后空气温度,以热泵烘干系统的COP为评价依据,探究空气循环与CO_(2)热泵循环的耦合机理。结果获得了CO_(2)循环系统最优排气压力随闭式空气循环系统在不同工况下的变化规律,并基于所建立的计算程序,获得了典型工艺参数下的热泵系统的热力学参数,为关键设备(风机、换热器、压缩机等)选型及系统控制方法提供了理论依据。结论研究表明,在CO_(2)热泵冷却器出口状态为临界状态时,系统的COP达到最优。

The work aims to conduct a theoretical study on the closed drying system powered by transcritical CO_(2) heat pump and obtain the method and principle of calculating the optimal working conditions of CO_(2) closed heat pump.A mathematical model of thermodynamic couple between CO_(2) cycle and air cycle was established.Based on the model,the temperature,enthalpy,relative humidity and moisture content of air in the drying cycle were calculated and the temperature,pressure and enthalpy of working medium in transcritical CO_(2) heat pump system were figured out.The coupling mechanism between air cycle and CO_(2) heat pump cycle was explored by varying the air temperature after condensation and drying and taking COP in the heat pump drying system as the evaluation basis.The optimal CO_(2) discharge pressure in the closed drying system under different working conditions was obtained.Based on the established calculation program,the thermodynamic parameters of heat pump system under typical process parameters were obtained,providing a theoretical basis for the selection of key equipment(fans,heat exchangers,compressors,etc.)and system control methods.The research shows that the COP of the system is optimal when the outlet of CO_(2) heat pump cooler is at critical state.