Thermodynamic Analysis Of An Ammonia-Water Solution Cross-Type Absorption-Resorption Heat Pump System

Global environmental problems such as ecological deterioration,climate warming and ozone layer destruction have aroused widespread concern of human beings.Developing new energy,reducing the use of ozone depleting substances（ODS）and recovering waste heat resources is of great significance to protect the environment.Conventional absorption heat pumps（AHP）can be driven by low-grade heat sources and have great potential for waste heat recovery.One of its disadvantages is that the operating pressure is high,which increases equipment investment and brings many security issues.The absorption-resorption technology can reduce the pressure of the system significantly without decreasing the heating temperature,but the traditional ammonia-water absorption-resorption heat pump has a low COP,which limits its practical application.In this paper,an ammonia-water solution"cross-type"absorption-resorption heat pump is proposed to improve the performance,and theoretical research in ARHP and ARHT applications is conducted.According to the Schulz ammonia-water state equation,the calculation model of the solution physical property parameters at the inlet and outlet of each equipment in the absorption-resorption heat pump is established.The mathematical model of the solution cross-type system and the traditional system is established,and the corresponding thermodynamic calculation program is programmed.Compared with the simulation data in the literature,the physical property calculation model is in good agreement.The mathematical model constructed in this paper is utilized to calculate the absorption-resorption heat pump in literature.The results show that the maximum relative differences of COP based on ARHP and ARHT are 2.56%and2.88%,which verify the accuracy of the mathematical model.The variable working conditions of the ammonia-water solution cross-type ARHP system are analyzed.Compared with traditional ARHP,the optimal low-pressure(P_L,optimal)is lower,and the operating temperature range is larger:the operating temperature range of the absorber and resorber is increased by 1℃,and that of the desorber is increased by 2℃.Besides,the Q_res of the proposed system and the Q_abs of the traditional system contribute greatly to COP,and the heat exchange of SHX1 is much more than that of SHX2.In general,the gas-emission range of the generator and the mass transfer potential of the resorber in the proposed system are larger.Based on the working conditions selected in this paper,the COP is increased by 8.1%and 6.4%,respectively,compared with the traditional system and the solution balanced-type system.The variable working conditions of the ammonia-water solution cross-type ARHT system are analyzed.Compared with traditional ARHT,the optimal low-pressure(P_L,optimal)is higher.TheΔx of the generator and the resorber increases significantly,which proves that the ARHT system still has a larger gas-emission range and mass transfer potential.The heat output Q_abs of the absorber,heat input of the generator and desorber(Q_gen and Q_des)are all reduced,but the latter dominates,which is the direct reason for COP value higher than that of the traditional system.Based on the selected working conditions,the COP is increased by 19%at most,and the corresponding gross temperature lift is 25℃.In general,the solution cross-type ARHT system has advantages in some working conditions.