Performance Optimization Simulation Of Ammonia Water Absorption GAX Heat Pump Recovering Rectification Heat

The gas-driven ammonia water absorption heat pump system can extract heat from low-temperature heat sources such as air,which has certain advantages over gas direct combustion heating.It has positive significance for improving energy utilization and adjusting energy consumption structure and so on.Under certain working conditions,there is a feature that the ammonia-water absorption heat pumps is the presence of temperature overlap between the absorber and generator,part of absorption heat,therefore,is recovered in Generator-Absorber heat exchange to reduce the generation heat for improving the performance of system.The GAX effect becomes less obvious or even fails when the evaporation temperature decreases or the cooling water temperature increases.The quantity and quality of rectification heat monotonically increases at same time.When the GAX effect becomes less obvious or even fails,one approach to improve the performance of ammonia water absorption GAX heat pump system is to recover rectification heat.Therefore,the theoretical study on the ammonia water absorption GAX heat pump system that recovers the rectification heat is conducted in this article.Firstly,based on MATLB software,the Schulz equation is programed to calculate the parameters of the ammonia solution.By comparing with the relevant literature data,the maximum relative errors of pure ammonia vapor phase and liquid phase enthalpy values are0.27%and 3.06%,respectively,and the maximum relative errors of ammonia solution gas phase and liquid phase enthalpy values are 0.05%and 2.7%,respectively.It is verified that the accuracy of the program.The mathematical model of the heat pump system is established according to the components and circulation characteristics of the ammonia water absorption GAX heat pump system that recovers rectification heat.Based on the Schultz equation program and the mathematical model,the calculation program of the heat pump system is written.On this basis,the numerical simulation of the ammonia absorption GAX heat pump systemfor recovering rectification heat is carried out.Compared with the primary single-stage ammonia water absorption heat pump system,the internal heat recovery capacity of the system is stronger and the performance coefficient is higher and the COP of the ammonia water absorption GAX heat pump system that recovers rectification heat is increased by up to 10.9%under the disscuss conditions.The internal heat recovery analysis results show that the enthalpy of the stronger solution at the generator inlet can be increased and the generator heat load can be reduced by using the method of using total strong solution to recover absorption heat after extracting rectification heat.However,it causes rectificator outlet strong solution temperature T₄to rise,which limits the recovery of absorption heat in the solution cooled absorber to a certain extent.In order to further improve the internal heat recovery capacity of the system,the solution splitting ammonia water absorption heat pump system is proposed.The strong solution at the outlet of the water-cooled absorber is split to recover absorption heat and rectification heat respectively.Since the solution split ratio K has an important influence on the intenernal recovery of the system,under certain working conditions,the selection range of the solution split ratio K and the value of the optimal solution split ratio K_op are analyzed.The solution splitting ammonia water absorption heat pump system is analyzed under variable conditions and the effects of evaporation temperature,cooling water temperature and generation temperature on the optimal solution split ratio K_op are analyzed.The results show that the optimal solution split ratio K_opdecreases with the increase of evaporation temperature and generation temperature.The optimum split ratio K_op also increases with the increase of cooling water temperature.Compared with the method of using total strong solution to recover absorption heat after extracting rectification heat,more heat is recovered by strong solution when using solution split method and the system COP is higher.When the temperature difference between the evaporation temperature and the condensation temperature is large,the advantage of the solution split method is more obvious.Compared to the ammonia water absorption GAX heat pump system that recovers rectification heat,the COP of the the solution splitting ammonia water absorption heat pump system is increased by up to 9.2%under the disscuss conditions.