Performance Investigation Of The Gas-fired Air-source Absorption Heat Pump With Flue Gas Heat Recovery For Heating

Developing clean heating technology in northern China is the only way to improve heating efficiency and energy conservation and emission reduction.The air source compression heat pump for heating has the problem of low primary energy efficiency,while the air source absorption heat pump has the advantages of high primary energy utilization efficiency,good heating performance in cold areas,easy to combine with buildings and safety which has been applied more and more.This paper proposed a gas-fired air-source absorption heat pump for heating,and studied its heating performance,heat and mass transfer model,working fluid pair selection and comprehensive performance.The main completed work is as follows:（i）A gas-fired air-source absorption heat pump with a heat of flue gas heat recovery for heating has been proposed.Generator and absorber are vertical falling film heat exchanger,with working fluid pair of R22-DEGDME.The heat transfer and flow mathematical model between variables and the system of heating performance with temperature,absorption temperature,ambient temperature and inlet temperature of heating water has been established;The system test rig was set up,and the heat transfer rate,heating capacity and COP parameters were calculated by mathematical model.The results showed that the COP reaches 1.58 when the ambient temperature was-12℃and the heating hot water temperature is 41℃,and the error between the simulated value and the experimental value of the mathematical model is less than10%.（ii）One-dimensional and two-dimensional heat and mass transfer models of vertical falling film generator and absorbor process were established,and the convective and diffusion terms of two-dimensional energy equation were modified based on the interdiffusion enthalpy transport.The thermodynamic properties of binary solution and steam in vertical falling film process were studied;the influence of different falling film height on temperature and concentration was analyzed;the applicability of the two models were expounded.Based on CFD numerical simulation,the falling film heat and mass transfer process of organic working fluid pair was studied.By establishing VOF multi-phase flow model and writing UDF program of mass transfer at gas-liquid interface,the limitation of traditional evaporation-condensation model applied to two-phase flow was solved.（iii）In view of the toxicity of NH₃-H₂O,the freezing of H₂O-Li Br below 0℃,and the phasing out of CFC refrigerants such as R22,a solution model based on fugidity and activity was established.The process flow of gas-fired air-source absorption heat pump system for district heating was constructed based on the Aspen Plus software,and the thermodynamic performance of two HFCs working medium pairs R134A-DMF and R161-DMF under different operating conditions was simulated,which provided a research method for the development of new environmental efficient working medium pairs.（iv）The comprehensive performance of the system is analyzed.Aiming at the frosting of finned tube in winter,a model of frost layer distribution was established to study the frosting characteristics and frost layer thickness of finned tube under different operating conditions,providing reference for predicting the defrosting time.In order to find the optimal operating condition of the system,the comprehensive evaluation model of energy,exergy,economy and environmental benefits of the system was established.Exergy loss and payback period were selected as the objective function,and NSGA-II technology and TOPSIS decision method were used to optimize the operating condition,and the optimal operating condition was obtained.