Numerical Simulation And Performance Study Of Absorption Heat Pump Based On R134a-DMF Working Fluid

In this thesis,relying on the major scientific and technological innovation project of Shandong Province--"Research on Solar and Electricity Driven Absorption Compression Heat Pump and Its Key Technologies",aiming at the R134a-DMF absorption heat pump driven by solar energy,an experimental platform with a design cooling capacity of 11.25 k W was built,and the experimental platform was run and the operation results were analyzed.A simple plate heat exchanger model was built based on Aspen Plus software,and the thermal property data of R134a-DMF binary solution with different refrigerant and absorbent ratio were collected.The thermal property parameters of refrigerant R134 a and saturated water were collated based on Refprop9.0 software.The correlation fitting of thermal properties was carried out by Matlab software.The mathematical model of each component of the R134a-DMF absorption heat pump was constructed on the basis of mass conservation and energy conservation.R134a-DMF absorption heat pump simulation model was built on the basis of thermal-physical correlation and mathematical model,and the operation results of the model under different variables were analyzed.The main research contents of this thesis are as follows:(1)An experimental platform for R134a-DMF absorption heat pump unit was built.According to the calculation and theoretical analysis of the key point temperature and pressure of each component of the R134a-DMF absorption heat pump unit under the condition of heat source temperature of 85 ?,the heat exchange area of each component is obtained,and the experimental platform of the absorption heat pump unit is built and operated.The operation of the unit at a heat source of 85°C is checked whether it meets the design standards,and the influence of the heat source temperature and the throttling device in the refrigeration cycle on the performance of the heat pump unit is analyzed.The COP of the unit increases from 0.344 to0.479 when the heat source temperature increases from 65? to 85?.The COP increases about1.09%-3.07% when the heat source temperature increases by 1?.The EEV1 opening of the electronic expansion of the throttle device in the refrigeration cycle increases from 80 to 260,and the COP of the unit decreases from 1.0448 to 0.6025,and the decreasing speed of COP of the unit slows down gradually with the increase of the opening.(2)Based on Aspen Plus software and NRTL physical property method,a simulation system of brazed plate heat exchanger for heat exchange parts of absorption heat pump unit was established.The input flow temperature and pressure were set through the simulation program to change the heat source/cold source temperature of brazed plate heat exchanger.Collect the density,enthalpy,kinematic viscosity,constant pressure specific heat and other thermophysical data of binary solution when the ratio of refrigerant R134 a and absorbent DMF is 300:200,250:250,200:300,and use the cftool toolbox of Matlab to perform correlation fitting on the thermophysical parameters;Based on Refprop9.0 software,the data of pressure,density,enthalpy,specific heat,thermal conductivity,kinematic viscosity and other thermal physical parameters of refrigerant R134 a saturated liquid phase,saturated gas phase and saturated aqueous solution were extracted under the condition of temperature as a variable.The same method is used to fit the correlation of saturated gas phase and saturated liquid phase of refrigerant R134 a with R134a-DMF binary solution.The polynomial least square method is used to approach the correlation of saturated water with 1Stops software.(3)The mathematical models of the generator,absorber,condenser,evaporator and solution heat exchanger of the R134a-DMF absorption heat pump unit are established according to the principles of mass conservation and energy conservation.Based on the mathematical model of the heat exchange equipment,the thermodynamic calculation process of each component of the heat pump unit is designed,and the simulation program flow for exploring the coefficient of performance of the heat pump unit is given.The value of each key point of the heat pump unit under the condition that the heat source temperature is 85 ? is co MPared with the value of the measurement point of the experimental platform under the condition to judge whether the simulation program is accurate.(4)Based on the accuracy of the simulation program,the effects of generator outlet temperature,condenser cooling effect and chilled water outlet temperature on the performance of the heat pump unit are analyzed.For R134a-DMF(3:2),R134a-DMF(1:1)and R134a-DMF(2:3),when the concentrated solution temperature at the outlet of the generator increases by 1?,the AVERAGE COP and cooling capacity increase by 0.85%,0.39% and 0.42% respectively.As the cooling effect of the condenser becomes stronger,the COP of the unit gradually increases but the growth rate gradually slows down,and the COP also gradually increases with the increase of refrigerant R134 a.The COP of R134a-DMF absorption heat pump system increases with the increase of evaporation temperature,and the greater the proportion of refrigerant in R134a-DMF binary solution,the greater the COP of R134a-DMF unit at the same temperature.According to the simulation results,it is found that there is a small amount of absorbent DMF in the refrigerant at the generator outlet of the heat pump unit,and it is proposed to improve it by adding a distillation unit.