Experimental And Simulation Study On Ammonia-water Absorption Refrigeration

With the implementation of energy conservation and emission reduction policies and the ban on Freon refrigerants,the unique advantages of absorption refrigeration unit have gradually appeared.The refrigeration unit can absorb low-grade energy such as flue gas waste heat for refrigeration,which can improve energy utilization rate.In addition,the refrigerant working pairs have the advantages of being green and pollution-free.In many absorption refrigeration systems,the refrigeration temperature of the ammonia-water refrigeration unit can reach-60°C,but the refrigeration system has the disadvantages of complicated equipment,large floor area and low COP.How to overcome these disadvantages becomes an urgent problem.In this paper,the state equations of Schulz ammonia-water system was solved firstly,and Matlab was used to program,which can calculate the state parameters?entropy,enthalpy,specific volume?and phase equilibrium parameters of the ammonia water system.According to different solution conditions,11 kinds of calculation programs were compiled,and the program was compiled as computing interface,which is convenient for quickly calculating the state parameters of the ammonia-water system in different states.The researchs showed that the program calculation results were more accurate,which layed a foundation for the establishment of distillation tower model and refrigeration system model.According to the rectification principle,the gas phase tray efficiency?EMV?was also introduced to establish a mathematical model of a non-equilibrium distillation column.Considering the influence of distillation effect on the whole refrigeration cycle,the calculation program of distillation column was compiled into the mathematical model of ammonia-water absorption refrigeration system.The refrigeration system model was used to calculate the state parameters of each point,equipment heat load and COP?ECOP?,and compared with the state parameter of the single-stage ammonia water absorption refrigeration system with a cooling capacity of3kW.The influences of cooling water temperature,cooling temperature,reflux ratio and distillation ratio on the refrigeration system was analyzed from"quantity"and"quality"aspects of energy.It is found that the changes of working conditions will affect the distillation effect and lead to different degrees of change in COP and ECOP.A single-stage ammonia-water absorption refrigeration cycle test-bed was set up to record the dynamic change process of temperature at each points during the period from start-up to steady-state operation.The process is divided into three phases:warm-up phase,operation phase,and stable phase.The temperature values of 8 groups at each point under steady-state conditions were measured,the heat absorbed and released by the experimental system was calculated,and COP and ECOP of the system were obtained.Compared with the simulation results of the refrigeration system model,it is found that the experimental values were basically consistent with the simulation values,which showed that the refrigeration model can be used to calculate and analyze the actual refrigeration cycle process.In order to improve energy efficiency,the mathematical model of the hybrid system of phosphoric acid fuel cell and pressurized two-stage absorption refrigeration was established.The COP of the two-stage refrigeration cycle decreased with the increase of the ambient temperature and increased with the increase of the compression ratio.The effects of working pressure,working temperature and electrolyte thickness on phosphoric acid fuel cell were studied.The influence of current density on the equivalent output power(P_sys)and efficiency(?_sys)of the whole hybrid system was analyzed.It is found that with the increase of current density,Psys increased first and then decreased,so there is an optimal current density value,while?_sysys decreased with the increase of current density.At the same time,the optimization intervals of Psys and?_sysys were P₁<P_sys<P_maxax and?₁<?_sys<?_max.Introducing the thermal coefficient of electric power quality?COP2?,It was found that under a certain current density,although the equivalent output power and efficiency of the hybrid system were slightly reduced,the COP₂ of the refrigeration cycle was higher than that of the conventional condition?thermal power generation?.Therefore,the hybrid refrigeration system is superior to the conventional two-stage refrigeration system,and has better refrigeration performance and energy-saving effect.