Performance Analysis Of A Novelrefrigeration Or Heat Pump System Based On Physico-Chemical Thermal Effect

The traditional physical phase change-based vapor compression refrigeration has a small coefficient of performance and a small amount of refrigeration per unit mass,which cannot be applied to the cooling of high heat flux devices.A novel refrigeration cycle based on physico-chemical thermal effect has been presented in this paper aiming to tackle with above problems.The system adopts an organic substance ammonium carbamate which undergoes endothermic decomposition with high enthalpy change as the refrigerant,and uses an inert liquid ethylene glycol as the working liquid which is easy to dissolve ammonium carbamate and has a high boiling point.The refrigeration is achieved by the high endothermic effect of the ammonium carbamate decomposition reaction and the decomposition product ammonia and carbon dioxide vaporization in the endothermic reactor.At the same time,a large amount of heat is released from the synthesis reaction of ammonia and carbon dioxide in the exothermic reactor to construct the refrigeration cycle.The vertical tube falling film process of ethylene glycol liquid has been simulated and the design of the experimental device was optimized.An experimental platform for the falling film decomposition reaction of ammonium carbamate has been established.The reaction and conversion rate of the falling film decomposition reaction of the ammonium carbamate-ethylene glycol solution has been investigated.On this basis,a model of the refrigeration system based on physico-chemical thermal effect has been constructed,and the system has been analyzed and structurally optimized.The basic flow of the new refrigeration cycle based on the thermal effect of materialization has been discribre.The effects of different working conditions on the thermal performance of the refrigeration cycle have been analyzed and compared with a conventional single-stage vapor compression refrigeration cycle.Theoretical analysis shows that the coefficient of performance of the ideal cycle can reach 7.16.The effects of the parameters such as endothermic temperature,exothermic temperature,intermediate pressure and intermediate temperature on the thermal coefficient and compression ratio of the system have been calculated and analyzed theoretically.The endothermic and exothermic temperature difference of the cycle should not be higher than40°C.There are different optimal intermediate pressures that maximize the coefficient of performance of the cycle,which is P_mopt.The optimum intermediate temperature is the equilibrium temperature of the ammonium carbamate reaction at the optimum pressure.At the same time,the heat pump cycle is proposed for the recycling of low-grade waste heat.The effects of different absorption and exothermic temperatures,intermediate pressures,intermediate temperatures,and working fluids on the cycle were analyzed.Compared with the traditional vapor compression industrial waste heat heat pump,the higher the heat absorption temperature and the larger the heat absorption temperature difference,the larger the thermal coefficient,and the closer the cycle is to the reverse Carnot cycle.The heat pump cycle is suitable for applications with an input temperature of 30 to 50°C and an output temperature difference of more than 40°C.The endothermic reactor is intended to adopt a falling film heat exchanger with small pressure drop and high heat transfer coefficient.The experimental platform of the falling film decomposition reaction of ammonium carbamate and the experimental process of falling film decomposition reaction have been introduced.At the same time,a numerical simulation study on the falling film process of the ethylene glycol liquid is needed.The effects of distribution gap,solution flow rate and pressure on the film falling process have been analyzed by simulation.The simulation results show that the solution flow rate and the distribution gap have great influence on the flow of liquid membrane.For different liquid flow rate,there are different distribution gap to make the liquid film flow uniformly and stably.However,the pressure has little effect on the falling film process.For the needs of the experiment,the distribution gap designed for the experimental device is 2 mm.Using the experimental platform,the decomposition of ammonium carbamate in the falling film process has been studied experimentally.In the experimental conditions,the liquid film is in laminar flow state?Re=1²0?,and the decomposition rate of ammonium carbamate reaches 0.0045 kg/?m²·s?.The effects of solution concentration,solution inlet temperature,average solution flow rate,hot water inlet temperature,pressure and other parameters on the decomposition rate and conversion rate of ammonium carbamate in the solution falling film process have been studied experimentally.The study provide experimental data support for the establishment of the system model.Referring to the results of cyclic thermal analysis and falling film decomposition reaction experiments,a refrigeration system based on physico-chemical thermal effect has been established using Aspen plus process simulation software.Combined with the thermodynamic data obtained from the simulation calculation of the system,the position and the cause of the energy loss and exergy loss of the whole refrigeration system have been revealed by using the chemical process thermodynamics analysis method.Furthermore,it provides the basis for the process improvement and optimization of the whole system.The simulation results show that the performance coefficient of the system is 7.22 and the exergy efficiency is 29.65%.The energy utilization of the system is relatively low,and the system still has a large space for structural optimization and performance improvement.The endothermic reactor,exothermic reactor and throttle valve have the largest exergy loss,accounting for 34.11%,34.08%and 9.34%of the total effective energy loss,respectively,which are the main components of the system structure optimization.The effective energy loss decomposition theory is used to analyze the components.It is pointed out that the avoidable loss of the exothermic reactor is relatively large,about 74.10%,mainly due to the mixing loss of CO2 and NH3 gas and solution,and the heat energy loss of cooling water.The irreversible loss in the reactor is reduced by reducing the temperature difference between the hot and cold fluids,the recovery of waste heat,and the temperature of the mixed gas entering the reactor.