Optimization Study Of Solar Powered Single-double-effect Coupled Absorption Refrigeration System

The single-double-effect coupled absorption refrigeration system can adapt to a wider range of heat sources by switching between single-effect operation mode,coupled operation mode and double-effect operation mode,which can improve the efficiency and stability of absorption refrigeration system by improving the problem of low effective utilization of high-temperature heat sources by single-effect system and unstable operation of double-effect system at lower heat source temperature.However,due to the relatively complex structure of the system,the influence law of parameter changes and operation mode changes on the system performance is more complex.In order to further analyze the influence law of parameter changes and operation mode changes on the performance,the coupled system is simulated and analyzed.This paper uses Aspen Plus software to build the system simulation model,and ELECNRTL physical property method is selected as the physical property calculation method of lithium bromide solution,and the finite Wegstein convergence method is adopted as the basic method of system simulation calculation for the system circulation process.The parameters such as driving heat source conditions,solution heat exchanger temperature difference,dilute solution concentration and solution distribution ratio of parallel process are optimized for single-and dual-effect operation modes;the changes of system performance of single-and dual-effect coupled absorption refrigeration system switching between the three operation modes and the influence law of dilute solution distribution ratio changes on the performance of coupled operation mode are further analyzed.Through simulation analysis,it was found that: the load and heat transfer area of each component of the series and parallel process in dual-effect mode differed to different degrees,and the total heat transfer area of the series process was 8.56% larger than that of the parallel process;the solution circulation multiplier of the parallel process was only about half of that of the series process,so that the performance coefficient,thermodynamic perfection,and efficiency of the parallel process were higher than that of the series process.And optimize the analysis of the heat source flow and temperature changes on the system,in the evaporation temperature of 5?,cooling water temperature of 30? working conditions,determine the relative flow rate of the heat source between 80% ? 120% of the system performance is better;system single-effect operation mode heat source temperature at 110? ? 125?,double-effect operation mode heat source temperature between 165? ? 175? performance is better.The optimization coefficients were used to optimize the system solution heat exchanger temperature difference,dilute solution concentration,parallel process solution distribution ratio and other parameters.When the high temperature solution heat exchanger temperature difference is between 8??20? and the low temperature solution heat exchanger temperature difference is between 10??17?,the system operation effect is better;considering the solution crystallization problem,the system performance is better when the dilute lithium bromide solution concentration is between 58%?61%;the parallel process high pressure generator solution distribution ratio is better between 50%?65%.The overall performance of the system is more stable when the heat source temperature is between 140??160? and operated in coupling mode.In this case,the instantaneous cooling capacity drop rate is 44% when the system is switched from single-effect operation mode to coupled operation mode,which is about half of the fluctuation of instantaneous cooling capacity than the direct switching to dual-effect operation mode;compared with the single-effect operation mode,the overall COP is increased by 8%.The effect of dilute solution distribution ratio on the performance of coupled operation mode shows that the effect of dilute solution distribution ratio on the cooling capacity and COP is opposite,and the closer the dilute solution distribution ratio of coupled operation mode is to 5:5,the better the comprehensive operation effect is.Further analysis of the calculation of the occurrence temperature of the high pressure generator under different pressure and bleed range,it is determined that the heat source temperature required for most cases of the series and parallel process system in the dual-effect operation mode is above150°C.It is recommended that U-tube vacuum collectors,heat pipe type collectors,Fresnel type and slot parabolic collectors are more suitable.