Characteristics Analysis And System Simulation Of Absorption Refrigerating System Driven By Low Grade Heat Source

Absorption refrigeration is a refrigerating type, which is driven by waste heat, solar and other low-grade heat source. The commonly working medium, such as LiBr/H2O, NH3/H2O and R134a/DMF are all environment-friendly refrigerants. The consumption of central air conditioning system accounts for a large proportion in building energy consumption. And the use of absorption refrigeration system driven by low-grade heat source has a very important significance to save conventional energy and protect the natural environment.We select thermodynamic properties of calculating binary working fluid in Aspen Plus combined with literature and manual data. ELECNRTL property method is used in Lithium bromide aqueous solution and Peng-Rob physical methods are used both in ammonia solution and R134a/DMF binary solutions. The results obtained by Aspen Plus are compared with the experimental data in literature. The results show that the maximum error was2.92%,2.91%and8.8%respectively to the three different working medium.Based on the method of physical properties, we analyze three kinds of working medium circulation characteristics. The results show that the P-x-y curve of R134a/DMF is similar to that of NH3/H2O. A discernible DMF gas composition can be found in the phase diagram and a distillation unit in circulation of R134a/DMF is needed.With the help of Aspen Plus software, the three working fluid circulations are established, and their simulation analysis are following. For lithium bromide absorption refrigeration system, the effects of generating temperature, condensing temperature and solution concentration on the system are analyzed. The rates of minimum cooling water on different condensation temperatures system are calculated and the way of cooling water, which is series or parallel are determined. When the condensation temperature is between42and45℃, the cooling water way is used in series. When the condensation temperature is between38and42℃, the cooling water way is in the form of parallel. For ammonia absorption refrigerating system, the effects on system performance of the distillation column reflux ratio and bottom temperature of rectifying are analyzed. Considering both the rectification effect and the performance of the system, the reflux ratio between0.4and0.6is more appropriate. When the gas discharge in the range is0.065to0.15, the system COP is much higher. For the R134a/DMF, the effects on the reflux ratio and the quality of R134a in the mixed solution are analyzed. The range of reasonable reflux ratio is between0.5and0.7. Within the range of deflation ratio from0.17to0.39, the system COP is much higher. When R134a is completely absorbed in absorber lower temperature of the cooling source is need. With the increasing of the gas phase fraction of absorber export solution, the requirement of the cooling source temperature is reduced. The applicability of three refrigerants are analyzed and compared. It is showed that R134a/DMF deflated range is the largest and fluctuation scope of generating temperature is the highest which is31.36℃. The lowest generating temperature is about62.9℃. The fluctuation scope of generating temperature of LiBr/H2O is the lowest, which is about6.3℃, but its COP is the highest. The COP of NH3/H2O is the lowest.Based on the solar energy resource and the relationship of solar radiation intensity and building load, the type of solar collector which matches the corresponding temperature of working medium are analyzed. Lithium bromide and ammonia absorption refrigeration system are more suitable for vacuum tube collectors, and R134a/DMF absorption refrigeration system is more suitable for flat-plate collectors for the lower generating temperature.