Theoretical And Experimental Study On Mixed Refrigerants Absorption Refrigeration System Used For Deep Freezing

Under the background of energy and environmental crisis, more and more attention has been put into the development of the absorption refrigeration which is a refrigeration technology driven by low grade thermal energy by the governments and researchers, and the absorption refrigeration is more worthy to be researched and put into the application. Traditional absorption refrigerators, such as LiBr/H2O absorption refrigerator and NH3/H2O absorption refrigerator, etc, have been widely used in the industrial process and living fields, however, they are very hard to be gotten the lower refrigeration temperature due to the properties of the selected working fluids and the cycle configuration, which limits the application of the absorption refrigerator in the deep freezing fields even where has a lot of waste heat to be released simultaneously. In this thesis, mixed refrigerants are used in the absorption refrigeration cycle, and a new mixed refrigerants absorption refrigeration cycle is proposed based on the study of the operating features and rules, and the influence of the configuration on the performance of the absorption refrigeration cycle using mixed refrigerants.The operating characteristics of the absorption refrigeration cycle using mixed refrigerants are analyzed based on the operation principle of the absorption refrigeration cycle and the phase equilibrium properties of the refrigerant-absorbent pairs The results show that it has more constraints when mixed refrigerants are used in the absorption refrigeration cycle, which not only strengthens the interaction constraints among the various operating parameters, but also limits the exertion of the features of different configurations of cycles.A method with constant high pressure of the cycle (generating pressure and condensing pressure) is proposed to be applied through the analysis and optimization of the absorption refrigeration cycle using mixed refrigerants based on the operating characteristics of the absorption refrigeration cycle using the mixed refrigerant, which can simplify the calculation of the cycle, and is helpful to the deep investigation in the influence of the pressure variable on the features of cycles as well as the natures of different cycles. Based on this method the influence of the key operating parameters, such as the composition of the refrigerant-absorbent working fluids, generation temperature, condensing temperature and absorption temperature, on the performance of cycles of traditional flow type and auto-cascade flow type as well as the rules of the influence have been investigate. And from the optimized COP of these cycles, the method of the optimized generating pressure is obtained at the given working condition.Based on the compared results from the performances of different cycles, the inherent mechanisms of the performance improvement of the auto-cascade absorption refrigeration cycle as well as the physical nature of the cascade module in the absorption refrigeration cycle using mixed refrigerants are revealed, and leading effect of the properties of the selected refrigerant-absorbent working fluid on the performance and flow type of the cycle has been validated.A new absorption refrigeration cycle using mixed refrigerants is proposed based on the features of the absorption refrigeration cycle using the mixed refrigerants and the mutual constraint relationships among parameters of the working condition in the actual operation. The new cycle uses two-staged absorption in series to reduce the evaporation pressure of the mixed refrigerants which can ensure the absorption system driven by the low grade thermal energy to obtain the lower refrigeration temperature. By the detailed thermodynamic analysis, the influence of the key parameters on the performances of the new cycle are analyzed and discussed. And the comparison of the thermodynamic performance the traditional absorption refrigeration cycle, the auto-cascade absorption refrigeration cycle and the new absorption refrigeration cycle is conducted under the same working condition.A experiment setup is built for investigating the influence of the key operating parameters on the operating performance of the traditional absorption refrigeration cycle, the auto-cascade refrigeration cycle and the new proposed cycle. The experimental results show that the new cycle can make the refrigeration at lower temperatures under the same working condition, and the refrigeration temperature of the new cycle can reach to-62.3℃with the COP of0.023, when generation temperature is184.4℃, the condensing temperature is18.8℃, and the absorption temperatures of the low-pressure absorber and high-pressure absorber are26.4℃, and28.5℃, respectively.