Performance Studies On NH₃-H₂O Absorption Refrigeration HGAX Cycles Using Low Temperature Exhaust Heat

Traditional single-stage NH3-H2O absorption refrigeration system consumes a large number of utilities. The cop of of which is low. Two-stage NH3-H2O absorption refrigeration system need more devices, larger volume, more steel consumption than the single-stage system. This is more complicated. In order to improve the cop of the absorption refrigeration system, some domestic scholars have proposed a single-stage ammonia GAX absorption refrigeration cycle. However, the GAX cycle need high temperature heat source. Its cop is low when the heat source temperature is not enough high. That is to say, this will be out of work in condition of low temperature exhaust heat. Under such background, there is of necessity to upgrade the equipment. In this paper, a detailed analysis of the ammonia-water HGAX absorption refrigeration cycle from the viewpoint of the first law of thermodynamics and the second law of thermodynamics respectively on the basis of previous studies,. Then the paper sets up a mathematical model for the cycle, including finding out the suitable working condition and the influence of the initial parameters variables. Finally, the paper comes up with the main advantages of the HGAX cycle and applies the model in practical. The specific works are as follows.The paper studies the thermodynamic properties of the refrigerant, according to ammonia water solution saturated vapor and saturated liquid state equation. Then write computational programs of ammonia water thermodynamic properties by VB software. The results accord well with the literature conclusion.The paper establishment a mathematical model of the HGAX cycle and preparation of a computer program to calculate the thermodynamic parameters of each state point and the heat load of each device based on the basic principles of the ammonia water absorption refrigeration cycle, and calculate the heat balance and the cop of the system. According to the status parameter to analysis the performance of HGAX cycle, the heat source temperature, the refrigeration temperature, the cooling water temperature and the intermediate pressure have a significant effect on the cop of the cycle. We compared the cycle with the conventional GAX cycle, general single-stage cycle and the middle pressure double-effect cascade cycle. Even on the low temperature heat source, the coefficient of performance of the HGAX cycle is significantly higher than the traditional cycle. This paper introduces pinch point analysis to analyze the NH3-H2O absorption refrigeration system. The method can recover maximum internal heat form the streams. So using the new method to analyze the NH3-H2O absorption refrigeration system could increase its cop.In this paper the GAX and HGAX absorption refrigeration cycles are studied and compared from the viewpoint of both first and second law of thermodynamics. Exergy analyses were performed in order to calculate the total exergy destruction rate within the cycles and also reveal the contribution of different components to the destructions. In order to evaluate the efficiencies of the cycles at different working conditions, particularly from the viewpoint of the second law, parametric studies were also performed.