Economic analysis of two stage dual fluid absorption cycle for optimizing generator temperatures

Abstract

Economic analysis of a flat plate solar collector for operating a two stage dual fluid absorption cycle has been performed to optimize the generator temperatures. The dual fluid absorption cycle uses a LiBr–H 2O solution in the first stage, while ammonia refrigerant with some suitable absorbent is used in the cycle at the second stage. The absorbents selected to be used with ammonia at the second stage are water, lithium nitrate and sodium thiocyanate. For the purpose of comparison, the analysis has also been done with an evacuated type solar collector, biogas and LPG as the sources of energy in the dual fluid cycle. Comparisons of the optimum generator temperatures, optimum values of coefficient of performance (COP) and the minimum operating costs obtained for the dual fluid cycle have been done with those of the single stage absorption cycle. The dual fluid cycle using NH 3–H 2O at the second stage when operated by the flat plate solar collector shows very good performance and becomes quite economical, especially at low evaporation and high condensing temperatures. Eventually, the single stage cycle, due to certain limitations in it, ceases to operate at such conditions. The optimum generator temperatures, optimum COPs and minimum operating costs obtained for a wide range of operating conditions have been exhibited graphically. Also, mathematical relationships have been developed for finding the optimum generator temperatures in the cycle at the second stage of the dual fluid system.