Double effect and double stage absorption refrigeration cycle thermodynamic study

Absorption refrigeration systems are thermal cycles activated by heat in which the presence of mechanical work is practically negligible. These cycles have become more attractive because they have low electricity consumption, low operating costs, and reduced environmental impact. They do not use gases harmful to the ozone layer and can be integrated into cogeneration systems. These systems show versatility in heat sources, operating solar energy and combustion gases from industrial processes. This study aims to study the performance of double-effect and double-stage absorption refrigeration cycles with different input parameters, using the NH₃-H₂O solution as the working fluid. A thermodynamic model of the cycle was developed by applying the law of conservation of mass and the First Law of Thermodynamics. The model was implemented and solved using the EES software. Operational temperatures of condenser, evaporator, generator and absorber, were varied. The thermodynamic analysis showed that the coefficient of performance (COP) of the cycle was higher for higher evaporation temperatures, lower condensing temperatures and lower absorber outlet temperatures. Considering all the simulations performed, the COP values were between 0.63 and 0.84, with the evaporation temperature being the most influential parameter of the cycle. It was observed that higher condensing temperatures require higher minimum temperatures in generator 2 due to heat transfers limitations that occur internally in the cycle. The influence of each stage of the cycle on the generation of refrigerant vapor varied with the cycle operating parameters, with the first stage being responsible for approximately 70 % of the mass flow generated.