Thermodynamic analysis of a modified branched GAX absorption refrigeration cycle

Refrigeration and air-conditioning systems are responsible of an important share of the energy consumed by utility companies. The use of absorption refrigeration (AR) driven by renewable heat or waste heat can help to alleviate this situation, nevertheless AR is characterized by low performance. To improve it, advanced AR cycles have been suggested, such as the branched GAX cycle (BGAX) which uses the temperature overlap between the generator and absorber to increase the coefficient of performance ($\mathrm{COP}$). To further improve the $\mathrm{COP}$, in this study it is proposed to replace the throttling valves with expanders in a BGAX cycle employing ammonia-water as working fluid. With the work recovered, a compressor is driven to increase the absorber pressure. In parallel, a reheat process of the weak solution is added. Through the two-stage expansion with reheating, energy is recovered from both liquid and gas streams, overcoming the low-power-output limitation of liquid expanders. The performance of this modified cycle, called EBGAX, is compared with that of the BGAX cycle. The modeling was done through parametric analysis in the software Engineering Equations Solver (EES). The results showed that the EBGAX cycle could operate at higher temperature lifts than the BGAX cycle, achieving also higher $\mathrm{COP}$ values at lower generator temperatures. A maximum $\mathrm{COP}$ increment of 49.38% was obtained. Moreover, it was observed that the reheating process strongly benefited the cycle performance, especially at low generator temperatures, accounting for up to 18.18% of the $\mathrm{COP}$ improvement. However, this effect was lost as the generator temperature rose.