CFD analysis of an evaporator in diffusion absorption refrigeration systems using helium as an auxiliary gas.

This paper details a computational fluid dynamics (CFD) simulation applied to the evaporator of a diffusion absorption refrigeration (DAR) system, using a water-ammonia mixture as the working fluid and helium as an auxiliary gas. Although hydrogen is traditionally preferred in DAR systems due to its favorable properties for separation in the absorber and enhanced mass transfer, its high flammability imposes safety constraints. Therefore, to address these concerns and improve system efficiency, helium is considered a safer alternative, particularly for high-power units. Moreover, building on a previously validated numerical model of the evaporator in CONVERGE CFD with the Reynolds-Averaged Navier-Stokes (RANS) approach, this study investigates the evaporator’s behavior across operating pressures of 10–25 bar, aiming to determine the optimal pressure when helium is used as the auxiliary gas. A series of simulations were performed for total pressure values ranging from 10 to 25 bar. The findings indicate that lower total pressures result in reduced evaporation temperatures across the evaporator, leading to improved evaporation and heat transfer efficiency. Notably, a total pressure of 10-12 bar is identified as optimal for maximizing cooling capacity when helium is used as the auxiliary gas in a water-ammonia DAR system. These findings underscore the potential of helium in solar-driven absorption–diffusion refrigeration systems, despite its scarcity and high cost, particularly under the limited thermal input characteristic of renewable sources. The results indicate that helium’s unique properties make it an attractive option for enhancing both safety and efficiency, with the DAR system performing noticeably better when operated with he