Influence of the mass diffusivity versus solubility on the performance of ammonia-ionic liquid absorption refrigeration systems

Most of the thermodynamic models present in the literature for absorption chillers consider that the sorption phenomena are completed at the outlet of the absorber and the desorber; this means that the solution reaches its solubility limit in both cases. This approach leads to a choice of potential absorbents for natural refrigerants, like ammonia and water, relying mostly on the solubility property. This choice, however, might not be optimal since working fluids with high solubility values might possess poor transport properties (e.g., high viscosity and low mass diffusivity). The present work illustrates the influence of transport properties, like the mass diffusivity (that was experimentally determined), and the limited size of the absorber on the performance of an ideal absorption system. Specifically, two ionic liquids used as absorbents for ammonia with different mass diffusivity and solubility values were compared using a thermodynamic model of a single-stage absorption refrigeration system coupled to an absorber model.