A Deep Eutectic Solvent as a Working Fluid Pair in an Absorption Refrigeration System

Designing efficient working fluid pairs for absorption refrigeration systems (ARSs) driven by low-grade heat remains a significant challenge. Here, we introduce a deep eutectic solvent (DES) comprising methanol and choline chloride–urea (ChCl–UR) as the working fluid pair. The as-synthesized DES has a viscosity of up to 52.69 mm2/s. Hydrogen bonding was confirmed by infrared spectroscopy, and the network transformed to urea-bridged aggregates as the concentration of ChCl–UR increased. The equilibrium vapor pressure of methanol was maximumly reduced to 5.76 kPa at room temperature, corresponding to a cooling temperature of 278.15 K. A modified nonrandom two-liquid (NRTL) model successfully described the liquid–vapor equilibrium phenomenon with an average relative error of up to 6.10%. With the fluid pair of methanol to ChCl–UR of 1.31:1 (mol/mol), a single-effect ARS achieved a coefficient of performance (COP) greater than 0.8. Furthermore, in a compression-assisted ARS, the refrigeration temperature further decreased, improving the overall efficiency.