Experimental analysis on falling film absorbers using ionic liquids for cold store conditioning

Frost formation on air coolers causes energy losses and operational disruptions in cold stores. This study investigates an ionic liquid-based open absorption system for frost-free air conditioning of cold stores. A dual-circuit absorber–regenerator test bench was developed to experimentally characterize the system under relevant operating conditions. The absorber and regenerator were evaluated using the mass transfer coefficient k m and Sherwood number Sh . Sherwood numbers in the range of Sh ≈ 4.4 − 7.0 were obtained, corresponding to mass transfer coefficients of k m ≈ 9.1 − 14.6 mm/s . The Sherwood number was found to be largely independent of desiccant solution mass flow rate and cooling or heating temperature, indicating gas-side diffusion-limited mass transfer with stable liquid-film wetting. Compared with a conventional air cooler, the absorber-based system prevented frost formation and maintained stable cooling performance while allowing regeneration using low-grade waste heat from the refrigeration system at 42 ° C. Frosting and defrosting losses in an idealized conventional system were found to account for at least 8% of the cooling energy. A system-level energy assessment showed that even the lab-scale absorber-based system could reduce electrical energy demand by 1.4 ± 0.6 % compared with the idealized conventional system. For a full-scale system operating under non-ideal conditions, the achievable savings are expected to be considerably higher. Moreover, the heat exchanger of the absorber-based system can be built 25% smaller while providing the same cooling capacity, as its performance is not degraded by frost formation. These findings demonstrate the potential of absorber-based systems for frost-free, stable, and energy-efficient cold store conditioning.