AbSorbEnt – On the search for alternative absorbents

Absorption heat pumps are a valuable technology for efficiently utilizing waste heat, e.g., from industrial processes. The common working fluid pair H2O/LiBr is favoured due to the high latent heat of water and its low saturation pressures. However, LiBr as a sorbent causes problems such as corrosion and crystallization, especially at high LiBr mass fractions, which usually occur at high desorber temperatures. To address these issues, alternative sorbents such as ionic liquids or deep eutectic solvents, compatible with water as a refrigerant are being developed and tested at saturation temperatures of the water-sorbent-mixture between 30 °C and 200 °C, as well as saturation pressures between 10 mbar and 1.4 bar as part of the “AbSorbEnt” project. Of particular interest is the application of deep eutectic solvents, which have not yet been investigated experimentally in absorption heat pumps. In the present publication, experimental results on the fluid properties such as the equilibrium mass fractions at pressures and temperatures representing cooling mode as well as densities and viscosities of the pure fluids of a first batch of alternative sorbents are examined. The results are used to compare the working fluid pairs with each other as well as with H2O-LiBr-mixtures.