On the Evaluation of Heat and Mass Transfer Capabilities of different Working Media in Absorption Heat Pumping Devices

The design of absorbers and desorbers in absorption heat pumping devices such as chillers or heat transformers predominantly relies on heat transfer coefficients, with the mass transfer resistance lumped in, or sometimes considered with a grade of subcooling. This works well for working pairs with enough empirical knowledge. For new working pairs a more fundamental approach is required. This paper provides some findings from experiments with aqueous solutions of LiBr and ionic liquids which may be helpful in this regard. The experimental data are interpreted in such a way that heat and mass transfer resistances can be separated. To this end, vapor pressure data of the fluids are needed, as well as a rough estimation of the liquid viscosity, heat conductivity and density. The latter data are used to determine the heat transfer resistance. Then, by using the vapor pressure data, a characteristic mass fraction difference and mass transfer resistance can be determined.