Extended temperature–entropy (T–s) diagrams for aqueous lithium bromide absorption refrigeration cycles

Temperature–entropy (T–s) diagrams have the unique capability of being able to quantify processes in terms of both the first and second laws of thermodynamics. Although use of generalised T–s diagrams has been made to indicate or represent generalised absorption cycles, with the exception for NH3/water systems, these diagrams have not been specifically tailored to scale to quantify LiBr/water systems. The main barrier for this is that the diagram needs to represent the necessary properties of both the refrigerant (water) and of the solution (LiBr/water). This paper describes the use of the T–s diagram of water extended with additional curves to represent real and ideal LiBr/water absorption cycles. An explanation is provided on several methods available, including details of the thermodynamic justification of the method that was used, to construct the extended diagrams. Finally, the extended T–s diagram is provided with the representation of a real single-effect LiBr/water absorption refrigeration cycle. This should prove to be a valuable tool for design and research engineers to study and optimise LiBr/water chillers.