Investigation of binary, ternary and quaternary mixtures across solution heat exchanger used in absorption refrigeration and process modifications to improve cycle performance

One area of vital importance in the field of absorption refrigeration (ABR) is the search of alternative combinations of refrigerant/absorbent pairs that can enhance its performance relatively to the widely used H₂O-NH₃ or H₂O-LiBr. In this work, three binary (H₂O-LiBr, H₂O-LiCl, H₂O-LiI), three ternary (H₂O-LiBr + LiI, H₂O-LiBr + C₂H₆O₂, H₂O-LiBr + LiCl) and four quaternary (H₂O-LiBr + LiCl + ZnCl₂, H₂O-LiBr + ZnCl₂+CaBr₂, H₂O-LiBr + ZnBr₂+LiCl, H₂O-LiBr + LiI + C₂H₆O₂) mixtures of refrigerant/absorbent are tested to investigate heat transfer and pressure drop characteristics across the solution heat exchanger used in ABR systems. Subsequently, seven different single effect absorption cooling flowsheet configurations are explored to assess the potential for exploitation of the generated results at the cycle level. The effects of the concentrations of the absorbent in the mixture of refrigerant/absorbent on heat transfer and pressure drop characteristics are addressed. As a result, H₂O-LiI, H₂O-LiBr + LiI and H₂O-LiBr + ZnCl₂+CaBr₂ shows higher heat transfer coefficient and lower pressure drop among the tested binary, ternary and quaternary mixtures respectively. Furthermore, it is concluded that with increase in mass fraction of the absorbent in the mixture, the heat transfer coefficient is decreased. A process configuration with part of the refrigerant mixed with the strong solution through an ejector, prior to the solution heat exchanger, is found to exhibit highest coefficient of performance.