Experimental study on the effect of an ionic liquid as anti-crystallization additive in a bi-adiabatic H2O-LiBr absorption chiller prototype

Identifier:  imarina:9393172

Handle: https://hdl.handle.net/20.500.11797/imarina9393172

Authors:  Tariq, HA; Altamirano, A; Collignon, R; Stutz, B; Coronas, A

Abstract:
Absorption chillers are attractive because they use natural refrigerants and can be powered by low-grade heat sources. Among the commercially available working fluids, the most common one, H2O-LiBr, has a critical drawback associated with the crystallization of the solution at low temperatures and high absorbent concentrations. This limitation restricts the operating range of these systems, especially when they are air-cooled or used as heat pumps. Additives can be used in H2O-LiBr to reduce the crystallization temperature by improving the solubility of LiBr in the solution. However, they often present disadvantages such as the requirement of a rectifier, and a negative impact on heat and mass transfer. Ionic Liquids (ILs) used as additives represent an alternative to overcome these drawbacks. In the present study, 6 % of [DMIM][Cl] by mass in absorbent (LiBr + [DMIM][Cl]) is added as an anti-crystallization additive to study its effect on the experimental behavior and crystallization limit of a H2O-LiBr single-effect bi-adiabatic absorption chiller prototype. Results of H2O-LiBr and H2O-(LiBr + [DMIM][Cl]) were compared for the individual heat transfer elements and the global system COP. The results show a decrease in the crystallization temperature using H2O-(LiBr + [DMIM][Cl]), which extended the operating range of the prototype. A decrease of 15 degrees C in crystallization temperature was found for H2O-(LiBr + [DMIM][Cl]) compared to H2O-LiBr at an absorbent mass of 65 %. Crystallization impeded the operation for H2O-LiBr at the highest driving temperature (100 degrees C) and lowest cold source inlet temperature (9 degrees C), whereas no crystallization was observed at same operating conditions for the (LiBr + [DMIM][Cl]) solution. Under the tested conditions, the addition of the IL as additive increased the chiller operating range without the requirement of a rectifier and with a negligible impact on the cooling capacity and thermal COP.