New green ionic liquids as next-generation industrial absorbents
Crystallisation and corrosion of widely used working fluids including lithium bromide at low temperatures have hindered introduction of a great number of absorption systems in the air conditioning market. In this working pair, water is the refrigerant. Unlike conventional working fluids, lack of flammability and volatility of ionic liquids eliminate safety and environmental concerns in chemical processing. The NARILAR (New working fluids based on natural refrigerants and ionic liquids for absorption refrigeration) project worked on developing novel and more efficient working pairs for absorption refrigeration and heat pump systems. Researchers combined natural refrigerants – water, ammonia or carbon dioxide – and absorbents based on ionic liquids. Ionic liquids are excellent candidates as absorbents in absorption systems. By choosing the proper anions and cations, one can design tailor-made ionic liquids with the desired characteristics. However, these liquids are highly viscous especially at low temperatures, restricting the flow of the absorbent in the machine. This problem can usually be overcome by adding a molecular solvent that can dramatically reduce viscosity. As a consequence, design of a proper mixture ionic liquid leads to more efficient cycles. After selection of proper heat pump systems, researchers' activities ranged across the whole spectrum of developing new working fluids. These included heat transfer studies, thermodynamic cycle simulation, analysis and optimisation of the working fluids, and experimental measurement of thermodynamic and transport properties. NARILAR was cooperation between five university research groups from Europe, Chile and India and one research institution from India.
Keywords
Ionic liquids, working fluids, absorption refrigerator, natural refrigerants, molecular solvent
