Highly efficient absorption heat pump and refrigeration systems based on ionic liquids: Fundamentals a Applications

Abstract

Improving efficiencies of thermal energy conversion systems is an important way to slow down global warming and mitigate climate change. Vapor absorption heat pump and refrigeration cycles are highly efficient ways of heating and cooling. These thermally activated systems also provide opportunities for the integration with a wide spectrum of low-grade and renewable heat sources, such as district heating networks, exhaust industrial heat, concentrated solar thermal energy and biomass. New fluids - ionic liquids - have been introduced into the absorption refrigeration/ heat pump field as absorbents to overcome drawbacks of traditional working fluids and to improve the energetic efficiency of systems. Some ionic liquids show high boiling points, superior thermal and chemical stabilities and strong affinities with refrigerants. Ammonia (NH3) is an environmentally friendly refrigerant with favorable thermodynamic and transport performance. Thus, studies in this thesis placed emphasis on the ammonia/ionic liquids working pairs. Studies in this thesis focus on exploring applications of ammonia/ionic liquid based vapor absorption refrigeration cycles, from a practical point of view in the refrigeration and heat pump field. By applying multi-scale evaluations covering thermodynamic and heat and mass transport aspects, it is intended to further understand the fundamentals of applying ionic liquids in heating and cooling systems. The highlights include: Assessments of equilibriummodels applied for ammonia-ionic liquid working fluids; Prediction of properties of ammoniaionic liquid fluids using molecular simulation; Collection and modeling of relevant thermophysical properties; Evaluation of the heat and mass transfer performance. Besides, concepts of using ionic liquids as absorbents with ammonia as the refrigerant in various thermodynamic cycles are analyzed and evaluated for applications in the built environment and industry...