SUMMARY

The use of conventional vapor-compression refrigeration and cooling systems is accompanied by a significant demand for high grade energy, typically in the form of electricity. Heat driven chillers, on the other hand, can use a variety of low-grade thermal energy sources such as waste heat and solar thermal, and their widespread application can significantly improve overall global energy utilization efficiency. Recent advances in microscale heat and mass exchangers have attracted interest in the development of small-capacity vapor-absorption systems. In the first part of the proposed study, a state-of-the-art small capacity ammonia-water absorption chiller is developed to assess the current state of the technology. The results of this development provide guidance for more detailed investigations of specific components and subsystems. While overall thermal compressor optimization emerges as one of the key focus areas, the core work in this study addresses the development of optimal vapor generation and purification components, i.e. the desorber and rectifier. Both are essential elements of the thermal compressor, determining its efficiency, weight and size. Optimal designs are informed by a proposed thermodynamic framework for quantitative thermal compressor characterization. This allows for the development of two novel and highly compact design concepts for application with a variety of heat sources. The feasibility of the proposed designs is established through a hydrodynamic characterization that is based on a methodology devised in this study. Non-equilibrium heat and mass transfer models are then developed for rigorous design of full-scale components. An experimental evaluation of both design concepts is proposed, whereby performance at the sub-component, component, and thermal compressor levels is evaluated. At the sub-component level, local temperature, flow and pressure measurements are used to determine heat and mass transfer coefficients. Component-level results enable refinement of the proposed heat and mass transfer model. Finally, treatment of the thermal compressor as a single entity is validated, and a control algorithm is developed for optimal system operation over a wide range of operating conditions. The results of this study guide the design of highly compact and optimized thermal compressors for applications in small-capacity absorption heat pumps.