SUMMARY

Application of absorption technology to space-conditioning systems offers several potential advantages over the widespread vapor-compression systems that currently dominate this market. Despite potential advantages, such as use of environmentally preferable working fluids, ability to employ low-grade thermal inputs as a driving energy source, and use of quieter and more reliable components, absorption systems have not seen significant adoption rates, particularly in applications demanding compact, inexpensive components, such as residential, light-commercial and mobile applications. Renewed interest and advances in the development of compact microchannel-based and monolithic systems have highlighted the need for a better understanding of coupled ammonia-water heat and mass transfer, particularly in compact high-flux components. The proposed study addresses two of the key processes in such systems: desorption and rectification, with a focus on compact geometries that integrate both processes into one small unit, in which stable counter-flow operation is challenging. Two compact, counter-flow desorber-rectifier concepts employing combinations of falling-film and pool-boiling heat and mass transfer will be investigated. Component heat and mass transfer models will be developed for both concepts and utilized in the design of both full-scale prototype desorber-rectifiers and separate heat and mass transfer test sections. Proof-of-concept will be achieved by demonstration of the full-scale components on breadboard absorption cooling systems. Local details of the underlying heat and mass transfer processes will be studied in test sections specifically designed to enable local measurements and visual access and mounted on a dedicated test facility for studying the desorption and rectification processes under a variety of representative operating conditions. Local temperature, pressure and flow measurements will be used to obtain the respective coupled heat and mass transfer coefficients. The results from these experiments, as well as observations from flow visualization, will be used to refine the component models. The resulting insights and understanding of these processes will enable the implementation of small-scale heat and mass transfer systems for air-conditioning, refrigeration, waste heat recovery and other related applications.