Design enhancement of an adiabatic LiBr-H2O absorber through a droplet flow optimization

[摘要] The increase of cooling demands is a widespread phenomenon that poses theproblem of identifying new efficient ways to provide the necessary input energy. Wasteheat is available in large quantities, and its recovery is a challenging problem.Additionally, small-scale applications are becoming more common in fields such aselectronics and/or automotive. This work aims at providing a solution for thedevelopment of a small-scale waste heat-to-cool conversion system.To achieve this, a first comparison of the potential conversion systems wasperformed. Parameters of efficiency, cost and size were considered both separately andcombined in a comprehensive performance index. From this analysis, the H2O-LiBrabsorption chiller emerged as the most suitable technology for the development of asmall-scale system.Further investigation of the selected technology identified the absorber as themost critical component preventing the system downsizing. A critical review of thecurrent state of the art in the absorber design and operation strategies led to theproposition of a pin-finned, adiabatic absorber, combined with a droplet flow regime.In the next phase the proposed design was optimized. Firstly, an analyticalmodel was developed to accurately describe the geometrical domain of a dropletforming on a solid surface, a phase which was found to be beneficial to the absorptionprocess. The model was then validated with experiments and used to optimize the pinshape.Secondly, the absorption process was analyzed. An analytical heat and masstransfer model of the phases of a falling droplet was developed and an experimentalsetup, replicating the operation of the absorber, was developed to validate the proposed17model. The validation process led to the identification of the best pin and distributionorifice sizes, completing the absorber design optimization.Finally, the performance improvement of the optimized absorber design wasevaluated with respect to a standard absorption chiller configuration.

[发布机构] Nanyang Technological University, Singapore

[效力级别] DRNTU::Engineering::Mechanical engineering::Fluid mechanics