SUBJECT: Ph.D. Dissertation Defense
BY: Jared Delahanty
TIME: Wednesday, October 28, 2015, 2:00 p.m.
PLACE: Love Building, 109
TITLE: Desorption of Ammonia-Water Mixtures in Microscale Geometries for Miniaturized Absorption Systems
COMMITTEE: Dr. Srinivas Garimella, Chair (ME)
Dr. Thomas Fuller (ChBE)
Dr. Caroline Genzale (ME)
Dr. Mostafa Ghiaasiaan (ME)
Dr. Samuel Graham (ME)


A study of ammonia-water desorption in compact counter-flow geometries was conducted. Two novel vapor generation units, comprising integrated desorber, analyzer, and rectifier segments that use microchannel geometries, were conceptualized. Segmented heat and mass transfer models, based on available correlations and modeling methodologies, were developed and used for the design of branched tray and vertical column test sections. Results of the heat and mass transfer experiments were compared with the predictions of correlations and modeling methods in the literature. The vapor generation unit (VGU) test sections were evaluated across a range of concentrated solution concentrations (0.400 โ€“ 0.550), desorber coupling-fluid inlet temperatures (170 โ€“ 190แต’C), and concentrated solution flow rates (0.70 โ€“ 1.3 g s-1). The novel VGUs were shown to achieve ideal cooling capacities as high as 432 W. Ideal COPs as high as 0.561 were also achieved. Experimental heat transfer coefficients were found to range from approximately 1860 to 11690 W m-2 K-1 for the pool-boiling desorption of the branched tray VGU. A new correlation was proposed and shown to provide good agreement with the data, achieving average and average absolute deviation of -5.2 and 16.1%, respectively, across the range of conditions tested. Falling-film evaporation/boiling heat transfer coefficients, determined for the desorption process in the vertical column VGU, were found to range from approximately 1290 to 4310 W m-2 K-1. Rectifier condensation heat transfer coefficients ranging from approximately 160 to 250 W m-2 K-1 were observed. Mass transfer coefficients for the desorbers of both concepts were also quantified. These results were used to develop revised heat and mass transfer models of the VGU concepts. The revised models were demonstrated to predict component-level performance with reasonable accuracy, and may be used in the design of future compact VGUs with similar geometries and operating conditions.