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. The branched-tray concept features a desorber segment that uses predominantly pool-boiling mechanisms for desorption, while the vertical column desorber relies on falling-film evaporation and boiling mechanisms. Both concepts rely on falling-film heat and mass transfer mechanisms in the analyzer and rectifier sections. 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. An experimental facility was designed and constructed to evaluate desorption and rectification heat and mass transfer processes within these components, under realistic operating conditions. Data were analyzed to determine the boiling/evaporation (desorber) and condensation (rectifier) heat transfer coefficients, and to determine values of the desorber liquid and vapor mass transfer coefficients. Additionally, high-speed video and images were used to gain insights into the hydrodynamic phenomena and heat transfer mechanisms in these vapor generation units. Results of the heat and mass transfer analysis 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 mass fractions (0.400 – 0.550), desorber coupling-fluid inlet temperatures (170 – 190ᵒC), and concentrated solution flow rates (0.70 – 1.3 g s-1). Flow rates in this range correspond to desorber liquid Reynolds numbers of approximately 175 to 410 for the branched tray design, and desorber film Reynolds numbers of approximately 90 to 215 for the vertical column. Pressures observed within the VGU test sections ranged from approximately 1620 to 2840 kPa during testing. The novel VGUs were shown to achieve ideal cooling capacities as high as 432 and 323 W for the branched tray and vertical column, respectively. This parameter indicates the cooling capacity that would be achieved by an idealized cooling system using the refrigerant stream produced by the experimental VGU. Ideal COPs of 0.561 and 0.496 were demonstrated for the branched tray and vertical column, respectively. 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.

An experimental and analytical study of a microchannel ammonia-water desorber was conducted in this study. The desorber consists of 5 passes of 16 tube rows each with 27, 1.575 mm outside diameter x 140 mm long tubes per row for a total of 2160 tubes. The desorber is an extremely compact 178 mm x 178 mm x 0.508 m tall component, and is capable of transferring the required heat load (~17.5 kW) for a representative residential heat pump system. Experimental results indicate that the heat duty ranged from 5.37 kW to 17.46 kW and the overall heat transfer coefficient ranges from 388 to 617 W/m2-K. The analytical model predicts temperature, concentration and mass flow rate profiles through the desorber, as well as the effective wetted area of the heat transfer surface. Heat and mass transfer correlations as well as locally measured variations in the heating fluid temperature are used to predict the effective wetted area. The average wetted area of the heat and mass exchanger ranged from 0.25 to 0.69 over the range of conditions tested in this study. Local mass transfer results indicate that water vapor is absorbed into the solution in the upper stages of the desorber leading to higher concentration ammonia vapor and therefore reducing the rectifier cooling capacity required. These experimentally validated results indicate that the microchannel geometry is well suited for use as a desorber. Previous experimental and analytical research has demonstrated the performance of this microchannel geometry as an absorber. Together, these studies show that this compact geometry is suitable for all components in an absorption heat pump, which would enable the increased use of absorption technology in the small capacity heat pump market.

The thesis is focused on the cooling cycles, namely cycles of absorption. The work is divided into several parts, as problems to be solved. The first part deals with the principles and using refrigeration cycles in practice, their involvement and by comparing the working pairs of substances circulating in the absorption unit. The practical part deals with making a proposal for one-and two-level modular absorption cycle of 6 kW, and the subsequent techno-economic comparison with commonly supplied absorption unit