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Research Papers: Micro/Nanoscale Heat Transfer

Effect of Channel Geometry Variations on the Performance of a Constrained Microscale-Film Ammonia-Water Bubble Absorber

[+] Author and Article Information
Jeromy Jenks

Department of Mechanical Engineering, Oregon State University, 204 Rogers Hall, Corvallis, OR 97331-6001

Vinod Narayanan1

Department of Mechanical Engineering, Oregon State University, 204 Rogers Hall, Corvallis, OR 97331-6001vinod.narayanan@oregonstate.edu

1

Corresponding author.

J. Heat Transfer 130(11), 112402 (Sep 05, 2008) (9 pages) doi:10.1115/1.2970065 History: Received August 08, 2007; Revised April 08, 2008; Published September 05, 2008

An experimental study of the absorption of ammonia vapor in a constrained thin film of ammonia-water solution is presented. A large aspect ratio microchannel with one of its walls formed of a porous material is used to constrain the thickness of the liquid film. Experiments are performed at a pressure of 2.5 bar absolute and 4 bar absolute and at a fixed weak solution inlet temperature. Weak solution flow rates are varied from 10 g/min to 30 g/min (corresponding to the weak solution Reynolds number, Re, from 15 to 45), inlet mass concentrations are varied from 0% to 15%, and gas flow rates are varied between 1 g/min and 3 g/min (corresponding to the vapor Re from 160 to 520). Six geometries, including three smooth-bottom-walled channels of differing depths and three channels with structured bottom walls, are considered. Results indicate that, for identical rates of vapor absorption, the overall heat transfer coefficient of the 400μm absorber is in most cases significantly larger than that of other absorbers. For the 150μm and 400μm absorbers, a trade-off between the high overall heat and mass transfer coefficients is achieved for the highest vapor to solution flow rate ratio.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the absorber test section

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Figure 2

Photographs of the three structured microchannels: (a) the CR channel, (b) the 45-deg ACR channel, and (c) the SF channel

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Figure 3

Schematic of the experimental facility

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Figure 7

Performance of the 150 μm absorber plotted against source to heat ratios: (a) overall heat transfer coefficient and (b) mass transfer coefficient. The system pressure is 2.5 bars.

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Figure 4

Effect of the channel depth on the absorber performance for various flow rate ratios: (a) overall heat transfer coefficient and (b) mass transfer coefficient. The nominal absorber pressure is 4.0 bars and Xws=0.15. The absorbers are of discrete nominal depths of 150 μm, 400 μm, and 1500 μm.

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Figure 5

Effect of the vapor flow rate on the absorber performance for various channel geometries and at a fixed inlet flow rate of 10 g/min: (a) overall heat transfer coefficient and (b) mass transfer coefficient. The nominal absorber pressure is 4.0 bars and Xws=0.15. The vapor flow rates are plotted in the abscissa at discrete values of 1 g/min, 2 g/min, and 3 g/min.

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Figure 6

Effect of the vapor flow rate on the absorber performance for various channel geometries and at a fixed inlet flow rate of 30 g/min: (a) overall heat transfer coefficient and (b) mass transfer coefficient. The nominal absorber pressure is 4.0 bars and Xws=0.15. The vapor flow rates are plotted in the abscissa at discrete values of 1 g/min, 2 g/min, and 3 g/min.

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