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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

## Abstract

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 $400 μm$ absorber is in most cases significantly larger than that of other absorbers. For the $150 μm$ and $400 μm$ 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

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.

Figure 1

Schematic of the absorber test section

Figure 2

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

Figure 3

Schematic of the experimental facility

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.

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.

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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