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.

1.
Garimella
,
S.
, 2005, “
Binary-Fluid Heat and Mass Transfer in Microchannel Geometries for Minuaturized Thermally Activated Absorption Heat Pumps
,”
Microscale Heat Transfer
,
S.
Kakac
,
L. L.
Vasiliev
,
Y.
Bayazitoglu
, and
Y.
Yener
, eds.,
Springer
,
Dordrecht, The Netherlands
, pp.
339
368
.
2.
Meachum
,
M. J.
, and
Garimella
,
S.
, 2004, “
Ammonia-Water Absorption Heat and Mass Transfer in Microchannel Absorbers With Visual Confirmation
,”
ASHRAE Transactions: Symposia
, Anaheim, CA, Jan. 24-28, pp.
525
532
, Paper No. AN-04-7-4.
3.
Goel
,
N.
, and
Goswami
,
D. Y.
, 2005, “
A Compact Falling Film Absorber
,”
ASME J. Heat Transfer
0022-1481,
127
, pp.
957
965
.
4.
Goel
,
N.
, and
Goswami
,
D. Y.
, 2007, “
Experimental Verification of a New Heat and Mass Transfer Enhancement Concept in a Microchannel Falling Film Absorber
,”
ASME J. Heat Transfer
0022-1481,
129
, pp.
154
161
.
5.
Staicovici
,
M. D.
, 2000, “
A Phenomenological Theory of Polycomponent Interactions in Non-Ideal Mixtures: Application to NH3/H2O and Other Working Pairs
,”
Int. J. Refrig.
0140-7007,
23
, pp.
153
167
.
6.
Helbing
,
U.
,
Würfel
,
R.
, and
Fratzscher
,
W.
, 2000, “
Comparative Investigations of Non-Adiabatic Absorption in Film Flow and Bubble Flow
,”
Chem. Eng. Technol.
,
23
, pp.
1081
1085
. 0930-7516
7.
Kang
,
Y. T.
,
Atsushi
,
A.
, and
Kashiwagi
,
T.
, 2000, “
Analytical Investigation of Two Different Absorption Modes: Falling Film and Bubble Types
,”
Int. J. Refrig.
0140-7007,
23
, pp.
430
443
.
8.
Lee
,
K. B.
,
Chun
,
B. H.
,
Lee
,
J. C.
,
Hyun
,
J. C.
, and
Kim
,
S. H.
, 2002, “
Comparison of Heat and Mass Transfer in Falling Film and Bubble Absorbers of Ammonia-Water
,”
Exp. Heat Transfer
0891-6152,
15
, pp.
191
205
.
9.
Lee
,
K. B.
,
Chun
,
B. H.
,
Lee
,
J. C.
,
Lee
,
C. H.
, and
Kim
,
S. H.
, 2002, “
Experimental Analysis of Bubble Mode in a Plate-Type Absorber
,”
Chem. Eng. Sci.
0009-2509,
57
, pp.
1923
1929
.
10.
Jenks
,
J.
, and
Narayanan
,
V.
, 2006, “
An Experimental Study of Ammonia-Water Bubble Absorption in a Large Aspect Ratio Microchannel
,”
Proceedings of the IMECE 2006
,
Chicago, IL
, Nov. 5-10, Paper No. IMECE2006-14036.
11.
,
S.
, and
Han
,
J.-C.
, 1997, “
Detailed Heat Transfer Distributions in Two-Pass Square Channels With Rib Turbulators
,”
Int. J. Heat Mass Transfer
0017-9310,
40
(
11
), pp.
2525
2537
.
12.
Ibrahim
,
O. M.
, and
Klein
,
S. A.
, 1993, “
Thermodynamic Properties of Ammonia-Water Mixtures
,”
ASHRAE Transactions: Symposia
, Chicago, IL, Jan. 23-27, Vol.
21
(
2
), p.
1495
.
13.
Narayanan
,
V.
,
Kanury
,
A. M.
, and
Jenks
,
J.
, 2007, “
Modified Heat Exchanger Analysis Accounting for Heat Generation
,”
Proceedings of the 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference
,
, July 8–12, Paper No. HT2007-33444.
14.
Figliola
,
R. S.
, and
Beasley
,
D. E.
, 2000,
Theory and Design for Mechanical Measurements
,
3rd ed.
,
Wiley
,
Hoboken, NJ
.
15.
Jenks
,
J.
, 2007, “
An Experimental Study of Ammonia-Water Bubble Absorption in a Constrained Microscale Film
,” MS thesis, Oregon State University, Corvallis, OR.