Flow mode transitions for a liquid film falling over flat tubes are studied for a wide range of conditions. Hydraulic oil, ethylene glycol, ethylene-glycol-water mixtures (at three different volume ratios), and water are used as working fluids in experiments conducted under adiabatic conditions, without an imposed vapor flow. The flow modes are observed over a range of flow rate and tube spacing. The flow modes are more complex but similar to those manifested on round tubes, and include the sheet, sheet-jet, jet, jet-droplet, and droplet modes. However, the transitions at Ga1/4 ≤ 16 (mainly for hydraulic oil, ethylene glycol) are very different from those on round tubes: there is no sheet-jet mode during transition between the sheet and jet flow modes. Moreover, at all Ga, the Re range over which the jet mode occurs is narrower than that for round tubes, and the hysteresis in mode transitions is not as pronounced as for round tubes. The transitional Re increases slowly with tube spacing, also in contrast to observations of round-tube falling films. The flat-tube falling-film flow regimes are described, and new correlations are provided to relate the transitional Re number to Ga and geometry. By analyzing repeated experiments, it is shown that the standard deviation of the measurements from the correlations is less than 5.2%.
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Flow Modes and Mode Transitions for Falling Films on Flat Tubes
Xiaofei Wang,
Xiaofei Wang
Xi’an Jiaotong University
, Xi’an 710049, People’s Republic of China
; Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801 e-mail:
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P. S. Hrnjak,
P. S. Hrnjak
Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801; Creative Thermal Solutions, 2209 North Willow Road, Urbana, IL
61802 e-mail:
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S. Elbel,
S. Elbel
Creative Thermal Solutions, 2209 North Willow Road, Urbana,
IL
61802 e-mail:
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A. M. Jacobi,
A. M. Jacobi
Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801 e-mail:
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Maogang He
Maogang He
Xi’an Jiaotong University
, Xi’an 710049, People’s Republic of China
e-mail:
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Xiaofei Wang
Xi’an Jiaotong University
, Xi’an 710049, People’s Republic of China
; Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801 e-mail:
P. S. Hrnjak
Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801; Creative Thermal Solutions, 2209 North Willow Road, Urbana, IL
61802 e-mail:
S. Elbel
Creative Thermal Solutions, 2209 North Willow Road, Urbana,
IL
61802 e-mail:
A. M. Jacobi
Mechanical Science and Engineering, University of Illinois
, Urbana, IL
61801 e-mail:
Maogang He
Xi’an Jiaotong University
, Xi’an 710049, People’s Republic of China
e-mail: J. Heat Transfer. Feb 2012, 134(2): 021801 (9 pages)
Published Online: December 13, 2011
Article history
Received:
October 6, 2010
Revised:
September 5, 2011
Online:
December 13, 2011
Published:
December 13, 2011
Citation
Wang, X., Hrnjak, P. S., Elbel, S., Jacobi, A. M., and He, M. (December 13, 2011). "Flow Modes and Mode Transitions for Falling Films on Flat Tubes." ASME. J. Heat Transfer. February 2012; 134(2): 021801. https://doi.org/10.1115/1.4005095
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