Repository logo
  • Log In
    Log in via Symplectic to deposit your publication(s).
Repository logo
  • Communities & Collections
  • Research Outputs
  • Statistics
  • Log In
    Log in via Symplectic to deposit your publication(s).
  1. Home
  2. Faculty of Engineering
  3. Faculty of Engineering
  4. Spatiotemporally resolved heat transfer measurements in falling liquid-films by simultaneous application of planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography
 
  • Details
Spatiotemporally resolved heat transfer measurements in falling liquid-films by simultaneous application of planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography
File(s)
ETFS_2018_1175_Manuscript_Revised.pdf (8.39 MB)
Accepted version
Author(s)
Charogiannis, Alexandros
Markides, Christos N
Type
Journal Article
Abstract
We present an optical technique that combines simultaneous planar laser-induced fluorescence (PLIF), particle tracking velocimetry (PTV) and infrared (IR) thermography for the space-and time-resolved measurement of the film-height, 2-D velocity and 2-D free-surface temperature in liquid films falling over an inclined, resistively-heated glass substrate. Using this information and knowledge of the wall temperature, local and instantaneous heat-transfer coefficients (HTCs) and Nusselt numbers, Nu, are also recovered along the waves of liquid films with Kapitza number, , and Prandtl number, . By employing this technique, falling-film flows are investigated with Reynolds numbers in the range , wave frequencies set to , 12 and 17 Hz, and a wall heat flux set to  W cm−2. Complementary data are also collected in equivalent (i.e., for the same mean-flow Re) flows with  W cm−2. Quality assurance experiments are performed that reveal deviations of up to 2-3% between PLIF/PTV-derived film heights, interfacial/bulk velocities and flow rates, and both analytical predictions and direct measurements of flat films over a range of conditions, while IR-based temperature measurements fall within 1 °C of thermocouple measurements. Highly localized film height, velocity, flow-rate and interface-temperature data are generated along the examined wave topologies by phase/wave locked averaging. The application of a heat flux ( W cm−2) results in a pronounced “thinning” of the investigated films (by 18%, on average), while the mean bulk velocities compensate by increasing by a similar extent to conserve the imposed flow rate. The axial-velocity profiles that are obtained in the heated cases are parabolic but “fuller” compared to equivalent isothermal flows, excluding any wave-regions where the interface slopes are high. As the Re is reduced, the heating applied at the wall penetrates through the film, resulting in a pronounced coupling between the HTC and the film height in thinner film regions. When the imposed wave frequency is increased, a narrower range of HTCs is observed, which we link to the evolution of the film topology and the associated redistribution of the fluid flow upstream of the imaging location, as the liquid viscosity decreases. The local and instantaneous Nu is strongly coupled to the film height and experiences variations that increase as is reduced.
Date Issued
2019-10-01
Date Acceptance
2018-11-01
Citation
Experimental Thermal and Fluid Science, 2019, 107, pp.169-191
URI
http://hdl.handle.net/10044/1/64875
DOI
https://www.dx.doi.org/10.1016/j.expthermflusci.2018.11.001
ISSN
0894-1777
Publisher
Elsevier BV
Start Page
169
End Page
191
Journal / Book Title
Experimental Thermal and Fluid Science
Volume
107
Copyright Statement
© 2018 Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
The Royal Society
Grant Number
EP/K008595/1
EP/L020564/1
EP/M021556/1
AQ150077
Subjects
Science & Technology
Physical Sciences
Technology
Thermodynamics
Engineering, Mechanical
Physics, Fluids & Plasmas
Engineering
Physics
Film flows
Unsteady heat transfer
Laser-induced fluorescence
Particle velocimetry
Infrared thermography
TEMPERATURE DISTRIBUTION
VELOCITY-MEASUREMENTS
FLOW CHARACTERISTICS
REGULAR STRUCTURES
ANNULAR-FLOW
WAVE
REYNOLDS
THICKNESS
HYDRODYNAMICS
EVOLUTION
Mechanical Engineering & Transports
09 Engineering
Publication Status
Published
Date Publish Online
2018-11-03
About
Spiral Depositing with Spiral Publishing with Spiral Symplectic
Contact us
Open access team Report an issue
Other Services
Scholarly Communications Library Services
logo

Imperial College London

South Kensington Campus

London SW7 2AZ, UK

tel: +44 (0)20 7589 5111

Accessibility Modern slavery statement Cookie Policy

Built with DSpace-CRIS software - Extension maintained and optimized by 4Science

  • Cookie settings
  • Privacy policy
  • End User Agreement
  • Send Feedback