The friction numbers for laminar flows of water in microtubes, determined from the temperature rise due to the viscous dissipation heating assuming a velocity slip, show a strong dependence on the diameter and aspect ratio. The calculated values compare well with those determined from experimental data for water flows in glass and diffused silica microtubes ( in diameter and aspect ratios ). With a slip, the friction number almost exponentially decreases as decreases and, to a lesser extent, as increases. For , the friction number approaches the theoretical Hagen–Poiseuille for macrotubes (64) when , but higher values at smaller . The developed semiempirical analytical expression for calculating the friction number is in good agreement with the numerical and experimental results. The results suggest the presence of a velocity slip in the experiments and the plausible presence of a thin nanolayer at the walls of the microtubes. For , this layer, if exists, is estimated to be , but increases to for , when and .
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Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes
Mohamed S. El-Genk,
Mohamed S. El-Genk
Regents Professor
Chemical and Nuclear Engineering Department, and Institute for Space and Nuclear Power Studies,
e-mail: mgenk@unm.edu
University of New Mexico
, Albuquerque, NM 87131
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In-Hwan Yang
In-Hwan Yang
Chemical and Nuclear Engineering Department, and Institute for Space and Nuclear Power Studies,
University of New Mexico
, Albuquerque, NM 87131
Search for other works by this author on:
Mohamed S. El-Genk
Regents Professor
Chemical and Nuclear Engineering Department, and Institute for Space and Nuclear Power Studies,
University of New Mexico
, Albuquerque, NM 87131e-mail: mgenk@unm.edu
In-Hwan Yang
Chemical and Nuclear Engineering Department, and Institute for Space and Nuclear Power Studies,
University of New Mexico
, Albuquerque, NM 87131J. Heat Transfer. Aug 2008, 130(8): 082405 (13 pages)
Published Online: June 4, 2008
Article history
Received:
July 2, 2007
Revised:
October 3, 2007
Published:
June 4, 2008
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El-Genk, M. S., and Yang, I. (June 4, 2008). "Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes." ASME. J. Heat Transfer. August 2008; 130(8): 082405. https://doi.org/10.1115/1.2909617
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