Experimental Investigation of Average Heat-Transfer and Friction Coefficients for Air Flowing in Circular Tubes Having Square-Thread-Type Roughness

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An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through electrically heated Inconel tubes having various degrees of square-thread-type roughness, an inside diameter of 1/2 inch, and a length of 24 inches. were obtained for tubes having conventional roughness ratios (height of thread/radius of tube) of 0 (smooth tube), 0.016, 0.025, and 0.037 over ranges of bulk Reynolds numbers up to 350,000, average inside-tube-wall temperatures up to 1950deg R, and heat-flux densities up to 115,000 Btu per hour per square foot. Data The experimental data showed that both heat transfer and friction increased with ... continued below

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Sams, E. W. June 27, 1952.

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  • Main Title: Experimental Investigation of Average Heat-Transfer and Friction Coefficients for Air Flowing in Circular Tubes Having Square-Thread-Type Roughness
  • Series Title: NACA Research Memorandums

Description

An investigation of forced-convection heat transfer and associated pressure drops was conducted with air flowing through electrically heated Inconel tubes having various degrees of square-thread-type roughness, an inside diameter of 1/2 inch, and a length of 24 inches. were obtained for tubes having conventional roughness ratios (height of thread/radius of tube) of 0 (smooth tube), 0.016, 0.025, and 0.037 over ranges of bulk Reynolds numbers up to 350,000, average inside-tube-wall temperatures up to 1950deg R, and heat-flux densities up to 115,000 Btu per hour per square foot. Data The experimental data showed that both heat transfer and friction increased with increase in surface roughness, becoming more pronounced with increase in Reynolds number; for a given roughness, both heat transfer and friction were also influenced by the tube wall-to-bulk temperature ratio. Good correlation of the heat-transfer data for all the tubes investigated was obtained by use of a modification of the conventional Nusselt correlation parameters wherein the mass velocity in the Reynolds number was replaced by the product of air density evaluated at the average film temperature and the so-called friction velocity; in addition, the physical properties of air were evaluated at the average film temperature. The isothermal friction data for the rough tubes, when plotted in the conventional manner, resulted in curves similar to those obtained by other investigators; that is, the curve for a given roughness breaks away from the Blasius line (representing turbulent flow in smooth tubes) at some value of Reynolds number, which decreases with increase in surface roughness, and then becomes a horizontal line (friction coefficient independent of Reynolds number). A comparison of the friction data for the rough tubes used herein
indicated that the conventional roughness ratio is not an adequate
measure of relative roughness for tubes having a square-thread-type
element. The present data, as well as those of other investigators,
were used to isolate the influence of ratios of thread height to width,
thread spacing to width, and the conventional roughness ratio on the
friction coefficient.
A fair correlation of the friction data was obtained for each tube
with heat addition when the friction coefficient and Reynolds number were
defined on the basis of film properties; however, the data for each tube
retained the curve characteristic of that particular roughness. The
friction data for all the rough tubes could be represented by a single
line for the complete turbulence region by incorporating a roughness
parameter in the film correlation. No correlation was obtained for the
region of incomplete turbulence.

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  • : 74N70398
  • URL: http://hdl.handle.net/2060/19740072459 External Link
  • Report No.: NACA-RM-E52D17
  • Center for AeroSpace Information Number: 19740072459
  • Archival Resource Key: ark:/67531/metadc53309

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National Advisory Committee for Aeronautics Collection

The National Advisory Committee for Aeronautics (NACA) was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and Space Administration (NASA).

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Creation Date

  • June 27, 1952

Added to The UNT Digital Library

  • Nov. 11, 2011, 7:22 p.m.

Description Last Updated

  • Jan. 27, 2017, 3:25 p.m.

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Sams, E. W. Experimental Investigation of Average Heat-Transfer and Friction Coefficients for Air Flowing in Circular Tubes Having Square-Thread-Type Roughness, report, June 27, 1952; (digital.library.unt.edu/ark:/67531/metadc53309/: accessed December 16, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.