An Investigation of Aircraft Heaters 27: Distribution of Heat-Transfer Rate in the Entrance Section of a Circular Tube Page: 4 of 54
53 p. : ill.View a full description of this report.
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NACA TN No. 1451
The results of tests (a) to (d) illustrate the effects of turbulence and
tests (a), (i), and (3) show the effects of entrance velocity distribution.
The remainder of the tests show the effect of the various more practical
entrance conditions, in which eddying flow is present.
Latzko (reference 2) developed analytical methods for approximating
the variation of the point unit thermal conductance for three entering-
gas conditions:
Case I: Both velocity and temperature distributions are uniform over
the cross section at the entrance. (This is approximately the actual
system of a heating section with a bellnouth at the entrance.)
Case II: The velocity distribution at the entrance corresponds to
that for fully developed turbulent flow, and the temperature distribution
is uniform over the cross section at the entrance. (The actual system
may be visualized as a heating section with a long calming section
upstream.)
Case III: The intermediate case between cases I and II, in which
the calming section of case II is too short for the fluid to have attained
a fully developed velocity distribution before entering the heating
section. (See appendix A for description of analytical methods.)
A method noted in reference 3 approximates the variation of the
point unit thermal conductance for air for case I. An expression for
estimating the integrated average unit thermal conductance for any length
of heating sections is also developed in reference 3.
In addition to the point unit thermal conductances, the average unit
thermal conductances for the circular tube were calculated as a function
of tube length for eight experimental conditions (fig. 1, cases a, b, g,
h, i, 3, k, and i). For two of these conditions the average unit thermal
conductances were analytically obtained by using the equations for f
given by Latzko, by Boelter and his associates, and by Iversen.
The average unit thermal conductance, the mean value taken over the
entire length of tube in question, is obtained from the following equation
f = f dx
cav =x r c
0
The effect of the entering-fluid condition on variations of the average
unit thermal conductance with length is presented in table I.
A distinction is made in this report between turbulence and eddying flow
conditions. Turbulence will be thought of as minute fluctuations of
particle velocities; whereas eddying flow is considered to be that charac-
terized by relatively large scale vortices, etc.
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Boelter, L. M. K.; Young, G. & Iversen, H. W. An Investigation of Aircraft Heaters 27: Distribution of Heat-Transfer Rate in the Entrance Section of a Circular Tube, report, July 1948; (https://digital.library.unt.edu/ark:/67531/metadc54233/m1/4/: accessed June 9, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.