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National Advisory Committee for Aeronautics, Technical Notes - An Investigation of Aircraft Heaters - XXXIV - Experimental Determination of Thermal and Hydrodynamical Behavior of Air Flowing Between a Flat and a Wave Shaped Plate

An experimental investigation has been performed on the thermal and
hydrodynamical behavior of air flowing along a passage of which one side
was flat (and steam-heated) and the other side was wave-shaped (and
unheated).

Two series of tests were conducted: One series in which the wave—
shaped plate and the steam-heated plate were placed in exact opposition
(thermal boundary layer at leading edge of flat plate and flow over
wave plate beginning at same point) and the other series in which the
leading edge of the wave plate was placed 9 inches upstream of the
leading edge of the heated plate, thereby promoting turbulence upstream
of the beginning of the thermal boundary layer. In the first series of
tests, two wave plates‘of different amplitude and wavelength were used.
A range of air weight rates and spacings between the heated plate and
the wave plate was investigated.

An analysis of the heat-transfer and pressure—dr0p data reveals
that the turbulence produced by air flowing over wavy surfaces approxi-
mately doubles the heat-transfer rate for narrow duct widths. Of course,
at large duct widths the effect is negligible. The pressure drop was
greatly increased over that for a straight duct. The pressure drop was
increased to at least h times for large duct widths and to at least
10 times for small duct widths.

Extensive tests on aircraft heat exchangers carried out in this
laboratory under the auspices of the National Advisory Committee for
Aeronautics indicated that some systems were easily predictable from
established empirical heat—transfer equations. However, many systems
encountered were not readily predictable. These systems consisted of
some finned surfaces and certain cases in which the passage was not
straight and of uniform cross-sectional area. A finned—surface system
was investigated and teported in reference 1. A study of heat-transfer
and pressure—drop data for the case of air flow between a heated plane
surface and an unheated wavy surface is presented herein.