Effect of hot-gas bleedback ice prevention on performance of a turbojet engine with fixed-area tail-pipe nozzle Page: 3 of 28
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2 NACA RM No. E9B23
prevention. The analysis was made for a turbojet engine operating
at rated engine speed and sea-level-pressure, zero-flight-speed
conditions. The ambient-air conditions of the investigation
covered a range of temperatures from -400 to 38 F at liquid-water
contents of 1.0 and 2.5 grams per cubic meter. Both the combustion
chamber and the tail pipe were considered as sources of the hot gas.
Ice formation is most likely to occur in the restricted pas-
sages of the engine inlet where the air velocity is highest. This
maximum velocity was assumed to be in the compressor-inlet guide
or turning vanes. Icing may be encountered with moist air at an
ambient temperature greater than 320 F, when the increased velocity
depresses the static temperature in the restricted passages, and
water droplets may condense and freeze on the guide vanes.
Criterions for ice prevention. - Ice formations in the inlet
of a turbojet engine may be prevented by heating the air until the
temperatures of the guide vanes and the walls exceed 32" F. If
the initial air temperatureis low, the addition of heat may evap-
orate all the free water at a temperature below 320 F. Icing
might therefore be avoided by heating the air until either the
wall temperatures exceed 320 F or the dew point is exceeded.
A modification of the second alternative is to heat the air
until the temperature in the bound&y layer exceeds the dew point.
In such a case the temperature of the air in the center of the
passage will be below the dew point and subfreezing droplets of
water will be thrown into the boundary layer. If the evaporation
rate exceeds the rate of water impingement, no ice till form.
Some doubt exists that heating the air until the temperature
of the main stream or the boundary layer exceeds the dew point
will always be effective, because the time available for heating
the water droplets may be insufficient for complete evaporation.
An experimental investigation reported in reference 2 shows that
ice accretions form at temperatures above the dew point of the
Because of the sparse experimental evidence available as to
the conditions under which inlet icing will occur, three analyses
of the_ use of hot bleedback gases for ice prevention based on the
following criterions have been made:
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Dietz, Robert O., Jr. & Krebs, Richard P. Effect of hot-gas bleedback ice prevention on performance of a turbojet engine with fixed-area tail-pipe nozzle, report, May 16, 1949; (https://digital.library.unt.edu/ark:/67531/metadc58308/m1/3/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.