Effect of pressure level on afterburner-wall temperatures Page: 9 of 25
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the experimental curve. The experimental and computed temperature curves
are similar in trend except in the region of station A for the reasons
previously noted. At station A the measured and computed wall tempera-
tures are approximately 1000 F different. About half this temperature
difference can be accounted for by including radiation from the screech
shield metal to station A.
An estimate of the nonluminous radiant heat transfer of the gases to
the wall was made for station E in the afterburner where it was felt that
conditions were well enough defined to permit estimation. The radiant
heat transfer from the gases to the afterburner walls was about equal to
the convective heat transfer and the wall at station E was from 2100 to
2800 F hotter than the value predicted from convective heat transfer alone.
This is in fair agreement with the observed wall temperature. The esti-
mated magnitude of radiant heat transfer that is accepted depends upon
the choice of an uncertain correction for the fact that the afterburner
walls have an emissivity less than 1.0. The methods used in the calcu-
lation of nonluminous radiant heat transfer are given in the appendix.
Shielding from gas radiation was previously used as an explanation
for the peculiar results of the wall-temperature measurements at station
A. Also, there is an inference in the comparison of the curves of
figure 10 that the contribution of nonluminous" radiant heat transfer was
roughly constant along the length of the afterburner. This could easily
be the case. Although the bulk temperature or average temperature of the
gases decreases with distance upstream toward the flameholder, local tem-
peratures in some regions of the flame are near stoichiometric mixture
temperature (over 36000 F). (Fuel-air-ratio surveys for this afterburner
configuration showing this to be the case are presented in fig. 9 of
ref. 4.) In this range of temperatures, radiation intensity varies ap-
proximately as the cube of the absolute temperature when changes in gas
emissivity are accounted for. This variation in radiation intensity could
offset the diminishing mass from which gas radiation occurs in the up-
stream parts of the burner.
CONCLUDING REMARKS
An investigation was conducted to determine the effect of pressure
level on afterburner-wall temperatures. It had been anticipated prior
to the investigation that luminous radiation might constitute a signif-
icant part of the total heat transferred to the afterburner walls. It was
also felt that luminous radiation, if present, might intensify with in-
creasing pressure.
The results obtained in this investigation indicated that heat trans-
fer by luminous radiation was not significant at any pressure level in-
vestigated (from 3700 to 6500 lb/sq ft abs). When the ratio ofCONFIDENTIAL
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Shillito, Thomas B. & Smolak, George R. Effect of pressure level on afterburner-wall temperatures, report, June 11, 1958; (https://digital.library.unt.edu/ark:/67531/metadc52844/m1/9/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.