ORNL-1816 - the Molten Salt Energy Technologies Web Site

TABLE 3.1. GAS-FIRED FURNACE OPERATING
CON DIT IONS
Design Actual
Sodium outlet 1500 1500
Sodium inlet te 1100 1215
400 285
Sodium flow, gprn 7.3 8.7
Heat output, kw 100 85
Efficiency
heat removed
x 100). %
heat released
66 55
and test operated at lowe
1400"F), higher efficiencies were obtained, not
only because of the increased temperature differ-
ential between the flue gas and the sodium but
also because of th condition of the inside
surfaces of the fu Over 100-kw output at
essentially design efficiency was attained through-
perature range, but,
because of an flame-fai lure safety
was impossible. After
ad been corrected,
continuous operation at 1500OF was resumed, and
it was found again that 55% was the best ef-
ficiency obtainable.
The furnace performed exceptionally well as a
compact, high-capacity heat source. At the
maximum operating condition of 166 kw total heat
released, the release rate based on the combustion
chamber volume was over 1.5 Mw/ft3, or over
5,000,000 Btu/hr/ft3. It is felt that this heat-
weakening rather than by simple melting. The
weakening of the walls was probably caused by
PERlOD ENDlNG DECEMBER 70, 7954
local boiling of the sodium coolant, by ~iccumu-
lation of a gas pocket in the line, by external
corrosion in the high-temperature exhaust gases,
or by higher-than-predicted local gas-side heat
transfer coefficients. The coolant tubes were
arranged in ten parallel passes that werle mani-
folded into two banks of five passes each. It
was observed in operation that the sodium outlet
temperature from one bank of five tubes was as
high as 155OoF, while that from the other was
only 1480°F. Temperature variation from tube to
tube within each bank of five tubes could con-
ceivably have been equally bad and have resulted
in hypothesized sodium temperatures of 1600 to
165OOF. The boiling point of sodium is 1620°F
at atmospheric pressure and about 1800°F at
2 atm, and thus local boiling of the sodium,
together with consequent reduction in the local
heat transfer coefficient, is certainly a con-
ceivable possibility. Although it seems possible
that small amounts of gas were trapped in the
spirally wound tube coils during initial filling
with sodium, the location of the tube failures
makes it difficult to visualize the accunwlation
of gas in stable gas pockets as contributing to
the failures.
Some external corrosion and erosion of the tubes
were observed, but there was no strong evidence
that they were advanced enough to have been the
cause of failure. The gas-side local maximum
heat transfer coefficient could have been con-
siderably higher than the predicted value! of 60
5tu/hr.ft2."F because of nonuniformity of gas
flow and combustion, and burning could have taken
place on or very near to the tubes in question.
This seems Dossible in view of the location of
t bends of the
let tubes bend
endicular to and
Division in order to obtain more information re-
garding the failures.
d 49