ORNL-1771 - Oak Ridge National Laboratory

used to photograph the event, and illumination is
supplied by an Edyerton stroboscopic flash unit
synchronized with the camera. A repetition rate
of 6000 tranies per second is obtainable with a
flash duration of 2 psec. Closing a single switch
initiates the operation of all the equipment; a time
delay is provided in which the camera can ac-
celerate to full speed before current is passed
through the filament.
FLUID FLOW STUDIES FOR CIRCULATING-
FUEL REACTORS
J. 0. Bradfute L. D. Palmer
F. E. Lynch
Reactor Exper imental Engineering Division
The flow system for the hydradynamic studies of
the ref lector-moderated reactor core, shown sche-
matically in Fig. 8.3, has been fabricated, as-
sembled, and tested. A detailed sketch of the test
section is also shown in Fig. 8.3. Since it will
be necessary to insert, photograph, and then re-
move a coordinate grid from time to time, the
system was designed so that it could be readily
assembled and disassembled. The cores are PO-
sitioned and supported by a brass sleeve, which
was attached to the test section support along its
center line before it was machined. The sleeve
was carefully bored and lapped so that the shafts
protruding downward from the cores would fit with
minimum clearance and yet loosely enough so that
they could be removed by hand. The upper surface
of the test section support flange was machined
perpendicular to the center line of the brass
sleeve. This arrangement permits accurate align-
ment of the core within the Plexiglas test section
without supporting members in or ahead of the test
region. Attempts are currently being made to
obtain some preliminary fluid flow information for
the reflector-moderated reactor core for the straight
entrance condition shown in Fig. 8.3 by photo-
graphing particle flow through the Plexiglas test
sect ion.
The phosphorescent flow-visual ization system,
which was described previously,’’ has been further
modified. The ZnCd sulfide phosphor has been
replaced by a ZnS (Cu-activated) phosphor whose
luminosity was found to be greater after excitation.
The duct work in the flow circuit has been im-
PERIOD ENDING SEPTEMBER JO, 1954
proved so that higher Reynolds numbers are now
attainable, and a diverging Lucite channel has
been constructed. Some of the flow features, such
as asymmetry, flow separation, and the effect of
entrance lengths, are to be observed for different
entrance configurations in such channel systems.
The phosphorescent flow-visualization method is
also to be used in the reflector-moderated reactor
core experiment.
HEAT TRANSFER STUDIES FOR CIRCULATING-
FUEL REACTORS
ti. F. Poppendiek L. Do Palmer
Reactor Experimental Engineering Division
The classical hydrodynamics study, conducted
by Nikuradse,” of converging and diverging
channels was reviewed. It is felt that some of
the fundamental flow features observed in con-
verging and diverging channel systems vyill also
exist in the ref lector-moderated reactor. The
results obtained by Nikuradse indicate that for
the case of turbulent flow in convergent channels
the flow becomes more stable or less turbulent in
nature and that the eddy diffusivities are signifi-
cantly lower than in a parallel-plate channel
system. For the case of turbulent, symmetrical
flow in diverging channels the tlow is tound to
be more turbulent than in the parallel-plate system.
When the total channel angle of a divergent system
is increased beyond 8 deg, asymmetrical flow re-
sults. For a 10-deg angle, a thin, low-velocity
layer of fluid flowing in a reverse direction to the
main stream is noted near one of the channel
walls. This separation phenomenon becomes more
pronounced at larger channel angles.
Some radial temperature distributions were calcu-
lated in the established-flow region of a few con-
verging and diverging flow channel systems con-
taining volume heat sources within the ducted
fluid. The experimental velocity and eddy dif-
fusivity data obtained by Nikuradse were used in
the analyses. The results indicated that wall-fluid
temperature differences con be significantly higher
in converging flow channels than in parallel-plate
systems; the converse is true for symmetrical
diverging #low channels. Asymmetrical divergent
flow passages are difficult to analyze at this time
because the diffusivity structure is not known.
“L. D. Palmer and G. M. Winn, A Feasibility Study
o/ €low Visualization Uszng a Phospharescent Particle 12J. Nikuradse, Forschung.sarbaiten VDI 289, 1-49
Method, .ORNL CF-54-4-205 (Apri I 30, 1954), (1929).
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