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ORNL-2199.txt
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MARTIM MARIETTA
ENERGY SYSTEWS LEBRARIES
3 4456 0350428 7
CENTRAL RESEARCH LIBRARY &
DOCUMENT COLLECTION 2
LIBRARY LOAN COPY
DO NOT TRANSFER TO ANOTHER PERSON
If you wish someone else to see this
document, send in name with document
and the library will arrange a loan.
¥EG
IR
Pt
ORNL -2199
C-84 - Reactors-Special
Features of Aircraft Reactors
This document consists of 148 pages.
Copy f/. of 280 copies. Series A.
Contract No. W-7405-eng-26
Reactor Projects Division
INVESTIGATION OF FLUID FLOW IN THE ART AND OTHER
REFLECTOR -MODERATED REACTOR CORES
Muller
Bradfute
Lynch
LD
H o
DATE ISSUED
- », TS L
"l'v.\‘r“' " 1Oy T
LR T e ’ - T
Toad X
" o, T (TN
UNION CARBIDE CORPORATION
for the 3 445 O3
U.S. ATOMIC ENERGY COMMISSION Ouzs 7
-1ii-
TABLE OF CONTENTS o
Page
SUMMARY .ivcvcveeernssnanoonsssssonsososnssaasosnsssas B 1
NOMENCIATURE . ..vvoveesosscessesossssssrsscnsooncocccasssas tseescrsesreas 6
INTRODUCTION . vsvevococssooonosasosssossoovacoccosrssssnossonnsossesessss 10
Statement of Problem ......... S 10
Developmeant of Project and Statement of Purpose ........... et tavens 10
EXPERTMENTAL APPARATUS .....ccc... ceecsiecesaseanenan ceciecosavecarasess 1D
Flow Systenl vecevsvesoaee s eeteareesetsarrerens cesescenens ceveerannne 15
The Core Models ...cce0ce sevses sessassatssasns settsesssccarssosannns 15
Core Entrance Systems ......... ceeessessssssesaanaans ceccane ceesecannn 21
MATHEMATICAL ANALYSES ....0cececeacranssanaas cecesenan cececracnnnsiases 27
Mean Velocities and Reynolds Numbers in "2l-inch" ART Core ......... 27
Pressure Distributions in ART COTre€ ..cieseecroconsssessssossonsasssos 29
Radial Pressure Differences ...e.ceeeesecens eestectesres st on e cecane 33
Core Desigr. Using the Nikuradse-Buri Parameter I' for rlow in
Divergent Channels ...cc.ceceevreccosrccssccnes recesrersesssssassa 3
Pressure Distribution in ART Heads .eeicevereseccccccnnanes ceerecaae 37
EXPERTMENTAL ERESULTS ........ ceesescesaas tcesecncene cresestesanasena cease Ll
Axial Flow Through Cores ...... Cesesneanaas cetececsscevesncocecnness Bl
Rotational Flow Through COres ........ ceeeenreanan cecoecrecosenaan oo Lo
Flow Through 10/44-Scale ART "21-inch" Core - Twin Tangential
Entrance Header - One-Pump Operation ..... ceceesesascasrssaarao e 55
Flow Through Cores with Turbulence Promotion ....c.ecececesvvoceocass 55
—iv— ! R ey
AT
Page
/;$Ve10city Fluctuations in the Full-Scale ''21-inch" ART Core Model .. 70
Fluid Velocities in the Full-Scale ART '"2l1-inch" Core ............. 82
Pressure Distributions in '"21-inch" ART Core .......... Cer e 82
DISCUSSION - Literature SULVEY .....civertersoronsntosansonsnsonanasass 89
Flow in Convergent and Divergent Channels ............ Ce e R 89
Flow in Curved Channels .......... e Che et 95
Flow Through SCTeens .......iceeivsnonssacsooonsnsnossscnsnsnnans - 98
Screens in Diffusers .................. C et e st et 101
DISCUSSION - Discussion of Results .............. C e 103
Axial Flow Through ART Core Models ........... Chee e Ce e 103
Axial Flow in Two Constant-Gap Core Models .......... Cehe e e e 104
Rotational Flow Through ART Cores ........... N 104
One-Pump Operation - ART Inlet Header ........ c e et 105
Flow Through Cores with Turbulence Promotion ...... Cee e ... 105
Flow Through Cores Packed with Screemns.............. .. iiueun, .... 109
Velocity Fluctuation Studies .............. L ec e s e c e eaan e ceees 113
Average Fluid Velocities in the Full-Scale "2l-inch" ART Core ..... 114
Pressure Distributions in the "21-inch" ART Core .................. 116
Pressure Distributions in ART Heads .........c. iiiiiiiiiinnonnnnns 116
CONCLUSIONS .......... Gt s e et e s e e e ceaer e e rera e 118
APPENDIX A ........... e f e e e ees e s T 122
Velocity Measurement and Flow Visualization Technique ............. 122
APPENDIX B .....c0vvvuns C et bt 133
Flow System Components ........ ettt eetaaas Cearereeersenana Cehaae 133
REFERENCES ....... C it s s e C ettt ee e . 136
INVESTIGATION OF FLUID FLOW IN THE ART AND OTHER
REFLECTOR-MODERATED REACTOR CORES
SUMMARY
The turbulent flow of liquid through ART reflector-moderated reactor
cores of annular cross section has been studied because of the need to ob-
tain a steady flow exclusive of the normal unsteadiness of turbulent flow
in ducts. This steadiness is important because when a large smount of heat
(100,000,000 Btu/hr-ft3) 1s being generated in the volume of liquid by nu-
clear fission at high temperatures (lEOOOF - 16OOOF), low-frequency temper-
ature fluctuations due to unsteady, irregular flow of the liquid can result
in hot spots, thermal cycling, and fatigue of the containing materials.
To facilitate the experimental work, studies were made of water flow-
ing through quarter-scale trafisparent plastic models of the cores so that
flow visualization techniques could be used in the work.
An extensive series of tests of many core systems were made over a
range of Reynolds moduli based on core midplane dimensions and axial flow
rate up to ~,90,000. The corresponding Reynolds modulus for the "2l-inch"
ART core was ~. 95,000, using the properties of fluoride mixture No. 30 at
1h250F. Also, analyses were made .of velocity and static pressure data ob-
teined oa a full-size "21-inch" ART core model with several different en-
trance conditions by Whitman, Stelzman, and Furgerson of ARED.
The following conclusions were reached as a result of this series of
experiments:
- . - . Ir
e
nmmfimmm‘b I
fimx’n*".{}:qg‘.,xg .
(a)
(b)
(c)
Axial flow through the cores with sufficiently large cross-sectional
area expansion rates considered here will always be accompanied by a
separation of the forward flow from a point on the outer wall near
the inlet and viclently unsteady reverse flow in the "separated" re-
gion. This separation at the outer wall is due to the large adverse
rressure gradient resulting from the large area expansion rate, the
lower fluid shear stress at the outer wall than at the inner wall
{common to flow through annular ducts), and the curvature of the
channel. The flow into the entrance of the core models was always
uniform radially and circumferentially, having passed through a calm-
ing length of 40 diameters of straight pipe into an annular "nozzle"
which was mounted on the core entrance.
Rotational, or spiral, fiow through the same cores is always accom-
panied by separation of the forward flow from a point on the inner
well near the inlet and unsteady reverse flow in the separated re-
gion with a velocity component in the direction of the rotation.
The separation in this case is caused by the same adverse pressure
gradient and the lower fluid shear stress at the inner wall relative
to the outer wall (a phenomenon of flow in curved channels). Agsain,
the flow at the core entrance was uniform radially and circumferen-
tlally, having passed through 40 diameters of straight pipe into an
annuler "nozzle" which preceded the turning-vene section which pro-
duced the rotational flow.
In rotational flow, the turbulent interchange of momentum and the eddy
S -3- LI
conductivity are diminished at the inner wall due to the centrifugal
force field set up by the fluid motion; and, therefore, increased tem-
peratures due to volume heat generation can be expected at the inner
wall over the temperatures obtained in straight flow at the same rate
in an equivalent channel.
(d) If the spiral velocities are very high, frictional forces become of
such megnitude that a decay of the spiral velocities becomes notice-
able and a backflow due to spiral vortex decay will begin. fhis was
noticed in the high spiral velocity case studied by Whitman, Stelzman,
and Furgerson. Backflow occurred on the inner well at the exit.plane.
(e) Turbulence promotion within the cores has been shown to overcome the
effects of adverse pressure gradients, but the promoters must be such
that they do not introduce unsteady flow; i.e., the scale of the pro-
moted turbulence must be very small. Woven-wire screens and perforated-
plate screens of low solidity and small wire diameter (or web thickness)
packed into the divergent part of the core flow channels are of such
nature. Turbulence promoters such as vortex generators or large ob-
structions placed in the core entrance cause unsteady flow although
they seem to eliminate the separation and the associated backflows.
(f) Straight annular cores and cores of sufficiently low expansion rates
can be constructed to give a steady, unseparated flow with axial flow.
Calculations show tpat the meximum midplane-to-inlet area ratio that
can be achieved with axial flow through & bare core is 1.33:1 within
an 18-in. length of a 21-in.-0.D. core with the same midplane area
G b £
{(g)
(h)
as the "21-inch"” ART core.
Calculations have shown that a pressure unbaslance (L lb/in.e) due to
momentum transfer exists in the header which is of the same order as
the friction losses in the core., This pressure discrepancy is in the
form of a rise in pressure as the fluid traverses the length of the
header from the inlet duct. The unbalance, plus any unsteadiness trans-
mitted to the flow by the fuel pumps, will also creste peripheral flow
asymietries and unsteady core flow,
The calculations also point up two considerations. One is that
the header pressure unbalances are primarily due to the average fluid
velocity level in the headers considered. Thus, header fluid veloc-
ities should be kept as low as practicable. The core pressure 1loss
should also be as large as practical to keep the relative importance
of the header unbalances small.
Since screen packing in the core has been shown to eliminate the un-
steady flow, which is an inherent characteristic of the core shape, it
1s proposed that this system be used in the core. An additional sdvan-
tage accrues from the use of the screens in an increase in core pres-
sure loss and the related velocity profile flattening. The peripheral
asymmetry due to pressure unbalances in the header will then be much
less than exists without the screens. It is felt that perforated-plate
screens with the same relative pressure loss and mesh size as the wire
screens tested would be more advantageous from the structural and fab-
rication standpoint than the wire screens.
Foo i
M
N -5-
The heat-transfer characteristics of the screens are in the proc-
ess of being investigated to determine whether any problems exist in
this regard.
(1) A header system has been designed which may afford smaller pressure un-
balances than the present header system and, being used in conjunction
with the screen-packed core, may allow single-pump operation without
large peripheral flow asymmetries. Further experimental work is in
process to establish the validity of this conclusion and conclusions (g)
and (h).
=
=
Re
Aol
-6- fi;-@ L,
NOMENCLATURE
constant, f’t2
core cross-sectional area perpendicular to core axis, ft2
header cross-sectional area perpendicular to flow direction, ft2
constant, ft
constant, fte/sec
constant, £72
2
constant, ft
typical dimension of screens; wire diameter, bar width, effective
web thickness of perforated-plate screen (d = M - 0.95 D), ete., ft
hole diameter in perforated-plate screen, ft
hydraulic diemeter, ft 7
eddy diffusivity, equal to -E , Tt°/sec
coefficient of friction in Fanning equation, dimensionless
gravitational constant, ft/sec2
head, f't
head at position 1, ft
head at position 2, ft
mixing length according to Prandtl, ft
flow path length in core, ft
axial length of core, ft
spiral flow path length in core, ft
mesh size of screen, ft
Reynolds modulus, dimensionless
=%
NRe,sc
NRe,avg
Reynolds modulus based on d, typical dimension of screen, dimensionless
axial flow Reynolds modulus based on average core dimensions and mass
flow rate in core, dimensionless
axial flow Reynolds modulus based on core midplane or equator dimen-
sions and mass flow rate in core, dimensionless
pressure, lb/ft2
pressure at inner core wall, lb/ft2
pressure at outer core wall, lb/f‘l:2
pressure at position 1, including pressure due to elevation, 1b/ft2
pressuré at position 2, including pressure due 1o elevation, lb/ft2
pressure at O-deg plane in header, lb/ft2 (see Figure 20)
pressure at 90-deg plane in header, lb/ft2 (see Figure 20)
pressure at 130-deg plane in header, 1b/ft2 (see Figure 20)
pressure difference, lb/ft2
axisl-flow pressure difference across core, lb/ft2
spiral~-flow pressure difference across core, lb/ft2
volume flow rate, ftg/sec
radius, ft
radius of inner weall of core, ft
radius of centerline of core flow channel, ft
radius of outer wall of core, ft
ratio of spiral flow path length to core length, dimensionless
a length along spiral flow path, ft
half-width of core flow channel perpendicular to channel centerline, ft
root-mean-square of fluctuating velocity component in direction per-
pendicular to plane of channel walls in two-dimensionasl flow, ft/sec
8. 2
axial component of velocity in core, ft/sec
average of above, ft/sec
fluid velocity in header, ft/sec
fluid velocity at inlet of header, ft/sec
mesn velocity in channel at any cross section, ft/sec
maximum cf above, ft/sec
2
t,ave * Ya,ave ’ ft/sec
average spiral velocity in core, equal to flJ-v
peripheral, rotational, or tangential velocity component, ft/sec
average of tangential velocity component in core, ft/sec
velocity at position 1, ft/sec
velocity at position 2, ft/sec
root-mean-square of fluctuating velocity component in direction
of flow, ft/sec
mass flow rate in header, lb/sec
mess flow rate at inlet of headér, 1b/sec
distance parallel to channel wall in direction of flow, ft
distance from core inlet along core axis, ft
distance from header O-degree plane along mean length of header, ft
(see Figure 20)
distance downstream from screen plane, ft
mean length of header, ft
differential element of length in direction of flow, ft
distance from channel wall perpendicular to plane of channel wall, ft
differential element of length perpendicular to plane of channel
wall, ft
distance from core midplane parallel to core axis, ft
_.9..:
angle between spiral-flow component and plane perpendicular to core
axis, deg ‘
density, lb/f'b3
boundary layer thickness, ft
turbulence factor, equal to pl2 %% ’ lb--sec/ft2
o
momentum thickness of boundary layer, equal to.f (1 - —) X dy, ft
0 Vmax mex
coefficient of viscosity, lb-sec/ft2
. . K 2
kinematic viscosity, equal to 0’ ft /sec
mass density, lb-—sece/-ft)+
shear stress, lb/ft2
— -10- fié;:i v
INTRODUCTION
*n
Statement of Problem
The design of circulating-fuel nuclear reactor systems which must operate
at high power densities (~-100,000,000 th/hr‘ft3) and at temperatures near to
the limits of endurance of their containers (lEOOoF - l600°F) places special
emphasis on the detailed knowledge of the behavior of the circulating-fuel tem-
peratures with respect to position and time.
According to analyses on forced-convection heat transfer with volume heat
sources within the liquid,l’ 2, 3 the temperature distribution depends upon the
velocity distribution, the heat-generation rate, the heat-removal rate at the
wall, and the molecular and turbulent heat transport properties of the liquid.
If the velocities and turbulent heat-transfer properties are unstable with time
and asymmetric with respect to the channel center and core circumference, then
fluctuating temperature distributions and hot spots will occur due to the asym-
metrical heat removal from the core. The magnitude of the temperature oscillé-
tions and hot spots may or may not exceed the endurance limits of the containing
materials.
The problem took two parts: the first, to find some way of obtaining sta-
ble and peripherally symmefrical flow in the ART cores proposed by A. P, Fraas
and W, T. Furgerson of the Osk Ridge National Leboratory Aircraft Reactor Engi-
neering Division; and second, to ihvestigate other designs for reflector- fl
moderated reactor cores in an effort to find some configurations which would
not have unstable flow,
Development of Project and Statement of Purpose
In 1952, R. E. BalllF observed the flow of air through a configuration
wni
called the "Fireball" reactor core which had an annular cross section prepen-
dicular to the flow. The center-to-inlet (or exit) area ratio was 5.4:1 while
the total length of the varying cross section was 24.6 in., A section parallel
to the core axis is seen in Figure 1.
Ball found that the forward flow separated from the outer shell at approx-
imately 5.3 in. from the inlet and that the separation increased in sevefity
with distance along the flow path. By filling in the region of separation using
plasticene, Ball was able to provide a flow contour which reduced the amount of
reverse flow. Since the velocities, as measured with a pitot tube, were still
low near the walls, vanes were added in the inlet which, after some exfierimen-
tation, produced a fairly flat velocity distribution. However, no observations
were made to determine fluctuations in the velocity with time.
Ball states that some pecularities in forming the Plexiglas outer shell of
the core resulted in a greater rate of divergence than anticipated. However,
since the originally designed rate of divergence was so much greater than the
limiting maximum value of 8 deg included angle for a conical diffuser in which
no separation takes place, separation would have occurred even without the vari-
ations introduced in fabrication. Filling in the flow passage reduced the rate
of divergence of the channel.
.Evidently, Ball's results were deemed inconclusive either because .of the
inaccuracies in fabricating the Plexiglas core shells or because of the reduced
core diameter resulting from the "filling in", since another investigation was
begun by Stumpf of ARED.26 During the second quarter of 1954, the experimental
> and H. F. Poppendiek.
study reported here was initiated by J. 0. Bradfute
—§2-
ORNL-LR-DWG 2244 9
10—in. DIA.
6-in, DIA,
9-in. DIA. _
6—in. DIA.
)
N
N
N
|
ORIGINAL CONTOUR g . N r;_:) g
It \ T
9-in. DIA. __[ .
3/ £
‘ 1794 ~in. DIA; g -1 9
\ 15.7—-in. DIA. ©
\ o
X\
£
Q
Ty \
Fig. 1. Cross-Section of Mode! of "Fireball" Reactor Core (Reference 4)
r
Lyt m A
B Cur, }%
E,:a(«{ capall s
N
36 in.
18 in,
Fig. 3. Cross—Section of 21-in. ART Core Flow Channel
Bradfute studied the flow of water through a quarter-scale model of a
core with an equatorial outer diameter of 18 in. This core was assembled
using stainless steel for the inner shell and Plexiglas for the outer shell,
both shells being carefully machined to the correct contours. The shape of
this "18-inch" core differed from that studied by Ball and is shown in
Figure 2. The full-scale core had a midplane-to-inlet area ratio of 3.8:1
and an over-all length of 36 in., The reduction in the area expansion ratio
was effected by increasing the outer shell diameter at the inlet from 8 in.
to 10 in. This change, coupled with an increase in core length, resulted in
a reduction in the channel divergence angle.
It was later found32 that the "18-inch" core required a larger UFA con-
centration (6.5 to 9 mole %) than was originally calculated (~.4 mole %). The
new calculations showed that a 21-in.-dia core would be required to obtain the
4 mole % concentration. The core shape was proposed by W. T. Furgerson. This
design had a midplane-to-inlet area ratio of h.36;l in the same length as the
"18-inch" core. This core is shown in Figure 3. Early in 1955 work was in-
itiated on a 10/44-scale model of this "21-inch" core.
Parallel to this investigation, full-size "21-inch" core mock-up studies
were carried out by G. D. Whitman, W. J. Stelzman, and W. T. Furgerson using
the header and pump system designed by Furgerson et al. “
Studies of circulating-fuel reactor core hydrodynamics have also been
made at Pratt and Whitney Aircraft in conjunction with their reactor research
program_33-uh Mention of these studies is made so that a complete reference
to all published reports known to the authors on this subject is at hand.
af
-— 2
Due to the lack of an adequate analytical technique for establishing
ey
velocity distributions in geometries as complex as those of the ART cores, re-
course was made to the experimental solution of the problem. The techniques
described were developed to provide a means for rapid qualitative examination
of the velocity distributions in the test core geometries.
Since it was felt that the phenomena of separation, backflow, and large-
scale unsteady flow observed in the "18-inch"” and "21-inch" cores were un-
desirable for a high-temperature, high-power-density core, much emphasis was
placed on the effort to find reflector-moderated reactor core systems which
possessed steady flow.
Most of the velocity distributions shown were sketched from visual obser-
vations of the deformation of a glowing band of excited phosphor particles as
they moved with the water through the core models. Measurements of the veloc-
ity distributions for the case of axial flow through the "18-inch™ ART core
model were made by the stroboscopic photography of tobacco seeds suspended in
the flowing water.
Analyses of the data obtained by the group studying flow in the full-
size model of the "21-inch" core with several different entrance systems are
also presented.
— 13-
EXPERTMENTAL APPARATUS
Flow System
The experimental flow system consisted of a recirculating loop contain-
ing fluid reservoirs, a centrifugal pump, flow and temperature measurement
and control devices, and a test section containing the core models and associ-
ated entrance and exit regions. A schematic drawing of the system is shown
in Pigure 4. PFurther details regarding the system components are presented
in Appendix B.
Water was used as the working fluid. Both stroboscopic particle photo-
graphy and phosphorescent particle visualization techniques were used to
establish the local velocities and flow characteristics of the core regions.
These methods are discussed in greater detail in Appendix A. The over-all
friction losses in the cores were determined using a 30-in., U-tube mercury-
manometer, Inlet and exit fluid temperatures were measured with mercury-
glass thermometers. The core models and entrance systems studied are de-
scribed in the following paragraphs.
The Core Models
The core models studied are tabulated below:
a. A 1/4-Scale Model of the "18-inch" ART Core. The outer shell was
machined from a solid Plexiglas piece and the island was machined from stain-
less steel. Figure 5 shows a cross-sectional view of this test section with
a table of typical dimensions. The dimensions of the inner and outer walls
of the full-size core are obtained from the cylinders of revolution described
SURGE CHAMBER
-16-
ORIFICE
UNCLASSIFIED
ORNL-LR-DWG 7170
STIRRER
TANK
MERCURY
MANOMETER
T
CENTRIFUGAL
PUMP
Fig. 4. Schematic Drawing of Experimental Flow System.
1]
TEST SECTION
CONTROL
VALVES
*TO DRAIN
Haw,
PLEXIGLAS SHELL
DISTANCE FROM MIDPLANE (in.))
INNER DIAMETER (in.)
OUTER DIAMETER (in.}
oo
Fig. 5.
| TR
—_ 7
ORNL—LR—-DEZZ44
I I
rY
k=g r A
nc-,;_:,—-\:
1
e STAINLESS STEEL ISLAND
][ MIDPLANE
T
Y [
) LA
Zk 7/ % ' [/l=—TEST SECTION SUPPORT
[ ] 2] I Z
g / !
0N
G 1 N
H : s
1 N
N 7 N
LA ] ;\ |
TN N
| /l
1 |
0 05 10 15 20 25 30 35 40 45
2.250 2.162 1.940 1.688 1.523 1.500 1.500 1.500 4.500 {.50C
4.500 4.42) 4.198 3.870 3493 3133 2.851 2.692 2.574 2.50C
Cross Section of Quaorter-Scale 48-in. ART Core Model.
_— 18-
by the equations,
r = 1.8230 cos %% + 7.1770 for 0 <z <13.5
Outer Wall r, = 7.0360 - 0.11799 2 for 13.5 < z < 16.5 (1)
r_ = 1.8230 cos 1’-(51;—3-)- + 6.8230 for 16.5 < z < 18
r. = 0.7500 cos % + 3.7500 for 0 <z< 9
Inner Wall * (2)
r, = 3.000 for 9 <z<18
Al) dimensions are in inches. The midplane-to-inlet area ratio was 3.8:1.
b. A 10/44-Scale Model of the "21-inch" ART Core. The outer shell and
island of this model were constructed as in a. Figure 6 shows a cross section
of this core. The dimensions of the core model are also given. The centerline
of the full-size flow passage 1s described by a cylinder of revolution generated
by the equation,
r, = 1.719 cos %§-+ 6.219 . (3)
The midplane-to-inlet area ratio was 4.36:1.
¢. A Constent-Gap-Width Core Model using the "Island" of the ART "2l-inch”
Core end a New Outer Shell. The ratio of the midplane to the inlet areas was
1.443:1. Figure 7 shows a cross section of this core model along with the core
dimensions.
d. Another Constant-Gap-Width Core Model using the Outer Shell of the
"21-inch" Core and a New Island. The Plexiglas shell was split in two pieces
to allow the "island" to be put in place, since it was too large to go through
the open end of the shell. Three long bolts compressed a lead gasket between
-49 -
ORNL-LR-DWG 224
//STAINLESS STEEL ISLAND