ORNL/TM-5335
Dist. Category UC-76

Contract No. W-7405-eng-26

Reactor Division

HEAT TRANSFER MEASUREMENTS IN A FORCED CONVECTION LOOP WITH
TWO MOLTEN-FLUORIDE SALTS: LiF-BeF»-ThF,-UF, AND
EUTECTIC NaBF,-NaF

M. D. Silverman W. R. Huntley H. E. Robertson

Date Published; October 1976

NOTICE
This report was prepared as an account of work
sponsored by the United States Government. Neither
the United States nor the United States Energy
Research and Development Administration, nor any of
their employees, nor any of their contractors,
subcontractors, or their employees, makes any
warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness
or usefulness of any information, apparatus, product or
process disclosed, or represents that its use would not
infringe ptivately owned rights.

 

 

 

 

 

Prepared by the
OAK RIDGE NATIONAL LABORATORY
Oak Ridge, Tennessee 37830
operated by
UNION CARBIDE CORPORATION

for the ' ?fi
ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION M QS’{E“

 
OAK RIDGE NATIONAL LABORATORY

OPERATED BY
UNION CARBIDE CORPORATION
NUCLEAR DIVISION

UNION
CARBIDE

POST OFFICE BOX X
OAK RIDGE, TENNESSEE 37830

November 10, 1976

To: Recipients of Subject Report

Report No.:___ ORNL/TM-5335 Classification: ___Unclassified

Author(s): M. D. Silverman, W. R, Huntley and H, E, Robertson

Subject:__Heat Transfer Measurements in a Forced Convection Loop with

 

Two Mo

Please make pen and ink corrections to your copy(ies) of subject report
as indicated below.

Title page (inside and outside in title, ThF, should read ThFy)

Page 1 in title, ThFy, should read ThFy

 

Page 1 in Abstract, Line 2, ThF2 should read ThFh

 

Page 1 third line from bottom, ThF2 should read ThFu.

DX gl

J. L. Langford, Supervisor
Laboratory Records Department
Information Division

JLL:we
CONTENTS
ABSTRACT ...vvvevrenncns teseaaras cesevnnn
INTRODUCTION ..... ceeenn ceeaas
EXPERIMENTAL ....vevviaeccenrannconss .o
DATA AND CALCULATIONS .......... sesens .
ANALYSIS AND RESULTS ..vneecenns sesssees
CONCLUSIONS ....... ceeessssane caresnaa .
NOMENCLATURE ...icceteennsansanes cereenne
ACKNOWLEDGMENTS ....ccicieceneannsss cesnes
REFERENCES ....cccvevenans ceeverteens .o

iii

ccccc

12
16
23
24
25
25
HEAT TRANSFER MEASUREMENTS IN A FORCED CONVECTION LOOP WITH
TWO MOLTEN-FLUORIDE SALTS: LiF-BeF,-ThF,-UF, AND
EUTECTIC NaBF,-NaF

M. D. Silverman W. R. Huntley H. E. Robertson

ABSTRACT

Heat transfer coefficients were determined experimentally
for two molten-fluoride salts [LiF-BeF,-ThF,-UF, (72-16-12-0.3
mole %) and NaBF,-NaF (92-8 mole 7)) proposed as the fuel salt
and coolant salt, respectively, for molten-salt breeder reactors.
Information was obtained over a wide range of variables, with
salt flowing through 12.7-mm-0D (0.5-in.) Hastelloy N tubing
in a forced convection loop (FCL-2b).

Satisfactory agreement with the empirical Sieder-Tate
correlation was obtained in the fully developed turbulent re-
gion at Reynolds moduli above 15,000 and with a modified Hausen
equation in the extended transition region (Re Vv2100-15,000).
Insufficient data were obtained in the laminar region to allow
any conclusions to be drawn. These results indicate that the
proposed salts behave as normal heat transfer fluids with an
extended transition region.

Key words: Heat transfer, molten-fluoride salts, sodium
fluoroborate, forced convection, transition flow regime, tur-
bulent flow.

INTRODUCTION

The heat transfer properties of various molten-salt mixtures are
needed for designing certain components for molten-salt breeder reactors
(MSBRs). Previous investigations have demonstrated that molten salts
usually behave like normal fluids;!™? however, nonwetting of metallic
surfaces or the formation of low-conductance surface films can occur,l+
indicating that heat transfer measurements for specific reactor salts are
necessary. A forced convection loop (FCL-2b), designed primarily for
corrosion testing, was used initially to obtain heat transfer information
on a proposed NaBF,-NaF (92-8 mole %) coolant salt. More recently, tests
were made in the same loop with a proposed fuel-salt mixture [LiF-BeF;-

ThF,-UF, (72-16-12~0.3 mole %)].

Heat transfer coefficients were obtained for a wide range of vari-

ables (see Table 1) for both salts flowing through 12.7-mm-0D (0.5-in.)
Table 1.

Variables used in heat transfer measurements

 

Reynolds modulus
Prandtl modulus
Fluid temperature
Heat flux

Heat transfer co-
efficient

Nusselt modulus

Reynolds modulus
Prandtl modulus
Fluid temperature
Heat flux

Heat transfer co-
efficient

Nusselt modulus

Fuel-salt data

154014, 200

6.6-14.2

549—765°C (1020—1440°F)

142,000—630,000 W/m® (45,000~200,000 Btu hr~! ft~2)

1320-11,800 W m~ 2 (K)~! [230—2080 Btu hr~! ft~?
(°F)~1] -

11-102

Coolant-salt data

5100—45,000

5.3-5.64

450—610°C (840~1130°F)

136,000~499,000 W/m® (43,000~158,000 Btu hr~! ft~2)

1380—10,100 W m~% (K)~! [240-1780 Btu hr~! ft~2
(°F)~1]

35-255

 

Hastelloy N tubing.

These results are compared with calculated coeffi-

cients, using accepted heat transfer correlations for the various flow

regimes and known values for the physical properties of the salts.

EXPERIMENTAL

Forced convection loop MSR-FCL-2b, designed primarily for corrosion

testing,5 was used for these experiments. The loop (Fig. 1) is constructed

of 12.7-mm-0D (0.5-in.), 1.09-mm-wall (0.043-in.) commercial Hastelloy N

tubing and contains three corrosion test specimen assemblies exposed to the

circulating salt at three different temperatures and bulk flow velocities

of 1.3 (4.3) and 2.5 m/sec (8.2 fps). Two independently controlled
HEATER LUGS (TYPICAL)-——u

RESISTANCE HEATED SECTION NO.1-.

A BALL VALVE

@_-‘ AUXILIARY TANK

N ——y

3
R D

HEATER LUGS (TYPICAL)

 

COOLER NO.1{

SALT PUMP

CORROSION

SPECIMENS- DRAIN AND

FILL LINE

   

   

CORROSION
COOLER NQ.2 -~ SPECIMENS

f

 

1150°F

, b "~ DRAIN AND FILL LINE
o T Ya=in.0D x 0.035-in. WALL

“ THERMOCOUPLE WELL

DRAIN AND FILL LINE

CRNL-DWG 70-5632

FREEZE VALVE
(TYPICAL) . T/
S

AR =y =
CORROSION SPECIMENS—_

 
 

 
 
   
 
      
  
 
   
 
 
      
    
  

-

" THERMOCOQUPLE
WELL. -

-Yo-in.0D x 0.042-in. WALL
HASTELLOY N

    
   

Fig. 1. Molten-Salt Forced Convection Corrosion Loop MSR-FCL-2.
resistance~-heated sections and two finned-tube coolers provide a tempera-
ture differential of V166°C (300°F) at the normal flow rate of 2.5 x 107"
m¥/sec (8.8 x 1073 ft3/sec). Resistance heating (I°R heaters) is supplied
by a four-lug system, with voltage potential applied to the two center
lugs while the two exterior lugs are at ground potential (Fig. 2). Thus,
there is an unheated section at the center lugs. Because the electrical
resistance of the molten salt is very high compared with that of the metal
tubing (whose resistance remains almost constant over the temperature
range of these experiments), this method of heating is well adapted to the
system. One resistance-heated section (the heat transfer test section,
designated No. 2) contains an actively heated length of 3.5 m (11.5 ft),
resulting in an L/D ratio of 331 and a heat transfer area of 0.115 m?
(1.08 ft?). Guard heaters (clamshells) are located on the heater lugs and
along the resistance~heated tube to make up heat losses during the heat
transfer runs (Fig. 3). Figure 4 shows the test loop with all heaters,
thermocouples, and thermal insulation installed.

The temperature of the bulk fluid is measured by three thermocouples
located in wells at the inlet and the exit of the test section. Wall
temperatures along the heated section are measured by 12 sheathed,
insulated-junction, 1.02-mm-0D (0.040-in.) Chromel-Alumel precalibrated
thermocouples that are wrapped 180° circumferentially around the tubing
and clamped against the wall at about 0.30-m (1-ft) intervals. Thermo-
couple readings during the experiments are recorded automatically by the
Dextir, a central digital data-acquisition system with an accuracy of
+0.107% of full scale and a resolution of 1 part in 10,000.

The actual dimensions of the tubifig in resistance-heated section 2
were determined before installation. The tubing outside diameter, mea-
sured by conventional outside micrometers, averaged 12.68 mm (0,499 in.);
the tube wall thickness, measured with an ultrasonic Vidigage, averaged
1.09 mm (0.043 in.). Therefore, the tube internal diameter at room tem-
perature was calculated to be 10.49 mm (0.413 in.), and this value was
used in all subsequent heat transfer calculations.

A variable-speed drive motor on the pump (Fig. 5) controls the salt

flow rate. 1In the fuel-salt experiments the pump speed was varied from
ORNL-DWG 76-13593

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12.7-mm~-0QD
HASTELLOY N
25 mm TUBING
GROUND CENTER GROUND
LUG LUGS LUG
0.15 m
0.10 0.10} [0.10 0.10
o 1.75 m |y 175 m————> e 0.46 m
1 t i | | l I I I | 04A,
T/C WELL ' ' ' : ' ! ! ' ' ' ' ' T/C{V)\IELL
L K J | H G F E D C B A (3 T/Cs)

{3 T/Cs)

FLOW

Fig. 2. Heater test section 2 — details.
 

 

 

 

 

Fig. 3.

Center lugs and clamshell heaters on No. 2 heater

| PHOTO 78422

 

section,

 

 
 

SALT DRAIN TANK

Fig. 4.

 

Sait test loop

with protective

 

PHOTO 3221-76

 

- RESISTANCE HEATED B8 b
SECTION NO. 2

 

metal enclosures removed.

 
 

ORNL-DWG 69-8961R
ELECTRIC LEVEL
PROBE

 
  
 
    
        
   
  
  

UPPER SEAL -

 

 

 

LUBRICATION
oL IN

 

 

N~ LIQUID SAMPLING
PORT -

 

 

 

 

 

GAS LINE - '
LOWER SEAL

 

 

COOLANT

GAS INLET . oIL

     
  
  
  
   
   
 

  

OIL SEAL
LEAKAGE , .

THERMAL
BARRIER - -

AUXILIARY
- TANK

LIQUID LEVEL

-IMPELLER

o 1 2
1.1 s
INCHES

Fig. 5. ‘Alp.ha pumpl.

 
1000 to 4700 rpm, yielding flow rates of 40 to 250 ml/sec, which corre-
sponds to a Reynolds modulus (NRe) of 1542 to 14,200. The lower flow
limit was set to avoid salt freezing, whereas the upper limit was dictated
by the horsepower required for driving the pump. Tests with the coolant
salt were done at pump speeds up to 5300 rpm, since this salt is less
dense and requires less pumping power for a given flow rate.

Initially, a series of heat loss measurements was made with no salt
in the loop in order to determine correct guard heater settings to be used
in the heat transfer experiments. In these tests, the power input to the
guard heaters was varied and subsequently plotted vs the average tempera-
ture obtained from readings of the 12 thermocouples (A—L) on the surface
of the loop piping. These data then were used to demonstrate the error
in surface-mounted thermocouple readings in a subsequent test where the
guard heaters were not energized and salt flow was V2.5 X 107" m3/sec.

For example, in run 1 (Fig 6) (line YY), 1250 W was the power input to the
guard heaters; the average temperatures of the bulk fluid obtained from
the three thermocouples in the inlet and outlet wells were 663°C (1225°F)
and 665°C (1129°F), respectively. The average of all the 12 thermocouple
readings (A—L) from the surface of the loop piping was 664°C, indicating
good agreement with the bulk fluid temperature. 1In run 2 (line XX), no
power was applied to the guard heaters; the bulk fluid temperatures ob-
tained from the three thermocouples in the wells at the inlet and exit
averaged 748°C and 750°C (1382°F), respectively. However, the 12 surface
thermocouples yielded an average temperature of only 732°C, indicating a
wall temperature error of approximately 17°C (31°F) without the guard
heaters. In all experiments, power input to the guard heaters was ad-
justed to balance any heat loss from the test section.

In each experiment, after power was supplied to the 1%R heaters,
steady-state conditions were established (with appropriate guard heater
wattage) before taking readings of the loop operating parameters [i.e.,
inlet and outlet temperatures, wall temperatures, power input to the
guard heaters, pump speed, and resistance heating wattage (the latter
measured by calibrated precision wattmeters having an accuracy of +0.25%)].
Two sets of readings, taken at least 10 min apart, were recorded for each

data point. The data for a typical experiment (Fig. 7) show the wall
TEMPERATURE (°F)

1500

1300

ORNL- DWG 76 13594

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

| | | | | [ | ! | |
LETTERS A-L
DENTIEY RUN 1 -7 — GUARD HEATERS ON — BULK FLUID TEMPERATURE A (LINE YY)
OUTER SURFACE N B
O N OCOUPLES RUN 2 —O — GUARD HEATERS OFF — BULK FLUID TEMPERATURE (O) (LINE XX)
FLOW
X
-©
O | O
O O O O
i O
C D E F G H | J K L
LET WELL < AVERAGE OF 3 T/Cs > QUTLET WELL
z v A
Avi A
7 7
v Vv 7 v
0.3 0.6 0.9 1.2 15 1.8 2.1 2.44 2.74 3.05 3.35 3.70
1 2 3 4 5 6 7 8 9 10 11 12

DISTANCE FROM FIRST HEATER LUG

Fig. 6. Heat loss tests, FCL-2b.

0T
TEMPERATURE (°F)

ORNL -DWG 76-13595

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1400 1 | | | |
NOTE: THERMOCOUPLES A AND C INOPERATIVE
8-6-75 (12:24) o .
FLOW RATE ~4.6 gpm FLOW . o
IR HEAT — 71.25 kW o
®
*
1300 . . .
®
A 8 C D E F G H | J K L
/‘/KC)Y
| /-/ .
1200 EP.ATUP‘E// OUTLET WELL-\
D TEMPE—] AVERAGE OF
LK FL 3 T/Cs
’/BU/
INLET WELL |
3 T/Cs
M
1100
(m} 0.3 0.6 0.9 1.2 15 1.8 2.1 2.44 2.74 3.05 3.35 3.70
(f1) 1 2 3 4 5 6 7 8 9 10 11 12

DISTANCE FROM FIRST HEATER LUG

Fig. 7. Heat transfer run 5 — fuel salt.

TT
12

temperatures recorded by the surface thermocouples at the appropriate
locations. There is a slight drop in wall temperature between the F and
G locations (Fig. 2) which is probably caused by an increased film coeffi-
cient due to turbulence from weld penetrations at the lugs (F is located
150 mm upstream of the center power lugs and G is 150 mm downstream).
However, the bulk fluid temperature at any location along the piping was
assumed to rise linearly by drawing a line connecting points X and Y,
which were the temperatures obtained by averaging the three thermocouple
readings from the inlet and outlet thermocouple wells, respectively.

Initially, there was concern that the sheathed thermocouples strapped
against the tube wall surface might not measure the surface temperature
accurately because they were not bonded to the wall. Therefore, four
0.25-mm-0D (0.010-in.) bare-wire thermocouples were spot welded to the
heated tube wall for comparison purposes. These four thermocouples were
read with a potentiometer, while the sheathed thermocouples were recorded
by the Dextir. Special test runs were made with the guard heaters both
on and off to observe the performance of the two types of thermocouples
at surface temperatures ranging from 444 to 605°C. With the guard heaters
set at the proper level to make up heat losses, the sheathed thermocouples
read randomly higher than the bare-wire thermocouples by 0.6 to 3.9°C.
Without guard heat, the sheathed thermocouples read randomly lower by 0.3
to 3.9°C. It was concluded from these measurements that the sheathed
thermocouple readings were sufficiently accurate for our tests.

The physical properties of the fuel salt and coolant salt®~® used in
these experiments are listed in Tables 2 and 3, chemical analyses are given

in Table 4, and properties of the Hastelloy N alloy9 are shown in Table 5.

DATA AND CALCULATIONS

Nine heat transfer tests were made with the coolant salt and twenty-
one with the fuel salt. The data from these experiments, along with the
necessary physical constants, were used to calculate the dimensionless
parameters such as the Reynolds, Prandtl, and Nusselt numbers by the
following procedure. Initially, the inside wall temperature of the tube

at each thermocouple location was obtained from the measured outside wall
13

Table 2. Thermophysical property data for molten-salt fuel
mixture LiF-BeFy~ThFy-UFy (72-16-12-0.3 mole %)

 

 

Parameter Value Uncertainty Ref.

Viscosity

1b ft~! hro! 0.264 exp [7370/T(°R) +10% 6

Pa/sec 1.09 x 10™"% exp [4090/T (K)] +10% 6
Thermal conductivity

Btu hr™! ft=! (°F)~! 0.71 +15% a

Wm !t (K)7! 1.23 +15% a
Density

1b/fte? 228.7 — 0.0205T (°F) +1% 6

kg/m> 3665 — 0.591T (°C) +1% 6
Heat capacity

Btu 1b~! (°F)~! 0.324 +47, 7

J kg™! (®)~! 1357 +47 7
Liquidus temperature

°F 932 +10°F 7

°C 500 +6°C 7

 

ZEstimated from values given in Ref. 8 for analogous salts.

Table 3. Thermophysical property data for molten-salt coolant
mixture NaBF,-NaF (92-8 mole %)

 

 

Parameter Value Uncertainty Ref.

Viscosity

1b ft~! hr! 0.212 exp [4032/T (°R)] +10% 6

Pa/sec 8.77 x 10~° exp [2240/T (K)] +10% 6
Thermal conductivity

Btu hr~! ft7! (°F)"! 0.24 +15% 8

Wwm ! (R)7! 0.42 +15% 8
Density

1b/ft? 141.4 — 0.0247T (°F) +1% 6

kg/m? 2252 — 0.0711T (°C) +1% 6
Heat capacity

Btu 1b~! (°F)~! 0.360 +2% 7

J kg™! (x)7! 1507 +2% 7
Liquidus temperature

°F 725 +2°F 7

°C 385 +1°C 7

 
14

Table 4. Typical analyses of
fuel salt LiF-BeF,-ThF,-UF,
(72-16-12-0.3 mole %) and
coolant salt NaBF,-NaF
(92-8 mole 7)

 

 

Constituent Weight % ppm
Fuel salt
Li 7.28
Be 2.03
Th 44 .97
U 1.00
F 45.03
Ni 70
Cr 85
Fe 45
0, 58
Coolant salt
Na 21.5
B 9.7
F 68.3
Ni 7
Cr 80
Fe 350
0- 700
H 30
Mo 3

 

Table 5

. Properties of Hastelloy N alloy9

 

Thermal conductivity, W em™ ! (°c)!

At 0—440°C
At 440-700°C

Electrical resistivity, ufi~cm

+1.25 x 10™* (°C)
7

0.1
0.07724 + 1.897 x 10~" (°C)

At 24°C 18.8
At 704°C 19.7
Mean coefficient of thermal expansion (20—650°C) 14 X 107%/°C
Chemical composition,?
Chromium 6.00-8.00
Molybdenum 15.00-18.00
Iron 5.00 (max)
Silicon 1.00 (max)
Manganese 0.80 (max)
Carbon 0.04—0.08
Nickel Balance

 
15

temperature by the equation10

q T r°—r;
=t —t,=—m———— (" In —— ———

wall 0 i 2 __ .2 ’

ZTrLkN(rO ri) r 2

AT
where ro and r, are the outside and inside radius of the tube, respec—
tively; tO and ti are the outside (surface) and inside wall temperatures;

L is the test-section length of tubing; kN is the thermal conductivity of
the Hastelloy N tubing at the corresponding outside wall temperature; and
q is the rate of heat transfer to the fluid.

The temperature drop through the fluid film was then obtained by
subtracting the temperature of the bulk fluid (estimated from the linear-
type plot shown in Fig. 7) from the inside wall temperature.

Local heat transfer coefficients were calculated from the experimental
data by employing the equation for convective heat transfer by forced flow

in tubes,

L (a/A)y
=Tt — £ 3y

exp (ti tm)X

where h is the film coefficient for heat transfer at position X along the

tube, A is the inner surface area for heat transfer, and tm is the tempera-

ture of the bulk fluid. The average linear velocity of the bulk fluid
through the test section, Vm, was not measured experimentally but was esti-
mated from the heat flux and bulk fluid AT according to
q
Vm ¢ AT A
p
where cp is the heat capacity of the salt (Table 2 or 3). The dimension-
*
less Reynolds, Prandtl, and Nusselt terms were calculated from the appro-

priate values of h and Vm and the appropriate physical constants (Table 2
or 3).

 

%
Defining equations for N

N nd N are given in the Nomen-
> YRe? @ Pr 8
clature.

Nu
16

Selected data, along with the calculated parameters, are summarized
in Tables 6 and 7. The calculations involve several assumptions made in
the treatment of the data. The straight line drawn between the mean inlet
and outlet fluid temperatures (thermocouple well readings, e.g., Fig. 7)
assumes constant physical properties for the salt and uniform heat transfer
over the inner surface of the test section. This treatment is supported by
the essentially constant heat capacity of both liquid salts in the experi-
mental temperature range and the relatively constant resistance of the

Hastelloy N test section (<1% wvariation).

ANALYSIS AND RESULTS

Although there is not complete agreement in the literature, the follow-
ing standard heat transfer correlations are well accepted and have been
used in comparing our results.

Laminar region — the Sieder-Tate equation,11

1/3
_ 0.1u
Ng, = 1-86[N, N, (D/L)] (ug/ug) ;
transition region — a modified form'? of the Hausen'?® equation,
_ 2/3 _ 1/3 0,14
Ny, = 0-116(N, 125) N, (g /1g) ;

turbulent region — the Sieder-Tate equationm,!!

Ny, = O.OZ?NReo-8 NPrl/3 (uB/uS)°°“+ .
These correlations for both salts along with the experimental values are
plotted in Figs. 8 and 9 using all thermocouple readings along the entire
length of resistance-heated section 2. Because the heat flux was inter-
rupted at the center lugs, a maximum L/D of 167 was used in the treatment
of these data. These results are quite similar, although the physical
properties of the coolant salt (Table 2) differ enough from those of the

fuel salt to provide a higher N_ range.

Re
b

 

 

 

Table 6. Experimental data for heat transfer studies using LiF-BeF;-ThF,-UF, (72-16-12-0.3 mole Z)a’
R Heat Average temperature (°F) Mass Q/A

Nun input flow (Btu hr~! ft™?2 exp NRe NP NN NHT

O (kW) Inlet Outlet (1b/hr) x 107"%) [Btu hr-! ft™2 (°F)~!] r v
3 63.20 1113 1248 4931 17.35 1427 7,488 11.2 69.6 29.8
1527 7,732 10.8 74.5 32.4
4 63.20 1109 1246 4859 17.35 1381 7,215 11.3 67.4 28.7
1527 7,445 11.0 74.5 32.2
5 71.25 1107 1237 5774 19.56 1610 8,416 11.5 78.6 33.3
1677 8,700 11.1 81.8 35.1
6 50.24 1095 1236 3727 13.79 997 5,318 11.8 48.6 20.3
1075 5,492 11.4 52.5 22.2
7 36.50 1111 1257 2633 10.02 670 3,954 11.2 32.7 13.9
733 4,081 10.8 35.8 15.4
8 25.44 1021 1190 1585 6.98 279 1,872 14.2 13.6 5.1
303 1,951 13.7 14.8 5.7
9 19.52 1037 1190 1344 5.36 253 1,633 13.8 12.4 4.8
284 1,703 13.2 13.9 5.5
11 45.60 1310 1396 5585 12.52 1896 13,000 7.2 92.5 47.0
1987 13,210 7.1 97.0 49.5
12 66.16 1115 1258 4874 18.16 1326 7,422 11.0 64.8 27.7
1365 7,664 10.7 66.7 29.0
13 49.52 1087 1233 3573 13.59 888 5.019 12.0 43.3 17.9
951 5,200 11.5 46.5 19.5
14 36.96 1095 1241 2667 10.15 632 3,836 11.7 30.9 12.9
684 3,970 11.3 33.4 14.2
15 18.48 1075 1194 1643 5.07 243 2,168 12.7 11.9 4,7
260 2,234 12.3 12.7 5.1
16 18.32 1054 1216 1187 5.03 244 1,542 12.9 11.9 4.7
272 1,605 12.4 13.3 5.4
17 33.68 1074 1149 4762 9.24 1119 5,960 13.4 54.7 22.3
1223 6,060 13.2 59.8 24,6

(1
Table 6 (continued)

 

 

 

 

R Heat Average temperature (°F) Mass Q/A h

Nun input flow (Btu hr~! ft~? exp NR NPr NNu NHT

(kW) Inlet Outlet (1b/hr) x 10™") [Beu hr=! £ft72 (°F)7}] ©
20 54.16 1162 1278 4919 14.87 1457 8,230 10.0 71.3 31.9
1578 8,450 9.8 77.2 34.9
21 21.76 1160 1284 1848 5.97 439 3,097 10.0 21.5 9.5
486 3,189 9.7 23.8 10.7
22 16.40 1061 1204 1208 4,50 234 1,566 13.0 11.5 4.5
259 1,627 12.5 12.7 5.1
23 61.84 1149 1287 4720 16.97 1385 7,795 10.2 67.7 29.9
' 1442 8,038 9.9 70.5  31.6
25 55.76 1295 1413 4990 15.31 1722 11,560 7.3 84,2 42.3
1822 11,810 7.1 89.1 45.2
26 56.72 1330 1437 5600 15.57 2027 13,930 6.7 99.1 51.2
2079 14,210 6.6 102.0 53.0
“The two sets of values in the last five columns correspond to the data obtained from the 1.3- and 1.6-m (4.25- and

5 25_f . . _ -1/3 ~0.14
t) thermocouple locations (see text); NHT NNu (NPr) (UB/US)

bTo obtain SI equivalents for the units in the table, multiply the values as follows: 1b/hr x 1.26 X 107" = kg/sec;

Btu hr™? ft™? x 3.152 = W/m%; Btu hr ! ft~2 (°F)~"! x 5.674 = Wm™?2 (K)~'.

8T
Table 7.

Experimental data for heat transfer studies using NaFBF,-NaF (92-8 mole %)a’

b

 

Heat

Average temperature (°F)

 

Mass

 

Run . Q/A h
input flow Y -2 exp N N N N

No. (i) Inlet Outlet (1b/hr) (Btu hr™" ££ ) (5 nem! £ (°F)] Re Pr Nu HT
1 46.8 934 1039 4226 128,459 1722 44,455 5.28 247 139
1782 44,965 5.22 255 145
2 57.0 896 1024 4222 156,456 1598 41,582 5.64 229 125
1647 42,486 5.52 236 130
3 57.7 881 1042 3398 158,378 1376 33,463 5.64 197 107
1402 34,191 5.52 201 110
4 56.8 872 1101 2351 155,908 1052 23,852 5.48 151 83
1068 24,663 5.3 153 85
5 15.7 842 1134 510 43,094 244 5,104 5.55 35 19
257 5,350 5.3 37 20
6 30.2 844 1134 987 82,894 460 9,878 5.55 66 36
474 10,354 5.3 68 37
7 39.9 858 1110 1501 109,520 696 15,023 5.55 100 54
716 15,746 5.3 103 57
9 50.7 916 1070 3121 139,164 1347 32,648 5.31 193 108
1392 33,598 5.16 200 113
12 27.6 977 1061 3115 75,758 1377 34,956 4.95 197 114
1403 35,384 4.89 201 117

 

See Table 6 for S1 conversions.

a . .
The two sets of values in the last five columns corres
5.25-ft) thermocouple locations (see text); N

HT u (NPr)

§95¢

to data obtained from the 1.3- and 1.6-m (4.25- and
(uB/uS)"0 1

6T
20

ORNL- DWG 76--13596

HEATED SECTION L/D = 167

0.14
- 08 173 [H
Ny, = 0.027 Noo N (fig)

Z

9 0.14
= .

u

Q _ 2/3 1/3 B
% NNu =0.116 (NRe -125) NPr (K)
W

o
i
[V
w

<

e

o«

-

-

g

uw

I

-

ofl\
a3 al v
Y - -t

2 T

 

103 2 5 104 2 5 105
Ng,. REYNOLDS MODULUS

Fig. 8. Heat transfer characteristics of LiF-BeF,-ThF4-UF, (72-16~
12-0.3 mole %) flowing in a 10.5-mm-ID tube, summary of all data.

Since the guard heaters on the tubing were set for an average tem-
perature, the guard heat flux would be high for the entrance section,
resulting in high thermocouple readings and therefore indicating low heat
transfer function, NHT'

N = "N .

0.14
N, 1/3 (Hp/Hg)

 
21

ORNL DWG 76 13598

0.14
. 08, Hg
NNu = (0.027 NRe NPr (FS_)

HEATED SECTION L/O RATIO = 167

“)0_14, HEAT TRANSFER FUNCTION

m]{ ¥ 2
SN Ny, = 0.116 (/va ~125)

30 0.14

= Ne, (71;)

 

103 2 5 104 2 5 10°
Nge, REYNOLDS MODULUS

Fig. 9. Heat transfer characteristics of NaBF,~NaF (92-8 mole %)
flowing in a 10.6-mm-ID tube, summary of all data.

Conversely, at the exit, the guard heater input is low, causing low thermo-
couple readings and high NHT values. Consequently, the best data should
be those obtained from the thermocouple readings near the center of the

test section. However, it was noted the NH results just downstream of

the center lugs were abnormally high. The 3eason for this, which was dis-
covered during inspection of the loop piping after the heat transfer runs
were completed, was excessive penetration of the butt welds where the lugs
joined the tubing. This disrupted the inner surface of the flow channel
and undoubtedly caused turbulence, with better downstream heat transfer.
Thus, it was concluded that the best data should be those obtained from
the E and F thermocouple locations [1.30 m (4.25 ft) and 1.60 m (5.25 ft)
downstream from the inlet]. Therefore these data points for both salts
are replotted with the standard correlations in Fig. 10 and Fig. 11.

There is satisfactory agreement with the Sieder-Tate correlation in
the fully developed turbulent region at Reynolds moduli above 15,000.

Between Reynolds moduli of 2100 and 15,000, the experimental data agree
 

 

2 ORNL-DWG 76-5259R

4
° = T 1 T 0] 7T T T 1T1TH
— = 08, V3 [Fgl " Y -
[ Ny = 0.027 Npg' Np,” | e _
5 — ‘8’ -

/o —

 

> -
3 7/

- | ]
>

= L

W s /a‘b 044 |
x 2/3 t/3| Hp

:f o ° Ny = 0416 (Mg, —125) Np, (Fg'

2 a

3 /°

- 10" 2

T — ]
W

z —  L/D=152 B
. / - —

W

  

M
Pr Hg
[6,]

173 K 0.44
My =1.86 [NpyMNp, (D/L (7;;)

L/0 =123 T

o {30 m FROM INLET CORRESPONDING L/D = 123
e 160 m FROM INLET CORRESPONDING L/D= 452

100 | b1 Illll il
10° 2 5 104 2 5 10°
Nge, REYNOLDS MODULUS

 

 

 

 

Fig. 10. Heat transfer characteristics of LiF-BeF;-ThF,-UF4 (72-16-
12-0.3 mole %) flowing in a 10.5-mm-ID tube, stable heat transfer zone.

very well with the modified!? Hausen!?® equation, which is normally appli-
cable to the transition region. The extended transition region is prob-
ably due to the high viscosity and large negative temperature coefficient
of viscosity of the fuel salt. It is known from hydrodynamic stability
that heat transfer from a solid interface to a fluid whose viscosity de-
creases with temperature can produce this effect. As noted earlier,
freezing of the salt at low velocities limited the data obtainable at
low Reynolds moduli. These data at the upper limit of the laminar flow
region are too meager to allow any conclusions to be drawn.

The results of these experiments are similar for both salts and indi-
cate that the proposed coolant and fuel salts behave as normal heat trans-

fer fluids with a somewhat extended transition region.
23

ORNL DWG 76- 13597
1000

O 1.30m FROM INLET CORRESPONDING L/D = 123
A 1.60m FROM INLET CORRESPONDING L/D = 152

500

0.14
_ 08 L 1/3 [H
Ny, - 0.027 N9® N (TSB_)

¥

i

200

100

, HEAT TRANSFER FUNCTION

0.14
B 2/3 113 {#B
Nyy = 0116 (NG -125) Np, (fig)

20 o = -

 

10
103 2 5 104 2 5 105
NR ., REYNCLDS MODULUS

Fig. 11. Heat transfer characteristics of NaBF,-NaF (92-8 mole %)
flowing in a 10.5-mm-ID tube, stable heat transfer zone.

CONCLUSTIONS

The heat transfer performance of a proposed MSBR coolant salt [NaBFy-
NaF (92-8 mole %)] and a fuel salt [LiF-BeF,-ThF,-UF, (72-16-12-0.3 mole
%2)] was measured in forced convection loop FCL-2b. Satisfactory agreement
with the empirical Sieder-Tate correlation was observed in the fully de-

veloped turbulent region at Reynolds moduli above 15,000. Between Reynolds
24

moduli of V2100 and 15,000, the experimental data follows a modified Hausen

equation which is normally applicable to the transition region. The ex-

tended transition region is probably due to the high viscosity and large

negative temperature coefficient of viscosity of the salts. Insufficient

data were taken in the laminar region to allow any conclusions to be drawn.

The results of these experiments are similar for both salts and indicate

that the proposed salts behave as normal heat transfer fluids with an ex-

tended transition region.

b

0

.-Q'OL"‘??‘;D‘U"O

rt
-
t "

<
8

ot
o]
=

Nu
Re
Pr

Z =z 2 =

HT

NOMENCLATURE

Heat transfer surface area

Heat capacity of fluid at constant pressure

Inside diameter of tube

Coefficient of heat transfer (film coefficient)

Thermal conductivity of Hastelloy N

Thermal conductivity of the bulk fluid

Length of test section

Density of the bulk fluid

Heat transfer rate to fluid

Test-section tube radius, outside and inside, respectively
Temperature, outer and inner surface of tube, respectively
Temperature of bulk fluid

Average linear velocity of fluid through the test section

Viscosity of the fluid at temperatures tm and ti’ respectively

Dimensionless Heat Transfer Moduli

 

Nusselt modulus, hD/k
Reynolds modulus, DVmp/uB
Prandtl modulus, cpuB/k

Heat transfer function (for plotting purposes), N N -1/3
-0.14 Nu Pr
(uB/uS)
25

ACKNOWLEDGMENTS

We would like to acknowledge H. C. Savage, who assisted in the assem-

bly of the test loop and initial heat transfer tests with sodium fluoro-

borate salt, and R. H. Guymon for valuable comments and suggestions in

reviewing this report.

1.

10.

11.

REFERENCES

H. W. Hoffman, Turbulent Forced-Convection Heat Transfer in Circular
Tubes Containing Molten Sodium Hydroxide, USAEC Report ORNL-1370
(October 1952); see also Proceedings of the 1953 Heat Transfer and
Fluid Mechanics Institute, p. 83, Stanford University Press, Stanford,
Calif., 1953.

M. M. Yarosh, '"Evaluation of the Performance of Liquid Metal and
Molten-Salt Heat Exchangers,' Nuecl. Sei. Eng. 8, 32—-43 (1960).

J. W. Cooke and B. Cox, Foreced Convection Heat Transfer Measurements
with a Molten Fluoride Salt Mixture in a Smooth Tube, USAEC Report
ORNL/TM-4079, Oak Ridge National Laboratory (March 1973).

H. W. Hoffman and J. Lones, Fused Salt Heat T'ransfer — Part II:

Forced Convection Heat Transfer in Circular Tubes Containing NaK-
KF-LiF Eutectic, USAEC Report ORNL-1777, Oak Ridge National Laboratory
(February 1955).

W. R. Huntley, J. W. Koger, and H. C. Savage, MSRP Semiannu. Progr.
Rep. Aug. 31, 1970, USAEC Report ORNL-4622, Oak Ridge National Lab-
oratory, pp. 176—78.

S. Cantor, Demsity and Viscosity of Several Molten Fluoride Mixtures,
USAEC Report ORNL/TM-4308, Oak Ridge National Laboratory (March 1973).

S. Cantor et al., Physical Properties of Molten-Salt Reactor Fuel,
Coolant, and Flush Salts, USAEC Report ORNL/TM-2316, Oak Ridge
National Laboratory (August 1968).

J. W. Cooke, MSRP Semiannu. Progr. Rep. Aug. 31, 1963, USAEC Report
ORNL-4449, Oak Ridge National Laboratory, p. 92.

D. L. McElroy et al., "Thermal Conductivity of INOR-8 Between 100 and
800°C," Trans. Amer. Soc. Met. 55, 749 (1962).

W. E. Kirst, W. M. Nagle, and J. B. Castner, Trans. AIChE 36, 371
(1940).

E. N. Sieder and G. E. Tate, 'Heat Transfer and Pressure Drops of
Liquids in Tubes," Ind. Eng. Chem. 28 (12), 142935 (1936).
26

12. H. W. Hoffman and S. I. Cohen, Fused Salt Heat Transfer — Part III:
Forced-Convection Heat Transfer in Circular Tubes Containing the Salt
Mixture NalNO,-NaNO3-KNO3, USAEC Report ORNL-2433, Oak Ridge National
Laboratory (March 1960).

13. H. Hausen. Z. Ver. Deut. Ing. Beih, Verfahrenstechnik 4, 91—98 (1943).
» » [ )

RO~ &~ LN

O
e .

=
o
[

12,
13.
14,
15,
16.
17.
18.
19.
20.
21—-28.
29.
30.
31.
32.
33.
34.

74.

75.

76-77.

78-182.

27

ORNL/TM~-5335
Dist. Category UC-76

Internal Distribution

 

E. S. Bettis 35. G. T. Mays

H. R. Bronstein 36. W. J. McCarthy, Jr.

S. Cantor 37. H. E. McCoy

C. J. Claffey 38. H. A, McLain

W. B. Cottrell 39—41. L. E. McNeese

J. L. Crowley 42, R. L. Moore

J. H. DeVan 43, H. E. Robertson

J. R. DiStefano 44, T. K. Roche

J. R. Engel 45, M. W. Rosenthal

G. G. Fee 46, W. E. Sallee

D. E. Ferguson 47. J. P. Sanders

L. M. Ferris 48. H. C. Savage

M. H. Fontana 49, Myrtleen Sheldon

A. P. Fraas 50-57. M. D. Silverman

M., J. Goglia 58, A. N. Smith

G. W. Greene 59. G. P. Smith

A. G. Grindell 60. I. Spiewak

R. H. Guymon 61. J. J. Taylor

J. R. Hightower, Jr. 62. D. B. Trauger

H. W, Hoffman 63. G. D, Whitman

W. R. Huntley 64, W. J. Wilcox

J. R. Keiser 65. L. V, Wilson

A. D. Kelmers 66. ORNL Patent Office

W. R. Laing 67—68. Central Research Library
R. E. MacPherson 69. Document Reference Section
G. Mamantov 70—-72. Laboratory Records

D. L. Manning 73. Laboratory Records (LRD-RC)

External Distribution

 

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Research and Development Administration, Washington, DC 20545
For distribution as shown in TID-4500 under UC-76, Molten-Salt
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