Ornl tm 5335 by The "E" Generation

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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-BeF2-ThF2-UFq AND EUTECTIC NaBF4-NaF

W. R. Huntley

M. D. Silverman

Date

H. E. Robertson

Published: October 1976 . NOTICE

Research and lkvclopment Adminirtntion. nor any Of their empbyctr, nor m y of their mntmclon, subcontractors. 01 their employees, m a k e any warranty exprea or implied, or assumes any I d liability responsibilityfor the accuracy, completenem 01 usefulness of m y information, apparatlu. product or p r o a u d w l o s d . or represents that its uy would not

Prepared by the OAK RIDGE NATIONAL LABORATORY

Oak Ridge, Tennessee 37830 operated by UNION CARBIDE CORPORATION for the ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION

OAK R I D G E NATIONAL LABORATORY OPERATED

U N I O N CARBIDE CORPORATION N U C L E A R DIVISION

POST O F F I C E BOX X O A K R I D G E . TENNESSEE 37830

November 10, 1976

To:

R e c i p i e n t s o f Subject Report

Report No. :

ORNL/TM-5335

Author(s):

M. D. Silverman, W. R. H u n t l e y and H. E. Robertson

Subject:

Classification:

Unclassified

Heat T r a n s f e r Measurements i n a Forced Convection Loop w i t h

Two Mollen-Flu0 r i d e

Salts:

I i F -BeF,-ThF,

-UF,

and E u t e c t i c NaBF,.-NaF. c

Please make pen and i n k c o r r e c t i o n s t o your copy(ies) of s u b j e c t r e p o r t as i n d i c a t e d below. T i t l e page ( i n s i d e and o u t s i d e i n t i t l e , ThF2 should read ThFb)

Page 1 i n t i t l e , ThF2, should read ThF4

Page 1 i n A b s t r a c t , L i n e 2, ThF2 should read ThF4 Page 1 t h i r d l i n e from bottom,

ThF2 should read ThF4. -

J?xT&

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

JLL :we

iii CONTENTS Page

....................................................... INTRODUCTION ................................................... EXPERIMENTAL ................................................... DATA AND CALCULATIONS .......................................... ANALYSIS AND RESULTS ........................................... CONCLUSIONS .................................................... NOMENCLATURE ................................................... ACKNOWLEDGMENTS ................................................ REFERENCES ..................................................... ABSTRACT

1 1 2 12

16 23 24

HEAT TRANSFER MEASUREMENTS IN A FORCED CONVECTION LOOP WITH TWO MOLTEN-FLUORIDE SALTS: LiF-BeF2-ThF2-UF4 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-BeF2-ThF*-UFb (72-16-12-0.3 mole X ) and NaBF4-NaF (92-8 mole % ) I 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-nun-OD (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 region at Reynolds moduli above 15,000 and with a modified Hausen equation in the extended transition region (Re ~21OG-15,OOO). 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, turbulent 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 4

surfaces o r the formation of low-conductance surface films can occur,

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 NaBF4-NaF (92-8 mole %) coolant salt.

More recently, tests

were made in the same loop with a proposed fuel-salt mixture [LiF-BeF2ThF2-UFs (72-16-12-0.3 mole % )3 . Heat transfer coefficients were obtained for a wide range of variables (see Table 1) for both salts flowing through 12.7-mm-OD (0.5-in.)

Table 1. Variables used in heat transfer measurements ~

Fuel-salt data Reynolds modulus

1540-14,200

Prandtl modulus

6.6-14.2

Fluid temperature

549-7 6 5"C (1020-14 40 F)

Heat flux

142,000-630,OOO W/m2 (45 ,000-200,000 Btu hr-' ft-2 )

Heat transfer coefficient

132041,800 W m-2 (K)-' ("F)"I 11-102

Nusselt modulus

[230-2080 Btu hr"

ft-2

Coolant-salt data Reynolds modulus

5100-45,OOO

Prandtl modulus

5.3-5.64

Fluid temperature

450-610"C (840-1130째F)

Heat flux

136,00C+499,000 W/m2 (43,000-158,000 Btu hr"

Heat transfer coefficient

1380-10,100 W m-' ("F)"I 35-255

Nusselt modulus

(K)-'

ft-2)

[240-1780 Btu hr-' ft-'

Hastelloy N tubing. These results are compared with calculated coefficients, 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,' was used for these experiments. of 12.7-m-OD (0.5-in.),

The loop (Fig. 1) is constructed

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

ORNL-DWG 7 0 - 5 6 3 2

9 FREEZE VALVE (TYPICAL)

.kc

AIRCORROSION SPECIMENS

.._

HEATER LUGS (TYPICAL)--,

RESISTANCE HEATED SECTION NO. I-.,,

THERMOCOUPLE, WELL DRAIN AND F I L L LIh B A L L VALVE

x 0 042-117WALL HASTELLOY N

%-in OD

UXILIARY TANK HEATER LUGS (TYPICAL)

CORROSION SPEC1M ENS -

RESISTANCE HEATED SECTION NO 2

FREEZE VALVES

'/e-in.OD x 0.035-~n.WALL THERMOCOUPLE WELL

Fig. 1. Molten-Salt Forced Convection Corrosion Loop MSR-FCL-2.

4 resistance-heated

s e c t i o n s and two f i n n e d - t u b e c o o l e r s p r o v i d e a tempera-

t u r e d i f f e r e n t i a l of 'L166'C

m3/sec (8.8

(300'F)

ft3/sec).

a t t h e normal flow r a t e of 2.5

R e s i s t a n c e h e a t i n g (12R h e a t e r s ) i s s u p p l i e d

by a f o u r - l u g system, w i t h v o l t a g e p o t e n t i a l a p p l i e d t o t h e two c e n t e r l u g s w h i l e t h e two e x t e r i o r l u g s are a t ground p o t e n t i a l ( F i g . 2 ) . t h e r e i s a n unheated s e c t i o n a t t h e c e n t e r l u g s .

Thus,

Because t h e e l e c t r i c a l

r e s i s t a n c e of t h e molten s a l t i s v e r y h i g h compared w i t h t h a t of t h e metal t u b i n g (whose r e s i s t a n c e remains a l m o s t c o n s t a n t o v e r t h e t e m p e r a t u r e r a n g e of t h e s e e x p e r i m e n t s ) , t h i s method of h e a t i n g i s w e l l a d a p t e d t o t h e system.

One r e s i s t a n c e - h e a t e d

s e c t i o n ( t h e h e a t t r a n s f e r test s e c t i o n ,

d e s i g n a t e d No. 2) c o n t a i n s a n a c t i v e l y h e a t e d l e n g t h of 3.5 m (11.5 f t ) , r e s u l t i n g i n a n L/D r a t i o of 331 and a h e a t t r a n s f e r area of 0.115 m2

(1.08 f t 2 ) .

Guard h e a t e r s ( c l a m s h e l l s ) are l o c a t e d on t h e h e a t e r l u g s and

along t h e resistance-heated t r a n s f e r runs (Fig. 3 ) .

t u b e t o make up h e a t l o s s e s d u r i n g t h e h e a t

F i g u r e 4 shows t h e test l o o p w i t h a l l h e a t e r s ,

thermocouples, and thermal i n s u l a t i o n i n s t a l l e d . The t e m p e r a t u r e of t h e b u l k f l u i d i s measured by t h r e e thermocouples l o c a t e d i n w e l l s a t t h e i n l e t and t h e e x i t of t h e t e s t s e c t i o n .

Wall

t e m p e r a t u r e s a l o n g t h e h e a t e d s e c t i o n a r e measured by 1 2 s h e a t h e d , insulated-junction,

1.02-mm-OD

(0.040-in.)

Chromel-Alumel

precalibrated

thermocouples t h a t a r e wrapped 180' c i r c u m f e r e n t i a l l y around t h e t u b i n g and clamped a g a i n s t t h e w a l l a t a b o u t 0.30-m

(1-ft)

intervals.

Thermo-

c o u p l e r e a d i n g s d u r i n g t h e experiments are r e c o r d e d a u t o m a t i c a l l y by t h e

D e x t i r , a c e n t r a l d i g i t a l d a t a - a c q u i s i t i o n system w i t h a n a c c u r a c y of 20.10% of f u l l scale and a r e s o l u t i o n of 1 p a r t i n 10,000. The a c t u a l dimensions of t h e t u b i n g i n r e s i s t a n c e - h e a t e d s e c t i o n 2

were determined b e f o r e i n s t a l l a t i o n .

The t u b i n g o u t s i d e d i a m e t e r , mea-

s u r e d by c o n v e n t i o n a l o u t s i d e micrometers, averaged 12.68 mm (0.499 i n . ) ; t h e t u b e w a l l t h i c k n e s s , measured w i t h a n u l t r a s o n i c Vidigage, averaged

1.09 mm (0.043 i n . ) .

T h e r e f o r e , t h e t u b e i n t e r n a l d i a m e t e r a t room t e m -

p e r a t u r e w a s c a l c u l a t e d t o b e 10.49 mm (0.413 i n . ) ,

and t h i s v a l u e w a s

used i n a l l subsequent h e a t t r a n s f e r c a l c u l a t i o n s .

A variable-speed flow r a t e .

d r i v e motor on t h e pump ( F i g . 5 ) c o n t r o l s t h e s a l t

I n t h e f u e l - s a l t experiments t h e pump speed w a s v a r i e d from

ORNL-DWG

76-13593

12.7-mm-OD HASTELLOY

25 mm

CENTER LUGS

GROUND LUG -

0.15 m 0.10, -m G T/C WELL (3 T/Cd

,O.lO m

1.75 m

GROUND

0.10, m

1.75 m

FLOW -

Fig.

Heater

test

section

2 - details.

, I B

EA, I A

TIC WELL (3 T/Cd

Fig. 3.

Center lugs and clamshell heaters on No. 2 heater section.

1 l

L' t i

F i g . 4.

Salt test loop with protective metal enclosures removed.

ORNL-DWG 69-8964R

u INCHES

Fig. 5 .

Alpha pump.

1000 to 4700 rpm, yielding flow rates of 40 to 250 ml/sec, which corresponds t o a Reynolds modulus (NRe) of 1542 to 14,200. The lower 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 temperature obtained from readings of the 12 thermocouples (A-L) of the loop piping.

on the surface

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 Q2.5 x

m3/sec.

For example, in run 1 (Fig 6) (line YY), 1250 W was the power input

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 664'12,

good agreement with the bulk fluid temperature.

indicating

In run 2 (line X X ) , no

power was applied to the guard heaters; the bulk fluid temperatures obtained 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 2 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

ORNL DWG 76 13594

1500

I LETTERS A - L IDENTIFY OUTER SURFACE TH E RMOCOUP LES

1400

RUN 1

-V - GUARD

HEATERS ON

RUN 2

-0- GUARD

HEATERS

I -

OFF

BULK FLUID TEMPERATURE

(LINE Y Y )

(LINE X X )

BULK FLUID TEMPERATURE

-ox

0 0

1300

lLhL

0.3

(ft)

0.6 2

0.9 3

7L 1I-

WELL

(rn)

-OUTLET

AVERAGE OF 3 Tics

1.2 4

v 1.5 5

V 1.8 6

2.1 7

DISTANCE FROM FIRST HEATER LUG

Fig. 6.

Heat loss tests,

FCL-2b.

2.44 8

V 2.74 9

V 3.05 10

3.35 11

3.70 12

P 0

ORNL -DWG 76-13595

1400

L-

NOTE: THERMOCOUPLES A AND C INOPERATIVE

8-6-75 ( 12124) FLOW RATE -4.6 gpm 12R HEAT - 71.25 kW

- 1300

FLOW

n 3

a K

0 -

1200

-INLET WELL AVERAGE OF 3 TICS

! -

- a-

OUTLET WELL AVERAGE OF 3 Tics

A-

I I

1100 (m)

0.3

(ft)

0.6 2

0.9 3

1.2 4

1.5 5

1.8 6

2.1 7

2.44 8

DISTANCE FROM FIRST HEATER LUG

F i g . 7.

Heat transfer run 5 - f u e l salt.

2.74 9

3.05 10

3.35 11

3.70 12

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-OD (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 605째C.

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 3.9OC. Without guard heat, the sheathed thermocouples read randomly lower by 0.3 to 3.9OC.

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 salt6-' used in these experiments are listed in Tables 2 and 3, chemical analyses are given in Table 4 , and properties of the Hastelloy N alloyg are shown in Table 5. DATA AND CALCULATIONS

Nine heat transfer tests were made with the coolant salt and twentyone 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

Table 2. Thermophysical property data €or molten-salt fuel mixture LiF-BeF2-ThFk-UFk (72-16-12-0.3 mole %) Parameter

Value

Uncertainty Ref.

Viscosity lb ft-’ hr-’ Pa/sec

0.264 exp [ 7370/T( OR) exp [4090/T ( K ) ] 1.09 x

210% 510%

6 6

0.71 1.23

515% +15%

a a

228.7 - 0.0205T (OF) 3665 - 0.591T ( “ C )

+1% 51%

6 6

0.324 1357

54% 54%

7 7

?lO°F 56OC

7 7

Thermal conductivity Btu hr-’ ft-’ (OF)-’ m-’ (K)-’

Density

Heat capacity Btu lb-’ (OF)-’ J kg-’ (K)-’ Liquidus temperature OF

932 500

“C

a Estimated from values given in Ref. 8 for analogous salts.

Table 3.

Thermophysical property data €or molten-salt coolant mixture NaBF4-NaF (92-8 mole %)

Value

Parameter viscosity lb ft-’ hr-’ Pa/sec

Uncertainty Ref.

0.212 exp [4032/T (OR)] 8.77 x lo-’ exp [2240/T ( K ) ]

210% 210%

6 6

0.24 0.42

215% 215%

141.4 - 0.0247T (OF) 2252 - 0.0711T (“C)

21% 21%

6 6

0.360 1507

22% 52%

7 7

22°F 21°C

7 7

Thermal conductivity Btu hr-’ ft-’ (OF)-’

w m-’

(K)-’

Density 1b/fj3 kg/m Heat capacity Btu lb-’

(OF)-’

J kg-’ (K)-

Liquidus temperature OF O C

725 385

Table 4. Typical analyses of fuel salt LiF-BeF2-ThFb-UFk (72-16-12-0.3 mole %) and coolant salt NaBF4-NaF (92-8 mole %)

Weight %

Constituent

PPm

Fuel salt 7.28 2.03 44.97 1.00

Li Be Th U F Ni Cr Fe

45.03

70 85 45 58

Coolant salt Na B F Ni Cr Fe

21.5 9.7 68.3

H Mo

Table 5 .

7 80 350 700 30 3

Properties of Hastelloy N alloyg

Thermal conductivity, W cm-' ("C)-' At 0-440"C At 440-7OO0C

0.1 + 1.25 x 0.07724 + 1.897

Electrical resistivity, pn-crn At 24째C At 704째C Mean coefficient of thermal expansion (2W5O"C)

18.8 19.7 14 x 10-6/oC

Chemical composition,% Chromium Molybdenum Iron Silicon Manganese Carbon Nickel

6.00-8.00 15.00-18.00 5.00 (max) 1.00 (max) 0.80 (max)

0.04-0.08 Balance

("c) x

("C)

temperature by the equationâ&#x20AC;&#x2122;

where r

and r are the outside and inside radius of the tube, respeci tively; t and t. are the outside (surface) and inside wall temperatures; 0

L is the test-section length of tubing;

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 lineartype 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,

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 t is the temperam ture of the bulk fluid. The average linear velocity of the bulk fluid through the test section, Vm, was not measured experimentally but was estimated from the heat flux and bulk fluid AT according to

where c

is the heat capacity of the salt (Table 2 or 3 ) .

The dimension-

less Reynolds, Prandtl, and Nusselt terms were calculated from the appropriate values of h and V and the appropriate physical constants (Table 2 m or 3 ) .

*Defining clature.

NRe, and Npr are given in the Nomenequations for N Nu â&#x20AC;&#x2122;

16 Selected data, along with the calculated parameters, are summarized in Tables 6 and 7.

The calculations involve several assumptions made in The straight line drawn between the mean inlet

the treatment of the data.

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 experimental temperature range and the relatively constant resistance of the Hastelloy N test section (<1% variation).

ANALYSIS AND RESULTS Although there is not complete agreement in the literature, the following standard heat transfer correlations are well accepted and have been used in comparing our results. Laminar region - the Sieder-Tate equation,1 1

transition region - a modified form12 of the Hausen13 equation,

â&#x20AC;?u

0.116(NRe2l3

turbulent region

125) Npr1/3 (p /U B S

;

the Sieder-Tate equation,â&#x20AC;?

NNu = 0.027NRe0*8Npr

(pB /p S)0*14

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

Table 6.

Run

Heat input

Experimental data for heat transfer studies using LiF-BeFz-ThFk-UF4 (72-16-12-0.3 mole %)a'b

Average temperature (OF)

Mass flow (lb/hr)

Q/A (Btu hr-' ft-*

h exp

NRe

Npr

1427 1527

7,488 7,732

11.2 10.8

69.6 74.5

29.8 32.4

17.35

1381 1527

7,215 7,445

11.3 11.0

67.4 74.5

28.7 32.2

5774

19.56

1610 1677

8,416 8,700

11.5 11.1

78.6 81.8

33.3 35.1

1236

3727

13.79

997 1075

5,318 5,492

11.8 11.4

48.6 52.5

20.3 22.2

1111

1257

2633

10.02

670 733

3,954 4,081

11.2 10.8

32.7 35.8

25.44

1021

1190

1585

6.98

279 303

1,872 1,951

14.2 13.7

13.6 14.8

13.9 15.4 5.1 5.7

19.52

1037

1190

1344

5.36

253 284

1,633 1,703

13.8 13.2

12.4 13.9

4.8 5.5

45.60

1310

1396

5585

12.52

1896 1987

13,000 13,210

7.2 7.1

92.5 97.0

47.0 49.5

66.16

1115

1258

4874

18.16

1326 1365

7,422 7,664

11.0 10.7

64.8 66.7

27.7 29.0

49.52

1087

1233

3573

13.59

888 951

5.019 5,200

12.0 11.5

43.3 46.5

17.9 19.5

36.96

1095

1241

2667

10.15

632 684

3,836 3,970

11.7 11.3

30.9 33.4

12.9 14.2

18.48

1075

1194

1643

5.07

243 260

2,168 2,234

12.7 12.3

11.9 12.7

4.7 5.1

18.32

1054

1216

1187

5.03

244 272

1,542 1,605

12.9 12.4

11.9 13.3

4.7 5.4

33.68

1074

1149

4762

9.24

1119 1223

5,960 6,060

13.4 13.2

54.7 59.8

22.3 24.6

No.

Inlet

Outlet

63.20

1113

1248

4931

17.35

63.20

1109

1246

4859

71.25

1107

1237

50.24

1095

36.50

[Btu hr-' ft-'

(OF)-']

Table 6 (continued)

Run

No.

Heat input (kW)

Average temperature ( O F ) Inlet

Outlet

Mass flow (lb/hr)

Q/A (Btu hr-' ft-' x

h exP [Btu hr-' ft-'

NRe

Npr

(OF)-']

54.16

1162

1278

4919

14.87

1457 1578

8,230 8,450

10.0 9.8

71.3 77.2

31.9 34.9

21.76

1160

1284

1848

5.97

439 486

3,097 3,189

10.0 9.7

21.5 23.8

9.5 10.7

16.40

1061

1204

1208

4.50

234 259

1,566 1,627

13.0 12.5

11.5 12.7

4.5 5.1

61.84

1149

1287

4720

16.97

1385 1442

7,795 8,038

10.2 9.9

67.7 70.5

29.9 31.6

55.76

1295

1413

4990

15.31

1722 1822

11,560 11,810

7.3 7.1

84.2 89.1

42.3 45.2

56.72

1330

1437

5600

15.57

2027 2079

13,930 14,210

6.7 6.6

99.1 102.0

51.2 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-ft) thermocouple locations (see text); "T = N ~ u(Npr)-l 1 (uB/Us)-'* 14. bTo obtain SI equivalents for the units in the table, multiply the values as follows: lb/hr x 1.26 x lod4 = kg/sec; Btu hr-' ft-2 x 3.152 = W/m2; Btu hr-' ft-2 (OF)-' x 5.674 = W m-' (K)-'.

F 03

Table 7.

Run No.

Heat input (kw)

Experimental data for heat transfer studies using NaFBF4-NaF (92-8 mole %)a , b

Average temperature Inlet

Outlet

(OF)

Mass flow (Ib/hr)

Qlf (Btu hr-

ft-')

,Btu

hr-l

h exp ft-2

NRe

N~ r

(OF)-ll

46.8

934

1039

4226

128,459

1722 1782

44,455 44,965

5.28 5.22

247 255

139 145

57.0

896

1024

4222

156,456

1598 1647

41,582 42 486

5.64 5.52

229 236

125 130

57.7

881

1042

3398

158,378

1376 1402

33 463 34,191

5.64 5.52

197 201

107 110

56.8

872

1101

2351

155,908

1052 1068

23,852 24,663

5.48 5.3

151 153

15.7

842

1134

510

43,094

244 257

5,104 5,350

5.55 5.3

35 37

a3 85 19 20

30.2

a44

1134

987

82,894

460 474

9,878 10,354

5.55 5.3

66 68

36 37

39.9

858

1110

1501

109,520

696 716

15,023 15,746

5.55 5.3

100 103

54 57

50.7

916

1070

3121

139,164

1347 1392

32 648 33 598

5.31 5.16

193 200

io8 113

27.6

977

1061

3115

75,758

1377 1403

34,956 35,384

4.95 4.89

197 201

114 117

a The two sets of values in the last five columns 5.25-ft) thermocouple locations (see text); NHT = NNu bSee Table 6 for SI conversions.

from the 1.3- and 1.6-m (4.25- and

20 ORNL DWG 76 -13596

f 0

io3

1o4

1o5

N R e , REYNOLDS MODULUS

Fig. 8. Heat transfer characteristics of LiF-BeFz-ThFk-UFk (72-16tube, summary of all data. 12-0.3 mole %) flowing in a 10.5-=-ID

Since the guard heaters on the tubing were set for an average temperature, the guard heat flux would be high for the entrance section, resulting in high thermocouple readings and therefore indicating low heat transfer function, "T

NPR

1/3

"u (11

' /u

B S

p.14

!02

2iz

5 NRc1

to4

!05

REYNOLDS MODULUS

Fig. 9. Heat transfer characteristics of NaBF4-NaF (92-8 mole W ) flowing in a 10.6-m-ID tube, summary of all data.

Conversely, at the exit, the guard heater input is low, causing low thermocouple readings and high N values. Consequently, the best data should HT be those obtained from the thermocouple readings near the center of the test section.

However, it was noted the NHT results just downstream of the center lugs were abnormally high. The reason for this, which was discovered 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 . 2 5 ft) and 1.60 m ( 5 . 2 5 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

22 ORNC-OWG 76-5259R

NN" =

0.027

0 L

a W

z Q

a t-

Io,

12-0.3

5 lo4 2 A ' R ~ ,REYNOLDS MODULUS

405

Fig. 10. Heat transfer characteristics of LiF-BeF2-ThFk-UFb (72-16mole X ) flowing in a 10.5-mm-ID tube, stable heat transfer zone.

very well with the modif iedI2 HausenI3 equation, which is normally applicable 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 decreases with temperature can produce this effect. A s 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 indicate that the proposed coolant and fuel salts behave as normal heat transfer fluids with a somewhat extended transition region.

ORNL DWG 7 6 - 13597

1000

I -.I I I I

- 0 1.30 m FROM INLET CORRESPONDING Liâ&#x20AC;&#x2122;D ~

1.60 m FROM INLET CORRESPONDING L/D

123

152

500

0 I0

200

2 Iz:

w U

100

I-

a Lu

1 03

1o4

1o5

NRf,. R E Y N O L D S MODULUS

Fig. 11. Heat transfer characteristics of NaBF4-NaF (92-8 mole %) flowing in a 10.5-mm-ID tube, stable heat transfer zone.

CONCLUSIONS The heat transfer performance of a proposed MSBR coolant salt [NaBFbNaF (92-8 mole X ) ] and a fuel salt [LiF-BeF2-ThF4-UF4 (72-16-12-0.3

X ) ] was measured in forced convection loop FCL-2b.

mole

Satisfactory agreement

with the empirical Sieder-Tate correlation was observed in the fully developed turbulent region at Reynolds moduli above 15,000.

Between Reynolds

moduli of 1.2100 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 extended transition region.

NOMENCLATURE A C

P D

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/pB Prandtl modulus, c p /k P B -lI3 Heat transfer function (for plotting purposes), N ~ N uPr (lJB/lJS)-O

25 ACKNOWLEDGMENTS We would like to acknowledge H. C. Savage, who assisted in the assembly of the test loop and initial heat transfer tests with sodium fluoroborate salt, and R. H. Guymon for valuable comments and suggestions in reviewing this report.

REFERENCES

1. H. W. Hoffman, Turbulent Forced-Convection Heat Transfer i n Circular Tubes Containing Molten Sodium Hydroxide, USAEC Report ORNL-1370 (October 1952); see also Proceedings of the 1953 Heat Transfer and Fluid Mechanics I n s t i t u t e , p. 83, Stanford University Press, Stanford, Calif., 1953. 2.

M. M. Yarosh, "Evaluation of the Performance of Liquid Metal and Molten-Salt Heat Exchangers," Nucl. S e i . Eng. 8, 32-43 (1960).

J. W. Cooke and B. Cox, Forced 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). 4. H. W. Hoffman and J. Lones, Fused Salt Heat Transfer - P a r t 11: Forced Convection Heat Transfer i n Circular Tubes Containing N a X KF-LiF Eutectic, USAEC Report ORNL-1777, Oak Ridge National Laboratory (February 1955). 5. W. R. Huntley, J. W. Koger, and H. C. Savage, MSRP Semiannu. Progr. Rep. Aug. 31, 1970, USAEC Report ORNL-4622, Oak Ridge National Laboratory, pp. 176-78. 6. S. Cantor, Density and Viscosity of Several Molten Fluoride Mixtures, USAEC Report ORNL/TM-4308, Oak Ridge National Laboratory (March 1973). 3.

8. 9. 10.

11.

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. A u g . 31, 1969, USAEC Report ORNL-4449, Oak Ridge National Laboratory, p. 92. D. L. McElroy et al., "Thermal Conductivity of INOR-8 Between 100 and 800째C," 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), 1429-35 (1936).

26 12.

H. W. Hoffman and S. I. Cohen, Fused S a l t Heat Transfer -Part

111:

Forced-Convection Heat Transfer i n Circular Tubes Containing the SaZt Mixture NaNO2-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).

27 ORNL/TM-5335 D i s t . Category UC-76 'Internal Distribution

1. E. S. B e t t i s 2. H. R. B r o n s t e i n 3. S. Cantor 4. C. J. C l a f f e y 5. W. B. C o t t r e l l 6. J. L. Crowley 7. J . H. DeVan 8. J. R. DiStefano 9. J. R. Engel 10. G. G. Fee 11. D. E. Ferguson 12. L. M. F e r r i s 13. M. H. Fontana 14. A. P. F r a a s 15. M. J. Goglia 16. G. W. Greene 1 7 . A. G. G r i n d e l l 18. R. H. Guymon 19. J. R. Hightower, Jr. 20. H. W. Hoffman W. R. Huntley 21-28. 29. J. R. Keiser 30. A. D. K e l m e r s 31. W. R. Laing 32. R. E. MacPherson 33. G. Mamantov 34. D. L. Manning

35. 36. 37. 38. 39-41. 42. 43. 44. 45. 46. 47. 48. 49. 50-57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67-68. 69. 70-72. 73.

G. T. Mays W. J . McCarthy, Jr. H. E. McCoy H. A. McLain L. E. McNeese R. L. Moore H. E. Robertson T. K. Roche M. W. R o s e n t h a l W. E. Sallee J. P. Sanders H. C. Savage Myrtleen Sheldon M. D. Silverman A. N. Smith G. P. Smith I. Spiewak J. J. T a y l o r D. B. Trauger G. D. Whitman W. J. Wilcox L. V. Wilson ORNL P a t e n t O f f i c e C e n t r a l Research L i b r a r y Document Reference S e c t i o n L a b o r a t o r y Records L a b o r a t o r y Records (LRD-RC)

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Research and T e c h n i c a l Support D i v i s i o n , Energy Research and Development A d m i n i s t r a t i o n , Oak Ridge O p e r a t i o n s O f f i c e , P o s t O f f i c e Box E , Oak Ridge, Tenn. 37830 D i r e c t o r , R e a c t o r D i v i s i o n , Energy Research and Development A d m i n i s t r a t i o n , Oak Ridge O p e r a t i o n s O f f i c e , P o s t O f f i c e Box E , Oak Ridge, Tenn. 37830 D i r e c t o r , D i v i s i o n of Nuclear Research and A p p l i c a t i o n s , Energy Research and Development A d m i n i s t r a t i o n , Washington, DC 20545 For d i s t r i b u t i o n as shown i n TID-4500 under UC-76, Molten-Salt Reactor Technology