FUSION HIGH POWER DENSITY COMPONENTS AND SYSTEM
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FUSION HIGH POWER DENSITY COMPONENTS AND SYSTEM and HEAT REMOVAL AND PLASMA-MATERIALS INTERACTIONS FOR FUSION Inn on the Alameda, Nov. 15-17, 2006. Heat Transfer performance for high Prandtl and high temperature molten salt flow in sphere-packed pipes. Tomoaki Satoh 1 , Kazuhisa Yuki 1 ,

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FUSION HIGH POWER DENSITY COMPONENTS AND SYSTEM

and

HEAT REMOVAL AND PLASMA-MATERIALS INTERACTIONS

FOR FUSION

Inn on the Alameda, Nov. 15-17, 2006

Heat Transfer performance for high Prandtl and high temperature molten salt flow in sphere-packed pipes

Tomoaki Satoh1, Kazuhisa Yuki1,

Hidetoshi Hashizume1, Akio Sagara2

1 Advanced Fusion Reactor Eng. Lab.

Dept. of Quantum Science and Energy Eng.,Tohoku University, Japan

2 National Institute for Fusion Science, Japan


1 background 1 1 fusion blanket
1. Background1-1. Fusion blanket

D-T Fusion Reaction

D(2H)+T(3H) →4He + n + 17.06MeV

Roles of a blanket in a fusion reactor

  • Generating and transporting heat energy

  • Shielding nuclear radiation

  • Producing and recovering Tritium

Fig. 1. 3D view of FFHR

In the design of a force-free helical reactor (FFHR),

molten salt Flibe (LiF : BeF2 = 66 : 34) is recommended

as a blanket material..


1 background 1 2 flibe blanket system
1. Background1-2. Flibe blanket system

Advantages

  • MHD pressure drop is low in comparison with Li flow.

  • Stable in high temperature and vapor pressure is low, etc.

Disadvantages

  • High Prandtl number fluid ⇒ Heat transfer performance is low

  • Electrolysis can occur due to induced current

It is necessary to enhance heat transfer performance

with relatively low flow velocity.

To investigate heat transfer performance of Flibe, Tohoku-NIFS Thermofluid loop (TNT loop) was built in 1998.


1 background 1 3 features of hts

Air cooler

Circulation pump

Dump Tank

Flibe

HTS

Test section

Fig. 1 Tohoku-NIFS Thermofluid loop

(Before modification)

Fig.2 Temperature dependance of Pr

1. Background1-3. Features of HTS

Flibe contains toxic Be ⇒ Using alternative molten salt, HTS

Comparison of features

between Flibe and HTS

Flibe (LiF - BeF2 : 66 - 34)

Melting point : 459 C

Pr : 35.6 @500 C

Difficult to treat

HTS (KNO3,NaNO2,NaNO3 : 53-40-7)

Melting point : 142 C

Pr :27.7 @200C

No toxic substances


1 background 1 4 early studies

Fig. 4 Comparison between Re and Nu

Causes of disagreements

  • Entrance region was too short to develop turbulence flow.

  • Heating method was not suitable for heat transfer experiment.

1. Background1-4. Early studies

450 mm

Fig. 3 Overview of previous test section


1 background 1 5 aim of this study
1. Background1-5. Aim of this study

TNT loop was modified.

Entrance region : nearly 50D

Direct electrical heating method

Fig. 5 Tohoku-NIFS Thermofluid loop

(After modification)

Aim of this study

  • To investigate heat-transfer performance in a circular pipe using modified TNT loop, and to get more accurate data.

  • To quantitatively evaluate heat transfer enhancement of SPP by comparing with the performances of other heat transfer promoter.


2 experimental 2 1 experimental apparatus

Fig. 5 Tohoku-NIFS Thermofluid loop

(After modification)

2. Experimental2-1. Experimental apparatus

Air cooler

Pump

Dump tank

Test section


2 experimental 2 1 experimental apparatus1
2. Experimental2-1. Experimental apparatus

450mm

About 1800mm

(b) Modified test section

(a) Previous test section

Fig. 6 Comparison between modified test section and previous test section


2 experimental 2 1 experimental apparatus2

Inner tube diameter:D=19mm

Material:SUS304

T.C. for measuring inlet bulk temp.

T.C. for measuring outlet bulk temp.

Test section:

About 50D

Entrance region : 30D

Flow

straightener

Stainless mesh

Electrodes

Flexible tubes

1000mm

1000mm

To alleviate an effect of thermal stress

2. Experimental2-1. Experimental apparatus

Length to develop boundary layer : lv

lv = 0.693 × Re0.25 × D

( Re : Reynolds number, D : Inner tube diameter )

When Re = 15000,

lv= 0.693 × 150000.25 × D ≈ 8D<< Entrance region

Fig.7Schematic view of the modified section


3 results and discussion 3 1 chemical effect
3. Results and Discussion3-1. Chemical effect

(a) Inlet

(b) Center

(c) Outlet

Fig. 8 Observations of test-section inner surfaces

HTS is thermally decomposed above 450C. Main reaction is as follows,

The present study is carried out under the condition of

HTS temperature up to 350C. ⇒ No chemical deposition

No effect for heat transfer experiment.


3 results and discussion 3 2 heat transfer of circular pipe cp

Transition

Entrance

3. Results and Discussion3-2. Heat transfer of circular pipe (CP)

Developed

Tin=200 [°C], Pr ≈ 27

Re=4610

q’’=30.6 [kW/m2]

Thermal boundary layer is fully developed from 500 mm position.

Temperatures measured in this region are used for evaluating heat transfer performance.

Fig. 9 Typical temperature profile

along the test section


3 results and discussion 3 2 heat transfer of circular pipe cp1
3. Results and Discussion3-2. Heat transfer of circular pipe (CP)

Modified Hausen equation

(3500≤Re≤10000)

Sieder-Tate equation

(10000≤Re)

Fig. 10 Comparison between acquired Nu and the empirical Eqs.

Good agreement with above Eqs.

Maximum error : 10%


3 results and discussion 3 2 heat transfer of circular pipe cp2
3. Results and Discussion3-2. Heat transfer of circular pipe (CP)

Modified Petukhov equation

(104 ≤ Re ≤ 5x106, 0.5 ≤ Pr ≤ 2000)

Also good agreement with above Eq.

Maximum error : 15%

Fig. 11 Comparison between acquired heat transfer coefficient and the modified Petukhov Eq.

Conclusion

Heat transfer correlations for general fluid in CP can be used to evaluate heat transfer characteristics for high temp. molten salt.


3 results and discussion 3 2 heat transfer of sphere packed pipes spp
3. Results and Discussion3-2. Heat transfer of sphere-packed pipes (SPP)

Manglik equation for swerl tube

4 times higher

Fand equation for SPP

m = 0.25, n = 1, p = 0.4054, q = 0.5260, r = -0.6511.

  • SPP performance is higher than that of other heat transfer promoter.

  • It significant, especially, at low flow velocity condition.

Fig. 12 Results of the heat transfer with packed bed under same velocity condition.


3 results and discussion 3 2 heat transfer of sphere packed pipes spp1
3. Results and Discussion3-2. Heat transfer of sphere-packed pipes (SPP)

In the case of using D/2 spheres, pressure drop gives good agreements with drag model. (by M. OKUMURA et. al)

Evaluating pumping power of SPP

Fig. 12 Results of the heat transfer with packed bed under same pumping power.


Is there any future for flibe
Is there any future for Flibe ?

Allowable temperature of structural material

  • =500C -> No solution

  • =550C ->

    Outlet temp. can be raised to 650C.

    Other coolant is necessary for first wall cooling.

    (or should we change the composition of Flibe to decrease melting temperature ?)

  • =650C -> Some possibility


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