Experimental and Numerical Study of Mist Cooling for the

Electra HibachiV.Novak, D.Sadowski, S.Shin, K.Schoonover,

and S. Abdel-Khalik

HAPL meeting, Madison, WI (September, 24-25, 2003)

G. W. Woodruff School ofMechanical Engineering

Atlanta, GA 30332–0405 USA

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Objectives

• Experimentally examine effectiveness of gas/liquid mist as a means of cooling the Electra Hibachi Foils

• Quantify effect of various operating parameters on mist cooling effectiveness for prototypical Hibachi geometry (gas/liquid combination, gas velocity, liquid mass fraction, droplet size)

• Develop a validated mechanistic model to predict Hibachi foils’ thermal response under prototypical pulsed operating conditions

Laser Gas1.3-2.0 atm

(Kr+F2)flow at 4 m/s

Diode(vacuum)

E-beam

HibachiRibs

HibachiFoils

PressureFoil

Water Layers

VACUUM

E-beam

LASERGAS

EMITTER

He(or Air)/Water mix

Anode Foil

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Experimental Setup

4

Air-Assisted Nozzle

Experimental ResultsAir/Water Mist Cooling – Rectangluar Channel (24 cm)

Water inlet mass fraction [%] Water inlet mass fraction [%]

Axial distance [cm] Air-assisted nozzle inlet pressure [psi]

Ave

rage

hea

t tra

nsfe

r co

effi

cien

t [W

/m2

K]

Loc

al h

eat t

rans

fer

coef

fici

ent [

W/m

2K

]

Ave

rage

hea

t tra

nsfe

r co

effi

cien

t [W

/m2

K]

Ave

rage

hea

t tra

nsfe

r co

effi

cien

t [W

/m2

K]

Ave

rage

enh

ance

men

t rat

io [

h/h

dry

air]

water inlet mass fraction [%]

Ultrasonic Nozzle

Max Twall=80-90oC

15m/s

10m/s

5m/s

15m/s10m/s

5m/s

15m/s,dry air

15m/s,15%

15m/s,10%

15m/s,5%

15m/s

10m/s

5m/s

Optimization of atomizing air mass fraction

(10m/s air,10% water)

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Numerical Simulation steady state experiment (Air/Water)

4 cm

60 cm

2 cm

Heating (Qw)

Heating (Qw)

foils(Hastelloy-X=0.25 mm)

insulated side wall

6 cm

Air/Water Mist Flow [100% Saturation]

(Tin=20 oC, 1 atm, rp=30 m)Coolant

TemperatureFront SurfaceTemperature

Back SurfaceTemperature

Coolant Distribution Particle Distribution

ParticleTemperature

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Numerical Simulation steady state experiment (Air/Water)

Coolant Exit TemperatureCoolant Bulk Temperature Pressure

T

[K]

P [

kPa]

z [cm] z [cm]

Solid line : Coolant bulk temperature Dash dot line : Wall temperature

Wall and Coolant Temperature Distribution

dry air (15m/s, Qw=250W)

0 % water4 % water 5 % water 10 % water15 % water

15m/s Air

Qw=250W

rp=30 m

Heat transfer coefficient at the wall Wall film thickness

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dry Helium (30m/s, Qw=250W)

Numerical Simulation steady state experiment (Helium/Water)

Coolant Exit Temperature

T [

K] Solid line : Coolant bulk temperature

Dash dot line : Wall temperature

Wall and Coolant Temperature Distribution

Heat transfer coefficient at the wall30m/s Helium

Qw=250W

rp=30 m

0 % water 16.7 % water 33.5 % water50.2 % water

Coolant Bulk Temperature Pressure

T

[K]

P [

kPa]

z [cm] z [cm]

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Numerical Simulation pulsed heating (10Hz)

time [sec]

Q [

W/c

m3]

0.1 s

587250 W/cm3

pulse start at 4.0 s0

0.1ms

30 cm

2 cm

Heating

Heating

foils (Titanium, =0.025mm)

insulated side wall

4 cm

Air/Water Mist Flow [0% Saturation]

(15m/s Air, 10% Water Tin=20 oC, 1 atm, rp=30m)

Coolant TemperatureFront Surface

TemperatureBack SurfaceTemperature

Coolant Distribution Particle Distribution

ParticleTemperature

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Numerical Simulation pulsed heating (10Hz)

Coolant Exit Temperature

Dry Air

Air/Water(15m/s, 15%)

Maximum Temperature at the wall

Dry Air

Air/Water(15m/s, 15%)

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Numerical Simulation pulsed heating (10Hz)

Coolant Temperature Distribution Surface Temperature Distribution Heat Transfer Coefficient Distribution

Dry Air

(15m/s,15%)

A B C t [sec]

A : just before pulseB : just after pulseC : one pulse later

Air/Water

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Conclusions

•Mist cooling provides the means to effectively cool the Electra Hibachi within specified constraints on cooling system power consumption, foil max temperature, and temperature gradient Heat transfer coefficient can be significantly increased especially for

prototypical transient condition

•A validated mechanistic model to predict the foils’ thermal response under prototypical conditions has been developed

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Future Efforts

•Examine effect of liquid film formation on e-beam transmission efficiency

•Examine system performance for other gas/liquid combinations

•Construct and test a multi-channel test module under prototypical conditions