Two-Phase Heat Transfer Lab May 28-30, 2003. Analytical And Experimental Investigation of...

May 28-30, 2003 Two-Phase Heat Transfer Lab

Analytical And Experimental Investigation of Analytical And Experimental Investigation of Evaporation from Porous Capillary StructuresEvaporation from Porous Capillary Structures

Presented toONR Materials Research Review Meeting

May 28-30, 2003Woods Hole, MA

G.P. “Bud” Peterson, C. Li and G. BenitizDepartment of Mechanical, Aerospace & Nuclear Engineering,

Rensselaer Polytechnic InstituteTroy, NY 12180


What is a What is a Heat PipeHeat Pipe??


How does it work?How does it work?


What is it good for?What is it good for?


Analytical Modeling Analytical Modeling • Formation of the thin liquid filmFormation of the thin liquid film• Evaporation limitEvaporation limit

Experimental InvestigationExperimental Investigation Results and DiscussionResults and Discussion Applications and SignificanceApplications and Significance AAckcknowledgementnowledgement

OOUTLINEUTLINE


Objective:Objective:– To investigate the formation of thin films on capillary surfaces;To investigate the formation of thin films on capillary surfaces;

– To determine the evaporation limit on capillary surface; To determine the evaporation limit on capillary surface;

– To enhance the evaporation limit through optimization of the To enhance the evaporation limit through optimization of the

pore structure, physical properties such as thermal conductivity pore structure, physical properties such as thermal conductivity

and wettability;and wettability;

– To maximize the capillary pumping capability through the To maximize the capillary pumping capability through the

optimization of the evaporation heat transfer limit. optimization of the evaporation heat transfer limit.

BBACKGROUNDACKGROUND


Results Results and Discussion (7)and Discussion (7)

Thin film surface

1.0E+03

1.0E+04

1.0E+05

1.0E+06

0.1 1 10 100

Superheat, oC

Hea

t flu

x, W

/m2

Pool BoilingSubmerged surface

Comparison of the heat fluxes through thin capillary wick, submerged wick surface and pool boiling.


Interfacial RegionInterfacial Region

Intrinsicmeniscus

Transitionregion

Liquid

Vapor

Liquid

Vapor

Thin filmregion


Heat Flux DistributionHeat Flux Distribution

Heat Flux & Film ThicknessHeat Flux & Film Thickness

1000

1200

1400

1600

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

0

200

400

600

800

0.9

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Film

Th

ickn

ess

,

(m

)

Distance, s (m)

He

at

Flu

x (W

/cm

2)


Capillary Structures of InterestCapillary Structures of Interest

Surfaces investigated include:– Sintered powders– Metal foams – Screen meshes– Micro channel polymers


Mathematical Model (1)Mathematical Model (1)

Solid wall

d w 2w+

d w

w

w

Screen mesh cellScreen mesh cell Cross-section of the Cross-section of the screen meshscreen mesh

Physical Model: Evaporation process on a heated surface coated Physical Model: Evaporation process on a heated surface coated with a single layer of porous material, here metal screen mesh, with a single layer of porous material, here metal screen mesh, with liquid supplied by capillary action, producing a wetted surface with liquid supplied by capillary action, producing a wetted surface with saturated liquid in the cells. with saturated liquid in the cells.


Mathematical Model Mathematical Model

oy

x

Solid wall

rm

Equilibriumregion

Thin filmregion

T v

o

R w w+

Meniscusregion

o

y

x

Solid wall

rmMeniscus

region

Thin filmregion

T lv

T v

o

R w w+

e

3

1

,

,,

,0 )(

ln)(1

c

v

iw

iwsat

vgliwsat

v

iwv P

T

T

TP

PTRTP

T

TP

A



The Formation of Bubbles in capillary structures is dominated by the porous structure and superheat between the heated wall and the bulk liquid-phase.

where

For ideal gas

llglsatlllsat PTRTPPvTPr

/)(exp)(

2b

)( dcvl PPPP

21 ccc KKp

3A

pd

)ln( blvgld aTRp

Critical bubble radius



Formation of the bubble Formation of the bubble in the sharp corner area:in the sharp corner area:

a). Superheata). Superheat

b). The geometric shape b). The geometric shape and size of the celland size of the cell

c). Capillary pressure c). Capillary pressure

d w w+

Solid wallTw

T l

Tvrm

BubbleLiquid

Vapor

Pv

WireWire



Critical boiling heat flux

Conduction through the layer

Boundary conditions

w

creffcr

Tkq

02

2

,2

2

,

yk

xk effyeffx

0,0

x

x

0),(

x

wrx w

qy

ky eff

,0

0),( xfy

vTT

Assumptions:1. Evaporation take places only on the liquid surface2. Heat transfer through the liquid layer is dominated by conduction


Liquid DistributionLiquid Distribution

w /2

z

y

l w 0

r m

R w

Thin film region

Meniscus region


Results Results and Discussion (1)and Discussion (1)

0.5

1

1.5

2

2.5

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

X (mm)

Y (

mm

)A

Temperature distribution in the thin liquid film formed between the wires at high heat fluxes.


Experimental Test Facility Experimental Test Facility (Saturated Structures)(Saturated Structures)

1. Test article-porous layer 2. Vacuum chamber 3. Steam Condenser 4. Vacuum pump5. Liquid tube. 6. Power supplier7. Thermal bath 8. Data acquisition system

Coolingwater

1

6

2

3

4

5

7

8


Test Facility – Test Facility – Test ArticlesTest Articles

Advantages:• Changeable porous surfaces• Changeable surface size• Adjustable surface level• Easy to measure the surface temperatures• Using camera to monitor the thin film profile on the porous surface.• Can measure pool boiling on thin porous surface.

Do

H

8

D i


Triangular Grooved Polymer FilmTriangular Grooved Polymer Film

V


EExperimental Test Facility xperimental Test Facility (Wicking Height Tests)(Wicking Height Tests)

PowerMeasurement

Test article

Liquid pool

Vacuum Jar

Heating bathHeat exchanger

Overflowcontainer

TemperatureMeasurement

Valve

Heater

VacuumSystem

LiquidFlask

Overflow


7.0 7.0 7.0 5.030.0 30.0 30.0 15.0 15.0

177.8

Heater Micro film25.4

Thermocouple hole (0.5) Aluminum plateA

A

25.4

13.0 14.8

La

Le

Test article

Liquid

1"

Crosssection of the film

2a

w

h g

h v

h b

2w t

2a

w

2w

h g

h v

h b

t

Wetting point

EExperimental Investigation - xperimental Investigation - Test ArticlesTest Articles


Results Results and Discussion and Discussion

Water-Copper mesh# 150

1.0E+04

1.0E+05

1.0E+06

1.0E+07

0 20 40 60 80 100 120 140 160 180

Tv, oC

Crit

ical

hea

t flu

x, W

/m2

Effect of operating temperature (vapor-phase pressure) on the boiling limit of copper screen mesh layer.



Mesh #150

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

1.4E+06

1.6E+06

0 1000 2000 3000 4000

Capillary pressure, Pa

Crit

ical

hea

t flu

x, W

/m2

Effect of the capillary pressure on the boiling limit of the thin liquid film.



Water-Mesh #150

Cu

Al

SS

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

0 50 100 150 200 250 300 350ks, W/m K

Crit

ical

hea

t flu

x, W

/m2

Effect of thermal conductivity of wick layer on the critical boiling heat flux on copper screen mesh.


Thin film evaporation has a dramatically higher heat transfer Thin film evaporation has a dramatically higher heat transfer coefficient than pool boiling or submerged surfaces covered with coefficient than pool boiling or submerged surfaces covered with a thin porous layer. a thin porous layer.

Thin film evaporation can be modeled using a single cell Thin film evaporation can be modeled using a single cell approach;approach;

The formation and profile of the thin film is affected by the The formation and profile of the thin film is affected by the wettability and surface tension of the working fluid as well as heat wettability and surface tension of the working fluid as well as heat flux;flux;

The majority of the heat transfer occurs in the thin film region of The majority of the heat transfer occurs in the thin film region of the liquid meniscus resulting in a very high heat flux in this area;the liquid meniscus resulting in a very high heat flux in this area;

The evaporation heat transfer is significantly affected by the The evaporation heat transfer is significantly affected by the capillary pressure, and increases in the capillary pressure results capillary pressure, and increases in the capillary pressure results in a reduction of the evaporation heat transport limit;in a reduction of the evaporation heat transport limit;

Higher thermal conductivity wicking structures have a higher Higher thermal conductivity wicking structures have a higher evaporation heat transfer coefficient; evaporation heat transfer coefficient;

ConclusionsConclusions


Electronics applicationsElectronics applications– Miniature Heat Pipes for Electronic ApplicationsMiniature Heat Pipes for Electronic Applications– Wore Bonded Heat PipesWore Bonded Heat Pipes

Spacecraft Thermal ControlSpacecraft Thermal Control– Onboard electronicsOnboard electronics– Deployable radiatorsDeployable radiators

Treatment of Neocortical EpilepsyTreatment of Neocortical Epilepsy– Implantable thermal devicesImplantable thermal devices

AApplications and Significancepplications and Significance


PC Wireboard CoolingPC Wireboard Cooling


Miniature Heat Pipes for Electronics ApplicationsMiniature Heat Pipes for Electronics Applications


Wire Bonded Heat PipesWire Bonded Heat Pipes

Evaporator Condenser

Metal wires Vapor channels

t

Vapor

Liquid

RcRe

d d

12"


Transhab Spacecraft (Stowed)Transhab Spacecraft (Stowed)


Transhab Spacecraft (Deployed)Transhab Spacecraft (Deployed)


Treatment of Neocortical EpilepsyTreatment of Neocortical Epilepsy

Effect of local cooling on neocortical seizures. A. Control seizure recorded ipsilateral to focal injection of the convulsant 4-aminopyridine lasts over 100 seconds. B. Activation of Peltier directly contacting cortex rapidly terminated a seizure.

0.2 mV

20 sec

0.2 mV

5 sec60C

60C

Seizure Detection


Treatment of Neocortical EpilepsyTreatment of Neocortical Epilepsy

Individual Peltier DeviceIndividual Peltier Device

TC


Rectangular Grooved Polymer FilmRectangular Grooved Polymer Film


The authors would like to acknowledge the support of the Office of Naval Research.

AcknowledgementAcknowledgement

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