High resolution heat transfer measurements · CONVECTIVE HEAT TRANSFER MEASUREMENTS ... Heat...

ONR Thermal Materials Workshop 2001 1

HIGH RESOLUTIONCONVECTIVE HEAT

TRANSFER MEASUREMENTS

Peter Ireland and Terry JonesR-R UTC in Heat Transfer and

AerodynamicsDept. Engineering Science,

University of Oxford


Acknowledgements

• Internal cooling– David Gillespie, Calvin Tsang, Changmin Son

• Stepped solution and fin research – Andrew Neely

• Recuperator research underway – Marty Cerza and Juan Adams

• Transition work– Richard Anthony


Content• High resolution htc measurements using temperature

sensitive liquid crystals– Need for high resolution htc data– Scaling strategy– Liquid crystal instrument features– Application and test details– Example applications new developments

• Thin film gauges– Instrument details and recent developments– Applications– High density platinum gauges

• Conclusions


Need for high resolution htc data in turbomachinery

• Detailed thermalmodel of the enginecomponent requiredfor component lifepredictions

• Aerospace turbineblades are small andcooling systems areusually compact.

Cooling passages close to the blade surface

Typical civil engine:-Mean gas temp = 1970KMax relative = 2375K

850K

950oC


Example blade cooling temp distribution•Blade far from isothermal•Biot number not small enough

khL=Biot

G. M Dailey0.001

0.01

0.1

1

10

0 0.01 0.02 0.03 0.04

Blade dimension (m)

Biot number

2000 4000 6000

Chor

k=25W/mK

Wall

htc=

50oCcontoursteps

1100K


Scaling issues• Large scale model improves effective resolution.• Switch off sideways (lateral) conduction to achieve

local htc measurement with 1-d processing.• No need for engine temperatures.• Fluid dynamics correct through use of Reynolds

number, Mach number and Prandtl number.

Mach)Pr,(Re,fNu �

Dimensionless heat transfer coefficient

Dimensionless flow speed


Transient method with liquid crystals for internal cooling

Pedestal bank

Film cooling hole

Impingement array

Inclined ribs


Temperature measurement

))I-(B+)I-(G+)I-6((RB-G-2R= (H)

222cos

Red Green Blue signals from video� Intensity or Hue processing

20µm

BGR= I ��


Tc

Time of crystal colour change depends on local hsu

rfac

e te

mp

T s gas temperature Tg

timestart of test

hTc

Calibration

Test data


Heat transfer inside a film-cooling hole fed in cross-flowHeat transfer inside a film-cooling hole fed in cross-flow

L=60mm

180 mm

Liquid crystalapplied to this surface

22 mm

200 mm

Film Cooling Hole

Test Plenum

High AspectRatio Duct

Gas Thermocouple

220 mm

200 mm

Orifice Plate

Hole diameter = 0.3mm

Hole diameter = 22mm


Recorded Colour Play within the HoleRecorded Colour Play within the Hole

50 pixels� 0.3mm1 pixel � 6 micron


Typical Intensity Histories at 6 Positions on the Film Cooling Hole Surface. Monochromatic processing.

htc


Local Nusselt Number Distribution, 90o Hole


2.84mm

1.02mm

8.20mm

Trailing EdgeFilm-Cooled from a Central Cavity

Lattice Cooling System to fit insidethis Cavity

Lattice cooling system for trailing edgeLattice cooling system for trailing edge

Geometric scaling essential for resolution


The Assembled Lattice Model

FLOWFLOW

HeaterHeaterTipTip Exit Film-Cooling HolesExit Film-Cooling Holes RootRoot


Inlet

Exit Holes (8 mm)

Ribs

Channel

Photographs of thePhotographs of theWorking SectionWorking Section


Nusselt number distribution at several Reynolds numbers


Rib roughened passage• 3 metres (60d) long, square cross section cooling passage• Perspex walls with temperature sensitive liquid crystal coated on

the inner surface.• Reynolds number from 20,000 to 60,000• Air is heated at the inlet using heater mesh• Test section situated from 40d to 60d• Fully developed flow established ahead of the test section• Rotation not simulated in the experiment


Heat transfer distribution

60o interrupted inline ribs


Heater Mesh Impingement

Plate

Air Flow

To Vacuum Pump

Target Plate

The perspex test rig isinstrumented with liquidcrystal coatedimpingement and targetplates, and fast responsegas thermocouples at theentrance and exit of theworking section

Impingement heat transfer rig


Impinging jet heat transfer

Rejavg = 26710


Heater Mesh Impingement

Plate

Air Flow

To Vacuum Pump

Target Plate

Data through the mesh heater

60�m square apertures


Heater convective efficiency

Estimate of the effect of wire diameter.�

00.10.20.30.40.50.60.70.8

0.01 0.1 1 10 100

Velocity (m/s)

Con

vect

ive e

fficie

ncy

40micron100micron200micron1mm

upstreamwire

downstreamwireCONVECTIVE TT

TT�

�

��

•High convective efficiency ( ~50%) so:–wires run cool–radiation insignificant–support easy to engineer

•Suitable for switching temperature of low speed flows


Ramp function withslope m

Exponential withasymptote Tg

Series of steps

Step change to Tg

Surface temperatureFluid temperature� �

��

�

�

��

�

�� )()exp(1

2

00 cktherfc

ckthTTTT gs

��

� � � ��

��

�

�

��

�

� ��

�

n

i

iigigs ck

therfc

ckth

TTTTi

1

2

0 )()exp(11

�

�

�

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�

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��

�

�

�

�

�

�

t n

n12+t1

hck

+1

hck + 1

1 - ck

hck + 1

hck

-1=TTTT

4n

1

2

t

ckt h

2

2

g

s

2

2

sinh

e

etherfc

e

-

-

0

0

��

��

�� 2

2

0)()exp(121

�

��

�

erfcmtTTs


y = -153.26x + 9790.7

y = -151.31x + 3467.1

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

6000

0 10 20 30 40 50 60 70

Temperature (deg C)

Hea

t Flu

x (W

/m2

K)

Heat FluxHeating ProcessCooling ProcessLinear (Heating Process)Linear (Cooling Process)

Taw=63.88Tg_avg=66.85

Tw_init=22.91Tg_init=23.25

Works heating or cooling


Use of stepped flow temperaturepixel position

20 40 60 80

510

152025

30

0 200 400 60010

20

30

40

50surface temperature history (red = best fit)

0 200 400 6000.5

1

1.5

2intensity history (blue = exp, red = best fit)

0

0.1

0.2

0.3

0.4

0.5RMS error in intensity fit (htc x Tbar)

20 40 60

51015202530


Increasing the number of steps

htc =63.3405Tbar =0.87

RMS error in intensity fit (htc x Tbar)

20 40 60

5

10

15

20

25

30

htc =63.3405Tbar =0.87


20 40 60

5

10

15

20

25

30

0

0.1

0.2

0.3

0.4

0.5

htc =63.3405Tbar =0.87


20 40 60

5

10

15

20

25

30

htc =63.3405Tbar =0.87


20 40 60

5

10

15

20

25

30

htc =63.3405Tbar =0.87


20 40 60

5

10

15

20

25

30

0

0.1

0.2

0.3

0.4

0.5

htc =63.3405Tbar =0.87


20 40 60

5

10

15

20

25

30

U-D-U-D-U-DU-D-U-DU-D

U U-D-U-D-UU-D-U


Film Cooling

Work on Dry Low Emission Combustor


0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1

F i lm C o o l in g E ffe c t ive n e s s2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

Film Cooling Effectiveness


Lateral Conduction Correction

��

��

�

�

��

�

��

�

�

�

�2

2

2

2

2

2

zT

yT

xT

tT

�

xyz

Step Two: Alternating Direction Methods (after Jim Douglas)

a) nzyxnx T

tT

t)222()2( 222*

12

��

��

�

b)

c) **1

21

2 2)2(��

��

�� nnznz T

tTT

t

*1

2**1

2 2)2(��

��

�� nnyny T

tTT

t

where 2,,,1,,,,,,1,,,

2 )/()2( xTTTT nkjinkjinkjinkjix ��


Lateral Conduction

Result:

0 5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 50

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0

3 5 0 0

Te m p e ra tu re In c re a s e

Q H

eat F

lux

Heat Flux at each pixel canbe then be calculated. TheFilm Cooling Effectivenessand Heat TransferCoefficient can bedetermined by theinterception of the

Temperature axis and thegradient of the heat fluxgraph shown above.

0 5 10 15 20 25 302.4

2.5

2.6

2.7

2.8

2.9

3

3.1

3.2

3.3x 10

-3

tes t durat ion t im e (s )

Nor

mal

ised

Gre

en In

tens

ity


• 832 channels in thespecimen.

• Length of eachchannel: 197 mm.

Current marine application


RR spiral recuperator


0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0D is ta n c e f r o m th e f in le a d in g e d g e [m m ]

Hea

t tra

nsfe

r coe

ffici

ent [

W/m

^2/K

] F la t c o n t in u o u s 9 .1 m /sIn te r ru p te d s = 1 2 m mIn te r ru p te d s = 6 m mIn te r ru p te d , s ta g g e re d

Earlier interrupted fin htc


Recuperator heat transfer research underway


DIFFUSION EQUATION

LAPLACETRANSFORM

FREQUENCY

tT

kc

xT

�

��

�

� �

2

2

Tsckq ��

� � � �� Tjckq ��

Early thin film gauges


� �tq� STEP

� � 2/1~ ttT

qT ��

Tsckq ��

sq 1~�

2/31~

sT

Analysis

ANALOGUE

tV

cr

xv

�

��

�

�

2

2

V�T qI ��


TWO LAYERED GAUGES

�

�

�

��1

1A1112222

kckc

�

��

��

�

�

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��

�

�

�

��

21

112exp1

21

112-exp -1

x

�

�

slA

slA

Tskcq 111��

Two layer gauges


Copper leads CGauge sensor (Platinum)

Upilex

Glue

Thermocouple

Gauge sensor

Glue

Upilex�x

Model


High Density Layout using Gauge Arrays

Voltage Leads

Voltage LeadsConstant

Current Path

Flow

Dire

ctio

n

1 cm


Model covered with sheet of TFG arrays


0.415 0.42 0.425 0.43 0.435 0.44 0.445 0.45 0.455 0.46 0.46530

35

30

35

30

35

40

Time (sec)

Hea

t flu

x [

kW/m

2 ] Turbulent Spot

Becalmed Region

X= 280mm

X= 260mm

X= 240mm

Turbulent Spot Detection with Surface TFG’s


ZX

U�

Freestream TurbulenceBar Grid

4 Spanwise Thin Film Arrays(27 Sensors each)

Flat Plate Model Flow Direction

134 2

Time [ms]

z [m

m]

run302 Rex = 1.3e+005 U = 48.0 m/s Tu = 2.4%

85 86 87 88 89

53

43.4

Turbulent Heat Flux

Laminar Heat Flux

Visualizing Transitional Heat Flux


Conclusions• Presentation of existing techniques for

miniature measurements.

• Scaling can be useful for determination ofconvective loads at high resolution.

• Miniature thin film gauges beingcontinuously developed.

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