Institute of Aerospace Thermodynamics H. Kamoun, G. Lamanna, B. Weigand Institute of Aerospace...

Institute of Aerospace Thermodynamics

H. Kamoun , G. Lamanna, B. WeigandInstitute of Aerospace Thermodynamics, Universität Stuttgart

70569 Stuttgart Germany

J. SteelantESTEC-ESA, 2200 AG Noordwijk, The Netherlands

Thermal characterisation of an ethanol flashing jet using

differential infrared thermography

Eucass 2011, St Petersburg

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Contents

Motivation & Objectives

Differential Infrared Thermography

Experimental Setup

Uncertainty analysis

Results

Summary

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Contents



Experimental Setup


Results

Summary

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Flashing: Sudden exposure of a superheated pressurized liquid to a low pressure environment Fast phase transition

Relevant in many technical application Accidental release of flammable and toxic pressure-liquefied gases in

nuclear and chemical industry. Benefit in propulsion system enhanced atomisation

P

T

Pinj

Psat(Tinj)

P∞

Tsat(P∞) Tinj

Liquid

VaporRp

ΔT

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Flash-atomisation/vaporisation model Temperature data for validation

Non-intrusive methods are needed

New method Differential Infrared Thermography (DIT)

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Contents



Experimental Setup


Results

Summary

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Problem: Spray emissivity: ε unknown For a liquid or a gas ε = f (T, λ, density)

DIT

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Differential Thermography

1,1 1 BackgroundSpraybSpraySprayCam III


12

121BackgroundBackground

CamCamSpray II

II

-

Liquid: ethanol, Tinj = 389K, pam = 0.2bar, pinj = 10bar

TBack = 286 K TBack = 366 K

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Contents



Experimental Setup


Results

Summary

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Experimental Setup

High-pressure liquid supply system

Liquid tank

Optical setup

Vacuum chamber

Vacuum Pump

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Experimental Setup

Heated modified diesel injector with D=150 μm and L/D= 6.6 Short injection and transient times → Constant backpressure Constant injection conditions (i.e. pressure & temperature) Reproducible test conditions

Courtesy of Bosch GmbH

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Experimental Setup

Heated background

Cooled background

303 K<TBack <389 K

280 K<TBack <290 K

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IR Kamera

Resolution: 640x512 pixel

Detector: InSb

Detector cooling: Stirling Cooler

Spectral range: 1.5 - 5µm

Integrationmode: Snapshot

Calibration range: 5°C – 300°C

FLIR Orion SC7000 Series

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Contents



Experimental Setup


Results

Summary

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The choice of the background temperatures

If Ispray < IBackground1,2 and for the spray dilute region (εspray<<1)

A calculation of the spray temperature is impossible

Key point: the selection of the background temperature should enhance the contrast between spray and surroundings



11 1 BackgroundsprayCam II

22 1 BackgroundsprayCam II

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4/1

42

41

42

41

42

41

41

42

414

1

1

BackBack

CamCam

BackBack

BackCamCamCam

spray

TT

TT

TTTTT

T

T

The sensitivity to measurement errors in e.g. the temperature recorded by the infrared camera TCam1

For a given Tspray and Tback1,2 ,the temperature recorded by the camera and the spray temperature error can be computed as a function of εspray

1Cam

spray

dT

dT

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Liquid: ethanol, Tinj = 389K, pam = 0.2bar, pinj = 10bar

The best results are obtained when the spray temperature distribution is intermediate between the two background values

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Tback1=286 K, Tback1=366 K

Max error: 4K

Tback1=337K, Tback1=366 K

Max error: 25K

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Uncertainty analysis (Outlook)

Influence of multiple scattering inside the spray:

Neglecting infrared scattering may lead to an overestimation of the emitted spray radiation

Further investigation are needed to evaluate this effect on the temperature results

Comparison of the temperature results with Global Rainbow Thermometry data to validate the assumption made here.

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Contents



Experimental Setup


Results

Summary

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Results (Validation)

Liquid: ethanol, Tinj = 403K, pam = 1 bar, pinj = 10bar

the window does not affect the temperature results

good agreement with the temperature measured by the thermocouples

Despite the good agreement a validation of the DIT can be accomplished only upon comparison with other non-

intrusive thermographic technique (e.g. GRT)

estimation of infrared scattering from a cloud of finely atomised droplets.

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Results

r

x

Example of flash a atomising spray. Liquid: Ethanol, Tinj = 389 K, pam = 0.2 bar,

p inj = 10 barNear the nozzle exit: narrow temperature profile

Downstream: flatter temperature profileRapidly decay of the temperature downstream the nozzle

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Results (Axial Profile)

Liquid: ethanol, Tinj = 342 K, pinj = 10bar

am

injsatp p

TpR

)(

Superheating Rp ↑ → Cooling rate ↑

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Contents



Experimental Setup


Results

Summary

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Summary and Outlook

The potential of the differential infrared thermography (DIT) for the characterisation of the temperature evolution in am flashing jet has been explored

Experiments were carried out under vacuum condition employing ethanol as test fluid.

The best results are obtained when the spray temperature is intermediate between the two background values

The temperature showed a decay along the spray centreline

With increasing superheat level, the cooling rate increases

Results with a good agreement with the thermocouple measurement.

Outlookfurther investigation are needed to evaluate the effect of radiative, infrared scattering on the temperature measurement

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Thank You

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Backup

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Experimental Setup

Requirements: Reproducible test conditions

• P∞: from 0.02 bar to 0.4 bar

• T∞=20°C

• Tinj: from 35 °C to 140°C

• Pinj= 10 bar

Good Vacuum (P∞=390 Pa)

Possibility to vary independently injection pressure and temperature

Problem: Maintaining a constant

backpressure

Solution: Fast response injection

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Injector

Requirements: Short injection and transient times → Constant backpressure Constant injection conditions (i.e. pressure & temperature) Reproducible test conditions

heated, modified diesel injector

Courtesy of Bosch GmbH

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Liquid: ethanol, pam = 0.1 bar, pinj = 10bar

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Liquid: ethanol, Tinj = 389 K, pinj = 10bar

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Vacuum Chamber

Water cooling → to prevent temperature gradients in the test chamber

Chamber temperature controlled through 3 thermocouples

Institute of Aerospace Thermodynamics H. Kamoun, G. Lamanna, B. Weigand Institute of Aerospace...

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