H. Abrahamsson, A. Borg, L. Ström Volvo Aero Corporation, S , Trollhättan, Sweden Internal Cooling of Hot Turbine Structures Z. G. Tari, L. Wang, B. Sundén Division of Heat Transfer, Department of Energy Sciences, Lund University (B. Sundén ) Research Managers:

 Industrial background  Our Project Plan Introduction of Test Rig 2 Measurement Techniques: 1. Liquid Crystal Thermography (LCT) 2. Particle Image Velocimetry (PIV) TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 2 Part (1)

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Studies of cooling processes have been carried out over many years and continuous development occurs. Thermochromic liquid crystals (TLC) have gradually been adopted for this purpose. Studies of cooling processes have been carried out over many years and continuous development occurs. Thermochromic liquid crystals (TLC) have gradually been adopted for this purpose. Division of Heat Transfer, Lund University 3 Background

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 4 Test Rig

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 5 Test Section

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 6 Test Section The flow of interest is in combination of smooth duct flow with :injection (jets),impinging effects, wall disturbances ( obstacles and ribs with various configurations)

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 7 Test Section The flow of interest is in combination of smooth duct flow with :injection (jets),impinging effects, wall disturbances ( obstacles and ribs with various configurations)

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 8 Measurement Techniques Liquid Crystal Thermography (LCT): to measure detailed heat transfer distribution. Particle Image Velocimetry (PIV): to provide fluid flow dynamics characteristics.

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 9 Part (2) Calibration of Wide-band Thermochromic Liquid Crystals (TLC R35C10W) for Heat Transfer Research Recent Work:

 Introduction of liquid crystal thermography (LCT)  Introduction of thermochromic liquid crystal (TLC) Introduction of TLC R35C10W  Calibration setup Calibration Procedure  Results  Conclusions & future work TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 10 Part (2)

 Liquid crystals (LCs) are substances in an intermediate phase that is between the pure solid and pure liquid phases.  Mechanically, LCs resemble liquids with viscosities ranging from runny glue to “solid” glass.  Optically, LCs exhibit many properties of crystals. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 11 Characteristics of LCs

3 classes of LCs according to their molecular structure: 1.Smectic 2.Nematic 3.Cholesteric  Molecular structure of the cholesteric liquid crystals is very delicately balance and can be easily upset.  All TLCs are cholesteric liquid crystals, which are used as temperature sensors. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Molecular structure of LC ( Fergason,1964) Division of Heat Transfer, Lund University Characteristics of LCs 12

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Characteristics of TLCs  TLCs display temperature-dependent colors by selectively reflecting incident white light.  Reflected light from the TLC is within the visible wavelength.  Reflected wavelength is typically decreased with rising temperatures.  The best color play performance appears when TLCs are applied as thin film on a light- absorbing black background. 13

TLC R35C10W description: TLC has the nominal R (red) start temperature at 35  C, and the bandwidth between R start and B (blue) start is 10  C.  At T below bandwidth, the TLC appears transparent.  As T rises through the TLC’s bandwidth, TLC turns R, G, and B sequentially.  As T exceeds the clearing point, the TLC enters the pure liquid state and reverts back to being transparent. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Characteristics of TLC R35C10W 14 TLC response to heating

 Wooden black box : to keep a uniform temperature inside the box.  Small fan & heater : to heat the air supplied to the calibration box.  Power supply: to adjust heat until the calibration plate was observed to change color.  1 thermocouple (K type): to measure the local surface temperature over the calibration plate.  Ice bath: to maintain reference junction of thermocouple(s) at 0  C.  Multi-meter: to record temperature- time history of the TLC. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Calibration Setup 15

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Calibration Setup 16 Black enclosure (covered the whole system) : to prevent influence from the background lighting

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 17 Calibration Setup 3 parameters affecting TLC calibration 1. Surrounding illumination disturbance 2. Direct illumination and viewing angle 3. Digital resolution of the image conversion system 2 white lights : to provide illumination of the TLC. CCD digital camera: to record color-time history by viewing the surface.

As the actual color image of TLC is affected by several environmental factors such as thickness of TLC, angle and distance of the light illuminating the liquid crystal coated surface channel, a color calibration is crucial for high resolutions in measurement. The experiments are carried out under the same conditions as those for the calibration. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Importance of TLC Calibration 18

 The dominant color on the calibration plate has different shades.  The original RGB (red, green, and blue) matrices are converted into HSI matrices, where H represents hue value.  As TLC reflects light at a wavelength dependent on temperature, the hue of the reflected light is also a function of temperature.  The hue value varies monotonically from 0-255,when the temperature of the TLC increases through its active interval.  The average hue value at a given temperature will be obtained from the TLC images and the calibration curve will thus be acquired. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Hue Technique 19

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan TLC R35C10W within temperature band (35  C-45  C) Division of Heat Transfer, Lund University 20 Results

 Hue technique allows TLC R35C10W to be calibrated with a considerable sensitivity over its entire bandwidth.  Wide-band TLC R35C10W is expected to have a considerable potential to measure surface temperatures to an accuracy of less than 0.1  C, and will be used in future work in the project. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University Conclusions 21

1. Calibration of 16 thermocouples (type K) 2. Calibration of TLC R35C10W using the calibrated thermocouples. Estimate the accuracy of TLC R35C10W 3. Heat transfer measurements in the test rig TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 22 Next Steps

The project is financially supported by the Swedish Energy Agency, Volvo Aero Corporation and Siemens Industrial Turbomachinery AB through the national Swedish research program TURBO POWER. TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Division of Heat Transfer, Lund University 23 Acknowledgement

TURBO POWER Program Conference 2009 April 23-24,Volvo Aero, Trollhättan Your Comments are Welcomed Division of Heat Transfer, Lund University 24