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Research Papers

Application of the Transient Heat Transfer Measurement Technique Using Thermochromic Liquid Crystals in a Network Configuration With Intersecting Circular Passages

[+] Author and Article Information
Anika Steurer

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart 70569, Germany
e-mail: anika.steurer@itlr.uni-stuttgart.de

Rico Poser, Jens von Wolfersdorf

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart 70569, Germany

Stefan Retzko

Ansaldo Energia Switzerland AG,
Römerstrasse 36,
Baden 5400, Switzerland

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 21, 2018; final manuscript received October 17, 2018; published online January 25, 2019. Editor: Kenneth Hall.

J. Turbomach 141(5), 051010 (Jan 25, 2019) (9 pages) Paper No: TURBO-18-1261; doi: 10.1115/1.4041807 History: Received September 21, 2018; Revised October 17, 2018

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20 mm that intersect coplanar at an angle θ = 40 deg, the innermost in three, the outermost in one intersection level. Two additional nonintersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional (3D) Reynolds-averaged Navier–Stokes equations (RANS) simulations using the shear-stress transport (SST) turbulence model. The presented analysis uncouples local heat transfer (HT) coefficients from actually measured local temperatures but uses the time information of the thermocouples (TC) instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether HT is locally enhanced due to higher mass flow rates or the intersection effects.

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References

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Figures

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Fig. 1

Top view (camera view) of experimental setup at ITLR

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Fig. 2

Schematic of half of the investigated flow network: geometry details and notation

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Fig. 3

Comparison of all passage mass flows across the test section, NUM, Re¯=25,000

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Fig. 4

Comparison of mass flow in P2, NUM, Re¯=10,000 and 40,000

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Fig. 5

Temperature field in the midplane of an intersection, NUM

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Fig. 6

Comparison of dimensionless centerline temperature with bulk temperature in P3, NUM, Re¯=25,000

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Fig. 7

Θ1: comparison of experimental values at each instant of time with steady-state CFD, P3, Re¯=25,000

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Fig. 8

ΘC: evolution of local fluid temperature over time at selected TC positions in P3, EXP, Re¯=25,000

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Fig. 9

Dimensionless numerical temperature profile (ΘB) and experimental time-dependent values at selected time steps after tstepC), all TC positions, P3, Re¯=25,000

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Fig. 10

Indication time of calibrated TLC temperature, P3, EXP, Re¯=25,000

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Fig. 11

Comparison of Nu averaged in x-direction based on Tin: NUM-EXP, P3, Re¯=25,000

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Fig. 12

Comparison of Nu averaged in x-direction based on Tin or Eq. (10) (TB,h), respectively: NUM-EXP, P3, Re¯=25,000.

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Fig. 13

Time-dependent ΘB at t = tstep and three instants later in time, EXP, P3, Re¯=25,000

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Fig. 14

Comparison of Nu averaged in x-direction based on Tin or new approach, respectively: NUM-EXP, P3, Re¯=25,000

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Fig. 15

Spatially resolved Nu from transient TLC experiment: (a) based on Tin and (b) new evaluation method, P3, Re¯=25,000

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Fig. 16

Averaged Nu in relation to Nueff (calculated with real local passage mass flow m˙eff) in comparison to Nu¯/Nu0: NUM-EXP, P3, Re¯=25,000

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Fig. 17

ΘB with estimated error band due to 20% discrepancies in computed heat transfer, NUM, P3, Re¯=25,000

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