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Research Papers: Conduction

Investigation of Anisotropic Thermal Conductivity in Polymers Using Infrared Thermography

[+] Author and Article Information
David Nieto Simavilla

Department of Chemical Engineering,
Illinois Institute of Technology,
Chicago, IL 60616
e-mail: dnietosi@hawk.iit.edu

David C. Venerus

Department of Chemical Engineering,
Illinois Institute of Technology,
Chicago, IL 60616
e-mail: venerus@iit.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 24, 2014; final manuscript received August 13, 2014; published online September 16, 2014. Assoc. Editor: Wilson K. S. Chiu.

J. Heat Transfer 136(11), 111303 (Sep 16, 2014) (8 pages) Paper No: HT-14-1041; doi: 10.1115/1.4028324 History: Received January 24, 2014; Revised August 13, 2014

A new experimental method based on infrared thermography (IRT) is developed to study deformation-induced anisotropic thermal conductivity in polymers. An analytic solution for the temperature field of samples heated by a point source is utilized with a robust fitting procedure allowing for quantitative measurement of two components of the normalized thermal conductivity tensor of uniaxially stretched samples. In order to validate the method, we compare measurements on a cross-linked polybutadiene network with those obtained from a previously developed technique based on forced Rayleigh scattering (FRS). We find excellent agreement between the two techniques. Uncertainty in the measurements using IRT method is estimated to be about 2–5%. The accuracy of the method and its potential application to nontransparent materials make it a good alternative to extend current research on anisotropic thermal transport in polymeric materials.

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Figures

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Fig. 1

Schematic of rectangular sheet with laser beam propagating in the z3-direction

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Fig. 2

Temperature profiles from analytic solution in Eq. (14) (solid) and from FE solution with three values of BiW (dashed): T(x1, 0) (black / blue online only) and T(0, x2) (gray / red online only). All the profiles are for unstretched (λ = 1) samples with Bi0 = 0.035.

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Fig. 7

Residuals distribution (bars) of the fit to Eq. (14) for the stretched sample thermograph (λ = 4.129) in Fig. 6(b) compared to a Gaussian distribution of the same average and standard deviation (solid line)

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Fig. 10

Thermal conductivity ratios α1 (squares) and α2 (circles) versus normalized stress σ = GN for cross-linked PBD200k subjected to uni-axial elongation. Comparison of IRT method (gray / red online only) and FRS technique (open black). Also shown are results from a previous study (filled black) [22].

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Fig. 8

Comparison of fits of Eq. (14) (solid lines) with data (circles) for the temperatures profiles T(x1, 0) (black / blue online only) and T(0, x2) (gray / red online only). (a) Unstretched sample, λ = 1 and Bi0 = 0.029 ± 0.001; (b) stretched sample, λ = 4:129, α1 = 1.23 ± 0.049 and α2 = 0.954 ± 0.039. Residuals distributions for the fits are shown in the insets.

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Fig. 3

Temperature profiles from analytic solution in Eq. (14) (solid) and from FE solution with BiW=0.35/λ (dashed): T(x1, 0) (black / blue online only) and T(0, x2) (gray / red online only). The Biot number on the faces of the sample is set to Bi = 0.035/λ. (a) Unstretched sample, λ = 1; (b) stretched sample with λ = 4:129, α1 = 1.23, and α2 = 0.954. Residuals between analytic and FE solutions are shown in the insets.

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Fig. 4

Schematic of a sample before and after stretching showing the camera field of view and the area that is used for the analysis of the thermographs

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Fig. 9

Thermal conductivity ratios α1 (squares) and α2 (circles) versus stretch ratio λ for cross-linked PBD200k subjected to uni-axial elongation. Comparison of IRT method (gray / red online only) and FRS (black) techniques.

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Fig. 5

Schematic of the IRT experimental setup

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Fig. 6

Averaged thermographs taken on a cross-linked PBD200k sample. (a) Unstretched sample, λ = 1 and Bi0 = 0.029 ± 0.001. (b) Stretched sample, λ = 4.129, α1 = 1.23 ± 0.049 and α2 = 0.954 ± 0.039. The colormap in the side of the figures give the temperature in  °C.

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Fig. 11

Test of the stress-thermal rule using IRT (gray / red online only) and FRS (open black) for cross-linked PBD200k subjected to uni-axial elongation. The slope of the line through the data gives the dimensionless stress thermal coefficient CtGN = 0.038 ± 0.009. Also shown are results from a previous study (filled black) [22].

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