Heat transfer properties of two expanded polystyrene (EPS) samples of similar density, one without (white) and one with graphite opacifier particles (gray), are compared. Tomographic scans are used to obtain cell sizes of the foams. Using established models for closed-cell polymer foams, the extinction coefficient and the effective thermal conductivity are obtained. The effect of opacifiers is modeled using (1) an effective refractive index for the polystyrene walls within a cell model for the EPS and (2) a superposition of extinction due to a particle cloud upon extinction predicted by the cell model, where particles are modeled as oblate spheroids, or equivalent volume, surface, or hydraulic diameter spheres. Modeled effective conductivities are compared with measurements done on a guarded hot-plate apparatus at sample mean temperatures in the range from 0 °C to 40 °C. Typically, cells of the gray EPS are about 40% larger than those of the white EPS and the cell walls in the gray EPS are thicker. The refractive index mixing model and the model with graphite opacifier particles as oblate spheroids overpredict extinction, however, the mean error in the effective conductivity predicted by the oblate spheroids model is only 2.7%. Equivalent volume/surface sphere models underpredict extinction, but still yield a low mean error in effective conductivity of around 4%. While the oblate spheroids model has a lower mean error, the computationally less expensive equivalent volume or equivalent surface models can also be recommended to model the inclusions.
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November 2018
This article was originally published in
Journal of Heat Transfer
Research-Article
Modeling the Effect of Infrared Opacifiers on Coupled Conduction-Radiation Heat Transfer in Expanded Polystyrene
A. Akolkar,
A. Akolkar
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria;
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria;
Unit for Material Technology,
University of Innsbruck,
Technikerstraße 13,
Innsbruck 6020, Austria
e-mail: anupam.akolkar@fhv.at
University of Innsbruck,
Technikerstraße 13,
Innsbruck 6020, Austria
e-mail: anupam.akolkar@fhv.at
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N. Rahmatian,
N. Rahmatian
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
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S. Unterberger,
S. Unterberger
Unit for Material Technology,
University of Innsbruck,
Christian Doppler Laboratory for Cement
and Concrete Technology,
Technikerstraße 13,
Innsbruck 6020, Austria
University of Innsbruck,
Christian Doppler Laboratory for Cement
and Concrete Technology,
Technikerstraße 13,
Innsbruck 6020, Austria
Search for other works by this author on:
J. Petrasch
J. Petrasch
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
Search for other works by this author on:
A. Akolkar
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria;
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria;
Unit for Material Technology,
University of Innsbruck,
Technikerstraße 13,
Innsbruck 6020, Austria
e-mail: anupam.akolkar@fhv.at
University of Innsbruck,
Technikerstraße 13,
Innsbruck 6020, Austria
e-mail: anupam.akolkar@fhv.at
N. Rahmatian
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
S. Unterberger
Unit for Material Technology,
University of Innsbruck,
Christian Doppler Laboratory for Cement
and Concrete Technology,
Technikerstraße 13,
Innsbruck 6020, Austria
University of Innsbruck,
Christian Doppler Laboratory for Cement
and Concrete Technology,
Technikerstraße 13,
Innsbruck 6020, Austria
J. Petrasch
illwerke vkw Professorship for Energy Efficiency,
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
Vorarlberg University of Applied Sciences,
Hochschulstrasse 1,
Dornbirn 6850, Austria
1Corresponding author.
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 13, 2018; final manuscript received June 27, 2018; published online August 20, 2018. Assoc. Editor: Zhixiong Guo.
J. Heat Transfer. Nov 2018, 140(11): 112005 (10 pages)
Published Online: August 20, 2018
Article history
Received:
April 13, 2018
Revised:
June 27, 2018
Citation
Akolkar, A., Rahmatian, N., Unterberger, S., and Petrasch, J. (August 20, 2018). "Modeling the Effect of Infrared Opacifiers on Coupled Conduction-Radiation Heat Transfer in Expanded Polystyrene." ASME. J. Heat Transfer. November 2018; 140(11): 112005. https://doi.org/10.1115/1.4040784
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