A combined experimental and numerical approach for radiation heat transfer in semi-crystalline thermoplastics

Abstract : This paper proposes a novel experimental-numerical approach for radiation heat transfer in semi-crystalline thermoplastics. The proposed experimental and numerical approaches were analyzed here for the case of IR heating of linear polyethylene (PE). The challenges for radiation transport in semi-crystalline polymers may be categorized into the two main aspects: optical heterogeneity in polymer medium due to semi-crystalline nature and, semi-transparency in certain type of such polymers, like PE. In this study, we address the temperature dependence in the thermo-optical properties of semi-crystalline thermoplastics concerning its effect as a thermal radiation parameter for radiation heat transfer modeling of such type of polymers. The temperature dependence in the optical properties of PE, namely transmittance and reflectance characteristics, were experimentally analyzed under heating condition and, the temperature-dependent thermo-optical properties of PE was determined. The experimental analyses showed that the change in the thermo-optical properties under heating is related to change in the optical scattering behavior in PE medium since it is strongly affected by its crystalline structure. The radiation heat transfer model was built based on optically homogeneous medium assumption at which the change in the amount of radiative energy absorbed by the PE medium under heating was introduced without modeling how the light scatters inside of the medium. Thus, the effect of optical scattering on the absorption characteristics of PE under varying temperature was taken into account without modeling the spatial distribution of the scattered light intensity at microscopic level, which offers computationally cost-effective numerical solutions. The accuracy of the numerical model was analyzed performing IR heating experiments where IR thermography and thermocouples were employed for the surface temperature measurements. Due to the semi-transparent nature of PE, an experimental method was developed for IR thermography of PE and its accuracy was analyzed. The experimental-numerical comparisons showed that the temperature field on PE can be closely predicted using its temperature-dependent thermo-optical properties. Thanks to the adopted comparative case study, it was demonstrated how the temperature field predictions may deviate from the experimental thermal measurements due to the ignorance of this temperature dependence. Considering any type of monochromatic or polychromatic radiation source, the combined experimental-numerical approach proposed here may be adopted for temperature field predictions and non-invasive surface temperature measurements on the radiatively heated semi-crystalline thermoplastics.
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Submitted on : Thursday, April 25, 2019 - 4:04:50 PM
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Sinan Boztepe, Olivier de Almeida, Rémi Gilblas, Yannick Le Maoult, Fabrice Schmidt, et al.. A combined experimental and numerical approach for radiation heat transfer in semi-crystalline thermoplastics. International Journal of Thermal Sciences, Elsevier, 2019, 142, pp.142-155. ⟨10.1016/j.ijthermalsci.2019.04.020⟩. ⟨hal-02109750⟩

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