Modeling in-depth transfer of thermal radiation in non-gray condensed materials

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School of Engineering | Doctoral thesis (article-based) | Defence date: 2023-05-12
Degree programme
66 + app. 78
Aalto University publication series DOCTORAL THESES, 61/2023
In-depth radiation absorption is a key mechanism in the flammability and decomposition of materials. This mechanism is commonly modeled by Beer's law or by solving the radiative transfer equation (RTE) by applying a mean value of the material's absorption coefficient. The mentioned approaches cannot be accurate because they neglect the spectral nature of the absorption coefficient and the real directional distribution of the thermal radiation inside the condensed materials. This research aims to efficiently address thermal radiation's spectral and directional details when modeling in-depth radiation absorption and emission for fire simulations. To handle the spectral aspect, a full spectrum k-distribution (FSK) method was developed for the condensed materials. This method greatly improved accuracy compared to the gray method (constant absorption coefficient). However, due to the weakness of the FSK method in estimating medium emission, the separated FSK (SFSK) method was developed to solve the issue by separately treating the irradiation of the source and medium emission. An ordinate weighting method (OWM) was developed for the finite volume method (FVM) to consider interface refraction in the directional distribution of the radiation. This method relates the angular distributions of the radiative heat fluxes at both sides of the interface by assigning a weighting parameter to each pair of control angles. The spectroscopy technique was used to extract the absorption coefficient spectrum and optical constants of black poly (methyl methacrylate) (PMMA). Then, an efficient level of thermal radiation details was proposed by applying different combinations of the developed methods and simplified approaches to the PMMA pyrolysis modeling problem. The proposed thermal radiation details are the two-flux method for RTE solution, the gray method with source temperature- and depth-dependent absorption coefficient, and the diffuse interface with equivalent reflectivities.
Supervising professor
Hostikka, Simo, Prof., Aalto University, Department of Civil Engineering, Finland
Thesis advisor
Bordbar, Hadi, Dr., Aalto University, Finland
in-depth radiation transfer, spectral modeling, interface treatment, optical constants, condensed materials pyrolysis
Other note
  • [Publication 1]: Alinejad, F., Bordbar, H., & Hostikka, S. (2020). Development of full spectrum correlated k-model for spectral radiation penetration within liquid fuels. International Journal of Heat and Mass Transfer, 158, 119990.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.ijheatmasstransfer.2020.119990 View at publisher
  • [Publication 2]: Alinejad, F., Bordbar, H., & Hostikka, S. (2021). The ordinate weighting method for solving radiative heat transfer through a Fresnel interface. Journal of Quantitative Spectroscopy and Radiative Transfer, 270, 107685.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.jqsrt.2021.107685 View at publisher
  • [Publication 3]: Alinejad, F., Bordbar, H., & Hostikka, S. (2021). Improving the modeling of spectral radiation penetration into the condensed materials with the separated full spectrum correlated-k method. International Journal of Heat and Mass Transfer, 176, 121448.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.ijheatmasstransfer.2021.121448 View at publisher
  • [Publication 4]: Alinejad, F., Bordbar, H., Makowska, M., & Hostikka, S. (2022). Spectroscopic determination of the optical constants and radiative properties of black PMMA for pyrolysis modeling. International Journal of Thermal Sciences, 176, 107501.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.ijthermalsci.2022.107501 View at publisher
  • [Publication 5]: Alinejad, F., Bordbar, H., & Hostikka, S. (2022). On the importance and modeling of in-depth spectral radiation absorption in the flammability analyses of black PMMA. Fire Safety Journal, 103706.
    Full text in Acris/Aaltodoc:
    DOI: 10.1016/j.firesaf.2022.103706 View at publisher