Control of Net Radiative Heat Transfer With a Variable-Emissivity Accordion Tessellation

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Rydge B. Mulford ◽  
Vivek H. Dwivedi ◽  
Matthew R. Jones ◽  
Brian D. Iverson
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Analytical Model ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Apparent Temperature ◽  
The Impact ◽  
Specular Surfaces ◽  
Cavity Effect

Origami tessellations have been proposed as a mechanism for control of radiative heat transfer through the use of the cavity effect. This work explores the impact of a changing projected surface area and varying apparent radiative properties on the net radiative heat transfer of an accordion fold comprised of V-grooves. The net radiative heat transfer of an accordion tessellation is obtained by a thermal energy balance at the cavity openings with radiative properties of the cavities given as a function of various cavity parameters. Results of the analytical model are experimentally confirmed. An accordion tessellation, constructed of stainless-steel shim stock, is positioned to achieve a specified fold angle and placed in a vacuum environment while heated by Joule heating. A thermal camera records the apparent temperature of the cavity openings for various fold angles. Results are compared to apparent temperatures predicted with the analytical model. Analytically and experimentally obtained temperatures agree within 5% and all measurements fall within experimental uncertainty. For diffusely irradiated surfaces, the decrease in projected surface area dominates, causing a continuous decrease in net radiative heat transfer for a collapsing accordion fold. Highly reflective specular surfaces exposed to diffuse irradiation experience large turn-down ratios (7.5× reduction in heat transfer) in the small angle ranges. Specular surfaces exposed to collimated irradiation achieve a turn down ratio of 3.35 between V-groove angles of 120 deg and 150 deg. The approach outlined here may be extended to modeling the net radiative heat transfer for other origami tessellations.

Modelling Radiative Heat Transfer in Oxycoal Combustion

2009 ◽  
Author(s):  
Rachael Porter ◽  
Mohamed Pourkashanian ◽  
Alan Williams ◽  
David Smith
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Radiative Heat Transfer ◽  
Flue Gas ◽  
Fossil Fuels ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Pure Oxygen ◽  
Distribution Method ◽  
The Impact

The reduction of greenhouse gas emissions is essential to mitigate the impact of energy production from fossil fuels on the environment. Oxyfuel technology is a process developed to reduce emissions from power stations by removing nitrogen from air and burning the fossil fuels in a stream of pure oxygen. The remaining oxidiser is composed of recycled flue gas from the furnace to reduce temperatures. The product of this system is a flue gas with very high carbon dioxide concentration enabling more efficient capture and storage. Accurate modelling of oxyfuel is essential to gain better understanding of the combustion fundamentals and obtain accurate predictions of properties within the furnace that cannot be measured. Heat transfer to the furnace walls will be affected due to the different composition of the gases in the furnace. Carbon dioxide has higher heat capacity than nitrogen. Water vapour and carbon dioxide also exhibit absorption spectra of radiation in the infra-red region of the spectrum relating to wavelengths observed in combustion. Accurate CFD modelling of radiative heat transfer in oxyfuel combustion will require improvements to the radiative properties model to account for the spectral nature of radiation. In addition the impact of the solid fuel particles, soot and ash are considered. Several different radiative properties models have been tested to assess the impact on the predicted radiation and temperatures under air and oxy firing conditions. The results for radiation transferred to the walls are highly dependent upon the model chosen and the need for an accurate radiative properties model for oxyfuel firing, such as the full-spectrum k-distribution method is demonstrated.

scholarly journals Assessing the Role of Particles in Radiative Heat Transfer during Oxy-Combustion of Coal and Biomass Blends

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Gautham Krishnamoorthy ◽  
Caitlyn Wolf
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Test Facility ◽  
Biomass Combustion ◽  
Radiative Fluxes ◽  
Scattering Phase ◽  
Scattering Phase Function ◽  
Fuel Fragmentation

This study assesses the required fidelities in modeling particle radiative properties and particle size distributions (PSDs) of combusting particles in Computational Fluid Dynamics (CFD) investigations of radiative heat transfer during oxy-combustion of coal and biomass blends. Simulations of air and oxy-combustion of coal/biomass blends in a 0.5 MW combustion test facility were carried out and compared against recent measurements of incident radiative fluxes. The prediction variations to the combusting particle radiative properties, particle swelling during devolatilization, scattering phase function, biomass devolatilization models, and the resolution (diameter intervals) employed in the fuel PSD were assessed. While the wall incident radiative flux predictions compared reasonably well with the experimental measurements, accounting for the variations in the fuel, char and ash radiative properties were deemed to be important as they strongly influenced the incident radiative fluxes and the temperature predictions in these strongly radiating flames. In addition, particle swelling and the diameter intervals also influenced the incident radiative fluxes primarily by impacting the particle extinction coefficients. This study highlights the necessity for careful selection of particle radiative property, and diameter interval parameters and the need for fuel fragmentation models to adequately predict the fly ash PSD in CFD simulations of coal/biomass combustion.

Spectral Radiative Heat Transfer Analysis of the Planar SOFC

2004 ◽  
Author(s):  
David L. Damm ◽  
Andrei G. Fedorov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Solid Oxide ◽  
Radiative Properties ◽  
Radiative Heat Flux ◽  
Oxide Fuel

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict the temperature fields within the stack, especially near the interfaces. Because of elevated operating temperatures (of the order of 1000 K or even higher), radiation heat transfer could become a dominant mode of heat transfer in the SOFCs. In this study, we extend our recent work on radiative effects in solid oxide fuel cells (Journal of Power Sources, Vol. 124, No. 2, pp. 453–458) by accounting for the spectral dependence of the radiative properties of the electrolyte material. The measurements of spectral radiative properties of the polycrystalline yttria-stabilized zirconia (YSZ) electrolyte we performed indicate that an optically thin approximation can be used for treatment of radiative heat transfer. To this end, the Schuster-Schwartzchild two-flux approximation is used to solve the radiative transfer equation (RTE) for the spectral radiative heat flux, which is then integrated over the entire spectrum using an N-band approximation to obtain the total heat flux due to thermal radiation. The divergence of the total radiative heat flux is then incorporated as a heat sink into a 3-D thermo-fluid model of a SOFC through the user-defined function utility in the commercial FLUENT CFD software. The results of sample calculations are reported and compared against the baseline cases when no radiation effects are included and when the spectrally gray approximation is used for treatment of radiative heat transfer.

Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames

2020 ◽  
Author(s):  
Kevin Torres Monclard ◽  
Olivier Gicquel ◽  
Ronan Vicquelin
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Radiative Properties ◽  
Jet Flame ◽  
Soot Particles

Abstract The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results. A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates. The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.

Spectral Radiative Heat Transfer Analysis of the Planar SOFC

2005 ◽  
Vol 2 (4) ◽  
pp. 258-262 ◽  
Author(s):  
David L. Damm ◽  
Andrei G. Fedorov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Solid Oxide ◽  
Radiative Properties ◽  
Radiative Heat Flux ◽  
Oxide Fuel

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict the temperature fields within the stack, especially near the interfaces. Because of elevated operating temperatures (of the order of 1000K or even higher), radiation heat transfer could become a dominant mode of heat transfer in the SOFCs. In this study, we extend our recent work on radiative effects in solid oxide fuel cells [J. Power Sources, 124, No. 2, pp. 453–458] by accounting for the spectral dependence of the radiative properties of the electrolyte material. The measurements of spectral radiative properties of the polycrystalline yttria-stabilized zirconia electrolyte we performed indicate that an optically thin approximation can be used for treatment of radiative heat transfer. To this end, the Schuster–Schwartzchild two-flux approximation is used to solve the radiative transfer equation for the spectral radiative heat flux, which is then integrated over the entire spectrum using an N-band approximation to obtain the total heat flux due to thermal radiation. The divergence of the total radiative heat flux is then incorporated as a heat sink into a three-dimensional thermo-fluid model of a SOFC through the user-defined function utility in the commercial FLUENT computational fluid dynamics software. The results of sample calculations are reported and compared against the base line cases when no radiation effects are included and when the spectrally gray approximation is used for treatment of radiative heat transfer.

SLMB Modeling of the Full Spectrum Cumulative k-Distribution of H2O

2009 ◽  
Author(s):  
Fre´de´ric Andre´ ◽  
Rodolphe Vaillon
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Comprehensive Description ◽  
Full Spectrum ◽  
Reliable Technique ◽  
Gaseous Media ◽  
Energy Exchanges ◽  
Atmospheric Heat

Radiative heat transfer is significant in many applications involving energy exchanges in gaseous media, such as combustion in engines or furnaces, atmospheric heat balances,.. The Line-By-Line (LBL) approach is the most reliable technique to determine the radiative properties of gases but is rarely used in radiative transfer simulations due to the associated prohibitive computational requirements. Approximate models are favored for such calculations. A comprehensive description of these existing methodologies can be found in Refs. [1, 2].

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