On the Role of Radiation in Low Density Silicon Carbide Foams

2012 ◽  
Author(s):  
Charles C. Tseng ◽  
Ruth L. Sikorski ◽  
R. Viskanta ◽  
Ming Y. Chen
Keyword(s):  
Heat Transfer ◽  
Silicon Carbide ◽  
High Temperature ◽  
Thermal Radiation ◽  
Thermal Protection ◽  
Mie Scattering ◽  
Radiative Properties ◽  
Void Space ◽  
Insulation Systems ◽  
Foam Properties

There are a variety of foams that can be used in thermal protection and/or thermal insulation systems. At high temperature (> 1000 K) thermal radiation may be important or dominate heat transfer in a foam; however, studies based on more detailed thermal radiation analysis are limited. In this paper foams are considered to be semitransparent, because radiation can penetrate through the pore (or void) space and/or foam skeleton (ligament), depending on the materials from which the foams are made. Of particular interest of this study is to understand how the properties of foam material such as its density, mean cell size, etc. affect the radiative transfer through silicon carbide (SiC) foams. In the paper, the dimensionless strut diameter is considered an important parameter of foams, and the radiative properties of the foams are analyzed by Mie scattering theory. The attenuation/extinction behavior of SiC foams can be considered as a function of the dimensionless strut diameter of the foam. The results reveal that the foam properties can significantly reduce radiative heat transfer through the high temperature foam used for the thermal protection.

Effect of Radiation on Heat Transfer in Open-Cell Foams at High Temperature

2011 ◽  
Author(s):  
Charles C. Tseng ◽  
Ruth L. Sikorski ◽  
R. Viskanta ◽  
Ming Y. Chen
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Thermal Radiation ◽  
Thermal Protection ◽  
Radiant Energy ◽  
Radiation Absorption ◽  
Solid Matrix ◽  
Void Space ◽  
Insulation Systems ◽  
Physical And Mathematical Models

There are a variety of foams that can be used in thermal protection and/or thermal insulation systems. At high temperature (> 1000 K) thermal radiation may be important or dominate heat transfer in the foam; however, studies based on more detailed thermal radiation analysis are limited. In this paper foams are considered to be semitransparent, because radiation can penetrate through the pore (or void) space and/or foam skeleton (solid matrix), depending on the materials from which the foams are made. Of particular interest of this study is to understand how the properties such as foam material its density, porosity, etc. affect thermal and radiant energy transfer. Physical and mathematical models are developed to account for conduction and radiation (absorption, emission and scattering) in the porous material. The spectral extinction coefficients of SiC foams are measured experimentally in the laboratory at room temperature, and the radiative transfer equation is solved using the spherical harmonics P1 and the Rosseland diffusion approximations. Parametric calculations have been carried out, and the results are reported in the paper for a range of parameters characterizing heat transfer in SiC foams of different porosities to identify desirable conditions for effectively reducing heat transfer in potential thermal protection concepts.

scholarly journals A Parametrical Study on Convective Heat Transfer between High-Temperature Gas and Regenerative Cooling Panel

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1784
Author(s):  
Jiangyu Hu ◽  
Ning Wang ◽  
Jin Zhou ◽  
Yu Pan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Thermal Protection ◽  
Flow Direction ◽  
Heated Surface ◽  
Heat Transfer Process ◽  
Cocurrent Flow ◽  
Regenerative Cooling ◽  
High Temperature Gas

Thermal protection is still one of the key challenges for successful scramjet operations. In this study, the three-dimensional coupled heat transfer between high-temperature gas and regenerative cooling panel with kerosene of supercritical pressure flowing in the cooling channels was numerically investigated to reveal the fundamental characteristics of regenerative cooling as well as its influencing factors. The SST k-ω turbulence model with low-Reynolds-number correction provided by the pressure-based solver of Fluent 19.2 is adopted for simulation. It was found that the heat flux of the gas heated surface is in the order of 106 W/m2, and it declines along the flow direction of gas due to the development of boundary layer. Compared with cocurrent flow, the temperature peak of the gas heated surface in counter flow is much higher. The temperature and heat flux of the gas heated surface both rises with the static pressure and total temperature of gas. The heat flux of the gas heated surface increases with the mass flow rate of kerosene, and it hardly changes with the pressure of kerosene. Results herein could help to understand the real heat transfer process of regenerative cooling and guide the design of thermal protection systems.

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.

Numerical Simulation of Heat Transfer Characteristics for Two Metallic TPS Structures

2010 ◽  
Vol 156-157 ◽  
pp. 1568-1573
Author(s):  
Hai Yong Liu ◽  
Hong Fu Qiang
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Heat Conductivity ◽  
Radiation Effect ◽  
Thermal Protection ◽  
Heating Temperature ◽  
Three Dimensional ◽  
Metallic Layer ◽  
Internal Cooling ◽  
Thermal Radiation Effect

Two structures of metallic thermal protection system(TPS) for hypersonic vehicle were presented. One model was a multi-layer construction and the other has cavities in the metallic layer. Numerical simulations were conducted on the three-dimensional TPS models using CFD software of Gambit and Fluent. Two heating temperatures of 1073K and 773K with constant temperature and isothermal boundary conditions were considered. Heat transfer was treated as single conductivity and thermal radiation effect was not involved. The results of simulation investigation showed that: The metallic layer had poor capability to restrict the heat conductivity. Heat was easier to transfer across the bracket into the internal part of the TPS. The ability of cavities in metallic layer to resist heat conductivity was limited. The temperature-heating time variation pattern was similar for different external heating temperature. Internal cooling was important for the TPS. The thermal radiation effect on the TPS would be focused in further research.

Apparent Emissivity of Combustion Soot Aggregate Coating at High Temperature

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Tai Ran Fu ◽  
Ji Bin Tian ◽  
Hua Sheng Wang
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Room Temperature ◽  
Spectral Emissivity ◽  
Radiative Properties ◽  
Nickel Substrate ◽  
Soot Aggregate ◽  
Different Temperatures ◽  
Few Data ◽  
Total Hemispherical Emissivity

Soot aggregates frequently occur during combustion or pyrolysis of fuels. The radiative properties of soot aggregates at high temperature are important for understanding soot characteristics and evaluating heat transfer in combustion systems. However, few data for soot radiative properties at high temperature were available. This work experimentally investigated the apparent emissivity of the soot aggregate coating at high temperature using spectral and total hemispherical measurements. The soot aggregate coatings were formed on nickel substrates by a paraffin flame. The surface and inner morphology of the coatings were characterized by scanning electron microscope (SEM). The thickness of the coating was 30.16 μm so the contribution of the smooth nickel substrate to the apparent radiation from the coating could be neglected. The total hemispherical emissivity of the coating on the nickel substrate was measured using the steady-state calorimetric method at different temperatures. The spectral directional emissivity of the coating was measured for the wavelength of 0.38–16.0 μm at the room temperature. The measurements show that the total hemispherical emissivity decreases from 0.895 to 0.746 as the temperature increases from 438 K to 1052 K. The total hemispherical emissivity of the coating deposited on the nickel substrate is much larger than those of the nickel substrate and a nickel oxidization film. The measured spectral emissivity of the coating at the room temperature was used to theoretically calculate the total hemispherical emissivity at different temperatures by integration with respect to wavelength. The measured and calculated total hemispherical emissivities were similar, but their changes relative to temperature were completely opposite. This difference is due to the fact that the spectral emissivity of the coating is a function of temperature. The present results provide useful reference data for analyzing radiative heat transfer at high temperature of soot aggregates in combustion processes.

Effect of Foam Properties on Heat Transfer in High Temperature Open-Cell Foam Inserts

2012 ◽  
Vol 95 (6) ◽  
pp. 2015-2021 ◽  
Author(s):  
Charles C. Tseng ◽  
Ruth L. Sikorski ◽  
Raymond Viskanta ◽  
Ming Y. Chen
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Open Cell ◽  
Open Cell Foam ◽  
Foam Properties ◽  
Cell Foam

scholarly journals Radiation Heat Transfer in SOFC Electrolytes

2005 ◽  
Author(s):  
K. J. Daun ◽  
S. B. Beale ◽  
F. Liu ◽  
G. J. Smallwood
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Thermal Radiation ◽  
Radiation Heat Transfer ◽  
Radiative Properties ◽  
Radiation Heat ◽  
Conduction Model ◽  
D Model ◽  
Sofc Electrolytes

Due to their high operating temperature, there has been speculation that thermal radiation may play an important role in the overall heat transfer within the electrode and electrolyte layers of solid oxide fuel cells (SOFCs). This paper presents a detailed characterization of the thermophysical and radiative properties of the composite materials, which are then used to define a simple 2-D model incorporating the heat transfer characteristics of the electrode and electrolyte layers of a typical planar SOFC. Subsequently, the importance of thermal radiation is assessed by comparing the temperature field obtained using a conduction model with fields obtained using coupled conduction/radiation models. Contrary to some published literature, these results show that radiation heat transfer has a negligible effect on the temperature field within these components, and does not need to be accommodated in comprehensive thermal models of planar SOFCs.

Innovative High-Temperature Aircraft Engine Fuel Nozzle Design

1993 ◽  
Vol 115 (3) ◽  
pp. 439-446 ◽  
Author(s):  
R. W. Stickles ◽  
W. J. Dodds ◽  
T. R. Koblish ◽  
J. Sager ◽  
S. Clouser
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Surface Finish ◽  
Thermal Protection ◽  
Aircraft Engine ◽  
Engine Fuel ◽  
Sample Tube ◽  
Current Production ◽  
Fuel Nozzle ◽  
A Current

The objective of the Innovative High-Temperature Aircraft Engine Fuel Nozzle Program was to design and evaluate a nozzle capable of operating at a combustor inlet air temperature of 1600°F (1144 K) and a fuel temperature of 350°F (450 K). The nozzle was designed to meet the same performance requirements and fit within the size envelope of a current production F404 dual orifice fuel nozzle. The design approach was to use improved thermal protection and fuel passage geometry in combination with fuel passage surface treatment to minimize coking at these extreme fuel and air temperatures. Heat transfer models of several fuel injector concepts were used to optimize the thermal protection, while a series of sample tube coking tests were run to evaluate the effect of surface finish, coatings, and tube material on the coking rate. Based on heat transfer analysis, additional air gaps, reduced fuel passage flow area, and ceramic tip components reduced local fuel wetted wall temperatures by more than 200°F (110 K) when compared to a current production F404 fuel nozzle. Sample tube coking test results showed the importance of surface finish on the fuel coking rate. Therefore, a 1 μin. (0.025 μm) roughness was specified for all fuel passage surfaces. A novel flow divider valve in the tip was also employed to reduce weight, allow room for additional thermal protection, and provide back pressure to reduce the risk of fuel vaporization. Phase II of this program will evaluate the fuel nozzle with a series of contaminated fuel and coking tests.

Thermal Assessment of a Latent Heat Energy Storage Module Using a High Temperature Phase Change Material With Enhanced Radiative Properties

2014 ◽  
Author(s):  
Antonio Ramos Archibold ◽  
Abhinav Bhardwaj ◽  
Muhammad M. Rahman ◽  
D. Yogi Goswami ◽  
Elias L. Stefanakos
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Natural Convection ◽  
Phase Change ◽  
Temperature Response ◽  
High Temperature Phase ◽  
Radiative Properties ◽  
Temperature Phase ◽  
Measured Temperature ◽  
Numerical Predictions

This paper presents a comprehensive analysis of the heat transfer during the melting process of a high temperature (> 800°C) PCM encapsulated in a vertical cylindrical container. The energy contributions from radiation, natural convection and conduction have been included in the mathematical model in order to capture most of the physics that describe and characterize the problem and quantify the role that each mechanism plays during the phase change process. Numerical predictions based on the finite volume method has been obtained by solving the mass, momentum and energy conservation principles along with the enthalpy porosity method to track the liquid/solid interface. Experiments were conducted to obtain the temperature response of the TES-cell during the sensible heating and phase change regions of the PCM. Continuous temperature measurements of porcelain crucibles filled with ACS grade NaCl were recorded. The temperature readings were recorded at the center of the sample and at the wall of the crucible as the samples were heated in a furnace over a temperature range of 700 °C to 850 °C. The numerical predictions have been validated by the experimental results and the effect of the controlling parameters of the system on the melt fraction rate, total and radiative heat transfer rates at the inner surface of the cell have been evaluated. Results showed that the natural convection is the dominant heat transfer mechanism. In all the experimental study cases, the measured temperature response captures the PCM melting trends with acceptable repeatability. The uncertainty analysis of the experiment yielded an approximate error of ±5.81°C.

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