scholarly journals New H 2 O weighted sum of gray gases model for natural convection flows within large cavities

2021 ◽  
Vol 2116 (1) ◽  
pp. 012064
Author(s):  
Xiongguo Liu ◽  
Stephan Kelm ◽  
Chungen Yin ◽  
Hans-Josef Allelein
Keyword(s):  
Thermal Radiation ◽  
Large Scale ◽  
Radiation Heat Transfer ◽  
Weighted Sum ◽  
Radiation Heat ◽  
Severe Accidents ◽  
Nuclear Containment ◽  
Buoyancy Driven Flows ◽  
Benchmark Solutions ◽  
Wsgg Model

Abstract Radiation heat transfer plays a significant role in buoyancy driven flows for large scale facilities. In the analysis of nuclear containment safety during severe accidents, it has been found that the thermal radiation particularly affects the temperature distribution and containment pressurization due to the humidity environment. In order to model thermal radiation, one of the main challenges is the description of nongray gas property for the steam-air mixtures. The weighted sum of gray gases model (WSGG) is a reasonable method in engineering applications because of its computational efficiency. There are many WSGG models available for combustion applications, but none of them is dedicated for low temperature applications. Furthermore, most of the existing WSGG models only provide the fixed partial pressure ratios (e.g., p H 2 O = 2p CO 2 for methane). To overcome this limitation, a tailored WSGG model is derived by the Line-by-Line model for a gas mixture composed of arbitrary concentrations of H 2 O. This tailored WSGG model is valid for the pressure path length ranging from 0.0001 to 10 atm · m, and for the temperature from 300 to 1200 K. The WSGG correlations are verified against the Line-by-Line benchmark solutions with isothermal/non-isothermal temperatures and homogeneous/non-homogeneous concentrations. The results demonstrate the ability and efficiency of the new tailored WSGG formulation.

Analysis to Reduce Thermal Stress in Oxide Single Crystal During Czochralski Growth

2004 ◽  
Author(s):  
Shigeki Hirasawa ◽  
Hiroyuki Ishibashi ◽  
Kazuhisa Kurashige ◽  
Akihiro Gunji
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Temperature Distribution ◽  
Thermal Radiation ◽  
Single Crystal ◽  
Radiation Heat Transfer ◽  
Heat Transfer Analysis ◽  
Czochralski Growth ◽  
Radiation Heat ◽  
Radial Temperature

Temperature distributions and thermal stress distributions in a semi-transparent GSO crystal during Czochralski (CZ) single crystal growth were numerically investigated by thermal radiation heat transfer analysis and anisotropy stress analysis. As GSO has special optical properties, such as semi-transparency at a wavelength shorter than 4.5 μm, thermal radiation heat transfer was calculated by the Monte Carlo method. These calculations showed that thermal stress is caused by the radial temperature distribution on the outside of the upper part of the crystal. To reduce this temperature distribution, the following three manufacturing conditions were found to be effective: use a sharp taper angle of the crystal, install a lid to the top of the insulator, and install a ring around the tapered part of the crystal.

Thermal Radiation Through a Nano Aperture

2006 ◽  
Author(s):  
Ravi Prasher
Keyword(s):  
Heat Flux ◽  
Thermal Radiation ◽  
Radiation Heat Transfer ◽  
Far Field ◽  
Boltzmann Constant ◽  
Aperture Size ◽  
Radiation Heat ◽  
Dominant Wavelength ◽  
Potential Applications ◽  
Diffraction Effects

Far-field thermal radiation through a nano aperture is calculated in this paper. Results show that for aperture size ≪ dominant wavelength of thermally excited photons, heat flux deviates significantly from the well known Planck blackbody expression of σT4, where σ is the Stefan-Boltzmann constant and T is the temperature. The heat flux through a nano-hole is proportional to T8 and a4, where a is the radius of the hole. Heat flux is proportional to T8 and a4 due to diffraction effects. Potential applications of radiation heat transfer through nano apertures are also discussed in the paper.

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