Learning Forum

[617283443]

Dear experts!
I want to simulate a hollow cylinder internal and external flow field and temperature field based on fluent, the temperature of the top surface of the cylinder is 500℃, the air temperature outside the cylinder is 20℃, the diameter of the cylinder is 500mm, the height is 500mm, the bottom of the cylinder is a quartz glass, the thickness is 25mm. the simulation process should consider the natural convection and radiation heat transfer.

In the modeling process, quartz glass is a semi-transparent medium, so I use DO radiative heat transfer model, I know that the transmittance of quartz glass plate is 0.9679, the reflectance is 0.0296 and the absorbance is 0.0025. How do I set the Absorption Coefficient, Scattering Coefficient, Refractive Index in the material properties of quartz glass? and Diffuse Fraction in the quartz glass boundary conditions?

 

[Mark O]

You have to look those properties up for your material. The transmittance is not very meaninful since it depends on the thickness. If you know the transmittance of a unidirectional beam through some thickness L then you can get the absorption coefficient a [m^-1] from the intensity as a fuction of penetration distance I(x) = I(0)* exp(-a*x) and sub x = L. 

[617283443]

Thank you very much for your reply!I have found in the literature that the transmittance of quartz glass plate is 0.9679, the reflectance is 0.0296, and the absorbance is 0.0025. These parameters are all dimensionless, whereas in Fluent, the units for the absorption coefficient and scattering coefficient are both 1/m. How should I convert the data from the literature into input parameters for Fluent?

[Mark O]

You must be misreading the literature. Saying "the transmittance of quartz glass plate is 0.9679" is meaningless. It depends on how thick the plate is. The thicker the plate the less will be transmitted throught it and the more will be absorbed by it. Transmittance is an extensive property. It depends on how much material is present and so not an intrinsic property of the material. The absorption coefficeint is an intensive property. See  https://en.wikipedia.org/wiki/Attenuation_coefficient