[amirokhovat]

Hi guys,

I'm modeling an evacuated solar collector that have two Concentric tube. outer tube is glass tube and inner tube has solar absorber to absorb solar irradiation. Between two tube we have vacuum and provide an isolation region. sun irradiation hit to outer glass tube and Sunlight passes through the glass tube and vacuum region, hit to absorber. fluid in the inner tube is water. because of thermosiphon Phenomenon, heat water go to a tank.
I want to model this system with fluent. I use DO radiation model and solar ray tracing. what is the value of absorption and scattering coef. and refractive index for absorber and glass?? How can I model vacuum region? Is density of vacuum very low value (i.e. 1e-10)??