Absorver tube model for a PTC
 

Hello everyone

Am working in my tesis project and i have to simulate a two-phase flow in an absorver tube of a parabolic solar collector. Am using FLUENT 6.3, but i have problems with the radiation models. Am doing in the first case a monofasic problem, in a 2D axisimetric tube using only a simple mesh. I don't know if somebody has worked with a simillar problem using FLUENT, but i don't know very well how to use the radiation conditions.
If somedoby please can help me i will be very thankfull