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 August 13, 2012, 02:35 #2 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,266 Rep Power: 22 You got this correctly, just one thing: In your second case, if you want to model it without the glass tube and thus without a radiation model, the operating temperature is not the temperature of the glass tube. Consider the glass tube fully transparent (which you have to do if you do not model it explicitly), the temperature the tube "sees" for radiation is still the temperature of the environment, not the glass tube.

August 13, 2012, 19:27
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n7310889
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Quote:
 Originally Posted by flotus1 You got this correctly, just one thing: In your second case, if you want to model it without the glass tube and thus without a radiation model, the operating temperature is not the temperature of the glass tube. Consider the glass tube fully transparent (which you have to do if you do not model it explicitly), the temperature the tube "sees" for radiation is still the temperature of the environment, not the glass tube.
Hi Alex,
That means even if I wanna simulate the condition for evacuated glass tube, I don't actually need to include glass tube physically in my design model. What I need is, to assume the glass is so transparent that the radiation is exchanged between the environment and the metal tube surface with the temperature of the tube surface and the environment. But the operating pressure and density must be the values for those of evacuation (i.e both values are zero) so that I can calculate convection loss if I want for (though theoretically no advection).
Is this the concept, dear Alex?
Many many thanks for your response.
Regards
n7310889

 August 14, 2012, 02:17 #4 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,266 Rep Power: 22 I doubt that the solver will run with both operating pressure and density set to zero. If you want to neglect conductive and convective heat losses, I would not model the glass tube around the collector tube. Just set the boundary contition of the collector wall to radiation with the ambient temperature. The thing is that neither glass is fully transparent nor is there an absolute vacuum in the glass tube. It would be quite interesting to see by what extent these factors alter the result of the simulation. n7310889 likes this.

August 14, 2012, 02:36
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n7310889
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Quote:
 Originally Posted by flotus1 The thing is that neither glass is fully transparent nor is there an absolute vacuum in the glass tube. It would be quite interesting to see by what extent these factors alter the result of the simulation.
Thanks Alex,
Most probably the operating density and pressures are misunderstood by me as the properties of the environment, where a system is being modeled, as in case of evacuated tube it is vacuum. Most probably they are actually some reference properties of the working domain itself. Could you have any suggestion to model convection loss for the evacuated tube considering a minimul pressure and density of air for the evacuation?

n7310889

 September 26, 2015, 05:11 #6 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,285 Blog Entries: 6 Rep Power: 43 Q# 1: For evacuated tube case (including glass cover, vacuum etc) , which model is best: a. Solar model with ray tracing with S2S b. Solar model with do irradiation. Only difference I can see is that: for S2S model the medium inside the evacuated tube (glass thickness, air etc) will not participate in radiation. Does it mean now we will not be able to get heat transfer through glass thickness, air etc? Q# 2 : What will be the effect of assumption of gray radiation (S2S or Do irradiation) on solar load modeling?

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