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Defining Vacuum region in Parabolic Trough Collector.

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Old   November 3, 2019, 05:29
Exclamation Defining Vacuum region in Parabolic Trough Collector.
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I want to define vacuum region in my space between absorber tube and glass cover for my Parabolic Trough Collector. In cell zone conditions, I've tried to set my required vacuum pressure through operating conditions window, but after this, it automatically sets this pressure to every other zone, which I don't want. I want vacuum in one region only in order to study conductive and radiative heat transfer in vacuum region. Kindly help.

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Old   November 4, 2019, 16:56
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You cannot define a vacuum region in Fluent. Fluent requires that there be domain (fluid or solid) between two surfaces for them to exchange heat.

You can work around this issue by meshing a fluid domain between the two surfaces you want to exchange heat, and then set the thermal conductivity of the fluid medium to a very low number and fix its velocities such that it is quiescent (remove effects of natural circulation).


Setup the radiation problem (eg S2S, DO) and compare the fluxes due to radiation to the total heat flux through the surface. If the "fluid" region is still and a low enough thermal conductivity, this fraction should be close to 1.
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Old   November 6, 2019, 10:22
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Quote:
Originally Posted by jbo214 View Post
You cannot define a vacuum region in Fluent. Fluent requires that there be domain (fluid or solid) between two surfaces for them to exchange heat.

You can work around this issue by meshing a fluid domain between the two surfaces you want to exchange heat, and then set the thermal conductivity of the fluid medium to a very low number and fix its velocities such that it is quiescent (remove effects of natural circulation).


Setup the radiation problem (eg S2S, DO) and compare the fluxes due to radiation to the total heat flux through the surface. If the "fluid" region is still and a low enough thermal conductivity, this fraction should be close to 1.
I will definitely give it a try. Thanks for the reply.
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Old   November 8, 2019, 05:39
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Quote:
Originally Posted by jbo214 View Post
You cannot define a vacuum region in Fluent. Fluent requires that there be domain (fluid or solid) between two surfaces for them to exchange heat.

You can work around this issue by meshing a fluid domain between the two surfaces you want to exchange heat, and then set the thermal conductivity of the fluid medium to a very low number and fix its velocities such that it is quiescent (remove effects of natural circulation).


Setup the radiation problem (eg S2S, DO) and compare the fluxes due to radiation to the total heat flux through the surface. If the "fluid" region is still and a low enough thermal conductivity, this fraction should be close to 1.
sir I have a question. I have designed an absorber tube of specific thickness and a glass cover of specific thickness with vacuum in-between glass and absorber while fluid flows inside absorber tube. I apply constant heat flux on absorber outer wall and absorber outerwall shadow both, I can see conduction effects of flux in the vacuum as it should be (right now normal still air is used) but heat is not transferred inside the fluid flow I don't know why.

Remember, if I put absorber outer wall shadow to zero heat flux, while applying constant flux to absorber outer wall, I the conduction in vacuum (air for now) just vanishes.
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Old   November 12, 2019, 12:46
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Quote:
Originally Posted by usamaa908 View Post
sir I have a question. I have designed an absorber tube of specific thickness and a glass cover of specific thickness with vacuum in-between glass and absorber while fluid flows inside absorber tube. I apply constant heat flux on absorber outer wall and absorber outerwall shadow both, I can see conduction effects of flux in the vacuum as it should be (right now normal still air is used) but heat is not transferred inside the fluid flow I don't know why.

Remember, if I put absorber outer wall shadow to zero heat flux, while applying constant flux to absorber outer wall, I the conduction in vacuum (air for now) just vanishes.
Do you have any pictures to better show what you are describing?
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Old   November 12, 2019, 13:43
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Do you have any pictures to better show what you are describing?
https://ibb.co/1rtvgFC
https://ibb.co/PMVF3fR
https://ibb.co/rHcjdKF
https://ibb.co/64dYRLv

These are the images describing my fluid flow region (annular), absorber tube, vacuum region and glass cover in sequence. I know how to set up the vacuum region (using low conductivity for air), I just need to know how can I simulate the below mentioned case.

"The flux should be applied on absorber tube outer wall, which would result in gain of fluid temperature inside me fluid domain. Also I want to simulate the heat transfer through absorber outer wall and vacuum region through conduction (I know it would be very little), the radiation heat transfer between absorber outer wall and glass inner wall and then finally radiation + convection heat transfer through glass outer wall to ambient (for which I have to use Mixed thermal B.C)"
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Old   November 12, 2019, 14:19
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Can you attach the photos directly to your reply? The hosting site is blocked for me.
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Old   November 13, 2019, 06:44
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Can you attach the photos directly to your reply? The hosting site is blocked for me.






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Old   November 13, 2019, 06:49
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Can you attach the photos directly to your reply? The hosting site is blocked for me.
Im unable to upload photos here. Can you name any image hosting site which is accessible by you ?
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