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#### How can we simulate a vacuum region like a vacuum gap between two shells. ?

• Yahyaalkaisi
Subscriber

Hello,

I have evacuated tube solar collector . The evacuated tube consists of two tubes, one external and the other internal. The tubes are made of borosilicate. The first tube is transparent, while the second tube is covered with a solar absorbent material.

There is a space between the two tubes to avoid wasting the energy gained in the second tube.

How we will apply a mesh to the region between two tube that is a vacuum. how to model thermal radiation in ANSYS. if temperature at a surface is 500 degree celcius and the other surface is at 20 degree. there is a vacuum between two surfaces . how we will mesh the region between two boundaries

• Yahyaalkaisi
Subscriber
• peteroznewman
Subscriber
I would guess that there is no need for a mesh where there is a vacuum. There is nothing that needs calculating in the volume that is the vacuum.
• Yahyaalkaisi
Subscriber
The vacuum isolates the heat produced in the inner tube from the outer tube. The outer tube stays cool while the inner tube reaches 150┬░C.
In the results the temperature of the two tubes was equal so I asked. Is there any advice to make this vacuum?
• peteroznewman
Subscriber
If it wasn't a vacuum, but filled with air, then you would need to mesh the air so that it would conduct heat from the inner to the outer.
But since it's a vacuum, there is no conduction except at each end of the tube. The thermal radiation is what you are interested in.
• Yahyaalkaisi
Subscriber
The geometry is attached below
When I draw tubes, the space between tubes is always solid. I want to make it vacuum. How can I do this process?

• peteroznewman
Subscriber
In SpaceClaim, on the Design tab, use the Select button and click on the inner face of the tube, hold the Ctrl key down and click on the outer face of the tube. Keyboard Ctrl-C and then Ctrl-V to execute a Copy/Paste. Now you will have two surfaces. Delete the solid.
• Yahyaalkaisi
Subscriber
Hello
I made two surfaces as you advised me. When applying boundary conditions, the outer surface did not appear. Do you know why ?

• peteroznewman
Subscriber
Please use Windows Snipping Tool or the new Snip & Sketch to get screen images to paste into your replies. The cell phone jpg images take a long time to download because they have way too many pixels, most of which are wasted.
Do you have Structural solvers like Steady State Thermal analysis or only Fluent?
What version of ANSYS are you using?

• Yahyaalkaisi
Subscriber
The version of Ansys are 2019 3R

• Yahyaalkaisi
Subscriber
The solution only for fluid
The absorber material not appear in results.
The glass surface not appear in boundary conditions.
• peteroznewman
Subscriber
Open the geometry in DesignModeler. The last item in the Outline shows one Part. Right click on that Part and select Explode from the pop-up menu. Now you will have three parts and three bodies.
Select the Fluid and Absorber items in the outline, Right Click and select Form New Part from the pop-up menu.
Bring that into Meshing. You can mark the solid body as fluid, and the two surface bodies as solid.
See if bringing that into a fresh copy of Fluent gives you what you want.
Don't use the initial Fluent analysis, because it can be difficult to clean out the old things created from the initial geometry.
• Yahyaalkaisi
Subscriber
thank you
I am drawing both the glass and the absorbent material to a certain thickness and the idea worked.
I am a PhD student and I am trying to model my project. The project is a evacuated tube solar water heater.
Can you give me your email? Now I'm trying to connect the tank with the tube.
• peteroznewman
Subscriber
Glad to hear you have something working. You are better off posting here than sending me email because I check this site more frequently than my email and other people may help you. I am not a CFD expert.
• Yahyaalkaisi
Subscriber
thank you. I'm glad there are people like you who love to help others
• Rowland
Subscriber
and others, please is it compulsory I mesh the glass cover?, I'm trying to model using ICEM CFD, I had a previous geometry where I didn't include the glass cover, and the mesh in ICEM CFD was perfect. Thank You, In advance.
• ami
Subscriber
how you make the vacuum in your project
• ShewaZenergY
Subscriber
Can you send your work on my email, I want it as a reference tool for my thesis on Solar Thermal Baking System. and How can I make the Fluent to know the #vacuum in the evacuated tube glass
and one more thing, is it necessary to draw the V-shape trough to do the analysis in fluent ???
• ShewaZenergY
Subscriber
Its working principle is, the nanofluid enters in the U tube copper tube. This copper tube is inserted on the hole of the evacuated tube glass. The bottom part of this evacuated glass is get additional heat flux by the V-shape concentrator. then the fluid is heated to certain temperature. this temperature is used for cooking purpose. That is it!
• peteroznewman
Subscriber
Start a New Discussion that can focus on the specifics of your problem.
I suggest you draw a diagram of all the heat transfers in a typical cross-section of the system.
You need the V-shaped trough to have radiation reflected onto the glass tube.
The glass and copper tubes will transfer heat by conduction.
The copper tube in the vacuum of the glass tube will only get heat by radiation.
The fluid will get heat by convection from the copper tube.