This is my first comment in youtube(in almost 10 years that i've been here). while we get too busy with theoretical approaches and different methods of numerical approaches to PDE equations, The Lack of such Practical information if very much experienced and of course very very much useful. very accurate and Cohesive lecture, would have definitely donated if my country wasn't under baking sanctions. but all i could do a huge appreciation(feel sorry about that). please keep the good work up sir.
Thanks again for a great lection! - Turns out I actually missed a few details about shells. 1) If wall distance (yp) is reduced according to the shell thickness - then what if shell thickness is higher than first prism layer thickness? 2) Do I get it right that shells (at least in Fluent/CFX) can be used in transient simulations and they actualy "store" heat? At least that's how it looks like since energy equation for the shell contains ∂T/∂t. 3) I seem to miss the concept of "heat flux is the same": if boundary conditions are set to fixed Tw and Tf - than adding shell between increases thermal resistance and thus heat flux should be smaller, no?
Hi Sergey, in answer to your questions: 1) im not sure how CFD codes deal with this (as i havent actually seen the source code ... 😅) but i assume they have something clever ... 2) yes, shells do have transient capacity and store heat. This is why you need to specify the material density and cp for the shells as well as conductivity.
3) Yes but the distance between the wall and the centroid decreases as well, so the temperature gradient stays the same. Therefore the heat flux stays the same (unless you have shell conduction on and then the heat can move along the surface as well) I hope this helps!
@@fluidmechanics101 Concerning Point Nr 2: I did a practical test if Capacitance has any effect in walls with enabled shell conduction. My test setup is simple: I have two neighbouring buildings with a different kind of wall-setup: 1 Building with non-meshed walls with shell conduction enabled 1 Building with explicitly meshed walls (having the same thickness as the non-explicit walls) I ran a transient case with solar load over 24 hours. During the evening hours the Explicitly-meshed walls were still slowly cooling down, while the Shell-Conduction-walls are cooled off immediately (following the decreasing solar intensity in the evening of course). So my verdict with that experiment is that walls which are non-explicitly modelled do not have the ability to store heat - basically the Specific Heat value in the material properties is neglected. I've used ANSYS Fluent 2020 R2 - The Official ANSYS Fluent Support has confirmed the above results. I have the hope that in a future version capacitance for shell-conduction-walls is implemented 🤞
I tried the shell conduction option to simulate the heat transfer through the steel tube wall (and additional insulation) of a tube containing hot fluid. When comparing the results obtained using shell conduction, with the results obtained by fully modeling and meshing also the steel tube wall and insulation, they differ significantly. I think this is because the heat flux is assumed to be constant when using shell conduction (as you have pointed out on slide 6). However, for a lot of (most?) 3D geometries (tube, ball, rectangle with additional layers on all sides...) this is not correct, since the surface area towards the out (or inside) will change which should result in an inverse change of the heat flux. Am i getting something wrong here or is this really the case (which would be quite a bummer tbh)?
Yes you are correct. If you are modelling the thickness of the wall and the insulation which is probably quite thick, then the outer area is quite different to the inner area (this is why we have different equations for the thermal resistance of cylindrical and polar elements). The shell conduction equations are for planar heat conduction, so there is no surprise that you have a noticeable difference here. From personal experience I have always found: if you can mesh the solid and the insulation, then it is usually worth it!
Thank you for the brilliant video!!! I have a small doubt. For the example conjugate heat transfer case shown in the video, if we are going with shell conduction option then we will not be modelling the wall thickness. Now, the commercial code ANSYS FLUENT will treat the interface as a Fluid-Fluid interface. In that scenario giving shell conduction on one wall (Fluid) will automatically enable shell conduction on the other. So in this case how to define wall thickness value and how will the geometry change??
This is a question that you should probably ask ANSYS support as I don't reallyyyy know what is happening in their code 😄 the best I can do is make deductions from their manuals
Thanks a lot of, I have question about how treat copper tube solar collector with or without thikness, when thikness of the tube is 2 mm and inner diameter is 8 mm, if take it the tube without thikness, in the heat flux boundary condition in fluent setup apply thikness yes or no?
Hi,Adan, thanks for your vidio! here i have a small question. A thin wall with uniform temperature distributioin, we can only set single shell layer, because the heat flux only can transform along the normal direction of this wall, if this thin wall with ununiform temperature, how many shell layers i should to set?
Good question, you probably need to make a simple test case and try different numbers of layers. If the profile is quite complex then you may actually need to mesh the thickness and run a conjugate heat transfer analysis
Hi Rahul, radiation is solved inside the fluid volume and not in solid or shell elements, so unfortunately you cant solve radiation in the shell. Remember radiation is a surface phenomena! I hope this helps 😊
What if she'll conduction or thickness is applied between 2 solid domains. In which side the elements will be created, just like as u said for fluid solid domain, elements will be created towards fluid side....?? And thank you so much for the content Aiden. Though I'm finding difficult at some points, still they have been clearing most of my doubts.
I think you can apply something called a ‘contact resistance’, although i havent looked into this much myself. If anyone else had any thoughts, they would be much appreciated
Hi Aiden, As per ur explanation, if wall thickness is modelled into the fluid volume for shell conduction or thickness case, then effective internal dimensions will shrink (provided thickness is considerably more). Is it right....?
As far as I understood the shell elements do not grow away into the fluid, they grow away into the solid. But in your presentation you say the opposite. Do I mislead smt?
The cells are 'virtual' so they aren't grown in a physical sense and don't take up any space. You could consider them to grow in either direction, you just need to be careful with your mathematics. I have chosen to grow them outwards out of personal preference
I thought the same, and also that - what if we are reducing the fluid volume/cross section in using the shell conduction approach...! Then I found this comment, and it clarifies. xD
![[CFD] Heat Transfer Coefficient (htc) in ANSYS Fluent, OpenFOAM and CFX](http://i.ytimg.com/vi/PuTl98d0iZ0/mqdefault.jpg)
![[CFD] Heat Transfer Coefficient (htc) in ANSYS Fluent, OpenFOAM and CFX](/img/tr.png)
![[CFD] Hexcore Meshes for CFD](http://i.ytimg.com/vi/59xfM0ayFE0/mqdefault.jpg)
![[CFD] What are Thermal (Temperature) Wall Functions?](http://i.ytimg.com/vi/2bJ-5gaeSE0/mqdefault.jpg)
![[CFD] Turbulence Intensity for RANS](/img/n.gif)
The explanation is what i required for my Engineering thesis. Thank you
I didn't think people smart enough to understand this were allowed to speak on it. Much thanks, really helped on my capstone project.
Hands down the best video explanation related to the shell conduction in CFD.
This is my first comment in youtube(in almost 10 years that i've been here). while we get too busy with theoretical approaches and different methods of numerical approaches to PDE equations, The Lack of such Practical information if very much experienced and of course very very much useful. very accurate and Cohesive lecture, would have definitely donated if my country wasn't under baking sanctions. but all i could do a huge appreciation(feel sorry about that). please keep the good work up sir.
Thanks again for a great lection! - Turns out I actually missed a few details about shells.
1) If wall distance (yp) is reduced according to the shell thickness - then what if shell thickness is higher than first prism layer thickness?
2) Do I get it right that shells (at least in Fluent/CFX) can be used in transient simulations and they actualy "store" heat?
At least that's how it looks like since energy equation for the shell contains ∂T/∂t.
3) I seem to miss the concept of "heat flux is the same": if boundary conditions are set to fixed Tw and Tf - than adding shell between increases thermal resistance and thus heat flux should be smaller, no?
Hi Sergey, in answer to your questions:
1) im not sure how CFD codes deal with this (as i havent actually seen the source code ... 😅) but i assume they have something clever ...
2) yes, shells do have transient capacity and store heat. This is why you need to specify the material density and cp for the shells as well as conductivity.
3) Yes but the distance between the wall and the centroid decreases as well, so the temperature gradient stays the same. Therefore the heat flux stays the same (unless you have shell conduction on and then the heat can move along the surface as well)
I hope this helps!
@@fluidmechanics101 Got it, thanx a million :>
@@fluidmechanics101 Concerning Point Nr 2:
I did a practical test if Capacitance has any effect in walls with enabled shell conduction.
My test setup is simple:
I have two neighbouring buildings with a different kind of wall-setup:
1 Building with non-meshed walls with shell conduction enabled
1 Building with explicitly meshed walls (having the same thickness as the non-explicit walls)
I ran a transient case with solar load over 24 hours. During the evening hours the Explicitly-meshed walls were still slowly cooling down, while the Shell-Conduction-walls are cooled off immediately (following the decreasing solar intensity in the evening of course).
So my verdict with that experiment is that walls which are non-explicitly modelled do not have the ability to store heat - basically the Specific Heat value in the material properties is neglected.
I've used ANSYS Fluent 2020 R2 - The Official ANSYS Fluent Support has confirmed the above results.
I have the hope that in a future version capacitance for shell-conduction-walls is implemented 🤞
Ah yes, I really hope that ANSYS implement capacitance in their shell conduction model. It would be really useful!
you are the boss sir
I tried the shell conduction option to simulate the heat transfer through the steel tube wall (and additional insulation) of a tube containing hot fluid. When comparing the results obtained using shell conduction, with the results obtained by fully modeling and meshing also the steel tube wall and insulation, they differ significantly. I think this is because the heat flux is assumed to be constant when using shell conduction (as you have pointed out on slide 6). However, for a lot of (most?) 3D geometries (tube, ball, rectangle with additional layers on all sides...) this is not correct, since the surface area towards the out (or inside) will change which should result in an inverse change of the heat flux.
Am i getting something wrong here or is this really the case (which would be quite a bummer tbh)?
Yes you are correct. If you are modelling the thickness of the wall and the insulation which is probably quite thick, then the outer area is quite different to the inner area (this is why we have different equations for the thermal resistance of cylindrical and polar elements). The shell conduction equations are for planar heat conduction, so there is no surprise that you have a noticeable difference here. From personal experience I have always found: if you can mesh the solid and the insulation, then it is usually worth it!
@@fluidmechanics101 thank you !
Thank you for the brilliant video!!! I have a small doubt.
For the example conjugate heat transfer case shown in the video, if we are going with shell conduction option then we will not be modelling the wall thickness. Now, the commercial code ANSYS FLUENT will treat the interface as a Fluid-Fluid interface. In that scenario giving shell conduction on one wall (Fluid) will automatically enable shell conduction on the other. So in this case how to define wall thickness value and how will the geometry change??
This is a question that you should probably ask ANSYS support as I don't reallyyyy know what is happening in their code 😄 the best I can do is make deductions from their manuals
Thanks a lot of, I have question about how treat copper tube solar collector with or without thikness, when thikness of the tube is 2 mm and inner diameter is 8 mm, if take it the tube without thikness, in the heat flux boundary condition in fluent setup apply thikness yes or no?
Is it possible to ignore the thickness and put shell conduction in an interface solid_fluid ? Is there any condition to do that ?
Hmmm I'm not sure, maybe you could contact ANSYS support as this is quite specific to Fluent itself?
Hi,Adan, thanks for your vidio! here i have a small question. A thin wall with uniform temperature distributioin, we can only set single shell layer, because the heat flux only can transform along the normal direction of this wall, if this thin wall with ununiform temperature, how many shell layers i should to set?
Good question, you probably need to make a simple test case and try different numbers of layers. If the profile is quite complex then you may actually need to mesh the thickness and run a conjugate heat transfer analysis
Thanks a lot for very interesting and informative video, is it possible to solve radiation in shell?
Hi Rahul, radiation is solved inside the fluid volume and not in solid or shell elements, so unfortunately you cant solve radiation in the shell. Remember radiation is a surface phenomena! I hope this helps 😊
Can I use this as contact resistance between solids?
What if she'll conduction or thickness is applied between 2 solid domains. In which side the elements will be created, just like as u said for fluid solid domain, elements will be created towards fluid side....??
And thank you so much for the content Aiden. Though I'm finding difficult at some points, still they have been clearing most of my doubts.
I got this doubt, when u want to apply thermal resistance between the 2solids in contact. Can anyone give explanation to this....??
Thanks in advance.
I think you can apply something called a ‘contact resistance’, although i havent looked into this much myself. If anyone else had any thoughts, they would be much appreciated
Hi Aiden,
As per ur explanation, if wall thickness is modelled into the fluid volume for shell conduction or thickness case, then effective internal dimensions will shrink (provided thickness is considerably more). Is it right....?
As far as I understood the shell elements do not grow away into the fluid, they grow away into the solid. But in your presentation you say the opposite. Do I mislead smt?
The cells are 'virtual' so they aren't grown in a physical sense and don't take up any space. You could consider them to grow in either direction, you just need to be careful with your mathematics. I have chosen to grow them outwards out of personal preference
I thought the same, and also that - what if we are reducing the fluid volume/cross section in using the shell conduction approach...! Then I found this comment, and it clarifies. xD
Is shell conduction implemented in OpenFOAM?
Yes (in a similar way) in 'externalTemperature' boundary condition
👍thank you