[Gandin]

Hello. I want to do a 3-D simulation of a periodic cell of a printed circuit heat exchanger. The geometric model consists in a prismatic solid domain with two wavy channels (semicircular cross-section) for the circulation of a hot fluid (up) and a cold fluid (down), in counterflow. I have meshed the model in Gambit, with 3 final volume meshes (2 for the fluids and 1 for the solid), and periodic conditions in the up, down, right and left faces of the solid domain. I put velocity-inlet and pressure-outlet boundary conditions for both fluids, with inlet-outlet temperatures, and I also put as interfaces the fluid and solid faces which are in contact.

Then I exported the mesh to Ansys Fluent 12. The solid material is stainless steel and the hot and cold fluids are air.

Well, I created two "mesh interface", with the option coupled wall; one between the solid and the hot fluid interfaces and other between the solid and the cold fluid interfaces.

Once the case is solved, the fluid dynamics solution seems correct, but there is no thermal coupling between the domains. There is no heat transfer from the hot fluid to the solid and from the solid to the cold fluid.

I see that several boundary condition (walls) are created with the two "mesh interfaces". Two are, in example, wall-20 and wall-20-shadow, one for the hot fluid and the other for the solid, which show "coupled" selected in the thermal tab, when you edit them. The same occurs for the cold fluid and the solid interfaces. But other 4 different walls are also created, 2 for the solid and 1 for each fluid, which show "Heat flux = 0" in their thermal tabs. This appears very strange to me.

Can anybody help me?

Many thanks in advance.

[MetalSupremacist]

Unfortunately, I do not have a solution for you. I am incurring the same problem with my model - fluid dynamics have converged successfully but no heat transfer between fluid/solids.

As I see it, there are two possible problems. Either the mesh is not being created in a way that the mesh from the fluid domain lines up with the solid domain, or Fluent has not received sufficient information to "know" to solve for heat transfer between the domains.

I am not using Gambit, I am using the built in meshing tool from Ansys workbench.

Does anyone know a way to check that the mesh is consistent at the boundaries between a fluid domain and a solid domain?

Does anyone know if special boundary conditions must be specified for fluid/solid boundaries?

[jlefevre76]

I'm having the exact same problem, and I THINK I've heard that Fluent can't do transient conduction. Can anybody verify this?

[MetalSupremacist]

Gentlemen, I have discovered what our (my) problem is. You need to define in Fluent an interface between the solid and fluid regions.

-Create a surface in your meshing program that occupies the entire interface between the solid and fluid boundary.
-In Fluent, under boundary conditions, set the boundary type for the interface to "interface"
-Under the "mesh interfaces" you will need to create/edit to make a mesh interface

Now when you run the simulation, it should simulate convection between them. Let me know if you are still having problems.

[m2montazari]

hi,
you can do what justin does, but a simpler and faster solution is as follows:
make mesh in a meshing software and make three domains (2 for fluids and one for solid). set all interfaces between solid and fluid to wall. dont forget that you MUST have ONLY one face in each interface, not two faces. then the only face in each interface should be used by two volumes(one side is solid and one is fluid).
if you are correct upto this, after exporting mesh to fluent, you should see a -shadow boundary condition of type wall for each interface wall. it is ok. one has fluid as adjacent zone and one has solid as adjacent zone. by default these two walls are coupled in thermal conditions. so just specify zone materials, velocity and pressures ion boundaries and solve the problem.(dont forget about enabling heat equation at the first step after importing mesh in fluent.)
yours,
mohammad

[jlefevre76]

Yeah, I did it the way Mohammad suggested and that seems to be working for me. Now if I could just get my UDF to compile....... (I'll save that for another thread.)

[Gandin]

Thank you all!

[Behnam Ghadimi]

hi mohammad
i do what you said but it seems that fluent is not able to couple heat transfer between solid and fluid.
my project is about railway brake disk cooling.
I need your help.
my mail: behnam67gh@yahoo.com
thanks a lot
Behnam Ghadimi

[Sree]

Hi all,
I have a cylinder in which water flows. I could able to see the conduction for the cylinder but not the convection in to water.
1. Do i need to supply the convection rate?
2. How to maintain conjugate contact between the interface.

In meshing I could see contact between the two surfaces(solid and fluid), but that connection I cannot see in boundary conditions.

Can some one help me..
Thanks alot for reading

[Behnam Ghadimi]

Originally Posted by Sree

Hi all,
I have a cylinder in which water flows. I could able to see the conduction for the cylinder but not the convection in to water.
1. Do i need to supply the convection rate?
2. How to maintain conjugate contact between the interface.

In meshing I could see contact between the two surfaces(solid and fluid), but that connection I cannot see in boundary conditions.

Can some one help me..
Thanks alot for reading

Hi Sree
To maintain conjugate contact you should define the interface as wall in Gambit and mesh both (solid and fluid) zone. Note that you should have only one surface between domains and define it as a wall. when you are read mesh file in fluent, Fluent add another wall as shadow wall. if you see the shadow wall in fluent, the heat transfer between solid and fluid is coupled.
Good Luck

[Vidit Sharma]

Originally Posted by m2montazari

hi,
you can do what justin does, but a simpler and faster solution is as follows:
make mesh in a meshing software and make three domains (2 for fluids and one for solid). set all interfaces between solid and fluid to wall. dont forget that you MUST have ONLY one face in each interface, not two faces. then the only face in each interface should be used by two volumes(one side is solid and one is fluid).
if you are correct upto this, after exporting mesh to fluent, you should see a -shadow boundary condition of type wall for each interface wall. it is ok. one has fluid as adjacent zone and one has solid as adjacent zone. by default these two walls are coupled in thermal conditions. so just specify zone materials, velocity and pressures ion boundaries and solve the problem.(dont forget about enabling heat equation at the first step after importing mesh in fluent.)
yours,
mohammad

Hi,

My problem is similar but the only difference is that i have to apply heat flux on one side of the wall. That i have done and running but conduction in between the two sides of the wall is not happening.What should I do???

Thanking You

[tumble]

Hi all,
I have a sphere fluid flow in a channel.
I want to study conduction in the sphere
1) I create 2 zone ( 1 fluid zone and 2 for solid zone (sphere)).
2) I set all interfaces between solid and fluid to wall.
3) After exporting mesh to fluent, I see a -shadow boundary condition of type wall for each interface wall.
4) I enable heat equation. (knowing that the two wall are coupled)

But the problem after running simulation there no transfers conjugate between fluid and solid the temperature of solid remains stable (initial temperature).


Best Regards...

[john c]

Originally Posted by tumble

Hi all,
I have a sphere fluid flow in a channel.
I want to study conduction in the sphere
1) I create 2 zone ( 1 fluid zone and 2 for solid zone (sphere)).
2) I set all interfaces between solid and fluid to wall.
3) After exporting mesh to fluent, I see a -shadow boundary condition of type wall for each interface wall.
4) I enable heat equation. (knowing that the two wall are coupled)

But the problem after running simulation there no transfers conjugate between fluid and solid the temperature of solid remains stable (initial temperature).


Best Regards...

Tumble,

I am doing a similar problem, I think what you have to do is set the wall to an interface in Fluent, then create a "Mesh Interface" and this should solve your problem.

[ajjagdale]

how to define interface between fluid and solid region for shell and tube heat exchanger.

[Cube]

A really simple solution would be to create a body (in ICEM) anywhere within the fluid (or domain of interest). After this step I exported my mesh using FLUENT and I did not have any problems with shadow walls.

I hope this helps.

[Pacific]

Hi every body
Please see below links:
1. http://web.stanford.edu/class/me469b...s/physical.pdf
2. http://aerojet.engr.ucdavis.edu/flue...ug/node567.htm

[a_Sarlak]

hi every one i have same problem.
in my fluent show shadow of interior wall(middle shadow) ,but it don't work.
in gambit i have two zone water flow in cylinder and air of environment.when hot flow pass the cylinder ,air don't have any changes.
the image is attached.

[zdunol]

Hello good people,

I'd liike to ask if somebody could explain the steps in creating this couple wall b.c more clearly

What I have is two bodies - fluid and solid, one of solid's wall is hot, I wanna see how much the fluid heats up, the solid does not cover the whole fluid domain - it works like plate heat exchanger and the inlet's and outlet's solid domain is not defined, only the part governing heat transfer

what I do is:

1/ When I create no named selections in mesher fluent creates a lot of walls and less shadow walls (chich is correct), but I cannot display the ones that are overlapping with connections, which are present in the mesher.

2. If i create named selection corresponding to the interface between solid and fluid, fluent oes not create ny shadow interface part ;<

Kind regards,
Pawel

[macfly]

No special treatment is needed at a fluid-solid interface. As long as your zones are well defined in your mesh, Fluent creates a wall/wall-shadow at the interface and heat transfer will occur across the wall.

If there is (almost) no heat transfer across the wall/wall-shadow, it's probably because of the physics of the problem. Run the same simulation for a longer time or modify thermal properties (k, Cp) in order to validate that heat transfer occurs.

[zdunol]

ok but there will be heat transfer between solind and fluid even though there is no shaow walls in boundary condtitions panel?