CFD Online Discussion Forums

Heat Exchanger Resistance

cfdonline10 — Wed, 19 Jun 2013 16:30:10 GMT

Assume that there a flat oval tube (thickness T1) of 50 mm width (W1)and 8 mm height (H1)with water flowing at a rate of 2.5 liters/min. Directly below this tube, there a plate (thickness T2) of width of 35 mm (W2). I want to come up with thermal resistance for this assuming there is heat source directly below plate.
Method 1:
Direct HT Resistance = r1=(T2/(K2 *A2) +T1/(K1*A1)+ 1/(hA))
Note that here, A2=A1=A=W2*length
The remaining portion of oval tube has (behave line fins) a length of S= (W2/2) (top of oval tube) + H2 +(W2-W1)/2 on left side and the same on the right side. Assume that entire plate and tube is adiabatic.
Parallel resistance is r2 =1/(Fineff*S*T2). Where Fineff =tanh (m*S)/(m*S)
Now we can find equivalent R using 1/R = 1/R1 + 1/R2
Method 2:
Area of oval tube At= 2*(W1+H1)*L
Total resistance =(T2/(K2 *A2) +T1/(K1*A1)+ 1/(hAt))
Which one is more accurate? Any suggestion or refrerences?
Thanks

Information about meshes

wemendibe — Wed, 19 Jun 2013 16:28:43 GMT

Hello
I am doing a project and I need to know what is the difference between the triangle mesh and the square mesh. I am doing a mixing tank and I need to know what difference are between them.

[GAMBIT] Difference between meshes

amodrego — Wed, 19 Jun 2013 16:22:37 GMT

Hello:

I am doing a research project and i would like to know which is the best mesh to use in a fluid, squared or triangle mesh.

Thank you.

chtMultiRegionSimpleFoam solid/fluid interface flow problem

steezorigineez — Wed, 19 Jun 2013 15:12:43 GMT

Hey Guys,

Recently I have been attempting to setup a basic 2D natural convection case that includes conduction through two solids for use in validation. The case setup is a region of air with a solid block on the top and the bottom. The bottom of the bottom solid is held at a constant hot temperature and the top of the top block is held at a constant colder temperature. The left and right sides of the domain are periodic.

The problem I am running into is an odd velocity field at the bottom corners at the interface between the bottom solid and the air. Attached are pictures of the glyphs associated with velocity field. As you can see the top corners of the air domain look normal and you would expect the bottom corners to look identical, but they don't.

I believe I have applied the correct boundary conditions for the solids and fluids, but I will attach the case files if someone would like to check them out.

I'm wondering if anyone has experienced anything like this while using the chtMultiRegionSimpleFoam solver. I've spent a while trying out different BCs to try and fix the problem, but nothing has worked yet.

I think there may possibly be a bug in the solver, but I will wait for some feedback before I send in a bug report.

Any help or guidance is greatly appreciated. Thanks

-Ian

Attachment 22821
Attachment 22820

Attached Images

VelocityGlyphs.jpg (50.5 KB)

Attached Files

2SolidConv.tar.gz (8.3 KB)

Graph register option

crevoise — Wed, 19 Jun 2013 15:06:40 GMT

Hello all

I am doing some post processing calculation on StarCD and I am facing a problem with the cell numbering.

I am using the command gload in order to load the cell number of a cset into a graph register, for further exportation of data.

My geometry has several millions cells, and a problem appears while using this command line.
In the graph register, instead of getting a cell number of 1150230, 1.15023e6 is loaded - the 0 is truncated. for the case of 11500239, it will load 1.15024e6
Thus it became no sense to export these data.

Does anyone knows how to change the scientific numbering option in Prostar?

Thanks for your help

Error Code: "collect2: ld returned 1 exit status" during buil

JasonBecker — Wed, 19 Jun 2013 15:05:56 GMT

I am currently using OpenFOAM 2.1.0. I am somewhat new to OpenFOAM and have been having some difficulty merging mhdFOAM with interFOAM. When I attempt to run wmake to build an .exe file, i get the following:

Quote:

g++ -m32 -Dlinux -DWM_DP -Wall -Wextra -Wno-unused-parameter -Wold-style-cast -O3 -DNoRepository -ftemplate-depth-100 -I/opt/openfoam210/src/transportModels -I/opt/openfoam210/src/transportModels/incompressible/lnInclude -I/opt/openfoam210/src/transportModels/interfaceProperties/lnInclude -I/opt/openfoam210/src/turbulenceModels/incompressible/turbulenceModel -I/opt/openfoam210/src/finiteVolume/lnInclude -IlnInclude -I. -I/opt/openfoam210/src/OpenFOAM/lnInclude -I/opt/openfoam210/src/OSspecific/POSIX/lnInclude -fPIC -Xlinker --add-needed -Xlinker --no-as-needed Make/linuxGccDPOpt/khiFoam.o -L/opt/openfoam210/platforms/linuxGccDPOpt/lib \
-ltwoPhaseInterfaceProperties -lincompressibleTransportModels -lincompressibleTurbulenceModel -lincompressibleRASModels -lincompressibleLESModels -lfiniteVolume -lOpenFOAM -ldl -lm -o /home/jasonb/OpenFOAM/jasonb-2.1.0/platforms/linuxGccDPOpt/bin/khiFoam
Make/linuxGccDPOpt/khiFoam.o: In function `main':
khiFoam.C:(.text+0x7dd6): undefined reference to `Foam::incompressible::turbulenceModel::New(Foam:: GeometricField, Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField const&, Foam::transportModel&)'
collect2: ld returned 1 exit status
make: *** [/home/jasonb/OpenFOAM/jasonb-2.1.0/platforms/linuxGccDPOpt/bin/khiFoam] Error 1

Any idea what I need to fix?
Thanks,
Jason Becker

continuation of stopped program

Niru — Wed, 19 Jun 2013 14:53:18 GMT

I was running a transient simulation in CFX . The total time steps is 10000.
Transient files are saved every 100 steps. The program stopped inbetween and ansys closed. I would like to know how to continue from where it stopped.

Dynamic meshing - UDF

Jiang — Wed, 19 Jun 2013 14:46:42 GMT

Hey,

I have started to work with dynamic meshing on a pressure valve for a moving valve disc. i have been using the UDF coding of a SDoF piston from ANSYS with some modifications. However it does not seem to be working
i have tried looking for turotials for UDF and dynamic meshing but many of the links have became invalid or not related.
If any one can guide me in the right directions for dynamic meshing or notice i might be doing something wrong

Thanks in Advance

Jiang

Attached Images

disc_closed2.jpg (95.0 KB)

Finding out nodal values

victoryv — Wed, 19 Jun 2013 14:29:34 GMT

I want to find the nodal/face values of the variables on a line/plane in the domain so that I can use them as boundary condition input in another simulation. Is there a way to export the nodal/face values of the variable from the fluent?

Torque Coefficient in a VAWT

Borjinho — Wed, 19 Jun 2013 14:16:26 GMT

Hello,
I am trying to simulate a Naca 0012 VAWT in 2D. As I increase the velocity inlet, the Torque coefficient decreasses. What could be the problem?
Thanks.

fluent convergence

sarsam.9296 — Wed, 19 Jun 2013 14:03:04 GMT

Hi,
I made models of tubes with different diameters keeping the flow rates the same in all of them. I used standard k-epsilon model in my simulation, but still the solution converges for low diameters and does not for higher diameters. Although on reducing the mesh density on higher diameter models, It again starts converging. Can anyone please tell me why this is happening??

Iso surfaces in fluet

sarsam.9296 — Wed, 19 Jun 2013 13:59:00 GMT

Hi,
I am doing multiple simulations (different conditions) on the similar models. Is there a way that I can import all the iso-surfaces defined in a simulation into another simulation (based on a different gambit model) because the number of surfaces that I am defining in a simulation is greater than 50 and it will save me a lot of work.

Thanx in advance

[ICEM] meshing problem

feizaghaee — Wed, 19 Jun 2013 13:54:42 GMT

hi. I'm trying to simulate an ogee weir in a channel. I want to use hexa dominant mesh in the model. but when I run it. something goes wrong and icem can't generate volume mesh. what is the problem?

Create an internal face

aylalisa — Wed, 19 Jun 2013 13:42:48 GMT

Hi to All,

I simulate a flow in a channel.

-fluid: water
-transport model: Newtonian
-very small velocity at inlet face that results in a laminar flow in the whole channel

The channel has a length of 3,1m (x-direction, width = y-direction = 0,250m, height = z-direction = 0,02m).

Attempt 1

I would like to define an internal face in the blockMeshDict to be able to map the final velocity field of that internal face on the inlet face of another channel model as boundary condition with help of mapFields utility.

The channel consists of three blocks. The desired internal face connects block 1 ( x = 0m - 1m = 1m) with block 2 ( x = 1m - 2,5m = 1,5m).

If I add two additional patches (outlet_block1, inlet_block2) in the boundary () subdictionary and list them up in subdict mergePatchPairs () I get an error message after starting blockMesh.

Quote:

--> FOAM FATAL ERROR:
Trying to specify a boundary face 4(0 3 7 4) on the face on cell 0 which is either an internal face or already belongs to some other patch. This is face 0 of patch 5 named Developing_outlet.

From function polyMesh::setTopology
(
const cellShapeList& cellsAsShapes,
const faceListList& boundaryFaces,
const wordList& boundaryPatchNames,
labelList& patchSizes,
labelList& patchStarts,
label& defaultPatchStart,
label& nFaces,
cellList& cells
)
in file meshes/polyMesh/polyMeshFromShapeMesh.C at line 360.

FOAM aborting

Attempt 2

I've created the velocity field of that internal face with sample utility --> folder surfaces is created and contains for each time step the required data. But then I am not able to map that data on the inlet boundary of the other model with help of mapFields.

MapFields maps the complete volume velocity field from model 1 to model 2. But I would like to map only the velocity field of the internal surface to the inlet surface (inlet boundary condition) of model 2.

Can anybody help???

Aylalisa

Help-bachelor thesis topic

Mahdi23 — Wed, 19 Jun 2013 13:41:45 GMT

I'm the last year
student of mechanical engineering. I should say I am having
difficulty coming up with a topic for the bachelor thesis topic although I
decide to work on CFD topics but I have no idea about a good topic.may
I ask to help me with suggesting topics?!
Thank you for your time and Thank you in advance for any help you
might be able to provide.