Modeling Heat Transfer from a Flame to a Copper Tube using ANSYS

[Vincenzo]

Homework Statement

Can't model a simplfied version of my problem, it's a Steady State Thermal problem. I'm trying to get the superficial temperature of a copper tube and the heat transfer from a flame to the tube(this is a simplified version of the problem).

Now my problem started when I couldn't find a way to modelate a flame or a heat source like a flame, so I did a cruel approximation and made some calculations changing the flame for a cylindrical body with superficial temperature equal to the adiabatic flame temperature(1500K) and a emisivity of 1.
To start an ANSYS simulation, after the having the geometry and the mesh done, one must introduce the boundary conditions, these as far as I know are:
1) The 1500K(1227°C) over the cylindrical body.
2)The existence of radiation between the bodies, with an emisivity of 1(flame). The temperature of the air around the tubes should start as 20°C. a "correlation" (I'm assuming this si to tell ANSYS the surfaces from where to take the vision/form factor) set as surface to surface.
3) The starting temperature of the copper tube, this is 20°C.(emisivity of 0,6)

So I set these conditions and then to the solution I set a Temperature over the copper tube, thing is,
1) I can't find a way to show me a progression over time to reach the 1500 K, it sets it inmediatly.
2) The amount of heat flow (W) absorved is way diferent to the one I calculated.

Homework Equations

Radiation Heat transfer Eq: Q'=ε*As*F*σ*(T₁⁴-T₂⁴)
Outside diameter of copper tube is 33,4 mm
Outside diameter of "flame" is 49,25 mm
Separation between centers of both cylinders: 46,7375
Form Factor:0,1937 (using crossed string method)

The Attempt at a Solution

I try to guide me from this course without sucess.
https://confluence.cornell.edu/display/SIMULATION/ANSYS+-+Radiation+Between+Surfaces
Any help is welcomed.

To add a sadness factor, this is for my thesis, I'm trying to do a propossal of a desing of an special steam generator and I already did several calculations by hand, just need the pretty color pictures and the data sheet of ansys to support my model... Well I'm still missing the part where I evaporate the saturated water, this is just to heat the water, not to change it's phase. I will get that part done this week hopefully.

Thanks for the time!

 

[Tom.G]

Not an expert, in fact I've never used ANSYS, just read the tutorial you linked to.
I'm assuming you are using a geometry similar that in the tutorial, with a half-shell being the flame and the specimen extended downward out of the shell.

Here's another tutorial that may be of help: https://confluence.cornell.edu/display/SIMULATION/ANSYS+-+Thermal+Stresses+in+a+Bar

Just some obvious things to check:

• Initial conditions (misplaced decimal?)
• Mesh size
• Static analysis vs Transient analysis (both needed, Static to set initial conditions, then Transient for time series results)
• Step size adequate for the thermal mass involved
• Geometry;
  • a misplaced decimal for size or mass
  • mechanical interference between the pieces (do they touch each other?)

 

[Vincenzo]

Thanks for the reply Tom, but I drop the model and change the heat transfer mechanism becuase I couldn't solve the radiation model. I change it to external forced convection.

 

[Tom.G]

I change it to external forced convection.

Sounds much more like a flame!