Plate Fin Simulation in Ansys Workbench 14.5

[shaun1]

Hi all,

I have started learning ansys workbench for steady state heat transfer based analysis.

I am doing this analysis to validate analytical results given for heat transfer from a single plate fin.
The fin tip is given a base temperature and heat transfer is calculated for natural convection considering a given volume for the plate fin in order to optimize its dimensions for maximum heat transfer. The analytical method was followed from the paper by R.Karvinen and T.Karvinen.

Title : " Optimum geometry of fixed volume plate fin for maximizing heat transfer".

As per the analytical relations, the heat flux for the fin is calculated by considering an isothermal fin with an insulated fin tip boundary condition. The value of the flux obtained is 7 W/m^2.

Fin Dimensions (optimized) : L (vertical length) x l (horizontal dimension) x 2to (thickness) = 0.08 x 0.09 x 0.000552 (all dimensions in metre)
to=half thickness

Fin Base Temperature : 125℃
Ambient Temperature : 25℃
Fluid Properties were obtained for mean film temperature i.e. 75℃

I will try to give the steps I followed in ansys to try to validate the analytical result.

1. I created the geometry in solidworks giving the above dimensions.
2. In engineering data, I created a new material with isotropic thermal conductivity 237 W/m*K
3. For the model, I accepted the default meshing given by the software.
4. Initial temperature was specified as 25℃.
5. Following are the conditions I specified in the analysis settings.
- Base Temperature 125℃.
- Perfectly insulated condition for the three small faces. (top,bottom and tip)
(Their areas : l x 2to for top and bottom faces and L x 2to for the tip)
- Convection at 25℃ for the remaining two faces (Area L x l).
- For an isothermal fin, I selected all the six faces and specified a temperature of 125℃ for them.
6. After getting the solution, I obtained the results for total heat flux and got the results in the range of 8.45*10^-6 to 2.98*10^-10 W/m^2. The analytical results gave a value of 7W/m^2 as specified above.

The analytical calculations have been checked and were found to be correct.

Could someone point out my mistake in doing the analysis ? I am doubtful about the isothermal condition as I just have manually selected all the faces and given the temperature. Is there any provision in work-bench to specify an isothermal fin ?

Thanks.

(I am attaching an image of the dimensional representation for the fin and the results image for heat flux.).

 

[AlephZero]

You gave us a lot of data, but you didn't mention the heat transfer coefficient for the convection between the fin and the air.

If your answers are ridiculously low, maybe you didn't include convection the model and you are only modeling heat conduction between the fin and the air?

 

[shaun1]

The heat transfer coefficient is 14 Wm^2K. And I gave the convection setting for the two large faces of the fin.

 

[AlephZero]

The heat transfer coefficient is 14 Wm^2K.

That's the right order of magnitude for free convection between the fin and air.

Ah... I just had a face-palm moment. Is your 10^-6 the total heat flux into the fin - i.e the difference between what flows in through the base and what flows out? That number should be zero, once you get to a steady state.

Otherwise, look at the temperature distribution in the fin and check it against common sense.