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Steady-State Variable Thickness Fin 
(Conduction & Convection)
EXAMPLE 3
 

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Problem Description

A mild steel fin, 300mm long x 25mm wide x 1.5mm thick, is attached to an object held at a constant 100°C.  The temperature at the end of the fin is measured as a constant 20°C.  Convection occurs at a rate of 10 w/m^2-k.  Find the steady-state temperature distribution.

The fin is created as a flat plate and assigned a thickness of 1.5mm mild steel (k=52.019 W/m-K).  The meshed fin is 100 elements long and 7 elements wide.  Again, to compensate for the fact that boundary conditions are applied element centroids, the fin is made 303.03mm long.  Boundary conditions were applied by holding strips of elements at the two ends at constant temperatures.

Boundary Conditions

  • The at x=0 the end is a constant 100°C.

  • The fin end (x=300mm) is a constant 20°C.

  • The ambient temperature TINFINITY   is 20°C.

Assumptions

  • Emissivity is set to zero (no radiation).

  • Steady state and One-Dimensional

  • Convection at 10 w/m^2 occurs only on the top and bottom surfaces.

Objective

Predict the steady-state temperature gradient along the fin for several different fin thicknesses.

Analytical Solution

TAI Results

The solution was converged its maximum in each case.  The theoretical and TAI results are very closely matched.   Observable differences are most likely the result of numerical error.

 

finresult.gif (22357 bytes)

finresult2.gif (18224 bytes)

Graph info: the solid lines represent the analytical prediction and the points represent the TAI results.

 

Element # X Distance Thickness Analytical RadTherm 5.0 WinTherm 5.0 MusesPro 5.0
541 97.0mm 1.5mm 36.9 37.3 37.3 37.3
229 215.2mm 1.5mm 22.4 22.4 22.4 22.4
541 97.0mm 5mm 53.4 53.8 53.8 53.8
229 215.2mm 5mm 29.4 29.4 29.4 29.4
541 97.0mm 100mm 72.5 72.7 72.7 72.7
229 215.2mm 100mm 41.5 41.3 41.3 41.3

Note: Test run by RES 3-2000 using versions 5.0.0.

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