Design Analysis: Thermal Bonded Contact

Design Analysis:

nTop Platform features built-in steady-state structural and thermal analysis using a range of boundary conditions.  When performing Design Analysis a user may want to assign material properties to a mesh based specific CAD or Implicit bodies.  This article will focus on the use of "Structural and Thermal Bonded Contact" Blocks in nTop Platform.

Block Name and Descriptions:

Thermal Bonded Contact:

This block creates a bonded contact between two FE boundaries which allows for heat flow between two components.  Contact resistance between the two boundaries can be defined to account for a thin membrane material at the boundary (ie thermal paste).  

In the figure below, a user would like to tie a copper slug into an aluminum frame.  The cad model on the left represents the geometry of the two materials and the subsequent mesh of the two regions is on the right.  Since the FEA meshes of two regions do not necessarily share common nodes and element faces it is necessary to "tie" these two regions together mathematically.  As such, this approach allows the user to mathematically “bond” two different objects (of different materials) together and couple them thermally.

1-Bonded_Contact__Copper_and_Aluminum_-bth.PNG

To tie these two materials together the user would use the "Thermal Bonded Contact" block.  This block creates a bonded contact between two FE boundaries which allows for heat flux between the two components.

Thermal_Bonded_Contact.png

Contact resistance can be defined to account for thin membrane material at the boundary such as thermal paste.  The contact resistance between two materials is often calculated from experimental tests of contact conductance.  A table of values is provided below with some common materials.

Table 1: Thermal contact conductance of some metal surfaces (from various sources)

Material
Surface Condition
Roughness
µm
Temperature
°C
Pressure
MPa
hc*
W/m2· °C
Identical Metal Pairs
416 Stainless steel
Ground
2.54
90–200
0.3–2.5
3800
304 Stainless steel
Ground
1.14
20
4–7
1900
Aluminum
Ground
2.54
150
1.2–2.5
11,400
Copper
Ground
1.27
20
1.2–20
143,000
Copper
Milled
3.81
20
1–5
55,500
Copper (vacuum)
Milled
0.25
30
0.7–7
11,400
Dissimilar Metal Pairs
Stainless steel-
Aluminum
-

20–30

20
10
20
2900
3600
Stainless steel-
Aluminum
-

1.0–2.0

20
10
20
16,400
20,800
Steel Ct-30-
Aluminum

Ground

1.4–2.0

20
10
15–35
50,000
59,000
Steel Ct-30-
Aluminum

Milled

4.5–7.2

20
10
30
4800
8300
Aluminum-
Copper

Ground

1.3–1.4

20
5
15
42,000
56,000
Aluminum-
Copper

Milled

4.4–4.5

20
10
20–35
12,000
22,000

*Divide the given values by 5.678 to convert to Btu/h · ft2 · °F.


It should be noted that the Thermal Bonded Contact Block requires Thermal Contact Resistance and the table above provides conductance values.  It is required to perform some math operations to get conductance values properly input into the block.  

mceclip0.png

With the contact resistance properly computed it is necessary to tie the two meshes together as shown in the image below.

mceclip1.png

To properly include Bonded Contact in your FEA analysis you must use include the thermal bonded contact block in the "Connectors" input of your FE Model as shown in the image below.

mceclip2.png

 

Once your thermal boundary conditions are input you can now run your thermal analysis using bonded contact!

mceclip4.png

Attachment:

Keywords:

 Finite FEA Thermal Bonded Contact Design Analysis Tie 
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