Rydstad
Mechanical
- Jul 4, 2008
- 1
We are a group of four Swedish girls studying engineering, and at the moment we are investigating the heat transfer of a heat sink. The heat sink shall cool a PC-board that generates 81 W, which naturally causes extremely high temperatures. Gap fillers are used as a TIM to fill out the space between the heat sink and the electric components, (to reduce the thermal resistance).
To analyze this we are using ANSYS and the gap fillers are represented by solid blocks. The thickness of the gap filler blocks is set to 2 mm. However, our gap fillers are in reality 1,78 mm thick when undeflected, and the deflection is about 20% (at kPa, 5 psi). We are now wondering:
1) If we were to use the 2 mm blocks in ANSYS, but want the heat flow to be equal to the use of the 1.78 mm gap filler in deflected state, how do we modify our calculations?
Our idea is to modify the coefficient of the thermal conductivity used in ANSYS. The apparent thermal conductivity is 3 W/(mK) for the 1.78 mm gap filler. Is this complete nonsense?
(conductivity of 1.78)/(1.78 mm) = (unknown conductivity)/(2 mm) --> (2/1.78)=(X/2)
2) It can be tricky to calculate the thermal conductance between the surfaces of the gap filler and the heat sink, as well as between the gap filler and the electric components. The gap filler fills up the microscopic gaps (the roughness of the surface) pretty well. Can we use ANSYS program control for the thermal conductance between the gap filler and the heat sink?
3) On one side, the gap filler has a carrier of woven glass. This side is in contact with the electronic components. We think that this will affect the thermal conductance, as the gap filler won’t fill out all the gaps. How do we calculate the thermal conductance if we want to use ANSYS manual option?
We are thankful for any thoughts or guidance that you might have!
To analyze this we are using ANSYS and the gap fillers are represented by solid blocks. The thickness of the gap filler blocks is set to 2 mm. However, our gap fillers are in reality 1,78 mm thick when undeflected, and the deflection is about 20% (at kPa, 5 psi). We are now wondering:
1) If we were to use the 2 mm blocks in ANSYS, but want the heat flow to be equal to the use of the 1.78 mm gap filler in deflected state, how do we modify our calculations?
Our idea is to modify the coefficient of the thermal conductivity used in ANSYS. The apparent thermal conductivity is 3 W/(mK) for the 1.78 mm gap filler. Is this complete nonsense?
(conductivity of 1.78)/(1.78 mm) = (unknown conductivity)/(2 mm) --> (2/1.78)=(X/2)
2) It can be tricky to calculate the thermal conductance between the surfaces of the gap filler and the heat sink, as well as between the gap filler and the electric components. The gap filler fills up the microscopic gaps (the roughness of the surface) pretty well. Can we use ANSYS program control for the thermal conductance between the gap filler and the heat sink?
3) On one side, the gap filler has a carrier of woven glass. This side is in contact with the electronic components. We think that this will affect the thermal conductance, as the gap filler won’t fill out all the gaps. How do we calculate the thermal conductance if we want to use ANSYS manual option?
We are thankful for any thoughts or guidance that you might have!
