Bus Bar with Heat Sink

This device is a rectangular bus bar with a heat sink mounted along its top. The bus bar is made of solid copper and carries a DC current of 10 kA. The heat sink is a commercial heat sink design Aavid model 67605, and it causes a temperature gradient from top to bottom. The conductivity of the copper is temperature dependent, causing a redistribution of the current as the bus bar heats up. The steady state behaviour is simulated in ThermNet using its static 2d solver magnetically coupled to MagNet's static 2d solver. The convective heat transfer coefficient on the surface of the heat sink is set to 127 W/m^2 C, based on this heat-sink's data charts, which corresponds to a forced air flow of about 2.2 m/s.

Results

Click image to see full size version

This image shows the steady-state temperature distribution, which varies by more than 10 degrees Celsius from top to bottom. This variation in temperature affects the conductivity of the copper, causing a redistribution of the current in the bus bar.

Click image to see full size version

Because conductivity decreases with temperature, more current flows on the cooler end of the bus bar (closer to the heat sink) as this image shows. Note that the scale has been adjusted to make this small effect more visible.

Click image to see full size version

One might expect that the higher temperature would be a result of a higher loss density, but this image shows that this in not the case. The loss density is actually higher on the cooler side, which can be explained by the fact that conductivity decreases with increasing temperature, and at constant voltage the loss density is directly proportional to conductivity.