I'm trying to run a transient heat transfer simulation for a heat sink on NASTRAN, but for whatever reason the graphs for the maximum and minimum temperatures over time come out completely flat. I know that the heat sink doesn't actually draw away heat like this because this heat sink was machined and tested in a lab. This is my first time using NASTRAN, so I'm pretty sure I'm just inputting values wrong. What exactly am I doing wrong?
The heat sink is subject to a constant 84C at its base
Natural convection on every surface other than the base at an ambient temperature of 25C, and a heat transfer coefficient of 6W/m^2K
And I assumed that the starting temperature of the heat sink was the same as the ambient temp.
In a lab setting, it took about 250 seconds for the heat sink to reach its' minimum temperature