I have a simplified model (see attached picture) which is part of a bigger model but for now the problem is as follows. I have a electropolished metal sheet which has spots on it which act as heat sinks because they are kept at constant temperature of 100K. The sheet is at room temperature initially (300K) and will loose heat to the white spots to get to 100K over time. I need to come up with some equation which can describe how heat will flow by conduction through the sheet. I know it's very easy in COMSOL, and in the COMSOL solution, the areas near the white spots will be blueish (indicating low temp) and away from the white spot will be reddish. Basically, i need to come up with an equation that shows the Comsol's solution.