Hi, I'll describe my problem more specific. I have a continuous flow of this polymer thread (polystyrene) at 465 °K (190°C sorry i'm metric) that needs cooling down. It passes trough a water bath wich is kept at 310°K (35°C). Now i try to calculate the heat exchange into the water, to determine the speed of the cooling, or to calculate how hot the thread still is after a time. approach: I was thinking using conduction from the thread's core to the exterior and then convection into the water. (water is not moving btw). Now another look at this approach: The core of the polymer will remain hot when the exterior is cold. Because there is a very low thermal conductivity (0,187 W/m.K). So maybe i ought to use another formula. Because my first approach does'nt cover this. But this is where my knowledge stops. And research doesn't seem to deliver results. (When a metal bar is put in water u can take a temperature that is uniform over the bar because the heat exchange in metal goes so fast, here it is not the case.) Any idea's or remarks would be of great use!