1. The problem statement, all variables and given/known data Given is a hollow cilinder with inner radius R1 and outer radius R2. The heat conductivity of the material is k. The cilinder has length l and an inner temperature of T1 and outer temperature T2. Determine the temperature gradient in the cilinder and the heat flow that leaks away radially. 2. Relevant equations Power = k*Area(Temperatureinside-Temperatureoutside)/(thickness) Area = 2*pi*R*l 3. The attempt at a solution The reason I can't solve this problem is the changing area when going from inside to outside the cilinder. Obviously the heat flow going from the inside to the outside should be minus the heat flow from outside to inside, since the areas are different I think the only way this is possible if the temperature gradient falls off quicker going inside causing the heat flow to be the equal despite the smaller area. So much for intuition though since I've tried fruitlessly to write this down mathematically. I also think the trick is to use an intermediate temperature T and equate the powers going through an area between R2 and R1 since we've used that one before.