Rate of Heat transfer

1. Jan 11, 2014

PotatoMerchant

1. The problem statement, all variables and given/known data

2. Relevant equations

(unsure)

3. The attempt at a solution

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jan 11, 2014

Staff: Mentor

It doesn't look like this has been done correctly. To begin with, the starting equation is incorrect.
For a single layer, it should read:

$$2πrLq =Q=2πkL\frac{ΔT}{Δlnr}$$

where Q is the total heat flow (watts) and q is the heat flow per unit area. This equation applies to each of the concentric layers. The problem is analogous to having two resistors in series, where ΔT is like the voltage drop across each layer and Q is the current flow through the resistors. You have to solve for the current flow, given the overall voltage drop across both layers (155 C).