Heat resistance

[yecko]

Homework Statement

solution:

Homework Equations

The Attempt at a Solution

I thought this question should use :

, but the solution manual used

instead, which 1/2 is missing... may I know what the 1/2 account for and why doesn't we need to multiply the equation by 1/2 ?
thank you

 

[stockzahn]

The Attempt at a Solution

I thought this question should use :View attachment 230458, but the solution manual usedView attachment 230459 instead, which 1/2 is missing... may I know what the 1/2 account for and why doesn't we need to multiply the equation by 1/2 ?

Since the the parts $A$ and $B$ of the pipe are only "half-pipes", their surfaces are halved resulting in a doubled thermal resistance (and the $2$ in the denominateor vanishes).