How to Calculate Heat Loss in an Aluminum Pipe with Fluid Flow?

[Bassalisk]

Homework Statement

Through a pipe made of aluminum, length of 1m which outer radius is r1=3,5 cm and inner radius is r2=3 cm flows a fluid with temperature of t1= 30 °C. How much heat does get lost through the walls of the pipe, in $$\tau$$=3h if the temperature around the pipe is 20 °C. Heat conductivity of aluminum is $$\chi$$=210 W/mK

Homework Equations

Heat lost: Q=XS(T2-T1)*$$\tau$$/L

where L is thickness of the pipe.

The Attempt at a Solution

Now I get the roughly 0,85 GJ.
But the solution says its 0,88 GJ and that a bit difference when you are talking about GIGA Jules.

I think I got the thickness of the pipe wrong and surface area through which heat is being transferred.

Can anybody help me here?

 

[Bassalisk]

Close the thread, I got the formula wrong. Btw can anybody here give me a good link with good theory with conduction of heat?