1. The problem statement, all variables and given/known data Problem data: http://imgur.com/a/hEz16 2. Relevant equations Rconduction=ln(rout/rin)/2*pi*Length*thermal conduct Rconvection=1/2*pi*Length*routside*convective heat transfer outside =>Qconduct=2*pi*Length*thermal conduct*(Tin-Tout)/ln(rout/rin) =>Qconv=2*pi*Length*routside*convective heat transfer outside*(Tout-Tair) 3. The attempt at a solution Solution: a) http://imgur.com/a/cH9hV b) For a) I do not understand why we need to find Toutside by equating Qcond=Qconv? And why we need to calculate Q from the pipe just as Qconvection instead of Q total? Why we cannot do Q=delta T/Resistance Total where: Rtotal=Rconduction+Rconvection,because we do not need temperatures in those 2 R formulas and delta T=(Tin-Tair) specifficaly 300 and 5 degrees celsius As for b) They do Rtotal and then Qtotal=delta T/Rtotal and then they do Qtotal=Qconv and they get T2. Why we cannot proceed the same for a)?