1. The problem statement, all variables and given/known data Water flowing at the rate 3.5 kg s−1 through a tube with an inner diameter of 2 cm is to be heated from 20 to 40◦C. If the tube wall temperature is maintained at 90◦C, determine the length of the tube required. 2. Relevant equations Q'=Cp*m*(DeltaT) Q=2*pi*r*L*Q' 3. The attempt at a solution Q=mass flowrate*Cp(DeltaT) =3.5*4.18*10^3*(40-20)=292600J/s L=Q/2*pi*rQ' However, I'm missing Q and L. I would like to know if I need the prandlt number for this question or the viscosity of water? Would I need more information to solve this problem? Any help will be greatly appreciated. Thanks.