Consider a circular tube of diameter D and length L, with a mass flow rate of m_dot. (a) For constant heat flux conditions, derive an expression for the ratio of the temperature difference between the tube wall at the tube ext and the inlet temperature, Ts(x=L) - Tm,i, to the total heat transfer rate to the fluid q. Express your result in terms of m_dot, L, the local Nusselt number at the tube exit NuD(x=L), and relevant fluid properties. (b) Repeat part (a) for constant surface temperature conditions. Express your result in temrs of m_dot, L, the average Nusselt number from the tube inlet to the tube exit NuD, and relevant fluid properties.