An engineer proposes to insert a solid rod of diameter Di into a circular tube of diameter D_o to enhance heat transfer from the flowing fluid of temperature Tm to the outer tube wall of temperature T_s,o. Assuming laminar flow, calculate the ratio of the heat flux from the fluid to the outer tube wall with the rod to the heat flux without the rod, q"_o/q"_o,wo, for D_i /D_o = 0, 0.10, 0.25 and 0.50. The rod is placed concentrically within the tube.