A fluid is flowing through two different tubes of same cross-section area. We are to compare the heat transfer rate in these two tubes over the same length. First tube is circular cross-section and the second one has a square cross-section. The flow is laminar and fully-developed in both cases. The tube surface can be approximated as isothermal in both cases. Also assume that the average temperature difference between the surface and the fluid is approximately the same in both cases. What is the ratio of the heat transfer rates (between the tube and the fluid) between the first and second tube?

4. For a thermally fully developed flow in a pipe for a fluid with constant properties, the local convection coefficient (a) Decreases as x-1/2 (b) Decreases as x-1/5 (c) Increase as x1/2 (d) Increases as x4/5 (e) Remains constant