Water at 1 atm and mean inlet temperature of 15 C enters into a rectangular cross section duct of sides a=50 mm, b= 25 mm and 10 m long, with Reynold number of 1800 (laminar flow). A constant heat flux is imposed on the tube wall. The exit mean temperature is 85 C. Assume fully developed conditions. a) Calculate the hydraulic diameter Dh and average velocity Vay. b) What is the convection heat transfer coefficient h? c) Determine the heat transfer rate in kW. d) Estimate the inner surface temperature Ts of the duct at the exit