If you could also help me out on this one, that would be much appreciated. I'm trying to use section 5.3.5 of the handbook to calculate Nusselt's number in order to derive the heat transfer coefficient, h. However, I end up with a Reynold's number of about 500,000 which does not fall on the chart provided. Defaulting to the highest values does not lead to an answer that matches any of the choices. Please point me to where I'm going wrong. In imperial units Question Air at 68F flows in a 20 ft 15 ft horizontal rectangular duct at a velocity of 5 ft/sec. The air has a kinematic viscosity of 17.17 105 ft2/sec, a thermal conductivity of 0.09 Btu/hr-ft-F, and a Prandtl number of 0.71. The walls of the duct are smooth and at a surface temperature of 86F dry-bulb. The heat transfer to the air is most nearly Answers 10 Btu/hr-ft2 20 Btu/hr-ft2 30 Btu/ hr-ft2 70 Btu/ hr-ft2