QUESTION: Air at 35°C enters a 10 m long section of a rectangular duct of cross section 25 cm by 15 cm made of commercial steel at an average velocity of 10 m/s.
*Take density of air and dynamic viscosity as 1.145 kg/m^3 and 1.895 x 10^-5 kg/m.s respectively.
Determine: (a) Reynolds number
i take the cross section 25cm * 15 cm as my area. I need help finding the diameter of pipe and please do confirm my workings cause i feel like its somewhat off since from my calculation above my Reynolds number is quite big.