Problem 3. (30 pts) Water flows inside a smooth circular thin-walled tube of diameter D = 25 mm at a mass flow rate of 50 g/s. Outside of the tube, air moves in cross flow over the tube at a velocity of V = 20 m/s and a temperature of T[infinity] = 10°C. If the mean temperature of the water is Tm = 50°C, determine (a) The Darcy friction factor for the water flow inside the tube. (b) The surface temperature of the tube. The internal flow can be assumed fully-developed. Use the following fluid properties for the analysis: Air: cp = 1007 J/kg·K, k = 0.0257 W/m∙K, μ = 1.86 × 10−5 kg/m·s, rho = 1.17 kg/m3 Water: cp = 4180 J/kg·K, k = 0.640 W/m∙K, μ = 0.577 × 10−3 kg/m·s, rho = 990 kg/m3