A long copper rod of diameter 2.0 cm is initially at a uniform temperature of 100C. It is now exposed to an air stream of 20C with a heat transfer coefficient of 200 W/m^2. How long would it take for the copper rod to cool to an average temperature of 25C

Air enters a horizontal, constant-diameter heating duct operating at steady state at 290 k, 1 bar, with a volumetric flow rate of 0.25 m°/s, and exits at 325 k, 0.95 bar. the flow area is 0.04 m2. assuming the ideal gas model with k = 1.4 for the air, determine (a) the velocity at the inlet and exit, each in m/s, and (c) the rate of heat transfer, in kw flow rate, in kg/s, (b) the mass kg 0.3