Atwo-position mode controller is used to control the water level in a tank by opening or closing a valve which in the open position allows water at the rate of 0.4 m^3/s to enter the tank. the tank has a cross-sectional area of 12 m^2 and water leaves it at the constant rate of 0.2 m^3/s. the valve opens when the water level reaches 4.0 m and closes at 4.4 m. what will be the times taken for (a) the valve opening to closing, (b) the valve closing to opening?

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.