Agas is contained in a vertical piston–cylinder assembly by a piston with a face area of 60 in2 and weight of 100 lbf. the atmosphere exerts a pressure of 14.7 lbf/in2 on top of the piston. a paddle wheel transfers 3 btu of energy to the gas during a process in which the elevation of the piston increases slowly by 1 ft. the piston and cylinder are poor thermal conductors, and friction between the piston and cylinder can be neglected. determine the change in internal energy of the gas, in btu.

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.