12.48 Moist air enters a device operating at steady state at 1 atm with a dry-bulb temperature of 55°C and a wet-bulb temperature of 25°C. Liquid water at 20°C is sprayed into the air stream, bringing it to 40°C, 1 atm at the exit. Determine a. the relative humidities at the inlet and exit. b. the rate that liquid water is sprayed into the air stream, in kg per kg of dry air.

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.