Asingle-phase thyristor-controlled rectifier supplies the lighting in a theater. the light control requires the reduction of the average dc voltage to 70% of the rated voltage when the lights are dimmed. the 60 hz ac input is 220 v, and the dc output rating is 120 v. the lights normally draw 2 kw at the rated conditions.

calculate the required delay angle

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.