Avery effective low-temperature insulation is made by evacuating the space between parallel metal sheets. convection is eliminated, conduction occurs only at spacers, and radiation is responsible for what little heat transfer occurs. calculate q between 150 k and 100 k for three cases: (a) two sheets of highly polished aluminum.(b) three sheets of highly polished aluminum. (c) three sheets of rolled sheet steel.

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.