Wearing layers of clothing in cold weather is often recommended because dead-air spaces between the layers keep the body warm by reducing the heat loss from the body. Compare the rate of heat loss for a single, 13 mm thick layer of wool to three 3 mm thick layers separated by 2 mm air gaps. Since the air gaps are so small, treat the air as stationary (i. e., assume heat is being conducted through the air gaps). Use kwool = 0.07 W/m-K and kair = 0.02 W/m-K.

What precautions should you take to prevent injuries when dealing with heavy loads?

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.

A2-m rigid tank initially contains saturated water vapor at 100 kpa. the tank is connected to a supply line through a valve. steam is flowing in the supply line at 600 kpa and 300 c. the valve is opened, and steam is allowed to enter the tank until the pressure in the tank reaches the line pressure, at which point the valve is closed. a thermometer placed in the tank indicates that the temperature at the final state is 200°c. determine (a) the mass of steam that has entered the tank (b) the amount of heat transfer.