An overhead 25-m-long, uninsulated industrial steam pipe of 100 mm diameter is routed through a building whose walls and air are at 25°C. Pressurized steam maintains a pipe surface temperature of 150°C, and the coefficient associated with natural convection is h = 10 W/m? · K. The surface emissivity is e = 0.8. (a) What is the rate of heat loss from the steam Jine? (b) If the steam is generated in a gas-fired boiler oper- ating at an efficiency of n = 0.90 and natural priced at C, = $0.01 per MJ, what is the annual cost of heat loss from the line? %3D gas is %3D

For heat transfer purposes, a standing man can be modeled as a 30-cmdiameter, 170-cm-long vertical cylinder with both the top and bottom surfaces insulated and with the side surface at an average temperature of 34°C. For a convection heat transfer coefficient of 15 W/m2 · °C, determine the rate of heat loss from this man by convection in an environment at 0°C.

In some countries, liquid nitrogen is used on dairy trucks instead of mechanical refrigerators. A 3.00-hour delivery trip requires 200 L of liquid nitrogen, which has a density of 808 kg/m³. Calculate the heat transfer necessary to evaporate this amount of liquid nitrogen and raise its temperature to 3.00°C. (Use Cp and assume it is constant over the temperature range.) This value is the amount of cooling the liquid nitrogen supplies. O A. None of the options provided is correct O B. 65.89 MJ O C. 161.6 MJ ○ D. 161.6 kg ○ E. 65.89 kJ

A homeowner is unhappy with her heating costs. One wall of her house is 4 meters tall and 8 meters wide and has no windows, and it is made of brick and mortar with a thermal conductivity of 1.0 W m K . It is 40 cm thick. The house is heated to a temperature of 20 ◦C inside. (a) What is the rate of heat loss through the wall on a day when it is 0◦C outside? (b) A layer of rock mineral wool, which has a thermal conductivity of 0.032 W m K is to be installed on the interior surface of the brick wall. How thick should the layer be to lower the rate of heat transfer through this wall to half its original value? (c) If the rock mineral wool is instead installed on the outer surface, is the thickness required the same?