A 200-ft-long section of a steam pipe whose outer diameter is 4 in passes through an open space at 50°F. The average temperature of the outer surface of the pipe is measured to be 280°F, and the average heat transfer coefficient on that surface is determined to be 6?Btu/h•ft2•°F. Determine (a) the rate of heat loss from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace having an efficiency of 86 percent and the price of natural gas is $1.10/therm (1 therm = 100,000 Btu).

Question

What will be an ideal response?

Answer 1

A 200-ft long section of a steam pipe passes through an open space at a specified temperature. The rate of heat loss from the steam pipe and the annual cost of this energy lost are to be determined.

Assumptions 1 Steady operating conditions exist. 2 Heat transfer by radiation is disregarded. 3 The convection heat transfer coefficient is constant and uniform over the surface.

Analysis (a) The rate of heat loss from the steam pipe is



(b) The amount of heat loss per year is



The amount of gas consumption per year in the furnace that has an efficiency of 86% is



Then the annual cost of the energy lost becomes