Contemporary Engineering Economics 6th Edition by Chan Park

تمرين 49

All industrial facilities have a network of piping that carries water or other liquids. According to a U.S. Department of Energy study 3 , 16% of a typical facility's electricity costs are for its pumping systems. Suppose that you are considering a pumping facility having 10,000 ft to carry 600 gpm of water continuously to a storage tank. The general equation for estimating fractional pumping costs is

where the friction factor (based on the pipe roughness), pipe diameter, and the Reynolds number can be obtained from an engineering handbook. For most applications, the value of this friction factor will be between 0.015 and 0.0225.
(a) Using clean iron and 6-inch steel pipe (schedule 40) for pumping 70°F water, an electricity cost of $0.05/kWh, 8,760 operating hours annually, and combined pump and motor efficiency of 70%, determine the pumping cost.
(b) With the same condition, determine the pumping cost with a 10-inch pipe.
(c) Find the current price of steel and determine the optimal size of pipe, assuming that the pumping operation would last 15 years and the savage value of the pipe at 10% of the initial investment. Assume also a discount rate of 12%.