solution

To save on electricity costs, a town water supply system uses gravity-driven flow from five large storage tanks during the day and then refills these tanks from 10 PM to 6AM at a cheaper night rate of 7?/kWh. The total resupplied needed each night varies from 5 E5 to 2 E6 gal, with no more than 5 E5 gallons to any one tank. Tank elevations vary from 40 to 100 ft. A single constant-speed pump, drawing from a large groundwater aquifer and valved into five different cast-iron tank supply lines, does this job. Distances from the pump to the five tanks vary more or less evenly from 1 to 3 mi. Each line averages one elbow every 100 ft and has four butterfly valves which can be controlled at any desirable angle. Select a suitable pump family from one of the six data sets in this chapter (See Figures and Tables attached at the end). Assume ideal similarity (no Reynolds-number or pump roughness effects). The goal is to determine pump and pipelines sizes which achieve minimum total cost over a 5-year period. Some suggested cost data are:

1.Pump and motor: $2500 plus $1500 per inch of pipe size

2.Valves: $100 plus $100 per inch of pipe size

3.Pipelines: 50? per inch of diameter per foot of length

Since the flow and elevation parameters vary considerably, a random daily variation within the specified ranges might give a realistic approach

Figure 1: Nondimensional plot of the pump performance data from (a) basic casing with three impeller sizes; (b) 20 percent larger casing with three larger impellers at slower speed

Supporting figures for Figure 1

Figure 2: Centrifugal Data for Centrifugal Pump

Figure 3: Performance Data for a family of centrifugal pump impellers.

able 1: 14.62-in-diameter centrifugal water pump at 2134 r/minTable 2: 18-in-diameter centrifugal pump running at 880 r/min

Table 3: 6.85-in-pump running at 3500r/min