Concept explainers
An oil pump is drawing 44 kW of electric power while pumping oil with ρ = 860 kg/m3 at a rate of 0.1 m3/s. The inlet and outlet diameters of the pipe are 8 cm and 12 cm, respectively. If the pressure rise of oil in the pump is measured to be 500 kPa and the motor efficiency is 90 percent, determine the
FIGURE P2–73
The mechanical efficiency of the pump.
Answer to Problem 73P
The mechanical efficiency of the pump is
Explanation of Solution
Calculate the rate at which mechanical energy of fluid supplied to the pump.
Here, the mechanical energy of water inlet and outlet are
Calculate the velocity of the pump at inlet.
Here, diameter of the pipe at inlet is
Calculate the velocity of the pump at exit.
Here, diameter of the pipe at exit is
Calculate the useful pumping power.
Calculate the shaft power.
Here, the efficiency of motor is
Calculate the mechanical efficiency of the pump.
Conclusion:
Substitute
Substitute
Substitute
Substitute 36.3 kW for
Substitute 0.90 for
Substitute 39.6 kW for
Thus, the mechanical efficiency of the pump is
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