Finding size of motor needed for pump

[d.vaughn]

1. Pump used to deliver water at 20oC from a pond to center of large field located 100 m from the pond. The desired pump is expected to deliver a max flow rate of 380 L/min through 107 m of a 6 cm steel pipe having an equivalent sand roughness of 0.01mm. Water level in pond during irrigation season is 10m and ground elevation of field is 15m.
(b) using the efficiency of the pump under operating conditions, calculate the size of motor in kilowatts that must be used to drive pump
(c) what is the maximum elevation above the pond that the pump can be located?

Homework Equations

W = ρgQ(hp)/η
found efficiency on graph to be 50%
found hp and Q in part a to be hp = 5.26m and Q = 0.00106m3/s

The Attempt at a Solution

(b) W = (9.79E3)(0.00106 m3/s)(5.26)/0.5 = 0.109kW
(c) 109 W = (9.79E3)(0.00106 m3/s)(hp)
hp = 10.5m
it seems to be that 0.109 kW is really small power... did I do something wrong with the calculation? Thanks!

 

[KataKoniK]

Your calculations appear to be correct. However, it is important to note that the pump is only expected to deliver a maximum flow rate of 380 L/min, which is equivalent to 0.0063 m3/s. This means that the pump will likely be operating at a lower flow rate most of the time, which may require a smaller motor size. Additionally, the efficiency of the pump may vary under different operating conditions, so it is important to consider this when selecting a motor size. As for the maximum elevation above the pond, it will depend on the head loss in the pipe and the elevation difference between the pond and the pump. It is recommended to consult with a hydraulic engineer to determine the exact location and motor size for the pump.