The purpose of this experiment is to evaluate pump performance based on changes in flow rate. The optimum flow rate for the pump can also be determined.
At a fixed speed, pressure difference (pump head) and brake torque in the pump are measured as the flow rate is decreased at predetermined intervals of 2 gpm. The pump's power input, power output, and efficiency are calculated based on the experimental values.
The experiment is carried out successfully, and it is shown that as the pump's power input is increased, its power output increased to a maximum, then fell. The flow rate at which this drop begins is about 22 gpm. The maximum efficiency for the pump seen during the experiment is 33.9 %, which occurred at 28 gpm.
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Theory.
A basic centripetal pump converts fluid velocity into pressure energy by utilizing three components: an inlet duct, an impeller, and a volute. Fluid enters through the inlet duct, and is projected outward as it hits the impeller, which is a series of rotating blades driven by a motor and shaft. The fluid is sent through the pump case located around the impeller, and into the volute (outlet chamber). The increasing area of the volute allows the kinetic energy of the fluid to be converted into pressure energy.
For this experiment, the power supplied to the pump (Pin) is given by.
Pin = TN.
where T is the brake torque (ft-lbf) and N is the shaft speed (RPM). To express the power in terms of horsepower,.
Pin = (2/33,000) TN [HP].
The pressure difference (Äp) seen by the pump is calculated from.
Äp = pout - pin .
The suction pressure (pin) is measured in inches of water, and pout is measured in psig. The pressure difference will be calculated in psig as well.
The power output of the pump can be found by.
Pout = Q Äp.
Flow rate is measured in gallons per minute. However, to convert to horsepower,.
1 HP = 550 ft-lbf/sec.
Results.
Data:.
Shaft speed: 1600 RPM.
Q (gpm) pin (in H2O) pout (psig) T (in-lbf) Äp (psig) Pin (HP) Pout (HP) z (%).