MECHANICS of FLUIDS LABORATORY - Mechanical Engineering

∆H = H 2
- H 1
= p 2
ρg + V 2 2
2g + z 2
p
- ⎛ 1
⎞
⎝ ρg + V 1 2
2g + z 1⎠
The dimension of the head H is L (ft or m). The
power imparted to the liquid is calculated with
the steady flow energy equation applied from
section 1 to 2:
- dW
dt
p 2
= m· g
⎡⎛
⎞
⎣⎝ ρg + V 2 2
2g + z 2
⎠
-
⎛
⎝
p 1
ρg + V 1 2
In terms of total head H, we have
⎞⎤
2g + z 1⎠
⎦
- dW
dt = m· g (H 2
- H 1
) = m· g ∆H (18.2)
The efficiency is determined with
η = dW/dt
dW a
/dt
(18.3)
Experimental Method
The experimental technique used in obtaining
data depends on the desired method of expressing
performance characteristics. For this experiment,
data are taken on only one impeller-casing-motor
combination. One data point is first taken at a
certain valve setting and at a preselected
rotational speed. The valve setting would then be
changed and the speed control on the motor (not
shown in Figure 18.1) is adjusted if necessary so
that the rotational speed remains constant, and
the next set of data are obtained. This procedure
is continued until 6 data points are obtained for
one rotational speed.
Next, the rotational speed is changed and
the procedure is repeated. Four rotational speeds
should be used, and at least 6 data points per
rotational speed should be obtained.
v-notch weir
return
valve
control panel
and gages
pressure
tap
1 nominal
schedule 40
PVC pipe
•
sump tank
inlet
z 2
pressure
tap
•
valve
motor
motor
shaft
pump
z 1
1-1/2 nominal
schedule 40
PVC pipe
FIGURE 18.1. Centrifugal pump testing setup.
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