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Mo d el No . M E- 8 5 98
(eq. 4)
where dF/dt is the rate of increasing force, g = 9.81 N/kg, and ρ = 1000 kg/m
Water-flow Measurement Method 4: Stopwatch
In this method, you measure a volume and elapsed time to determine the average flow. Do this
before collecting pressure data.
Other Parts Required or Recommended
Stopwatch
Water Reservoir (or other graduated cylinder)
If are using the model ME-8594 Water Reservoir, or similar container, a separate
graduated cylinder is not necessary; simply note the initial and final volumes in the
reservoir.
1.
Start with the catch basin empty.
2.
Start the stopwatch and open the clamp to start water flow.
3.
After a measurable amount of water has flowed through, stop the stopwatch and
close the clamp.
4.
Measure the volume of water that flowed out of (or into) the apparatus.
5.
Calculate the average flow rate:
(eq. 5)
where ΔV is the volume of water and Δt is the elapsed time.
Typically the flow rate varies with the level of water in the reservoir. To keep the flow
rate close to constant, make the pressure measurements with the water level approxi-
mately the same as it was for the flow rate measurement.
Appendix C: Constants
Density of dry air at 20 °C and 1 atm:
Density of water:
Wide cross-sectional area of channel:
Narrow cross-sectional area of channel:
®
dF
1
------ -
----- -
R
=
dt
gρ
SE-8702B
ME-8594
ΔV Δt
⁄
R
=
3
1.2 kg/m
3
1000 kg/m
2
1.99 cm
2
0.452 cm
A pp e nd i x C : Co ns t an t s
3
.
13
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