|
OBJECTIVES:
You will learn the basic types of pumps and how they
work in terms of pressure, velocity, and elevation differences.
You will build two examples of gravity-driven water pumps.
STEPS TO FOLLOW:
 |
Review the information in the background section.
We will talk about data collection, and we will
be computing flow rates and velocities.
|
 |
Carefully make small holes in the
cylinder (middle - where the diameter is
constant) part of the plastic bottle.
If you are only using one, we recommend
1 hole about 1.5" down from the top
of the cylinder (about 6" from the top of
the bottle) and a second below it about 1"
above the bottom part of the cylinder (about
3.5" from the bottom of the bottle). Cover
holes with a piece of tape. Add water to the top
of the cylinder part. If several bottles will be
used, try different hole placements!.
|
 |
Prepare the data collection sheet. Take all
necessary measurements.
You will need:
Diameter of cylinder. (You can get this by
wrapping the tape measure tightly around
the cylinder and reading the circumference.
This is equal to
p
times the diameter.)
Diameter of the hole(s).
Distance from each hole to the fluid surface.
|
 |
Have one person hold the cylinder under
one of the holes and carefully pull down the tape
to get a clear flow out of the hole as a second person
turns on the stop watch as the flow starts (this may
take some practice!). Time the flow for 10 to 20
seconds - less for bigger holes, more for smaller
holes. Push the tape back up to stop the flow and
stop the watch at the same time.
|
| |
MATERIALS:
- One or More 2 Liter Plastic Bottles
- Big Flat Pan with Sides
- Small Cylinder
- Duct Tape
- Tape Measure
- Stop Watch
- Awl or Another Sharp Pointed Tool
- Data Chart
- Calculator
 |
Record the time in the proper column.
Measure the height of the water in the cylinder and
record that on your data sheet. Be careful to measure
from the inside bottom of the cylinder to the fluid
surface. Repeat steps 4 and 5 at least 2 more times
for a total of at least 3 trials per hole. Be sure to pour
the water back into the bottle to the same
fluid surface height for each trial for best results. Repeat these
steps for all other holes, recording the data as you
go. Follow this link
for a sample data sheet.
|
 |
In an area away from the bottles and the water,
start calculating the values on the data sheet to get
the flow rates and then the velocity of the flow at
each hole. The flow rate, Q, is the volume of fluid
in the cylinder divided by the time in inches cubed
per second. Take the average of the trials to use for
the velocity calculation. The average is the sum total
of the trial values divided by the number of trials.
This averaged flow rate is divided by the area of
the hole to get the fluid velocity at that hole.
|
 |
Discuss your results with others. The
lower the hole is on the bottle, the higher the fluid
velocity should be. How do your results compare?
|
 |
If you would like to check your results
with the theory (and scientists prefer to do this),
you can calculate the ideal velocity (meaning under
perfect conditions) from the Bernoulli equation.
The pressures are both atmospheric, and the
velocity in the bottle is zero, so the velocity at
the hole is the square root of 2 times g (gravity) times
the height of the fluid above the hole. Your results
will likely be less than the ideal values. There are 2
reasons for this. One, it is very hard to be catch all
of the fluid consistently every time. That's why we
take several data trials at each hole to get an average
value. However, there will still be some error. The
major reason for the difference is that the theory assumes
that the diameter of the container is much, much larger
than the diameter of the hole, and that the height of
the fluid is much greater than the diameter of the
container. Our example set-up isn't large enough to
satisfy these constraints, but we can obtain reasonable results
for learning about pumps and data collection.
|
|
