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T h e
D e m o n s t r a t i o n
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(1) |
Give a brief (3-minute) overview of the need to
develop renewable energy sources and the potential of ocean waves.
A chalkboard sketch of Figure 3 of this guide might help the
students better understand the oscillating water column process.
Also pose the following problem to the students: "How can the
reversing air flow of the oscillating water column be converted to
one-way rotation of a generator shaft?" Each team should come up
with its best solution while waiting for (and after) its turn to
watch the demonstration. |
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(2) |
Fill the bucket or sink to within 2-3 inches of
the top, if this hasn’t already been done. |
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(3) |
Demonstrate to each team that as the bottomless bottle is moved up
and down, the turbine "whistles." The students should be given a
chance to look down into the whistle to see the turbine blades
reversing direction at the top and bottom of each stroke
(Figure7). Ask them to speculate on the negative consequences of
this direction reversal ("interrupted or uneven flow of power,"
"high stress on the turbine |
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Figure7 |
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(4) |
Once all teams have seen the first part of the
demonstration, each one should describe its best solution to the
direction reversal problem. Ask the teacher to list these on the
board. Some teams may suggest complex gear mechanisms or hinged
turbine blades. Others may say it can’t be solved. Any team
suggesting a one-way valve will be rewarded with the satisfaction
of seeing their idea work in actual practice! |
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(5) |
While going over the list of solutions on the
board, emphasise that engineers are creative problem solvers, and
that part of the engineering process is to find solutions that are
"elegant but simple." A gear mechanism for the oscillating water
column may be elegant, but is more complex than other solutions,
involving many moving parts requiring lubrication and eventual
replacement when they wear out. Hinged turbine blades are subject
to high stress as they flip at the end of each stroke—the failure
of a single blade may require disassembly of the entire turbine to
replace the failed blade. In addition to being functional, a
well-engineered design should also be reliable (long-term
durability), economical (both to build and maintain) and practical
(ease of repair or replacement) |
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(6) |
A one-way flap valve is a better solution
because it has fewer moving parts (only the flap valve hinge, as
opposed to multiple gears or turbine blade hinges), can use the
standard turbine design without requiring new manufacturing
equipment (£££!), and is totally removed from the power train for
ease of repair or replacement. |
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(7) |
Remove the strip of tape that was covering the flap valve window,
and repeat the demonstration of Step (3), so that each team of
students can verify that indeed, the turbine blades spin in one
direction regardless of whether the bottomless bottle is moving up
or down (Figure 8). |
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Suction |
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Figure 8 |
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Compression |
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(8) |
If time permits, you can explain that it is the flywheel inertia
of the turbine that keeps it spinning while air is being drawn in
through the flap valve. Can the students think of a valve system
that would direct air through the turbine on both strokes? One
possible solution is shown in Figure 9 |
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