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Creating
a Liquid Oxygen Dropper
Problem
number one: the
stopper condensed and fell out of the tube
Problem
number two: drops leaked off of the sides of the cork
For
this project we originally intended to create liquid oxygen and photograph its
splashes. We hoped to obtain
pictures of a drop evaporating off of a room-temperature surface.
We also intended to splash liquid oxygen drops into an insulated
container filled with liquid oxygen. Furthermore,
we had planned on studying its paramagnetic properties by manipulating the
splash with magnets. For example,
by placing a magnet underneath the surface we were going to splash on and seeing
how its acceleration increases. We
had also planned on placing magnets around the splash to manipulate its fall.
We
started off by creating liquid oxygen. In
order to make splashes we had to come up with a method that allowed us to drop a
liquid at an extremely low temperature.
To
create liquid oxygen we used liquid nitrogen to cool oxygen gas to a low enough
temperature so that it would condense.
Using a ring stand and clamps we suspended a glass test tube into a dewar
filled with liquid nitrogen. The
liquid nitrogen surrounded the tube and thus cooled the air inside the tube.
We had to lower the tube into the liquid nitrogen fairly slowly so that
it would not crack from the extremely low temperature.
We put a rubber stopper that had two holes into a glass test tube.
Through these holes we stuck two metal tubes, one shorter than the other.
We connected the longer metal tube to an oxygen gas pump using a plastic
tube. The oxygen was pumped into the glass tube and condensed into
liquid as it entered the cold environment.
Excess oxygen left through the smaller metal tube.
We could feel the cold air escaping through it.
In less than half an hour we were able to fill the tube with liquid
oxygen. As expected, it was an
interesting shade of blue and displayed paramagnetic properties.
Diagram of setup for creating liquid oxygen:
For more information, see our Video section.
We
had to design a liquid oxygen dropper that created drops at a slow, steady pace.
We took a glass tube that was open on both ends and stuck
a rubber stopper with one hole into one end of the tube.
Into the hole we placed a glass, pipette-like tube with that decreased to
an almost capillary thickness. We
were able to fill the glass tube up with liquid oxygen and have it drop through
the glass pipette. However, the
oxygen would evaporate quickly, and a lot of condensation would form on the
sides of the tube. To fix this
problem we took a block of dense foam and cut a hole into its center.
We stuck the glass tube through the foam in order to insulate the oxygen
while it was in the tube. We also
put glass wool into the pipette in order to slow the rate of the drop.
We tested the rate with water until we got it to the desired drop rate.
We had to pre-cool the dropper with liquid nitrogen
so that the liquid
oxygen would not evaporate, but flow through the dropper.
We
tested the test tube with liquid nitrogen to see how it would function with
liquids at very low temperatures. The
foam insulated the liquid nitrogen quite well. However, after a few minutes the stopper fell out
because it shrank due to the low temperature.
In order to fix this problem we did two things.
We used a cork stopper instead of a rubber one because the cork would
shrink less and we also made a wire net to secure the stopper.
We drilled a hole into a cork stopper for the pipette.
We also decided to use a shorter glass pipette so that it would take less
time to cool down.
PROBLEM
NUMBER TWO: drops leaked off of the sides of the cork
We continued by testing our new dropper with liquid nitrogen.
Luckily, the cork did not fall out.
We started getting drops, but soon realized that they were not out of the
dropper. Rather, when the cork
contracted it allowed for extra space between the cork and the glass tube and
thus the liquid nitrogen leaked through. The
drops that we were getting were running off of the side of the cork and dropper,
rather than from the actual pipette itself.
As a result the drops were very unregulated.
In order to resolve this problem, we took another block of foam, cut a
slit through it and stuck the pipette through it so that it was touching the
cork. This way, any liquid
nitrogen/oxygen that did leak through the sides was absorbed by the foam block.
We also made sure that the cork was more firmly pushed into the tube.
Diagram of dropper:
Once we finished creating our dropper, we raised it above a surface using a ring stand and two round clamps that held it on the top and bottom. We taped a small photogate to a clamp right below the dropper for our timing. We used a computer as an intervalometer to control the time delay of our flashes. The computer5 received an input from the photogate as the drop passed through it, thus breaking the beam of light between its two ends. The processor/computer is triggered by the input signal given by the photogate. The computer generates a time interval, and sends an output signal through the I/O parallel-port interface, which triggered the flashes at the desired time delay. The software control was through the Intervalometer program4. We placed our flash behind an opaque white sheet of plastic propped up with blocks of wood. This allowed for greater detail to be seen in the splash. The flash was approximately 1 meter from the dropper. We placed the camera on a tripod fairly close to the dropper (about .4 m). We took shots from different angles: eye level and a bird’s eye view. We learned about how to use a digital motion camera and were able to capture some footage. Later we also used a Nikon D1 with a 55mm Micro-Nikkor lens using PK-1 extension ring to get better resolution still photos, but these photos did not turn out well enough for analysis or presentation.
Diagram of I/O interface5:
Our
flash went off once the drop passed through the photogate because the beam of
light through the photogate was broken. We
adjusted our timing by calculating the time of that the drop would fall assuming
constant acceleration and an initial velocity of zero.
The dropper was placed ~10 cm above the surface where the oxygen would
splash, and thus we calculated a 100ms time delay.
We wanted the flash to go off exactly when the drop hit the surface so
that we could obtain the picture of a splash.
Diagram of overall setup:
Once
we had our equipment set up, we continued by creating different methods of
splashing and surfaces on which to splash our liquid oxygen: water, clear
graduated cylinder, base of the ring stand, and pipettes.
We
started off by splashing into water. However,
since we planned to be splashing liquid oxygen into liquid oxygen later on in
the project, we took a Styrofoam block and cut two wells into it to place our
glass bowl and watch glass into. We hoped that the Styrofoam would insulate the liquid oxygen
some so that it would not evaporate as quickly.
Once we got that to work we started splashing liquid nitrogen into water.
We soon realized that the drops rolled off, as well as gave off a lot of
vapor as some evaporated. We tried
to film this phenomenon from different angles.
We continually blew on the water so that the vapor would not hide the
splash. We once tried putting blue
food coloring in the water to give a different visual effect.
We also took footage from the side as well as from the top.
However, once we looked over it, we didn’t find it very interesting.
Furthermore, the drops didn’t really create splashes; instead, they
simply rolled off the top. Sometimes
our flash did not work properly because the flow of drops was too fast.
We tried to splash into a tall clear graduated cylinder with an
approximate radius of 2 cm. We
practiced with water to once again adjust our timing.
We next proceeded to using liquid nitrogen.
However, we soon realized that again the drops did not sink but rather
rolled off to the water to the sides of the cylinder.
Then it slowly evaporated creating a lot of vapor that once again
hindered the view.
Lastly we tried simply dropping on the base of the ring stand.
We used a still digital camera and tried to obtain some pictures. However, we realized that the drops simply rolled off rather
than splashing. We used liquid
oxygen this time to drop between two magnets.
Even though we could see that the drops revolved around the magnets due
to their paramagnetic property, the pictures did not turn out well as well as
there was nothing to analyze.
We could not get our dropper to do what we intended.
We could not slow the rate of the drops to a desired pace, neither could
we make if very constant. Furthermore,
the drops weren’t large enough to even create a splash but rather rolled off
to the sides. To solve these
problems, we tried using pipettes made out of both plastic and glass.
However, these did not work because as soon as the pipette sucked up
liquid nitrogen, the liquid nitrogen would evaporate slightly when removed from
the dewar, and thus create pressure inside the pipette which forced the liquid
out. As a result we could not keep
any fluids with any very low boiling points in the pipette because they would
evacuate as soon as exposed to a room temperature environment.
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