Download Liquid_Nitrogen_Session2

Thermal Dynamics
Mauricio Vazquez
Alberto Servin
Virgil Alameda
Desiree Seales
Jessica Sodhi
Tuesday the 17 of 2007 our group worked with liquid nitrogen (LN2) and
observed the different outcomes depended on the cup holding the LN2. We used three
different types of cups (plastic, Styrofoam, and vacuum) to hold the nitrogen, which were
in different environments such as ice baths, with a lid or simply on a table. We learned
that after a minute or so, the liquid nitrogen evaporated out of the plastic cup in the ice
bath (filled with water) and another plastic cup in ice without water in the ice. On the
other hand, the vacuum cup kept the liquid nitrogen longer than the other cups.
The second experiment we conducted had to do with vapor pressure and the fact
that it can change the temperature of liquid. To prove this we used a special vacuum that
sucked oxygen out of the chamber sealing it tight. When we placed a Styrofoam cup
filled with water inside it began to bubble as the oxygen left the chamber. Once we
removed the cup, we compared its temperature and the water was colder than another cup
of water at room temperature. Next we placed a cup filled with liquid nitrogen in the
vacuum and as oxygen left the confined area, the nitrogen froze. Immediately after
removing the vacuum cap, oxygen rushed back into the frozen nitrogen cup and instantly
turned it back into a liquid.
In conclusion, we learned that boiling liquid nitrogen stays at the same
temperature (77 Kelvin). We also learned from the experiment that plastic (cups) is a
good conductor for liquid nitrogen. So plastic is good for making heat (heating things
up). Styrofoam is good for insulating liquid nitrogen. What this shows is that it keeps
things at its temperature. An example how Styrofoam is used (for insulating) in a real life
situation is when drinking hot liquids such as coffee. It keeps the heat inside to prevent
burning. Overall, we learned about the several properties of liquid nitrogen and how it
can be affected by various types of temperatures.
In this lab we also learned about current, voltage, and resistance. Current is the
flow of electrons. To measure current you must divide charge over time which translates
to amps equal coulombs, the number of electrons at an internal time, over seconds.
Current = (Delta) Q
------------(Delta) T
Amp = coulombs
-------------seconds
Next we learned about voltage. Volts are units of electricity. Voltage is the amount
of electricity in something. Electrical potential is the amount of energy needed to have a
change in an electrical field.
e- e- e- e- e-----------------Electrical field {
e-< opposites attract
-----------------p+ p+ p+ p+
The last thing we learned is resistance in metal wires. Resistance is used to impede
the flow of electrons through wires. Resistors are used to create resistance. Ohms law,
which is V = IR is energy stored in a resistor. Ohms are signaled by the omega sign.
We then learned how to run the glass Dewar and also learned how to get the
liquid nitrogen and liquid helium into it. First we turned on the lamp and tested for leaks
in the liquid helium line. Then we emptied out the bolometer with the turbo pump. We
had to fill one of spaces between glass Dewars with liquid nitrogen and we let it sit for
about 30 minutes. Using a transfer tube we put the liquid helium through the rotator rig
into the glass Dewar. We put the helium pump on the liquid helium to reduce its
temperature and to allow for easy transfer. We then used a vacuum to get rid of the water
vapor and made sure the cooling water was on. Then we took measurements of the
pressure and temperature.
From doing this experiment, we learned how to use a glass Dewar and turbo
pump. We found out that turbo pumps work by having blades that spin the air out. We
also learned that vacuums are good ways to thermally isolate things. We also learned that
Tacions isolation was a way to check the level of helium in a tank. The isolation effect
which can be felt as vibration depends on the geometry of the probe. When isolation
increases that means that you are on the surface of the helium in the tank, thus giving you
the level of helium in the tank.