Cloud Chamber Cooling Analysis

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Cloud Chamber Cooling Analysis

• Heather B. Brown
• December 4, 2006

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Motivation

• From experience, we know that the bottom of the
  chamber must be cooled to a rather low
  temperature, generally as cold or colder than dry
  ice (-70 deg C).
• Dry ice is easy to acquire but entails
  maintenance every few hours and does not provide
  a flat surface.
• Since chambers have been made successfully and
  consistently with dry ice, the next step is to
  devise a perpetual cooling system to provide
  constant entertainment.
• The continuous cooling would ideally be provided
  indirectly through an electrical outlet.

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Thermoelectric Module (TEM)How they work

• Thermoelectric modules are solid state devices
  (no moving parts) that convert electrical energy
  into a temperature gradient. They are inefficient
  and little power is produced.
• They are typically 1.5 inches square (40mm x
  40mm) or smaller and approximately 0.25 inches
  (4mm) thick.

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Initial heat sinks used to cool the ceramic hot
side

• The hot side was the motivation for heat sinks.
• Theoretically, with a Delta T of 70 deg Celcius,
  cooling the hot side would further cool the cold
  side.
• The heat sinks are the same length and width as
  the TEMs.
• Ice water was circulated through the heat sinks
  as Figure 1 shows to cool the ceramic hot side of
  TEMs.
• Result These heat sinks did not have enough
  cooling power needed for the TEMs (cool side
  reached maximum -11 deg C).

Figure 1. Schematic setup with TEMs
Figure 2. Top and bottom views of heat sink.
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Heat Sink / Fan Design

• A CPU cooling fan was purchased from Frys to
  cool TEMs.
• This heat sink / fan combo consumes 2.4W of power
  and has optimum operation at 12V.
• Its dimensions are 83 X 73 X 61 mm.
• Result This attempt at cooling the ceramic hot
  side was the worst. The lowest temperature
  reached with the TEM was 15 deg C.

Figure 3. Upside down view of the Copper X478.
The TEM hot side sits on the copper side.
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Solid Copper Heat Sink Design

• Purchased from the same company as the TEMs so we
  were hoping for better results.
• Was hooked up directly to our water pump with
  rubber tubing.
• The dimensions of this all copper liquid heat
  exchanger are 89 X 64 X 12.7 mm.
• This was the first all copper heat sink we used.
• Result It did not transfer the cold from ice
  water as well as we needed. The minimum
  temperature reached with the TEM cold side was 5
  deg C. This was the end of our TEM usage.

Figure 4. (Top) All copper constructed liquid
heat exchanger made by the same company that sold
us the TEMs. (Right) Yay! No more TEMs!
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Liquid Nitrogen Cooling

• Purchased from MSC distributors, this all
  aluminum, 2-fin system provides better heat
  exchanging than copper.
• The recommended liquid to be used with this
  plate is ethyline glycol (typical antifreeze for
  a car or CPU).
• Dimensions are 279.4 X 198.12 X 19.05 mm.
• We glued polyethyline tubing into the fittings
  and tested ways to create a flow of liquid
  nitrogen through the cold plate.
• This was by far the most expensive item purchased
  for the cooling team.

Figure 5. All aluminum cold plate used with
liquid nitrogen testing.
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Liquid Nitro ExperimentCompetency

• We achieved the lowest temperatures experienced
  yet (avg. -18 deg C) in various placements of the
  cold plate (i.e. the plate exhibits the same
  behavior in many different positions).

Figure 7. Horizontal transfer of liquid

• With a direct flow of liquid nitrogen into the
  plate, the temperature went below -70 deg C
  (thermometers measuring limit).

Figure 6. Vertical transfer of liquid
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Liquid Nitro Experiment Incopetency

• Proper fittings and funnel would reduce or
  eliminate the leakage found at the unification of
  tubing and cold plate and provide a safer method
  of transferring the liquid nitrogen.
• We now understand that the cold plate must be
  cooled to roughly -60 deg C before trying to
  circulate the liquid nitrogen due to the plate
  being too warm and rejecting the liquid.
• The pump used was made for 3 V but needs at least
  20 V to work constantly with the liquid.

Figure 8. Unsafe method of transferring liquid
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Conclusions

• TEMs are completely incapable of providing a low
  enough temperature.
• Liquid Nitrogen was definitely the best method
  used so far because of the temperature results
  attained.
• A more independent circulating system would need
  to be devised to continue using the liquid
  nitrogen. A manufactured chiller would be the
  best idea.

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Future Plans

• www.thermo.com has many types of chillers,
  circulators and baths.
• One example of a circulator/bath combo is the
  Neslab ULT-80 and it operates from -80C to 10C.
• Ultimately, a similar apparatus would be the most
  effective for achieving our desired temperatures
  constantly.

Figure 9. Neslab ULT-80 Work area (L X W X D) in
cm is 13.7 X 17.8 X 24.1 weighs 336 lbs. 4
gallon bath cooling capacity 250W at -70C costs
13,533 Tax