4
$\begingroup$

I'm planning to build a small cloud chamber.

The design is the usual: alcohol evaporates at the top by gently heating it with a thin wire and small current. The vapour sinks to the bottom of the chamber, where the temperature is significantly lower than at the top, and causes the vapour to super-cool. Ion tracks caused by fast moving particles can be observed as mist tracks.

My question is about the bottom plate temperature.

The usual design uses a (near) room temperature solvent and very cold bottom plate to achieve a big temperature gradient.

Could a cloud chamber be constructed that would use just a slightly cold bottom plate, and a more aggressively heated liquid? I'm thinking about ethanol or isopropyl alcohol evaporated at 60°C, and a bottom plate temperature at maybe only 0°C

Could this work? Is it just the temperature gradient, or the temperature itself is important?

$\endgroup$
4
  • $\begingroup$ I expect that for supercooling it is the temperature itself, not the gradient.en.wikipedia.org/wiki/Supercooling $\endgroup$
    – anna v
    Commented May 22, 2014 at 10:40
  • $\begingroup$ That's not what's going on in a chamber. The alcohol is always below it's boiling point and always above it's freezing point in both "traditional" dry-ice or peltier cooled chambers and the "warm chamber" described in the question. The chamber works by cooling the air with alcohol vapour until it is too much alcohol vapour in it. My question is that is the low temperature is a requirement for the tracks to form and be seen, or just the gradient is enough. If it's not enough then why. $\endgroup$
    – netom
    Commented May 22, 2014 at 10:49
  • $\begingroup$ isn't it a phase transition that is not happening that the passage of the ionizing particle seeds? The phase diagrams are with temperature not gradients $\endgroup$
    – anna v
    Commented May 22, 2014 at 10:55
  • $\begingroup$ Yes, but you can get alcohol vapour into the air below the boiling point, and also can get alcohol mist. The phase transition happens not because the temperature goes from above boiling point down below that, but because the air gets supersaturated. I actually did an experiment with this, and you can get alcohol mist by evaporating alcohol at about 20-30°C and then cooling the air / vapour mixture to something like 0°C. (No tracks though, it was just a quick experiment) $\endgroup$
    – netom
    Commented May 22, 2014 at 15:04

3 Answers 3

1
$\begingroup$

This is a generic phase diagram :

phase diagram

I looked up the construction of a demonstration for classes cloud chamber using alcohol. For the air/alcohol gas line 3, constant pressure, change in temperature is where you want to work for your cloud chamber. Cooling it without condensation. The gradient of temperature in your chamber will define the thickness over the iced bottom where supersaturation can be maintained. So your choice of alcohol should depend on how slowly the phase diagram changes with temperature as to have a larger distance from the cold plate where the vapors will be supersaturated and tracks can form.

I do not think it is the gradient in the chamber that is decisive, but the one from the triple point to the vapor phase in line 3.The hot on top is to generate the vapour phase in the chamber. It will all depend on the phase diagram of your specific choice for vapor.

$\endgroup$
5
  • $\begingroup$ Thank you very much, I have to contemplate on this for a moment :) $\endgroup$
    – netom
    Commented May 24, 2014 at 7:07
  • $\begingroup$ Ok, I still have some questions: 1: "The gradient of temperature in your chamber will define the thickness .. where supersaturation can be maintained". Why is it so? 2: Do you suggest that I need an alcohol with a slowly changing phase diagram in order to create this large gradient (to have more "temperature space" to work with)? $\endgroup$
    – netom
    Commented Jun 5, 2014 at 5:57
  • $\begingroup$ Yes, more or less. How far the cold from the floor can penetrate into the chamber depends on the composition of the gas means actually how slowly the heat from the chamber is transferred to the cold floor. If the heat flow is slow enough then a larger part of the bottom will stay cool enough to be supersaturated. $\endgroup$
    – anna v
    Commented Jun 5, 2014 at 8:45
  • $\begingroup$ So cool air-alcohol mixture is easier to supersaturate? This is the point of the low temperature? If it is, then why? $\endgroup$
    – netom
    Commented Jun 6, 2014 at 12:02
  • $\begingroup$ Yes, you get alcohol fumes on the top, which do not condense on the cool bottom until there is a seed to condense around. Like the tracks of jets in the sky $\endgroup$
    – anna v
    Commented Jun 6, 2014 at 13:29
1
$\begingroup$

Hi please refer to this article and related literature:

Yoshinaga, K., Kubota, M., & Kamata, M. (2014). Simple cloud chambers using a freezing mixture of ice and cooking salt. Physics Education, 50, 23-27.

I am not in a position to comment about the underlying physics and probably cloud chambers with lower bottom temperatures work better. Anyways, yesterday I managed to observe clearly tracks for around 20 minutes using a frozen mixture of water and salt encased an aluminum jar while the top was heated with hot water. I measured previously the temperature of the jar and it was beteeen -16 and -18 C. There are also commercial (educational) prototypes of cloud chambers that work that way. For the vapor, I used, generously, 2-propanol 99.9%.

Hope this helps regards

$\endgroup$
1
  • $\begingroup$ That is an interesting article, thank you. $\endgroup$
    – netom
    Commented Feb 17, 2021 at 9:25
0
$\begingroup$

Yes, the original cloud chamber user water to form the supersaturated vapour, and ethylene glycol has also been used. Alcohol just happens to be very convenient as it's easy to get a lot of vapour and it doesn't freeze at the the chamber operating temperatures.

$\endgroup$
1
  • $\begingroup$ And of course bubble-chambers run in super-heated mode (achieved by dropping the pressure rather than changing the temperature, but still) with a variety of working fluids. $\endgroup$ Commented May 22, 2014 at 14:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.