Vacuum Chamber Demo: Investigating Temperature & Humidity Changes

In summary, the conversation was about a demonstration using a vacuum pump and chamber, where a burning candle was placed inside. This resulted in the formation of a cloud for a few seconds before disappearing due to the decrease in pressure. The discussion also touched on the decrease in relative humidity and the role of temperature and dew point in cloud formation. It was also mentioned that the Kestrel 4000 instrument was used to measure these changes. There was also a mention of a similar experiment done with a soda bottle in school. The conversation ends with a question about whether the cloud formation was due to cloud condensation or just smoke from the candle.
  • #1
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I did a demo for my students, using a simple vacuum pump and a vacuum chamber. I put a burning candle in the vacuum chamber. This generates numerous CCNs (cloud condensation nuclei) (I believe) and perhaps some larger-than-normal CCNs. A cloud forms in the vacuum chamber for a few seconds, then disappears, as the air gets sucked out. I don't believe the heat output of the candle significantly affects the situation.



Why did the cloud form if the temperature did not change much? The relative humidity did not shoot up to 100%, according to the pocket sized meteorological instrument Kestrel 4000, it went down! Clouds form when relative humidity goes up to near 100%, right?? Was there some not-so-simple thermodynamics going on here??


In the chamber, the pressure decreases quickly and I believe it drops over 50mb in the first few seconds. I got the pressure to change from 850 to 180mb in 30 seconds to a minute. (note: 850mb is normal for my altitude.) The temperature only decreased a couple of degrees F, according to the Kestrel 4000. I had a temp. of about 70 and a dew point of about 50. The temp went down to 68, and the dew point decreased. The RH decreased, because dew point started going down rapidly and is in the 20's (F) after 15-30 seconds. The Kestrel can measure a several degree change in a couple of seconds, and the same is true for dew point.
 
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  • #2
CCI... Very high tech.

When I was in school we had 2 liter soda bottles, add a match, water cover, shake, then squeeze the bottle and see a cloud formation :)
 
  • #3
2-gallon-vacuum-chamber-w-mastercool-6cfm-11.gif

this is simple vaccum chamber demo.
 
  • #4
windshear said:
I did a demo for my students, using a simple vacuum pump and a vacuum chamber. I put a burning candle in the vacuum chamber. This generates numerous CCNs (cloud condensation nuclei) (I believe) and perhaps some larger-than-normal CCNs. A cloud forms in the vacuum chamber for a few seconds, then disappears, as the air gets sucked out. I don't believe the heat output of the candle significantly affects the situation.
Why did the cloud form if the temperature did not change much? The relative humidity did not shoot up to 100%, according to the pocket sized meteorological instrument Kestrel 4000, it went down! Clouds form when relative humidity goes up to near 100%, right?? Was there some not-so-simple thermodynamics going on here??In the chamber, the pressure decreases quickly and I believe it drops over 50mb in the first few seconds. I got the pressure to change from 850 to 180mb in 30 seconds to a minute. (note: 850mb is normal for my altitude.) The temperature only decreased a couple of degrees F, according to the Kestrel 4000. I had a temp. of about 70 and a dew point of about 50. The temp went down to 68, and the dew point decreased. The RH decreased, because dew point started going down rapidly and is in the 20's (F) after 15-30 seconds. The Kestrel can measure a several degree change in a couple of seconds, and the same is true for dew point.

So, do you know for sure that it is cloud condensation and not just smoke from the candle?

Zz.
 

1. What is a vacuum chamber demo and how does it work?

A vacuum chamber demo is a scientific experiment that involves placing a sample inside a sealed chamber and removing all air and gases to create a vacuum. This creates a controlled environment where changes in temperature and humidity can be observed and measured over time.

2. Why is a vacuum chamber used for this experiment instead of a regular chamber?

A regular chamber may have air and gases present, which can affect the accuracy of the experiment. By creating a vacuum, the only changes in temperature and humidity are due to the sample itself, providing more precise and controlled results.

3. How is temperature and humidity measured in a vacuum chamber?

Temperature and humidity can be measured using sensors or probes that are placed inside the chamber. These sensors can be connected to a computer or data logger to record and analyze the data over time.

4. What are the potential applications of a vacuum chamber demo?

A vacuum chamber demo can be used to study the effects of temperature and humidity on various materials, such as food, electronics, and medical devices. It can also be used to simulate extreme conditions, such as high altitude or outer space, for testing purposes.

5. Are there any safety precautions to consider when using a vacuum chamber?

Yes, it is important to follow safety guidelines when using a vacuum chamber, as it involves removing all air and gases from the chamber. This can create a hazardous environment if not done properly. It is also important to wear protective gear and follow proper handling procedures for the sample being tested.

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