Vacuum by condensation causes water to boil?

In summary, vacuum by condensation refers to the process where lowering the pressure in a system allows water to boil at a temperature lower than its normal boiling point. When the pressure is reduced, the vapor pressure of the water can exceed the surrounding pressure, enabling it to transition from liquid to gas. This phenomenon is utilized in various applications, such as vacuum distillation and freeze-drying, where controlling pressure is essential for efficient phase changes.
  • #1
askingask
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So basically if I have a closed container with a valve, and inside the container there is water. Now i heat the container and boil the water. The valve is open so steam escapes form there. I now close the valve and cool the container causing the steam to condense inside. Inside the container is a vacuum now.

Will this vacuum cause the water to boil? Or will only so much steam have condensed, to create the exact pressure which matches the evaporation point of the water to that of the ambient temperature?
 
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  • #2
askingask said:
... Inside the container is a vacuum now.

Will this vacuum cause the water to boil?
It would, but then there will no longer be a vacuum. The temperature of the water in the container, will decide the vapour pressure of the steam in the container. The contents of the container are then in equilibrium.

askingask said:
Or will only so much steam have condensed, to create the exact pressure which matches the evaporation point of the water to that of the ambient temperature?
The "evaporation point" is confusing because evaporation and condensation take place continuously. Evaporation is equal to condensation when at equilibrium. The equilibrium vapour pressure is a function of temperature. At 100°C the vapour pressure of water is one atmosphere, so it boils. It is not zero at 0°C, it is 611 Pa.
Code:
'  Temp       pp_H2O        Atm
'   °C        pascal         %
'  100.0     101,331.      100.0
'   95.0      84,524.       83.4
'   90.0      70,113.       69.2
'   85.0      57,811.       57.1
'   80.0      47,368.       46.7
'   75.0      38,556.       38.1
'   70.0      31,168.       30.8
'   65.0      25,015.       24.7
'   60.0      19,926.       19.7
'   55.0      15,746.       15.5
'   50.0      12,340.       12.2
'   45.0       9,586.        9.5
'   40.0       7,378.        7.3
'   35.0       5,624.        5.6
'   30.0       4,243.        4.2
'   25.0       3,167.        3.1
'   20.0       2,337.        2.3
'   15.0       1,704.        1.7
'   10.0       1,227.        1.2
'    5.0         872.        0.9
'    0.0         611.        0.6
'   -5.0         421.        0.4
'  -10.0         286.        0.3
'  -15.0         191.        0.2
'  -20.0         125.        0.1
'  -25.0          81.        0.1
'  -30.0          51.        0.1
'  -35.0          31.        0.0
'  -40.0          19.        0.0
'  -45.0          11.        0.0
'  -50.0           6.        0.0
 
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  • #3
askingask said:
So basically if I have a closed container with a valve, and inside the container there is water. Now i heat the container and boil the water. The valve is open so steam escapes form there. I now close the valve and cool the container causing the steam to condense inside. Inside the container is a vacuum now.

Will this vacuum cause the water to boil? Or will only so much steam have condensed, to create the exact pressure which matches the evaporation point of the water to that of the ambient temperature?
You can do this experiment with a canning jar filled halfway with water and heated to boiling in a microwave. Just make sure the lid is loose enough to let the steam out, and new enough to maintain a seal. The lid acts like a one way check valve, letting out steam and air while heating. But once the heat is removed, the lid should seal the jar. To work, all the air needs to be pushed out, so I would recommend heating to a violent boil.
If the experiment is successful, it will boil for as long as it takes the water in the jar to reach room temperature. And then if you put it in the refrigerator, or put an ice cube on the lid, it will start boiling again! If the experiment fails, which is when, post heating, air gets into the jar, then it won't do this, and you'll just have a very boring jar full of hot water.

You can read up on this effect in food canning forums.
Example:
I just canned up some ground turkey. It's been 3 hours and the jars are still bubbling!
...
ref: https://permies.com/t/138925/Jars-bubbling-hours

I learned of this effect about a year ago, when I delved into the art of food canning.
 
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  • #4
OmCheeto said:
To work, all the air needs to be pushed out, so I would recommend heating to a violent boil.
Yes, boil it vigorously.
The molecular weight of water is 18 g/mole, while air averages 29 g/mole.
Water vapour is lighter than air, so it rises. You must therefore stir the gasses to progressively dilute and remove the air from the bottom of the ullage space.
 
  • #5
OmCheeto said:
If the experiment is successful, it will boil for as long as it takes the water in the jar to reach room temperature.
Alright that’s really interesting thanks for sharing.


Baluncore said:
Yes, boil it vigorously.
The molecular weight of water is 18 g/mole, while air averages 29 g/mole.
Water vapour is lighter than air, so it rises. You must therefore stir the gasses to progressively dilute and remove the air from the bottom of the ullage space.
So if I create a vacuum using this method with water and place a salt solution in another container, which is connected ( both containers connected being evacuated), could I create something similar to the Icyball?
https://en.wikipedia.org/wiki/Icyball

I know that salt is really bad at absorbing moisture, but in the case of a vacuum how strongly would it absorb the water vapor formed?
 
  • #6
askingask said:
Alright that’s really interesting thanks for sharing.



So if I create a vacuum using this method with water and place a salt solution in another container, which is connected ( both containers connected being evacuated), could I create something similar to the Icyball?
https://en.wikipedia.org/wiki/Icyball

I know that salt is really bad at absorbing moisture, but in the case of a vacuum how strongly would it absorb the water vapor formed?
That all depends on what you mean by salt. Lithium Bromide salts are commonly used in absorption refrigeration devices, which is what your Icyball is. As to whether or not Sodium Chloride would work, I can't say for sure, but I've never heard of such a device.
 
  • #7
OmCheeto said:
That all depends on what you mean by salt. Lithium Bromide salts are commonly used in absorption refrigeration devices, which is what your Icyball is. As to whether or not Sodium Chloride would work, I can't say for sure, but I've never heard of such a device.
I know about lithium bromide. Thing is, sodium chloride is known to be very ineffective when it comes to being a desiccant. My question is: does that change if its operating in a vacuum, where the water evaporates and the system fills up with steam?
 
  • #8
askingask said:
My question is: does that change if its operating in a vacuum, where the water evaporates and the system fills up with steam?
NaCl is a very poor desiccant.

The best way to remove water vapour, is physically with a vacuum pump, or in a chemical reaction with CaO, but that can get angry when it expands, and is difficult to reverse without an 825°C kiln.

The cheapest way would be with silica gel, sold in the supermarket as cat litter.
 
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FAQ: Vacuum by condensation causes water to boil?

What does "vacuum by condensation" mean?

"Vacuum by condensation" refers to the process where a vacuum is created in a closed system by condensing vapor into liquid, which reduces the pressure within the system. This lower pressure can lead to a decrease in the boiling point of liquids, allowing them to boil at lower temperatures.

How does reducing pressure cause water to boil?

Water boils when its vapor pressure equals the surrounding atmospheric pressure. By reducing the pressure in a system, the vapor pressure required for water to boil is achieved at a lower temperature, leading to the boiling of water even at temperatures below 100°C (212°F).

What applications utilize vacuum by condensation to boil water?

This principle is commonly used in various industrial processes, such as vacuum distillation, where it allows for the separation of components at lower temperatures. It's also used in food processing, where maintaining lower temperatures helps preserve flavor and nutrients.

Is boiling water in a vacuum safe?

Boiling water in a vacuum can be safe when conducted in controlled environments, such as laboratories or industrial settings. However, precautions must be taken to manage the risks associated with rapid boiling and the potential for splashing or steam release.

Can vacuum boiling be used for cooking?

Yes, vacuum boiling can be used in cooking, particularly in sous-vide techniques. This method allows food to be cooked at lower temperatures over longer periods, enhancing flavors and textures while minimizing nutrient loss.

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