Evaporative cooling in a vacuum

In summary, the conversation discusses a problem with a Focused Ion beam and insulator deposition using a siloxane liquid. The liquid is stored in a small container inside a vacuum chamber, and when the valve is opened, the pressure rises to the desired level for deposition. However, there is a slow linear drop in pressure with time, causing the deposition process to fail. The questions raised include whether the pressure drop is due to evaporative cooling, if there is a formula to calculate vapor pressure and cooling rate in a vacuum, if the pressure gauge used could be affected by the insulator, and if there could be other factors at play. The conversation also briefly mentions Boyle's law as a potential solution.
  • #1
kawikdx225
83
0
I am having a problem at work and I'm hoping some of the brains on this board can help.

I'm using a Focused Ion beam to induce insulator deposition using a siloxane liquid. The liquid is stored in a small container with a valve to let the gas escape the container. This small container is located inside a vacuum chamber.

The vacuum chamber has a pressure of 1.5e-6 millibar when the siloxane valve is closed.

When the valve is opened I see the pressure rise to 8.0e-6 which is where I want to perform deposition.

As I watch the pressure I notice a slow linear drop with time. This effect causes the deposition process to fail.

As far as I know the chamber pressure is determined by the vapor pressure of the liquid and the size of the valve(which also has a limiting aperture in it)

My questions are:
1. Is this pressure drop due to the temperature of the liquid dropping due to evaporative cooling? This drop in temperature would also drop the vapor pressure right?

2. Is there a formula to calculate the vapor pressure vs temperature, or to calculate how fast the liquid will cool in the presence of a vacuum? or some other formula to help me characterize this effect.

3. Could the gauge used to measure the pressure level become inaccurate in the presence of an insulator like siloxane? It's a hot cathode Ionization gauge.

4. Is there something else that could be going on that I haven't mentioned.

Thanks for any help
 
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  • #2
Would Boyle's law's be of any help?
 
  • #3
I don't know, where do I find information on this law?

Thanks
 
  • #4
I had found several citations when I ran a google search.
 

What is evaporative cooling in a vacuum?

Evaporative cooling in a vacuum is a process in which a liquid is converted into a gas, causing a decrease in temperature due to the energy required for the phase change. In a vacuum, the pressure is low, so the liquid molecules can easily escape into the gas phase, resulting in a significant cooling effect.

How does evaporative cooling in a vacuum work?

In a vacuum, the pressure is low, which means that the boiling point of the liquid is also low. When the liquid is exposed to this low pressure, its molecules can easily escape into the gas phase, taking energy with them. This energy comes from the remaining liquid, resulting in a decrease in temperature.

What are some real-world applications of evaporative cooling in a vacuum?

Evaporative cooling in a vacuum has various applications, including in refrigeration and air conditioning systems. It is also used in the production of freeze-dried foods, where the water is removed from the food through sublimation in a vacuum. Additionally, it is used in some scientific experiments that require extremely low temperatures.

What are the limitations of evaporative cooling in a vacuum?

One of the main limitations of evaporative cooling in a vacuum is that it requires a low-pressure environment. This can be difficult and expensive to achieve, especially on a large scale. Additionally, the cooling effect is limited by the vapor pressure of the liquid, so it may not be suitable for cooling to extremely low temperatures.

How does evaporative cooling in a vacuum compare to other cooling methods?

Evaporative cooling in a vacuum is often more efficient than other cooling methods, such as using a refrigerant, because it does not require any external energy sources. However, it may not be suitable for all applications and is limited by the properties of the liquid being used. Other cooling methods may be more suitable for specific situations.

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