Can high air velocity in vacuum system create "freezing" of the pipe?

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Discussion Overview

The discussion centers on the potential for air to "freeze" within a pipe in a vacuum system when high air velocity occurs, particularly in areas of reduced cross-section. The context includes considerations of moisture content, temperature, and the physical behavior of gases under varying conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether high air velocity in a vacuum system can lead to freezing, particularly in moist air at room temperature.
  • Another participant suggests that freezing is possible under favorable conditions, referencing carburetor icing as a related phenomenon.
  • A different perspective emphasizes that the parameters provided may be incorrect, noting that compressibility and changes in temperature and pressure are critical factors in determining the formation of non-gases.
  • This participant also mentions that in high-speed wind tunnels, preheating is necessary to prevent liquefaction of gases due to temperature drops associated with increased velocity.
  • Another contribution highlights the Joule-Thomson effect, explaining that a drop in pressure can lead to a temperature decrease, which may cause icing issues in natural gas distribution networks.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for freezing to occur, with some suggesting it is possible while others challenge the initial parameters and assumptions. The discussion remains unresolved regarding specific conditions and outcomes.

Contextual Notes

Participants note the importance of temperature and pressure in the context of air velocity and moisture, but the specific thresholds for freezing and the exact conditions under which it occurs are not clearly defined.

kaigoss69
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Can high air velocity in vacuum system create "freezing" of the pipe?
Hi folks, very simple question, but have not been able to find an answer: Assume a vacuum pump pulls air through a pipe. Also assume that within the pipe run, there is an area with reduced cross section, creating a temporary increase in air velocity. Also assume the air is very moist, and is at room temperature. Question: Does the air in the section where the cross section is reduced have a possibility to "freeze" given a high-enough air velocity? If yes, at what velocity of air would "freezing" occur?
 
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Sure, though you parameters are all wrong. A few things to consider:
  • The system will also be highly compressible so an increase in velocity could require an area increase or decrease depending on the specific conditions.
  • Temperature and pressure are the relevant quantities to determine whether you get any fun non-gases that form. They both decrease when velocity goes up.
  • It's not just water that can get interesting like this. High-speed wind tunnels at Mach 5 or higher have to heat their reservoir air because it expands so much that the temperature gets low enough for oxygen to liquefy. Preheating prevents this from happening, making sure the test gas remains a gas.
  • Given the above, the air must also be dried to avoid liquid water or ice crystals forming in the test region.
In short, it's a very real phenomenon.
 
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