Gas confusion -- cooling air in a pipe using venturis and mixing

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SUMMARY

The discussion centers on cooling compressed air using a series of venturis. The setup involves a steel pipe with a pressurized air flow of 1.4 bar at 450 cfm and an initial temperature of 90°C. By introducing colder ambient air at 8°C through multiple venturis, the user anticipates a temperature drop of approximately 20°C over a 5-meter length of pipe. The final temperature will be determined by the weighted average of the mixed airstreams, factoring in flow fractions.

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  • Understanding of fluid dynamics principles
  • Basic knowledge of venturi effect and jet mixing
  • Familiarity with thermodynamics, specifically gas behavior
  • Ability to perform calculations involving flow rates and temperature changes
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  • Research the principles of the venturi effect in fluid dynamics
  • Learn about the thermodynamic properties of gases, particularly air
  • Explore calculations for mixing airstreams and temperature changes
  • Investigate practical applications of jet mixers in industrial cooling systems
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Engineers, HVAC professionals, and anyone involved in thermal management of compressed air systems will benefit from this discussion.

shaunedinburgh
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Hello everyone! I am new here. I have used this forum on and off through google searches in the past and learned a fair bit from the posts. This is the first time asking anything.

The question is probably extremely simple but has been overrun in my head for a week! It is in regards to compressed gas and its behaviour.

A flows through a steel pipe, the pressurised flow in the pipe is 1.4bar at a velocity of 450cfm. This air has a temperature too high (90°c) and needs cooling.

I have a basic knowledge of venturis and jet mixers but it is a subject where I had to learn to think backwards at the beginning and now no longer trust my judgement.

The idea...
The pressurised high flow warm air is passed through a venturi where a small amount of colder ambient (8°c) air is entrained. This combined air then travels to another venturi with the same setup and finally another, all three entraining the same amount of colder air. The pipe is 5m long and approx 30mm diameter

Will this have any cooling abilities at all and what will the end result be regarding flow and pressure roughly?

I have been thinking somewhere around a drop of 20°c at the end of the 5m pipe and an increase in volumetric flow but this is back of the eyelids mathematics with almost no working out. There are so many equations to this and the behaviour of the air. These have been attempted but I am unsure if they conflict with each other in practice or if the actually apply to this problem.

Please note: I am a complete novice in the physics world and apologise profusely if this is considered ridiculously obvious either in its stupidity or result!
 
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Welcome to PF!

Yes, if you mix airstreams, the temperature will be the weighted-average of the streams (temperature times flow fraction).
 

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