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

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1. Apr 14, 2015

### shaunedinburgh

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 eachother 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!

2. Apr 14, 2015

### Staff: Mentor

Welcome to PF!

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