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

In summary, the individual is seeking advice on using a venturi system to cool pressurized, high-velocity air with a temperature of 90°C, by entraining a small amount of colder air (8°C) at each venturi. The goal is to achieve a drop of approximately 20°C at the end of a 5m pipe with a 30mm diameter. The individual is unsure of the equations and behavior of the air and is seeking guidance from experts.
  • #1
shaunedinburgh
1
0
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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  • #2
Welcome to PF!

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

1. How does the venturi effect cool air in a pipe?

The venturi effect is a phenomenon in fluid dynamics where a decrease in pressure occurs when a fluid flows through a constricted section of a pipe. This decrease in pressure causes a corresponding decrease in temperature, resulting in cooling of the air in the pipe.

2. What is the purpose of using multiple venturis in a cooling system?

Using multiple venturis in a cooling system allows for more efficient cooling as it creates multiple areas of low pressure, resulting in a greater temperature decrease. It also allows for a larger volume of air to be cooled at once.

3. Can the cooling effect of a venturi be adjusted?

Yes, the cooling effect of a venturi can be adjusted by changing the size and shape of the constricted section of the pipe. A smaller and more constricted area will result in a greater decrease in pressure and temperature.

4. Is it possible to cool air to below its dew point using venturis?

No, it is not possible to cool air to below its dew point using venturis alone. The venturi effect can only cool air to its dew point, at which point condensation will occur. To achieve lower temperatures, additional cooling methods must be used.

5. Can venturis be used to cool other fluids besides air?

Yes, the venturi effect can be used to cool other fluids besides air. However, the design and dimensions of the venturi may need to be altered to suit the specific fluid being cooled. Additionally, the fluid properties such as viscosity and density may also affect the cooling efficiency.

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