What is the most efficient way to cool air using a Vortex Tube (Ranque-Hilsch)?

In summary, the paper discusses the optimization theory of the Vortex Tube and states that the initial separation of hot and cold air is complete at the left hand side of the tube. The interaction between the two streams is deemed undesirable and it is ideal for the cooled air to return to the right hand side without any further interaction. The paper also suggests that the process of returning the cold air degrades performance due to unwanted heat exchange between the streams. The first question is whether the actual cooling of the cold stream only occurs during the inward deflection at the far end of the tube. The second question is if it would be better to skim off the cold air in a way that isolates it from the warm stream. Additionally, the paper mentions a
  • #1
Swamp Thing
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Ref: https://s3.wp.wsu.edu/uploads/sites/44/2015/12/VortexTubeOptimizationTheory.pdf

The above paper says that the initial separation of hot and cold air is complete once the flow is partly deflected backwards at the left hand side (HOT) end. See Fig. 1 in the paper.

It also says that the further interaction of the two streams is actually undesirable, and that one would want that process to be like a "weak" or "bad" heat exchanger. So ideally we would want the cooled air (inner stream) to make its way back to the right hand side (COLD) end without any interaction with the outer stream.

So the process of returning the cold air to the right hand side, passing all the way through the tube, actually degrades the performance due to unwanted heat exchange between the inner and outer streams. This idea is elaborated in Fig. 3 of the paper.

My first question is -- is it true that the actual cooling of the cold stream happens entirely during the inward / backward deflection at the far end of the tube, and that all further interaction between the streams is merely an undesired dilution of performance?

Second question -- If the above is true, won't it be better to skim off the cold air in some other way that will keep it more isolated from the warm stream? For example:

1674214767061.jpeg


Or maybe like this:

1674214830497.jpeg
 
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  • #2
Another point of confusion is that some papers talk about a "double circuit vortex tube". For example, Fig. 7 in this paper: https://uhra.herts.ac.uk/bitstream/..._for_Resubmission_Without_Mark.pdf?sequence=1

If the answer to my question #1 in the original post is yes, then the double circuit thing doesn't seem to make much sense. The double circuit concept would only make sense if the cooling happens during the interaction between the two streams along the tube.
 

FAQ: What is the most efficient way to cool air using a Vortex Tube (Ranque-Hilsch)?

What is a Vortex Tube and how does it work?

A Vortex Tube, also known as a Ranque-Hilsch tube, is a device that separates compressed gas into hot and cold streams without any moving parts. It works by injecting compressed air tangentially into a cylindrical chamber, which creates a vortex. The air spirals down the tube, and due to the conservation of angular momentum, the outer layers of the air become hot while the inner layers become cold. The hot air exits through one end, and the cold air exits through the other.

What factors affect the efficiency of a Vortex Tube?

The efficiency of a Vortex Tube is influenced by several factors including the inlet pressure of the compressed air, the geometry of the tube (such as the diameter and length of the tube), the material of the tube, the quality of the compressed air, and the proportion of hot to cold air that is allowed to exit the tube. Adjusting these parameters can optimize the cooling performance.

What is the typical temperature drop that can be achieved with a Vortex Tube?

The temperature drop achievable with a Vortex Tube can vary, but typically, a temperature reduction of up to 50°C (90°F) from the inlet air temperature can be achieved. The exact temperature drop depends on the inlet pressure and the specific design of the Vortex Tube.

How much compressed air is required to operate a Vortex Tube efficiently?

The amount of compressed air required to operate a Vortex Tube efficiently depends on the desired cooling capacity and the specific design of the tube. Generally, Vortex Tubes require a minimum inlet pressure of around 80-100 psi (5.5-7 bar) to function effectively. The flow rate can vary, but typical industrial applications might require anywhere from 15 to 150 SCFM (Standard Cubic Feet per Minute) of compressed air.

What are the practical applications of Vortex Tubes for cooling?

Vortex Tubes are used in a variety of practical applications for cooling, including spot cooling for industrial processes, cooling of electronic control cabinets, cooling machining operations to extend tool life, cooling workers in hot environments, and in laboratory settings for rapid cooling of samples. Their simplicity, lack of moving parts, and ability to provide localized cooling make them versatile and useful in many scenarios.

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