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I am not able to understand the reason for temperature separation and flow reversal in a counter-flow vortex tube refrigeration system.

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As per some sources, "Compressed air is passed through the nozzle .Then air expands and acquires high velocity due to particular shape of the nozzle. A vortex flow is created in the chamber and air travels in spiral like motion along the periphery of the hot side. This flow is restricted by the valve. When the pressure of the air near valve is made more than outside by partly closing the valve, a reversed axial flow through the core of the hot side starts from high-pressure region to low-pressure region. During this process, heat transfer takes place between reversed stream and forward stream. Therefore, air stream through the core gets cooled below the inlet temperature of the air in the vortex tube, while air stream in forward direction gets heated up. The cold stream is escaped through the back side cold part, while hot stream is passed through the opening of the valve."

But if energy is being transferred from reversed stream (colder one) to the forward stream (hotter one) then doesn't it violate the 2nd law of thermodynamics?

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    $\begingroup$ What happens with free expansion? An aerosol can… $\endgroup$
    – Solar Mike
    Commented Dec 22, 2022 at 7:25
  • $\begingroup$ @SolarMike Sorry, I didn't get you $\endgroup$
    – MechaTrex
    Commented Dec 22, 2022 at 7:49
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    $\begingroup$ Then worth some research. $\endgroup$
    – Solar Mike
    Commented Dec 22, 2022 at 7:52
  • $\begingroup$ this question has an answer on the physics stack exchange. go there are search on "vortex tube". $\endgroup$
    – niels nielsen
    Commented Dec 22, 2022 at 18:41
  • $\begingroup$ @nielsnielsen but they are wrong answers - including the one that references this faulty paper - researchgate.net/publication/…. $\endgroup$
    – Phil Sweet
    Commented Dec 22, 2022 at 21:12

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It does not violate the 2nd law of thermodynamics since it is a open system with acceleration far away from a steady state. The above mentioned explanation is wrong. Since this technology is used in nuclear isotope separation it is part of non disclosure knowledge to prevent proliferation. Please take this into account.

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