# How can I understand a Vortex Tube and its efficiency?

A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon.

Both linked sources are scarce with information about how and why this works. Now, I have two questions:

• Why does it work, specifically why should the situation in the vortex lead to a transfer of thermal energy from the inner stream to the outer one?

• How efficient can it be?

• How do you define the efficiency of a device that may be closer to Maxwell's Demon than to a heat pump? My feeling is that any analysis should not only take into account the sum of input energy (thermal and mechanical energy instream) and sum output (thermal energies and pressures of both gas streams), but also the Temperature differential that is created - since that contains an ability to create work.*

• If course it's pointless to create heat from high grade 8mech.) energy to transform it back to mech. energy - but it gives an idea on the worth of the output.

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This is a very interesting question - I hadn't heard of these things before. –  Nathaniel May 7 at 9:07

I have performed few tests with Vortex tube to find its effeciency comparing with a refrigeration system.objective was to determine whether we can use compressed air or CO2 to replace refrigeration system.vortex tube works only with pressurised fluid.when sudden drop on pressure reduces temperature and the spiral form seperator inside the vortex tube which circulates the fluid around it causing it to seperate hot fluid and cold and directs it to 2 different direction.using cold air which got seperated i could cool water up to 2 degree centigrade in c scale.but it require high flow rate and pressure to drops down any further.its efficiency is too low compared. I used 75 psig and flow rate was .5liter per sec.

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GReat to find someone with actual experience! do you have actual figures? –  mart Sep 24 at 9:50
Yes. I have temp diff between inlet and outlet.mass flow rate diff between inlet and outlet.and various temp drop at different pressure and flow rate.i could get finally at 80psig inlet pressure and mass flow rate of 260lpm.a temp drop of .2 degree C and cold outlet.i have data on doe.the noise level is higher at hot air outlet. –  nemu Oct 1 at 15:03

The input stream does not only have a thermal energy - it also has a mechanical one. Mechanical energy can be used for work, and the gas temperature is easily changed by work - in adiabatic processes it rises when gas is pressed, and falls when gas is able to expand. This gives a general idea why this tube could work and at the same time not be a Maxwell's Demon. Though detailed picture can be very complex and ask for advanced understanding of gas dynamics.

If we calculate total thermal and mechanical energies of both output streams, we would find that some mechanical energy is lost, and total entropy has risen. Mixing those streams back in one would give us a slower and somewhat hotter gas than it was initially. This is the same effect as simple slowing down the stream on some obstacles.

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1) can you expand on, um, why part of the gas is expanding in the tube? 2) for any heat engine or heat pump $\Delta T$ plays a large role ... why not here? –  mart May 7 at 9:44
1) Please think of this not only as of heat engine but also as of a mechanical system. Gas mechanics here is highly relevant. Gas has inertia, and it can hit walls, thus making regions of higher and lower pressure. Also there are other streams of gas besides walls, and possibly some acoustic phenomena. 2) $\Delta T$ plays large role here too, as in the heat pump: it poses constraints on what can be done and what cannot be done with such a device. But $\Delta T$ is not the source of the work here - at least, basically. –  firtree May 7 at 10:11