Thermodynamics > Entropy and the Second Law > Entropy DCS# 4F10.30


vortex tube

Hilsch-Ranque vortex tube with pipe insulation
compressed air supply 201A
thermocouple probe with digital display or thermometer
ask John

Connect the hose to the compressed air supply and open the valve all the way.  The tube separates the faster and slower moving molecules in the incoming air stream and sends them to opposite ends.  Use the thermometer to show that colder air comes out the short end of the tube and warmer air comes out the long end.  Tc < 0 C is easily obtained.
The air enters the tube directed tangentially and follows a vortical path with faster moving molecules at the outer radii and slower ones at inner radii.  The hot air exits at the circumference of the tube and the cold air exits near the axis.
The airflow at the hot air outlet is adjustable.  Opening up the valve reduces the fraction of air ejected from the cold air exhaust and lowers its temperature.  Closing it down results in less but hotter hot air.

R. Hilsch, The Use of the Expansion of Gases in A Centrifugal Field as Cooling Process, The Review of Scientific Instruments, vol. 18(2), 108-1113, (1947).

C. L. Stong, The "Hilsch" Vortex Tube, The Amateur Scientist, Scientific American, 514-519.

J. J. Van Deemter, On the Theory of the Ranque-Hilsch Cooling Effect, Applied Science Research 3, 174-196.