"Hilsch Tube" for the "Vortex Tube", as it is called by Dr. Hilsch in a recent article.[1]
The American Chemical Society has very kindly consented to our reproducing the working drawings of the Hilsch tube—Figure No. 1—so that any good machine shop can quite easily construct one for you. When I first saw the tube in operation, I sat with a thermodynamics textbook in my hand for some time. Then I closed it and said wearily to myself, "Well, there goes the Second Law!" For I certainly saw one stream going in and two streams coming out, and one of the outlet streams was cold and the other was hot. And if that weren't effective sorting of molecules according to energy content what was it?
It took quite a while before I realized that the major part of my difficulties arose because the following statements of the Second Law are incomplete; but these partial statements seemed perfectly reasonable to me at the time. More than one politician has found that half-truths make better propaganda than outright falsehood.
"Water won't flow up hill (two words missing)."
"Heat won't flow from cold bodies to hot (two words missing)."
"A system will not proceed from a more probable state to a less probable state (two words missing)."
In each case the missing two words are the same. They are "WITHOUT COMPENSATION!" In the case of the Hilsch tube, mechanical compensation for the loss of entropy by the gaseous system is provided by the compression and expansion of air. Thermodynamics doesn't give a hoot about mechanism—it is concerned only with the inherent possibilities of a given system.
But it is not even necessary to postulate that there has been a sorting of molecules, and there is much
Figure 2.
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Maxwell's Demon Lives Here!
- ↑ Hilsch, R. The Use of the Expansion of Gases in a Centrifugal Field as Cooling Process. The Review of Scientific Instruments. 18, 2, February, 1947.
