| The Ranque-Hilsch effect or the vortex tube effect is a striking phenomenon observed in swirling flows where air injected tangentially into a single pipe, separates spontaneously into two streams: the colder stream near the tube centerline and the hotter stream near its periphery. In spite of the simplicity of the Ranque-Hilsch tube, the mechanism of the total temperature separation, in the absence of any apparent external work, has not satisfactorily been resolved.; Previously the mechanism has been purported to be due to the turbulent motion. However, if this were the mechanism, one could not explain why, in other turbulent swirling devices, the turbulence does not separate the total temperature in the same manner.; Here experiments are conducted to substantiate a theory that acoustic streaming induced by the pure tone, a spinning wave present in swirling flows, deforms the base Rankine vortex into a forced vortex, resulting in total temperature separation in the radial direction. To verify this, acoustic suppressors of organ pipe type, tuned to the frequency of the vortex whistle, are installed on the Ranque-Hilsch tube. When the pitch of the vortex whistle, which increases as the flow through the tube is increased, hit the tuned frequency, the sound level suddenly tumbled, changing from a shrill whistle to a muffled hiss. At that very instant, the centerline temperature, which had gone down as low as -58(DEGREES)F immediately leapt upwards to +1(DEGREES)F corresponding to a sudden drop of temperature separation equal to 59(DEGREES)F; the temperature near the tube periphery plummeted by 10(DEGREES)F. This attests the theory that the vortex whistle is indeed the main cause of the Ranque-Hilsch effect. |
