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Transient Phenomena Observed during Operation of a Ranque-Hilsch Vortex Tube Dramatic transient effects have been observed following abrupt interruption of the compressed air supply to a 1 -inch-diameter Ranque-Hilsch vortex tube. During decompression of the tube, sharp decreases in the cold-end stagnation temperature levels were noted. Initial data characterizing these effects are presented and questions regarding the performance of vortex tubes under pulsed-flow conditions are posed.
T h e Ranque-Hilsch vort'ex tube has been the subject of substantial theoret'ical and experimental concern ever since its revival by Hilsch in the 1940's (Hilsch, 1946). While practical applications of the device continue to seem remote, the uniqueness and complexity of the phenomena involved have encouraged continued invest,igation. I n brief, the t'ypical vortex tube consists of a straight cylindrical conduit into which compressed gas is fed through a tangential nozzle located near one end. This tangential angle of entry creates a n intense vortical motion in the tube. Part of the gas is drawn off from the central portion of t,he vortex through a n orifice plate located a t the end of the tube nearest the nozzle, while the remaining fraction of the gas (from the periphery of the vortex) is drawn off through a throttling valve at. the opposite end of the t'ube. For reasons which are not unequivocal, but a t least reasonably well ascertained, the streams leaving t'hrough the orifice plate and throttling valve are usually very much colder and hotter, respect'ively, than the supply st'ream. Product stream temperahre differences of more than 100°C have been commonly achieved. The basis for t'he energy separation, although difficult to describe quantitatively, is a t least fairly well understood in a qualitative sense. The incoming gas is initially cooled by expansion. The vortex created near t'he entry point initially tends toward a "free vortex" state in which the angular velocities are low near the periphery and high in the center. However, not far from the entry point internal friction tends to alter the vortex strongly, driving it toward a state charact'erized b y uniform angular velocity. Thus, a speeding up of the out'er layers and a slowing down of the inner layers are induced. The inner portions of the gas therefore do considerable shear work on the out,er port'ions, creating a net total temperature separation. Wit'h respect to this shear work, it has been indicated (Deissler and Perlmutter, 1960) that the viscous dissipat'ion component is highly important in the peripheral region, while kinetic energy and pressure energy contributions are important near the core. The purpose of the present, note is not', however, to review or interpret either the many exist'ing vortex tube designs or the various theories of their operat,ion. Thus, we omit further treatment of these points, the above discussion--admittedly somewhat oversimplified-being proffered only as a brief introduction to enable those unfamiliar wit,h vortex tubes to peruse what follows. Apparatus
-isimple vortey tube, originally set up iii our laboratory as a n educational exercise, was very similar in design to the tube of Scheller and Brown ( 1 9 5 ) . The main tube consisted of 308
Ind. Eng. Chem. Fundam., Vol. 10, No. 2, 1971
1-inch I P S steel pipe, 48 inches long, having a standard globe valve on one end and a flat-ended threaded cap on the other end. This cap was bored in the center to a l/d-inch-diameter opening, and several thin orifice plate inserts (bored to diameters of '/le, I/*, and inch) were constructed to fit inside the cap, against the end of the pipe.(?his was found to be a convenient way of changing the cold-end" orifice size. The gas entry nozzle consisted of a n l/s-inch-i.d. copper tube brazed tangentially into the main pipe, 1 inch from the cold end and trimmed off flush with the interior curvature of the pipe wall. The gas supply was compressed air a t approximately 96 psia and 68°F. Stagnation temperatures were measured using a conventional copper-constantan thermocouple, made of 30-gauge wire. Observed Behavior at Steady State
Steady flow measurements were made with all orifice plate sizes, with the throttling valve varied so as to maximize the temperature differences between the hot and cold ends. Flow from the cold end was not regulated, being determined b y the equilibrium discharge rate as influenced by orifice size, throttling valve setting, and air supply conditions. Temperature separations of approximately 40°F were obtained, a typical result being 86°F a t the hot end and 47°F a t the cold end, and these were not strongly influenced by orifice size. These results agree with Scheller and Brown (1957), who observed stagnation temperature differences of roughly 45°F in a 1-inch pipe of similar construction a t an air inlet pressure of 7 5 psia. The lack of a significant effect of the cold end orifice diameter confirms Sibulkin's (1961) theory, and agrees with the results of Hilsch (1946)) which show that, except for very small orifice diameters, the cold-end bore is not of great influence. Additionally, since the cold-end flow rates varied, a critical evaluation is difficult. Suffice it to say that these very few data indicate that our vortex tube behaved under steady-state conditions about as one would expect. Unsteady-State Phenomena
The primary objective of this note is to describe transient phenomena that n ere detected quite by accident during our studies. Specifically, it was noticed that after a n abiupt shutoff of the air supply and during the subsequent decompression of the tube, the temperature of the cold stream dropped very suddenly to a much loner level. This effect, mhich to our knonledge has ne\ er before been repoited, would piobably be difficult to detect in many of the smaller diameter vortex tubes n hich are commonly used, since theqe smaller tubes, hile generally pioduciiig larger steady-state energy separations, decompress very quickly. Our particular device required perhaps 3 to 5 seconds to undergo the gieater part of
the decompression process, during which time approximate temperature measurement’s were possible. Measurements were made with the tip of the thermocouple centered in the cold-end orifice. Figure 1 indicates the magnitude of t,he observed temperature drops a t the cold end. These initial data are undoubtedly crude, since the inherent response time of the t,hermocouple was large enough to affect the readings. The actual magnitude of the transient effect is therefore even greater than the measured values. Frost formation on the thermocouple was observed during many measurements. The hot-end temperatures during decompression were measured and found to increase only very slightly. However, since the hot air exited through a 1-inch globe valve, the stream diameter was very large. Under the reduced flow conditions of decompression, heat transfer through t’he long “hot end” of the pipe, and mixing with the surrounding air a t the outlet made the hot end temperat’urerise very difficult to detect. Substantial revision of the apparatus will be required before any t’ruly accurate characterization of these t’ransient phenomena will be possible. Implications
The observed phenomena lead one without hesitation t o wonder what Tvould occur if a n ordinary vortex tube were operated with a pulsating air supply. Questions which arise include whether opposite effects would prevail during the recompression phase of pulsation, and whether the timeaverage stream temperatures would be the same as the steadystate stream temperatures a t the same average operating pressure. Additionally, the duration and magnitude of these transient effects may be affected strongly by tube design, particularly tube diameter. A theoretical interpretation of the results obtained thus
SUPPLY A I R TEMP.
APPROX. COLD E N D TEMP,
0
0.10 0.20 0.30 COLD END ORIFICE DIAMETER,INCH
Figure 1 . Tra nsient cold-end tem pe ra tu re effects in a 1 -inch VOI ‘ex tube
far will not be set forth a t this point. -2great amount of additional data should be obtained before attempting a n analysis, since the complexity of the phenomena deserves such. It is hoped that in reporting our initial data, we may encourage further investigations of these transient phenomena. literature Cited
Deissler, R. G., Perlmutter, XI.,Int. J . Heat M a s s Transfer 1, 173 (1960). Hilsch, R., Rev. Sci. Instr. 18, 108 (1947); 2. Saturforsch. 1, 208 ( 1946).
Scheller, W. A , , Brown, G. AI., Ind. Eng. Chem. 49, 1013 (1967). Sibulkin, M., J . Fluid Mech. 12, 269 (1961). DAVID 0. COOXEY Clarkson College of Technology Potsdam, 9 . Y . 13676
RECEIVED for review Bugust 26, 1970 ACCEPTEDOctober 29, 1970
The Use of an Auxiliary ligand in the Foam Fractionation of Copper An experimental investigation into the removal of copper from dilute aqueous solution b y foam fractionation with sodium lauryl sulfate has been carried out. The primary purpose of the investigation was to determine the optimum conditions for the removal of copper and to attempt to improve the efficiency of the process b y the addition of an auxiliary ligand. Distribution factors were therefore determined for copper as a function of pH, auxiliary ligand concentration, surfactant concentration, electrolyte concentration, and the bulk concentration of copper. In general it was found that the addition of the auxiliary ligand THPED (THPED i s the convenient abbreviation for the substituted amine N,NfN’,N’-tetrakis(2-hydroxypropyl)ethylenediamine; available commercially from the Wyandotte Chemical Corporation under the trade name of Quadrol) improved the distribution factor significantly, particularly in the presence of much added NaCl and a t low bulk copper concentrations.
B e c a u s e of its potential for the separation of surface active substances and trace quantities of metal ions in aqueous solution, foam fractionation has received much attention in recent years. Most workers have limited themselves to laboratory scale experiments, although pilot plant sized units were operated by Haas (1965), and reported by Brunner and Stephan (1965). d full-sized unit treating 12 mgpd of domestic
sewage removed ABS successfully until the introduction of biodegradeable detergents made its operation unnecessary. S o other full-sized units have been reported in the literature; however, in view of the amount of work being carried out, it should only be a matter of time until the process finds application in areas such as radioactive waste cleanup or in cation removal for pollution control. Ind. Eng. Chem. Fundom., Vol. 10, NO. 2, 1971
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