US2861431A - Expanding gas in a plurality of vortex tubes - Google Patents

Description

Nov. 25, 1958 J. J. VAN DEEMTER 2,861,431

EXPANDING GAS IN A PLURALITY OF VORTEX TUBES Filed July 23, 195s FIG. I

INVENTOR: JAN J. VAN DEEMTER MZCWMW HIS ATTORNEY as the hot end.

EXPANDING GAS IN A PLURALITY OF VORTEX TUBES Jan J. van Deemter, Amsterdam, Netherlands, assignor to Shell Development Company, New York, N. Y., a corporation of Delaware Application July 23, 1956, Serial No. 599,635

Claims priority, application Netherlands November 15, 1955 18 Claims. (Cl. 62-5) This invention relates to separating a gas into relatively Warmer and colder fractions by expanding the gas with gyratory motion within a vortex tube. More particularly, the invention is concerned with an improvement involving the transfer ofheat between one or both of the gas fractions while in motion within the vortex tube, employing for this purpose an auxiliary, coaxial vortex tube within which gas is simultaneously expanded. Broadly considered, either the inner or the auxiliary vortex tube may be used either to cool or to heat gas in the main tube, according to the desire to produce a useful gaseous effiuent which is colder or hotter than the initial gas; since, however, the most usual application of vortex tubes is to generate cold, only theformer will be specifically described herein.

The vortex tube, also known as the Ranquetube or Hilsch tube, uses no moving parts and is low in cost. It is described in U. S. Patent No. 1,952,281 to Ranque,

. and Hilsch drew further attention to it in articles published in Zeitschrift fiir Naturforschung, vol. 1, pp. 208- .'/.l4 (Wiebsaden, Germany, 1946) and in Review of Scientific Instruments, vol. 18, pp. 108-113 (New York, 1947). A bibliography on vortex tubes was published by Curley and MacGee, Jr., in Refrigeration Engineering, vol. 59, 1951, pp. 66 and 191-193. As disclosed in these publications, the vortex tube includes a vortex chamber having the shape of a body of revolution, such as a cylinder, an inlet for admitting a feed gas under pressure with a gyratory motion, e. g., one or more inlet pipes situated near one end of the tube and disposed tangentially and in the same circumferential direction,

and suitable outlet means for discharging oneor' both of the gas fractions which are produced within the tube.

' These fractions are formed respectivelyas a peripheral stream in contact with the inner surface of the tube Wall and as a core (usually solid but possibly annular) rotatmg coaxially within the peripheral stream, the former being warmer and the latter being colder than the feed 7 gas in the case of an adiabatic arrangement. Bothfractions have pressures lower than that of the feed gas but the pressure of the fraction having the higher temperature exceeds that of the other fraction, in accordance with the Ranque effect. This phenomenon ofthe separation of the gas by expansion Within the vortextube into hot and cold fractions is hereinafter referred to as the heatseparation effect; it results in the heating of at least a part of the outer vortex tube wall, unless it is extraneously cooled.

Stiltfig ate t n The dimensions of such tubes may vary Within Wide Various outlet arrangements are possible, some resulting in the separate discharge of the hot and cold fractions from the vortex chamber and others resulting in re-mixing of these fractions and the discharge of. all gas asa single stream. By throttling one or both efliuent streams from a tube having separate outlets for the hot and cold gases, e. g., by a throttle valve in one of the outlets, the ratio of the discharged streams and, hence, their temperatures can be varied; typical temperature effects are indicated graphically by Hilsch, op. cit. Regardless of Whether the fractions are discharged separately, their separate occurrence within the tube affords a ready means of abstracting heat from or adding heat to one orthe other of the fractions by heat exchange With a fluid having a temperature that is the same as or only moderately different from that of the initial gas. A Thus, cooling of the hot fraction may be effected by providing cooling vanes on the outside of the tube Wall, to dissipate. heat to the surrounding air, as suggested in Figures 5 and 6 of German patent to Rotter, No. 858,260. More intensive cooling of the tube wall can be effected bycirculating a liquid through a space defined by a jacket surrounding the tube. Because of the elevated temperature of the hot gas fraction it is easy to remove heat from the gas into the atmosphere or cooling liquid and thereby reduce the temperature of the eflluent stream, both when the latter stream contains all of the expanded gas and when it consists of only the cold fraction thereof.

In general, cooling of the tube by a gas in the known manner is ineffective to achieve intensive cooling of the vortex tube wall because of the low heat transfer coefficient. Refrigeration of the gas to promote heat transfer is not feasible because it.necessitates refrigeration machinery; this, if provided, would usually make it unnecessary to'use the vortex tube. An increase in the heat transfer coefficient by placing the cooling gas in rapid motion is also not feasible under previously known conditions, sincean insufficiently small increase in heat transfer results unless refrigeration is provided. The converse effects are and limitations occur when one'seeks to heat gas in the tube.

It is the object of this invention to provide an improved processand apparatus for changing the temperature of a gas stream wherein a gas is used effectively to transport heat to or from a bounding wall of a main; vortex tube within which a gas is expanded to separate it therein into hot and cold fractions by the heat-separation effect.

A further object is to provide an improved process and apparatus employing a main and an auxiliary vortex tubes, wherein the latter is used to cool or heat one of the gas fractions in the main vortex tube. Ancillary thereto, it is an object to provide a process and apparatus wherein the auxiliary vortex tube is temperature-condihoned, e. g., cooled, by a coolant which may be a liquid.

In summary, according to the invention, gas is expanded with gyratory motion simultaneously in two vortex tubes having different diameters and disposed in at least partial overlapping relation, so that there are formed within each tube a pair of coaxially moving gas fractions of different temperatures in accordance with the heatseparation effect, the warmerfraction in the inner tube and the colder fraction in the outer tube being in contact respectively with the inner and outer surfaces of the Wall of the inner tube, resulting in a flow of heat from the former to the latter fraction. In this operation the said 4 Wall of the inner tube is cooled by the rapidly moving cold gas fraction which is produced in situ on the outer surface thereof; the rapid motion increases the heat transfer coefficient While the reduced temperature further augments the flow of heat.

As applied for the generation of cold wherein heat must be removed from the gas in the main vortex tube,

this tube is on the inside. Production of the cold gas in situ ishere especially advantageous in 'that'cold losses by convection or radiation during flow from the point of refrigeration of the coolant to the point of utilization are avoidedand the need forthermal insulation "on pipes is obviated, because the cold -frztcti'on5is' broug' "into existence only Where it is utilizedg f'andfhe gen ration of cold bythe heat-separation'efiectisuseful'in that it requires 'no refrigeration machinerywith'moving parts,

only a source of gas 'underpressure bing -reqiiiiecl. Such a sourceis frequentlyfavailable in various plants in the form of 'efiiuent'streams from' units operated at superatmospheric pressure.

"The-gas expanded in one of the vortex tubes'l'r'nay havebeen previously partly expanded'in the other; or 'adiiferent'gas"stream','originating in a common or in different sourc'esgmay'be charged to each tube. In the formenserial arrangement, 'one may, for example, pass '1 the cold gas 'dis'charged from the main vortex tube through a heat exchanger wherein it is 'used tocool some 'warmerj'medium" and then admit it. 'into the auxiliary vortex'tube for further expansion.

' The 'coldgas produced in situ in the'outer, auxiliary "vortex tube may'be' brought to a still lower temperaj tur eby'intensively cooling the outer wall of the auxiliary 'tube,leither with aliquid circulated through a jacket or through-cooling'coils' or, when the use of a liquid is impracticable or' objectionable, by yet another auxiliary "vortex'chamber.

""Each of' the vortex tubes may be selected without restriction from among various types, and the two tubes may be of the same or of diflferent types. For convenlience in "identification, the following classification of tubes onthebasis of the gas outlet arrangements is used i herein:

6 Type 'Ai -lnthisftube a cold fraction is withdrawn through a central, restricted orifice at the'cold end and a hot fraction out from the extremity. of the-hot end, usually through a throttle valve.

Type Br such a tube is closed at the cold endyand thehot and cold fractions flow through the hot end as coaxialstreamswhich:are discharged either separately oi" as a single compositemixture from the extremity of "the tube. Separate discharge may be eflected by means of a specialdevice, the -simplest form=of which is a tube I mounted concentrically within the vortex tube near the -'--closed--in-the above rrientioned German patent to Rotter.

; It I is evident 1 from theforegoing tliat- 'in' apparatus employing two vortex tubes nine possible arrangements are possible. However, 'for-thecasewhere thegeneration of cold is theobject, ibis-preferable to'em lo a '7 tube Q- of yp C as he inner, main t'ube, and

a tubeof type B as the outer, auxiliary tube.

Certain arrangements are"illustratedfbyway' of examples, in the accompanying "drawings'forming apart of this specification, wherein:

Figure 1 is a'Ion'gitu dinal sectional view'of a vortex tube apparatus according to the invention employing a type A inner tube and a type B outer tube;

Figures 2 and 3 are transverse sectional views taken on the correspondinglynumbered sectionlines of Figure 1; and a Figure 4 is a longitudinal sectional -view of ainodified vortex tube apparatus employinga type C inner tube and a type B outer tube.

Referring to Figures l-3 in detail, the apparatus may include 'an'in'ner main'vortex tube 10, the hot end'of which may include a divergent section 10a and a cylindrical section 10b; these sections are surrounded by a larger, auxiliary vortex tube11. These tubes are formed with surfacesof revolution about a common axis. The tube lfl'has aftangentially directed inlet nozzle 12 which is advantageously joined to the tube wall by a spiral -1wall-13, soas to center the resulting gas vortex at the axis of t'he" tube. Similarly, the tube 11 has a tangential inlet nozzle 14 connected to the tube wall by a spiral 15. The tube 10 has a restricted, cold-gas discharge orifice 16 form'ed'in the end wall 17 at the cold end by which the tube is in communication with a pipe 18 leading to a heat exchanger 19. The gas discharged from the heat exchanger flows through the pipe 20 to the nozzle 14. A medium to be cooled flows through the heat exchanger via pipes:21 and 22. .The extremity of the hot end of thetube 10 communicates with a hot-gas discharge Jpipe 23 whichmay be provided with a throttle valve 24. Thegtube 11 is closed at its cold'end by awall 25 and atitshot end 110: by a wall 26 which has an annular-opening 27.

By way of example, the inner tube 10 may be made of thin-walled materialwhich preferably has good heatconducting properties and have an internal diameter of 10 mm and alength of 200 mm., the outer tube 11 may then'haveaninternal diameter of 25 mm. and a length of 250mm. -It will be-recognized that when the throttle 1 valve 23 is entirelyclosed the inner tube becomes a type Ovortex; tube.

Example "The apparatusmay beoperated as follows: Gas, e. g.,

'lair at er-pressure of 20 atm. abs; and a temperature of 68 F5; is admitted to-the nozzle 12 and is partially ex- ?pan'ded tang entially within the'main, inner tube 10. The j" throt'tle val ve :24 is adjusted so that 20% of the introdueedgasescapes from this vortex tube through the pipe 1 23 inthe form of hot gas; the remaining 80% of the gas flows thr ough the orifice 16" into the pipe 18 at a pressure of 4 atm. abs. and a temperature of 4 F. After giving up its coldto the fluid which circulates through the "heat exchanger 19 and the pipes 21 and 22, the gas flows "and a' temperature of 59 F. This gas is expanded tanthrough the pipe 20 at a pressure of about 4 atm. abs.

""gentially into the auxiliary, outer tube 11 through the nozzle 14,'thereby producing a vortex and a separation of 1 thejigas into'an' outer, hot fraction and an inner, cold fraction'which are in contact respectively with the inner lf surface of the tube 11 and the outer surface of the tube and in rapid rotational movement about it. As the latter fraction has a very high velocity, a reasonably high "heat transfercoefiicient can be realized and it is possible to cool the'wall of the inner tube'10 intensely. The hot and. cold fractions inthe auxiliary tube 11 become commingled toward theextr'einity of-the hot end, where their 'fi'otation'al velocity. is diminished considerably. The'gas finally" leaves the" tube 11 through the opening 27 at a.

pressure of 1 atm. abs. anda temperature of 109 F.

The serial connection of the two vortex tubes shown in 7 Figures 1-'-3 is of particular advantage when the object is not to reach the lowest possible temperatures, but to 1 extract the largest possible number of calories from the 'cold "gas stream so as to produce a large heat transfer in the heat exchanger 19.

\ Figure-4. shows another connection and a different construc tion.of the two vortex tubes; reference numbers 'denote parts corresponding to those denoted in Figures1-3 i bynumbers increasedby twenty. Again, the inner tube 130 is the r nain tube and the coaxial, outer tube 31 is the -auxiliary tube. The vortex tubes have inlet nozzles 32 and 34, respectively, arranged tangentially with connectingispiralstasrpreviouslyFdescribed. Separate gas streams,

either from the same or from difierent'soure'esi are expanded tangentially through these nozzles. In thisc'ase the hot end 30a30b of the main tube is closed by a Wall 48, so that the tube is of typeC and all gas is disexpanded in the outer tube is discharged at the extremity of the but end through an annular opening 47.

The connection of the two vortex tubes according to Figure 4 is advantageous when the pressure of the initial gas is insufiicient to permit successive partial expansion in the two tubes, or when it is desired to recover the gas at an elevated pressure after flow through the heat exchanger.

Optionally, the outer tube may have the enclosing wall thereof cooled intensively. Such an arrangement is indicated in Figure 4, wherein a jacket 49 surrounds the tube 31 and is provided with nozzles 50 and 51 for the circulation of a cooling liquid, such as Water.

I claim as my invention:

1. Process for changing the temperature of a gas comprising the steps of expanding gas with gyratory motion simultaneously within each of two coaxial vortex tubes of difierent diameters whereof the tube having the larger diameter surrounds at least a part of the other tube in spaced relation and thereby producing within each of said tubes by the heat-separation efifect a pair of coaxially rotating gas fractions of different temperatures, the warmer fraction within the inner tube moving peripherally in contact with the inside of the inner tube wall and the colder fraction within the outer tube moving in contact with the outside of the inner tube wall, and discharging gas from each of said tubes.

2. In a process of producing a cold gas by the heatseparation elfect wherein a gas is expanded with a gyratory motion within a vortex tube and cold gas is discharged from the tube, the improvement of cooling the outer wall of said tube by a stream of cold gas which moves rapidly in direct contact with said wall and is produced in situ by the heat-separation effect resulting from the expansion of a gas with gyratory motion within a second vortex tube which at least partially surrounds the firstmentioned tube.

3. Process according to claim 2 wherein said firstmentioned tube has a cold end and a hot end situated respectively on opposite sides of the inlet by which the gas is admitted thereto, said hot end being longer and said cold gas being discharged through an axial orifice at said cold end, and the said rapidly moving stream of cold gas in the second tube is produced by admitting a gas tangentially thereto near the said cold end of the first-mentioned tube, flowing said admitted gas as hot and cold fractions moving helically and coaxially about the first tube along the hot end thereof in a direction away from said inlet, and discharging all said admitted gas from the second tube at the end thereof which is situated in the said direction.

4. Process according to claim 2 wherein the gas which is expanded in the second vortex tube is the cold gas discharged from the first-mentioned tube, said cold gas being flowed in heat exchange with a warmer medium prior to expansion in the second tube.

5. Process according to claim 2, wherein said firstmentioned vortex'tube has a cold end and a hot end situated respectively on opposite sides of the inlet by which the gas is admitted thereto, said cold gas is discharged at the said cold end, through an axial orifice with a diameter less than that of the tube, and a separate fraction of hot gas is discharged from said hot end.

6. Process according to claim 2 wherein the confining wall "of the second vortex tube is cooled by v applying a cooling medium thereto. 4

7. Process according to claim 2 wherein said firstmentioned vortex tube has a cold end and a hot end situated respectively on opposite sides of the inlet by whichthe gas is admitted thereto, and all of the gas admitted to said first-mentioned tube is-discharged at the i said cold end "through an axial orifice ofdiameter less than that of the tube. s I 8. Method of producing cold gas in a gas stream which is initially under pressure comprising the steps of expanding said gas in a first vortex tube by admitting the gas thereto tangentially nearer one end than the other and eflecting a separation of said gas into a hot fraction moving as a peripheral stream in contact with the inner surface of the tube and a cold fraction rotating coaxially within said peripheral stream; discharging cold gas from said tube;- and cooling said hot fraction while within said first tube by similarly expanding gas with gyratory motion a second vortex tube which at least partially surrounds the latter end of the first tube substantially coaxially thereto and thereby producing a second hot fraction moving peripherally within the second tube and a second cold fraction rotating about and in contact with the outer surface of the first vortex tube, thereby cooling the first tube with cold gas. which is in rapid motion and is produced in situ, and discharging gas from the second tube.

9. Vortex apparatus for changing the temperature of gas comprising a pair of coaxial vortex tubes of different diameters, the tube of larger diameter surrounding at least a part of the other tube in radially spacedrelation; one or more inlets for each said tube disposed for the admission of gas with gyratory motions to produce within each tube a pair of coaxially rotating gas fractions-of different temperatures by the heat-separation effect; and discharge means for discharging gas from each of said tubes.

10. Vortex apparatus according to claim 9 wherein the inlet of one of said tubes is connected to a discharge means of the other tube, for the flow of gas successively through said tubes with successive expansions.

l1. Vortex apparatus according to claim 10 including aheat-exchanger interconnected between the inlet and discharge means recited in said claim.

12. In combination with the vortex apparatus according to claim 9, means for cooling the gas fraction in the tube of larger diameter which moves in contact with the outer wall thereof.

13. Vortex apparatus according to claim 9 wherein said tube of larger diameter has'the gas-inlet situated near one end thereof and the discharge means situated Y viding an orifice at the tube axis having a diameter less V than that of the tube.

15. Vortex apparatus according to claim 14 wherein said inner vortex tube has a second discharge opening at the end of the hot end for the discharge of hot gas.

16. Vortex apparatus for producing cold 'gas from a gas stream by the heat-separation elfect comprising: a thin-walled tubular body defining a first vortex chamber and having interior and exterior surfaces of revolution, one or more gas-inlets disposed tangentially to said interior surface and dividing said tube into hot and cold ends which are, respectively, relatively longer and shorter and situated on opposite sides of the gas-inlet, and wall means at said cold end providing an axially disposed, cold-gas discharge orifice with a diameter less than that of the tube; a chambered body including a confining wall whichvencloseslavsecond, tube-shaped vortexchamber with an interior surface of revolution surroundingsaid 17. Vortex apparatus according t0':.claim,16 including :meansforcirculating a? cooling fluidjabout thev second vortex chamber near to and injheat: exchanger relation to; said confining wall fthereof.

'18.- Vortex apparatusaccording tolclairn 16 including heat exchangerihaving flowpassagesf r heflow of e aramgases;:onexof t qs vpa s in c c t a itogrecei vezcold;gassfirom said cold-gas discharge orifice ,of .the ;fi'rst =yortex; chamber and to discharge gas; to. the

-' 5 gas-inlet ofthegsecondi vortex: chamber.

.flReierenice s Cit ed infthe file of. t nis patent ,JUNITED STATESZPATENTS

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