CA1290159C - Refrigerant expansion device with means for capturing condensed contaminants to prevent blockage - Google Patents

Abstract

ABSTRACT
A refrigerant expansion device such as a Joule-Thomson expander has a surface with grooves or recesses which capture contaminants that condense from the refrigerant flow in the device, thereby avoiding blockage of the device by the condensed contaminants.

Description

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This applicatlon is a division of Canadian Patent Application Serial No. 520,910 filed October 20, 1986.

~:5 This invention pertains generally to refrigeration :
: systems and is more particularly concerned with an~
improved refrigerant~ expansion d~evice~having means~;for~
capturing contaminants condensed from the refrigeran~
~10~ fluid so ~hat~blockage of the device~by~such contaminants is avoided. The invention is espec:ially ~:
use~ul in cryogenic gas liquefaotion systems employing~
Joule-Thomson expansion~devices,~

;1~5~ Gases may be cooled below their~liquefaction ;temperatures;by expanding from a high:pressure to a l~ow~
: pressure in a constant enthalpy process known as ::~
` Joule-Thomson expansion. When the temperature of the :~ : gas ~ust prior to expansion is sufficiently below the 20; inversion temperature of the gas (the temperature below : which expansion~resul~s in a:decrease in~temperature), the~gas undergoes a phase change upon expansion, ~:

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~.~90159 forming two distinct fluids -- saturated liquid (the useful procduct) and saturated vapor. The expansion of gases in this manner is generally effected by a so-called Joule-Thomson expansion valve.
The present invention is especially applicable to miniature liquefiers of the Linde-l~ampson class, which customarily employ cryostats includillg a Joule-'l`llomso expansion valve made integral with a final stage eontra-flow, recuperative heat exchanyer (u~sually referred to as a Giaque-llampson lleat exchanyer).
Fig. 1 illustrates a conventional cryostat of the foregoing type. The cryostat, designated by reference numeral 10, includes an elongate mandrel or core 12 about which a length of fine bore finned tubiny 14 is helically wound. The tube 14 terminates ~t an end 16 having a fixed opening which is partially restricted and which constitutes the Joule-Thomson eY~pansion ori~ice. The ~tound tubing 14 an~ Joule-Thomson orifice~
1,6 are contained in a sheath 18 closed at one end 20 whieh eorresponds to the cold end of the device.
Usually the sheath will be incorporated as part of a dewar vessel and the previously described components will be inserted therein.
~25 In operation of cryostat 10, high pressure coolant fluid (gas) is supplied to expansion orifice 16 througi tubing 14. The non-liquefiecd portion of the coolant fluid 10ws baek along the heat exchancJer (to the left in Fig. 1) to pre-cool the incomillg gas and is then reeyeled through the cooling system. Spacer strands 22 are ordinarily wrapped about the core 12 and the inner periphery of the sheath 18, between adjacent passes of the finned tubing 14 so that the non-liquefied coolant flows between the fins o~ the tubing 14 for good heat ::
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~29(~ ii9 exchange. Liquefied coolant is removed (as -throuyh an opening in the sheath) as useful product.
Cool-down of the device just described takes place basically as follows. Initially, assuming the incoming high pressure gas is at a temperature below the inversion temperature, the ~as will expand through the Joule-Thomson orifice to a lower temperature. At start-up the ini-tial temperature of the yas is not su~ficiently low to form li~uid. All of the e~panded gas will thus be returned along the fi.nned tubing heat exchanger for recycling. As the cool expanded gas flows along the heat exchanger, it absorbs heat from further incominy gas which is thus pre-cooled. The ~urther gas will therefore expand from a lower tempera-ture than did the initial gas and will therefore attain a lower post-expansion temperature. It then pre-cools yet additional incoming gas to an evel~ lower pre-expansion temperature/ and so on. This bootstrappiny process continues until the illCOmilly gas is pre-cooled sufficiently below the inversion temperature th~t a liquid componen-t is formed, whereafter the system reaches equilibrium with the li~uid beiny removed and additional yas beiny supplied as makeup.
Conventional fixed orifice Joule-Thomson devices such as that in ~ig. 1 suffer ~rom two significant d-isadvantayes in practice. First, due to the fi~ed expansion orifice, such devices are characterized by slow initial cool-down and poor temperat~lre regulation.
~ore particularly, with a fixed orifice the fluid mass flow rate increases as cool-down procJresses. Increas-ing flow, however, is precisely opposite the criteria for rapid cool-down and good temperature regulation (i.e., maintaiiling an even temperature). To achieve these objectives it is necessary that the initial flow :

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A second major problem with fixed orifice Joule-Thomson systems is clogging caused by the accumulation of condensed contaminants from the coolant fluid stream. More particularly, as the incoming gas expands through the ~oule-Thomson orifice, contaminants contained in the gas s-tream condense, freeze and then accumulate in the oriEice -- eventually leadin~ to complete blockage of the flow. The flow is thereafter restored when the temperature of the device rises sufEiciently that the contaminants melt and are discharged by the pressure of the coolant gas.
A number of Joule-Thomson expanders have been proposed in the prior art which include mechanisms for throttling the gas flow to improve upon the temperature characteristics of fixed orifice devices. Temperature responsive needle valves are perhaps the most commonly ~1~ proposed meohanism for this purpo~e. Various arrangements have been devised to impart the required temperature sensitivity to the needle valve, including, for example, temperature responsive bellows arrangements and assemblies incorporating structural components having different coefficients of thermal expansion.
Generally, these devices have been quite complex, due largely to the required structure for moving the needle element into and out of the expansion opening. These devices also frequently exhibit poor temperature sensitivity. Moreover, needle valve type devices are susceptible to blockage by condensed contaminants.
I

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', "'," '' 1290~s9 In one of its principal aspects, parent application Serial No. 520,910 was concerned with an expansion valve and a cryostat designed to eliminate the problems of slow cool-down and poor temperature regulation by the use of a self-regulated, temperature-responsive construction based on materials having different coefficients of thermal expansion.
The parent application also disclosed another important concept -- in particular, an expansion device incorporating special means for capturing contaminants condensed from the refrigerant stream to avoid blockage of the expansion orifice. It is this latter concept with which the present application is especially concerned.
More particularly stated, in one of its broad aspects, the present invention provides an improved refrigerant expansion device in a refrigeration system of the type wherein a refrigerant fluid is compressed ~20 and subsequently expanded to effect cooling. The device includes means defining an annular passageway having an upstream end into which the refrigerant fluid ~` is introduced under pressure and~ a downstream end ~ -terminating at an annular expansion opening through ~25 which the introduced fluid is expanded, the passageway being subj~ect to accumulation therein of condensed contaminants from the refrigerant fluid. The device further includes means disposed along the passageway for capturing the condensed contaminants such that ~the passageway does not become blocked by such contaminants.

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129()~59 In another of its aspects, the present invention provides cryogenic cooling apparatus including a ~oule~
Thomson expansion device having an inner member and an outer member surrounding the inner member, with an outer peripheral surface of the inner member and an inner peripheral of the outer member defining an annular passageway. The passageway has an inlet toward an upstream end thereof into which high pressure refrigerant fluid is to be introduced and an annular outlet orifice at a downstream end thereof throu~h which the introduced fluid is to be expanded. The device further includes recess means formed in the respective peripheral surface of at least one of the aforementioned members for capturing contaminants which condense out of the refrigerant fluid, thereby inhibiting blockage of the passageway by the condensed contaminants.
In yet another of its broad aspects, the subject invention provides an improved refrigeration expansion ~20 device of the type in which a refrigerant fluid flows along a surface which leads to an expansion orifice from which the fluid is expanded. In the improved device, this surface has recess means formed therein for capturing condensed contaminants from the fluid as the fluid passes along the surface.

The subject invention and its advantages will be appreciated more fully from the following detailed description which is given in the context of a self-regulated Joule-Thomson cryostat of the type described in the parent application. The description refers to the accompanying drawings, wherein:
Fig. l is a side viéw, shown partly in section, of a cryostat in accordan_e with the prior art;

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' ~2~3~159 Fig. 2 is a cross-sectional side view~of a cryostat in accordance with the invention;
Fig. 3 is an enlarged cross-sectional view of the expansion valve portion of the cryostat of Fig. 2;
Fig. 4 is a fragmentary sectional view showing details of an alternative embodiment of the cryostat;
and Fig. 5 is a fragmentary sectional view showiny details of yet another embodiment of the cryostat.

10 ' Fig. 2 depicts a cryostat 30 incorporating a Joule-Thomson expansion valve 60 in accordance with the present invention. In the illustrative embodiment, ~ expansion valve 60 includes a substantially frusto-conical valve member 62 supported at an end of first means in the form of elongate core shaft 40 of substan-tially cylindrical cross section. For purposes which will become apparent hereinafter, the core shaft 40 includes a main section 42 having the valve member 62 and an extension 44 supported at its opposite ends, as shown.
Expansion valve 60 further includes a tapered valve seat 64 supported circumferentially adjacant a ~ lengthwise portion of valve member 62 by second means ln the form of a tubular sheath 50 slidably received over and coaxial with the core shaft 40. Sheath 50 surrounds core shaft 40 along the major portion of the core shaft length, as shown. Core shaft 40 and sheath 50 constitute, in part, a mandrel about which finned coolant fluid tubiny 32 is wrapped and secured in a conventional manner. One end 33 of tubing 32 is connected to the expansion valve 60 in a manner to be described later. As will be explained in detail :

, : . , :' , . ' , ~: ~ , ~' :, , ~L~9~59 hereinafter, the core assembly constituted by shaft sections 42 and 44 and valve member 62 is constructed to have a lower effective coefficienk of thermal expansion than the sheath 50 in order to render valve 60 adjustable in response to the temperature of the fluid expanded from the valve 60.
With continued reference to Fig. 2, it will be seen that the heat exchanyer and e~pander portions of cryostat 30 are contained within an outer sheath 34 in the form of a cylinder which i5 closed at one end. The closed end of outer sheath 34 deEines an expansion chamber 36 for yas exiting valve 60 and from which - liquefied coolant gas may be recovered by suitable conventional means (not shown). The non-liquefied portion of the e~panded coolant gas flows back alo~ny the wrapped tubing 32, between sheath 50 and outer sheath 3~, and absorbs heat from incoming hiyh pressure gas within the tubing, whereby the incominy yas is pre-cooled prior to expansion. ~he expanded gas then exits from an outlet (not sho~n) at the open end of the outer sheath 34.
It will be appreciated that in praGtice, outer sheath 34 will ordinarily be incorporated into a dewar 25 ~ vessel employed in conjunction ~iith the cryostat 30 for containing the liquefied product and that the~heat ~
exchanger and Joule-Thomson expander portions of the~ ;
cryostat will be inserted into the sheath, which is ~ illustrated herein to Pacilitate understanding of the ;~ 30 invention~
The structural details oE Joule-Thomson expansion valve 60 will now be described. Referriny additionally to Fig. 3, the generally frusto-conical valve member 62 will be seen to co~nverge to~lard a free extrernity 66 thereo~ from a base portion 68 ~hich is attached to .
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~2~ 9 main section 42 oE core shaft 40. The outer periphery of the base portion 68 of the valve memher i5 non-tapered to conform to the inner circumference of tubular sheath 50, with the free extremity 66 being of reduced cross dimension relative to the base portion 68. Valve member 62 is attached to the main section 42 of tlle core shaft by means of an a pin 70 projecting axially from the base portion 68 and received in a corresponding socket 46 at the associated end of core shaft section 42. Pin 70 may be externally grooved, as shown, to facilitate fixation of the valve member 62 to core shaft section 42 (e.q., to receive an epoxy adhesive). Valve member 62 may also be formed inte-grally with core section 42.
Valve seat 64 essentially has the form of an annular wedye which converges from a wider cross dimension toward base portion 68 o~ the valve member to a narrower cross dimension toward free extremity 66 of the valve member. To simplify manufacturing of the valve 60, the valve seat 64 may be formed as a separate element which is inserted and secured within the inner periphery of sheath 50, althouqh the seat may, of course, be formed integrally with sheath 50.
In accordance with the invention as shown in Fig.
3, valve member 62 and valve seat 64 are arranged with their opposing peripheral surfaces spaced slightly apart to define an annular passage~,Jay 72 which conver-ges toward free extremity 66 of valve member G2 and terminate~; at an annular expansion openinq 7~ adjacent the free extremity 66 of the valve member. Passageway 72 oE the illustrative embodiment is interrupted along its length by one of a pair o~ circumferential qrooves 76, 77 which are C-lt into the external periplleral surface of valve member 62. Tlle grooves 76, 77 (which, , .

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in the form shown, are cut substantially perpendicular to the valve member surface) serve -two very important practical purposes which will be discussed shortly.
To permit the introduction of high pressure gas into valve 60, sheath 50 includes peripheral openings 52 in communication with an upstream end 78 o~ converg-ing annular passageway 72. In the ~orm shown, the openings 52 are aligned with spoiler yroove 77 adjacent end 78 o~ the passageway 7Z. Coolant gas is fed into the aliyned ~roove, and thus the passageway, -throuyh openinys 52 by means of an annular high pressure adapter 80 secured to the outer periphery of sheath 50.
Hiyh pressure adapter ~0 is provided with an opening 82 wherein end 33 of tubing 32 is received, and an internal peripheral channel or groove 8~ in communica-tion with both opening 82 of the adapter and openings 52 of the sheath.
Referring again to Fig. 2, it will be seen that at the end of the cryostat 30 opposite e~pander 60 (i.e., at the "warm" end of the cryostat) the ends of core shaft 40 and sheath 50 are connected to a calibration assembly 100 which holds the core shaft and sheath in selected relative axial positions. The selected ~25 positions of the core and sheath are adjustable in a manner to be described later.
Given the basic structure of cryostat 30 as described hereinabove, the purpose of constructing the core assembly ~2, ~, 62 so as to have a lower effec-tive coefficlent o~` thermal expansion than sheath 50 will be readily understood. In particular, it will be appreciated that as the temperature of the cryostat 30 decreases, the sheath will contract more rapidly than the core assembly. ~s a resultj valve seat 6~ is drawn axially over valve member 62 in the direction of base , ' .

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portion 68 (to the left in Figs. 2 and 3). The clearance bet~een the opposing peripheral surfaces of valve member 62 and valve seat 68 is therefore reduced, thus decreasing the effective flow area of converging annular passayeway 72. Conversely, as the temperature of the coolant fluid increases, sheath 50 expands more rapidly than the core assembly, thereby with~rawing the valve seat axially away from the valve member (to the right in Fiys. 2 and 3). This action increases the ClearallCe betWeell t}le OppOSillg peripheral sur~aces of the valve member and seat, thus increasing the e~fec- , ;
tive flow area of converging passayeway 72. The . differential longitudinal contraction and eY~pansion : :15 between the core assembly and sheath as just described : is accompanied by differential diametric contraction ; and expansion between the expansion valve elememts 62 and 64, which contributes to the temperature sensitiv-ity of the converging passageway 72.
~:20 As noted earlier, the grooves:76, 77 cut into th~e : sur~ace of valve member 62 serve ~lo part:icularly ~ :
~:; important purposes. First, the grooves act as laby- ~
rinth spoilers, caus~ing degradation in the coolant :.
; fluid flow through the Joule-Tilomson valve to enhance :
the~pressure difference between the inlet and outlet ~:~ : sides of the valve. Second, the grooves act as catchment reservoirs for capturing contaminants contained in the coolant gas stream. The effect of the spoilers as catchlllent reservo.irs i5 oL substantial practical signi~icance in that the expansion valve 60 is thereby rendered highly resistant to clogging.by condensed contaminants. The resistance to blockage results in highly reliable long-term operation, makiny the invention especially suitable for applications in which maintenance requirements must be kept to a : : ~
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, 1.290159 minimum. Additionally, because the design of valve 60 is less susceptible to blockage, the valve can operate with coolant gases of far lower purity than can be employed in conventional Joule-Thomson devices. The high purity requirements of conventional devices increase the costs of not only the coolant fluid, but of the en-tire associated cryogenic cooling system as well (due to the need for filtra-tion, as well as other accommodations).
In practice of the invention, a number of yrooves other than 2 may be employed depending upon the requirements of a given application. Indeed, for some applications adequate performance may be obtained without the grooves being present, as the converginy annular passageway is itself more resistal~t to blockage than a circular expansion orifice. T~le presence of the grooves is contemplated as a general rule, ho~lever, due ~ to the significant advantages ~Jhich they provide.
Referriny again to ~ig. 2, in order that cryostat 30 may accommodate prescribed flow criteria for particular applications, holding means assembly 100 is adjustable so that core shaft 40 and sheath 50 may~be held in selected relative axial positions. More particularly, assembly 100 permits adjustment of the ~
positional relationship between respective ends 48 and 54 of the core and sheath opposite valve 60 in order to vary the clearance between the cpposing peripheral surEaces oE va:lvc member 62 and valve r,eat 6~. l3y varyiny the aforementioned clearance, the e~fective ~low area o~ converginy annular passacJeway 72 may be calibrated.
In the embodimellt of Fig. 2, the adjustable means 100 includes an adapter member 102 ~ ich is of a generally tubular configuration and slidably received , 1~90~ 9 over the core extension 44. The adapter 102 has an eccentric bore 104 connecting an inlet end 35 of tubing 32 to a coolant ~luid supply line 1()6 as s~lowr. ~`
Adapter 102 furtller has a central bore with a ~orward end portion of enlarged diameter as indicated at 108 wherein the end 54 of sheath 50 is secured. O-ring seals 110 are placed in correspondin~ circumferential grooves in extension 44 to provide a seal between the periphery of extension 44 and the inrler peripheral surface of adapter 102 and thereby prevent coolant ~1as leakage past enc~ 54 o slleath 50 aloll~ tlle opr)osed peripheral surfaces of core extension 44 and adal~ter 102.
Adapter 102 and core extension 44 llave key and keyway means 112 114 cooperable tllerebetween ~e key 112 being-in ~orm of a pin which is partially inserted in a socket in core extension 44 and partially located in keyway 114 in adapter member 102. The key and keyway means 112 114 permits relative lo~ itudirlal Inovelnellt 20~ between core shaft 40 and adapter 102 hut prevent~
relative rotational movement between tllese elemerlts.
For effectin~ calibrating movemerlt betweell core shaft 40 and slleath 50 ~more speciEically vaLve member 62 and valve seat h4) and adjustmellt melilber 120 llas a ~longitudinal bore 112 which threadably receives a threaded end pin 116 of core extension 44. ~djustment member 120 is also connected to adapter 102 by rneans of a retainer clip 118 which may be a C-clip cooperable between opposing grooves in the interrlal periphery of adjustment member 120 and the external peripllery of adapter 102 as showrl. Adjustment melrlber 120 ~unctions as a turnbuckle with C-clip 118 actiny ~o ~)ermit rotation o~ the adjustment rrlember about the axis of .

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~L~90~9 core shaft 40 and to maintain adapter 102 and a~just-ment member 120 in axially ~i~ed relation.
To adjust converging annular passageway 72 for calibration, adjustment member 120 is rotated about the axis of core shaft 40. By virtue of C-clip 118, there is no axial displacement of adjustment member 120 relative to adapter 102. However, due to the threaded engagement of adjustment member 120 with core shaft extension 42 and the cooperation o~ key and keyway means 112, 11~, tlle core sllaft (specifically, extells:io 44) is caused to slide within adapter men~ber 102 Because sheath 50 is fixedly secured to a~apter 102 ~and slidably received over the core shaft 40), the foregoing sliding movement of the core shaft results in axial displacement of the core shaft ~0 relative to sheath 50, thereby causing a corresponding change in clearance between valve member 62 ~nd valve seat 6~.
Once the desired settiny of converying annular ~20 passageway 72 has been attained, the ad~ustment member 120 may be locked in place by mealls of a lockiny cap 124 which fits over a rear end of adjustment member ;~ 120, as shown. Locking cap 124 includes a central threaded plug 126 which threads into bore 122 from the .
rear. Locking cap 124 is rotated u~ltil plucJ 126 is threaded into endwise abutment with pin 116 of core extension 44, thus providing a locking effect. It~will be apparent that the calibration assembly 100 of~ers the siyllificallt ~clval~tage o:E adjustal:).ility durirlg operation of the cryostat 30.
Insofar as particular materials of construction are concerned, it will be apparent -to those skilled in the art that many combinations of materials may be employed to implement the present invention. However, certain desirable characteristics 'or the various .

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: ' , ~L29(~159 structural elements should be considered. For the frusto-conical valve member 62, a hard material, resistant to the erosive effects of the high speed gas flow through the converging annular passayeway is desirable. The material for the valve member should also have a low coefficien-t of thermal expansion.
Invar, a hard metal composed of 34~ nickel and 66%
iron, is exemplary of suitable makerials for the valve member. For the main core section 42, a material having a low coePficient of thermal expansion and low thermal conductivity is desirable -- for example, glass reinforced epoxy composites, one such composite being G-10 which is a thermosetting plastic with 10% glass lS fiber reinforcement. G-10 is readily available commercially, one source beiny Synthane-Taylor of Laverne, California (which supplies -this material under the designation G-lOCR).
Regarding sheath 50, a high coefficient of thermal expansion and hiyh thermal conductivity are desirable.
7075-T6 aluminum may be employed for both the sheath 50 and valve seat 64. The coefficient of expansion of this particular aluminum is relatively small, generally ~speaking, but the dimensional changes achievable Wit}l this material are significant within the fine toler-ances employed in miniature Joule-T}lomson expanders.
The basic components 102, 120, and 124 of the calibration assembly 100 may suitably be constructed o~
303 stainless steel or the like, and i.t is therefore advantayeous Por core extension ~4 to be made of the same materi.al. Ilore particularly, hecause stainless steel is more easily machilled than G~10 to form the necessary features for coupliny the core to the calibration assembly, the use of a separate core extens~ion which is attached to the main coFe section :

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,,.: : . ., 12~01S9 can be advantageous. The O-rinc~ seals 110 of the calibr~tion assembly may be macle of TEFLOI~.
Without limiting the invention, exemplary con-struction parameters which may be employed are as ~ollows:

Valve Member (Invar): .412" total length .312" lenyth base to free end .05" diameter at free end .09" diameter of base portion 9-10 apex angle 0-4 spc-,ilers (.015" depth, .02" wicdth) Main Core Section: 1.66" length (G-lo) .09" diameter Core Extension: .80" length (303 stainless steel) .09" diameter Sheath (7075-T6 Al): 2.125" length .0935" inner diameter .113" outer diameter (.125" at enlargecl end) ;- 20 Valve Seat: .235" length (7075-T6 Al) .0932" inner diameter converging to .05"
10 ~ included angle High Press. Adapter .07" lenyth (7075-T6 Al) .1135" inner diameter Calib. Adapter rlemb. .375" length (303 stainless steel) .0935" inner diameter (.125" at enlarged end) Adjustment Member .375" lengtll (303 stainless steel) 72 bore thread pitch For securing the various elements oi~ cryostat 30 to one anot}ler, so~t solderiny is the preferred technique for strength and durability. Ilowever, the 3~5 invention has been successfully :implernentecl USilly other .
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It will be appreciated, of course, that construc-tion parameters may vary substantially from case to case, depending upon the requirements o~ particular applications. For example, for typical applications the apex angle defined by the converging peripheral surface of khe frusto-conical valve member may be in the range from about SD to about 30, ~1ith tlle included anyle of the converging peripheral GUr~ace o ~he valve seat being in the same range an~ yenerally complemen-tary to the taper of the valve member. The larger angles will, of course, produce a greater change in the effective area of the converginy annular passageway 72 for a given amount of contraction of sheath 50 relative to core assembly 40, 62. To prevent the opposing surfaces defining the passageway from sticking to one another upon complete closure of the valve (l.e., when the seat has been drawn over the valve member suffi-ciently to bring the opposing surfaces into contact)j the apex angle of the valve member may advantageously be made up to about 1 less than the included angle of the valve seat, preferably at least about l/4 less.
Turning no~ to Figs. 4 and~5, wherein elements corresponding to those in Figs. 2 and 3 are indicated by corresponding reference numerals, two additional embodiments of the invention will now be described.
Fiys. 4 and 5 respectively depict an alternative Eorm of attachment of the coolant fluid supply tubing end to the Joule-Thomson expander and a1l a].ternative calibra-tiO11 mechanism for the expander.
In the apparatus of Fig. 4, the hlgh pressure adapter 80 has been eliminated by direct connection of tube end 33' to the Joule-Thomson expander. In : `
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1;~9~)~S9 particular, tube end 33 ' is inserted into an opening 52 ' in sheath 50 ', the opening being aligned with a labyrinth spoiler groove 77 ' to ensure even distribu-tion of incoming coolant fluid into the upstream end of converginy annular passageway 72 ' .
Fig. S depicts a differential thread type calibra-tion mechanism 100 ' according to the invention. In this embodiment, main core section 42 ' ~there is no core extension) has an end pin 143 externally threaded at a first pitch (e . q ., 40 threacls per inch), whereas sheath end 54 ' is -threaded externally at a different pitch ~., 39 threads per inch). The respective threads of core and sheath portions 143 and 54 l are threaded ~in the same rotational sense ( e_g ., both right-handed threads). An adjustmellt memher 130 in the form of a thimble has threaded bores 132 ancl 134 wh:ich receive the ends of the core and sheath, respectively.
The core and sheath are coupled by cooperable ~;ey alid~ ~ ;
~20 keyway means, indicated diagrammatically at 136, which permits relative axial movement bét~,Jeell t:he core and sheath but prevents relative rotational movement there-between. Hence, upon each ~ull rotation of thimble 130 ~; about the axis of the core shaft, the core shaft and 25 ~ sheath are axially displaced relative to one another by an amount equal to the di~ference in~ the res~pective ; ~ thread pitches o~ the two members -- here, . 02564"
(1/39") less .025" (1/40") or .0006~". It will be appreciated that the foregoing calibration assembly 100 ' is adjustable during operation of the associated cryos tat .
While the invclltion has hereinabove been dess~ribed ~ ~ in connection with several preferred embodiments, it ; 3S wlll be apparent to those skilled in the art that various changes and modifications are possible consis-., ~ . .. . - , . : : : :

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tent Witil the principles of the invention, the scope of which is defined in the appended claims. Within its hroader range of applicability, exemplary practical uses of the invention could include condensation of vapor boil-off from liquid hydrogen and o~y~en fuel supplies stored on spacecraft in insulated dewar vessels at cryoc~ellic temperatures, and the li~uefaction of heIium and nitrogen for conventional industrial, medical, research, and defense applica-tions.
In comparative tests (US:itlC~ l)itrOgel-) of pro-totype cryostats in accordance with the invention against a conventional fixed orifice type cryostat, the devices according to the invention exhibited rapid cool-down and smooth temperature regulation and achieved hours of continuous operation without hlocka~e by condensed contaminants. The conventional device, on the other hand, required substantially greater cool-do~n time, was poorly temperature regulated, and e~perienced ~20 blockage by condensed contaminants in as little as 6-60 minutes of continuous operation dependiny on test conditions. Devices in accordance with the invention have tested successf~ully under a variety of conditions, including inlet gas pressures of 1000-3000 psi and ~25 ~ initial gas flow rates of 15-30 lpm, with typical cool-down periods being on the order of only one minute.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a refrigeration system in which a refrigerant fluid is compressed and subsequently expanded to effect cooling, a refrigerant expansion device including means defining an annular passageway having an upstream end into which said refrigerant fluid is introduced under pressure and a downstream end terminating at an annular expansion opening through Which the introduced fluid is expanded, said passageway being subject to the accumulation therein of condensed contaminants from said refrigerant fluid, and means disposed adjacent said passageway upstream form said expansion opening for capturing said condensed contaminants such that said passageway does not become blocked by said condensed contaminants.

2. A refrigerant expansion device according to claim 1, wherein said passageway is tapered from said upstream end to said downstream end.

3. A refrigerant expansion device according to claim 2, wherein said passageway is tapered convergently.

4. A refrigerant expansion device according to claim 1, wherein said capturing means includes means defining a recess adjacent to and in communication with said passageway.

5. A refrigerant expansion device according to claim 4, wherein said recess extends about a circumference of said passageway.

6. A refrigerant expansion device according to claim 5, wherein said circumference is an inner circumference of said passageway.

7. A refrigerant expansion device according to claim 5, wherein said recess is disposed intermediate said upstream end and said downstream end.

8. Cryogenic cooling apparatus, comprising a Joule-Thomson expansion device including a inner member and an outer member surrounding said inner member, with an outer peripheral surface of said inner member and an inner peripheral surface of said outer member defining an annular passageway having an inlet toward an upstream end of said passageway into which refrigerant fluid is to be introduced under pressure and an annular outlet opening at a downstream end of said passageway through which the introduced refrigerant fluid is to be expanded, and including recess means formed upstream from said outlet opening in the respective peripheral surface of at least one of said members for capturing contaminants which condense out of the refrigerant fluid, thereby to inhibit blockage of said passageway by the condensed contaminants.

9. Apparatus according to claim 8 , wherein said recess means comprises at least one circumferential groove.

10. Apparatus according to claim 9 , wherein said circumferential groove is formed on said inner member.

11. Apparatus according to claim 10, wherein said circumferential groove is cut substantially perpendicular to said outer peripheral surface of said inner member.

12. Apparatus according to claim 8, wherein said passageway is tapered.

13. Apparatus according to claim 8 , wherein said inner member and said outer member are supported by respective members having different thermal coefficients of expansion.

14. In a refrigerant expansion device in which a refrigerant fluid flows along a surface to an expansion opening through which the refrigerant fluid is to be expanded, the improvement wherein said surface has recess means formed therein upstream from said expansion opening for capturing condensed contaminants from said refrigerant fluid as said fluid passes along said surface and thereby inhibiting blockage of flow of said refrigerant fluid to said expansion opening.

15. The refrigerant expansion device of claim 14, wherein said surface is a wall of a passageway through which said fluid flows toward said expansion opening.

16. The refrigerant expansion device of claim 15, wherein said recess means comprises a groove.

17. The refrigerant expansion device of claim 15, wherein said passageway is annular and wherein said wall is an inner peripheral wall of said passageway.

18. The refrigerant expansion device of claim 15, wherein said passageway is tapered.

19. The refrigerant expansion device of claim 14, wherein said recess means comprises a groove.

20. The refrigerant expansion device of claim 54, wherein said groove extends lengthwise transverse to the direction of fluid flow along said surface.

21. A refrigerant expansion device according to claim 4 , wherein said recess is in the form of a groove which extends lengthwise transverse to the axis of said passageway.