US3596474A

US3596474A - Gas-handling apparatus and method

Info

Publication number: US3596474A
Application number: US784597A
Authority: US
Inventors: Alden T Bloxham; Harry C Fischer
Original assignee: Kellogg American Inc
Current assignee: Kellogg American Inc
Priority date: 1968-12-18
Filing date: 1968-12-18
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03

Abstract

We disclose gas-handling apparatus comprising a primary evaporator, first conduit connections for establishing a flow path for a compressed gas and the like through said evaporator, second conduit connections for establishing a flow path of a refrigerant fluid through said primary evaporator in heat exchanging relation with said gas path, a refrigerant unit coupled to said second conduit connections, and an auxiliary evaporator coupled between said refrigerating unit and said primary evaporator.

Description

United States Patent 1,853,236 4/1932 Shadle inventors Alden '1. Bluxhnm Brldgcvilk. Pm: Harry (J. Fischer. Royal Oak. Milli. Appl. No. 784,597 Filed Dec. 18. 1968 Patented Aug. 3. 1971 Assignee Kellogg American. inc.

Oakmont, Pa. by said Harry C. Fiscimr GAS-HANDLING APPARATUS AND METMQD 16 Claims. 7 Drawing Figs.

US. Cl 62/93. 62/113. 62/85. 62/513. 62/272 Int. Cl F256 17/116 Field of Search 62/85. 93. 513. l 13, 272

Rclercnces (31ml UNITED STATES PATENTS 1.969.227 15/1933 62/272 2.051.971 6/1926 62/513 2.120.764 6/1938 62/573 2.477.772 6/1949 62/93 2.766.254 6/1966 Mallmfi.......... 62/513 2.841.965 7/1959 Ethiirington 62/113 3.041.842 7/1962 Hiiirmfliifi 62/93 3.050.954 13/1962 62/93 3.359.763 12/1967 Fimilm 62/93 Primary Examiner william .1. Wyn Anamey man .1. Smith AHSTWWT: W6 disnlosm gwhnnclling apparatus comprising a primary avapnrator. first caonciuit mnneqtiuns for establish ing a flow path fur a rmmprmmmi gm; and this like through said mvapormm. amend wncluii qonnmtiuna for establishing a flow path of a refrigqmm fluid ihruugh said primary evaporator in heat axchnnging ralation with said gas path. a refrigerant unit coupled in said :mcond qoncluit aonnemiona. and an auxilinry evapmator euuplqcl bmwman said mfrigarming; unit and said primary cwnpormm.

GAS-HANDLING APPARATUS AND METHOD The present invention relates to means and methods of handling compressed gases and more particularly to dryers of the refrigeration type for compressed air and other gases.

Although our invention is described herein primarily with reference .to compressed air handling equipment, it will be obvious as this description proceeds that our invention can be used with other gases or combinations of gases.

A variety of equipment for cleaning and/or drying compressed airand other gasesis known. Widely ranging operating conditions have made such equipment difficult to control with the desired .stability. For example, in known refrigeration drying systems, stable control is difficult where the drying function is variable, i.e., when the compressed air or other gas is supplied .in differingdegrees of wetness. Simple pressure and temperature control means usually are not adequate for the required degree of control. The separated moisture may freeze .in parts of the system and render it inoperative.

The operational difficulties of conventional equipment for handling compressed air and other gases are further aggravated where the compressed gas must be supplied at widely varying conditions of pressure and temperature. Conventional equipment hasbeen unable to supply, without complex controls and other complicated components, a consistent dewpoint dryness under these varyingconditions, which are further complicated by variations in ambient air temperatures. For example, in industrial applications, compressed air handlingequipment may be used for hot wet incoming air varying from p.s.i.g. to 1,000 p.s.i.g. at an inlet temperature of 130 F. or higher. Ambient temperatures may vary between 40 F. and i10 F. Under these conditions rather complicated conventional. equipment is required to provide cooled, com pressed gas. with an acceptable and consistent dewpoint dryness. insofar aswe are aware there is no available equipment which is capable of continuous operation and wherein the compressed air drying function can bevaried at will between zero load and full load while maintaining a consistent dewpoint dryness.

in the past, a number of air handling systems have been proposed, typified by the U.S. patents to Coblentz, U.S. Pat. No. 2,632,315; Ritter, U.S. Pat. No. 2,5l3,679; Meckler, U.S. Pat. No. 3,102,399; Shipman, U.S. Pat. No. 2,257,983; Cook et al.. U.S. Pat. No. 2,1 l9,20l; Schweller, U.S. Pat. No. 2,692,481; Newton, U.S. Pat. No. 2,367,305; Carrier, U.S. Pat. No. 2,154,263; Kohut, U.S. Pat. No. 2,835,476; and Lund, U.S. Pat. No. 2,451,682,-al| of which suffer from the aforementioned defects. Most of these prior systems utilize various arrangements of evaporators and regenerative heat exchangers for the incoming airor other gas which is being cooled, cleaned and/or dehumidified. However, one of these systems is capable of an output of compressed air having consistent dewpoint dryness over a wide range of operating or am bient conditions. in particular, none of these references em ploys primary and auxiliaryevaporators together with other novel features of our invention, which are described below. As mentioned above, freezing is likely to occur under certain load conditions.

Freezing of moisture in such equipment has been prevented in the past by brute force techniques involving for example a capillary expansion valve coupled with a hot-gas bypass valve.

The hot-gas bypass valve is particularly subject to erosion of the bypassed gases asa result of scouring and cavitation. The bypass valve is complicated in construction and difficult to manufacture and repair. The capillary expansion valve cannot be regulated properly, save by replacing with a differently sized valve.

Thermostatic expansion valves also are commonly used for controlling gas handling and drying equipment. These valves are rather complex and are subject to hunting. Moreover, the control function provided by thermostatic expansion valves is confined to a very narrow range of operating conditions.

3 When the design limits of these valves are exceeded, even slightly, the control function is largely lost.

We overcome these deficiencies of the prior art by providing a continuously operable refrigeration drying system capable of consistent dryness in output air irrespective of variable operating and ambient conditions. Our invention'engenders stability and controllability through the use of a unique arrangement of primary and auxiliary evaporators. These characteristics are further enhanced by use of an automatic expansion valve or the like, in conjunction with our evaporative system. The refrigeration system of our invention is capable of continuous noncycling operation, and the actual compressed air drying function thereof can be selectively varied from zero to full load, while producing a consistent dewpoint dryness of exit air. Although we describe our novel gas-handling equipment primarily in terms of removing or controlling the moisture content of compressed air, the compressed air or other gas is further cleaned by removal of oil and other entrained foreign matter along with condensed moisture. Compressed gas can be dried or otherwise cleaned by removal of other condensibles or entrained matter with our novel equip ment.

Our invention also contemplates the use of an automatic" expansion valve, which in this example is pressure sensitive. This type of expansion valve is of known construction but is provided with an internal pressure transmitting aperture where the valve is sensitized to line pressure. Alternatively, the valve can be provided instead with a bleed line where it is desired to sensitize he valve to pressure changes in an external conduit.

in conventional refrigeration drying systems, a pressuresensitive expansion valve exhibits relatively poor responses to load changes in the system. We have found, however, that a pressure sensitive expansion valve exhibits an admirable control characteristic and readily adjusts itself to the compressor load, when the compressor is run constantly and at the same speed. it is also desirable that the refrigerant compressor be provided with adequate size so that it is capable of forcing the automatic" expansion valve further open under certain conditions. As a result the expansion valve responds quickly to changes in load demand upon the equipment. In this respect, the expansion valve of the invention adjusts readily to load changes at the refrigerant evaporator and compressor. The pressure sensitive means of the expansion valve in conjunc tion with the continuously operated compressor controls the expansion valve such that the flow of refrigerant varies through main and auxiliary evaporators of the invention with variation in load on the load or air side of the main evaporator. This diverts the evaporation or condensation from a conventional condenser of the refrigeration unit to the aforementioned auxiliary evaporator and/or diverts evaporation from the main evaporator to the auxiliary evaporator, depending upon the amount and direction of load change. For this purpose, the pressure-sensitive means is coupled to the refrigerant path adjacent its outlet from the main evaporator.

With this arrangement of our invention, freezing of the removed moisture is obviated. Expansion of the refrigerant fluid is closely controlled with respect to load changes, irrespective of variable input and ambient conditions. The arrangement is not sensitive to narrow design limitations nor is it subject to hunting.

We accomplish these desirable results by providing gashandling apparatus comprising a primary evaporator, first conduit connections for establishing a flow path for a compressed gas or the like through said evaporator, second conduit connec tions for establishing a flow path of a refrigerant fluid through said primary evaporator in heat exchanging relation with said gas path, a refrigerating unit coupled to said second conduit connections, and an auxiliary evaporator coupled between said refrigerating unit and said primary evaporator.

We also desirably provide similar gashandling apparatus wherein said auxiliary evaporator is coupled regeneratively to said secpnd conduit connections.

We also desirably provide similar gas-handling apparatus wherein a second heat exchanger for said gas is coupled regeneratively to said first-mentioned conduit connections.

We also desirably provide similar gas-handling apparatus 'wherein an expansion valve and a third conduit connection are coupled between said primary evaporator and said refrigerating unit in bypassing relation to said auxiliary evaporator. 1

We also desirably provide a heat-exchanging structure for an evaporator and the like, said structure comprising a plurality of sheath tubes, a plurality of inner tubes inserted respectively and spacediy within said sheath tubes, and flow means for connecting one group of the group of sheath tubes and the group of coaxial tubes in series and for connecting at least some of the other group of tubes in parallel.

We also desirably provide a method for operating refrigerating gas-handling apparatus having a compressor, condenser, evaporator, and expansion valve, said valve being mounted for expansion of a refrigerant fluid into said evaporator, said method comprising the steps of operating said compressor continuously, preventing complete closure of said valve, sensitizing opening and closing movements of said valve to pressure fluctuations at a given point in said apparatus, and sizing said compressor for operation at constant speed and for forcing said valve furtheropen in response to load changes in a given direction.

During the foregoing discussion, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together with structural details thereof will be elaborated upon during the forthcoming description of presently preferred embodiments of the invention and presently preferred methods of practicing the same.

in the accompanying drawings we have shown certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same, wherein:

FIG. 1 is a schematic fluid circuit of one arrangement of our compressed gas handling equipment;

FIG. 2 is top plan view, with parts broken away and other parts removed, of a packaged equipment assembly arranged in accordance with FIG. 1;

FIG. 3 is a front elevational view of the apparatus as shown in F IG. 2;

FIG. 4 is a left side elevational view of the apparatus as shown in FIG. 3;

FIG. 5 is a cross-sectional view of the primary evaporator shown in FIG. 2 and taken along reference line V-V thereof;

FIG. 6 is another cross-sectional view of the evaporator of FIG. 2 and taken along reference line Vl-Vl thereof; and

FIG. 7 is still another cross-sectional view of the evaporator of FIG. 2 taken along reference line Vll-Vll thereof.

Referring now more particularly to the drawings, an exemplary gas-handling equipment 10 of our invention comprises a refrigeration and condensing unit 12 of known construction, regenerative heat exchanger 14, primary evaporator 16 and auxiliary evaporator 18. The receiver 20 of the refrigeration and condensing unit 12 is connected through conduit 22 to expansion valve 24 and thence to the main evaporator 16 where the refrigerant fluid is vaporized. in this example, the expansion valve 24 is controlled automatically by pressure which is the function of degree of vaporization of the refrigerant fluid within the main evaporator 16.

The refrigerant is further vaporized within the evaporator 16 by heat transfer from hot wet compressed air supplied to the main evaporator 16 through conduit 26. Between the end ofthe conduit 26 connected to the evaporator 16 and the inlet end 28 of the conduit 26, the regenerative heat exchanger 14 is coupled. in this example, conduit 26 is effectively extended through the hut exchanger 14, which is formed in this exsm= ple from s prlr of coaxial tubes 30. 32. The outer heat exchanger tube 30 is coupled to conduit 34 forming the outlet of the main evaporator 16. Before reaching the main cvupora= tor 16, the pressurized and dried outgoing air or other gas is therefore warmed regeneratively by heat-exchanging association with the hot wet compressed air passing through inner coaxial tube 32.

Within the main evaporator 16, water, lubricating oil, dirt and other foreign matter are condensed or leached out of the pressurized gas passing through the evaporator 16 by heatexchanging association with the expanding refrigerant. Water or other foreign material is periodically drained from the evaporator 16 through drain valve 36.

The refrigerant, which is partially or completely vaporized in the evaporator 16 flows thence to the auxiliary evaporator 18, in this example, consisting of outer and inner

coaxial tubes

38, 40. Suitable instrumentation 42 can be coupled to outlet refrigerant conduit 44, by which the primary evaporator 16 is connected to the outer coaxial tube 38 of the auxiliary evaporator 18. in passing through the auxiliary evaporator 18, the output refrigerant from the primary evaporator 16 is expanded further and returns to compressor 46 through conduit 48. The expansion of refrigerant in the auxiliary evaporator 18 in turn removes heat from refrigerant flowing from condenser 50 through conduit 52 which is coupled to the inner tube 40 of the auxiliary evaporator 18 from which it flows to receiver 20 through connecting conduit 56. The refrigerant is then recycled from the receiver 20 to expansion valve 24 and primary evaporator 16 through conduit 22.

in effect, then, both the incoming hot wet compressed air and the refrigerant supplied to the main evaporator 16 are cooled regeneratively before entering the primary evaporator 16. This arrangement permits the gas-handling equipment 10 to be controlled in the stable fashion under a wide range of operation and ambient conditions. in particular, refrigerant is supplied to the condensing unit 50 (conduit 52) and to the primary evaporator 16 (conduit 22) at correspondingly lower temperatures, whereby a marked increase in efficiency is obtained.

The valve 24 itself is of conventional construction but is provided with an internal pressure-transmitting aperture 25 to render the valve 24 sensitive to fluctuations in line pressure. Alternatively as denoted by conduit outline 27 the valve 24 can be sensitized through conduit 27 to pressures elsewhere in the apparatus, for example the evaporator outlet conduit 44. A suitable valve is available from Alco Controls Corp., St. Louis, Mo, for example catalog No. ACP-Z (internal pressure transmitting), ACPE-S (external pressure transmitting) or GI -300. Other sizes are available depending on particular equipment capacities. Additionally, the valve 24 is provided with a stop member 29 to avoid complete closure of the valve 24.

in conventional gas-handling apparatus of this type, it is expected that a pressure-sensitive valve, such as the valve 24, will not closely follow load changes in the system, i.e., both the stability and the control in the system will be poor, However, we attain an unexpectedly stable system having an excellent control characteristic by employing the pressure-sensitive valve 24 in conjunction with a continuously operated compressor 46. The compressor 46 is not operated intermittently or cyclically as in conventional systems. This eliminates one source of the phenomenon known as hunting in the system.

The use of a continuously operated compressor, such as the compressor 46 in conjunction with the pressure-sensitive valve 24 lays a basis for the vastly improved control characteristic exhibited by our novel apparatus. As the valve 24 is prevented from complete closure, the compressor 46 is sized so that it is onpuhlr of f cing he alve 24 m re near y c o when requir for ad changes in tho increasing direction. The valve 24 moves toward its open position upon oooroasing load, which increases load on the auxiliary evaporator 18. While the main evaporator 16 loads, the auxiliary evaporator 18 unlosdo The compressor 46 also is solootod on tho oasis of known criteria, for oonstannspood operation rogurdioss ottho load upon the system, within system capability. The use of o prouure sensitive valve, and a continuously operated oon= stant-speed compressor, coupled with the ability of the compressor toadjust the expansion valve opening endows the apparatus with considerable stability and with a control characteristic which is capable of compensating wide variations in incoming gas, pressure, temperature, and moisture content, as well as widely varying changes in ambient conditions. Our apparatus, therefore, is capable of supplying cool and dry compressed air or other gas at a consistent dewpoint dryness. At the same time, the cooperative aspects ofthe pressure-sensitive valve 24 and the continuously operated compressor 46 positively prevent freezing of condensed moisture in any part of the equipment.

As better shown in Figures 2-4 the package equipment unit is arranged such that the refrigeration and condensing unit 12 is mounted within an appropriately shaped individual casing 58, while the primary evaporator 16, auxiliary evaporator 18 and the regenerative eat exchanger 14 are supported within a separate casing 60. Inlet and

outlet conduits

28, 34 respectively are supported upon a wall portion of the casing 60 t Figure 2 of the drawings further illustrates a unique form of our primary evaporator 16 which is useful in the operation of our novel gas handling apparatus 10 or 10'. The evaporator 16 is arranged for obtaining an unusually high coefficient of heat transfer between air or other pressurized gas entering and leaving the evaporator via

conduits

26, 34 respectively and the refrigerant or other heat exchange fluid entering and leaving the evaporator 16 via

conduits

22 and 44 respectively (Figure 4 v In this arrangement of the invention, the evaporator 16 is provided with a heat-exchanging structure denoted generally by reference character 62. The heat exchanger 62 in this ex ample includes a plurality of sheath tubes 64 each of which contains a spined inner tube 66 supported substantially coaxially within the respective sheath tubes 64. The convecting spines 68 of each tube 66 are made by lancing and erecting narrow strips of the wall material of the tubes 66, and the outer ends of the spines 68 are closely fitted within the as sociated sheath or tube 64. The spines 68 are substantially less in thickness than that of the tube walls to avoid any possibility of leakage. Because bases of the spines are rooted integrally in the tube walls, the heat transfer characteristics are excellent.

In the illustrated arrangement the heat exchanger 62 includes four such sheath tubes 64 and a like number of associated or inner spined tubes 66, although a different number of sheaths and tubes obviously can be utilized as required.

Two of the sheath tubes 64, for example 64a, and the associated coaxial tubes as better shown in Figure 5 are extended beyond the ends of the remaining sheath tubes 64b at the right end of the evaporator 16 as viewed in Figure 2 and are secured to baffle plate 70 where they communicate with plenum chamber 72 which in turn communicates with air inlet conduit 26.

The other ends of the sheath tubes 640 are secured to baffle plate 74 adjacent the other end of the evaporator 16 and thus communicate with opposite end plenum chamber 76. Desirably, the remaining sheath tubes, such as the tubes 64b, likewise are secured to the right-hand baffle plate 74 for com munication with the adjacent plenum chamber 76 and with the first group of sheath tubes 64a. The tubes 646 however terminate short of the right hand baffle plate 70 at the opposite end of the evaporator 16 and are supported relative to one of the longer sheath tubes 640 by semicircular ring or bracket '78 (Figure 7) which desirably is welded or otherwise secured to each of the shorter sheath tubes 64b and to one of the longer sheath tubes 64a. Use of the bracket 78 does not interfere with the flow of fluid between and around the outer surfaces of the

sheath tubes

64a, 64b the purpose of which flow is described below. The flow baffle 74 at the opposite end of the evaporator 16 is provided with a central opening 80 as better shown in Figures 6 and 7 whereat the gas exit conduit 34 is Joined and sealed (as by welding or the like-Figure 2) for communication with fluid flowing between and around the sheath tubes 64.

With the urrungtu'nont just described, it will be seen that compressed air or other gas is caused to flow in parallel-series first through the longer shouth tubes 64a and then through the shorter sheath tubes 64b. in addition, the compressed air or other fluid is induced to flow transversely of the spines 68 to enhance heat transfer between the respective fluids within

tubes

64, 66. More specifically, compressed air enters the lefthand plenum chamber 74, sis-viewed in FlCi. 4, from inlet conduit 26 as denoted by flow arrow 64. From the chamber "is compressed air flows into both of the longer sheath tubes 64a as denoted by flow arrows 64 in FIG. 6. After following parallel annular paths through the sheath tubes 64o the compressed air enters plenum chamber '76 at: the opposite end of the evaporator 16. in the plenum chamber 76 the compressed gas flows from the adjacent ends of the sheath tubes 64a to the ends of the sheath tubes 64b as denoted by flow arrows 66 in FIG. 6. Thence, the compressed gas again follows parallel paths through the spines 68 of the shorter sheath tubes 646.

At the opposite ends of the shorter sheath tubes 646 the compressed gas enters a third plenum chamber 06 which is segregated from the adjacent end plenum chamber '73 by baffle 70. From the plenum chamber 66, as denoted by flow arrows 90, the compressed gas flows between and around the outer surfaces of the sheath tubes 64 to the central opening of the baffle 74 at the opposite end of the evaporator 16. From the baffle opening 80, the compressed gas exits from the evaporator 16 through conduit 34 as denoted by flow arrow 92. Alternatively, the exit conduit 34 can be closed or the con duit 34 and the baffle opening 60 can be omitted, and the compressed gas can be withdrawn via chain-outlined exit conduit 94 which communicates with the plenum 66 through the spaces between and around the sheath tube 64 as denoted by flow arrows 96.

From the foregoing paragraph, it will be seen that pressure drops are reduced by causing the compressed gas to flow through successive pairs of the sheath tubes 64 in series-parallel fashion. The pressure drop if desired can be further minimized by flowing the gas through all of the sheath tubes in simple parallel fashion. 0n the other hand, the refrigerant fluid, because of lesser pressure drops, is flowed in series through the refrigerant tubes 66. Thus, the refrigerant fluid enters conduit 22 as denoted by arrow 98 and flows through refrigerant tube 66a. At the other end of the refrigerant tube 66o, the fluid is conducted to refrigerant tube 66b through a reverse bend fitting or hose section. 90. The refrigerant tube 666 at its opposite end is similarly coupled by a second hose section 1100 to refrigerant tube 66c, which in turn is coupled to refrigerant tube 66d through a third hose fitting M3. The refrigerant tubes 66a and 66d are disposed in sheath tubes 64a while refrigerant tubes 66!; and 66c are in the shorter sheath tubes 64b. The fourth refrigerant tube 66d communicates with exit refrigerant conduit 44 as shown in FIG. 5. For convenience, the reverse fittings 98, 102, are disposed in plenum 76 while the reverse fitting 1106 is in the third plenum 66, of the evaporator R6. The flow of refrigerant successively through the refrigerant tubes 66a, 66b, 66c and 66d and the respectively associated

fittings

98, 100, 102 is denoted respectively by flow arrows 104, R06, 106.

It will be understood, of course, that other flow paths for the compressed gas and the refrigerant fluid respectively can be provided through our novel heat exchanger structure 62. We have found however that the aforedescribed flow paths are very effective in the efiicient transfer of heat between com pressed gas and a refrigerant fluid. It will be further understood that other heat-exchanging fluids can be utilized in place of those noted above.

From the foregoing it will be apparent that novel and efficient forms of compressed air cleaners andlor dryers have been disclosed herein. While we have shown and described certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same, it is o be distinctly understood that the invention is not limited thereto but may be variously embodied and practiced within the scope of be following claims.

We claim:

l. Gas-handling apparatus comprising a primary evaporator, first conduit connections for establishing a flow path for a compressed gas and the like through said evaporator, second conduit connections for establishing a flow path of a refrigerant fluid through said primary evaporator in heat exchanging relation with said gas path, a pressure-sensitive expansion valve in said refrigerant path, a refrigerating unit coupied to said second conduit connections, an auxiliary evaporator coupled between said refrigerating unit and said primary evaporator, and pressure-sensitive means coupled to said refrigerant path adjacent its low-pressure side of the evaporator for controlling said expansion valve so that a variation in said compressed gas flow varies the flow of said refrigerant so as to divert condensation thereof from said refrigerating unit to said auxiliary evaporator .and/or to divert evaporation thereof from said main evaporator to said auxiliary evaporatOl.

2. The combination according to claim 1 wherein said auxiliary evaporator is coupled regeneratively to said second conduit connections.

3. The combination according to claim 1 wherein said refrigerating unit includes a condensing unit therefor, some of said second conduit connections couple said condensing unit to one side of said auxiliary evaporator and others of said second conduit connections couple the other side of said auxiliary evaporator to said refrigerating unit and to said primary evaporator.

4. The combination according to claim 1 wherein a heat exchanger for said gas is coupled regeneratively to said first mentioned conduit connections.

5. The combination according to claim 1 wherein said expansion valve and a third conduit connection are coupled between said primary evaporator and said refrigerating unit in bypassing relation to said auxiliary evaporator.

6. The combination according to claim 5 wherein said expansion valve is provided with means for preventing its complete closure.

7. The combination according to claim 1 wherein said primary evaporator includes a heat exchanger structure having flow means associated with the structure for inducing serpentine heat exchanging paths of said gas and of said refrigerant fluid therethrough.

8. Gas-handling apparatus comprising a primary evaporator, first conduit connections for establishing a flow path for a compressed gas and the like through said evaporator, second conduit connections for establishing a flow path of a refrigerant fluid through said primary evaporator in heatexchanging relation with said gas path, a refrigerating unit coupled to said second conduit connections, and an auxiliary evaporator coupled between said refrigerating unit and said primary evaporator, said primary evaporator including a heat exchanger structure having flow means associated with the structure for inducing serpentine heat-exchanging paths of said gas and of said refrigerant fluid therethrough, said heatexchanging means including a plurality of sheath tubes and inner tubes mounted spacedly within said sheath tubes, and flow means for conducting one of said gas and said fluid sequentially through one group of the group of sheath tubes and the group of inner tubes and for conducting the other of said gas and said fluid in parallel through at least some of the remainder of said tubes.

9. The combination according to claim 8 wherein said inner tubes are each provided with a plurality of heat transfer spines extending transversely between each coaxial tube and the as sociated sheath tube.

10. The combination according to claim 8 wherein said flow-conducting means are arranged to couple said inner tubes in series and said sheath tubes in series-parallel.

11. A method for operating refrigerating gas-handling apparatus having a compressor, condenser, main evaporator, auxiliary evaporator and expansion valve, said valve being mounted for expansion of a refrigerant fluid into said main evaporator, said method comprising the steps of operating said compressor continuously, preventing complete closure of said valve, sensitizing opening and closing movements of said valve to pressure fluctuations in the path of said refrigerant fluid between the refrigerant outlet of said main evaporator and said auxiliary evaporator, and operating said compressor at constant speed for forcing said valve further open in response to load changes.

12. The combination according to claim 1 wherein said ex pansion valve is coupled in an inlet portion of said refrigerant flow path relative to said primary evaporator, and said pres sure-sensitive means are coupled in an outlet portion of said refrigerant flow path relative to said primary evaporator.

13. The combination according to claim 12 wherein said pressure-sensitive means are coupled between said primary evaporator and said auxiliary evaporator.

14. The combination according to claim 1 wherein said primary evaporator includes a heat exchanger structure having flow means therein for inducing a serpentine heatexchanging path in the flow of at least one of said gas and of said refrigerant therethrough.

15. The combination according to claim 7 wherein said serpentine heat-exchanging paths are coaxial.

16. The combination according to claim 4 wherein auxiliary evaporator and said heat exchanger are each shaped to define coaxial heat-exchanging paths therethrough.

Claims

2. The combination according to claim 1 wherein said auxIliary evaporator is coupled regeneratively to said second conduit connections.
3. The combination according to claim 1 wherein said refrigerating unit includes a condensing unit therefor, some of said second conduit connections couple said condensing unit to one side of said auxiliary evaporator and others of said second conduit connections couple the other side of said auxiliary evaporator to said refrigerating unit and to said primary evaporator.
4. The combination according to claim 1 wherein a heat exchanger for said gas is coupled regeneratively to said first-mentioned conduit connections.
5. The combination according to claim 1 wherein said expansion valve and a third conduit connection are coupled between said primary evaporator and said refrigerating unit in bypassing relation to said auxiliary evaporator.
6. The combination according to claim 5 wherein said expansion valve is provided with means for preventing its complete closure.
7. The combination according to claim 1 wherein said primary evaporator includes a heat exchanger structure having flow means associated with the structure for inducing serpentine heat exchanging paths of said gas and of said refrigerant fluid therethrough.
8. Gas-handling apparatus comprising a primary evaporator, first conduit connections for establishing a flow path for a compressed gas and the like through said evaporator, second conduit connections for establishing a flow path of a refrigerant fluid through said primary evaporator in heat-exchanging relation with said gas path, a refrigerating unit coupled to said second conduit connections, and an auxiliary evaporator coupled between said refrigerating unit and said primary evaporator, said primary evaporator including a heat exchanger structure having flow means associated with the structure for inducing serpentine heat-exchanging paths of said gas and of said refrigerant fluid therethrough, said heat-exchanging means including a plurality of sheath tubes and inner tubes mounted spacedly within said sheath tubes, and flow means for conducting one of said gas and said fluid sequentially through one group of the group of sheath tubes and the group of inner tubes and for conducting the other of said gas and said fluid in parallel through at least some of the remainder of said tubes.
9. The combination according to claim 8 wherein said inner tubes are each provided with a plurality of heat transfer spines extending transversely between each coaxial tube and the associated sheath tube.
10. The combination according to claim 8 wherein said flow-conducting means are arranged to couple said inner tubes in series and said sheath tubes in series-parallel.
11. A method for operating refrigerating gas-handling apparatus having a compressor, condenser, main evaporator, auxiliary evaporator and expansion valve, said valve being mounted for expansion of a refrigerant fluid into said main evaporator, said method comprising the steps of operating said compressor continuously, preventing complete closure of said valve, sensitizing opening and closing movements of said valve to pressure fluctuations in the path of said refrigerant fluid between the refrigerant outlet of said main evaporator and said auxiliary evaporator, and operating said compressor at constant speed for forcing said valve further open in response to load changes.
12. The combination according to claim 1 wherein said expansion valve is coupled in an inlet portion of said refrigerant flow path relative to said primary evaporator, and said pressure-sensitive means are coupled in an outlet portion of said refrigerant flow path relative to said primary evaporator.
13. The combination according to claim 12 wherein said pressure-sensitive means are coupled between said primary evaporator and said auxiliary evaporator.
14. The combination according to claim 1 wherein said primary evaporator includes a heat exchanger structure having flow means therein for inducing a serpentine heat-exchanging patH in the flow of at least one of said gas and of said refrigerant therethrough.
15. The combination according to claim 7 wherein said serpentine heat-exchanging paths are coaxial.
16. The combination according to claim 4 wherein auxiliary evaporator and said heat exchanger are each shaped to define coaxial heat-exchanging paths therethrough.