US2379286A

US2379286A - Refrigerating system

Info

Publication number: US2379286A
Application number: US488187A
Authority: US
Inventors: Wayne E Dodson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1943-05-24
Filing date: 1943-05-24
Publication date: 1945-06-26
Anticipated expiration: 1962-06-26

Description

June 26, 1945. w. E. DODSON REFRIGERATING SYSTEM Fil ed May 24, 1943 2 Sheets-Sheet 1 Inventor: Wayne Dodson, b WW y H15 Attbrney.

June 26, 1945. w, DODSON REFRIGERATING SYSTEM Filed May 24, 1943 2 Sheets-Sheet Luau/m Inventor: Wayne E. Dodson,

AtbOTney.

Patented June 26, 1945.

' REFRIGERATING SYSTEM Wayne E. Dodson, Bloomfield, N. .I., assignor to General Electric Company,

New York a corporation of Application May 24, 1943, Serial No. 488,187

(Cl/6H) Claims.

My invention relates to refrigerating systems and particularly to such systems which include evaporators of the multiple conduit type.

. rality of refrigerant tubes or conduits connected through a. manifold to receive refrigerant in parallel from a common condensing unit. These systems commonly employ refrigerant expansion valves of the thermostatic type which operate to maintain a predetermined degree of superheat of the vaporized refrigerant withdrawn from the evaporator. In multiple conduit evaporator systems, it is necessarly to insure equal distribution of the refrigerant to the several conduits so that each conduit carries its proportionate share of the cooling load. A distribution header comprising a chamber having a plurality of symmetrically located radial outlets is one form of load equalizing device. The header is located between the expansion valve and the evaporator and frequently is built into the valve as an integral part thereof.

When an air conditioning system, for example,

is required to operate over a wide range of refrigerant demand caused by changes of load, or of refrigerant temperatures, or of air temperatures, or of a combination of such conditions, it is difficult to provide. an expansion valve which will regulate the flow of refrigerant satisfactorily throughout the entire range. A there mostatic expansion valve sufllcietly large to control the system during the heaviest refrigerant demand may provide poor regulation during low demands and produce overshooting" and hunting so that the operation of the evaporator is,

irregular in the low demand range. irregularities may be caused, for example, by the inability of the high capacity valve to move with suflicient precision to produce regular and proportionate flow of refrigerant at greatly reduced rates so that the valve upon opening may introduce too much liquid refrigerant which must then be compensated by closing the valve. It is obvious, for example, that a given lift or movemerit from the closed position of a large diameter valve provides a much greater flow cross section than the same movement in a small diameter valve. Accordingly, itis an object of my invention to provide a refrigerating system including an improved arrangement for insuring the maintenance of predetermined conditions in the evaporator over a wide range of operating conditions.

' of the multiple conduits of It is another object of my invention to provide a refrigerating system including a multiple conduit evaporator and an improved control for maintaining predetermined operating characteristics throughout a wide range of operating conditions and for insuring even distribution of the refrigerant among the several conduits.

Further objects and advantages of my invention will become apparent as the following description proceeds, and the features of novelty which characterize my invention will be pointed out with particularity in the, claims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to the accompanying drawings in which Fig. 1 represents diagrammatically anair cooling system including a refgrigerating machine embodying my invention; Fig. 2 is a sectional elevation view of the main expansion valve shown in Fig. l; and Fig. 3 is an illustration similar to Fig. 1 showing another em bodiment of my invention.

Briefly, the refrigerating system shown in the drawings comprises a refrigerant condensing unit, a multiple conduit evaporator, and an expansion valve provided with an arrangement for conducting equal amounts of refrigerant to each the evaporator. A main-thermostatic expansion valve is provided which supplies liquid refrigerant to a distributing header having connections for leading the refrigerant in equal quantities to the several evaporator conduits. In order to provide even distribution and control of the flow of refrigerant under conditions prevailing in the portion of the operating range in which there is the least refrigerant demand, a second valve having much smaller capacity is connected in parallel with the main valve to control the passage of a small amount of refrigerant from maintain substantially the same degree of superheat of the vaporized refrigerant withdrawn from the evaporator. The main valve provides correct control during normal and high refrigthe -condensing unit to the distributing header.

Both valves are controlled, for example, to.

main valve cooperates with chamber through one of the radial outlet eonnections, theremaining outlets being employed as the refrigerant distributing outlets.

Referring now to the drawings, the air cooling system illustrated in Fig. 1 comprises an air circulating duct ll within which is arranged a multiple conduit evaporator ii. The evaporator ii is supplied with refrigerant from a condensing unit comprislng'a compressor It, a condenser I3, and a liquid receiver II. The control of liquid refrigerant flowing from the receiver I to the evaporator II is accomplished through the operation of thermostatic expansion valves II and II. A refrigerant distributor i1 is provided to supply the refrigerant in substantially equal quantities to a plurality of conduits ll each connected to a separate conduit or pass of the evaporator ll. During the operation of the refrigerating system, liquid refrigerant within the evaporator II is vaporized by the absorption of heat from the air flowing through the duct it, and the vaporized refrigerant is withdrawn from the evaporator ll through a manifold i connected to the several multiple conduits of the evaporator and flows through a suction line 20 to the compressor II. The vaporized refrigerant is compressed and-discharged into the condenser II where it is cooled and liquefied and from which it flows to the liquid receiver ll. liquid refrigerant is returned to the evaporator through the operation of valves II and I. having asvaase in "which the admission of refrigerant to the evaporator may be controlled accurately, the valve II trol the admission of small quantities of.refrigerant to the evaporator in such manner as to Y maintain steady superheat conditions at mini- The thermal bulbs 23 and 2l,'respoctively, both secured in heat exchange relation with the suction line "and responsive to the temperature of the vaporized refrigerant withdrawn from the evaporator. Valves i5 and I. are also connected to be responsive to the pressure in. the suction line through a so-called equalizer conduit 25 'which is connected to pressure responsive elements in both valves.

The thermostatic expansion valve operates in accordance with the difference between forces produced by the pressure and by the temperature of the vaporized refrigerant withdrawn fromthe evaporator, the valve tending to open upon an increase in temperature and to close upon an increase in pressure. The differential action of the temperature and pressure responsive elements provides a measure of the superheat in .the-

withdrawn vaporized refrigerant, and the valve,

, therefore, controls the operation of the system to maintain a predetermined substantially constant degree of superheat. This type of valve prevents the return of slugs of liquid refrigerant to the compressor.

a An air conditioning system such as that illustrated may be required to operate over a wide range of conditions such as load, air temperature, and refrigerant temperature, and while a single thermostatic expansion valve may be sufiicient to provide accurate control of the superheat over a limited range, difliculty may be encountered when it is attempted to extend the -range, because the characteristics of the valve mum refrigerant demands. Valve II then operates to maintain the required superheat of the vaporized refrigerant at the outlet of the evaporator and this prevents operation of't e hilhcapacity valve I! such that amount-sot liquid refrigerant in excess of that required are not admitted to the evaporator. While the valve It operates throughout the entire range of operating conditions, its operation is effective to control the superheat of the withdrawn refrigerant substan-' tially only when the system is operating under conditions resulting in refrigerant demands in the lowermost portion of the range. Liquid refrigerant flows from the receiver it through a liquid line it having a main branch 21 for conducting liquid refrigerant to the valve II and an auxiliary branch 28 for conducting the refrigerant 'to the valve it. The expanded refrigerant flowing from the outlet of'the valve I I passes through a connection 2! to the refrigerant distributin header II.

The construction of the main expansion valve II is' shown in Fig. 2. This valve comprises a casing ll closed by a'block ll constituting the distributor I1 and provided with a refrigerant distributing chamber 32. Liquid refrigerant from the line 21 flows, to the chamber 32 through a' valve opening controlled'by a valve member II.

The operation of the valve II is dependent upon the amount of superheat in the refrigerant withdrawn through the suction line 2.. In order to accomplish this operation a diaphragm II is provided in the valve, the lower side of the diaphragm being subject to the pressure of the withdrawn refrigerant and the upper side being subject to a pressure dependent upon the temperatureof the withdrawn refrigerant. The lower side 01' the diaphragm is connected to the pressure conduit 25 through a fixture II. The up per-side of the valve is connected by a capillary tube 31 to receive the pressure dependent upon the temperature of the withdrawn refrigerant as determined by the thermal bulb 23 which is partially illled with a vaporizable liquid. The pressure of the vaporizable liquid is, of course, dependent upon the temperature of the suction line 2|. It'will be evident that this .valve operates in the conventional manner so that it tends to let connected to the connection 2!.

o en upon an increase in suction line temp ture and to close upon an increase in evaporator pressure. The valve I8 is of similar construction but smaller and is not provided with the distributing header l1 but instead has a single out- Tlie several evaporator inlet conduits II are placed in communication with the chamber 82 through radial outlets 3! in the block ii. In order that a single distributing header may be empl ed. one of the outlets I8,'which has been indicated at 88.

is arranged to serve instead as an auxiliary for refrigerant flowing from the valve I. through the connection 2!. It will be noted that the valve 33 is actuated by movement of the diaphragm II transmitted through a valve operating rod ll. When the auxiliary inlet "a is in operation. refrigerant entering the chamber from this inlet. is directed against the valve stem ll which minimizes any direct flow of refrigerant from the inlet 38a into the one of the outlets 38 diametrically opposite. low load conditions refrigerant isjsubstantially equally divided among the several conduits, even though the inlet 38a enters the chamber 32 at erant tosaidevap'o'rator throughout the operation -of said system, each of said valves including an It has been found that under" right angles to the main inlet through the valve stantially the same number of degrees of superheat over the entire range of operating conditions of the system. Under other conditions of operation, it may be desirable to calibrate the valve 56 to maintain a lower amount of superheat than the valve is so that it may operate to control the how of refrigerant through the evaporator although there is not' sufiicient'superheat v to operate the main valve is.

In Fig. 3, there is illustrated an arrangement similar to that of Fig. 1, and corresponding parts have been designated by the same numeralswith the addition of the letter a. In this system, the

distributing header 61a is separate from the valve We, the valve iiia being of the same type as the valve lfia and the valve is in that it is provided with a single outlet connection. The'outlet' connection of the valve i511 communicates with the header Ila through an outlet conduit 4!. Solenoid operated valves 83 and M are provided in the liquid lines lid and 28a, respectively. Valve 83 is provided with a solneoid 45' controlled by a thermostat in the duct Illa. This thermostat is arranged to close when the temperature of the air flowing through the duct indicates that normal or heavy refrigerant demand conditions prevail. 31 operated by a thermostatic switch 58 which closes whenever there is a demand for cooling.

It will, therefore. be evident that the valve I5!!- is operated only when there is a refrigerant demand suflicient to require the larger valve. viously, control valves corresponding to the

valves

13 and 44 may be employed also in the system of Fig. 1.

7 From the foregoing, it is apparent that I have provided a simple and effective arrangement making possible the operation of a refrigerating system over a wide range of loads or other conditions and which provides predetermined operating characteristics throughout the entre operating range.

While I have illustrated my invention in 'connection with an air conditioning system, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular arrangements shown and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invent on.

The valve 46 is controlled by a solenoid individual control element responsive to the temperature of the vaporized refrigerantwithdrawn I from said evaporator, both ofsaid control elements being set to operate their respective valves independently for maintaining substantially the same predetermined amount of superheat .of the vaporized refrigerant withdrawn from said evaporator, said. low capacity valve acting to extend the range within which the operation of said evaporator may be controlled effectively'to maintain said predetermined superheat beyondthe range of effective controlfobtainable with said high capacity valve alone. I

2. A refrigerating system including a refrigerant' condensing unit and a refrigerant evaporator, said evaporatorcomprising a plurality of refrigerant conduits arranged in parallel, a liquid refrigerant distributing header having separate outlet connections for each of said conduits for dividing the liquid refrigerant equally among said conduits, a thermostatic expansion valve connected between said unit and said header for maintaining a predetermined amount of superheat of the vaporized refrigerant withdrawn from said evaporator duringnormal refrigerant demands on-said system, and a relatively small capacity thermostatic expansion valve'connected in parallelwith said, flrstmentioned valve for maintaining substantially said predetermined amount of superheat at low refrigerant demands on said system, said small capacity valve cooperating with said first mentioned valve to extend the effective range of operation of said system.

3. A refrigerating system including a refrig-' erant condensing unit and a refrigerant evaporator, said evaporator comprising a plurality of refrigerant conduits arranged in parallel, a thening each of said conduits to a corresponding one of said outlets whereby refrigerant is divided equally among said conduits, a second expansion valve having a substantially lower capacity than that of said first mentioned valve and connected between said condensing unit and said auxiliary erant into said chamber and said valves are con- What I claim as new and desire to secure by valve connected in parallel between said unit and said evaporator for controlling the flow of refrignected in parallel, and means for controlling said valves to maintain predetermined conditions within said evaporatorover a desired range of operating conditions of said system.

'4. A refrigerating system including a, refriginlet whereby said second valve discharges refri8- erant condensing unit and a refrigerant evaporator, said evaporator comprising a" plurality of refrigerant conduits arranged in arallel, a thermostatic expansion valve for maintaining apredetermined amount of 'superheat of the vaporized refrigerant withdrawn from said evaporating unit during normal refrigerant demand conditions, said valve being connected between said unit and said evaporator and including an outlet chamber having a plurality of outlets and a main inlet and an auxiliary inlet, means connecting said refrigerant conduits to corresponding ones of said outlets whereby refrigerant is distributed equally to said conduits, a second thermostatic expansion valve having a capacity relatively small with rerespect to that of said first mentioned valve and connected between said condensing unit and said outlet chamber through said auxiliary inlet for maintaining substantially the same amount of superheat during low refrigerant demand conditions erant condensing unit, a refrigerant evaporator,

a high capacity thermostatic expansion valve and a low capacity thermostatic expansion valve connected in parallel between said .unit and said evaporator for controlling the flowof refrigerant to said evaporator throughout the operation of said system, each of said valves including an individual control element responsive to the temperature of the vaporized refrigerant withdrawn from said evaporator, both of said control elements being set to operate their respective valves independently for maintaining substantially the 5. refrigerating system including a refrig same predetermined amount of superheat of the vaporlled refrigerant withdrawn from said evaporator, and means dependent upon the refrigerant demand on said system for preventing the operation of said high capacity expansion valve to control said system during the lower portion of the range of refrigerant demands on said system,

. said low capacity valve acting to extend the range within which the operation of said evaporator may be controlled effectively to maintain said predetermined superheat beyondthe range of effective control obtainable with said high capacity valve alone.

WAYNE E. DODSON.