US2359595A

US2359595A - Refrigerating system

Info

Publication number: US2359595A
Application number: US496321A
Authority: US
Inventors: Fred O Urban
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1943-07-27
Filing date: 1943-07-27
Publication date: 1944-10-03
Anticipated expiration: 1961-10-03

Description

Oct; 3, 1944. r-'. 0. URBAN REFRIGERATING SYSTEM Filed July 27, 1943 Ihventor: Fred O Liv an,

His Attorney.

Patented Oct. 3, 1944 nnrmenna'rme srs'rEM Fred 0. Urban, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application July 27, 1943, Serial No. 496,321

Claims.

My invention relates to refrigerating systems and particularly to such systems which are provided with refrigerant expansion devices of the fixed restrictor or capillary tube type.

A mechanical refrigerating machine commonly comprises a condensing unit and an evaporating -unit. In compression type systems, thecondensing unit comprises a motor driven compressor and an air or liquid cooled condenser for liquefying the compressed refrigerant. In.order to control the flow of refrigerant from the high pressure of the condensing unit to the low pressure of the evaporating unit, some form of expansion valve or device is necessary. It has been found practicable in many cases to-employ a capillary tube or other device providing a fixed restriction between the condensing unit and the evaporator. Refrigerating machines equipped with capillary tubes must be designed. specifically for the range of temperatures and pressures within which they are expected to be employed. The flow of refrigerant through, a F

capillary tube decreases with a decrease in'tfiepressure difference across the tube, and even though there is no change in the conditions surrounding the evaporator, a decrease in condensing pressure may produce an objectionable decrease in flow of refrigerant. One important.

tion will become apparent as the following description proceeds, and the features of noveltywhich characterize my invention will be pointed outwith 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 drawing in which Fig. 1 represents diagrammatically a refrigerating system embodying my invention, and Figs. 2 and 3 represent other embodiments of my invention.

Briefly, each of the refrigerating systems disclosed in the drawing comprises a compressor, a condenser and an evaporator connected in series to provide a normal refrigerant circuit, a capillary tube restrictor is provided in the circuit between the condenser and the evaporator to con trol the flow of liquid'refrigerant from the high pressure side to the low pressure side of the refrigerant circuit. A refrigerant storage chamberis connected in restricted communication with the condensing unit and a controlis pro! vided which causes an-interchange of liquid refrigerant' between the refrigerant circuit and the chamber. The control is actuated in accordance with a predetermined condition of operation of the system, and the effective capacity of the system is varied by storing more or less liquid factor whichis involved in the determination of the range of operation of the refrigerating machine is the quantity of the charge of refrigerant employed in the system. It has been found, for example, that a refrigerating machine will'prodlice different suction pressures when the machine ischarged with different amounts of refrigerant. The charge of refrigerant placed in the system critically determines the practical range of operation of the system.

It is an object of my invention to provide a1 refrigerating machine employingan expansion device of the fixed restrictor type and including an improved arrangement for increasing the'effecti've range of operation of the machine.

It is another object of my invention to provide a refrigerating machine having an expan-' refrigerant in the chamber out of the path of flow of the refrigerant in the circuit.

Referring now to the drawing, the refrigeration system shown in Fig. 1 comprises an evaporator I 0 arranged in an air duct I I for cooling the air passing therethrough. vaporized refrigerant is withdrawn from the evaporator by operation of a compressor l2, and the hot compressed refrigerant is cooled and liquefied in a condenser and capillary tube will operate satisfactorily sion device of the fixed restrictor type and includtem is operated so that there is no superheat at the evaporator outlet the change in refrigerant vided with an expansion device of the fixed restrictor type. i 5

Furthar objects and advantages of my invenwithin a predetermined range of operating conditions, the limitations of satisfactory operation depending upon the quantity ct -refrigerant with .which the circuit is charged.

I have found that the suction pressure of a refrigerating machine of, the above type'maybe effectively controlled 'by varying the quantity of refrigerant in the system. As long as the syscharge results in a change in both the evaporator and the condenser pressures, and by selecting the quantity of refrigerant in the circulating walls of the condenser.

system, the evaporator can be operated at any desired percentage of its maximum capacity. The effect of changing the refrigerant charge in a system such as shown in Fig. 1 is to vary the effective area of the condenser, the greater' or tank I5 outside the refrigerant circuit and in communication with the circuit through a restricted tube or duct I6 connecting the bottom of the chamber with the lowermost portion of the condenser. Liquid refrigerant flowing from. the condenser I3 fills a liquid line indicated at H as a continuation of the condenser and a portion of this liquid may be cooled by heat exchange with the cold vapor withdrawn from the evaporator through thesuction line indicated at I8. For this purpose portions of the lines I1 and I8 are connected in heat exchange relation at IS. The chamber I5 may be located at any suitable position where it is normally in an ambient have ing a temperature lower than the condensing temperature of the refrigerant in the condenser.

In Fig. 1, the chamber I5 i'sarranged in the same The selection of theabove design structure to provide a long time constant for the chamber and a short timeeconstant for the thermostatic control provides inherent stability. The control bulb or feeler 24 has been shown responsive to the evaporator inlet temperature only by way of example, it being obvious that the system may be controlled in accordance with other operating conditions if desired. The control as shown in ambient as, the condensing unit. The tube I5 is of sufficiently small diameter to prevent the liqerant circuit through the duct I6 into the tank I5 until a state of equilibrium is established. In

order to change the temperature. within the chamber I 5 and thereby change the pressure and the amount of refrigerant stored within the chamber, an electric heater is arranged within a recess 2I in the chamber wall and is energized from a suitable source of electriccurrent byclosing a switch 22 in accordance with the temperature at the outlet of the capillary tube I4. The switch 22 is operated'by a bellows 23 actuated in accordance with the pressure within a thermal bulb 24 secured'in heat exchange relation with the inlet of the evaporator Ill adjacent the capillary tube I4. When the temperature falls the switch 22 'is closed and the heater is energized todecrease the amount of refrigerant in the chamber I5. If desired, the chamber I5 may be provided with a covering 25 of thermal insulation to decrease the rate of change of the tank temperature with changes in the temperature of the ambient medium. The tank I5is relatively small because a considerable change in operating conditions may be effected by relatively small changes in the amount of refrigerant charge, By selecting the proportions of the'mass and of the insulation of the tank I5, the capacity of may be of any suitable type and may be made to be sensitive to small changes and have a low time constant, that is, a rapid response characterist c.

the tube 28 results; however, if the tube 28 is sufficiently restricted, the resulting loss in refrigera'ting efllciency may be made negligible, for

- example, the loss may be made only one tenth of one per cent.

The refrigerating system of Fig. 1 may, for example, be employed in a room cooler which circulates air over the evaporator Ill and which provides for circulation 'of withdrawn air over the condensing unit including the compresser I2, condenser I3 and tank I 5. Let us assume that the withdrawn temperature is 95 F. and that the.

room cooler is maintaining the room air at a dry bulb temperature of F. and a wet bulb temperature at 67 F. These conditions will produce a predetermined average suction pressure and an average head pressure dependent upon the particular refrigerant employed. The chamber might, for example, be somewhat over half 'full of liquid refrigerantand under the control of the thermostatic switch 22, the heater 20 would be furnishing heat at an average rate to maintain a predetermined temperature within the tank I5. If the weather conditions change and lower the outdoor temperature to F., the

head pressure will drop quickly and will reduce the flow through the capillary tube I4 and result refrigerant flow causes an increase in the evaporator superheat. Momentarily, .at the time off." the change, there will be a fiow of liquid refrig-1 erant out of the tank but there will also be evaporation of liquid to fill the displaced volume and this willcool the small mass of liquid to a new temperature at which equilibrium will be reached,

and the flow of liquid refrigerant through the duct I6 'will stop. Further cooling of the tank I5 because of the new low temperatufe of the air circulating around the condensing unit may then reverse the flow and begin to fill the tank. However, the decrease in eva rator temperature at the bulb 24 due to the lower pressure will close the switch 22 and supply heat to the tank I5 and increase the temperature of the tank so that liquid refrigerant will be forced back into the refrigerant circuit. The additional liquid refrigerant forced into the circuit will flow back into the condenser and reduce the effective condensing surface, thereby raising the condensingtemperature, and the increased amount of liquid refrigerant in the condenser also will cause greater subcooling of the liquid than before the change. The higher condenser pressure and the greater subcooling results in an increased flow through the capillary tube and increases the evaporator capacity to that required to handle the room cooling load.

It was assumed above merely for purposes of example that the change in operating conditions I was produced by a change in the ambient temperature of the condensing unit. system also operates to produce capacity changes to meet different conditions due to changes in the evaporator ambient temperature or a com-, bination of changes of both condensing and evaporating temperatures. v

The size of the tank I is determined by the volume of the condenser l3 and by the proportion of the condenser surface which is to be blocked off by flooding at the extreme end of the control range. However, except for the additional heat input required to make up for higher loss in a larger tank, there is no objection to making the tank sufficiently large to contain the entire refrigerant charge of the system. The tank should be located so that it will drain completely by gravity during the shutdown period; this minimizes the accumulation of oil in the tank.-

The modification of my invention illustrated in Fig. 2 is similar to that of Fig. 1 and corre-' sponding parts have been designated by the same numerals. The system of Fig. 2 differs from that of Fig. 1 in the arrangement for controlling the interchange of liquid refrigerant between the refrigerant circuit and the tank l5. In Fig. 2, a thermosiphon pump comprising a. liquid leg and a liquid-vapor leg 3! is connected be-,

tween the lowermost portion of the liquid line l1 and the vapor space between the upper portion of the tank l5. When it is desired to supply liquid refrigerant to the tank IS, an electric heater 32 is energized and heats liquid in the leg 31 to vaporize a portion of the liquid and change the average density of the refrigerant. in that portion and also to produce a vapor lift A resulting in a flow of liquid refrigerant from the liquid line I1 to the chamber I5. The return of liquid refrigerant from the chamber l5 to the line I! is effected through a restricted duct 33 connectingthe bottom of the tank with the liquid line H. The duct 33 tends-to drain the tank l5 at a substantially constant rate and the thermosiphon pump is designed to provide a maxi-- mum rate of flow of, say, twice the rate of flow through the duct/33. It is thus apparent that by control of the thermosiphon pump the average amount of liquid refrigerant in the chamber l5 may beheld at any predetermined desired average level. The electric heater 32 has been shown connected toa suitable source .of alternating current through a transformer 34 and the switch 22. In order to prevent any appreciable change in the operation of the thermosiphon pump because of the saturation pressure-temperature characteristics of the refrigerant, a. pressure equalizing tube 35 is connected between the vapor space of the chamber l5 and the high pressure vapor space of the condensing unit, that is the high pressure space between the compressor discharge "port and the liquid in the condenser.

The operation of the system shown in Fig. 2 is essentially the same as is shown in Fig. 1 except that the changes in level of the liquid refrigerant in the tank I5 are effected solely by However, the

energization of the heater 32.

the operation of the thermosiphon pump and no substantial transient changes are produced due to changes in the saturation pressuresand temperatures.

In Fig. 3, I have illustrated another modification of my invention which is similar to that shown in Fig. 2 and corresponding parts have again been designated by the same numerals. The difference between the systems of Figs. 2 and 3 lies in the arrangement for controlling the In Fig. 3 the heater is controlled in accordance with the amount of superheat in the vaporized refrigerant returned to the compressor instead of in accordance with the inlet evaporator temperature.

Theheater 32 is energized by the operation of a thermal bulb '4! responsive to the temperature the evaporator.

" to energize the heater 32.

tur'es,

frigerating systems inwhich the control is'deat the outlet of the evaporator. The bellows 38 tends to open the switch 31 upon an increase in temperature at the inlet of the evaporator, and the bellows 39 tends to close the switch 31 upon an increase in the temperature at the outlet of The difference between these temperatures is dependent upon the superheating of the refrigerant vapor withdrawn from the evaporator and the systein is therefore controlled in accordance with suction vapor superh eating. It is obvious that other forms of superheat sensitive controls knowntothe art may be employed The arrangement of Fig. 3 is the preferred control for'dry expansion systems but may be employed equally well on flooded systems; the control arrangements of Figs. 1 and 2 are primarily for systems employing normally flooded evaporators.

In the foregoing description it has been assumed by way of example that the-changes in operating conditions are produced by changes in the ambient temperature of the condensing unit.

It is obvious, however, that the changes mayv be produced by other causes such as changes [in evaporator ambient temperature or in both evaporator and condensing unit ambient tempera.-

Furthermore, it is recognized that rependent merely upon the evaporator pressure may be required to operate under certain unfavorable conditions which produce unsatisfactory operation because of the characteristics of the control. It is obvious,' therefore, that the use of a particular type of control for a refrig- It will be noted in Figs. 2 and 3 that no heat interchanger has been employed between the liquid line and the suction line. Such heat interchangers are frequently employed to better the economy of the system but are not essential to the operation of the system.

It is readily apparent from the foregoing that I have provided a .simple'and effective arrangement for varying the efiective capacity of a. refrigerating machine employing an expansion device of the fixed restrictor type and that my in- Letters Patent of the United States is:

1. A refrigerating system comprising a compressor and a condenser and an evaporator con-.

nected in series to provide a normal refrigerant circuit, a fixed restrictor in said circuit for controlling the flow of refrigerant from said conerant storage chamber arranged outsidethe normal series path of refrigerant in saidcjrcuitand having restricted communication affording pas-" sage of liquid refrigerant between said chamber and said condenser, and means dependent upon a condition of operation ofsaid system for varying the ratio of the amount of refrigerant in said chamber to the amount in said circuit to vary the capacity of said system.

2. A refrigerating system comprising av compressor and a condenser and an evaporator connected in series toprovi'de a normal refrigerant circuit, a fixed restrictor in said circuit for controlling the flow of refrigerant from said condenser tosaid evaporator, a closed liquid refri 5. A refrigerating system comprising a compress'or and a condenser and an evaporator connected in series to provide a normal refrigerant circuit, a fixed restrictor in said circuit for con-' trolling the flow of refrigerant from said condenser to said evaporator, a closed liquid refrigerant storage chamber arranged outside the normal series path of refrigerant in said circuit and having restricted communication affording passage of liquid refrigerant between said chamber and said circuit, means including a thermosyphon pump for conveying liquid refrigerant from said circuit'to said chamber, and means dependent upon a condition of operation of said system for operating said pump to determine the amount of refrigerant stored in said chamber whereby the capacity of said system is varied in accordance with said condition of operation.

6. A refrigerating system comprising""a condensing unit and an evaporating unit and a dried restrictor for controllin the flow of refrigerant from said condensing'unit to said evaporating unit, means including a closed thermally indenser to said evaporator, a closed liquid refrigerant storage chamber arranged outside the normal series path of refrigerant in said circuit and having restricted communication affording passage of liquid refrigerant between said chamber and said condenser, and means dependent upon the temperature of the refrigerant admitted to said evaporator for controlling the interchange of liquid refrigerant between said chamber and said circuit to vary the capacity -of said system.

3. A refrigerating system comprising a compressor and a condenser and an evaporator connected in series'to provide a normal refrigerant circuit, a fixed restrictor in said circuit for controlling the flow of refrigerant from said condenser to said evaporator, a closed liquid refrigerant storage chamber arranged outside the normal series path of refrigerant in said circuit and having restricted communication affording passulated chamber for storin a quantity of liquid refrigerant and for restricting the circulation of said quantity of liquid refrigerant through said system, and means dependent upon a condition of operation of said system for effecting an interchange of liquid between said system and said chamber for varying the ratio of the amount of refrigerant in said chamber to the'amount in the remainder of said-system whereby the capacity of said system is varied in accordance with said condition. I v

' .7. A refrigerating system comprising a condensing unit and an evaporating unit and a fixed restrictor for controlling the flow of refrigerant from said condensing unit to said evaporating unit, means including a closed thermally in-' .sulated chamber for storing a quantity of liquid refrigerant and for preventing the circulation of said quantity of liquidrefrigerant through said sage of liquid refrigerant between said chamber and said condenser, and means dependent upon a condition of operation of said system for sunplying heat to said chamber to determine the amount of refrigerant stored in saidchamber .whereby the capacity of said system is varied in accordance with said condition of operation.

4.- A refrigerating system comprising a comp essor and a condenser and an evaporator connected in series to provide a normal refrigerant circuit, afixed restrictor in said circuit for controlling the flow of refrigerant from said con denser to said evaporator, a closed liquid refrigerant storage chamber arranged outside the normal series path of refrigerant in said circuit and having restricted communication affording passage of liquid refrigerant between said chamber and said condenser, and means dependent upon the difference in temperature betweenthe inlet of said evaporator and the'outlet thereof and controlling the relative amounts of refrigerant in said chamber and in said circuit for varying the capacity of said system.

system, means including a thermosyphon pump and a restricted return duct for effecting an interchange of liquid refrigerant between said system and said chamber, and means dependent upon a condition of operation of said system for actuating said pump to determine the relative amounts ofrefrigerant in said chamber and in the remainder of said system.

8. A refrigerating system comprising a condensing unit and an evaporating unit and a fixed restrictor for controlling the flow of refrigerant from said condensing unit to said evaporating unit, means including a closed chamber arranged in an ambient having a temperature lower than the condensing temperature of refrigerant in said system for storing a quantity of liquid refrigerant and for restricting the circulation of said quantity of liquid refrigerant through said system, and.

means dependent upon a condition of operation of said system for effecting an interchange. of

- liquid between said system and said chamber for varying the ratio of the amount of refrigerant in said chamber to the amountin the remainder of said system whereby the capacity of said system is varied in accordance with said condition.

9. A refrigerating system comprising a compressor and a condenser and an evaporator connected in series'to provide a normal refrigerant circuit, said circuit including a fixed restrictor for controlling the flow of refrigerant from saidrcondenser to said evaporator, a closed liquid refrigerant storage chamber arranged outside the normal series path of refrigerant in said circuit and and said circuit whereby liquid refrigerant may in the upper portion of said chamber for conveyin; liquid refrigerant from said circuit to said chamber, means dependent upon a condition vof restrictor for controlling the flow of liquid refrigerant irom said condensing unit to said evapoperation of said system for operating'said pump to determine the amount of refrigerant stored in said chamber whereby' the capacity of said 7 system is varied in accordance with said condition of operation, and a restricted duct connect-' 10.- A refrigerating system comprisin a con densing'unit and-an evaporating unit and a fixed orating unit, means providing a closed chamber having restricted communication with said condensing unit for storing a quantity of liquid refrigerant and for restricting the circulation .of said quantity of liquid refrigerant through said system. means dependent upon a condition 01 operation of said system for heating said chamber to eflect an interchange of liqui between aid condensing unit and said chamber for varying the capacity of said system in accordance with said condition, and a restricted duct connecting said, chamber above the level of liquid therein with a relatively low pressure portion oi fsaid condensing unit for removing noncondensabie gas from said chamber.

I FRED 0. URBAN.