US2956419A

US2956419A - Pressure stabilizer system

Info

Publication number: US2956419A
Application number: US548668A
Authority: US
Inventors: Boling Cecil
Original assignee: Dunham Bush Inc
Current assignee: Dunham Bush Inc
Priority date: 1955-11-23
Filing date: 1955-11-23
Publication date: 1960-10-18
Anticipated expiration: 1977-10-18

Description

Oct. 18, 1960 c. BOLING 2,956,419

PRESSURE STABILIZER' SYSTEM Filed Nov. 23, 1955 3 Sheets-Sheet 1 'TTET l.

XNVENTOR ATTORN Oct. 18, 1960 c. BOLING PRESSURE STABILIZER SYSTEM 3 Sheets-Sheet 2 Filed Nov. 23, 1955 NVENTOB Cec I; Z ,5 o 61/21 r- I m Mom W W ATTORNE Oct. 18, 1960 c. BOLING PRESSURE STABILIZER SYSTEM 3 Sheets-Sheet 3 Filed Nov. 23, 1955 INVENTOR Cecil flow in WWW? I ATTORNE United States Patent PRESSURE STABILIZER SYSTEM Cecil Boling, West Hartford, Conn., assignor, by mesne assignments, to Dunham-Bush, Inc., West Hartford, Conn, a corporation of Connecticut Filed Nov. 23, 1955, Ser. No. 548,668

9 Claims. (Cl. 62196) This invention relates to refrigeration, and more in particular to maintaining stable operation of refrigeration systems having air-cooled condensers throughout Wide variations in the temperature of the cooling air. The invention also provides for maintaining stable operation of refrigeration systems having other types of condensers, such as evaporative condensers or condensers used with cooling towers.

It is an object of the present invention to provide improved refrigeration systems and modes of operation which overcome difliculties which have been encountered in the past. It is a particular object to provide a thoroughly practical solution to certain problems caused by unstable operation of refrigeration systems with air-cooled condensers at low ambient temperatures. It is a further object to provide for the solution of problems which have been encountered with different types of refrigeration systems where there is a tendency for overcooling the refrigerant in the condenser during some conditions of operation.

In the refrigeration field, it has become important to provide air-cooled condensers, i.e., which require no cooling water and are cooled by the ambient air only. With such a system, the condenser must be of suficient size to give satisfactory performance at peak loads and with the cooling air at maximum temperature. A refrigeration system which has an air-cooled condenser and which operates to cool a storage compartment for food or other products or articles must operate with absolute assurance that the system will not fail because of a rise in the outside temperature.

Ths is apt to be a particularly serious problem where the system has its condenser located on the outside of a building and is subjected to very high temperatures during the hot season and very low temperatures during the cold season. With such installations, considerable difficulty has been encountered during cold weather because of excessive cooling of the liquid refrigerant in the condenser, i.e., prior to passage to the receiver. Such excessive cooling causes an objectionably low head pressure; that is, the pressure in the receiver and at the expansion valve (or restrictor) is reduced to such a low value that the refrigerant does not flow through the expansion valve to the evaporator at a sufficiently rapid rate. Particularly, the refrigerant pressure in the receiver is so close to the suction pressure in the evaporator that the refrigerant flow is sluggish, and there is insufiicient liquid refrigerant flow to handle the cooling load. Hence, the evaporator is starved and is so ineffectual that the refrigerated compartment is not maintained at the desired low temperature. Under extreme conditions, the head pressure at the receiver may become so low that the solid column of liquid refrigerant flowing to the expansion valve may be broken by the formation of gas. In accordance with the present invention, these and related difliculties are overcome in a thoroughly practical manner and with apparatus which is eflicient and dependable m use.

ice

Difficulties similar to those discussed above may be encountered with refrigeration systems having evaporative condensers or even water-cooled condensers where the water is cooled in a cooling tower. The present invention provides a solution for the above difficulties with various refrigeration systems with these other types of condensers.

In the drawings:

Figure 1 is a somewhat schematic representation of one embodiment of the invention;

Figures 2 and 3 are side and top views respectively of the unit of Figure 2;

Figure 4 is an enlarged view of the heat interchange unit of the refrigeration system of Figure 1; and,

Figures 5 and 6 are sectional views respectively on the lines 55 and 6-6 of Figure 4.

Referring to Figure 1 of the drawings, a motor driven compressor 2 discharges hot compressed gas through a line 4, the gas passageway or circuit of a heat interchange unit 6 and a line 8 to the top of an air-cooled condenser 10. The condensed refrigerant flows from the bottom of the condenser through a line 11, a noranally open valve 12 and a line 14 to a receiver 16. The liquid refrigerant flows from the receiver through a line 18 having an expansion valve 20 therein to an evaporator 22. The gaseous refrigerant is withdrawn from the evaporator through a line 24. Standard control and safety devices are provided.

Extending parallel to valve 12, is a bypass circuit formed by a line 26 connected to line 11, the liquid circuit of unit 6 and a line 27 connected to line 14. As will be explained more fully below, liquid flowing through this bypass circuit encounters resistance to flow and is passed in heat interchange relationship with the hot refrigerant gas from the compressor.

The details of construction of the heat exchange unit 6 are shown in Figures 2 to 6. Unit 6 has three vertical heat interchange assemblies 28, 30, and 32, each formed of a set of three concentric tubes with internal annular spaces having radial fins therein. These tube assemblies incorporate certain inventions covered by my prior US. Patents Nos. 2,611,585 and 2,611,587. Assembly 28 is formed (see Figure 6) by an outer tube 34, an intermediate tube 36, an inner tube 38, a fin assembly 40 positioned in the annular passageway 42 between

tubes

34 and 36, and a fin assembly 44 similarly positioned in the annular space between

tubes

36 and 38. During assembly, tube 36 and its fin assembly are positioned within tube 34, and then tube 36 is expanded to place the fin assembly under radial compression. Tube 38 and its fin assembly 44 are then placed within tube 36, and tube 38 is expanded so as to place the fin assembly under compression in a similar manner. Fin assembly 40 provides a high rate of heat transfer from the gas flowing through passageway 42; and, intermediate tube 36 provides the liquid passageway with the fin assembly 44 and the inner tube 38 providing the high rate of heat transfer to the liquid flowing therethrough. Assembly 30 is similarly constructed, with an outer tube 31 and intermediate tube 33, and an inner tube and fin assemblies which are not shown. Assembly 32 has an outer tube 41 and intermediate tube 43, and an inner tube and fin assemblies (not shown).

The three

tube assemblies

28, 30 and 32 are mounted in a pair of

headers

46 and 48, with the headers open to the annular passageway 42 between

tubes

34 and 36 of assembly 28 and the corresponding passageway of the other assemblies. Hence, these passageways are connected in parallel to provide three parallel paths for refrigerant gas passing from the inlet headers 46 to the outlet headers 48. The

intermediate tubes

36, 33 and 43 of the three tube assemblies extend through the head ers, and are connected in series by a pair of U-tubes 50 and 52. The upper end of tube 43 is connected to tube 26 which acts as the liquid refrigerant inlet line, and the. lower end of tube 36 is connected to tubeor line 27 which is the liquid outlet line.

Rigidly mounted in the upper end of the intermediate tube 43 of assembly 32 is an orifice ring or perforated disc 54 (see Figure 5) which has a center opening therethrough which acts as the restricting orifice 56 for the fiow of liquid refrigerant through the bypass circuit. Hence, liquid may flow from the upper end of line 11 through line 26 to the upper end of tube 43, through this orifice 56, and thence in series through

tubes

43, 33 and 36, and from the lower end of tube 36 through line 27 to line 14. I

It has been indicated that the orifice 56 provides a fixed resistance to liquid flow, and there is some resistance to flow through the liquid circuit of unit 6, so that the liquid bypass circuit has designed into it a predetermined total resistance to liquid flow or restriction. However, the gas circuit has extremely low resistance to gas fiow because of the headers and the parallel tube arrangement. At the same time, the fin assemblies insure that the liquid flowing through the bypass circuit is in intimate heat exchange relationship with the gas flowing through the gas circuit of unit 6 to transfer heat from the hot gas to the liquid refrigerant.

As has been pointed out above, valve 12 is noirnally open, but this valve is of the self-closing type, and it closes gradually as the pressure in line 11 drops below a predetermined value. Valve 12 has a valve member 6! which is supported by a bellows 62, and is adapted to move into the valve o'pening 64 aginst its seat, thus to completely close the valve. A compression spring 61 rests against the valve member 6%) at the top of the bellows, and the bottom of the spring rests against an adjusting unit 63 carrying an adjusting knob 65. By manually turning knob 65,'the spring 61 may be compressed more or less so as to adjust the pressure exerted by the spring upwardly on the valve member. The liquid refrigerant pushes downwardly on the top of the valve member, and the spring and atmosphere pressure push upwardly thereon. However, the spring is so adjusted that the differential in pressure above and below the valve member holds the valve in its fully open position during normal operation of the refrigeration system. That is, when there is sufiicient head pressure at line 11 to insure that there will be satisfactory fiow of liquid refrigerant through the expansion valve 20, the refrigerant pressure is sufficiently high above the valve member 12 to hold the valve open. But, whenever the pressure in line 11 drops appreciably below a predetermined acceptable value, the pressure below the valve member is sufficient to move the valve member 60 toward its seat, thus to partially close or fully close the valve.

The closing of valve 12 tends to divert liquid refrigerant from line 11 through the bypass circuit formed by line 26, the liquid circuit of unit 6 and line 27. The fixed resistance to liquid flow in this bypass liquid circuit is such that there is no refrigerant flow therethrough when valve 12 is open. However, as valve 12 is gradually closed, an increasing portion of the liquid refrigerant is diverted through the bypass circuit. In the illustrative embodiment, when valve 12 isfully closed, there is a pressure drop of thirty pounds per square inch through this bypass liquid circuit.

During normal operation of the illustrative embodiment of the invention, with valve 12 open, the head pressure in the condenser is 140 pounds per square inch. Valve 12 is adjusted to start closing whenever the pressure in line 11 drops below 120 pounds per square inch. With the valve fully closed so that there is a pressure drop of 30 pounds through the liquid bypass circuit, the effective head pressure in the receiver and at the expansion valve is 90 poundsper square inch, i.e., the 120 pounds pressure which is maintained in the condenser, minus the 30 pounds drop in the bypass circuit. During operation, with valve 12 partially or completely closed, the liquid refrigerant is heated by the hot gas refrigerant, and an equilibrium condition is reached for any given condition of operation, with suflicient liquid refrigerant being supplied to the evaporator. It should be noted that the heating of the liquid refrigerant by the heat interchange unit 6 is necessary to compensate for the excessive subcooling of the refrigerant in the condenser, and in that way the temperature of the liquid refrigerant fiowing to the receiver is raised to the value necessary to produce the desired equilibrium condition in the receiver. Liquid refrigerant tends to accumulate automatically in the lower portion of the condenser to reduce the effective condenser surface. That is, as liquid refrigerant accumulates in the bottom of the condenser, only a reduced upper portion of the condenser is completely effective to condense refrigerant. The liquid refrigerant is subco'oled in the condenser, but it is reheated again in unit 6. Simultaneously, the hot gas is cooled somewhat before it is passed to the condenser, and that reduces the temperature gradient between the refrigerant and the condensing medium so that there is a reduced rate of heat transfer from the refrigerant in the condenser. Also, as indicated, the heating of the liquid refrigerant raises the temperature and pressure in the receiver. Therefore, even though the temperature of the condensercooling medium is very low, the pressure tends to build up.

The system of the present invention requires no manual or external control operation to cause the system to accommodate itself to changes in ambient temperatures.

The shifts from the normal mode of operation, with valve 12 open and with a relatively high head pressure, to a condition where valve 12 is partially or fully closed, and vice versa, take place without any attention by the 3 operating personnel, and the system maintains satisfactory performance at all times. The construction is not unduly complicated, and the performance during normal operation is not penalized by the presence of the unit 6 and valve 12.

' the form of the tube assemblies to produce the maximum desired heating of the liquid refrigerant, and these tube assemblies provide some resistance to liquid flow while the remainder of such resistance is provided by the orifice 56. Hence, unit 6 is designed to perform the desired heat interchange functions and the desired resistance to liquid flow, and provides minimum resistance to gas flow. The illustrative pressures and operating conditions are for one particular installation, and other pressures and operating conditions will be encountered for other systems.

In the illustrative embodiment of the invention, unit 6 is positioned at the outlet from the condenser, and it heats the refrigerant flowing to the receiver. Under some circumstances, this unit may be positioned between the receiver and the expansion valve or other type of restrictor while still attaining certain of the advantages of the present invention. In such case, the liquid line extends to the bottom of the receiver.

It has been indicated above that the present invention is applicable to refrigeration systems having evaporative condensers or even water-cooled condensers equipped with cooling towers. For example, an evaporative condenser is cooled with the aid of water evaporation during hot weather, and then cooled solely by air during cold weather, and there may be excessive subcooling of the refrigerant during extremely cold weather. It will be understood that the present invention may be utilized to solve the.

problem of instability resulting from such excessive condenser cooling.

As many possible embodiments may be made of the steps of the method and the mechanical features of the above invention herein described, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a refrigeration system which includes, an evaporator and restrictor means through which refrigerant flows to said evaporator and a condenser which tends to produce an excessively low head pressure whereby insufiicient liquid refrigerant flows through said restrictor means to said evaporator, the combination therewith of a normally open valve positioned in the liquid refrigerant line between said condenser and said restrictor means and operative to close in response to -a drop in the head pressure below a predetermined value, and a refrigerant bypass circuit connected in parallel with said valve and having suflicient resistance to refrigerant flow to prevent any substantial flow therethrough when said valve is open, said bypass circuit including means to heat the refrigerant flowing therethrough.

2. In a refrigeration system, the combination of, a compressor, an air cooled condenser, a receiver, a restrictor, an evaporator, a heat interchange unit having a gas flow path through which refrigerant gas flows from the compressor and a liquid flow path through which the liquid refrigerant flows after leaving the condenser and before reaching the restrictor, said liquid flow-path including means providing resistance to liquid flow, and a normally open valve connected in parallel with said liquid refrigerant flow path, said valve being adapted to throttle the flow of liquid refrigerant through as it is moved from its open position whereby refrigerant is diverted through said liquid flow path and is heated by the hot refrigerant to said expansion valve.

3. A system as described in claim 2 which includes, means operative to close said valve automatically in response to a drop in the pressure of the liquid refrigerant flowing from the condenser.

4. In a refrigeration system of the character described, the combination of, a compressor, an evaporator, an aircooled condenser which is apt to be subjected to low ambient temperatures whereby the refrigerant pressure therein is reduced to such a value that liquid refrigerant does not flow to said evaporator at a satisfactory rate, and means responsive to a drop in said refrigerant pressure to pass refrigerant from said condenser into heat exchange relationship with refrigerant flowing from said compressor, thereby to heat the liquid refrigerant and increase its pressure.

5. Apparatus as described in claim 8, wherein said lastnamed means comprises, a pair of gas heaters connected respectively to receive hot gas from said compressor and to deliver gas to said condenser, a plurality of tube assemblies mounted in said headers and each having a pair of concentrically positioned tubes with an annular space therebetween open to said headers and having a fin assembly therein, the inner tube of each of said tube assemblies being connected in a liquid refrigerant bypass circuit and having a fin assembly therein, and a valve connected in parallel with said bypass circuit and including means responsive to the pressure of the liquid refrigerant to open the valve at high refrigerant pressure and close the valve when the pressure drops whereby liquid refrigerant is diverted through said bypass circuit by the closing of said valve.

6. A system as described in claim 5, wherein said bypass circuit includes orifice means constituting a restriction to the flow of liquid refrigerant.

7. The method of maintaining stable operating conditions in a refrigeration system which includes a condenser to which refrigerant flows to be condensed and from which liquid refrigerant flows to an evaporator and which includes a restrictor in the path of flow from the condenser and where there is a tendency for the refrigerant to flow to the evaporator at an objectionably low rate when the head pressure drops, the steps of, diverting refrigerant from its normal flow path from the condenser to the restrictor along a secondary path toward said restrictor in response to a drop in head pressure, and heating the liquid refrigerant so diverted thereby to raise the head pressure.

8. In a refrigeration system which includes a compressor which delivers refrigerant to a condenser and wherein there is a tendency for excessive cooling of refrigerant in the condenser to reduce the pressure of the condensed refrigerant below a desired value, a heat interchange unit which is adapted to pass a stream of the refrigerant gas flowing from the compressor to the condenser into heat exchange relationship with the refrigerant liquid flowing from the condenser thereby to cool the refrigerant gas and to heat the refrigerant liquid, and means responsive to a rise in the pressure of the condensed refrigerant to reduce the rate of heat transfer within said heat interchange unit.

9. The method of maintaining stable operating conditions in a refrigeration system which includes a condenser to which refrigerant flows to be condensed and from which liquid refrigerant flows to an evaporator and which includes a restrictor in the path of flow from the condenser and where there is a tendency for the refrigerant to flow to the evaporator at an objectionably low rate when the head pressure drops, the steps of, diverting refrigerant from its normal flow path from the condenser to the restrictor along a secondary path toward said restrictor in response to a drop in head pressure, and heating the liquid refrigerant so diverted by passing it in heat exchange relationship with hot gas refrigerant flowing toward the condenser.

References Cited in the file of this patent UNITED STATES PATENTS 2,252,300 McGrath Aug. 12, 1941 2,404,112 Urban July 16, 1946 2,423,382 Graham July 1, 1947 2,645,101 La Porte July 14, 1953 2,691,273 Kramer Oct. 12, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,956,419 October 18, 1960 Cecil Boling It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

line 55, for the claim reference numeral "8" Column 5,

line 56, for "heaters" read headers read 4 Signed and sealed this 19th day of December 1961 (SEAL) Attest: ERNEST W. SWIDER DAVID L. LADD Commissioner of Patents Attesting Officer USCOMM-DC