US3580002A - Freeze limiting absorption refrigeration machine - Google Patents

Abstract

An absorption refrigeration system utilizing chilled water as a heat exchange medium. The system includes a chiller which provides reduced heat exchange area upon a drop in ambient air temperature by selectively block water flow paths between the chiller coils by the formation of ice to prevent complete freezeup of the chiller.

Description

United States Patent John T. Fisher Indianapolis, Ind. 735,380

June 7, 1968 May 25, 1971 Carrier Corporation Syracuse, N.Y.

Inventor Appl. No. Filed Patented Assignee FREEZE LIMITING ABSORPTION REFRIGERATION MACHINE 2 Claims, 5 Drawing Figs.

U.S. Cl

62/118,62/389, 62/399, 165/1, 165/117, 165/134 Int. Cl ..F25b 15/04,

Field of Search References Cited UNITED STATES PATENTS 2,056,970 10/1936 Leopold Primary Examiner-Meyer Perlin Assistant Examiner-P. D. Ferguson Attorneys-Herman Seid and Harry G. Martin, Jr.

ABSTRACT: An absorption refrigeration system utilizing chilled water as a heat exchange medium. The system includes a chiller which provides reduced heat exchange area upon a drop in ambient air temperature by selectively block water flow paths between the chiller coils by the formation of ice to prevent complete freezeup of the chiller.

Patented May 25, 1971 2 Sheets-Sheet l (I) 00 00 00 OD OO 0000 INVENTOR.

JOHN T. FISHER.

ATTORNEY.

Patented May 25, 1971 2 Sheets-Sheet 2 OOOOOOOOOOO OOOOOOOOOAWOOO OOOOOOOOOOO m OOOOOOOOOOOO FIG. 2

FIG. 5

INVENTOR. T. FISHER.

ATTORNEY.

FREEZE LIMITING ABSORPTION GERATION MACIHNE BACKGROUND OF THE INVENTION Absorption refrigeration systems of the type with which this invention is concerned generally include a chiller having an evaporator coil through which refrigerant is passed in heat exchange relation with liquid heat exchange medium distributed over the evaporator coil, the medium being cooled by heat exchange with, the refrigerant, thereby evaporating the refrigerant. The chilled heat exchange medium is forwarded to a heat exchanger in a remote location to satisfy a cooling load and is returned from the remote location to be recooled in the chiller. It is desirable to use water as the heat exchange medium due to its favorable heat transfer characteristics, low cost and availability. However, when ambient temperatures drop, the temperature of the water chiller may drop below the freezing point of water. It is therefore desirable to reduce the heat exchange surface of the evaporator coil for limiting the ice buildup in the chiller to maintain circulation of chilled water to the area being conditioned.

SUMMARY OF THE INVENTION This invention relates to an absorption refrigeration machine employing an improved chiller construction including a double row evaporator coil adapted for refrigerant flow therethrough, the coil i'ows being spaced to promote the formation of ice during low ambient temperature operating conditions so as to reduce the heat exchange area thereof. The coils are arranged to block the flow of heat exchange medium thereover in three steps. First, by blocking the vertical spaces between the coil turns in each row, second, by blocking the area between the two coil rows, and third, by blocking the space between the outer coil row and the chiller coil, thereby reducing the heat transfer surface area of the coil to the inner surface of the inner coil.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flow diagram of an absorption refrigeration system employing the present invention;

FIG. 2 is a sectional view of the water chiller employed in the refrigeration system;

FIG. 3 is a sectional view of a portion of the chiller illustrating the formation of ice in the vertical spaces between the coil turns;

FIG. 4 is a sectional view similar to FIG. 3 showing a further formation of ice in the space between the two coil rows;

FIG. 5 is a sectional view similar to FIGS. 3 and 4 showing further formation of ice to block the flow of heat exchange medium over the outside surface of the outer coilrow.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, there is shown a refrigeration system comprising a primary absorber 10, a condenser 11, an evaporator or chiller 12, a generator 13, a solution-cooled absorber l4 and a iiquid-suction heat exchanger 15 connected to provide refrigeration. A pump 16 is employed to circulate weak absorbent solution from primary absorber to generator 13. As used herein the term weak absorbent solution" refers to a solution which is weak in absorbent power and the term strong absorbent solution refers to a solution which is strong in absorbent power. A suitable absorbent solution for use in the system described is water and a suitable refrigerant is ammonia.

Liquid refrigerant condensed in condenser 11 passes through refrigerant liqttid passage 18, and refrigerant restriction 20 to heat exchange tube 22 of liquid-suction heat exchanger 15. The liquid refrigerant is cooled in tube 22 and emerges from the liquid-suction heat exchanger and passes through refrigerant restriction 24 into heat exchanger 26 in chiller 12.

A fluid medium such as water to be chilled passes over the exterior of heat exchanger 26 where it is chilled by giving up heat to evaporate refrigerant within the heat exchanger. The chilled medium passes out of the chiller 12 through line 28 to suitable remote heat exchangers (not shown) after which it is returned to the chiller through inlet 30 for rechilling.

The cold refrigerant evaporated in heat exchanger 26 passes through refrigerant vapor passage 32 and through liquid-suction heat exchanger 15 in heat exchange relation with liquid refrigerant passing through tube 22. The refrigerant vapor then passes through refrigerant vapor passage 34 into solution-cooled absorber 14.

The solution-cooled absorber 14 is formed within a tubular or cylindrical vessel 38 by a tubular, preferably, cylindrical internal baffle 36 which divides the tubular cylindrical vessel 38 into the solution-cooled absorber l4 and a second solution chamber 40. Vessel 38 is preferably closed at both ends. Baffle 36 may be provided with a top cover plate 37 having a plurality of vapor discharge apertures 42 therein to allow vapor to escape from solution-cooled absorber 14 into chamber 40.

A weak solution heat exchanger 44, preferably comprising a helical coil is disposed within solution-cooled absorber 14. A plurality of horizontal plates 46 are secured to a central support 48 and arranged within baffle 36 to cooperate with annular grooves 50 and heat exchanger 44 to provide a tortuous path for passage of vapor and solution through solutioncooled absorber 14. Suitable packing such as Raschig rings 52 may fill the space between the uppermost plate 46 and the top of the solution-cooled absorber to reduce the tendency for solution froth to escape through discharge apertures 42.

A refrigerant vapor distributor header 54 is secured to close the bottom of baffle 36. Header 54 is provided with refrigerant vapor ports 56 for passage of refrigerant vapor from line 34 into solution-cooled absorber l4 and chamber 40. Strong solution from generator 13 is supplied to the top portion of solution-cooled absorber 14 through line 58. The strong solution passes downwardly through the solution-cooled absorber in counterflow relation to upwardly passing refrigerant vapor and weak solution passing through coil 44. A strong solution discharge passage 60 is provided adjacent the lower portion of baffle 36 for passage of solution from the solution-cooled absorber into chamber 40.

Solution discharge passages 62 are provided for passing a mixture of refrigerant vapor and solution from chamber 40 to primary absorber 10. Each of the discharge passages comprises a tubular member having an upper open end for admission of vapor and a solution inlet aperture 64 which is disposed below the level of absorbent solution in chamber 40. This insures a mixed flow of liquid and vapor to the primary absorber.

A cooling medium, preferably ambient air, is passed through the primary absorber 10 in heat exchange relation with the absorbent solution to cool the absorbent solution to promote the absorption of the refrigerant vapor in the absorber. The same cooling medium may be supplied to condenser 11 in heat exchange relation with refrigerant therein to condense the refrigerant.

Cold weak absorbent solution passes from primary absorber 10 through line 66 into pump inlet tank 68. Weak solution from inlet tank 68 is supplied to weak solution pump 16 through line 72. Liquid from pump 16 passes through pump discharge tank 74 to a rectifier heat exchange coil 76. From coil 76, the weak solution passes through line 78 to weak solution heat exchanger 44 in solution-cooled absorber 14. The weak solution from coil 44 passes through line 80 into the upper portion of generator 13 alongwith any vapor formed in coil 44.

Generator 13 comprises a shell 82 having fins 84 suitably affixed thereto as by welding. The generator is heated by a gas burner 86 or other suitable heating means. The weak solution is boiled in generator 13 to concentrate the solution, thereby forming a strong solution and refrigerant vapor.

The hot strong absorbent solution passes upwardly through the analyzer section of generator 13 through analyzer coil 88 in heat exchange with weak solution passing downwardly over the coil. The warm strong solution then passes through line 58 which has solution restrictor 87 therein and is discharged into the upper portion of solution-cooled absorber l4.

Refrigerant vapor formed in generator 13 passes upwardly through the analyzer section thereof where it is concentrated by mass heat transfer with weak solution passing downwardly over analyzer coil 88. Analyzer plates 90 in generator 13 pro vide a tortuous path for flow of solution and vapor to assure intimate contact therebetween to improve the mass heat transfer. The refrigerant vapor from the analyzer section passes through reflux plate 92 in heat exchange relation with absorbent condensed in rectifier 94. The vapor then passes through rectifier 94 in heat exchange relation with rectifier heat exchange coil 76. Absorbent condensed in rectifier 94 flows downwardly onto plate 92 where it is heated by the refrigerant vapor passing therethrough. The heated absorbent is then passed to the generator along with the weak solution discharged into the generator from line 80. Refrigerant vapor passes from rectifier 94 through line 96 to condenser 11 to complete the refrigeration cycle.

The water chiller 12 as illustrated in FIG. 2 comprises an outer cylindrical shell 102 having a top member 104 secured thereto. A cylindrical liner 106 is disposed within shell 102 in spaced relation thereto. A suitable insulating material 108 such as urethane foam is provided between shell 102 and liner 106 and on the bottom of the liner. The insulation is preferably foamed in place to form a complete assembly. The double row, helically shaped tube-type heat exchange coil 26 in chiller 12 is disposed within liner 106 for passage of refrigerant therethrough. A distribution tray 110 which is disposed above coil 26 receives water returned from the remote heat exchangers through return water line 30. Distribution tray 110 is provided with two concentric rows of downwardly directed nozzles 112 which are aligned above the two rows of coil 26 for discharge of water from tray 110 onto the coil. A cap 114 is suitably affixed to tray 110 to deflect the stream of water from line downward into tray 110. Overflow towers 116 are provided on tray 110 to prevent an exces sive accumulation of water therein.

When outdoor ambient temperatures drop, the chiller temperature may drop to a level sufficient to cause freezing of the water being circulated therethrough. Unless this freezing is controlled, all of the water in the chiller will freeze which will prevent flow of chilled water to the remote heat exchangers. To prevent complete freezeup of the chiller, applicant has provided a novel chiller heat exchanger configuration which assures selective freezing of the water in the chiller to reduce the heat transfer area of the heat exchanger to prevent complete freezeup of the chiller, thereby assuring sufficient water for circulation to the remote heat exchangers irrespective of chiller temperature. FIG. 3 illustrates a first chiller condition wherein ice has formed in the vertical spaces between the coil turns of the heat exchanger. This reduces coil surface by the amount of the surface covered by the ice on the bottom and top of the individual coil turns. If this reduced heat exchange area is great enough to cause further freezing of water in the chiller, ice will form in the space between the two concentric coil rows, This will reduce the heat exchange surface to include only the outer surface of the larger coil row and the inner surface of the smaller coil row. If this heat exchange surface is still excessive in relation to coil temperatures, further icing will occur as illustrated in FIG. 5 to block the passage of chilled water along the outer surface of the larger coil row. This effectively reduces the heat exchange area of the coil to the inner surface of the smaller coil row. Any further icing of the chiller would cause a greater blanket of ice to be built up on the inside surface of the inner coil row. This ice will act as insulation to further reduce the heat transfer between the coil and the chilled water. As can be seen from FIG. 5, the iced chiller will have a cylinder of ice surrounding the coil. After icing of the chiller as illustrated in FIG. 5 has occurred, there is still a sufiicient quantity of water in the chiller for circulation to the remote heat exchangers.

While I have described a preferred embodiment of my invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.

Iclaim: l. A method for varying the heat exchange between refrigerant and a heat exchange medium in an absorption refrigeration system chiller having a tube-type heat exchanger therein including the steps of:

reducing the heat exchange surface of the heat exchanger by forming relatively small ice bridges in the vertical spaces between adjacent tubes of the heat exchanger to prevent flow of heat exchange medium therebetween;

further reducing the heat exchange surface of the heat exchanger by forming an ice bridge, larger than those between the vertical rows of the heat exchanger, between one row of heat exchanger tubes and a second adjacent row to prevent flow of heat exchange medium therebetween; and

further reducing the heat exchange surface by forming an ice bridge larger than that between adjacent rows of the heat exchanger between the heat exchanger tubes and the chiller wall to prevent flow of heat exchange medium therebetween.

2. An absorption refrigeration system comprising an absorber, a generator, a condenser, and a chiller adapted to provide refrigeration, said chiller comprising:

a casing; and

a tube-type heat exchanger disposed in said casing adapted for refrigerant flow therethrough, said heat exchanger comprising two concentric helically shaped tube rows, said rows being spaced from each other a distance greater than the vertical spaces between said tubes and less than the space between the tube row and said casing so that upon a drop in temperature of the heat exchange medium, after initial formation of ice in the vertical spaces between the tubes, ice will form in the space between the tube rows and thereafter form between the outer tube row and said casing to permit flow of heat exchange medium only over the ice coating on the inner surface of the inner tube row for heat transfer between the refrigerant and the heat exchange medium.

Claims (2)

1. A method for varying the heat exchange between refrigerant and a heat exchange medium in an absorption refrigeration system chiller having a tube-type heat exchanger therein including the steps of: reducing the heat exchange surface of the heat exchanger by forming relatively small ice bridges in the vertical spaces between adjacent tubes of the heat exchanger to prevent flow of heat exchange medium therebetween; further reducing the heat exchange surface of the heat exchanger by forming an ice bridge, larger than those between the vertical rows of the heat exchanger, between one row of heat exchanger tubes and a second adjacent row to prevent flow of heat exchange medium therebetween; and further reducing the heat exchange surface by forming an ice bridge larger than that between adjacent rows of the heat exchanger between the heat exchanger tubes and the chiller wall to prevent flow of heat exchange medium therebetween.

2. An absorption refrigeration system comprising an absorber, a generator, a condenser, and a chiller adapted to provide refrigeration, said chiller comprising: a casing; and a tube-type heat exchanger disposed in said casing adapted for refrigerant flow therethrough, said heat exchanger comprising two concentric helically shaped tube rows, said rows being spaced from each other a distance greater than the vertical spaces between said tubes and less than the space between the tube row and said casing so that upon a drop in temperature of the heat exchange medium, after initial formation of ice in the vertical spaces between the tubes, ice will form in the space between the tube rows and thereafter form between the outer tube row and said casing to permit flow of heat exchange medium only over the ice coating on the inner surface of the inner tube row for heat transfer between the refrigerant and the heat exchange medium.

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