US2625801A - Absorption refrigeration - Google Patents

Description

Jan. 20, 1953 E. P. WHITLOW 2,625,801

- ABSORPTION REFRIGERATION Filed April 9, 1951 2 SHEETS SHEET 1 IN V EN TOR.

Jan. 20, 1953 E. P. WHITLOW 2,625,801

ABSORPTION REFRIGERATION Filed April 9, 1951 2 SHEETS-SHEET 2 IN V EN TOR.

operate satisfactorily at low pressures.

Patented Jan. 20, 1953 OFFICE ABSORPTION REFRIGERATION Eugene P. Whitlow, Evansville, Ind., assignor to Servel, Inc., New York, N. Y., a corporation of Delaware Application April 9, 1951, Serial No. 220,002

12 Claims. (01. 62119) solution for gravity fiow through the solution circuit.

Such vapor liquid-lifts have been commonly used in absorption refrigeration systems but all such lifts have a straight cylindrical tube. With a bubble type lift, vapor bubbles are introduced into liquid at the base of a cylindrical lift-tube of relatively small diameter to reduce the density of the mixture which rises in a continuous liquid phase in the tube. This type of lift operates well at high pressures but does not More specifically, the bubble type lift is not suitable for use in vacuum type absorption refrigeration systems when the liquid being lifted is at a temperature near its boiling point as the liquid flashes into Vapor as it rises in the lift-tube. When the liquid being lifted is at a temperature below that at which it flashes, the vapor contacting the cooler liquid condenses. In either case, due to the tremendous volume of vapor relative to liquid per unit of weight in a vacuum type system, the lifting of liquid is erratic and uncontrollable.

Also, when a lift tube larger than one-half inch in diameter is used, the vapor bubbles flow upwardly through the lift-tube without carrying much liquid with them. Therefore when the desired rate of circulation of liquid exceeds the capacity of a single lift-tube, it is necessary to use multiple tubes which increases the cost of the apparatus and introduce another factor which may result in erratic and uncontrolled circulation of liquid.

With a climbing film type of lift, vapor is expelled from solution in a cylindrical tube of relatively small diameter, usually heated throughout its length, and the expelled vapor flows upwardly through the center of the tube at high velocity. The drag of the high velocity vapor on the solution produces a rising film of solution on the Wall of the lift-tube. This type of lift operates well at low pressure but an individual tube has a limited capacity and also requires a relatively high hydrostatic reaction head. The limited capacity is due to the fact that the periphery of the tube on which the film is lifted varies as the first power of the radius of the tube while its cross-sectional area which controls the vapor velocity varies as the square of the radius, Therefore, only one, tubesize will produce a particular relative circulation of vapor and liquid and when a greater capacity is desired than can be produced by a single tube, a plurality of tubes must be provided.

When such a climbing film tube is heated the problem is further aggravated by the unequal variation in the peripheral heating surface and vapor velocity with changes in the radius of the tube. In other words, the tube requires a fixed heat transfer surface to transmit the amount of heat necessary to generate vapor at a rate correlated with a cross-sectional area to produce the required velocity. As the periphery of the tube is the heat controlling factor, which increases as the first power of increments of increase in radius, and the cross-sectional area is the velocity controlling factor, which increases as the square of increments of increase in radius, there is only one optimum tube diameter which will give the heat transfer surface and crosssectional area required to produce an optimum climbing film action. Such a tube is of relatively small diameter, one-half inch inside diameter for a tube sixty inches long used in a vacuum type absorption refrigeration system using a water solution of 50% lithium bromide by weight when heated by steam at atmospheric pressure, so that two or more lift-tubes must be used when the desired circulation rate exceeds the capacity of a single tube.

Also in the climbing film type of lift, the pressure drop in the lift tube consists of the force of gravity acting on the annular column of solution constituting the climbing film, inertia of the liquid in the film and the frictional drag of the climbing film on the wall of the tube which is equal to and opposes the frictional drag of the vapor on the climbing film. The height of the hydrostatic head of liquid required to balance these forces is a considerable part of the total height of the lift-tube and in practice constitutes nearly one-third of the total height.

With a droplet type lift as described and claimed in an application for United States Let ters Patent of Norton E. Berry, Serial No. 164,059 filed May 25, 1950, a boiler is provided having a sufficient heating surface to expel refrigerant vapor at a predetermined fixed rate and a cylindrical lift tube extending upwardly from the boiler. The cross-sectional area of the lift tube is correlated to the rate of vapor generation to cause vapor to flow upwardly therethrough in continuous vapor phase at sufficient velocity to lift, small droplets of liquid at a controlled reproducible rate at any given capacity. Such a droplet type lift constitutes a considerable improvement in vacuum type absorption refrigeration systems over the bubble and climbing film types of lifts previously used as it produces a controlled. liquid circulation and reduces the height of the hydrostatic reaction head required and the overall height of the apparatus besides providing a simpler construction having a single tube instead of a plurality of tubes which reduces the cost of manufacture and the possibility of leaks.

One of the objects of the present invention is to provide an improved vapor liquid-lift construction which reduces the pressure drop along the tube and the height of the reaction head required to balance the liquid lifting forces.

Another object of the present invention is to provide an improved vapor liquid-lift of the type indicated having a single conduit with a throat for producing the required initial velocity and a progressively divergent passageway above the throat.

Another object is to provide a combined generator and vapor liquid-lift having a single conduit adapted to be heated throughout its length and so formed as to provide both the necessary cross-sectional area and heating surface to lift liquid at any particular capacity.

Still another object is to provide a vapor liquidlift of the type indicated which operates at a relatively low solution temperature to lift liquid at a uniform rate and one which requires a relatively small heat transfer surface to expel the required volume of vapor.

These and other objects will become more apparent from the following description and drawings in which like reference characters denote like parts throughout the several views. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and not a definition of the limits of the invention, reference being had for this purpose to the appended claims. In the drawings:

Fig. 1 is a diagrammatic view of an absorption refrigeration system incorporating a tapered vapor liquid-lift conduit to provide the divergent passage;

Fig. 2 is a sectional side elevational view of a vapor liquid-lift of modified construction and .having a divergent passage formed by progressively flattening the opposite sides of a cylindrical tube;

Fig. 3 is a plan view taken on line 33 of Fig. 2

showing the progressivley divergent passage from the restricted throat at the bottom to the circular outlet at the top;

Fig. 4 is a transverse sectional view taken on line 6-4 of Fig. 2 showing the oval contour of the restricted throat at the lower end of the lift tube;

Fig. 5 is a sectional side elevational view of a vapor liquid-lift conduit of further modified construction adapted for full length heating and having flattened sides to provide a converging lower portion, a throat and a diverging portion above the throat;

Fig. 6 is a plan view taken on line 66 of Fig. 5 showing the cylindrical upper portion and divergent intermediate portion of the conduit;

Fig. 7 is a transverse sectional view taken on line 7-7 of Fig. 5 showing the restricting throat between the converging and diverging portions of the conduit;

Fig. 8 is a transverse sectional view taken on line 88 of Fig. 5 showing the contour at the bottom of the conduit;

Fig. 9 is a sectional side elevational view of a heated vapor liquid-lift conduit of still further modified construction in which a cylindrical tube is deformed on one side to provide arcuate shaped converging and diverging portions with a throat therebetween Fig. 10 is a plan view taken on line |E||0 of Fig. 9 showing the circular outlet at the top of the lift conduit;

Fig. 11 is a transverse sectional view taken on line of Fig. 9 showing the arcuate form of the restricted throat; and

Fig. 12 is a transverse sectional view taken on line |2|2 of Fig. 9 showing the contour at the bottom of the conduit.

Referring to Fig. 1 of the drawings, the present invention is shown applied to a vacuum type absorption refrigeration system of the type described and claimed in United States Letters Patent to Albert R, Thomas et al. No. 2,282,503 issued May 12, 1942, and utilizing water as a refrigerant and a salt solution as an absorbent. Such a system comprises generally a generator I 4, a vapor liquid lift l5, 2. separating chamber It, a condenser ll, an evaporator it, an absorber l9 and liquid heat exchanger 20 interconnected for the circulation of refrigerant and absorbent.

Generator I4 is of novel construction comprising a rectangular vessel having tube sheets Ma at each end and a rounded top Mb, see Fig. 2. Two horizontal rows of tubes 2| extend between the tube sheets Ma. with the upper row inclined toward the left and the lower row inclined toward the right as viewed in Fig. 1. A header 22 overlies a tube sheet Ma and encloses the right hand ends of the upper top row of tubes 2| and the header is connected by a conduit 23 to a source of heating medium such as steam. A header 24 overlying the opposite tube sheet Ma encloses the ends of the upper and lower rows of tubes 2|. A header 25 below header 22 encloses the outlet end of the lower row of tubes 2|. Thus, steam supplied through conduit 23 flows from header 22 through the upper row of tubes and then back into the header 25. Condensate flows from the upper inclined row of tubes 2| into header 2 and condensate flows from the lower inclined row of tubes into the header 25. The lower end of header 24 is connected to header 25 by a pipe 26 and condensate from both headers is drained through a waste pipe 21. Preferably, steam is supplied at atmospheric pressure to the header 22 and is maintained at atmospheric pressure by a vent opening 28 in the header 25. With steam at atmospheric pressure heat will be transferred to the solution in the generator vessel M at a predetermined fixed rate corresponding to the area of the heat transfer surface of the tubes 2| and sides of the tube sheets I la enclosed by the headers 22, 24 and 25. The lower end of the vapor liquid-lift 5, later to be described in detail, projects into the generator vessel Id for a short distance below the top thereof as shown in Fig. 1 and the liquid-lift utilizes the vapor expelled in the generator vessel to lift solution to the separating chamber It.

The separating chamber I8 surrounds the upper end of the vapor liquid-lift l5 and has a conical deflecting baflle 29 overlying the upper end of the lift and a plurality of other baffles 30 for separating liquid entrained in the vapor. The top of the separating chamber I6 is connected to the condenser I? by a conduit 3| and the outlet from the condenser is connected to the top of evaporator l8 by a conduit 32 having a device 33 therein permitting the flow of liquid refrigerant and non-condensable gases while maintaining a difference in pressure as described and claimed in a copending application of Norton E. Berry, Serial No. 725,000 filed January 29, 1947.

The evaporator I8 comprises a plurality of horizontally arranged tubes 34 having their opposite ends projecting into laterally spaced headers 35 and 36. Conduit 32 from condenser extends into one end of the uppermost evaporator tube 34 in header 35. The end of the next lower tube 34 projecting intoheader 36 has a cup 31 underlying the end of the uppermost tube to receive liquid refrigerant flowing therefrom and direct it for flow through said next lower tube. Each of the tubes 34 has a cup 3'! at one end underlying the end of the tube above to cause the liquid refrigerant to flow successively through each tube from the top to the bottom of the evapor tor. Between the headers 35 and 36 the tubes, 34 are provided with spaced heat transfer fins 38.

p The lower ends of the headers 35 and 36 overlie openin s 39 in the top of the absorber Hi. The absorber I9 is in the form of a cylindrical shell having a plurality of vertically arranged serpentine coils 40 and a liquid distributing means 4| therein. The liquid distributing means 4| uniformly distributes absorption liquid over the top of the coils 40 which drips from each horizontalcoil section 40a onto the next lower most coil section from the'top to the bottom of the coils. "Cooling" water is supplied to the interior of the coils 40 from any suitable source of supply through a pipe 42 and header 43. 'C001- ing water from the upper ends of the coil sections 40 is delivered through a header 44 and conduit 45 to the condenser H and water from the condenser is discharged through conduit 45. Thus, the same cooling water is used to cool the absorber l9 and the condenser Absorption solution flows by gravity from the separating chamber l6 through the absorption solution circuit back to the generator l4. Absorption solution weak in refrigerant flows from the separating chamber it to the liquid distributor 4| in a path of flow comprising conduit 49, inner passages 50 of the liquid heat exchanger 20 and conduit 5| connected to the liquid distributor. Absorption solution strong in refrigerant flows from the absorber l9 to the generator H in a path of flow comprising conduit 52, outer passages 53 of the liquid heat exchanger 20, leveling vessel 54 and conduit 55 to the base of the generator. Liquid heat exchanger 20 is arranged with its passages 50 and 53 arranged generally horizontal to take advantage of the decrease in height of the apparatus resulting from the improved lift-tube construction l5, as later explained, but is inclined at a slight angle to the horizontal to prevent the accumulation of vapor or gas bubbles on the heat transfer surfaces. Leveling vessel 54 has a relatively large volume so that variations in liquid flow in the solution circuit will have a negligible effect'on the liquid level a: in the vessel during operation of the system.

A purging device 56 is connected to the absorber l9 by a suction pipe 5'! and has a cooling coil 58 connected between cooling water conduits 42 and 45 and a fall tube 59 depending therefrom. The purging device 56 is connected to conduit 5| to receive a portion of the absorption solutionweak in refrigerant flowing toward the absorber'lil which flows over coil 58 to produce a relative vacuum for withdrawing non-condensable gases from the absorbent and deliver them through the fall tube 59. The bottom of the fall tube 59 is connected to a riser 50 connected at its lower end to conduit 52 and having a storage vessel 6| at the upper end. With such a construction non-condensable gases are withdrawn from the system and delivered to the storage vessel 6| while the absorption solution is delivered to the conduit 52 flowing toward the generator vessel l4.

A concentration control of the type described and claimed in United States Letters Patent to Lowell McNeely 2,465,904 issued March 29, 1949 is provided for storing liquid refrigerant in accordance with the difference in pressure between the'high and low pressure sides of the system. The concentration control comprises a vessel 52 having. a conduit 63 connected to receive refrigerant overflowing from the lowermost tube of the evaporator IS, a vent tube 64 connecting the top of the vessel to header 35, and a conduit 65 connecting the bottom of the vessel to the generatorvessel H.

:The' generator M and condenser operate at a'subatmospheric pressure corresponding to the vapor pressure of the refrigerant at its condensing temperature, for example, one pound per square inch absolute, and the evaporator I8 and absorber i9 operate at a lower pressure corresponding to the :vapor pressure of the refrigerant in the absorbent, for exampleyone-tenth of a pound per square inch absolute. The pressure difference is maintained between the condenser and evaporator by the device 33 and between the generator and absorber byliquid columns in conduits 5| and 52. To this end, the liquid heat exchanger 20 is located below the absorber I9 and solution will stand at a level 3 in: leveling chamber 54 only a few inches above the bottom of the vapor liquidlift |5,- at a level y in conduit 49 connected to conduit 5| through liquid heat exchanger 20 and at a level a in conduit 52.

In accordance with the present invention the vapor liquid-lift l5 comprises an upright conduit having a restricting throat a and a progressively increasing cross-sectional area above the throat. The cross-sectional area of the throat a is correlated to the rate of vapor generation in the generator Hi to cause vapor to flow upwardly through the conduit in continuous vapor phase at suflicient velocity to lift droplets of liquid at the desired rate. The individual droplets of liquid are lifted by the frictional drag of the vapor on their surface and the throat area a is of a size to produce an initial vapor velocity and upward force on a number of droplets corresponding to the amount of liquid to be raised sufficient to 'overbalance their inertia and the force of gravity to impart momentum to the droplets. The area b at the upper end of the diverging portion is of a size to produce a velocity and upward force on the droplets just sufilcient to overbalance the force of gravity. Actually in certain lift conduit constructions the velocity at area bmay be slightly less than that required to balance the force of gravity due to the residual momentum of the droplets. Thus, the crosssectional area of the lift conduit i5 gradually increases from the area a to the area b to produce a varying velocity sufiicient to lift liquid at the desired rate with a minimum pressure drop through the conduit.

In the embodiment of the invention illustrated in Fig. 1 the vapor liquid-lift conduit I is in the form of a tapered tube having the required crosssectional area a at the bottom and cross-sectional area b at the top and progressively diverging from the bottom to the top. The lower end of the tube I5 projects into the top of the generator vessel I4 and the upper end of the tube projects through the bottom of the separating chamber I6. For any particular capacity the surface of the tubes 2 I' and tube sheets I la underlying the headers 22, 24 and 25 is designed to provide the heat transfer surface required to expel the amount of vapor for that capacity. With steam at atmospheric pressure and temperature and a fixed heat transfer surface, the rate of heat transfer will be constant for a given generator pressure. A tapered lift-tube I5 is then selected having crosssectional areas a and b of the largest size to produce stable operation at the lowest heat input and highest condenser pressure to be encountered. Such a vapor liquid-lift will operate with a minimum pressure drop in the conduit. When operating with a minimum pressure drop, the rate of liquid circulation may be controlled by a restricting orifice 55a in conduit 55. For example, with a vacuum type absorption refrigeration system of 20 tons ice-melting capacity per 24 hours, utilizing a 50% Water solution of lithium bromide by weight and heated by steam at atmospheric pressure, a lift-tube 56 inches long having a crosssectional area or throat a of 9.8 square inches and a cross-sectional area b of 26.5 square inches produces a controlled relative circulation of 4 pounds of vapor to 64 pounds of solution per minute with a 2-inch difference in height it between the liquid level as in leveling chamber 54 and the bottom of the lift-tube 55. A refrigeration system of 5 tons ice-melting capacity operating under similar conditions with a lift-tube 45 inches long having a cross-sectional area a of 1.7 square inches and a cross-sectional area b of 4.4 square inches will produce a controlled relative circulation of 1 to 16 with a difference in height h at both full and half heat input capacity. One form of the invention having now been described in detail, the mode of operation of the complete apparatus is described as follows:

To initiate operation of the refrigeration system, a heating medium such as steam is supplied through conduit 23 to header 22 where it is directed into one end of the upper row of inclined heating ill of the generator vessel I4. The steam flows through the upper row of tubes 2I and is then directed by the header 24 into the opposite end of the lower row of tubes 2| through which it flows to the header 25. Heat from the steam is transmitted through the tube sheets Ma underlying the headers 22, 24 and 25 and walls of the tubes 2| to heat the solution in the generator vessel It at a constant rate. Steam condensate flows through the inclined tubes 2| into the headers 24 and 25, respectively, and condensate in header 24 is delivered through pipe 26 to conduit 25 where it flows through the condensate drain 2?.

Solution initially stands in the vapor liquidlift conduit I5 at the same level as in the leveling vessel 54 and vapor expelled from solution in the generator I 4 accumulates in the space 6 at the top of the generator vessel until it depresses the liquid level below the end of lift conduit I5 and escapes therethrough. When vapor commences to flow into the lower end of the lift conduit I5 the liquid in the conduit will tend to be broken up and toflow down the sides of the lift tube by gravity until the conduit is cleared of liquid. The vapor will then flow through the conduit toward the separating chamber I 6 in a continuous vapor phase. Due to the correlation of the-area a of the lift conduit I5 with the rate of vapor generation in the generator I4 after the latter is operating at full capacity, the vapor will flow through the throat at a velocity sufficientto lift small droplets of liquid as it flows upwardly therethrough. It is believed that the violent agitation of the solution caused by rapid boiling creates a froth or foam in the space e at the top of the generator vessel which flows with the vapor toward the open end of the lift conduit. The flow of vapor into the end of the tube at high velocity tears the froth or foam into fragments which coalesce into small droplets. Vapor flowing past the droplets at high velocity imparts a frictional drag suflicient to overcome inertia and the force of gravity acting on the droplets to cause them to rise through the lift tube. After momentum has been initially imparted to the droplets the frictional drag need only slightly exceed the force of gravity acting on the droplets. By providing the upper or outlet end of conduit I5 with a cross-sectional area b and vapor velocity just sufficient to overcome the force of gravity on the droplets a minimum resistance to flow and pressure drop through the tube results. It is therefore apparent that the tapered lift conduit I5 reduces the pressure drop through the conduit to a minimum and reduces to a minimum the hydrostatic reaction head requiredto balance the lifting forces in the lift tube. With a minimum pressure dropv in lift tube I5 and a minimum reaction head acting on the generator I4, the solution boils at a low pressure and temperature providing a maximum temperature differential between the solution and steam so that a minimum heating surface is required. The reaction head constitutes the diiference in levels h and the difference in density of the solution in conduit 55 and in the generator I4 but the reduced reaction head permits a small difference in levels h and a decreased overall height of the apparatus.

Vapor entering the separating chamber I6 continues to fiow upwardly through the baffles 29 and 30 and conduit 3| into the condenser I! where it is condensed to a liquid. The liquid re frigerant flows through the restricting device. 33 and conduit 32 into the uppermost tube 34 of the evaporator I8. Liquid refrigerant then flows through each tube 34 successively from the top to the bottom of the evaporator and evaporates at a low pressure and temperature corresponding to the vapor pressure of refrigerant in absorbent at the absorber temperature to cool air or other medium flowing over the exterior of the tubes and between the fins 38.

Absorption solution, weak in refrigerant, separated from vapor in the separating chamber I6, flows by gravity to the absorber I9 in the path of flow including the conduit 49, inner passages 50 of liquid heat exchanger 20, and conduit 5| to liquid distributor ML The absorption solution is then distributed by the liquid distributor 4! for gravity flow over the relatively cool serpentine coils 4G to provide a large absorption surface. Due to the affinity of the absorption solution for refrigerant vapor the vaporized refrigerant from the evaporator tubes 34 flows through the headers 35 and 36 into the absorber I9 where it is absorbed in the absorption solution. Such absorption of refrigerant vapor reduces the vapor pressure and temperature at which the refrigerant evaporates to produce the refrigerating effect. Absorption solution strong in refrigerant then flows by gravity from the absorber I9 back to the generator vessel I4 in the path of flow including the conduit 52, outer passages 53 of the liquid heat exchanger 20, leveling vessel 54 and conduit 55 to complete the cycle of operation.

During operation of the refrigeration system, non-condensable gases are continuously purged from the condenser ll through the device 33 and from the absorber l9 through the purge device 55 which transfers them to the storage vessel 6|. Liquid refrigerant overflowing from the evaporator l8 accumulates in the concentration chamber 82 to regulate the concentration of the absorption solution until an equilibrium is reached for the particular operating conditions. The amount of storage of liquid refrigerant in chamber 62 is controlled by the diiference in pressure between the high and low pressure sides of the system.

Fig. 2 illustrates a vapor liquid-lift 10 of modified construction having a divergent passage formed by flattening the opposite sides of a cylindrical tube. As shown in Figs. 3 and 4, the upper or outlet end H of the lift conduit 10 is circular while the lower or inlet end 12 of the tube is flattened to an oval shape and the crosssectional area of the tube diverges from the bottom to the top thereof. It will be noted that the area a at the lower end 12 of the tube 10 provides a throat of such size as to produce the required vapor velocity and the area b at the upper or outlet end H is of a larger size to produce a lesser vapor velocity. For any particular capacity a tube 10 will be selected having the cross-sectional area b desired and the tube is progressively flattened to provide a throat a of a size correlated to the rate of vapor generation to produce the particular velocity required t lift liquid at the desired rate. Lift conduit 10 operates in the same way as lift conduit [5.

Fig. 5 illustrates a further modified construction of vapor liquid-lift conduit 15 which is heated throughout its length. Vapor liquid-lift conduit l5 has an upper portion 16, a throat a, and a lower converging portion TI. The upper portion 16 may diverge progressively from throat a to its upper end as illustrated in Figs. 1 and 2 but preferably the upper portion has a section 16a which diverges from the throat for about .one third the height of the upper portion and a cylindrical section 16b above the diverging section. The intermediate divergent section 16a preferably has its sides flattened from the cylindrical cross-section I), see Fig. 6, to an oval crosssection a forming the throat. The lower portion .16 progressively converges from its closed bottom having a cross-sectional contour c to the throat a.

The conduit 15 'is enclosed throughout its length by a jacket 18 providing a heating chamber 19 around the conduit. The end of conduit 55 from the leveling vessel 54 is connected to the portion ll of lift conduit 15 adjacent its lower end and the jacket is provided with an inlet conduit 80 for a heating medium such as steam, a vent conduit 8| adjacent the upper end of the jacket and a condensate drain 82 at the bottom of the jacket. The construction illustrated in Fig. 5 provides a lift conduit 15 having a relatively large heat transfer surface while providing a throat a sufficiently small to produce the vapor velocity required. If for any particular installation it is found that the surface area of the lift conduit 15 is not sufficient to produce the heating required with a circular cross-sectional area b, the entire tube may be flattened to maintain the same cross-sectional area while providing an increased heat transfer surface. Thus, the construction illustrated in Fig. 5 adapts a single heated conduit to be used with an absorption refrigeration system in a large range of capacities to produce both the vapor velocity and heat transfer surface required. While the divergent lift conduit of the present invention is preferably used in a droplet type lift, it may be used on a climbing film type lift.

In operation, steam supplied to chamber 19 transfers heat through the wall of the lift conduit T5 to expel vapor from solution standing at the levelx. The cross-sectional area a at the throat is correlated to the heat transfer surface of the lower portion "ill to cause vapor to flow through the throat at sumcient velocity to raise droplets of liquid at the desired rate. It has been found that a lift conduit having a divergent section 'Hia extending about one-third the height of the upper portion 75 operates equally as well as a conduit diverging throughout its length and is more easily manufactured in large sizes. The cross-sectional area b need only be of a size sufi'icient to overbalance the force of gravity acting on the liquid droplets at the outlet from divergent section 15a. The droplets are further heated in the upper cylindrical section 161) to expel additional vapor so that the passage may be even more divergent with additional heating surface than the previously described forms.

Fig. 9 illustrates a still further modified construction of vapor liquid-lift conduit 35 adapted for full length heating. The vapor liquid-lift conduit comprises a cylindrical tube deformed by folding one side inwardly to arcuate shape to increase the heating surface without increasing the lateral dimensions of the conduit. It will be noted that the lift conduit 85 has an upper divergent portion 86 and a lower converging portion 87 with a throat a therebetween. Fig. 10 illustrates the outlet area b, Fig. 11 illustrates the throat portion a while Fig. 12 illustrates the area 0 at the lower end of the conduit. The lift conduit 85 is enclosed in a heating jacket 88 having a steam inlet 39 adjacent the bottom, a vent conduit 9%) adjacent the top, and a condensate drain 9! at the bottom of the jacket. The conduit 55 for solution strong in refrigerant is connected to the lower converging portion of the vapor-lift conduit 85.

It will now be observed that the present inven tion provides an improved vapor liquid-lift for use in absorption refrigeration systems and having a restricting throat to produce a vapor velocity suificient to lift liquid at the desired rate and a diverging cross-sectional area above the throat. It will also be observed that the present invention provides an improved vapor liquid-lift having a single conduit so constructed as to provide the necessary cross-sectional area and heating surface for any particular operating condition. It will still further be observed that the present invention provides an improved vapor liquid-lift which operates with a minimum pressure drop, a low solution temperature and a minimum heat transfer surface.

While several forms of the invention are herein illustrated and described, it will be understood that further modifications may be made in the construction and arrangement of elements without departing from the spirit or scope of the present invention. Therefore without limitation in this respect, the invention is defined by the following claims.

I claim:

1. In an absorption refrigeration system, an absorption solution circuit having an upright lift conduit, the parts of said circuit being arranged for the gravity flow of absorption liquid to the bottom of said lift conduit, means for heating liquid in said circuit to expel refrigerant vapor, and at least a portion of said lift conduit having diverging walls to provide a passage of progressively increasing cross-sectional area.

2. In an absorption refrigeration system, an absorption solution circuit having an upright lift conduit, the parts of said circuit being arranged to maintain absorption liquid in said circuit at a level above the bottom of said lift conduit, means for heating the absorption solution in said conduit to expel vapor therefrom at a constant rate, and said lift conduit having a throat adjacent its lower end of a cross-sectional area correlated to the rate of vapor generation to cause vapor to flow therethrough at sufiicient velocity to initiate upward movement of liquid and diverging walls above the throat.

3. In an absorption refrigeration system, an absorption solution circuit having an upright lift conduit, means to maintain absorption liquid in said circuit at a level above the base of the lift conduit, means for heating liquid in said circuit to expel refrigerant vapor, and said lift conduit having a throat of a cross-sectional area correlated to the rate of vapor generation to cause vapor to flow upwardly therethrough in continuous vapor phase at sufficient velocity to raise droplets of liquid and shaped to provide a di vergent passage above the throat for lifting the liquid with a minimum pressure drop.

4. In an absorption refrigeration system, an absorption solution circuit comprising a generator vessel in which refrigerant vapor is expelled from solution by the application of heat, an absorber above the generator in which refrigerant vapor is absorbed into absorption solution, a separating chamber above the absorber, a vapor liquid-lift for lifting absorption solution from the generator to the separating chamber for gravity flow through the absorber back to the generator, means for heating said generator, and said vapor liquidlift consisting of a single upright conduit connected between the generator and separating chamber and formed to provide at least a section of progressively increasing. cross-sectional area.

5. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a tube progressively tapered from the bottom to the top of the tube.

6. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a cylindrical tube having at least one side flattened progressively from one end toward the other to provide a gradually in* creasing cross-sectional area from the bottom to the top of the tube.

7., An absorption refrigeration system in accordance with claim 1 in which the heating means is in the form of a generator vessel and the vapor liquid-lift conduit is a tube formed to provide a divergent passageway upwardly from the generator vessel.

8. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a tube formed to provide a converging lower portion and a divergingupper portion with a restricting throat between the portions.

9. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a tube having a side flattened intermediate its ends to provide a converging lower portion and a diverging upper portion with a restricting throat therebetween, and the heating means comprises a chamber surrounding the conduit throughout its length.

10. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a lower heat transfer section, a section above the heat transfer portion having divergent walls to provide a restricting throat therebetween, a section above the divergent section having the same cross-sectional area as the latter, and the heating means comprises a chamber surrounding the conduit throughout its length. I

11. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a tube progressively deformed from a cylindrical contour at one end to an arcuate contour at the opposite end to provide a passage therethrough of gradually increasing cross-sectional area.

12. An absorption refrigeration system in accordance with claim 1 in which the vapor liquidlift conduit comprises a tube progressively deformed to arcuate shape intermediate its ends to provide a converging lower portion and a diverging upper portion with a restricting throat therebetween, and said heating means comprises a chamber enclosing the conduit throughout its length.

EUGENE P. WHITLOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,003,776 Mumford Sept. 19, 1911 1,985,973 Boynton Jan. 1, 1935 2,282,503 Thomas May 12, 1942

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