US2625802A - Absorption refrigeration - Google Patents

Description

Jan. 20, 1953 E. P. WHlTL-OW 2,625,802

ABSORPTION REFRIGERATION Filed April 9, 1951 2 SHEETSSHEET 1 JNVENTOR.

E. P. WHITLOW ABSORPTION REFRIGERATION Jan. 2O, 1953 2 SHEETS-SHEET 2 Filed April 9, 1951 INVENTOR.

Patented Jan. 20, 1 953 ABSORPTION REFRIGERATION Eugene P. Whitlow, Evan sville, Ind., assignor to Scrvel, Inc., New York, N. Y., a corporation of Delaware Application April 9, 1951, Serial No. 220,001

13 Claims. 1

The present invention relates to absorption refrigeration systems and more particularly to heating the absorption solution in such systems.

It is a common practice in absorption refrig eration systems to provide a vapor liquid-lift utilizing refrigerant vapor expelled from absorption solution to lift the solution for gravity flow through the absorption solution circuit. When a bubble type vapor liquid-lift is used, vapor is expelled in a generator vessel and enters the lift tube as bubbles which reduce the density of the mixture and cause it to rise in a continuous liquid phase. Such a vapor liquid-lift operates well in a high pressure system but is erratic and uncontrollable in a vacuum type system due to the tremendous volume of the vapor at low pressure. Furthermore, with a tube larger than one-half inch diameter, the bubbles rise freely without lifting any liquid which limits the capacity of a refrigeration system using a single lift tube.

In a climbing film type lift used in vacuum type absorption refrigeration systems the vapor is expelled by heat applied to the periphery of the lift tube. The expelled vapor flows upwardly through the center of the lift tube at high velocity which produces a frictional drag to lift an annular film of liquid up the wall of the tube. However, due to the fixed ratio of the peripheral heating surface to cross-sectional area for producing the required velocity in any particular lift tube, a plurality of small tubes are usually necessary to obtain the required heating surface.

With a droplet type lift described and claimed in an application for United States Letters Patent of Norton E. Berry, Serial No. 164,059, filed May 1950, also adapted for use in vacuum type absorption refrigeration systems, all of the vapor is expelled from solution in a generator vessel and at the highest pressure and temperature in the solution circuit. The cross-sectional area of the lift tube and rate of vapor generation are correlated to cause the vapor to flow upwardly through the lift conduit in continuous vapor phase at sufficient velocity to lift droplets of liquid. Such a droplet type lift avoids the use of multiple tubes usually required in the climbing film type of lift but all of the vapor is expelled at relatively high pressure and temperature even though the liquid could be lifted by a lesser amount of vapor.

One of the objects of the present invention :is to provide an improved heating arrangement .in a vacuum type absorption refrigeration systerm adapted to heat solution at a plurality of places in the solution circuit to decrease the solution temperature and heating surface required.

Anotherobject is to provide a heating arrange ment in a vacuum type absorption refrigeration system which expels a portion of the refrigerant vapor at the base of a lift conduit to lift solution and expels the remainder of the vapor from solution as the latter issues from the upper end of the lift conduit.

Another object is to utilize the wall of a droplet type vapor liquid-lift conduit as an auxiliary heat transfer surface-to expel refrigerant vapor from solution at a lower pressure and temperature than in the generator.

Still another object is to provide a combined generator and vapor liquid-lift in a single conduit which is heated throughout its length and so constructed as to increase the heat transfer surface of the conduit.-

These and other objects will become more apparent from the following description and drawings in which like reference characters denote like parts through 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 bad for this purpose to the appended claims. In the drawings:

Fig. l is a diagrammatic view of a vacuum type absorption refrigeration system incorporating the present invention and. showing a generator vessel for heating solution at the lower end of vapor liquid-lift conduit and an auxiliary heating means at the-upper end of the conduit;

Fig. 2 is a sectional. side elevational view of the heating arrangement illustrated in Fig. 1' as applied to a lift conduit of modified construction;

Fig. 3 is a sectional side elevational view of a further modified construction showing a generator at the base of the lift conduit and a heating jacket surrounding. the conduit; and

Fig. 4 is a sectional side elevational view of a still further modified construction having a combined generator and lift conduit enclosedv in a heating jacket and an additional heating means in the separating chamber. 7

Referring to Fig. 1 of the drawings, the present invention is shown applied toavacuum type absorption refrigeration system of the type described and claimed in United States Letters Patent to Albert R. Thomas et 9.1., 2,282,503, issued May 12, 1942, which utilizes water as a refrigerant and a salt solution as an absorbent.

Such a system comprises generally a generator 5, a vapor liquid-lift 6, a separating chamber 1, a condenser 3, an evaporator 9, an absorber IE3 and liquid heat exchanger II interconnected for the circulation of refrigerant and absorbent.

Generator is described and claimed in a copending application for United States Letters Patent filed concurrently herewith and comprises a rectangular vessel having tube sheets I2 at each end and a rounded top I3, see Fig. 2. Two horizontal rows of tubes I4 extend between the tube sheets I2 with the upper row inclined toward the left and the lower row inclined toward the right as viewed in Fig. 1. A header I5 overlies a tube sheet I2 and encloses the right-hand ends of the upper row of tubes I 4. A header I5 overlying the opposite tube sheet l2 encloses the ends of the upper and lower rows of tubes I4. A header I! below header I5 encloses the outlet end of the lower row of tubes I4. A conduit l8 connects header I5 to a source of heating medium such as steam and a conduit I9 connects the header I! to an additional heating surface, as later described in detail. The lower end of header I6 is connected to header I! by a pipe and condensate from both headers is drained through a waste pipe 2|. The lower end of the vapor liquid-lift conduit 6 constituting a restriction or throat in the path of vapor flowing from the generator vessel 5 and projects into the generator vessel for a short distance below the top thereof as shown in Fig. 1 and the liquid-lift conduit utilizes the vapor expelled in the gen orator vessel to lift solution to the separating chamber I. Fig. l, the lift conduit is in the form of a cylindrical tube.

Separating chamber 1 surrounds the upper end of the vapor liquid-lift conduit 6 and has a coni cal deflecting baifle 22 overlying the upper end of the lift and a plurality of other bafiies 23 for separating liquid entrained in the vapor. The top of the separating chamber 1 is connected to the condenser 8 by a conduit 24 and the outlet from the condenser is connected to the evaporator 9 by a conduit 25 having a device 25 therein for maintaining a pressure differential while permitting the flow of liquid refrigerant and noncond-ensable gases as described and claimed in a copending application of Norton E. Berry, Serial No. 725.000. filed January 29, 1947', now Patent No. 2,563,575.

The evaporator 9 comprises a plurality of horizontally arranged tubes 27 having their opposite ends rojecting into laterally spaced headers 28 and 29. Conduit 25 from condenser 8 is connected to one end of the uppermost evaporator tube 21 in header 28. The end of the next lowermost tube 21 proiecting into head-er 29 has a cup 30 at its end underlying the end of the uppermost tube to receive liquid refrigerant flowing therefrom and directing it for flow through said next lo ermost tube. Each of the tubes 2'! has a cup 30 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 evaporator. Between the headers 28 and 29 the tubes 21 are provided with spaced heat transfer fins 3|.

The lower ends of the headers 28 and 29 overlie openings 32in the top of the absorber I B. The absorber I0 is in the form of a cylindrical shell having a plurality of vertically arranged serpentine coils 33 and a liquid distributing means 3-1. The liquid distributing means 34 uniforrmy dis- In the embodiment illustrated in fit tributes absorption liquid over the top of each coil 33 which drips from each coil section onto the next lowermost coil section from the top to the bottom of the coils. Cooling water is supplied to the interior of the coils 33 from any suitable source of supply through a pipe 35 and header 36. Cooling water from the upper ends of coils 33 is delivered through a header 3! and conduit 38 to condenser 8 and cooling water from the condenser is discharged through a conduit 39. Thus, the same cooling water is used to cool the absorber II! and condenser 8.

Absorption solution flows by gravity from the separating chamber 1 through the absorption solution circuit back to the generator 5. Solution weak in refrigerant flows from the separating chamber 7 to the liquid distributor 34 in a path of flow comprising conduit 40, inner passages es of the liquid heat exchanger II and conduit 42 connected to the liquid distributor. Absorption solution strong in refrigerant flows from the absorber ID to the generator 5 in a path of flow comprising conduit 43, outer passages M of the liquid heat exchanger I I and accumulates in the upper part of the liquid heat exchanger casing constituting a leveling vessel #35 and from the leveling Vessel through a conduit is to the base of the generator. Leveling vessel 45 has a relatively large volume so that variations in liquid flow in the solution circuit will have a negligible effect on the liquid level at in the vessel during operation of the system.

A purge device i! of the type described and claimed in United States Letters Patent to Charles H. Roswell, No. 2,384,861, issued September 18, 1948, is provided for withdrawing noncondensable gases from the active part of the system. The purge device 41 is in the form of an auxiliary absorber and comprises a vessel connected to conduit 42 to receive absorption solution weak in refrigerant and having a suction pipe 48 extending to the bottom and center of the main absorber I!) where the gases accumulate A cooling coil 49 in the purge device 4'! is conneoted between cooling water conduits 35 and 3B in parallel with the absorber coils 33 and a fall tube 53 depends from the bottom of the vessel. The purge device M utilizes a portion of the absorption solution flowing toward the absorber I2} to withdraw non-condensable gases from the main absorber and deliver them through the fall tube 50 to a riser 5| connected to conduit 63 at its lower end and having a storage vessel 52 at its upper end. With such a construction, non-condensaible gases are withdrawn from the system and delivered to the storage vessel 52 while the absorption solution is delivered to the conduit 53 flowing toward the generator vessel 5.

A concentration control of the type illustrated and described in United States Letters Patent of Lowell McNeely, 2,465,904, issued March 29, 1949, is provided for storing liquid refrigerant in acoordance with the difference in pressure between the high and low pressure sides of the system. The concentration control comprises a vessel 53 having a conduit 54 connected to receive liquid refrigerant overflowing from the lowermost tube of the evaporator 9 and a conduit 55 connecting the bottom of the vessel to the generator 5. A pressure equalizing conduit 56 is also connected between the top of the vessel and the side of the evaporator header 28.

The generator 5 and condenser 8 operate at one pressure corresponding to the condensing temperature of the condenser 8, for example, one

pound per square inch absolute, and the evaporator 9 and absorber l operate at a lower pressure corresponding to the vapor pressure of refrigerant in the absorbent, for example, one-tenth of a pound per square inch absolute, and the pressure difference is maintained between the condenser 8 and evaporator 9 by the device 26 and between the generator and absorber I!) by liquid columns in conduits 42 and 43. The liquid heat exchanger H is located below absorber l0 and during operation of the system solution will stand at a level a: in leveling chamber 45 to produce a hydrostatic reaction head it on the vapor liquidlift 6 and solution will stand at a level y in conduit 40 connected to conduit 42 through liquid heat exchanger I l and at a level 2 in conduit 43.

In accordance with the present invention, the solution is heated at a plurality of places in the absorption solution circuit to expel refrigerant vapor from solution. In the embodiment of the invention illustrated in Fig. l, a heating coil 60 is provided in the separating chamber 1 in addition to the generator. The heating coil 60 is supplied with heating medium, such as steam, by conduit I9 connecting header I! of generator 5 to one end of the coil. The opposite end of the coil 60 is vented to the atmosphere to maintain the steam at atmospheric pressure. The steam supplied from a source through conduit l8 flows from header [5 through the upper row of heating tubes [4 into header l6, then through the lower row of tubes 14 into header H and from the latter through the conduit H! to heating coil 63 in the separating chamber I.

The heating surface of the generator tubes l4 and tube sheets I2 underlying the headers l5, l6 and I! is so proportioned as to transfer an amount of heat which will expel the required volume of refrigerant vapor to lift solution at the desired relative circulation rate. This is accomplished by designing the lift conduit 6 for the particular capacity desired so that its lower end which constitutes a throat in the path of vapor flow will produce a vapor velocity through the conduit sufficient to lift liquid at a controlled reproducible relative circulation rate. To maintain a minimum pressure drop through the lift conduit 6, a conduit is used having the largest cross-sectional area which will produce stable operation at condenser pressure expected to be encountered. Preferably the conduit 6 is designed to lift a maximum volume of liquid with a minimum volume of vapor and if necessary in a particular installation a restricting orifice 6! may be provided in conduit 46 to regulate the rate of flow of solution to the lift conduit. The auxiliary coil 60 is proportioned to give the heat transfer surface required to expel the amount of additional refrigerant necessary to produce full capacity and adjust the concentration of absorption solution to produce the desired evaporator temperature.

Absorption liquid issuing from the upper or outlet end of liquid lift conduit 6 is directed by the conical baffle 22 onto the auxiliary or secondary heating coil 60 to expel the additional refrigerant vapor from solution. By dividing the heating surfaces in the generator 5 and separating chamber 1, respectively, a smaller generator may be used, vapor may be expelled from solution at a lower temperature due to the higher refrigerant content of the solution being lifted and a smaller heat transfer surface may be used because of the lower temperature at which the refrigerant is expelled. For example, when all of the lowest heat input and highest 6. the vapor is expelled in the generator of a vacuum type absorption refrigeration unit using a Water solution of lithium bromide and operating between concentrations of 59% and 54% by weight of lithium bromide with the solution in the boiler at 67 mm. Hg pressure, the solution will have a boiler temperature of 185 F. Thus, the temperature difference between atmospheric steam at 212 F. and the solution temperature is only 27 F. On the other hand, if only one-half of the vapor is expelled in th generator, the solution will have a concentration of 56.5% lithium bromide by weight and at the same pressure of 67 mm. Hg the solution in the generator will have a boiling temperature of 175 F. and provide a difference in temperature of 37 F., permitting the use of a much smaller heat transfer surface. The other half of the vapor is expelled from the solution by heat suppliedfrom the coil at a lower pressure than in the generator'5 corresponding to the pressure drop in the lift conduit 6. Therefore, the refrigerant is expelled by heat from coil 60 at a lower temperature than would be the case if all of the refrigerant were expelled in generator 5. One form of the invention having now been described in detail, the mode of operation is explained as follows.

To initiate operation, steam is supplied through conduit l8 which flows from header l5 through the upper row and then through the lower row of tubes [4 to heat the solution in the generator 5. Vapor expelled from solution accumulates in the space e at the top of the generator vessel 5 until it depresses the liquid level below the end of the lift conduit 6 and flows upwardly therethrough at high velocity. As the lower end of the lift conduit 6, constituting a throat in the path of vapor flow, is designed to correlate its cross-sectional area with the rate of vapor generation in the generator 5, the vapor will flow at a high velocity sufiicient to raise droplets of liquid through the lift conduit at the desired rate. It is believed that the violent boiling of solution in the generator vessel 5 produces a froth or foam in the space e which is drawn into the base of the lift conduit 6 where it coalesces into small droplets in the high velocity stream of vapor. Vapor and liquid issuing from the upper end of lift conduit 6 is directed by the conical baffle 22 into contact with the auxiliary heating coil Bil where additional vapor is expelled from solution at a relatively low pressure and temperature to produce the required refrigerant and solution concentration. Bailles 22 and 23 will separate vapor from solution and the vapor will flow through the conduit 24 to the condenser 8 where it is condensed to a liquid. Liquid refrigerant flows from condenser 8 through conduit 25 to the evaporator 9 and then flows by gravity through the tubes 21 from the top to the bottom of the evaporator.

Absorption solution, weak in refrigerant, flows from the separating chamber I to the liquid distributor 34 in the absorber It in a path of flow including the conduit 4i), inner passages 4! of liquid heat exchanger H and conduit 42. The

absorption solution is distributed by the liquid distributor 34 for gravity flow over the coils 33. Due to the high affinity of refrigerant vapor for absorption solution the vapor pressure of the refrigerant is reduced to cause it to evaporate at a low pressure and temperature and cool air or other medium flowing over the exterior of the evaporator coils 2'! and heat transfer fins 3 i. The coils 33 provide an extensive surface of absorption solution to enhance absorption of refrigerant vapor and. the. solution, strong in refrigerant flows back to the base of the enerator 5 in path of flow including the conduits 43., outer passages 44 of liquid heat exchanger ll. leveling chamber 45 and conduit 46' to complete the cycle of operation. Non-condensable gases are withdrawn from the system by the purge device a? and transferred to the storage vessel 52. The concentration of the solution is controlled by the accumulation of liquid refrigerant in the concentration vessel 53 as controlled by the difference in pressure between the high and low pressure sides of the system.

Fig. 2 illustrates the invention applied to a vacuum type absorption refrigeration system having a tapered vapor-lift conduit 62 instead of a cylindrical lift tube as illustrated in Fig. 1 to even further reduce the boiling temperature of solution in the generator 5. In this, form of construction the lower end of lift conduit 62 also constitutes a throat in the path of vapor flowing from the generator vessel 5. Such a tapered lift tube is described and claimed in my application for United States Letters Patent filed concurrently herewith. The heating arrangement is identical with that illustrated'in Fig. 1 comprising a genorator 5 and heating coil to in the separating chamber 1.

In Fig. 3 a further modified construction is illustrated in which the additional heat is applied through the wall of the lift conduit 62. While a tapered lift tube 62 is illustrated in Fig. 3, it will be understood that a strai ht tube as illustrated in Fig. 1 may be used if desired. The auxiliary or additional heating means for lift conduit 62 comprises a jacket 54 surrounding the tube and 2 providin a heating chamber 65. A conduit 66 connects the outlet header ll of the generator 5 to the bottom of the jacket 5:3 so that steam from a source flows successively through the upper and lower rows of tubes Hi in the generator and then I through the heating chamber 55. The heating surface of the generator 5 is designed to expel the amount of refrigerant vapor required to lift solution at the desired rate and the heating surface of the lift tube is designed to xpel the additional refrigerant required at a lower pressure than that in the generator. A vent pipe Bl is connected to the upper end of jacket 64 to maintain the heat ing steam at atmospheric pressure and a condensate drain pipe 68 is provided at the bottom of the heating chamber.

Fig. 4 illustrates a still further modified construction in which the generator and lift conduit are combined in a single element is which is heated throughout its length. has a lower generator portion in the form of an annular chamber H and an upper divergent lift portion 12 with a restriction or throat therebetween. By forming the lower generator portion in the form of an annular chamber H a reentrant wall surface 13 is provided to increase the heating surface. The element i9 is enclosed throughout its length in a jacket I'd providing a heating chamber 75. A steam inlet conduit it is connected to the jacket l4 below the generator portion H for supplying steam to the heating chamber 75 to heat the element 70 throughout its length. Preferably, a guide element H is so arranged as to direct part of the heating steam to the reentrant portion of the generator H to insure heating of the wall portion 13. Th lower generator portion fl is designed to provide the heating surface required to produce an amount of vapor sufficient to raise solution at the desired rate and the wall of the upper lift portion 12 provides the additional The element to heatin u f e e uired: In me s t ons f large apac y an dd i nal a x ar h at ng coil 18; may be required in the separating chamber 7 and in such installations the coil may be supplied with steam through a conduit 79 connecting the upper end of jacket 14 and one end of coil 18. The opposite end so of the coil would be vented at the atmosphere to maintain the steam at atmospheric pressure. A condensate drain pipe 8| is provided at the lower end of the jacket M.

It will now be observed that, the present invention provides an improved heating arrangement for a vacuum type absorption refrigeration systour by which the solution is heated at a plurality of places in the absorption solution circuit.

It will also be observed that in accordance with the present invention the wall of the lift conduit may be utilized as an additional or auxiliary heating surface. It will still further be observed that the present invention is applicable to a combined generator and. vapor liquid-lift conduit so constructed as to increase the heat transfer surface of the conduit.

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

What is claimed is:

1. In a low pressure absorption refrigeration system, an absorption solution circuit having an upwardly directed lift conduit for any particular capacity and provided with a throat, the parts of said circuit being arranged to maintain a level of absorption solution in the circuit above the throat in said lift conduit, means for heating the liquid in said circuit below the throat of said lift conduit to expel refrigerant vapor at a constant rate, the cross-sectional area of said throat being correlated to the rate of vapor generation to cause the expelled vapor to flow through said throat and the lift conduit above the throat in continuous vapor phase at the desired rate and lift liquid suspended therein, and an additional heating means above the throat of said lift conduit to expel additional refrigerant vapor.

2. In a two pressure vacuum type absorption refrigeration system, an absorption solution circult having a generator vessel, 2. single lift conduit proiecting upwardly from the top of the genera-tor vessel, the lower end of said lift conduit constituting a throat at the outlet from said generator vessel, an absorber, conduits interconnecting the generator, liouid lift and absorber to provide a path for the flow of solution therethrough and maintain. pressure balancing liquid columns, means for heating the liquid in said generator vessel to expel refrigerant vapor at a constant rate, the cross-sectional area of saidthroat at the lower end of said conduit being correlated to the rate of vapor generation in said vessel to cause the expelled vapor to flow through said lift conduit in continuous vapor phase at sufficient velocity to lift liquid at the desired rate, and additional heating means in the solution circuit above the generator vessel to expel additional refrigerant vapor.

3. In an absorption refrigeration system, an absorption solution circuit having an upright lift conduitthe parts of said circuit being arranged to maintain a level of absorption solution in the constant rate, said lift conduit being formed to provide an upwardly divergent passage and having across-sectional area correlated to the rate of vapor generation to cause the expelled vapor to flow through said lift conduit in continuous vapor phase at sufficient velocity to lift liquid at the desired rate, and an additional heating means above the bottom of said lift conduit to expel additional refrigerant vapor. 4. In an absorption refrigeration system, an absorption solution circuit having a single upright lift conduit for any particular capacity and provided with a throat, the parts of said circu t being arranged to maintain a level of absorptionsolution in the circuit above the throat in said lift conduit, means for heating said lift conduit to expel refrigerant vapor from solution flowing therethrugh, additional heating means for heating solution at a location in the solution circuit other than the lift conduit, and the cross-sectional area of said throat in the lift conduit being correlated to the amount of vapor flowing therethrough to cause it to flow in continuous vapor phase at sumcient velocity to lift finely divided particles of liquid by frictional drag at the desired rate.

5. An absorption refrigeration system in accordance with claim 1 in which the additional heating means is located at the outlet from the lift conduit.

6. An absorption refrigeration system in accordance with claim 1 having a separating chamber surrounding the outlet at the top of the lift conduit, and the additional heating means being located in the separating chamber for engagement by the solution issuing from the lift conduit.

'7. An absorption refrigeration system in accordance with claim 1 in which the additional heating means comprises a heating chamber surrounding the vapor liquid-lift tube.

8. An absorption refrigeration system in accordance with claim 1 in which the heating means comprises a generator vessel having a chamber in heat exchange relation therewith, the additional heating means comprises a chamber in heat exchange relation with the solution circuit at another location, and conduits connecting the chambers in series for directing a heating medium through the chambers in succession.

9. In an absorption refrigeration system in accordance with claim 1 in which the heating means comprises a generator vessel having tubes extending through the vessel, the additional heating means comprises a coil located at the outlet from the lift conduit, and conduits connecting the generator tubes and coil for the flow of heating medium through the generator and coil successively.

10. An absorption refrigeration system in accordance with claim 1 in which the heating means comprises a generator vessel at the lower end of the lift conduit and having a heating chamber,

the additional heating means comprises a heating chamber surrounding the vapor liquid-lift conduit, and conduit means connecting the heating chambers for the generator vessel and lift conduit in series.

, 11. An absorption refrigeration system in accordance with claim 1 in which the heating means is a vessel below the lift conduit, the additional heating means is the wall of the lift conduit, a heating chamber enclosing the vessel and lift conduit, and means for supplying heating medium to the heating chamber.

12. An absorption refrigeration system in accordance with claim 1 in which the heating means is a vessel having a reentrant wall to provide an increased heating surface, the additional heating means is the wall of the lift conduit, the reduced throat being located between the vessel and lift conduit, a heating chamber enclosing the vessel and lift conduit, and means for supplying steam to the heating chamber.

13. An absorption refrigeration system in accordance with claim 1 in which the solution circuit comprises a combined generator vessel and vapor liquid-lift conduit, the heating means comprises a chamber surrounding the combined generator and vapor liquid-lift conduit, and the additional heating means comprises a heating coil located at the outlet from the lift conduit.

EUGENE P. WHITLOW.

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

UNITED STATES PATENTS

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