US2250254A - Refrigeration - Google Patents

Description

July 22, 1941. a. A. BRACE 2,250,254 REFRIGERATION Filed on. 10, 1938 2 Sheets-Sheet 1 ATTORNEY Ff? BY m /5 INVENTOR I GeoryeA.Brace REFRIGERATION Filed Oct. 10, 1938 2 Sheets-Sheet 2 INVENTOR George A.Bra cc ATTORNEY Patented July 22, 1941 REFRIGERATION George A. Brace, Winnetka, 11L, assignor to The Hoover Company, North Canton, Ohio, a corporation of Ohio Application October 10, 1938, Serial No. 234,167

17 Claims.

This invention relates to the art of absorption refrigeration and more particularly to a novel evaporator construction for such system.

While it is possible to drag or sweep the liquid refrigerant through the evaporator from the lowest to the highest points thereof, it is not always desirable to do so. It may be desirable to use evaporator conduits of such diameter that the inert gas stream will not flow therethrough with a velocity high enough to drag or sweep the liquid refrigerant along therewith; the height of the evaporator may be so great that the gas circulating through the evaporator-absorber system is not placed under suflicient pressure to lift the liquid refrigerant entirely through the evaporator; the inert gas may be too light to elevate the liquid through the full height of the evaporator; and with some systems it may be desirable to extend the evaporator below the condenser and to connect the two by a short direct connection.

In the co-pending application of Curtis C. Coons and William H. Kitto, Serial No. 220,187, filed July 20, 1938, there is disclosed an absorption refrigerating system including an evaporator of the type in which liquid refrigerant is supplied from the condenser to an intermediate portion of the evaporator where it divides into two streams. One stream of the liquid refrigerant is conveyed through the evaporator by the propelling action of the inert gas to the upper portion thereof as it is evaporating into the inert gas stream. The other stream of the liquid refrigerant counterflows downwardly from its point of connection to the evaporator to the bottom portion thereof where it enters a very large diameter conduit through which it can flow by gravity counter to the inert gasstream by reason of the fact that the velocity of the inert gas in this conduit is too small to exert any propelling action on the liquid. This evaporator, while functionally operative, has the disadvantage that it requires a rather complex conduit system where the liquid refrigerant supply conduit and the evaporator conduits of difierent diameters are connected together. Furthermore, while this construction, permits the evaporator to be made of a height materially greater than that which would be possible, other things being equal; with an evaporator of the type in which the liquid refrigerant supplied to the lowest portion thereof is circulated entirely through the evaporator to the top thereof, the amount by which the evaporator can thus be heightened is limited because of the propelling action of the inert gas stream in the conduit connecting the high gas velocity portions of the evaporator to the low gas velocity portions thereof.

Accordingly, it is an object of the present invent-ion to provide an absorption refrigerating system of the above referred to type including an evaporator which is constructed and arranged to provide simple, economical and effective means which will carry liquid refrigerant downwardly through an evaporator conduit counter to a high velocity gas stream for any distance desired without interfering with proper operation of other portions of the evaporator .construction.

It is a further object of this invention to provide'an absorption refrigerating system including an evaporator in which the liquid refrigerant -is propelled throu h portions of the evaporator by the inert gas stream flowing therethrough and in which the liquid refrigerant is conveyed counter to the direction of flow of the inert gas stream in other portions of theevaporator.

More specifically, it is an object of the invention to provide an evaporator for an absorption refrigerating system in which the liquid refrigerant is propelled through portions of the evapthe propelling action of the inert gas stream, inwhich the liquid refrigerant is conveyed through other portions of the evaporator counter to the direction of flow of the inert gas stream by capilliary action, and in which liquid refrigerant is conveyed through still further portions of the evaporator by gravity counter to the direction of how of theinert gas stream.

Further, it is an object of the present invention to provide an evaporator having the above referred to characteristicsand advantages which is simple in construction, economical to manufacture, and efficient and reliable in operation.

Other objects and advantages of the invention will become apparent as the description proceeds when taken in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of an absorption refrigerating system embodying the invention in which the evaporator is shown on an enlarged scale and in perspective.

Figure 2 is an enlarged scale perspective partial orator.

Figure 3 is an enlarged scale cross-sectional view illustrating an element of the evaporator.

Referring now to Figure 1'in detail, there is disclosed a continuous absorption refrigerating system'of the three-fluid type embodying a boiler be charged in any suitable manner with a refrigerant, such as ammonia, an absorbent, such as water, and an inert pressure equalizing medium, preferably a dense inert gas such as nitrogen.

A The boiler B may be heated in any desired manner as by an electrical cartridge heateror by a combustible fuel burner.

The circulating motor M and the heater for the boiler B will also be controlled in any desired manner. A preferred control mechanism is disclosed in the co-pending application of Curtis C. Coons, Serial No. 148,424, filed June 16, 1937.

The application of heat to the boiler B generates refrigerant vapor from the strong solution normally contained therein. The refrigerant vapor so generated passes upwardly through the analyzer D in counterflow to strong solution flowing downwardly therethrough. In the analyzer, vapor of absorption solution generated in the boiler is condensed by contact with the strong solution and the heat of condensation serves to generate further refrigerant vapor which then passes through the conduit II to the upper portion of a tubular air-cooled'condenser .C. The conduit ll includes the rectifier R which serves to cause condensation of any vapor of absorption solution which may pass through the analyzer D.

The refrigerant vapor discharges into the condenser C which extends to a level appreciably below the level or the top portion of the evaporator E and flows downwardly therethrough as it is being condensed by heat exchange with cooling air flowing over the outer surfa'ce'of the condenser and the fins attached thereto. The condensate formed in the condenser C is then drained therefrom through a conduit l2 including a U-shaped portion forming a liquid seal into the evaporator E to which reference will be made in more detail hereinafter. The trap is vented by a conduit l3 to the inner pass of the gas heat exchanger G.

The weak solution formed in the boiler B by r the generation of refrigerant vapor is conveyed therefrom through a conduit IS, the inner path. of the liquid heatexchanger L and a conduit l6 which discharges into the upper end of the tubular air-cooled absorber A. For purposes of convenience, the absorber A has been shown as being vertically positioned herein. However, it may be positioned in any plane from the vertical to a plane inclined slightly to the horizontal. It is apparent that the upper portion of the absorber is at an elevation above the liquid level normally prevailing in the boiler-analyzer system wherefore. some eans must be provided to elevate the weak solut onthereinto. For this purpose a small bleed conduit I1 is connected between the gas discharge conduit it of the circulating fan F and sectional view of a'modified form of the evapthe weak solution conduit l6 below the liquid level normally prevailing therein, whereby the Weak solution is elevated into the absorber by gas lift action. The weak solution flows downwardly through the absorber in counterfiow relationship to a rich mixture of pressure equalizing medium and refrigerant vapor which is conveyed thereto in a manner to be described more fully hereinafter. In the absorber the refrigerant vapor content of the mixture is absorbed by the solution which then becomes strong solution and flows to the bottom portion of the absorber from whichit is drained th ough a conduit 20 into the strong solution reservoir S. The heat of absorption generated by the absorption process is rejected to air flowing over the outer walls of the absorber vessel and in contact with the air-cooling fins mounted thereon. The strong solution is conveyed from the reservoir S through the conduit 22, the outer path of the liquid heat exchanger L, and the conduit 23 to the upper portion of the analyzer D.

The lean inert gas discharged by the circulating fan F through the conduit l8 enters the outer path of the gas heat exchanger G from which it is conveyed through the conduit 25 to the bottom portion of the evaporator E. The evaporator E will be described in detail hereinafter. For the present it is suflicient to state that the propelled stream of inert gas discharging through the conduit 25 circulates upwardly through all portions of the evaporator carrying the liquid refrigerant upwardly therewith as it evaporates into the inert gas stream. The rich mixture formed in the evaporator is discharged therefrom through the conduit 28 into the inner path of the gas heat exchanger G from which it is conveyed through the conduit 29 to the bottom portion of the absorber A. The rich mixture passes upwardly through the absorber A in counterflow relationship to the solution flowing downwardly therethrough by gravity in the manner described herebefore. conveyed from the upper portion thereof into the suction line of the circulating fan F by a conduit 21, thus completing the inert gas circuit.

The evaporator per se comprises a series of parallel vertically spaced U-shaped coil sections 30, 3| and 32 with the legsof each U-shaped section facing forwardly. The coil sections 30 and 3| are connected by a riser conduit 34. The coil sections 3| and 32 are connected by a riser conduit 35, and the coil section 32 is connected to a finned box-cooling conduit 31 by an L-shaped riser conduit 38. The inert gas inlet conduit 25 connects to the left hand closed end of the coil section 30 and the inert gas outlet conduit 28 connects to the rear end of the box-cooling section 31. 'A suitable drain 40 for unevaporated liquid refrigerant is connected to the forward closed end of the U-shaped conduit 30. The liquid refrigerant supply conduit l2 opens into the right hand leg of the U-shaped coil section 3| adjacent to the point of connection with the riser conduit 34. The riser conduit 34 and the bottom coil section 30 house a tubular wick 4| to provide for capillary feed of liquid refrigerant from the conduit 3| through the conduits 34 and 30 to the point of connection between the conduit 30 and the gas inlet conduit 25.

The operation of this form of the invention is as follows: When the circulating motor M is energized and heat is applied to the boiler B liquid refrigerant is discharged through the conduit l2 into the right hand leg of the coil section 3|. A

The lean gas formed in the absorber is portion of this liquid stream is absorbed by the throughout the length thereof counter to the direction of flow of the inert gas stream. Thereis continual evaporation of liquid refrigerant from the wick 4| throughout its length whereby refrigeration is produced in all portions of the conduits 30 and 34. The balance of the liquid refrigerant discharged through the conduit I2 is conveyed through the conduits 3|, 35, 32, 38 into the conduit 31 by the sweeping or dragging action of the high velocity inert gas stream flowing through this conduit. The liquid refrigerant discharged into the conduit 31 flows downwardly therethrough by gravity toward its point of connection with the conduit 28 as the inert gas is moving at too slow a rate through this conduit to exert any propelling action on the liquid. The liquid refrigerant which flows downwardly through the conduits 30 and 34 through the wick material 4| is distributed around all surfaces of those conduits by the capillary action of the wicking and evaporation from the wicking occurs adjacent all surfaces of those conduits thereby providing for excellent heat transfer and highly desirable evaporating conditions.

The wicking 4| may consist of textile material of any desired coarseness or fineness to provide for any desired rat of liquid refrigerant distribution therethrough. Likewise the wicking material 4| could be constructed from metallic or mineral material of any desired fineness or coarseness to provide desired distribution oi liquid refrigerant therethrough.

In Figure 3 there is shown an enlarged sectional view of a portion of the conduit 30 illustrating the manner in which the Wicking 4| is mounted therein in close engagement with the inner walls of the conduit 30 to provid a large bore through the wicking for the flow of inert gas.

Referring now to Figure 2 there is disclosed a modified form of the invention, certain portions of which'are identical with elements previously described and are given the same reference characters primed. This evaporator is designed and constructed to be used with a refrigerating system exactly like that illustrated in Figure 1.

This evaporator comprises three horizontal vertically spaced coil sections 5|), 5| and 52, respectively. The box-cooling conduit 81' is positioned vertically above the uppermost coil section 52. The coil sections 50 and 5| each comprise a pair of U-shaped conduit elements 55 and 55 having the outer legs thereof serially connected of the conduit section 50, and the inert gas outlet conduit 28' joins the rear end of the box-cooling conduit section 3]. The coil sections 50 and 5| are connected by a riser conduit 5|, and the coil sections 5| and 52 are connected by a riser con-- duit 52. The coil section 50 is of an appreciably larger diameter than the superposed coil section and scribed. The wicking 54 extends downwardlythrough the conduit 6| from a point adjacent the point of connection between the liquid refrigerf ant supply conduit l2 and the coil section 5| to extend slightly beyond the points of connection: between the small diameter conduit 54 and the large diameter coil section 50. The drain conduit 40' connects to the inert gas inlet portion of the coil section 50.

This form of the invention operates a follows: Liquid refrigerant supplied to the conduit l2 divides into two streams as it enters the inlet por-. tion of the coil section 5|. Onestream of the liquid refrigerant is propelled through the coil section 5|, riser conduit 52, the coil section 52, and riser conduit 59 into the forward end of the box-cooling conduit 31'. Of course, liquid refrigerant is continuously evaporating into the inert gas stream as it is being propelled thereby; however, some of the liquid will be unevaporated and will flow into the conduit section 31' through which it will flow by'gravlty as it evaporates into the inert gas stream. Liquid refrigerant is not propelled through the coil section 31' because of the low velocity of the inert gas therein. The balance of the liquid refrigerant supplied to the conduit l2 flows downwardly through the wicking 64 counter to the inert gas stream flowing upwardly therethrough and is discharged from the lower end of the wicking into the large diameter bottom coil section 50 through which it flows by gravity counter to the slowly moving inert gas stream flowing therethrough. As in the case of cooling conduit 31". As will be noted, the inert gas supply conduit 25 opens into the inner leg the box-cooling conduit 31, the velocity of flow of the inert gas through the conduit 50 is insumcient to propel liquid refrigerant 'therethrough or to prevent counterflow of the liquid with respect to the gas stream.

It will be understood that the evaporators described in connection with each form of the invention will be enclosed in suitable casings which will be provided with shelves in heat transfer relationship with the various evaporator conduits which are adapted to support ice trays or similar The evaporators may, if desired, be constructed of a single piece of tubing. except that evaporator sections of diiferent diameters will be constructed of separate pieces of tubing welded together.

In the construction of Figure 1 the capillary material or wicking maybe inserted in the evaporator tube from the open lower end thereof after which the end will be closed by a suitable welded cap, or if the evaporator is constructed of a plurator.

In the case of the construction illustrated in A Figure 2, the wicking will preferably be inserted in the riser 6| prior toestablishment of the Joint between the riser SI and the large diameter coil section 50.

The conduit diameters to be chosen for the various sections of each form of the evaporator herein disclosed will depend upon various conditions found in different refrigerating systems; however, the following will give general rules to be followed in determining evaporator conduit size.

The propelling action of the inert gas is a function of its density, pressure and velocity of flow. In a refrigerating system in which the total pressure ranges between 270 and 400 pounds per square inch, a dense inert gas, like nitrogen, will circulate the liquid refrigerant satisfactorily through an evaporator approximately 10" or 11" in height constructed of tubing of approximately /2" inside diameter with a pressure drop of between 2 /2" and 4" of water between the gas inlet and outlet connections to the evaporator. Of course, these dimensions are all mutually inter-dependent and a variation in any one will in the co-pending application of Curtis C. Coons and William H. Kitto, Serial No; 220,189, filed July 20th, 1938.

The box-cooling conduits 31 and 31' could be made of tubing of 1 /2" or 2" inside diameter and the large diameter coil section .50 of the evaporator illustrated in Figure 2 may be satisfactorily formed from tubing of 1" or 1 /2" inside diameter if it is to operate under the conditions explained in the paragraph immediately above. a

Though each form of the invention has been illustrated herein as the same is applied to domestic refrigeration requirements, the invention is not so limited. The invention may be applied to other forms and arrangements of refrigerating apparatus. For example, the conduits need not be of the rising type, they may be horizontal with sections in which the liquid is propelled by an auxiliary medium and other sections in which the liquid is conveyed counter to the propelling action of the auxiliary medium by a wicking or other similar conveying medium. Also the invention is not limited in its application to evaporators; it may, for example, be applied to absorbers or other similar apparatus.

As is fully explained in the above mentioned co-pending application, the liquid is conveyed through the conduits by the gas stream under turbulent conditions which promote efllcient gas and liquid contact. In the sections in which the liquid is conveyed by capillary action, efficient in the height between the liquid refrigerant inlet and the point at which the liquid discharges into the box-cooling conduitcan be made equal to the maximum possible height through which the inert gas will circulate liquid refrigerant in the particular system with the allowable pressure drop and other factors therein included. However, the total height of the evaporator may materially exceed this value by reason of the fact that the lifting power of the inert gas stream is not utilized to circulate liquid refrigerant through the lowest portion of the evaporator and through the lowest riser conduit. For example, the distance between the central coil section at which the evaporator is supplied with liquid refrigerant and the lowest coil section may be made suiiiciently deep to accommodate a plurality of double depth ice trays without materially affecting the operation of the evaporator and without imposing any undue lifting strain on the inert gas circulating system.

Accordingly, it will be appreciated that the present invention provides means whereby an evaporator of an extraordinary height may be incorporated in a refrigerating system without necessitating re-organization of any other parts of the system, such as increases in dimensions of such parts as the fan and inert gas circulating conduits, repositioning of the condenser, or changes in system pressure drop distributions of the inert gas circuit. This is extremely advantageous because of the rigid space limitations imposed upon the cabinets of domestic refrigerating systems. For example, the evaporator heights normally could not be increased without increasing the pressure drop therethrough, which in turn would necessitate an increase in the discharge pressure and consequentlyin the size of the circulating fan. However, an increase in the gas and liquid contact is insured by reason of the enormous surface presented by the wicking which preferably entirely surrounds the gas stream. Eflicient heat transfer is assured in all size of the circulating fan necessarily means an increase in the depth of the mechanism compartment at the rear of the cabinet structure, thereby consuming a relatively enormous amount of space for the simple expedient of increasing the fan diameter.

Moreover, the present invention provides a convenient means whereby the resistances of the gas heat exchanger, absorber and inert gas cir-. cuit connections may be increased without exceeding the allowable maximum resistance in the gas circuit. This is accomplished by constructing the evaporator in the manner disclosed herein but of conventional size. Under this practice the gas flow resistance of the evaporator will be relatively small, thereby permitting the above mentioned resistance increases without alteration of the"'circulating fan.

While the invention has been illustrated and described herein in considerable detail,,it is not to be limited thereto but various changes may be made in the construction arrangement and proportion of parts without departing, from the spirit of the invention or the scope of the appended claims.

I claim:

1. Refrigerating apparatus comprising a gas and liquid contact element, means forsupplying liquid to said element, means for propelling gas through said element at a velocity suflicient to propel liquid therethrough as it is brought into contact with the gas, and means for conveying liquid through a portion of said element in contact with and counter to the gas.

2. Refrigerating apparatus comprising a,vertically extending gas and liquid contact element,

means for supplying liquid to an intermediate portion of said element, means for propelling a gas upwardly through said element at a velocity sufficient to propel liquid upwardly therethrough, and capillary means for feeding liquid. downwardly through at least a portion of said element counter to the flow of gas.

3.'Refrigerating apparatus comprising an evaporator, means for supplying liquid refrigerant to an intermediate portion of said evaporator, means for propelling a dense inert gas through said evaporator with sufficient velocity and pressure to circulate liquid refrigerant therethrough by the frictional drag of the inert gas, and means within said evaporator constructed and arranged to convey a portion of the liquid refrigerant supplied thereto downwardly in counterflow relationship to the inert gas stream as it is evaporating thereinto.

4. Refrigerating apparatus comprising an evaporator, means for supplying liquid refrigerant to an intermediate portion of said evaporator, means for propelling a dense inert gas through said evaporator with sufficient velocity and pressure to circulate liquid refrigerant therethrough by the frictional drag of the inert gas, and capillary means for conveying liquid refrigerant through a portion of said evaporator counter to the direction of flow of the inert gas stream.

5. Refrigerating apparatus comprising an evaporator, means for supplying liquid refrigmeans for propelling a pressure equalizing medium through said evaporator, said evaporator comprising a lower section of large cross-sectional area and an upper section having a crosssectlonal area sufficiently small to cause said pressure equalizing medium to flow therethrough at a velocity such that the pressure equalizing medium will drag or sweep refrigerant along therewith, and a capillary conveyor in those portions of said evaporator between the liquid inlet and the section of large cross-sectional area.

10. That improvement in the art of absorption refrigeration which includes the steps of supplying refrigerant to an evaporating zone, conveying a portion of the refrigerant through part of the evaporating zone by propelling ahigh velocity stream of dense inert gas through the erant to an intermediate portion thereof, means erant to an. intermediate portion thereof, means v for propelling a portion of said liquid refrigerant in one direction through said evaporator, and means for conveying a portion of said liquid refrigerant through a portion of the evaporator in the opposite direction against the force of said propelling means, said last mentioned means comprising a wick extending through said evaporator from the liquid inlet portion thereof in a direction opposite to said first-mentioned direction.

7. That improvement in 'the art of refrigeration which includes the steps of applying a liquid propelling force to all portions of an evaporating zone, supplying refrigerant to an intermediate portion of the evaporating zone, conveying a portion of the liquid through a portion of the evaporating zone under "the influence of such force as it is evaporating, and conveying the balance .of the liquid through another portion of the evaporating zone counter to such force by capillary action as it is evaporating,

8. A'refrigerating system including an evaporator, means for supplying refrigerant to said evaporator between the ends thereof, means for propelling a dense inert gas through said evaporator from end to end thereof under conditions such that it will drag or sweep refrigerant through said evaporator, and means for convey-- 9. Refrigerating apparatus comprising an evaporator, means for supplying refrigerant to an intermediate portion of said evaporator,

evaporating zone in contact with the liquid, and conveying the balance of the liquid through another portion of the evaporating zone by capillary action counter to the high velocity inert gas stream into which the liquid evaporates.

11. A refrigerating system comprising a solution circuit including a boiler and an absorber, a pressure equalizing medium circuit including cuit being constructed and arranged to cause said pressure equalizing medium to flow through portions of said evaporator at a velocity suflicient to sweep or drag refrigerant therethrough, and capillary means in said evaporator for conveying liquid refrigerant through a part of the evaporator counter to said pressure equalizing medium,

12. Refrigerating apparatus including a vertically extending evaporator comprising a plurality of vertically spaced freezing sections, means serially connecting said sections, the lowest of said sections having a cross-sectional area materially larger than the cross-sectional area of superposed sections, means for supplying liquid refrigerant to the section of said evaporator immediately above said section of large cross-sectional area, a capillary element in the means connecting said section of large cross-sectional area, and means for propelling a pressure equalizing medium through said evaporator at a velocity sufllcient to sweep or drag liquid refrigerant through all but said section of large cross-sectional area.

13.Refrigerating apparatus including a vertically extending evaporator comprising a plurality of vertically spaced U-shaped freezing sections, means serially connecting said-'U-shaped sections, means for supplying refrigerant to an elevated section of said evaporator, capillary means extending through said evaporator from the point of liquid inlet to the remote end of the lowest section, and means for propelling a pressure equalizing medium through said evaporator from the bottom to the top thereof at a velocity sufficient to drag or sweep refrigerant therethrough.

'14. Refrigerating apparatus comprising an means for conveying a portion of the liquid refrigerant through at least a portion of saidevaporating element against the drag ing or sweeping action or the inert gas.

15. Refrigerating apparatus. comprising an evaporating element, means tor supplying liquid refrigerant to said evaporating element, means for propelling an inert gas through said evaporating element at a velocity suflicient to drag or sweep liquid refrigerant therethrough, and means for conveying a portion of the liquid refrigerant through at least a portion oi said evap= crating element against the dragging or sweeping action of the inert gas, said evaporating element also including a section through which the inert gas flows at a velocity insuflicient to sweep or drag the refrigerant therethrough and into -which said conveying means discharges.

16. An evaporator adapted for use in absorption refrigerating systems of the type in which an inert gas is circulated through the evaporator at a high v'ei'ocity comprising a plurality of superposed conduit sections connected by riser conduits. gas inlet and outlet connections at opposite ends of said evaporator, a liquid inlet connection intermediate the ends or said evaporator, a capillary lining in at least partor that portion of said evaporator between the liquid and gas inlet connections thereto, those portions of said evaporator conduits between the liquid inlet and gas outlet-connections thereto and housing said capillary lining being oi small cross-sectional area whereby the inert gas will flow therethrough with sufllcientvelocity to propel refrigerant liquid and the balance of said evaporator being constructed of conduit or relatively large crosssectional area whereby the refrigerant may flow therethrough by gravity counter to the inert gas stream.

17. Refrigerating apparatus comprising a gas and liquid contact element, means for propelling a gas through said element with sufficient velocity and pressure to propel liquid therethrough by the frictional drag of the inert gas flowing in contact with the liquid, means for supplying a liquid to said element, and means for conveying liquid through at least a portion of said element in contact with the inertgas and counter theretoagainst the frictional propelling force oi the inert gas.

GEO. A. BRACE.

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