US3050959A

US3050959A - Refigeration apparatus

Info

Publication number: US3050959A
Application number: US24312A
Authority: US
Inventors: Donald G Rich
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1960-04-25
Filing date: 1960-04-25
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28

Description

Aug. 28, 1962 D. G. RICH REFRIGERATION APPARATUS Filed April 25, 1960 FIG. I

MA TATA'A'F A A AA A l V H HIH u n if AWAWMV'AV (i III FIG. 3

INVENTOR.

DONALD e. RICH ATTORNEY.

United States Patent Qfifice i atented Aug. 28, 1962 ware Filed Apr. 25, 1960, Ser. No. 24,312 4 Claims. ((1 623tl5) This invention relates to air conditioning apparatus and, more particularly to air conditioning apparatus including heat exchangers of the evaporative type.

The basic principle of operation of a heat exchanger involves the passage of two heat exchange mediums in relationship with each other such that heat is transmitted from one of the heat exchange mediums to the other. By way of example, a condenser in a standard refrigeration system may pass compressed refrigerant gas through a series of pipes which form a heat exchanger. Air or water may be passed across the surface of the pipes to remove heat from the compressed gas and condense it to a liquid. Obviously, a heat exchanger of this type is limited in its capacity by the temperature difference between the internal fluid e.g., refrigerant, and the external fluid e.g., air. Another obvious limitation arises by reason of the fact that the temperature of air or other external heat exchange medium which is passed across the exterior surface of the heat exchange pipes rises due to absorption of heat from the heat exchanger and as more capacity is required, it is frequently necessary to increase the volume of air which is passed by using fans or other means. One of the Well known techniques for increasing the capacity of a given size heat exchanger is to employ fins on the outside of the heat exchange tubes to increase the area available for heat transfer. Another method is to employ an evaporative heat exchanger. In an evaporative heat exchanger a heat exchange medium is flowed across the exterior of the heat exchange pipes. Since a substantial quantity of heat must be added to any liquid in order to vaporize it, heat may be removed from the fluid on the interior of the pipes by conduction through the pipe walls and be carried away from the heat exchanger by vaporizing the liquid heat exchange medium which is flowed across the exterior of the pipes.

Typical evaporative heat exchangers of prior art construction employ spray systems or other means for discharging a quantity of liquid over the exterior surfaces of a heat exchanger. In order to secure maximum heat transfer capacity, it is desirable to maintain the entire ex terior surface of the heat exchange tubes wetted with a thin film of exterior liquid heat exchange medium such as Water. If substantially the entire exterior surface of the heat exchange tubes is not wetted, dry areas will be present on the tubes or on the fins where only convective heat transfer may take place and at which the advantages of evaporative heat transfer may not be obtained clue to the lack of liquid available for evaporation. On the other hand, if too great a quantity of liquid is flowed over the surface of the heat exchange tubes, a thick layer of liquid may be built up on the tubes and fins which Will tend to insulate the tube and actually inhibit heat transfer.

In a typical heat exchanger construction employing a spray system for discharging droplets of Water over the exterior surface of a heat exchange tube, the surface tension of the liquid tends to make the liquid coalesce into a numher of discrete droplets on the surface of the tube and fins. The droplets possess the disadvantage of being relatively thick and at the same time, the areas between the droplets tend to be dry. Another disadvantage of a spray system is that if a large number of tubes are disposed vertically beneath the spray, the lower tubes will not be directly wetted by the spray but depend upon liquid dripping from the tubes above. Consequently, the tubes belowmay not be uniformly wetted. In order to overcome this tendency, it is frequent practice to spray a very large excess of liquid over the heat exchange tubes and to collect the liquid which drips olf the tubes into a sump. This liquid is then pumped back to the spray system Where it is again discharged over the surface of the heat exchange tubes. While this system produces more complete wetting of the heat exchange tubes, it introduces additional disadvantages. For example, the liquid from the spray system tends to become entrained in the air surrounding the heat exchanger. If the heat exchanger is employed as a condenser on the top of a low building the entrained moisture from the condenser may find its way to the street below where it is disagreeable to passersby. More serious, however, is the loss of liquid from the system and the necessity for maintaining an open sump over the heat exchanger to collect the excess liquid. The open sump involves the additional expense of a pump and other piping must be associated with it to return the liquid to the spray system. Furthermore, since heat exchangers of this type are frequently located on the roof of a building, an open sump tends to collect dust, smoke, soot, insects and other foreign material which must be periodically removed from it in order to prevent fouliug'of the spray system. A layer of algae frequently builds up in an open sump of a conventional evaporative heat exchanger which can be removed only with great difficulty and which tends to foul the pumps and piping in the system.

It is, therefore, desirable to provide some means of maintaining a uniformly thin film of liquid on substantially the entire surface of an evaporative heat exchanger without the necessity for employing an open sump or a spray system with their attendant disadvantages.

Accordingly, it is an object of this invention to provide an improved evaporative heat exchanger.

It is a further object of this invention to provide an improved air conditioner.

It is a still further object of this invention to provide an improved method of making an evaporative heat exchanger.

These objects are achieved in the embodiment shown by providing a plurality of hollow porous metal fins about one or more pipes which form an evaporative heat exchanger. A liquid heat exchange medium such as Water is flowed into the interior of the hollow fins and due to their porosity is allowed to seep from the interior of the fins to the exterior thereof where it is constantly available for evaporation. 'By this means substantially the entire porous exterior surface of the hollow metal fins maybe continually wetted with a thin film of liquid thereby providing maximum capacity for a heat exchanger of this type.

A heat exchanger of the type described may be made by rolling a porous sheet of compacted metal powder and stamping therefrom a plurality of lipped Walls. The lipped walls may then be assembled with alternate lips 3 facing each other on a heat exchange tube to form a hollow finned heat transfer surface. Adjacent lips may then be sealed together by furnace brazing or other appropriate means to form a plurality of hollow fins disposed about the surface of the heat exchange pipes.

These and other objects of this invention will become apparent by reference to the following specification and attached drawings wherein:

FIGURE 1 is a side view partially broken away showing an evaporative heat exchanger constructed in accordance With this invention mounted on the roof of a build- FIGURE 2 is a cross-sectional view taken substantially on lines II-II of FIGURE 1; and

FIGURE 3 illustrates a method of sealing the lip portions of the walls of heat exchange fins made in accordance with the described method.

Referring particularly to FIGURE 1, a heat exchanger in accordance with this invention is shown mounted on supports 18 which may hold the heat exchanger in a slightly tilted position on the roof of a building. It will be understood that for purposes of illustration the heat exchanger described is adapted to be employed as an evaporative condenser on the exterior of a building. However, other applications of such a heat exchanger will be readily apparent to those skilled in the art. For example, a heat exchanger of the type described is particularly suited to location within the interior of a building because of the elimination of a spray system and consequent entrainment problems.

Heat exchanger lt) comprises a plurality of heat exchange tubes or pipes 11 having disposed thereon a plurality of fins 12. Fins 12 each comprise a first porous wall 13 and a second porous wall 14 as can best be seen in FIGURE 2.

Porous walls

13 and 14 are desirably made of a compacted metal powder having good thermal conductivity characteristics such as copper.

Walls

13 and 14 may be generally flat sided as shown in FIGURE 2 or if desired they may be corrugated.

Edge portions

31, 32 and 33 are provided with lips 15 which are bent out of the plane of

walls

13 and 14 and which have a narrow flat portion for engagement with a corresponding lip of another wall. For convenience of manufacture, wall 13 is preferably identical to wall 14 and engagement between corresponding lip portions is secured by reversing alternate walls comprising the fins and positioning them so that the flat portions of lips 15 are closely adjacent each other asshown in FIGURE 2. Appropriate holes are formed in

walls

13 and 14 for accommodation of impervious heat exchange pipes 11 such as copper which pass therethrough. 7

Each pair of adjacent lips 15 form and are sealed to each other on three

edges

31, 32, and 33 of fin 12. Consequently, fin 12 comprises a hollow envelope 16 having sealed lip portions and spaced wall portions for the accommodation of a heat exchange fluidmediurn such as water therein. The remaining of fourth edge of fins 12 may be left substantially open and communicates with a header 17 for the purpose of supplying the heat exchange medium to the interior of the fins. A conduit 19 supplies liquid to header 1.7. The supply of liquid into header 17 is controlled by a pressure regulating valve 20 and a pump 21. Valve 20 may serve to regulate the pressure of fluid in header 17 and consequently in the interior of fins 12 if desired. Alternatively, header 17 may comprise a storage tank or the lower portion of a storage tank where pressure regulation of the fluid in fins 12 is not required.

In operation, heat exchange pipes 11 are connected to the desired supply and discharge conduits of the system with which heat exchanger 10 is to be used. For example, if heat exchanger 10 comprises the condenser of a refrigeration system, one end of heat exchange pipes 11 would be connected with the discharge line of a compressor (not shown) and the other end of heat exchange tube 11 would be connected with the expansion device (not shown) of the refrigeration system. The hot fluid such as refrigerant gas which is to be cooled or condensed flows through the interior of heat exchange pipes 11. A volatile liquid refrigerant such as water is introduced into the interior 16 of fins 12 by means of header 17. Since the

walls

13 and 14 of fins 12 are porous, the volatile liquid is enabled to seep by capillary action through the walls where it may be evaporated from their exterior surface. As used herein, the term porous refers to the characteristic of a body having a large number of small internal pores or voids which communicate with each other and with the surface of the body.

When in use, heat is conducted from a fluid in pipes 11 through the walls of the pipes to the

Walls

13 and 14 of fins 12. Since the material of pipes 11 and fins 12 is preferably a relatively good heat conductor, a relatively low resistance thermal path is established to dissipate heat from pipes 11. Heat reaching the surface of fins 12 is absorbed by the film of water or other volatile liquid on the surface of the fins and the liquid vaporizes. The vapor then escapes into the ambient atmosphere carrying with it the latent heat of vaporization of the liquid which was removed from the fluid in pipes 11. As the volatile liquid heat exchange medium is vaporized from the exterior of fins 12, additional liquid is supplied to the exterior surface of the fins by capillary action from the interior 16 thereof. Therefore, substantially the entire exterior surfaces of fins 12 are continuously supplied with a thin film of the liquid heat exchange medium which is available for vaporization therefrom.

Heat exchanger 10 may be suitably manufactured by compacting and rolling a powdered metal such as copper having relatively high thermal conductivity. In order to provide rig'dity to the sheet of compacted metal, it is desirable that the sheet be sintered. However, care must be taken not to carry the sintering operation so far that the internal voids in the metal are sealed off from communication with each other or with the surface, or entirely eliminated by this operation.

The sheet of compacted metal may be then positioned in a hydraulic punch press where

walls

13 or 14 of fins 12 are shaped and trimmed. As has been previously described, it is desirable that

walls

13 and 14 be identical with each. other and merely reversed in respect to each other to form fin 12. and 14 are formed in the punch press, apertures 23 may be formed for the accommodation of pipes 11.

Walls

13 and 14 are then assembled on pipes 11 either by first positioning the walls of fins 12 in a nesting die and thereafter inserting pipes 11 through apertures 23 or by 10- cating pipes 11 in position and sliding

walls

13 and 14 of fins 12 over the pipes. In either event,

walls

13 and 14 are positioned to such that the lip portions thereof face in alternate directions so that pairs of the lips are relatively closed adjacent each other and when subsequently sealed, they will form a hollow envelope shaped fin 12.

In order to facilitate the sealing of lips 15 and to facilitate the creation of a good low resistance thermal bond 'between pipes 11 and fins 12, it is desirable to tin the surfaces which will be joined to each other with solder. For example, pipe 11 may desirably be a copper tube having a tinned surface and the mating surface of lips 15 may be cleaned and fluxed in an acid bath and thereafter tinned. The assembly of pipes 11 and faces 13 and 14 after being properly tinned may be inserted into a brazing oven 35 which will melt the liquid solder at their contacting surfaces and upon cooling, a rigid and sealed assembly is thereby provided. Alternatively, the assembled sides and pipes may be salt bath brazed to accomplish a similar result. Since lips 15 of

faces

13 and 14 are relatively closely adjacent each other in comparison with the distance between lips 15 of adjacent fins 12, another means of sealing

edges

31, 32 and 33' would be to dip the edge portions of the fins into a molten bath of solder or plastic and allowing the molten material which accumu- At the same time that walls 13 will lates between lips to cool thereby sealing the appropriate edges of fins 12. In each of the described alternatives, it will be noted that liquid material is permitted to solidify between adjacent lips 15 of the sides of fin 12 to form a liquid type enclosure or envelope.

While it is not necessary to do so, it is convenient to space each of

sides

13 and 14 the same distance apart on pipe 11 and construct lips 15 of an appropriate size so that when the sides are assembled on pipe 11 with the lips placed in alternating directions along the tube, that pairs of the lips are relatively closely adjacent or in contact with each other. If the fins are relatively thin, this construction will accommodate a large number of fins per unit length of pipe and give a substantial heat transfer surface. If desired, however, the fins may be either thicker or thinner than the space in between them on pipe 11. It will be understood that the relative sizes of fins 12 and heat exchange pipes 11 have been exaggerated in the drawings for purposes of illustration and that in actual practice the fins may be much narrower than shown in the drawings.

The construction illustrated possesses a number of advantages of prior art heat exchangers. For example, since all spray systems and open sumps can be eliminated by this construction, a heat exchanger of the type described may be located inside a building where the elimination of entrained moisture might otherwise become a problem. Furthermore, because of the principle of a completely closed heat exchanger construction, problems encountered with prior art evaporative heat exchangers such as the accumulation of dirt and soot or the build up of algae on the surface of the heat exchanger are completely eliminated.

Another advantage of the construction described is the elimination of the sump, recirculating pump, and spray system which is frequently required in prior art heat exchangers. The elimination of these elements not only reduces the initial cost of the system but tends to make it more reliable and less expensive to maintain because of the reduction in associated system components. In addition, exceptionally fine evaporative heat exchange characteristics are available by use of the construction described because substantially the entire surface of the heat exchange fins may be uniformly wetted with a thin film of volatile liquid thereby overcoming the tendency of external sprays to coalesce into droplets on the surface of the heat exchange tubes and to create regions of thick film and dry regions which unduly limit the capacity of prior art heat exchangers.

While reference has been specifically made to heat exchangers such as evapora-tive condensers, it should be understood that the principles of this invention are applicable to other heat exchangers as well. If desired a heat exchange construction of the type described may be used as an air conditioning apparatus to humidify, disinfect, or odorize a conditioned area. For example, high humidity or bacteria control may be maintained in a hospital operating room by placing a heat exchanger of this type functioning as an air conditioner in the room without the danger of entraining moisture in the air. The heat exchanger is then used to vaporize water or a germicide which is supplied to the interior of the hollow fins and a hot fluid may be passed through the heat exchange pipes to vaporize the liquid more rapidly. Various other applications, embodiments and modifications will occur to those skilled in the art and it is to be understood that this invention is not limited to the described embodiments but may be otherwise practiced within the scope of the following claims.

I claim:

1. In a refrigeration system, apparatus comprising a hollow rigid relatively impervious relatively good heat conducting metal pipe having an exterior surface and an interior surface, means to pass a first fluid medium in heat exchange relation with one surface of said metal pipe, a

metal heat transfer member secured to the other surface of said pipe and forming a plurality of relatively low resistance thermal bonds therewith, said heat transfer member comprising a relatively good heat conducting porous metal member having a large number of internal pores in communication with each other and with the surfaces of said member, said heat transfer member having a portion thereof between said relatively low resistance thermal bonds which is spaced from said other surface of said impervious metal pipe and forming with said pipe a hollow fluid passage having a porous wall through which a second fluid medium may pass While being in heat exchange relation with said first fiuid medium which is in contact with said one surface of said metal pipe, said heat exchange taking place directly through the walls of said metal pipe and said porous metal heat transfer member and through said plurality of relatively low resistance thermal bonds therebetween.

2. An apparatus as defined in claim 1 wherein said hollow fluid passage is defined by said tube and a pair of substantially identical porous heat transfer members made of compacted metal powder, said identical porous members having lips offset from the body of the member, said members being reversed in orientation with respect to each other on said pipe so that said lip portions are adjacent each other while said body portions are spaced from each other to form said hollow envelope, and means retaining said adjacent lip portions in fluid tight engagement with each other.

3. A condenser for use in a refrigeration system comprising a hollow heat conducting tubular metal member having an exterior surface and an impervious interior surface defining a first fluid passage, means to pass a first fluid medium through said first fluid passage in contact with said impervious inner wall of said tubular memher to promote heat exchange between said first fluid medium and said tubular member, a heat conducting metal heat transfer member disposed on the exterior wall of said tubular metal member, said heat transfer member forming a plurality of spaced relatively low resistance thermal bonds with the exterior surface of said tubular metal member at spaced locations thereon to provide a plurality of spaced heat conducting paths therebetween, a portion of said heat transfer member intermediate said spaced heat conducting paths being spaced from the exterior Wall of said tubular metal memher to define a second fluid passage disposed therebetween having a porous metal heat conducting wall, so that a second fluid medium passes through the porous metal wall of said second fluid passage, said second fluid medium being in heat exchange relation With said first fluid medium by conduction of heat through said heat conducting paths and through the heat conducting metal of said tubular member and said heat transfer member, said heat transfer member comprising a relatively porous metal heat conducting structure having a relatively large number of internal pores communicating with each other and with the surfaces of said porous structure, so that said second fluid medium may pass through the pores of said porous heat transfer member while simultaneously exchanging heat with said first fluid medium and undergoing a change in state.

4. A refrigeration system including a condenser comprising a hollow impervious heat conducting metal tube having an exterior surface and an impervious interior surface defining a first fluid passage therein, a porous metal heat conducting heat transfer member disposed on the exterior surface of said metal tube, said heat transfer member comprising a compacted heat conducting metal powder member having a relatively large number of internal pores in communication with each other and with the surfaces of said member, said porous metal member having portions thereof disposed in heat conducting relation with spaced portions on the exterior surface of said impervious metal tube to establish spaced heat conduct- '3 a ing bonds therebetween, and said porous metal memher having another portion thereof between said spaced heat conducting bonds that is spaced from the exterior surface of said impervious tube, the portion of said porous metal member spaced from the exterior surface of said impervious metal tube defining with the exterior surface of said tube a second fluid passage, means to pass a first fluid medium through said first fluid passage defined in said impervious metal tube so that said first fluid medium contacts the interior surface thereof and is enabled to exchange heat therewith, means to pass a second lfluid medium through said portion of the wall of said porous metal member which is spaced from the exterior surface of said impervious metal tube to exchange heat between said second fluid medium and said porous 15 2,941,759

metal member therebv placing said first and'second fluid mediums in heat transfer relation through said spaced heat conducting bonds, said heat exchange relation being accompanied by a change of state of said second fluid medium passing through said porous metal mem ber.

References Cited in the file of this patent UNITED STATES PATENTS 1,571,438 Schopf Feb. 2, 1926 2,082,756 Pridham June 1, 1937 2,766,597 Gieck Oct. 16, 1956 2,838,830 Huggins June 17, 1958 2,914,842 Modine Dec. 1, 1959 Rice June 21, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N055 3 0503959 August 28, 1962 Donald G, Rich It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 56 for 0f"" first occurrence read or column 4,, line 55, for "closed" read closely Signed and sealed this 15th day of January 1963.,

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents