US3052105A - Heat exchanger - Google Patents

Description

United States Patent O Filed June 15, 1960, Ser. No. 36,369 9 Claims. (Cl. 62--305) This invention relates to heat exchangers and more particularly to improvements in air-cooled heat exchangers.

An important application of this invention is with condensers employed in refrigerating systems. Heat must be removed from the condenser to cool and condense the refrigerant flowing therethrough. Various methods of cooling have been used. One of these consists of passing cool Water over tubes filled with refrigerant to be cooled. The cool water is effective in removing heat from the refrigerant, but the use of Water requires a Water recirculation system that is expensive and often difficult to install. Because of the continual evaporation occurring in this type of condenser, the concentration of salts introduced with the Water becomes a problem that must be attended to through periodic draining and cleaning. Further there are algae and corrosion problems attendant to the use of evaporative condensers. The tubes are usually bare rather than finned because of the difficulty in cleaning scale formed when other than soft or treated water is used. During intermediate season use, the Water may be shut off and air alone may be employed to cool the refrigerant within the tubes. The so-called evaporative condenser is not efficient during intermediate season operating conditions for the tubes themselves provide inadequate heat transfer surface.

Another method of cooling the uid within the condenser consists of passing air over the condenser. Normally the air-cooled condenser is larger than the evaporative-condenser and uses finned coils to increase the heat transfer capacity thereof. As the temperature of the air is widely variable and is often too high, being at the dry bulb rather than at the Wet bulb, the capacity of the aircooled condenser is uncertain and often a larger condenser than is desirable must be employed. Too, the dirt in the air is deposited on the finned coils and this dirt must be periodically removed.

To improve the performance of air-cooled condensers, it has been proposed that Water be sprayed into the air stream to clean and cool the air prior to passage over the heat exchange coil. In this fashion, the dry bulb ternperature of the air is reduced approximately -to the Wet bulb temperature. The reduced temperature of the air passing over the condenser provides higher heat transfer efficiency. The Gygax Patent No. 2,353,233, suggests placing copper screening in the shape of a horizontally disposed V beneath the heat exchange coil and spraying liquid into the V-shaped screening. Air passes through the screening and then over the heat exchange coil. In another arrangement, shown in Kohl et al. Patent No. 2,833,122, water is sprayed directly into the path of the air stream and eliminators are used to remove entrained moisture from the air. These arrangements are not altogether satisfactory in uniformly presaturating the air and in removing entrained moisture from the air prior to passage over the heat exchange coil.

v A primary object of this invention is to provide a heat exchange unit wherein the disadvantages and shortcomings of prior art constructions are obviated.

An object of this invention is to provide an improved heat exchange unit having means therein to more uniformly and effectively cool a gas prior to its passage over the heat exchange coil in such unit.

Another object of this invention is to provide an im- ICC proved heat exchange unit having a finned heat exchange coil that remains substantially dry in use.

Still another object of this invention is to provide an improved heat exchange unit having means for saturating and washing the air passing over the heat exchange coil of such unit.

Another object of this invention is to provide an improved heat exchange unit that is simple in design, clean in operation and requires virtually no maintenance.

This invention pertains to a heat exchange unit which includes a casing having an air inlet and an air outlet therein, means for passing air through the casing, a uid conducting heat exchange coil positioned in the path of air passing through the casing, a packing in the casing beneath the heat exchange, coil, and means for distributing liquid onto the top of the packing. If desired, lter means for confining splashing liquid to the top of the packing may be provided. The packing comprises thin partition Walls of fibrous material impregnated with a substance to provide the wet strength required While maintaining the Walls absorbent, the walls being constructed and arranged to dene a plurality of adjacent parallel cells open at the top and bottom. The cross-sectional areas of the cells are so small that liquid can bridge the walls of the cells by surface tension. There are means on the packaging for breaking the bridging of the liquid. Thus, air passing through the packing is evaporatively cooled and washed prior to passage over the heat exchange coil, and the heat exchange coil may be operated substantially dry.

The above and other objects and advantages of the invention Will be obvious from the following detailed description, which will be most clearly understood by reference to the attached drawings which illustrate a preferred embodiment of the invention and in which:

FIGURE l is a vertical transverse section through a heat exchange unit constructed in accordance with the present invention;

FIGURE 2 is an enlarged fragmentary perspective view of the packing employed in the heat exchange unit; and

`FIGURE 3 is a perspective view of the rotating spray eliminator employed in the heat exchange unit of the present invention.

Referring to FIGURE 1, there is shown aheat exchange unit having a casing 2, preferably cylindrical in cross section. The casing comprises side Wall 3 having louvered openings 4 therein, top wall 5 having an opening 6 therein, and a bottom 10 forming a sump in which water may be collected. The side wall and top wall may be made from zinc-coated steel, cement asbestos board or coated metals. The bottom is made of heavy steel plate coated with a bitumastic paint. Disposed within opening 6 is a fan 7 for inducing air through openings 4 and discharging the air upwardly from the casing. The propeller-type fan is driven by motor 8 through suitable drive means 9, for example, a chain and sprocket arrangement. The casing is supported by suitable members 11.

Mounted beneath fan 7 is a serpentine heat exchange coil 13 having yfins 14 thereon to increase the heat transfer capacity of the coil. The coil is preferably made from copper and the tins are preferably made from aluminum. Lines 15 and 16 connect the heat exchange coil 13 to a conventional refrigerating system, not shown. The coil is supported Within the casing by members 13.

A packing \17 is supported on rods 18 connected to the inside of the casing 2. The packing comprises a plurality of alternate plain sheets 29 and corrugated sheets 30. The sheets, Iwhich are made of cellulose impregnated with a plastic material such as, for example, melamine or phenoleformaldehyde resin, are attached at their points of contact to lform a plurality of cells 31 open at their top and bottom. The cells are of such a size that the water discharged over the packing will normally tend to bridge between the walls of the cells. At this particular size a great surface area per unit of volume is achieved and there is an optimum amount of contact between the water and air passing through the packing. The bottom of the packing is cut to form serrations or tips 32 which prevent bridging of liquid in the cells.

Mounted above packing 1'7 are means for distributing liquid uniformly over the top surface of packing 17. Preferably such means include a rotary sprayer I19 comprised of arms 20 having suitable openings 19 therein to affect a uniform distribution of liquid over the top of the packing. The reactive `force of water discharging from the openings may be used to rotate sprayer `19. The arms are aixed to hub 21 which is connected to the top of riser or supply pipe 22 by bearing assembly 123. Pump 24 located shown below the sump draws water collected in the sump in through strainer or filter Z and forces it through the supply pipe 22 into sprayer 19 for `distribution over the top of the packing. To compensate for the small amount of water lost in the evaporative cool-ing process, make-up line 26, connected to a suitable source of water, is provided. Float 28 suitably connected to valve 27 in make-up line 26 regulates the level of water in the sump.

Mounted in opening 34 in the top of casing 2 is bypass damper 35, preferably of the multi-louver type. A suitable control 37, either manual or automatic, is provided to actuate damper 35.

Under some circumstances rwater discharged lfrom openings 19 in the sprayer strikes the top surface of packing 17 and a light spray of splashing water is created. This spray may be caught up in the ai-r stream passing through packing 17 and deposited upon heat exchange coil 13. To substantially eliminate even this light spray, means 40 are provided on sprayer 19. Such means include a `framework comprised of supports 4l, interconnecting member 42 and end brace '43 and a lter 44 suitably connected to the framework by an adhesive, by nuts and bolts or like fastening means. The iilter, preferably, is detachably mounted on the lframework to :facilitate cleaning and for replacement thereof. The filter is made, preferably, from polyurethane foam or glass fiber to provide a high degree of wet strength and is of a density to provide minimum air resistance and high filtration. Thus the lter permits substantially free flow of air therethrough while at the same time containing the minute particles of water enabling the heat exchange coil to function with an essentially dry surface. The framework is spaced from arm of sprayer 19, a distance greater than the maximum trajectory of liquid discharging from opening I19. rl'ihis is done to assure that all of the splashing liquid is confined beneath the filter 44.

In summer operation of the heat exchange unit, water is drawn into riser pipe 22 lby pump 24 and is discharged from sprayer 19 over the surface of packing 17. At the same time air drawn in louvered openings 4 by fan 7 passes through packing i7, the heat exchange coil .13, and is discharged from opening 6. The air passing through the packing in Icounterflow relationship with the water sprayed on the top of packing 17 is evaporatively cooled and saturated. The air passing over the coil 13 is essentially at the -wet bulb temperature, The greater temperature diierence between the air entering the unit and the air passing over coil 13 provides higher heat transfer eliiciency of the unit. Lint and dirt are removed from the air at this time as it passes throu-gh packing 17. The cleaned, cooled and saturated air passes over the heat `exchange coil to cool the refrigerant owing therethrough. The cooled air extracts more heat from the medium flowing through the heat exchange coil than would be extracted by air that had not been cooled. The air is essentially moisture free and as a consequence no scale will be formed `on the surface of heat exchange coil 13, If the nature of Ithe environment requires it,

means 40 may be employed on sprayer -19 to eliminate the tine spray resulting from the water splashing against the top of packing 17. A finned heat exchange coil may be used effectively in the present heat exchange unit and such coil will be much cleaner in operation and require less maintenance than a conventional aircooled heat exchange coil. The finned coil will likewise function effectively in corrosive atmospheres or in places where corrosive water is employed, for it is operated dry.

In `winter operation the iiow of water through the rotary sprayer will be discontinued and the unit may be operated as an air-cooled condenser. Control 37 may be actuated -to open damper `35 to bypass air about coil 13.

The heat exchange unit may be used in a heat pump design wherein the air is precooled in the summer and the coil i3 is employed as a heat rejection device, while lin the winter with the water shut off the heat exchange coil -13 would function as a heat source.

We have, therefore, provided an improved air-cooled heat exchange unit 'which will uniformly presaturate the air passing over the heat lexchange coil in such unit and which will remove entrained moisture from the air such that the finned Icoil used in the heat exchange unit will operate dry. It will be obvious that fluids other than refrigerants may be passed through heat exchange coil i3 to be cooled.

Increased heat transfer capacity for the same coil surface may be achieved by staging The coil may be separated into an upper and lower portion or stage. Below each portion is provided a packing and a liquid `distribution arrangement. A single `fan may be employed to draw air through the lower packing and lower portion of the coil and then through the upper packing and upper portion of the coil. By virtue of employing cooler air over the second stage, the capacity of the swo-stage heat exchange unit is considerably greater than the capacity of the single-stage heat exchange unit having the same coil surface.

While we have shown a preferred embodiment of our invention, it is obvious that other embodiments will be apparent to those skilled in the art and it is, therefore, intended that the invention be limited only within the scope of the appended claims.

We claim:

l. In a heat exchange unit, a casing having an air inlet adjacent the bottom thereof and an air oulet in the top thereof, fan means for moving air through the casing, a fluid-conducting heat exchange coil positioned in the path of air moving through the casing, a packing in said casing beneath said heat exchange coil, means for distributing liquid over the top of said packing, said packing comprising thin partition walls at least a portion of said par-tition walls undulating to engage other of said walls at spaced intervals to mutually support each other and define a plurality of adjacent parallel cells l open at the top and bottom, the cross-sectional area of each cell being so small that liquid can bridge the wall of the cell by surface tension, said packing having means for breaking the bridging of said liquid so that air passing through the packing is cleaned and cooled prior to passage over the heat exchange coil.

2. A heat exchange unit as in claim 1 wherein the fluid-conducting heat exchange coil comprises a serpentine finned coil.

3. A heat exchange unit as in claim 2, wherein the fins are made from aluminum.

4. In a heat exchange unit, a casing having and air inlet in the side thereof and an air outlet in the top thereof; fan means for moving air through the air inlet, upwardly through the casing and out of the air outlet; a Huid-conducting -finned heat exchange coil positioned in the path of the upwardly moving air; a packing in said casing beneath said heat exchange coil; and means for distributing liquid over the packing; said packing being fixed in a substantially horizontal plane and comprising thin partition walls of brons material impregnated with a substance to provide the wet strength required while maintaining the walls absorbent, said walls constructed and arranged to form a plurality of tubular cells open at the top and bottom, the cells being of such small cross-sectional areas that liquid can bridge the walls of the cells by surface tension, said packing having means for breaking the bridging of the liquid to maintain the cells open for the flow of air whereby air moving through the packing is saturated and cooled prior to passage over the heat exchange coil and the surface of the rnned heat exchange coil remains substantially dry during operation.

5. In a heat exchange unit, a casing, means for moving air through the casing, a fluid-conducting heat exchange coil in said casing, said coil having closely spaced ns thereon, means for communicating said coil with a source of hot fluid, a packing beneath said heat exchange coil, and means for distributing liquid over said packing, said packing comprising alternate plain and corrugated sheets of librous material impregnated with a substance to provide the wet strength required While maintaining it absorbent, said sheets forming a plurality of adjacent peripherally enclosed tubular cells open at the top and bottom, liquid owing downwardly over each side of the common partition walls between cells maintaining lms of liquid thereon for contacting air flowing through the cells, the cross-sectional area of each cell being so small that liquid can bridge the walls of the cells by surface tension, and means to cause air and liquid to flow through the cells whereby air flowing through the packing is uniformly saturated prior to passage over the heat exchange coil and the heat exchange coil is maintained substantially dry during operation.

6. A heat exchange unit as in claim 5 wherein said distributing means comprises a rotatable sprayer and means on said sprayer for substantially eliminating liquid carryover.

7. A heat exchange unit as in claim 5 wherein said distributing means comprises a rotatable sprayer and a lter on said sprayer for substantially eliminating liquid carryover.

8. In a heat exchange unit, a casing; fan means for drawing air through the casing; a Warm fluid-conducting heat exchange coil in said casing; said coil having closely spaced iins thereon; a packing beneath said coil; and means for distributing liquid over said packing; said packing comprising alternate plain and corrugated sheets of brous material impregnated with a substance to provide the wet strength required while maintaining it absorbent, said sheets forming a plurality of adjacent peripherally enclosed tubular cells open at the top and bottom, liquid flowing downwardly over each side of the common partition walls between cells maintaining lms of liquid thereon for contacting air flowing through the cells, the cross-sectional area of each cell being so small that liquid can bridge the walls of the cells by surface tension, and means for breaking the bridging of liquid; said distributing means comprising a rotatable sprayer disposed between said coil and said packing and filter means on said sprayer for substantially eliminating particles of liquid from the air prior to passage of the cleaned and saturated air over the heat exchange coil.

9. In a heat exchange unit, a warm fluid conducting heat exchange coil, said coil having closely-spaced heat transfer iins thereon, means for moving gas said heat exchange coil, and means for saturating and cleaning the gas prior to passage over the heat exchange coil, said latter means comprising a packing disposed beneath said heat exchange coil, rotary means for distributing liquid uniformly over said packing disposed betwen said coil and said packing, and filter means extending from a trailing edge of said rotary means for eliminating ne particles of liquid from the gas prior to passage of the washed and saturated gas over the heat exchange coil.

References Cited in the tile of this patent UNITED STATES PATENTS 302,163 Saladin July 15, 1884 1,042,864 Winks Oct. 29, 1912 1,729,135 Slauson Sept. 24, 1929 2,038,071 Wilhelm Apr. 21, 1936 2,405,812 Binder Aug. 13, 1946 2,703,228 Fleisher Mar. 1, 1955 2,780,306 Boyle et al. Feb. 5, 1957 FOREIGN PATENTS 336,828 Germany May 14, 1921 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 3,052,105 September 4, 1962 Urban Bowman et al.

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 2, line l5, after exchange" strike out the comma; line 25, for "packaging" reaol packing column 3, line 5l, for "opening" read openings column 3, line 63, forV "temperature, read temperature, column 4, line 30, after "and" insert a line 36, for "swomstage"Y read two-stage column 6, line 22, after "gas" insert over Signed and sealed this 26th day of March 1963 (SEAL) Attest:

ESTON G. JOHNSON DAVID L, LADD Attesting Officer Commissioner of Patents

Images