US1694395A - Air cooler - Google Patents

Description

Patented Dec. 11, 1928.

UNITED STATES PATENT OFFICE.

JOSEPH PRICE, OFWEST BRIGHTON, NEW YORK, ASSIGNOR TO THE GRISCOM- RUSSELL COMPANY, OF NEW YORK, N. Y., A CORPORATION OFDELAWARE.

AIR COOLER.

Application filed June 16, 1923. Serial No. 645,735.

This invention relates to heat-exchanging apparatus and more particularly to the structure of apparatus intended to effect the interchange of heat between a gas and a liquid, the object of the invention being to provide a heat-exchanger of improved con struction.

In my copending application, Serial No. 483,355, filed July 8, 1921, now Patent 1,- 509,566, there is disclosed a heat-exchanger in which a plurality of heat-exchanging elements are connected to a single header or drum. These heat-exchanging elements each consist of a pair of substantially parallel tubes interconnected-at one end to form a U-shaped structure, the lower open ends of these tubes being connected to the header. The header itself is provided with partitions separating the ends of the tubes communicating w1th 1t so as to form passageways for conducting the working fluid to and from the U-shaped heatexchanging elements, The passageways thus formed are interconnected longitudinally of the header so that a plurality of rows, or groups, of the IU-shaped elements may be connected in parallel.

This apparatus is intended primarily as a heat-exchanger to be installed in a closed air circuit with an electric generator casing for the purpose of cooling the air circulated through the generator. In an installation of this kind it has been found desirable, for several reasons, to utilize as small a volume of air as possible in this closed circuit. Among these reasons is the fact that a small volume of air tends tokeepdown the size of the apparatus, and also it reduces the amount of oxygen available for combustion should the insulation of the generator become overheated.

Long investigation has shown me that the U-tube and header construction above referred to is the most desirable construction which, as far as I am aware, has yet been devised for use in the cooling of a generator where the air must be circulated through the cooler at relatively high velocity and where the cooling must be done rapidly.

The high velocity of the air passing through the heat-exchanger, which in such cooling systems is in the neighborhood of 1500 to 2000 ft. per minute, causes an undesirable vibration of the U-tubes carrying the cooling liquid.

To increase the area of the heat-transferring surface and to prevent the vibration of the Ushaped heat-transferring elements has proved a difficult problem. For increasing the heat-radiating surface, the tubes heretofore have been provided, in some instances,

with helical ribs, and, in others, round or square washer-like discs have been independently threaded upon the individual tubes and soldered, or otherwise secured in heat-conducting relation thereto, these washers being disposed in spaced relation with each other so as to allow the passage of air between them and form heat-radiating vanes. In the case of a U-shaped heat-transferring element, however, the size of these Washers has been limited by the distance between the parallel tubes of the U and the necessit of allowing suficient space between vanes o ad acent tu es to accommodate tubesupporting plates or grids at intervals between the tubes, as the placing of heat-radiating vanes of this type upon the individual tubes, does not impart any additional rigidity to the heat-transferring element.

After a great deal of study and investigation in an endeavor to increase the radiating surface and prevent the vibration of these heat-exchanging elements, I have, to a remarkable degree, attained the results desired. My present mvention provides means for at once increasing the rigidity of the heat-exchanging element to such an extent as to ef-' fectively prevent their vibration and to do away with the necessity of employing tubesupporting plates for this purpose, and for increasing the area of the heat-transferring surface which increases the amount of heatexchange. In carrying out my invention, I-

provide the U shaped heat-exchanging ele- Inent with a plurality of sheet metal vanes, each joined in heat-conducting relation, as, for example, by soldering, brazing, or the like, to both of the parallel tubes, these vanes being disposed preferably in closely spaced relation along the tubes. Thus, the tubes are tied together by means of these vanes at relatively frequent intervals throughout a'substantial portion of their length and the mechanically Weak 'U-shaped element is transformed into an extremely rigid structure. These vanes are preferably rectangular in shape and, embracing both of the parallel tubes, they present a greater heat-transferring surface to the air passirag through the heat-exchanger than is secure by the use of se arate vanes for each tube.

hese and other novel features of the invention will be better understood by referring to the following description, taken in connection with the accompanying drawings illustrating one embodiment of my invention. In these drawings:

Fig. 1 is a view, partly in elevation and partly in section, of a single heat-exchanging element and a portion of the header;

Fig. 2 is a plan view ofv a heat-exchanger showing the arrangement of a plurality of heat-exchanging elements therein;

Fig. 3 is a plan view of a portion of a heatexchan er similar to the one shown in Fig. 2, and illustrates a modified arrangement of the heat-exchanging elements;

Figs. 4 to 6, inclusive, illustrate details of the rectangular heat-radiating vane; and

Figs. 7 and 8 are views of a modified form of connection which may be'used at the upper ends of the tubes.

There is shown in Fig. 1 a single heat-exchanging element comprising a pair of parallel tubes 10 and 11, preferably of some good heat-conducting and non-corrosive material, such as copper, brass, or the like, these tubes being interconnected at their upper ends by means of the return bend 12 which may be sweated or brazed to the outer ends of the tubes, as indicated at 13. The lower ends of these tubes pass through a tube sheet 14 of the header 15, and are suitably secured in openings in the tube sheet, the lower ends being allowed to'project for a short distance below the lower surface of the tube sheet, as shown at 16, in order to facilitate the removal of the heat-exchanging element. In securing the tubes 10 and 11 to the tube sheet, it is not necessary to upset the inner ends of the tubes as in steam boiler practice, and it. is quite suflicient to provide a reasonably close fit be-- tween the apertures in the tube sheet and the surface of the tubes, and then expand the tubes slightly by means of an appropriate tool.

The U-shaped heat-exchanging elements illustrated in Fig. 1 are arranged in the heatexchanger in a plurality of transverse rows 17 (Fig. 2). The header 15 is provided with a plurality of transverse partitions, three of which are indicated at 18, 19, and 20, each of these partitions serving to separate the open ends of adjacent rows of-tubes. Thus, for example, the partition 19 separates the open ends of tubes 10 and 11, and the cooling liquid flowing into the transverse passage 21 formed between partitions 18 and 19 enters the open end of tube 10 and, passing upwardly there through, returns through tube 11 and passes out at its lower end into the transverse passageway 22 formed between walls 19 and 20. Inasmuch as the heat-exchangmg elements are arranged in' rows, the passageways 21 and 22 communicate with a plurality of heat? exchanging elements, thus placing all the elements in each row in parallel.

The transverse passageways, of which those indicated at 21 and 22 are examples, are alternately placed in communication with each other by means of longitudinal passageways such as the one indicated at 23, which serves to lead the cooling-[liquid from the transverse passage, shown broken away at the right of Fig. 1, to the passage 21 from which it enters the tube 10, as previously dcscribed. In this way the transverse rows or groups of heat-exchanging elements are connect-ed in arallel and supplied with cooling liquid whlch enters and leaves the heat-exchanger through manifolds (not shown) at one end of the apparatus.

The heat-exchanging element thus far described consists merely of the two parallel tubes 10 and 11 interconnected at the upper end by means of return bend 12 and sup ported onl at their lower ends where they are secure ture is not rigid and is, in fact, mechanic-ally weak when it is considered that the length of the tubes is large in proportion to their diameter and spacing. The circulating air passing through the heat-exchanger'across and between the heat-exchanging tubes at the relatively high velocity which is necessary causes these U-shaped tubes to vibrate to such an extent that it is necessary to provide some means for reducing or preventing this vibration.

In order to prevent this vibration and at the same time to increase the radiating surface of the heat-exchanging elements, there are placed upon the element a plurality of metallic vanes 24 (Figs. 4, 5, and 6). vanes are stamped. preferably in rectangular form, from a relatively thin sheet of metal and a pair of holes 25, spaced from each other by a distance equal to the spacing of tubes 10 and 11, is punched in each. The holes 25 are somewhat smaller than the outside diameter of tubes 10 and 11, so that a plurality of radial slits 26 may be cut around the periphery of these holes and the metal intermediate these slits be bent at right angles to the sur-' face of the vane to form a plurality of projections which constitute base portions 27 for securing the vane to the tubes. These rectangu lar vanes 24 are threaded upon the tubular heat-exchanging elements before they are placed in position in the tube sheet, the length of the bases 27 serving to automatically space the vanes by the amount desired. The entire length of the tubes from the return bend 12 to a point relatively close to the tube sheet 14 is preferably occupied by these spaced metallic vanes.

- After the vanes have been threaded upon the heat-exchanging element, the bases 27 are These rigidly joined in heat-conducting relation to the surface of the tubes 10 and 11 with which they, are in contact. This may be done in any appropriate manner, such as by dipping the entire element in a bath of molten solder, or by brazing, welding, or the like. The material employed in the vanes 24 is preferably a metal which possesses good heat-conductinlg properties, such as copper, brass, or the The heat-exchanging element, which was previously weak mechanically, has, by the addition of these vanes 24, been converted into a structure which is extremely rigid. The vanes 24, although they may be made of relatively-thin sheet metal, are each rigidly attached to the parallel tubes 10 and 11, and

serve to tie these tubes together at cl gsely spaced intervals throughout the greater portion of their length. In addition to increasing the strength of the element a-nd making it into a rigid structure, these vanes also add a greater amount of heat-radiating surface to the-tubes than could be secured by the use of separate vanes for each tube. As mentioned above, both helical vanes or fins, and

vanes made of round and square washers threaded upon the tubes have been tried. The square washer type of vane provides a greater amount of heat-radiating surface than the circular washer type, or the helical type, but by the use of the rectangular vane the radiating surface for a given spacing of tubes may be made still greater than it is possible to obtain with square vanes on'tubes of the same spacing. This is for the reason that when separate or individual vanes for each tube are used, in order to reduce the vibra tion, sufiicient space must be allowed between the vanes on the parallel tubes of each element to insert tube-supporting plates or grids at intervals lengthwise of the U-shaped element.

Let us suppose that the spacing between the tubes 10 and 11 as indicated at A in Fig. 5 is 1 inches, and that it is desired to use vanes of the square washer type threaded upon each tube independently. To accommodate the tube-supporting plates, it is neces-\ sary to allow approximately inch between the inner edges of the individual washers, as indicated by the dotted lines in Fig. 5. Thus, with the tube spacing assumed, the maximum size of the individual square washers would be 1 inch square, whereas it is entirely feasible as a manufacturing proposition to place rectangular washers, in accordance with my invention, which measure 1 inch by 2 inches, upon parallel tubes having the same spacing assumed above, namely, 1% inches. The increase in radiating surface by the use of the rectangular vane is thus, in the example. given, approximately 36%, the cost of assembly in the two cases being substantially the same.

In place of the closed return bend 12, shown in Fig. 1, it may be in some cases desirable to em loy a casting 28 of the form shown in Fig. In this case, the tubes 10 and 11 may be expanded instead of sweated into the openings 29 and 30, respectively, these openings being connected by the cored passageway 31. Removable plugs 32 are threaded into the upper'surface of the casting 28 in allgnment with the openings 29 and 30, the openings being large enough to accommodate an appropriate expanding tool. Also, by taklng out these plugs and removing header 15, a cleaning brush may be passed through the interior of tubes 10 and 11 and the entire interi or of tube surface may be inspected. Referring to Fig. 2 of the accompanying drawings, which shows in plan view an assembly of a plurality of the heat-exchanging elements above described arranged in transverse rows, these heat-exchanging elements are surrounded by a sheet metal casing, indicated at 33, and provided with openings 34 and 35. The air conduit leading fromthe generatorto be cooled may be secured to the faces of these openings and the air thus circulates through the longitudinal passageway between them, within which it is brought into intimate contact with the surfaces of the vanes 24 and the other exposed port-ions of the heat-radiating elements. In Fig. 3 there is shown a modified arrangement of the heatradia-ting elements in. which the air passing through the heat-exchanger will more readily come in contact with the heat-exchanging surfaces. To accomplish this, the tubes of each element are positioned in the tube sheet so that the center line 36 between the tubes makes an angle with the direct path of the air through the exchanger, as indicated by the arrows. By thus arranging the tubes in the tube sheet, the direct path of the air through the exchanger lies between the tubes 10 an 11 of each element and thus compels the air to travel between the tubes-andscour the surfaces of the vanes 24 which are inter- 110 mediate the tubes.

- As previously mentioned, the heat-exchanger constructed in accordance with my invention is provided with elements that are extremely rigid and mechanically strong. The

advantages of this increased strength are not 'limlted to the reduction in the vibration of covering plate resting u n the connections and having apertures or receiving these there is less waste of sheet metal stock from which they are stamped since a fewer number of parts is required than with other stamped heat-radiating vanes.

I claim:

A heat exchanger of the class described including a passage for the gas being treated,

a heat transferring unit comprising a plurality of fluid conveying elements extending into heat exchanging relation with the gas traversing the apparatus, said elements each comprising a pair of parallel tubes interconnected at one end of the element, a plurality of heatconducting vanes each spanning both tubes of each of said fluid conveying elements, a header having passa es for delivering the working fluid in onev irection through one tube of each element and collecting the fluid returning in the opposite directionthrough the other tube of each of the elements, said fluid conveying elements being identical with one another and each of said elements being supported independently of the others and being removable from said header independently of every other element.

In testimony whereof I aflix my signature.

JOSEPH PRICE.

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