US2294137A

US2294137A - Heat exchanger

Info

Publication number: US2294137A
Application number: US390363A
Authority: US
Inventors: Warren A Spofford
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1941-04-25
Filing date: 1941-04-25
Publication date: 1942-08-25
Anticipated expiration: 1959-08-25

Description

w. A. SPOFFORD 5 HEAT EXCHANGER Filed April 25, 1941 H is Attormey Patented Aug. 25,1942

nanrnxcr Warren A. Spofi'ord, Glen Ridge, N. 3., assignor to General Electric Company, a corporation of New York Application April 25, 1941, Serial No. 390,363

5 Glaims. (ill. ldS-d) M invention relates to heat exchangers and more particularly to heat exchangers having relatively thin walls which are subject to distortion caused by internal pressures.

This is a continuation-m-part of my copending application, Serial No. 323,219, filed March 9, 1940, and assigned to the same as'signee as the present invention.

It has been proposed to constructheat exchangers in which the fluid conveying tubes are formed from relatively thin metal. It has also been proposed to provide some sort of internal stay for such tubes. Thus, it has been proposed to provide flat tubes with pins or rods extending through opposite walls of the tube, the pins or rods acting as heat exchange members, and also stay members to prevent such distortion. With such a construction, it is necessary to secure the members to the walls of the tube at the two places where each wire passes through the tube, or if the through type member is not used to secure the ends of an internal heat exchange and stay member to the opposite walls. When the members are soft soldered, it is usually possible to make the joint without annealing the wires but whenever it is necessary or desirable to secure the members by a relatively high temperature securing operation as silver soldering or brazing,

the members may be annealed at the soldering temperatures. tensile strength of all cold-worked ductile metals is reduced by annealing so that whenever the material utilized for the fins and stay members or tubes or both anneals at the securing temperature or lower, the structure is weakened when the parts are so secured. In order to restore the strength to the fins after the securing operation, or to increase the strength of the assembly, I cold work the fins or tube walls or both by stretching. The cold working step must be carried out at a temperature below that at which recrystallization takes place. For example, copper, which is commonly used for the aforementioned purposes because of its relatively high heat conductivity and corrosion resistance to water, becomes annealed at about 400 C. and since the temperature of brazing is about 750 C., the fins become annealed during the brazing operation. Recrystallization takes place at about 200 C. so that the cold working step is carried out below this temperature. Room temperature is satisfactory for this step.

Accordingly, it is an object of my invention to assemble a heat exchange element in a manner to restore the strength of the heat exchange and It is known that the ultimate stay members which have been weakened by annealing.

Even when the heat transfer members are not annealed during the assembly process, it may be desirable to strengthen the members or fins by cold-working. Therefore, it is another object of my invention to assemble a heat exchange element in a manner to increase the strength or the heat transfer members.

It is another object of my invention to provide a new and improved heat exchange element and a new and improved method for constructing the same.

Still another object of my invention is to in= crease the strength of external heat transfer members or the external portions of heat trans fer members whenever such a result is desired.

Further objects and advantages of my invention will become apparent as the following description p'roceedsancl the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. l is a side elevational partial view of a heat exchanger embodying the principles of my invention; Fig. 2 is a perspective exploded view of a portion of a heat exchanger and the apparatus used in forming heat exchange elements of the type illustrated in Fig. 1; Fig. 3 is a cross-sectional view of the apparatus shown in Fig. 2 preceding the operation of cold working the heat exchange element; and Fig. 4

l is a view similar to Fig. 3 illustrating the heat exchange element after the cold working opera- 7 tion.

In the drawing I have illustrated a heat exchange element comprising a fluid conveying conduit Ill and a plurality of heat exchange members or fins I I formed from a material having relatively good heat conductivity and extending through opposite walls of the tube it. In order to permit cold working of the members it following brazing or silver-soldering to the tube H) at the points of passage through the walls thereof, I space the two sides or walls I2 and I3 of the tube I0 nearer together during the operation of soldering or brazing the members to the walls than is ultimately desired. The flanged T ture members l4 and I5 and hydraulic pressure is applied to the interior or the tube III in order to force apart the walls l2 and I3 oi the tube thereby cold working by stretching the wires or pins li a predetermined amount, thereby providing a combined stay and fin member which has been strengthened by cold working after having been secured in position.

Describing my invention in greater detail I have shown in Fig. 1 a plurality. of fluid conveying tubes In communicating at opposite ends with headers l8 and I1 and having heat exchange members or fins II. The heat exchanger is enclosed in a suitable casing l8. Thus, a heat exchange fluid, ,such as water, may enter the heat exchanger, as a condenser, for example, at the header l8, and flow through the tubes l into the header l1 irom which the fluid may be discharged. If the heat exchanger is being used as a condenser, the fluid to be condensed will be passed across the outside of the tubes in contact with the tube l0 and the fins H.

In Figs. 2 to 4, inclusive, 1 have illustrated suitable apparatus for obtaining the aims of my invention. In order to render the tubes l0 fluidtight, the pinsor fins II are silver soldered or brazed at the points of passage through the walls l2 and I3, as previously described. As

illustrated, the walls I 2 and I3 are spaced apart but in order to form a complete tube the members l2 and I3 have been provided with side wall portions l9 and 20 and longitudinally extending marginal flanges 2| and .22 for securing purposes. Following the attachment or the pins or rods II, the flanges 2| and 22 are secured together in fluid-tight relationship as by soldering or welding. In order to render the ends of the tubes fluid-tight I have provided

suitable plugs

23 and 24, the latter being provided with a suitable connecting member 25 for connection with a supply of suitable fluid.

. In order to limit the expansion of the -walls of the tube l0 and the portions 26 of the wires or pins H to a uniform degree and a predetermined amount I have provided a suitable fixture comprising elements I4 and I5. elements or members I4 and I5 is recessed as indicated by the numeral 21, to receive the oppositely disposed walls l2 and I3 of the member ID. The recessed portions 21 are dimensioned to permit the walls I2 and I3 to be forced apart to the ultimately desired dimension. In order .to secure the members l4 and I5 together and prevent them from being forced apart I have provided the member l5 with a plurality of threaded members 28 arranged to extend through suitable openings 29in the upper member l4 and engage threaded fastening members or nuts 30.

Whenever the fluid conveying tubes III are provided with external fins it is necessary to provide corresponding depressions or openings in the walls of the members l4 and I5 communicatlug-with the recesses 21. Thus, in the pin type heat exchanger illustrated in the drawing I have,

provided openings 3i extending entirely through the members I 4 and I5.

In Fig. 3 there is illustrated the arrangement of the apparatus after the heat exchanger has been placed between the members I4 and I5 and the nuts 30 applied to the members 28. It will be observed that the walls [2 and I3 are spaced from the corresponding walls of the members l4 and I5, respectively. In Fig. 4, there is illustrated the heat exchanger of Fig. 3 after the Each of the application of fluid pressure to the interior of the tube In illustrating the walls of tube ID in their forced-apart condition, the portions 26 of the pins ll having been stretched. The nuts 30 are preferablyloose enough to permit relative movement between the longitudinally extending side flanges of the tube l0 and the

surfaces

32 and 33 of the members 14 and I5, respectively.

I have found that if walls 12 and i3 of copper are spaced apart a distance of one-half an inch before the application of the hydraulic pressure, the ultimate strength of pins ll of copper may be increased approximately 22 per cent by an elongation of the pins of- 55 of an inch. Not only .will the pins I I be cold worked but the edges or side walls of'the tube ID will also be cold worked adjacent the flanges thereby restoring or increasing the strength of the tubes l0 adjacent the aforementioned flanges.

Many modifications of my invention will be apparent to those, skilled in the art. For example, threaded members such as 28.and nuts 30 need not be employed. Any arrangement for maintaining the blocks H and IS in a position for permitting expansion of the tube In to itsultimately desired position will be satisfactory. Moreover, any arrangements for sealing the ends of the tube during assembly may be employed.

In the practice of my invention a fixture is not essential, although convenient. Another method of accomplishing the desired purpose would be to stretch the wires by mechanical means before the tube walls are welded or brazed together. This method would also increase the strength of the pins ll externally of the tube In.

My invention is not limited to a particular type of fin but is applicable wherever internal stays may be used, wherever it is desirable to utilize a fln or stay member to reinforce a conduit against deformation from pressure on one or the other side of the fluid conveying tube, or wherever it is desirable to increase the strength of external or internal fins after assembly.

While I have shown a particular embodiment of my invention, I do not desire my invention to be limited to the particular construction shown and described and I intend in the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of forming heat exchange elements of the type having a relatively thin-walled conduit with members disposed internally thereof and serving not only to transfer heat between a fluid flowing in said conduit and the conduit Walls but also to reinforce the conduit walls, comprising the steps of spacing two conduit wall members nearer together than ultimately desired, providing heat transfer elements of a material having relatively good heat conductive properties and which is weakened by annealing between said walls, securing said elements to said walls at a temperature above the annealing temperature of said material, securing together adjacent marginal edges of said walls to provide a fluid-tight fluid conveying tube and moving apart said wall members into the ultimately desired positions at a temperature less than the temperature of recrystallization of the material of said elements thereby cold working said elements by stretching whereby said elements are strengthened.

2. The method of forming heat exchange elements of the type having a relatively thin-walled and applying fluid pressure to the interior of conduit with members disposed internally thereof and'serving not only to transfer heat between a fluid flowing in said conduit and the conduit walls but also to reinforce the conduit 'walls comprising the steps of spacing two conduit wall members nearer together than ultimately desired, providing heat transfer elements of a material having relatively good heat conductive properties and which is weakened by annealing between said walls, securing said elements to .said walls at a temperature above the annealing tempera- ,ture of said material, securing together adjacent marginal edges of said walls to provide a fluidtight fiuid'conveying tube and applying fluid pressure to the interior ofsaid tube for moving apart said wall members into the ultimately desired positions, thereby cold working said elements by stretching whereby said elements are strengthened, said cold working step being carried out at a'temperature less than the temperature of recrystallization of the material.

3. The method of forming heat exchange elements of the type having a relatively'thin-walled conduit with members disposed internally thereof and serving not only to transfer heat between a fluid flowing in said conduit and the conduit walls but also to reinforce the conduit walls comprising the steps of spacing two conduit wall members nearer together than ultimately desired providing heat transfer elements of a. material having relatively good heat conductive properties I and which is weakened by annealing between said walls, securing said element to said walls at a temperature above the annealing temperature of said material, securing together adjacent marginal edges of said walls to provide a fluid-tight fluid conveying tube, providing a fixture having said tube for moving apart said wall members into the ultimately desired position and also cold working said element by stretching whereby said elements are strengthened to resist distortion of said wall members from internal pressure, the cold working step being carried out at a temperature less than the temperature of recrystallization of the material.

'4. A heat exchange element having a thinwalled fluid conveying conduit with members formed from a material having relatively good heat conductivity and which is weakened by annealing disposed internally thereof for transferring heat between afluid flowing through said conduit and said conduit walls and also for reinforcing said conduit walls, said members being secured between opposite walls at a temperature above the annealing temperatures of said material, said members also having been strengthened by moving apart said opposite walls from a first position into the ultimately desired position, said strengthening step being carried out below the temperature of recrystallization of said material.

5. A heat exchange element having a thinwalled fluid conveying conduit of copper with copper members disposed internally thereof for transferring heat between a fluid flowing through.

said conduit and said conduit walls and also for reinforcing said conduit walls, said members having been secured between opposite walls at a temperature above the annealing temperature of copper, said members also having been strengthened by-moving apart said opposite walls at a temperature below the temperature of recrystala recess, the walls of the recess being spacedapart a distance equal to the ultimately desired spacing of the conduit wall members, placing the assembled tube and members in said fixture lization of copper from a first position into the ultimately desired position thereby cold working said members.

WARREN A. SPOFFORD.