US2874943A - Heat exchanger - Google Patents

Description

, 24, 1959 A. AJFENNELL 2,874,943

HEAT EXCHANGER Filed Sept. 21. 1954 2 Sheets-Sheet 1 Feb. 24, 1959 A. A. FENNELL 2,874,943

HEAT EXCHANGER Filed Sept. 21, 1954 2 Sheets-Sheet 2 of fluid flowing over 'the pipe United States Patent HEAT EXCHANGER Anthony A. Fennel], Homewood, 11].

Application September 21, 1954, Serial No. 457,432 4 Claims. (Cl. 257-26245) The present invention relates to novel heat exchangers and, more particularly to novel heat exchangers for transferring heat from one fluid to another and especially useful as a recuperator in an industrial furnace.

Heat exchangers now in general use for purposes contemplated by the present invention, usually include a circular pipe or a plurality of telescoping circular pipes adapted to extend into the'flue of a furnace and adapted to be connected to inlet and outlet conduits for a fluid to be heated such as combustion air for the furnace. Such heretofore known heat exchangers, while being satisfactory in many respects, have been subject to several disadvantages. For example, heat exchangers having circular pipes extending transversely into a flue are relatively ineflicient since a vacuum is created at the downstream side of the pipes so that the hot flue gases do not contact the entire surfaces of the pipes. It has been proposed to provide such pipes or tubes with a streamlined crose section to inereasethe area of the pipe contacted by the hot gases, but such proposals have not been entirely Satisfactory since a laminar fluid flow is obtained around a streamlined pipe so that the layer of fluid immediately adjacent the pipe is rapidly cooled and insulates the pipe from the outer hotter layers of fluid. Another difiiculty arising with many heat exchangers now in use is that the exchangers cannot be easily sealed as aresult of different amounts of expansion or contraction between parts thereof.

An object of the present invention is to provide a novel heat exchanger which is constructed so as to eliminate the above mentioned disadvantages of heat exchangers haying either circular pipes or streamlined pipes and thereby obtain greater heat transferring efliciency.

A more specific object of the present invention is to provide a novel heat exchanger of the above described type which includes a pipe constructed so as to insure ntimate contaet of all surface portions thereof with the fluid flowing thereover, and which novel heat exchanger is provided with means for insuring mixing of the layers to thereby promote greater efliciency. h

A further object of the present invention is to prono vc l heat exchanger as set forth in the preceding paragraph wherein the means for mixing the layers of fluid is in the form of simple and novel pin means whichrnay be assembled and secured within apertures in the pipe in arapid and economical manner.

Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings wherein:

Fig. 1 is an elevational view of a furnace or the like of known eonstruction having a heat exchanger embodying the principles ofthis invention associated therewith;

Fig. 2 is an 'enlarged fragmentary perspective view showing the novel heat exchanger of the present invention disposed in assembled relationship with aflue pipe of a furnace; r r

ice

Fig. 3 is a cross sectional view taken along line 37-3 in Fig. 1 I

Fig. 4 is a horizontal cross sectional view taken along line 4-4 in Fig. 3;

Fig. 5 is an enlarged fragmentary side view of a portion of the novel heat exchanger of this invention;

Fig. 6 is a cross sectional view taken along line 6-3-76 in Fig. 5;

Fig. 7 is an enlarged fragmentary sectional view showing a portion of the novel structure including a pin assembled in the wall of a pipe in greater detail;

i Fig. 8 is a view similar to Fig. 7 but showing a modified pin structure;

Fig. 9 is also a view similar to Fig. 7 but showing a further modified pin structure;

Fig. 10 is a fragmentary plan view of a length of sheet material stock scored or crimped so that it may be easily formed into a heat exchanger pipe or tube having the cross sectional shape shown in Fig. 6; and

Fig. 11 is a diagrammatic cross sectional view showing how the sheet material stock may be scored or crimped.

Referring now more specifically to the drawings wherein like parts are designated by thesame numerals throughout the various figures, a heat exchanger unit 20 embodying the principles of this invention is shown mounted in a flue pipe 22 of a furnace 24 for transferring heat from escaping flue gases to combustion air supplied to the furnace. It is understood that while the heat exchanger of the present invention is particularly adapted to be assembled with a furnace for heating combustion air, the heat exchanger 20 is adaptable for many uses and may be used for cooling purposes as well as heating purposes.

As shown best in Figs. 1 through 4 the heat exchanger unit 20 includes one or more generally U-shaped tubes or pipes 26 which are preferably made from heat and corrosion resistant sheet alloy steel. Each of the tubes 26 has one leg 28 thereof connected to a combustion air or other fluid inlet header or manifold 30 and another leg 32 connected to a combustion air or fluid outlet header 34. The legs 28 and 32 of each of the U-shaped tubes extend through suitable openings in the flue pipe 22, which openings are disposed so that the U-shaped tubes are arranged transversely of the flue pipe. Suitable asbestos or other heat resisting material packing and sealing members 36 and 38 are provided forsealing the opennigs in the flue pipe through which the tube legs 28 and 32 respectively extend. In certain instances when the flue pipe is made from an alloy steel similar to the alloy steel of the pipes or tubes 26 the legs 28 and 32 of the tubes may be welded directly to the flue pipe and the welds may be used to seal the openings in the flue pipe. Since the portions of the U-shaped tubes 26 extending within the flue pipe are continuous it is seen that. sealing problems arising in some heretofore known structures utilizing telescoping tubes or otherwise connected tubes have been eliminated.

As shown in Figs. 4 and 6 the tubes 26 are formed so that they have a streamlined or so-called air foil cross section and they are disposed within the flue pipe so that the larger or thicker forward edges thereof face upstream. By providing the tubes with such a streamlined cross section, efficiency of the heat exchanger unit is increased over conventional circular tube structures since the tendency for a vacuum or dead spots to be created at thetrailing or downstream thinner edges of the tubes is substantially eliminated and the flue gases come into intimate contact with substantially all portions of thetube of pins 40 are assembled with each of the tubes and spaced both transversely across and longitudinally of the tube. As shown best in Figs. 6 and 7 each of the pins 40 has a portion 42 adapted to.extendinto the tube 26 through an opening 44 in the wall of the tube, and an outer end portion 46 adapted to extend radially outwardly from the tube. It will be appreciated thattheouter portions 46 of the pins serve to break up and mix thelayers of fluid flowing around the tubes 26 so as to prevent a single layer of fluid from flowing smoothly across the tube and insulating outer layers of fluid from the tube. Hence, as shown in Fig. 5, the pins 40 are arranged in a plurality of rows extending longitudinally of the tube with the pins in each row being staggered with respect to pins in an adjacent row to provide for the most eflicicnt mixing action. Is should also be noted that each of the pins 40 provide a direct conductor for the heat between the exterior and interior of the tube 26 whereby even further to promote more rapid exchange of heat between the fluids flowing within and without the tubes. By proportioning the area of the outer pin portions 46 with respect to the area of the inner pin portions 42 in a predetermined manner the rate of heat exchange between the fluids may be closely controlled and may be varied by changing the ratio of these surface areas.

The pins 40 may be rapidly and economically assembled with the tubes 26 by utilizing a stud welding apparatus, not shown, of known construction, which ap paratus usually includes a chuck or the like for gripping the outer end of the pin whereupon the apparatus may be operated to insert the inner end of the pin through the aperture in the tube. distance which the pins 40 may be inserted through the apertures, each pin is formed with an annular shoulder 48 between its inner and outer ends. This shoulder serves to engage the outer surface of the tube and locate the pin with respect to the tube in a positive manner. Furthermore, after the pin has been located, an electric welding current is applied to the pin by the welding apparatus so that a weld will be formed between the pin and the tube 26 as will be understood, and this weld will at least in part be formed between the tube and the annular shoulder 48 which serves to insure the formation of a continuous annular weld for sealing the opening 44. Before the pins are assembled with the tube a coating 50 of a suitable fluxing material is applied to the pins and particularly to the annular shoulder 48 to promote the formation of a good air tight weld. It will be seen that by placing the fiuxing material on the shoulder 48, the fluxing material cannot be scraped ofl during assembly of the pin with the tube since the shoulder is merely brought into abutting relationship with the tube as dis tinguished from the relative sliding contact taking place between the inner end 42 of the pin and the edge of the tube opening 44 during assembly of the pin.

In Fig. 8 there is shown a modified form of the present invention wherein pins 52 are substituted for the above described pins 40. The pins 52 are especially useful when it is desired to reduce the area of the outer pin portion as compared with the relatively large diameter outer pin portion 46 of the pin 40, and in the embodiment illustrated in Fig. 8, the pin 52 is provided with an outer pin portion 54 which has substantially the same diameter as the inner pin portion 56. In order to provide means for positively locating the pin 52 with respect to the tube 26 and to insure a continuous annular air tight weld between the pin and the tube, the pin 52 is provided with an annular flange 58 between its ends. A coating 60 of suitable fluxing material is applied to the surface of the flange 58 adjacent the inner pin end portion 56, whereby the pin 52 may be assembled with a tube 26 in substantially the same manner as the pin 40 described above.

I A further modification of the pin structure is shown in Pig. 9. In this modification the pin structure 62 in- In order positively to limit the cludes an inner pin portion 64 having a head 66 and a separate outer pin portion 68. A coating of suitable fluxing material is appliedto both sides of the head 66. The pin structure 62 may be assembled with a tube 26 by first inserting the inner pin portion 64 through the opening until the head abuts against the tube whereupon the outer pin portion 68 is positioned against the outer end of the head 66 in the manner shown by means of a suitable stud welding apparatus. With the pin portions positioned in this manner, the application of an electric welding current to the pin structure causes a weld to be formed between the pin portion 68 and the head portion 66 and a continuous annular air tight weld to be formed between the head 66 and the tube.

As indicated in Figs. 6, 10 and 11, each tube 26 is preferably made from an elongated sheet of alloy steel stock material, which sheet is bent to provide the tube with the cross section shown in Fig. 6 with the edges of the sheet butt welded as indicated at 72. In order to provide the tube 26 with flat outer surface portions, for cooperation with the above, described shoulders or flanges of the pins to insure continuous annular airtight welds between the pins in the tube, the sheet material stock is formed to provide the tube with flat sides 74 and 76, flat sections 78 joined by sharp bends 80 at the forward or leading edge of the tube and fiat sections 82 joined by sharp bends 84 at the rear or trailing edge of the tube. The formation of the sharp bends 80 and 84 and the flat section therebetween may be facilitated by initially scoring or crimping the sheet material stock along lines 86 shown in Fig. 10. Such scored or crimped lines may be easily provided on the sheet material stock bymeans of cooperating rollers 88 and 90 indicated diagrammatically in Fig. 11.

From the above description it is seen that the present invention has provided a heat exchanger unit having a novel tube structure formed so as to insure intimate contact of fluid flowing over the tube structure with substantially all portions thereof while at the same time such fluid is broken up and mixed so as to promote the most eflicient heat transfer between the fluid and the tube structure. More specifically, it is seen that the present invention has provided novel pin means for promoting more eflicient operation of the heat exchanger, which pin means may be easily secured in a predetermined assembled relationship with a tube. It is also seen that the present invention has provided a novel heat exchanger unit which is of relatively simple construction so that it may be easily assembled with a furnace flue pipe or thelike without necessitating any complicated or expensive sealing means to prevent escape of the flue gases or escape of the fluid flowing through the heat exchanger tubes. 7

While the preferred embodiments of the present invention have been shown and described herein, it is obvious that many structural details may be changed without departing from the spirit and'scope of the appended claims.

The invention is claimed as follows:

1. In a heat exchanger a tube to be positioned transversely in fluid passageway means and havingia streamlined cross section for promoting flow of fluid around the tube and in contact with substantially all portions of the tube, and a plurality of pin means extending outwardly from opposite sides and leading and trailing edges-of the tube for mixing fluid flowing over the tube, said 'tube having flat outer surface sections providing opposite sides and leading and trailing edges of the streamlined cross section and said pin means each having a flat surface mating with and secured and sealed to one of said flat surface tube sections. V 1

2. In a heat exchanger a tube tobe positioned transversely in fluid passageway means and having a streamlined cross section for promoting flow of fluidaround the tube and in contact with substantially all portions of the tube, said tube having a plurality of longitudinally .extending circumferentially arranged substantiallyflat sections providing its opposite sides and leading and trailing edges, a plurality of openings through the tube and in each of said flat sections, a plurality of pin means each having a portion insertable through one of said openings and another portion for extending outwardly from the tube and mixing fluid flowing over the tube, each of said pin means having shoulder means with a radially extending substantially flat surface mating with one of said substantially fiat tube sections, each of said pin means initially having a coating of flux on said substantially flat surface, and weld means between the substantially flat surface of each pin means and its associated substantially flat tube section for securing the pin means to the tube and for sealing the openings through which the-pin means extend.

3. A heat exchanger, as defined in claim 2, wherein each of said pin means has an outer portion with a diameter larger than the diameter of its inner portion, and

wherein said shoulder means is provided at the junction between the inner and outer pin means portions.

4. A heat exchanger, as defined in claim 2, wherein said shoulder means is provided by an integral annular flange.

References Cited in the file of this patent UNITED STATES PATENTS 166,461 Houghton Aug. 10, 1875 1,891,538 Hicks Dec. 20, 1932 1,958,364 Govers May 8, 1934 2,212,250 Schutt Aug. 20, 1940 2,395,757 Peters Feb. 26, 1946 FOREIGN PATENTS 568 France .Feb..14, 1903 (Addition to No. 276,619) 766,665 France Apr. 16, 1934

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