US2021117A

US2021117A - Heat exchanger

Info

Publication number: US2021117A
Application number: US524252A
Authority: US
Inventors: Charles E Lucke
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1931-03-21
Filing date: 1931-03-21
Publication date: 1935-11-12
Anticipated expiration: 1952-11-12

Description

Nov. 12, 1935. C LUCKE 2,021,117

HEAT EXCHANGER Filed March 21, 1931 2 Sheets-Sheet 1 Fig f 1 INVENTOR ATTORNEY Charles E Z ucke Nov. 12, 1935. c. E. LucKE 2,021,117

HEAT EXCHANGER Filed March 21, 1931 2 Sheets-Sheet 2 Upward Defleclian unk" IIH 9, a;

' INVENTOR Charles E. Luoke ATTORNEY heat exchange. apparatus.

I tube, and in the opposite direction on'the op- V have. advantages Patented Nov. 12, 1935 UNITED STATES 2,021,117 I HEAT EXCHANGER Charles E. Lucke,

The Babcock &

New York, N. Y., assignor to Wilcox Company, Bayonne,

N. J., a corporation of New Jersey Application March 21, 1931, Serial No. 524,252 12 Claims. (01. 251-230) This invention relates to improvements in fluid Specifically "it presents an arrangement of helically finned tubes, as an improvement in fluid heat transfer apparatus' An object is to render more effective and complete theheat exchange from one fluid to an-' other.

The invention is also intended to reduce heat losses resulting from ineffective and incomplete scouring action along fluid containing tubes receiving heat from passing gases.

A further object isto promote economy of cost of installation and the compactness of fluid heat exchangers. I

The invention is set forth with particular reference, to the accompanying drawings, in which:

Fig. 1 is a sectional view indicating a part of a return bend economizer having adjacent fluid conducting tubes formed with oppositely projecting fins, which are interlocked.

Fig. 2 is a detailed view of a section of one of the finned tubes of a heat exchange apparatus such as that shown in Fig. 1.

Fig. 3 is a detailed view of sections of adjoining finned tubes with oppositely directed interlocked fins.

Fig. 4: is a diagrammatic view with legends in dicating the action of gases upon finned tubes having a. pitch greater than their critical pitch.

Fig. 5 is a fragmentary view showing adjoining fluid heat exchange tubes with fins arranged as right hand and left hand helices and practi-' .cally completely overlapped.

v Fig. 6 is a fragmentary sectional view indicating finned sections which may be formed by making radial saw 1; ts in the illustrative fins.

The passage of astream of gas transversely of a helically finned tube results in a deflection of the gas in one direction on one side of the posite side of the tube.. Thedeflection of the gas is inopposite to the characteristics of the helices. Such tubes transfer apparatus but they cannot be used ef-' fectively in such apparatus without the present invention.

For. the best utilization er helically finned tubes in fluid heat exchange apparatus there must be a maximum heat transfer per cubic foot of space occupied by the apparatus. This. condition requires that, in an apparatus using a bank of hellcally finned tubes, they be overlapped.

directions on,opposite sides ofthe tubes, this action taking place according when used as parts of heat- If adjoining overlapped helicallyflnned tubes all have their flns arranged as left handhelices. or if all of the tubes have their fins arranged as right hand helices, the tubes cannot be completely interlocked or overlapped'under certain 5 conditions. One condition pertains when the pitch is of sufiicient length, and the fin is of sufilcient length.- In such a situation, the -upward slant of one fln, and-the downward slant of the other wouldcause the fins of adjoining 10 tubes to contact so as to cause the fins to touch before the fln of one tube touched the adjoin: ing tube. v A maximum interlocking of adjoining helically finned tubes is necssary'toobt'ain the maximum amount of heat transfer'surface per cubic foot of space occupied by the fluid heat exchange apparatus. To permit such a maximum of interlocking there must be a limit of pitch for a given depth of fin.

It is a part of this invention to arrange helically finned tubes in a single row, the adjacent tubes in a row having helices of-alternate directipns. That is to say, the first and third tubes of the row have, for example, flns arranged as right hand helices, and the second and fourth tubes have flns arranged as left hand helices.

A second consideration of the action rtaking place when a stream of gas encounters one of the tubes above mentioned, will now be considered. The gas passing a tube encounters a fin on both sides of the tube, at an angle to the direction of motion of the stream of gas. The fin then acts like a deflection band. The up,-stream side of the fin actually deflects the gas. The gas passing on the down-stream side of the same fin or band will not change its direction to follow the fin more than a small angle. If the angle of the fin is sufliciently large, there will be a loss of contact between the fin and the gas. This loss of contact causes a part of the down-stream side of the fln to become inefl'ective because it is not scoured by the gas. In this situation,-the heat transfer is not as complete as it is when the fin is at the proper angle. By the expres'sionflower side of the fln. the downstream side of the-fin is meant; it is the side opposite the side causing actual de flection of a part of the fluid stream flowing acrossthe tubes. 1

Referringto Fig. 4 of the drawings it will be seen that there is a legend Short circuiting.- This indicates an action taking place at the loweror downstream side of a fin arranged at an Y angle greater than the critical angle. In the event that action takes place as indicated in Fig.

' downward on account of the position of the elements Fig. 4 merely for the purpose of illustration) due to the fact that the fin is shown at an. angle greater than the critical angle.

It is a part of this invention to limit the helical fins to those of a pitch less than the critical pitch. The critical pitch is the greatest pitch at which there is no tendency to short circuit the gas relative to'the down-stream side of the fin. When the fin has a pitch equal to or less than the critical pitch, there iscomplete contact with the gas. When the pitch of the fin is above the critical pitch there is short circuiting on the lower side of the fin. By short circuiting" reference is made to the loss of gas and fin'contact.

Corresponding to the critical pitch of the helical finther'e is a corresponding critical angle for the boundary face of the fin section whether that section be a part of a. fin or otherwise. The fin might not be helical in form, but it must comply with the teachings of this invention. It must be inclined to the tube surface at less than the critical angle. The fins may be interrupted, in which case, they will be the equivalents of vanes. Also the fins may have plane surfaces in which case they are inclined, fins. The objective always is to limit the fins so'that the air or gas can contact with the downstream side inspite of the inclinations of the fins. r

If the fins of adjoining tubes turn in the same direction, then the gas passing between those tubes will have a part of its body deflected-in one direction, and an adjoining part of the same gas stream will be deflected oppositely. For exam- 'ple,one part ofthe gas stream would be deflected downwardly and an arfioinin'g part of the same stream deflected upwardly under those conditions. Such action produces eddy currents, and

causes loss of energy, which energy might otherwise be available for scrubbing the heat transfer surface and promoting efiective heat transfer. In the illustrative arrangement of helically finned tubes here described, the gas stream parts between the helically finned tubes are deflected in the same direction, and loss of energy is thereby obviated. The downward and upward gas deflections mentioned take place when the tank of finned tubes extends across a gas stream flowing,

horizontally. I This invention which the fiow of an external fluid past fluid heat exchange tubes is such that the flow is within a range capable of economically effecting desirable results in industrial installations. This range is referred to as the turbulent "velocity solid and fluid contact. solid to the direction of fluid flow may be, there range; It is such-that the fluid velocities may cause such extensive eddy currents that there is a tremendous loss in rate of heat exchange due to loss of contact between the external fluid and the tubes contacted by the fluid. This is accepted terminology, in the science of aerodynam-' ics, for fluid conditions in which it is a distinct problem to provide for complete fluid and is complete is concerned with apparatus in a contact between the' fluid and the solid. 7

With the illustrative device, there is less eddy current loss of energy. There is an adequately increased proportion of fiow energy used to pro- 5 mote heat absorption in the arrangement wherein adjoining tubes having oppositely directed helices are used. k

The illustrative apparatus minimizes eddy current loss and also'lossesof heat due to ineffective heat transfer by the pitch limitations of the fins whereby all surfaces on both sides of the fin are effective and short circuits are eliminated. a A maximum amount of heat transfer per cubic foot of space occupied by the apparatus 7 is effected by the interlocking of the fins of adjoining tubes.- This arrangement also provides a more compact apparatus and increases the eifective heat transfer for a given draft loss. 20

In Fig.1 there is shown'a heat exchanger havingfluid conducting tubes liland l2. The tubes ID are indicated as having fins I4 in heat s transfer contact therewith and formed substan- I tially as a continuous .left hand helix about the 25 Fig. 1 includes return bend connections l8, connecting adjacent tubes in such manner that the 35 contained fluid flows back and forth across the gas stream, the direction of which is indicated by the arrow 20. Preferably the finned sections of the tubes are mounted in a casing indicated by Y the walls 22 'andjfl. Between these walls there 40 is confined a fluid current.

Securing the fins to the tube by arc,fiame, pressure or resistance welding brings about good heat transfer relations between the tube and the fins. Under certain conditions the fins may be brazed or 45 solderedto the tubes In Fig. 2, a section of the illustrative tube is shown cut away longitudinally through the tube .and through the fins. There are lines of weld nietal 28 indicated in this figure. The cross sec- 50 tion relationships of the bases of the fins and weld metal is indicated bythe upper part of Fig. 2, wherein deposits 28 and .30 of weld metal are shown as constituting a broad heat transfer base uniting the fin to the tube. 55 ,In Fig. 1, the return bends l8 are shown as provided with flanges 32, preferably held in fluid tight contact with the flanges 34 on the fluid conducting tubes. 7

.While this invention has been described with 00 reference to particular constructions it is to be understood that the invention is not limited there: to, but that it is of a. scope commensurate with the scope of the appended'claims.

What is claimed is:

1. Fluid heat exchange apparatus comprising,

' in combination, a row of parallel tubes conveying one fluid, means for causing a second fiuid to move across the rowof tubes, and helically ar-, ranged external fins on each tube making thermal contact therewith, there being alternate right hand and left hand fins on successive tubesalong the row...

2. Fluid heat exchange apparatus comprising,

in combination, a row of parallel tubes conveying The fluid heat exchahgwapparatus shown in A one fluid, means for causing a second fluid to move across the row of tubes, and helically arranged fins of less than the critical pitch on each tube, each flnmaking thermal contact with its tub"e, there being alternate right hand and left hand fins on successive tubes along the row.

3. In fluid heat exchange apparatus, a bank of parallel tubes through which one fluid moves, means for causing a second fluid to flow across the tubes of the bank, and helical fins in thermal contact with the tubes and alternately arranged on successive tubes as right and left hand helices, the fins and the tube being completely overlapped or interlocked so that the fins on one tube are in contact with an adjoining tube.

4. In fluid heat exchange apparatus, a bank of parallel tubes through which one fluid moves, means for causing a second fluid to flow across the bank of tubes, and helical fins in thermal contact with the tubes, and alternately arranged on successive tubes as right and left hand helices, the fins on adjoining tubes being interlocked.

5. Fluid heat exchange apparatus comprising, in combination, a row of parallel tubes conveying one fluid, means for causing a second fluid to move across the row of tubes, and helically arranged fins electrically welded on each tube and making thermal contact therewith, there being alternate right hand and left hand fins on successive tubes along the row.

6. In fluid heat exchange apparatus, parallel tubes each having helical flns, the fins on adjoining tubes overlapping and being formed respectively as right and left hand helices.

and left hand helices.

7. In fluidheat exchange apparatus, parallel tubes each having helically extending fins, the fins on adjoining tubes overlapping and being formed respectively as right and left hand helices,

and wide bases securing the fins to the tubes and 5 acting as a high capacity heat transfer part.

8. In fluid heat exchange apparatus, parallel tubes each having a helical fin, the fins on adjoining tubes overlapping and being formed respectively as right and left hand helices. l0

9. In fluid heat exchange apparatus, a bank of tubes conducting a fluid, and helically arranged fins in thermal contact with the tubes, the fins on adjacent tubes being arranged respectively as right and left hand helices. i5

10. In fluid heat exchange apparatus, a plurality of tubes conducting a fluid, and helically arranged fins secured on the tubes in thermal contact therewith, the fins on adjacent tubes being interlocked and arranged respectively as right 20 and left hand helices.

11. In fluid heat exchange apparatus, a plurality of tubes conducting a fluid, and helically arranged flns of less than critical pitch in thermal contact with the tubes, the fins on alter- 26 nating tubes being arranged respectively as'right and left hand helices.

12. In fluid heat exchange apparatus, a plurality of tubes conducting a fluid, and helically arranged fins of less than critical pitch in ther- 80 mal contact with the tubes, the fins on alternating tubes interlocking and arranged as right CHARLES E. LUCKE.