US3400758A

US3400758A - Helical baffle means in a tubular heat exchanger

Info

Publication number: US3400758A
Application number: US550256A
Authority: US
Inventors: Lee Man Suk
Original assignee: United Aircraft Products Inc
Current assignee: United Aircraft Products Inc
Priority date: 1966-05-16
Filing date: 1966-05-16
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10

Description

Sept. 10, 1968 MAN SUK LEE 3,400,758

HELICAL BAFFLE MEANS IN A TUBULAR HEAT EXCHANGBR Filed May 16, 1966 FIG-l INVENTOR. MAN SUK LEE HIS ATTO NEY United States Patent 3,400,758 HELICAL BAFFLE MEANS IN A TUBULAR HEAT EXCHANGER Man Suk Lee, Dayton, Ohio, assignor to United Aircraft Products, Inc., Dayton, Ohio, a corporation of Ohio Filed May 16, 1966, Ser. No. 550,256 9 Claims. (Cl. 165-459) ABSTRACT OF THE DISCLOSURE A tube and shell type heat exchanger wherein the shell side fluid is caused to flow over the tubes in a helical path, baffle means being provided in the form of longitudinally spaced segmental plate elements having flow control surfaces which are perpendicular to the axes of the tubes simplifying installation and removal of the tubes.

This invention relates to tube and shell heat exchangers, that is, to heat exchangers comprised of a tube bundle installed in a shell for flow of a first fluid through the tubes and for flow of a second fluid over and around the tubes, the fluids being segregated and a transfer of heat taking place through the tube walls. Although not so limited, the invention has special reference to compact forms of heat exchangers having high density cores comprised of a large number of closely spaced apart tubes.

Tubular heat exchanger cores customarily incorporate baffles. These make possible a maximum use of available pressure drop and are usually arranged to effect repeated crossing and re-crossing of the tube bundle by the described second fluid for optimum heat transfer effect. In the past this has been done by installing in the tube bundle a series of separated, longitudinally spaced apart bafiles which enforce a serpentine flow of fluid over the tubes between shell openings defining an inlet and an outlet. Such a baffling arrangement has certain disadvantages, as when portions of the provided heat transfer surface may be by-passed by the flowing fluid. More uniform flow at different flow rates is possible in a helical flow path with possibly superior heat transfer efficiency. However, the installing of battle means to obtain a helical flow has heretofore been impractical, particularly in high density cores.

The advantages of such a construction have not been seen to outweigh the difficulties of fabrication, including the forming of the helix and the installation in the baffle means of large numbers of closely spaced tubes.

In accordance with the instant invention, however, generally new and improved results are achieved with helical baffle means and problems of fabrication are simplified or eliminated. The provision of a heat exchanger core having helical baflie means so characterized is an object of the invention.

Another object of the invention is to provide helical baffle means wherein openings in the baffles accommodating heat exchanger tubes are aligned for easy insertion and withdrawal of such tubes.

A further object of the invention is to construct a helical baflie means as described with steps interposing restrictions in the path of movement of the flowing fluid over the tubes in such manner that the flow intermittently is restricted.

Still another object of the invention is to present a generally new baffle means comprised of a plurality of component elements cooperating with one another to define a helix and being individually in a mutually supporting relation to tubes of the tube bundle.

Other objects and structural details of the invention will appear from the following description, when read "ice in connection with the accompanying drawings, wherein:

FIG. 1 is a partly diagrammatic view of a tube and shell heat exchanger, the shell being shown in longitudinal section with the core therein in side elevation;

FIG. 2 is a fragmentary view in perspective of the core of FIG. 1, a portion of the core being exploded to show details of baflie elements;

FIG. 3 is a detail view of a series of related bafile elements comprising the baffle means; and

FIG. 4 is a detail view of a modified form of baflle elements.

Referring to the drawings, a heat: exchanger in accordance with the invention may comprise a shell 10 near respectively opposite ends of which are bosses 11 and 12 respectively for the inlet and outlet of a flowing fluid. The ends of the shell are open for flow therethrough of another fluid. The two fluids achieve a segregated, heat transfer relation within the shell 10, the heat transfer surface being afforded by tubes 13. These have their ends mounted in

header plates

14 and 15 which are suitably perforated, as indicated at 16 in FIG. 2, to receive and pass the tubes with a comparatively close fit. A large number of closely spaced apart openings 16 provide for a large number of tubes 13. For simplicity and clarity of illustration most of such openings are not here shown, and only a few tubes 13 are shown.

The

header plates

14 and 15 have a peripheral bearing in the shell 10 and may be joined thereto in a leak proof manner. The fluid described as entering one end of the shell 10 and flowing longitudinally thereof to and through the opposite end is compelled to do so by flowing through the tubes 13. The fluid entering the shell 10 by way of inlet 11 and exiting by way of outlet 12 moves through the shell exteriorly of the tubes 13. The interior wall surface of the tubes 13 is thus contacted by one fluid of one temperature while the exterior wall surfaces of the tubes are contacted by another fluid at a different temperature. Heat transfer through the tube walls occurs, the fluid of higher temperature yielding up some of its heat to the fluid of lower temperature. As heretofore seen, in order to make optimal use of the heat transfer surface the fluid flowing exteriorly of the tubes is bafiied to move repeatedly in a generally cross flow relation to the tubes. Such baflling is accomplished in accordance with the instant invention by helical baflle means 16. Along with the tubes 13 and

header plates

14 and 15 the baffle means 16 comprises the core of the heat exchanger. conventionally the core is separately assembled and installed as a unit in the shell 10.

The baffle means 17 achieves its extended character by a succession of angularly displaced steps. A perfect helix baflle is possible. It presents manufacturing difiiculties, however, and affords no means by which the holes to ac commodate the tubes 13 may be aligned in successive flights and may be round properly to receive the round tubes. Also, as will hereinafter more clearly appear, a perfect helix baifle does not provide the intermittent flow restriction of the present invention. Accordingly, the baffle means 17 has a stepped configuration and includes in the main segmental lands 18 disposed to lie in planes perpendicular to the axes of the tubes 13.

Considering the baffle construction in greater detail, in the illustrated instance of FIGS. 1, 2 and 3, the baflie means is comprised of a plurality of formed plate-like elements 19. Each element 19 is comprised of a pair of lands 18 which may be considered as occupying a side-by-side relation offset in a longitudinal sense by a wall or ledge 21 which unitarily joins the two lands at their adjacent edges. Opposite edges of the respective lands have turned over extremities 22 which project oppositely of one another out of and at right angles to the planes of their respective lands. The bent over extremities 22 of each element 19 are in a common plane and define what may be considered one side edge of the element. The opposite side edge is defined by a curved periphery 23 conforming to and adapted substantially to seat against the interior surface of the shell 10.

In assembling the baffle means, one of a pair of elements 19 in substantially face to face relation is rotated to achieve the laterally offset reversely disposed position illustrated by the exploded elements at the right hand end of FIG. 4. Moved in a relatively approaching direction, corresponding turned over extremities 22 are caused to interfit with one another and in limiting against respective lands 18 interrupt such relative approaching motion. While a pair of elements 19 is held so positioned, as for example by clamp means applied to the interfitting extremities 22, other plate elements of appropriate rotary displacement are caused to approach and engage the assembled pair of frame elements at opposite ends thereof. The result is to extend the baflle means and this action is continued until a baflle means of desired length is achieved. The assembly results in a continuous helix formed of angularly displaced lands 18 interconnected either by integral walls 21 or by interfitting extremities 22 which are at right angles to the walls 21 and serve the same purpose. Ledges 21 and interfitting extremities 22 provide steps longitudinally spacing the lands 18 of individual plate elements and of corresponding lands of adjacent elements. A helical flow path is formed having its entrance end at the inlet 11 and its exit at the outlet 12. The fluid in flowing through such path has a swirling motion in generally cross flo'w relation to the tubes 13 and is conducted from the inlet 11 to the outlet 12 in a number of turns appropriate to the heat rejection requirements, the allowed flow rates and pressure drops and other data pertinent to a particular heat exchanger.

In considering flow through the helical path as described it will be seen that the baffle construction intermittently enforces a flow restriction where the ledges 21 of adjacent flights of the helix or where the interfitting bent over extremities 22 of adjacent flights are aligned with one another. A passage 24 (FIG. 1) is defined at these locations of reduced cross sectional area as compared to the area immediately preceding and immediately beyond the such locations. Fluid encountering a passage 24 and an interposed step at the location of such passage has its flow constricted. The flow into the space beyond the passage, which space may be considered an expansion chamber, occurs under increased velocity conditions producing random flow and turbulence. A higher heat transfer rate through the tube walls results. Additionally, in advance of the passage 24 the restricted fluid breaks up in the corner of the step, producing eddies and turbulence in a manner to obviate pools or locations of low flow.

The individual plate elements may be circular in form as shown in FIG. 4, rather than semi-circular as in FIGS. 1 to 3. Thus, a plurality of circumferentially off-set lands 24 are positioned to occupy the quadrants of a circle. The circular configuration is split in one-half portion of the element and extremities are bent over to define

opposite projections

25 and 26. These correspond to the projections 22 of the plate elements 19 and are similarly adapted to interfit with corresponding projecting portions of companion elements. The remaining lands or quadrants of the circular plate element are joined by integral connecting walls 27 disposed at right angles to the lands 24 and achieving a longitudinally oflset relation of the several such lands.

The

lands

18 and 24 may be described as defining surfaces, each baffle means providing a succession of longitudinally spaced, angularly displaced such surfaces.

It will be evident that other modifications in the instant heat exchanger structure are possible within the spirit and concept of the invention as contained in the accompany- 4 ing drawings and in the foregoing description, and in accordance with the claims to follow.

What is claimed is:

1. A core for a tubulous heat exchanger, including a plurality of tubes arranged in a bundle of parallel tubes for flow through the tubes of a first fluid and for flow over and around the tubes of a second fluid, heat transfer between the fluids occurring through the tube walls, and baflle means in the form of longitudinally spaced baflle elements in said tube bundle directing the flow of said second fluid, said baflle elements providing a succession of longitudinally spaced angularly displaced surfaces, said surfaces being interconnected at adjacent edges and adjacent elements being interconnected to define a helix forming a helical flow path for said second fluid, said surfaces being disposed substantially perpendicular to the longitudinal axes of said tubes and having openings receiving said tubes, said surfaces each conforming to a quadrant of a circle, the connected adjacent edges of said surfaces defining walls disposed angularly of said surfaces.

2. A core for a tubulous heat exchanger, including a plurality of tubes arranged in a bundle of parallel tubes for flow through the tubes of a first fluid and for flow over and around the tubes of a second fluid, heat transfer between the fluids occurring through the tube walls, and baffle means in said tube bundle directing the flow of said second fluid, said baflle means providing a succession of longitudinally spaced angularly displaced surfaces, said surfaces being interconnected at adjacent edges to define a helix forming a helical flow path for said second fluid, said surfaces being disposed substantially perpendicular to the longitudinal axes of said tubes and having openings receiving said tubes, said baffle means being formed of plate-like elements, each comprised of a plurality of lands in offset parallel relation to one another and interconnected at adjacent edges by relatively angularly disposed portions, other angularly disposed portions projecting oppositely from each element to achieve interengaging relation with corresponding projecting portions of adjacent elements, said lands defining said surfaces.

3. A core for a tubulous heat exchanger, including a plurality of tubes arranged in a bundle of parallel tubes for flow through the tubes of a first fluid and for flow over and around the tubes of a second fluid, heat transfer between the fluids occurring through the tube walls, and baflle means in said tube bundle directing the flow of said second fluid, said batfle means providing a succession of longitudinally spaced angularly displaced surfaces, said surfaces being interconnected at adjacent edges to define a helix forming a helical flow path for said second fluid, said surfaces being disposed substantially perpendicular to the longitudinal axes of said tubes and having openings receiving said tubes, said baffle means being formed of plate-like elements, each comprised of a succession of angularly displaced longitudinally spaced apart parallel lands, said lands defining said surfaces, said succession of lands terminating at its ends in portions projecting oppositely of one another substantially at right angles to said lands whereby each element may be joined to adjacent elements to form continuing baflle means as described.

4. A core according to claim 3, characterized in that at least one of said elements is circular in configuration providing four lands as described defining the quadrants of a circle.

5. A core according to claim 3, characterized in that at least one of said elements is semi-circular in configuration having two lands as described in a side-by-side relation.

6. A core for a tubulous heat exchanger, including a plurality of tubes arranged in a bundle of parallel tubes for flow through the tubes of a first fluid and for flow over and around the tubes of a second fluid, heat transfer between the fluids occurring through the tube walls, baffle means in said tube bundle directing the flow of said second fluid, said baflie means providing a succession of longitudinally spaced angularly displaced surfaces, said surfaces being interconnected at adjacent edges to define a helix forming a helical flow path for said second fluid, said surfaces being disposed substantially perpendicular to the longitudinal axis of said tubes and having openings receiving said tubes, .and steps in said baffle means resulting in longitudinally spaced lands defining said surfaces, correspondingly positioned lands defining a flow path therebetween, said flow path having on account of said steps alternating portions of greater and lesser flow restriction.

7. A core for a tubulous heat exchanger, including a plurality of tubes arranged in a bundle of parallel tubes for flow through the tubes of a first fluid and for flow over and around the tubes of a second fluid, heat transfer between the fluids occurring through the tube walls, and balfle means in said tube bundle directing the flow of said second fluid, said bafile means providing a succession of longitudinally spaced angularly displaced surfaces, said surfaces being interconnected at adjacent edges to define a helix forming a helical flow path for said second fluid, said surfaces being disposed substantially perpendicular to the longitudinal axes of said tubes and having openings receiving said tubes, said baflle means being com prised of a helix made up of a succession of lands parallel to one another to define said surfaces, adjoining lands being connected to one another along adjacent marginal edges by steps approximately at right angles to said lands, said steps narrowing said flow path at the locations thereof to provide for alternate restriction and expansion of the fluid flowing through said path.

8. A tubulous heat exchanger, including a cylindrical shell, perforate header plates in spaced relation to one another in said shell, fluid flowing tubes extending between and opening through said header plates, inlet and outlet openings in said shell for flowing a fluid through said shell over and around said tubes, and perforate baflie means intermediate said inlet and outlet openings through which said tubes extend, said baflle means having the form of a helix having an outer edge substantially in contact with said shell and being comprised of a succession of lands parallel to one another and approximately at right angles to the axis of said shell, successive lands being angularly displaced from one another and interconnected by steps approximately parallel to the axis of said shell, said steps interposing restrictions to flow in the helical flow path defined by said 'baflle means.

9. A tubulous heat exchanger according to claim 8, characterized in that said baffle means is comprised of a succession of like elements, each element comprising a plurality of lands as described and terminating in portions of relatively opposite projection disposed approximately at right angles to said lands and cooperating with like portions on adjacent elements to define steps as described.

References Cited UNITED STATES PATENTS 1,335,506 3/1920 Jones l-16l 1,469,193 9/1923 Sims 161 1,505,429 8/1924 Ripley 165--159 1,522,866 1/1925 Colston 165161 1,764,200 6/1930 Dean 165-161 1,782,409 11/1930 Chute 165-161 ROBERT A. OLEARY, Primary Examiner. A. W. DAVIS, Assistant Examiner,