US 3380518 A
Description (OCR text may contain errors)
April 30, 1968 CANTELOUBE ET AL 3,380,518
FINNED HEAT EXCHANGER 2 Sheets-Sheet 1 Filed Feb. 15. 1966 & i3 U MU U K I. EEB W EE. .rgwmi iwlmw Tu 3 m g in Axvoes' (AA/2220065 /740 TAVERIVA April 1968 A. CANTELOUBE IY-ZT AL 3,380,518
FINNED HEAT EXCHANGER 2 Sheets-Sheet 2 Filed Feb. 15. 1966 Ana/Wakes I Ava/e: ('fl/VIZLOUIE lnaa f rmer/v United States Patent 3,380,518 FINNED HEAT EXCHANGER Andr Canteloube, Ave. de Bretteville, Neuilly-sur- Seine, France, and Italo Taverna, 80 Blvd. de Valmy, Colombes, France Filed Feb. 15, 1966, Ser. No. 527,714 Claims priority, application France, Feb. 26, 1965,
7,159, Patent 1,434,385 3 Claims. (Cl. 165171) ABSTRACT OF THE DISCLOSURE A finned heat exchanger comprises a plate carrying a sinuous tube, and fins stamped from the material of the plate between and perpendicular to the lengths of the tube. The stamped fins are arched bridges extending alternately from opposite sides of the plates and having between at least some of them flat fins comprised by re maining portions of the plate. The bridges extend outwardly from the plane of the plate farther than the tubes. The flat fins between the bridge-type fins may be at an acute angle to the plate.
This invention relates to a finned heat exchanger of improved design, useful mainly as a condenser or evaporator in cooling and refrigerating systems.
Many different types of heat exchange apparatus already exist in which an internal fluid circulating within a tube system transfers heat by either natural or forced convection to an externally flowing gas. Heat exchangers of this type usually have the shape of a plate which has either a plane or, more often, a developable surface; and the process of convective heat transfer is improved by the provision of fins which are cut-out from the metal of the plate.
In a first type of heat exchanger, the tube system is secured to the plate by welding, bonding or mechanical assembly of a coiled tube. In a second type of heat exchanger, the tube system is formed by expansion within the thickness of the plate which is in that case made up of two sheets having deformations which correspond to the fluid-circulation system and which are assembled by a' number of different methods outside the expanded sections, this arrangement being known as an integrated tube system.
Another known method of construction of heat exchangers of the integrated tube type consists in forming fins by die-stamping, cutting and folding portions of the tube plate which are located between the tube sections, wherein the rectilineal fins formed extend slantwise with respect to the plane of the plate.
A further known method of construction which is employed in a heat exchanger of the built-up sheet or integrated tube type consists in deforming the sheet by cutting-out and stamping in such a manner as to form between two lengths of the sinuous tube having an undulated path a succession of transverse undulations which are similar .to sinusoids and project alternately on each side of the plane of the plate. The direction of these undulations is reversed from one line to the next.
There is thus obtained a plate having a fluted surface in which is formed a series of ducts for the flow of air, said ducts extending parallel to the rectilineal lengths of the tube.
Heat exchangers of this type are characterized by an improved heat transfer coefficient but nevertheless do not derive the maximum thermal advantage from the surfaces of the fins "for the following reasons:
In the first place, the cutting of multiple undulations sets a limitation on the amplitude of the undulation or wave, with the result that optimum permeability of the surface to gas flow is not afforded. In the second place, since each fin is made up of a number of consecutive halfwaves, the central portions of the fins which are located between two tube-lengths are at a distance from these latter which is great compared with the thickness of the sheet. The temperature gradient between these portions of the fins and the surrounding atmosphere is therefor low as a result of limited transmission of heat flow through the sheet. As a consequence, heat transfer is reduced.
It has also been proved by experience that heat exchangers of the type referred to above do not provide sufficient mechanical ruggedness inasmuch as the fins are prevented by their small amplitude from creating a protection zone which extends a sufficient distance away from the tubes. Moreover, the fins afford low resistance to compressive stresses which are normal to the plane of the plate.
The different systems of fins proposed in devices of the prior art are usually intended to produce uniform flow of surrounding gas layers by causing these latter to pass through the mid-plane of the heat exchanger apparatus in a substantially laminar flow pattern.
The present invention is based on the discovery that the thermal efficiency of heat exchangers of the type discussed in the foregoing can be improved to a very appreciable extent by means of fins designed to produce a substantial modification in the air flow pattern. It is therefor one of the objects of the present invention to improve the efficiency of the finned heat exchangers.
A further advantage of the heat exchange structure in accordance with the invention lies in the fact that it provides distinctly improved mechanical strength. It is therefor another object of the invention to improve the mechanical strength of the finned heat exchangers.
In accordance with the invention, the'heat exchanger such as a condenser or evaporator for use in a cooling or refrigerating apparatus comprises a sinuous tube in heatconducting relation with a plate provided with fins which are cut-out and cambered so as to project from said plate between the lengths of said sinuous tube and in staggered vertical relation on said plate, and is chiefly characterized in that a first group of fins is formed in a manner known per se by punched-out bridges which project either on one side or on the other side of the plane of the plate whilst a second group which also extends between the tube-lengths consists of fins which are substantially flat.
The second group of fins is primarily intended to deflect the air streams which are established by convection within the chimneys which are formed parallel to the tubelengths and on each side of the plate by the bridge-type fins. It is thus possible to transform the gas-flow from a laminar to a turbulent flow pattern. The flat fins have the additional function of spacer members between the tubelengths, thereby strengthening the plate.
As a preferred feature, said flat fins are generally inclined to the mid-plane of the tube if it is desired to increase the turbulence of the gas streamlines which move by convection along the heat exchanger.
The complete heat exchanger unit can be obtained by reproducing a particular configuration of a group of 3, 4 or n fins according to a predetermined periodic law. In all cases, the heat exchange unit can be obtained by cutting out and stamping in opposite directions a flat metallic sheet which is either plain or which preferably comprises an integrated tube system.
When the heat exchanger is of the integrated tube type, the improvements contemplated by the invention result in additional technical advantages which will be explained hereinafter.
Further characteristic features and objects of the invention will become apparent from the description which now follows:
In the accompanying drawings, which are given by way of non-limitative example,
FIG. 1 is a partial view in elevation of a particular embodiment of cooling condenser in accordance with the invention, designed on the integrated tube principle;
FIG. 2 is a partial view in perspective of the bottom left-hand portion of the above-mentioned condenser;
FIG. 3 is a transverse sectional view along the line III- III of FIG. 1;
FIG. 4 is a transverse sectional view of the fins taken along the transverse plane IVIV of FIG. 1;
FIGS. 5 to 11 are partial transverse sectional views of the fins which are similar to FIG. 4 and which relate to various alternative embodiments.
In the particular construction of the invention which is shown in FIGS. 1 to 4, the heat exchanger is a cooling condenser. Said condenser comprises an integrated tube system consisting of a sinuous or snake-like tube 1 which is formed by expansion in accordance with a known technique from a double-walled plate 2 of aluminum or aluminum-base alloy. The end sections of the tube 1 are provided with unions 3 for connecting purposes.
Provision is made between the consecutive rectilineal and parallel tube-length 1a, 1b of the heat exchanger for rows of transverse fins which are arranged in two groups.
The fins of the first group are formed by means of punched-out strips or bridges 11, which project respectively on each side of the plane of the plate 2. The longitudinal edges such as 12 and 13 of each bridge are parallel to each other. The ends of the bridges are located in proximity to the adjacent tube-lengths 1a and 1b of the tube 1 and each bridge extends substantially at right angles to said tube-lengths. The perimeter of each bridge corresponds to an isosceles trapezium (as shown in FIG. 3), the large base of which is located in the plane of the plate 2. According to another characteristic feature of the invention, steps are preferably taken to ensure that height H of the bridges 11 (or 15) relatively to the plane of the plate 2 is greater than the height h or distance to which the tube-lengths 1a, 1b of the tube 1 project from said plane (as shown in FIG. 3).
The fins 14 of the second group are flat and extend in the plane of the plate 2 from one tube-length 1a to the adjacent tube-length 1b. In addition, the fiat fins 14 are located between two successive bridge fins 11, 15 of opposite convexity.
The combined assembly of fins of plate 2 thus corresponds to the repetition of a unitary pattern in which each fin 14 located in the plane of the plate 2 is in adjacent relation with two bridges 11 and 15 which extend transversely in opposite directions relatively of the plane of the plate 2. Under these conditions, looking on the condenser in the position shown in FIG. 2, it can be seen that the fins 11 are raised and the fins 15 are concave. In the embodiment considered, the fins 11 and 15 have a prismatic surface, the generator-lines of which are parallel to the plane of the plate 2, the two end faces of said surface being oriented slantwise with respect to the plane considered.
The complete assembly of fins can be formed by cutting-out the flat portion of the plate 2 which is located between the tube lengths 1a, 1b. The bridges 11 and 15 are formed by means of die-stamping punches which produce elongation of the fins without resulting in fracture of the metal.
In addition to the fins which are formed between the tube-lengths considered, the plate 2 of the heat exchanger is preferably provided with complementary fins 16 located beyond the path of the sinuous tube 1.
The structure as thus formed has a high thermal transparency and is preferably placed in such a manner that the tube-lengths 1a, 1b of the tube 1 are vertical or, better still, at an angle of 4 to 8 with respect to the vertical, in which position the overall thermal efiiciency of the condenser is particularly high.
In this manner, it has been possible to obtain a heat transfer coefficient equal to 10.95 c.g.s. Whereas a condenser of conventional type and equivalent size having a sinuous tube 1 which is bonded to a louvered sheet gives a value of 5.05 c.g.s. under similar operating conditions.
This technical improvement can be explained, although it will be understood that the invention is not dependent on this explanation, by pointing out that the structure which is contemplated by the invention produces a circulation of air by convection according to a turbulent flow pattern. The punched-out strips or bridges 11 and 15 are in contact with relatively thick layers of gas which flow on each side of the mid-plane of the heat exchanger. Turbulent flow conditions are improved by the flat fins 14 since these latter counteract the chimney effect which can be created by the projecting fins 11, 15.
Inasmuch as each bridge 11 or 15 also extends between two adjacent tube-lengths 1a, 1b of the tube 1, the temperature gradient between the central portion of the bridge and the end roots of the bridge is of maximum value, thereby improving the heat transfer processes. The fact that the fins perimeter is trapezoidal instead of circular makes it possible for the ends of the bridges to be raised from the plane of the plate 2 to a greater extent, with the result that inter-fin air flow is more effective.
Since the bridges 11 and 15 are formed by die-stamping, the sloping sections of these latter are subjected during the stamping operation to elongation which reduces their thickness. By virtue of this circumstance, the invention is of particular interest in integrated tube exchangers, in which the initial thickness of the sheet metal employed is greater than the thickness required for maximum heat transfer performance of the fins. The thinning of the fins which results from the die-stamping operation makes it possible to restore the fins to optimum conditions of thickness.
From the mechanical standpoint, the structure which is contemplated for the fins also provides substantial advantages. In fact, on the one hand, the height H to which the bridges 11 and 15 project with respect to the tubelengths 1a, 1b ensures mechanical protection of these latter. Inasmuch as the bridges 11 and 15 are in adjacent relation to a flat fin 14 which serves as a spacer member, the compressive strength of the heat exchanger is particularly high in view of the fact that, in the event of compressive stress exerted on the bridges 1.1 and 15, said bridges tend to buckle and not to fold. The structure as herein described is therefore endowed wit-h high strength.
By virture of the above-mentioned property which is combined with the protection given to the tube-lengths 1a, 1b, condensers fabricated of aluminum sheet can be mounted directly and without danger on the rear of refrigerators without requiring any form of protection.
In the version of FIG. 5, the turbulent-flow effect is increased by the arrangement of bridges 19, 21 or 22, 23 which are located at different distances from the plane of the plate 2. It is apparent that, in this manner, the upfiowing air streams which pass between the end bridges 21 (or 23) and the flat central fins 20 are deflected by the intermediate bridges 19 (or 22) which are located at a medium distance from the plate. Under these conditions, there is no passageway for the free conduction of surrounding gas.
In the embodiment which is shown in FIG. 6, the various bridges 41, 42, 44, 45 which have different spacing are separated from each other by the flat fins 43.
The versions of FIGS. 7 and 8 are characterized in that they comprise flat fins 25 which are turned down by stamping in such a manner as to present a certain inclination with respect to the plane of the plate 2, the center-line of said fins being located in this plane. This inclination is preferably comprised between 20 and 40. The fins 25 can have a tendency to direct the deflected air streams towards the exterior (which is the case shown in FIG. 7) or towards a bridge 26 or 27 (as shown in FIG. 8).
The flat fins 25 can have contrary inclinations from one ,row to another (case of FIGS. 7 and 8) or, on the contrary, they can all be parallel with each other, which is the case of the fins 28 shown in FIG. 9. This last-mentioned armrangement tends to establish a general displacement of the gas flow from one side to the other of the heat exchanger. Such a displacement is increased in the case of FIG. in which the fiat fins 29 and the bridge-type fins 30 and 31 are turned down in the same direction.
Finally, the combined arrangement of the inclined fins 32 and bridge-type fins 33, 34 as progressively spaced is shown in FIG. 11.
As will be readily understood, it would not constitute a departure from the scope of the invention to construct heat exchangers by making use of a plain finned sheet on which the sinuous tube is fixed in known manner either by welding or bonding, the locations for the lengths of said tube being reserved between the rows of fins.
1. A heat exchanger comprising a plate, a sinuous tube for circulation of a heat-exchange fluid borne by said plate in heat-exchange relation therewith, said sinuous tube having several tube lengths, a plurality of fins comprising arched bridges punched out from said plate and extending some on one side and some on the other side of the plate, said bridge-type fins extending away from the plate a greater distance than the tube so that the bridge-type fins protect the tube from damage and partake more fully in convective heat transfer, and further fins comprising substantially flat strips disposed between at least some of said bridge-type fins at acute angles with respect to the plate.
2. A heat exchanger as claimed in claim 1, some of said further fins being disposed at acute angles of a given sense to the plate and others of said further fins being disposed at acute angles of the opposite sense to the plate.
3. A natural convection heat exchanger comprising a substantially vertical plane plate, a sinuous tube for circulation of a heat exchange fiuid borne by said plate in heat-exchange relation therewith, said sinuous tube having several parallel and substantially vertical tube lengths having their axes in the plane of said plate and a plurality of fins comprising arched bridges punched out from said plate, each fin joining two successive tube lengths and extending some on one side and some on the other side of the plate, and further fins comprising substantially flat strips disposed between at least some of said bridge-type fins, the lengthwise extent of all fins being horizontally disposed, said heat exchanger being of the integrated tube type, said arched bridge-type fins having a substantially trapezoidal contour comprising two sloping sections and wherein the thickness of said sloping sections is smaller than the thickness of said exchanger plate, said bridge-type fins extending away from the plate a greater distance than the tube so that the bridge-type fins protect the tube from damage and partake more fully in convective heat transfer.
References Cited UNITED STATES PATENTS 3,135,320 6/1964 Forgo -151 3,224,503 12/1965 Konanz 165l71 3,265,127 8/1966 Nickol et a1. 165152 3,273,637 9/ 1966 Pa-uls 165171 FOREIGN PATENTS 1,191,954 4/1959 France.
1,212,813 10/1959 France.
ROBERT A. OLEARY, Primary Examiner.
M. A. ANTONAKAS, Assistant Examiner.