EP0058628A2 - Heat exchanger with capillary structure for refrigerating machines and/or heat pumps - Google Patents

Abstract

Heat exchanger for refrigeration machines and / or heat pumps, of the type in which an annular capillary structure is applied against the internal wall of the tubular heat exchange network, characterized in that said capillary structure (4) consists of a set of free and smooth fibers (5) of suitable material substantially rectilinear and parallel to the axis of the tubular elements rectilinear and parallel to the axis of the tubular elements concerned (3), regularly distributed in a ring and plated by any appropriate means (6 ) against the internal wall of said tubular elements, preferably over the entire length of the latter. Application to refrigeration machines and / or heat pumps.

Description

The present invention relates to heat exchangers using the energy supplied during the change of liquid / vapor or vapor / liquid phase of certain fluids and, more particularly, those used in refrigeration machines and / or heat pumps.

In machines of this type, the heat exchangers are either constructed and dimensioned with a view to playing a specific predetermined role, either as an evaporator or as a condenser, or else produced so as to serve both as an evaporator and as a condenser.

In the case where the heat exchanger is designed to be used exclusively as an evaporator, it is underused because it is only half filled with liquid in general and at most 2/3 full, in order to 'avoid "liquid blows" to the compressor.

Only 2/3, or even half, of the evaporator exchange surface when the fluid flow decreases, are therefore used. In addition, since the exchange takes place at reduced cold surfaces, the formation of frost is favored in the case of air evaporators, which obviously affects performance.

In the case of condensers designed essentially as such, it is necessary, for technological reasons, that the vapors arriving at the condenser are completely condensed at the outlet. This results in an over-sizing increasing the production costs of these exchangers.

Finally, currently, the use of reversible refrigeration machines requires the production of exchangers which are a compromise between evaporator and condenser, since they must operate as well in evaporator as in condenser, and which, therefore, in addition to the disadvantages of specific exchangers recalled above, have poor performance.

In order to improve the heat exchange efficiency, it has already been imagined to line the internal wall of the exchanger tubes with a capillary structure in order to have a better distribution of the liquid phase on the internal wall of these tubes.

However, the various solutions of this type designed so far are not satisfactory on two important points.

All the capillary structures proposed, either do not make it possible to have capillarity over the entire internal surface of the tubes, or (this is particularly the case with structures based on woven or meshed metallic fabrics) constitute baffles and obstacles braking and retaining the lubricating oil from the compressor of the system, certain structures combining the two disadvantages.

The object of the present invention is to overcome these two major drawbacks simultaneously by proposing a new capillary structure for heat exchangers allowing heat exchanges over the entire useful surface of the exchangers with a significantly increased efficiency, while not impeding the circulation of lubricating oil.

To this end, the subject of the invention is a heat exchanger for refrigeration machines and / or heat pumps, of the type in which an annular capillary structure is applied against the internal wall of the tubular heat exchange network, characterized in that that said capillary structure is constituted by a set of free and smooth fibers of suitable material, substantially rectilinear and parallel to the axis of the tubular elements concerned, regularly distributed in a ring and pressed by any appropriate means against the internal wall of said tubular elements, preferably over the entire length of the latter.

Such an arrangement allows, thanks to the wicking effect provided by the free fibers over the entire internal surface, an excellent distribution of the liquid phase without any hindrance to the circulation of oil because the fibers are smooth, straight and parallel to the 'axis of the tubes.

In addition, such a structure is particularly simple and inexpensive to produce.

• - Fig. 1 représente une coupe schématique d'un échangeur conforme à l'invention et pouvant fonctionner en évaporateur ou en condenseur :
• - Fig. 2 représente une vue en section transversale d'un élément tubulaire de l'échangeur de la Fig. 1 ;
• - Fig. 3 représente une coupe longitudinale partielle d'un élément tubulaire de l'échangeur de la Fig. 1 ;
• - Fig. 4 représente une coupe schématique d'un évaporateur conforme à l'invention;
• - Fig. 5 représente une coupe schématique d'un condenseur également conforme à l'invention;
• - Fig. 6 est une coupe partielle d'un mode de réalisation préféré d'une structure capillaire selon l'invention ;
• - Fig. 7 est une variante de réalisation du dispositif de la Fig. 6 , et
• - Fig. 8 est une coupe axiale d'un dispositif permettant la réalisation et la mise en place d'une structure capillaire suivant la Fig. 6 ou 7 associé à une tête d'extrusion de tubes dans laquelle est intégré ledit dispositif.

Other characteristics and advantages will emerge from the description which follows of various embodiments of such a capillary structure according to the invention, as well as of a method of producing and implementing a preferred mode of said structure. capillary, description given by way of example only and with reference to the appended drawings in which:

• - Fig. 1 represents a schematic section of an exchanger according to the invention and capable of operating as an evaporator or a condenser:
• - Fig. 2 shows a cross-sectional view of a tubular element of the exchanger of FIG. 1;
• - Fig. 3 shows a partial longitudinal section of a tubular element of the exchanger of FIG. 1;
• - Fig. 4 shows a schematic section of an evaporator according to the invention;
• - Fig. 5 shows a schematic section of a condenser also according to the invention;
• - Fig. 6 is a partial section of a preferred embodiment of a capillary structure according to the invention;
• - Fig. 7 is an alternative embodiment of the device of FIG. 6, and
• - Fig. 8 is an axial section of a device allowing the production and installation of a capillary structure according to FIG. 6 or 7 associated with a tube extrusion head in which said device is integrated.

The exchanger of FIG. 1 comprises two collectors 1 and 2 connected by a network of heat exchange tubes 3, parallel and identical rectilinear, made of a material which is a good thermal conductor such as copper for example.

According to the invention, all of the tubes 3 have a capillary annular structure 4 over their entire length, as does the collector of the liquid phase (collector 1 in FIG.) Of the heat transfer fluid (or refrigerant).

Figs. 2 and 3 illustrate an embodiment of said capillary annular structure 4 according to which this structure consists of a number of identical individual fibers 5, smooth, straight and of constant diameter. These fibers are free from each other while being in contact with each other and with the internal wall of the tube (1 or 3) and confined in an annular space by any suitable means. The distribution of the fibers 5 is uniform, the thickness of the annular layer being in a proportion determined relative to the diameter of the tube in order to have an appropriate circulation and flow of the fluid in the liquid phase in the conduits 1 and 3.

The fibers 5 line the internal wall of the latter over their entire useful length and are applied against the wall of the tubes, for example in the known manner by a helical element 6 (Fig. 3) forming a spring, engaged in the central part of the tubes ( 3.1).

This helical element 6 could of course be replaced by any other member capable of pressing the fibers against the wall such as rings for example.

The fibers 5 and the holding members 6 are made of metallic or plastic material, or the like, compatible with the nature of the fluid circulating in the exchanger.

The diameter of the fibers 5 can vary insofar as the interstitial spaces between fibers make it possible to obtain the capillary effect sought for the coolant or refrigerant considered.

The fibers 5 arranged in the collector 1 ensure a uniform distribution of the liquid towards the exchanger tubes 3, while the fibers 5 of the latter allow the liquid to "wet" absolutely the entire useful surface of the tubes 3 and therefore ensure maximum heat exchange between the liquid phase fluid in contact with the internal wall of the tubes 3 and the external fluid.

On the other hand, due to the geometry of the spaces interstitial both between fibers 5 and between these and the internal wall of the tubes 3 and the absence of a transverse obstacle to the axial flow of the lubricating oil, the latter is not retained and can s '' flow freely.

There is therefore no risk of the system compressor running out of oil.

When the working fluid arrives in the liquid phase at 1 and leaves again in the gas phase at 2, the exchanger works as an evaporator and cools the fluid (for example air) circulating in 7 between the tubes 3.

The fluid circulating in the tubes 3 is then called refrigerant.

If, on the contrary, the working fluid arrives in the gaseous phase at 2 and leaves by 1 in the liquid phase, the fluid is heat-transferable and transfers part of its calories to the fluid circulating in 7. When the latter is air, we can advantageously provide the tubes 3 externally with fins of aluminum or other material that is a good conductor of heat. The exchanger then works as a condenser.

The liquid phase is distributed over the tubes 3 as it is formed and is evacuated and the capillary structure 4 thus ensures a good distribution of the temperature and therefore improves the heat exchanges.

Thus, an exchanger such as that of FIG. 1 working in an evaporator has a much higher efficiency than that of traditional evaporators, the filling of the exchange tubes in liquid phase is usually of the order of half and at most 2/3 while, thanks to the capillary structure 4 according to the invention in the evaporator arranged according to FIG. 1, the entire internal surface of the exchange tubes 3 is in contact with the liquid phase, uniformly, thanks to the effect of capillary wick.

It therefore therefore eliminates, in the case where the fluid flowing at 7 is air, the premature appearance of cold spots causing the formation of frost on the tubes 3. It has thus been found that with an evaporator according to In the invention, the formation of frost appeared only for a temperature of the air circulating in 7 4 to 5 ° C. lower than that at which frost usually appears on conventional evaporators.

The exchanger shown in FIG. 1 operating either as an evaporator or as a condenser, improves the coefficient of performance of reversible machines in substantial proportions (of the order of 30 to 40%).

Fig. 4 illustrates an exchanger according to the invention designed essentially to operate as an evaporator.

The refrigerant arrives in the liquid phase in the collector 8 having internally a capillary structure 4 like the collector 1 of FIG. 1. The fluid is distributed in identical flow for each exchange tube 9 also provided internally with a capillary annular structure 4 over its entire length.

These tubes 9 are dead-end. the liquid is distributed along each tube 9 uniformly and evaporates completely and uniformly under the effect of the heat provided by the fluid circulating at 10. The vapor produced is collected by conduits 11 pitted on the exhaust manifold 12 of the gas phase and engaged in the end of the tubes 9 coaxially with the latter.

Fig. 5 schematically shows an exchanger according to the invention designed to work essentially as a condenser.

The heat transfer fluid arrives in the gas phase in the collector 13, condenses in the liquid phase on contact with the internal wall, provided with a capillary annular structure 4, exchange tubes 14 and leaves in the liquid phase through the collector 15 also provided of a capillary annular structure 4. in accordance with the invention.

Conduits 16 stitched onto the collector 13 for supplying the heat transfer fluid in the liquid phase and each engaged in the end of one of the tubes 14, coaxially with the latter, make it possible to distribute the heat transfer fluid uniformly.

Of course, the invention is not limited to the embodiment shown and described above, but on the contrary covers all variants, in particular those concerning the nature of the material constituting the fibers 5, their sizing, their distribution along the internal wall of the tubular exchange members and collectors of the liquid phase of the working fluid as well as the means for pressing or containing said fibers against the internal wall of said tubular members.

The sheet of fibers 5 may comprise only a single layer of fibers more or less parallel to the axis of the tube and contiguous or not.

Fig. 6 shows a particularly interesting embodiment by its simplicity and its efficiency. In this FIG., A sheet of fibers 5 is shown, consisting of a single layer of parallel and non-contiguous fibers, said sheet being pressed against the internal wall of the tube 3 by an elastic system constituted by a sheet of wires 17 of spring steel (or material likely to have the same elasticity characteristics). The wires 17 are parallel, non-contiguous and wound in a helix.

The fibers 5 have an axis substantially parallel to the axis of the tube 3, while the wires 17 form a more or less significant acute angle with the fibers 5.

The propeller produced by the wires 17 does not comprise a single wire but several in parallel, the bundle of wires being wound in a helix. It is therefore possible to easily vary the inclination between the fibers 5 and the wires 17 while having a tight network of wires 17 in contact at numerous points with the sheet of fibers 5.

It should be noted that by appropriate dimensioning and distribution of the wires 17, the elastic sheet made up of these wires increases the capillarity effects provided by the capillary structure 5.

Fig. 7 illustrates a variant according to which the internal wall of the tube 3 is no longer smooth but striated, grooved or grooved. To this end, streaks 18 or the like are produced by any suitable means, parallel to the axis of the tube 3 and preferably with a generally flared V-shaped cross section. These recesses 18 are responsible for facilitating the correct positioning of the fibers 5, it being understood that the depth of these streaks or the like is less than the radius of the fibers 5 which are held in place by an elastic system identical to that of FIG. 6 or different.

Furthermore, the capillary structure may consist of two layers of fibers 5 with identical or nonparallel dimensional characteristics and not contiguous, the fibers of one of the layers being inclined with respect wearing the fibers of the other layer and the whole of this structure being pressed against the tube by an elastic system identical or not to that of FIG. 6.

It should be noted that one of the layers may comprise fibers parallel to the axis of the tube, this layer being either in contact with the internal wall of the tube, or in contact with said elastic system (vapor side). ,

Fig. 8 illustrates a process for producing a capillary structure according to Fi ^g. 6 and its insertion into an aluminum or light alloy tube produced by extrusion. On a cylindrical mandrel 19 is helically wound a sheet 20 of spring wires or the like, made of steel for example. The wires 21 of this nanope form contiguous turns on the mandrel 19.

The ply 20 is wrapped in a ply 22 of free smooth fibers 5 parallel to the axis of the mandrel 19. The fibers 5 are regularly distributed in a single layer around the helical ply 20.

The plies 20 and 22 at the outlet of the mandrel 19 are guided and held in shape by a cylindrical sleeve 23 in the extension of the mandrel 19 and integrated in an extrusion head 24 coaxially with the annular orifice 25 for extruding a tube 3 for example made of aluminum, said orifice 25 being delimited between the sleeve 23 and the die 26.

As the tube 3 is formed, it is automatically provided internally with the capillary ply 22 and the elastic retaining ply 20, the plies 20 and 22 being formed continuously and introduced into the tube 3 at the same speed. scrolling.

At the outlet of the sleeve 23, the plies 20 and 22 expand radially under the elastic action of the spring wires 21 and are pressed against the internal wall of the tube 3.

The tube thus equipped conforms to what is shown in Fi ^g . 6.

The tube 3 may internally have grooves such as 18 (Fig. 7) made during the extrusion.

The tube 3 can, of course, be obtained in another way, for example by rolling a flat plate and then welding or from a strip wound helically on a mandrel, these two techniques being perfectly known.

In this case, it is the assembly of the two plies 2p - 22 which is introduced into the tube 3 previously formed.

In the case where the fluid to be vaporized or to be condensed circulates outside the tubes, such a capillary structure is applied to the outside of the tube as in the case of water condensers where the latter circulates inside the tubes, the refrigerant evaporating or condensing outside the tubes.

Claims (12)

1. Heat exchanger for refrigerating machines and / or heat pumps, of the type in which a structure. annular capillary is applied against the internal wall of the tubular heat exchange network, characterized in that said capillary structure (4) consists of a set of free and smooth fibers (5) of suitable material, substantially rectilinear and parallel to the axis of the tubular elements concerned (3), regularly distributed in a ring and pressed by any appropriate means (6) against the internal wall of said tubular elements, preferably over the entire length of the latter. 2. Exchanger according to claim l, characterized in that said fibers (5) are distributed in a single layer of non-contiguous fibers. 3. Exchanger according to claim 1 or 2, characterized in that the internal wall of the tubular elements (3) equipped with said capillary structure comprises grooves, grooves or longitudinal grooves serving as housing for the fibers of the capillary structure, the depth of the streaks or the like being substantially smaller than the radius of the fibers. 4. Exchanger according to claim 3, characterized in that the groove or the like has a generally V-shaped section flared. 5. Exchanger according to claim 1, characterized in that said fibers (5) are distributed in at least one layer of contiguous fibers of identical or different diameters. 6. Exchanger according to claim 1, characterized in that said fibers (5) are distributed in a first layer of non-contiguous fibers substantially parallel to the axis of the tubular elements and in a second layer of non-contiguous fibers which are parallel and helically wound with large steps and pressed against the first layer, the internal wall of the tubular elements being in direct contact, either with the first layer or with the second. 7. Exchanger according to one of claims 1 to 6, characterized in that said means for applying the struc capillary structure against the internal wall of the tubular elements consist of a ply of spring wires or the like., parallel, not contiguous, wound in a helix, the dimensional characteristics of the wires, of the ply and of the winding being such that said ply increases the capillary effects provided by the capillary structure. 8. Exchanger according to one of claims 1 to 7, characterized in that the heat exchange network comprises several parallel rectilinear tubes connected to a collector ( ₁ ) of the common liquid phase, rectilinear and also internally provided with said structure capillary with free fibers (5), such an exchanger being able to function as well in evaporator as in condenser. 9. Exchanger according to one of claims 1 to 8, and more particularly intended to operate as an evaporator, characterized in that the exchange tubes (9) provided with their capillary annular structure (4) with free fibers (5) are connected in a dead end on the manifold (8) for the arrival of the working fluid in the liquid phase, also provided with said capillary annular structure (4), the manifold (12) for evacuating the working fluid in the gaseous phase being connected to said exchange tubes (9) via conduits (11) engaged in the outlet of the exchange tubes coaxially with them. 10. Exchanger according to one of claims 1 to 8 and more particularly intended to operate as a condenser, characterized in that the exchange tubes (14) provided with their capillary annular structure (4) with free fibers (5) are connected dead end on the manifold (15) for evacuating the working fluid in the liquid phase, also provided with said annular capillary structure, the manifold (13) for supplying the working fluid in the vapor phase being connected to said tubes exchange (14) via conduits (16) engaged in the outlet of the exchange tubes coaxially therewith. 11. A method of obtaining and installing, in the tubular exchange elements, a capillary structure according to claim 6 and one of claims 2 to 4, characterized in that it consists in winding in a helix. in continuous on a cylindrical mandrel (19) a ply 120) of spring wires or similar (21) contiguous, to continuously surround said helical ply with a sleeve formed by a ply (22) of fibers (5) parallel to the axis of the helix and constituting the capillary structure and to be introduced continuously inside a tube (3) the internal wall of which is striated or not, the two coaxial plies mentioned above, the tube (3) and the two plies (20,22) running at the same speed relative to said mandrel (19), the diameter of said sleeve in line with the mandrel (19) being substantially less than the internal diameter of the tube so that by elasticity of said helix, said fibers ( 5) of the capillary structure are pressed and held against the internal wall of said tube. 12. Method according to claim 11, characterized in that the two coaxial plies (20,22) leave the mandrel (19) and are introduced inside a tube (3) during extrusion via a sleeve (23) extending said mandrel (19), integrated in the extrusion head (24) and opening out inside the tube (3) at the birth of the latter.

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