Patent Application
20200370836
The present invention relates to a distribution element configured to be arranged in a distribution zone of a heat exchanger of the plate and fin type, and to a heat exchanger comprising such a distribution element and at least one set of passages for a fluid to be put into a heat-exchange relationship with at least one other fluid. The element according to the invention allows more homogeneous distribution of the fluid across the width of said passages.
The present invention finds application notably in the field of the cryogenic separation of gases, in particular the cryogenic separation of air, in what is known as an ASU (air separation unit) used to produce pressurized gaseous oxygen. In particular, the present invention may be applied to a heat exchanger that vaporizes a flow of liquid, for example oxygen, nitrogen and/or argon by exchange of heat with a gas.
The present invention may also be applied to a heat exchanger that vaporizes at least one flow of liquid-gas mixture, in particular a flow of multi-constituent mixture, for example a mixture of hydrocarbons, through exchange of heat with at least one other fluid, for example natural gas.
The technology commonly used for a heat exchanger is that of aluminum brazed plate and fin heat exchangers, which make it possible to obtain devices that are very compact and afford a large heat-exchange surface area.
These heat exchangers comprise plates, between which are inserted heat-exchange corrugations, formed of a succession of fins or corrugation legs, thereby constituting a stack of passages for the various fluids to be put into a heat-exchange relationship.
These passages comprise zones referred to as distribution zones, which are arranged, in the overall direction of flow of the fluid in the passage in question, upstream and downstream of the actual heat-exchange zone. The distribution zones are fluidly connected to semi-tubular headers configured to distribute the various fluids selectively to the various passages, and to remove said fluids from said passages.
In a known way, these distributors generally comprise distribution corrugations, arranged in the form of corrugated sheets between two successive plates. The distribution corrugations are generally perforated straight corrugations cut into the shape of triangles or trapeziums. They divert the fluid coming from the inlet header of the heat exchanger in order to spread it across the width of the heat-exchange zones, and recover the fluid coming from said heat-exchange zone. The distribution corrugations also act as spacers in order to ensure the mechanical integrity upon brazing and during operation of the distribution zone of the passage. Such distribution corrugations are known from the documents U.S. Pat. No. 6,044,902 and EP-A-0507649. Also known, from the document EP-A-3150952, is a plate heat exchanger in which the distribution elements are formed by the actual plates, which are pressed.
One of the problems that arise with the configuration of the current distribution zones is the poor distribution of fluids toward toward the heat-exchange zones. Specifically, the distribution zones are occupied by at least two pads of corrugations in order to optimize the offcuts from the shaping process, thus increasing the risk of clearance between the pads. The assembly of the corrugation pads can also cause incidents along the flow path of the fluid, and this contributes to increasing the pressure drops in the distribution zones. Because of these imperfections in the distribution zones, variations in flow rate with an amplitude of around 10% may arise, these being detrimental to the correct operation of the heat exchanger.
Similarly, distribution defects are found in the distribution zones dedicated to the recovery of the fluids coming from the heat-exchange zones.
Another problem relates to the mechanical integrity of the distribution zones. Specifically, these zones are provided with corrugations with lower densities, typically between 6 and 10 legs per inch, than those of the heat-exchange zones. Currently, the distribution zone of a passage extends typically along a length, measured in a longitudinal direction corresponding to the direction of flow of the fluid in the heat-exchange zone of the same passage, of around 200 to 600 mm, and across a width, measured perpendicularly to said longitudinal direction, of around 500 to 1500 mm. Since the distribution zones constitute parts with lower mechanical integrity than the heat-exchange zones, it is desirable to limit the longitudinal extent thereof as much as possible in order to ensure better resistance of the heat exchanger during the circulation of fluids at high pressure within the passages.
It is an object of the present invention to fully or partially solve the abovementioned problems, notably by proposing a heat exchanger in which the distribution of the fluid(s) in the heat-exchange zones is as uniform as possible, and which also has distribution zones that take up less space than in the prior art.
The solution according to the invention is therefore a heat exchanger of the brazed plate and fin type, comprising:
As the case may be, the element of the invention may comprise one or more of the following technical features:
The present invention will now be understood better by virtue of the following description, which is given solely by way of nonlimiting example and with reference to the appended drawings, in which:
As can be seen in
Preferably, each passage has a flat and parallelepipedal shape. The passages extend lengthwise in the longitudinal direction z and widthwise in the lateral direction y. The separation between two successive plates is small in comparison with the length and the width of each successive plate.
Each passage 3, 4, 5 is divided, in the longitudinal direction z, into at least one distribution zone 20 and one heat-exchange zone 21. The flow of the fluids within the distribution zones takes place overall parallel to the longitudinal direction z. The distribution zone 20 and heat-exchange zone 21 are preferably juxtaposed along the longitudinal axis z.
According to the depiction in
In a manner known per se, the heat exchanger 1 comprises semi-tubular headers 7, 9 provided with openings 10 for introducing the fluids into the heat exchanger 1 and evacuating the fluids from the heat exchange 1. These headers have openings that are less wide than the passages. The distribution zones 20 serve to distribute the fluids introduced through the openings in the headers across the entire width of the passages.
According to the invention, a distribution element is arranged in at least one distribution zone 20 of a passage 3 of the heat exchanger, this element comprising a plurality of dividing walls 25 that are arranged so as to divide said distribution zone 20 into a plurality of channels 26 for the fluid F1 to flow through. Said channels 26 define flow paths with different lengths and have variable passage sections for fluid along said flow paths. Subdividing the distribution zone into a plurality of separate channels with variable lengths and sections makes it possible to divert the fluid while finely controlling the flow conditions for the fluid within each channel. In particular, it is possible to balance out the velocities of the fluid flowing through the different channels, so as to obtain more or less identical fluid velocities at the outlet of each channel, and hence a uniform or quasi-uniform distribution of the fluid across the width of the passages at the outlet of the distribution zone, while minimizing pressure drops in the distribution zone.
Moreover, the distribution element confers structural rigidity on the distribution zone of the heat exchanger since the spacer function can be ensured by the dividing walls.
It should be noted that, within the scope of the invention, the heat exchanger is of the brazed plate and fin type, meaning that the separate elements that make up the heat exchangers are secured, directly or indirectly, by brazing. The distribution element according to the invention is separate from the plates 2.
“Brazed support” is understood as meaning that the support is connected or secured by brazing to an adjacent plate of the heat exchanger via at least a portion of the respective surfaces thereof.
It should be noted that the expression “passage section for fluid” means the area through which the fluid flows within the channel, this being measured in a plane perpendicular to the direction of movement of the fluid F1 in said channel, i.e. perpendicular to the stream lines of the moving fluid F1.
The length of the flow paths is understood to be the distance to be covered by the fluid F1 between the inlet and the outlet of the channel in question.
According to the invention, the distribution element also comprises a support 27 configured to keep the walls 25 secured together. An example of such an element is presented in
It will thus be understood that the distribution element is not a corrugated product, in contrast to the distribution corrugations conventionally disposed in the distribution zones of a brazed plate and fin heat exchanger. The walls 25 are secured together via one and the same support 27, thereby conferring greater rigidity on the distribution element. This also makes it possible to simplify the brazing operations. Moreover, such a configuration affords greater design freedom for the distribution element and geometric freedom for the channels thereof.
Thus, it is possible to dispose walls 25 with a relatively great height, typically at least 2 mm, preferably at least 5 mm, more preferably up to 15 mm, or more, in the passages, this not being the case with heat exchangers in which the walls result from pressing of the dividing plates.
Preferably, said support comprises a bottom 27, preferably a flat bottom that can be formed from a flat sheet, from which the dividing walls 25 are erected. The walls 25 are preferably erected in the vertical direction x. The walls 25 can have heights h of typically between 2 and 15 mm. Preferably, the heights are chosen such that the walls 25 extend over virtually all, if not all, of the height of the passage in the vertical direction x.
The configuration of the distribution element 22 according to the invention, in which the distribution element is a separate part from the plates, also makes it possible to design different distribution profiles on either side of one and the same plate.
Preferably, a distribution element according to the invention is housed in several, if not all, of the distribution zones of one or more sets of passages of the heat exchanger. Said element extends over virtually all, if not all, of the height of the passages, measured in the vertical direction x, such that the structure is advantageously in contact with each plate 2 forming the passage 20.
The channels are preferably fluidically isolated from one another. The flow parameters of each channel are thus controlled independently of those of the adjacent channels, thereby making it possible to precisely adjust the distribution of the fluid across the width of the passages at the outlet of the distribution zone. Advantageously, the separating walls 25 are erected perpendicularly to the plates 2.
Preferably, the number of channels 26 is at least 6, more preferably between 5 and 50. Specifically, the number of channels 26 on the one hand has to be high enough to give the element 22 its mechanical rigidity but on the other hand should not be too high in order to leave enough free volume for the fluid to flow and to limit pressure drops.
Advantageously, the distribution element 22 comprises a first end 23 forming an inlet or an outlet for the fluid F1, and a second end 24 fluidically connected to the heat-exchange zone 21.
More specifically, as can be seen in
The first and second ends 23, 24 extend preferably in a plane parallel to the lateral direction y and perpendicular to the longitudinal direction z. The dividing walls 25 extend between the first and second ends 23, 24 and form channels 26 that lead out at the second end 24 and are configured to distribute the fluid F1 uniformly in the lateral direction y so as to obtain homogeneous or quasi-homogeneous distribution towards or from the entire width of the heat-exchange zone 21 when the other of said first and second ends 23, 24 is fed with fluid F1.
Advantageously, each channel is provided with first openings 26a and second openings 26b. Advantageously, as schematically depicted in
The openings 26a, 26b of the channels 26 could have passage sections for fluid that are identical or variable depending on the channels 26 in question. The passage sections for fluid of the openings 26a and 26b correspond to the internal areas of the channels 26 measured at the first and second ends 23, 24 in a plane parallel to the lateral direction y.
Preferably, at least one first opening 26a has a passage section for fluid that is different than the passage section for fluid of another first opening 26a, and/or at least one second opening 26b has a passage section for fluid that is different than the passage section for fluid of another second opening 26b.
Advantageously, the first openings 26a and/or the second openings 26b of one and the same channel 26 have passage sections for fluid that are larger the longer the flow path defined by said channel 26, i.e. the greater the distance to be covered by the fluid F1 between the first opening 26a and the second opening 26b.
Thus, in the example in
According to another example (
This compensates for the natural tendency of the fluid to pass into the region of the distribution zone that is situated next to the header rather than through the zones that are further away from the header, and thus to homogenize the distribution of the fluid across the width of the passage 3 of the heat exchanger.
Advantageously, when the distribution element 22 is disposed in the distribution zone 20 of a heat exchanger, the first end 23 is situated by the inlet header 7 of the heat exchanger and forms an inlet for the fluid F1. The first openings 26a in the first end 23 have passage sections for fluid that are variable depending on their position along the lateral direction y.
By virtue of the use of openings 26a with different passage sections, it is notably possible to overfeed the channels that are less favorable to the passage of the fluid, specifically from the inlet of the fluid F1 into the distribution zone 20, this causing fewer pressure drops and thus leading to a more efficient fluid distribution system.
According to an advantageous embodiment of the invention, all or some of the channels 26 comprise means 28 for modifying the linear flow resistance of said channels 26. The linear flow resistance of each channel can thus be adjusted depending on the flow characteristics desired in each channel 26, in particular fluid flow rate and velocity. Thus, the linear flow resistance of the channels can be adjusted such that each channel 26 has a similar overall flow resistance. The characteristics of the fluid at the outlet of the channels 26 are thus homogenized in the lateral direction y, thereby allowing uniform distribution toward or from the heat-exchange zone 21.
The expression “flow resistance” is understood to mean the capability of the channel not only to generate viscous friction but also to divert the flow (pressure force normal to the wall). This resistance is expressed in the form of a reaction force of the solid structure to the flow in newtons, this resulting in the fluid in a pressure drop in pascals. This force depends firstly on the kinetic energy of the fluid (rho*u2) and secondly on the Reynolds number (rho*u*D/mu). The linear flow resistance corresponds to the flow resistance of the channel expressed per unit of length.
Advantageously, a channel 26 will comprise modification means 28 that are configured to produce an increase in the linear flow resistance that is all the greater the closer the opening 26a of said channel is, in terms of distance to be covered by the fluid F1, to the other opening 26b. For example, in the configuration illustrated in
The channels 26 could have internal profiles that are shaped to produce different variations in flow resistance.
Obstacles 28 that produce different flow resistances could also be arranged within one or more channels 26. The insertion of a porous structure 28, for example a metal foam, into a channel will make it possible to increase the flow resistance thereof. The linear flow resistance of the channels 26 could thus be adjusted by varying the characteristics of the inserted structures 28, such as volume, density, etc. in accordance with the channels. In the example illustrated in
According to the example schematically indicated in
As the case may be, the dividing walls 25 and/or the partitions 28 may have, in longitudinal section, rectilinear profiles, as illustrated in
According to a particularly advantageous embodiment, the dividing walls 25 have predetermined curvilinear profiles comprising at least one inflection point P.
Such a geometry makes it possible to divert the fluid more quickly, that is to say over a shorter distance L1, specifically across a great width of the passage of the heat exchanger. It is thus possible to reduce the longitudinal extent of the distribution zone 20 and consequently to increase the mechanical integrity of the heat exchanger since the compactness of what is known as the “weak” zone of the heat exchanger is increased.
This also affords the possibility of reducing the width of the first end 23 of the distribution element 22 and thus the width of the header 7, which is a relatively expensive part. Preferably, the first end 23 forming the inlet or outlet of the distribution element 22 has, in the lateral direction y, a width L3 of between 50 and 1000 mm, more preferably between 100 and 500 mm.
Such profiles also make it possible to reduce the pressure drops within the channels 26, sudden changes in channel profiles being known to bring about fluid recirculations that cause pressure drops.
Preferably, the distribution element 22 has, parallel to the longitudinal direction z, a length L1 less than 500 mm, preferably between 50 and 200 mm, more preferably between 80 and 100 mm. Preferably, the length L1 of the distribution element 22 represents less than 20% of the length of the heat-exchange zone 21. Parallel to the lateral direction y, the distribution element 22 has a width L2, the ratio between a length L1 and the width L2 being less than 20%, preferably between 5 and 10%. The width L2 is preferably between 500 and 1500 mm.
The distribution element 22 is advantageously formed from a metal material, preferably aluminum or an aluminum alloy. The element may be formed in particular from a porous material, preferably with closed pores, for example a metal foam.
Preferably, the distribution element 22 is monolithic, thereby making it possible to minimize incidents along the flow paths of the fluid.
The element 22 may be manufactured using an additive manufacturing method, preferably by thermal spraying, making it possible to produce parts with complex geometries in one piece. In particular, a cold spray method could be used.
It should be noted that the additive manufacturing method can also be referred to as “3D printing”. Additive manufacturing makes it possible to produce a real object using a specific printer, which deposits and/or solidifies material, layer by layer, to obtain the final part. The stack of these layers makes it possible to create a volume.
The element 22 may also be manufactured using the following additive manufacturing methods:
Alternatively, the distribution element 22 may be manufactured by casting. This manufacturing method makes it possible to produce parts with complex geometries at a relatively low cost compared with additive manufacturing. Preferably, the element 22 is formed from an aluminum alloy by casting, that is to say an alloy of which the main constituent is aluminum, with a density lower than intended to be converted by casting techniques.
As regards the heat-exchange zones 21 of the heat exchanger, these advantageously comprise heat-exchange structures 8 disposed between the plates 2, as shown in
Preferably, these structures comprise heat-exchange corrugations 8 which advantageously extend across the width and along the length of the passages of the heat exchanger, parallel to the plates 2. These corrugations 8 may be formed in the form of corrugated sheets. In this case, the corrugation legs that connect the successive tops and bottoms of the corrugation are referred to as “fins”. The heat-exchange structures 8 can also cover other particular shapes defined depending on the desired fluid flow characteristics. More generally, the term “fins” covers blades or other secondary heat-exchange surfaces, which extend from the primary heat-exchange surfaces, that is to say the plates of the heat exchanger, into the passages of the heat exchanger.
Within a passage, the distribution element 22 according to the invention and the heat-exchange structure 8 are preferably juxtaposed along the longitudinal axis z, that is to say positioned end to end. Note that a small clearance can exist between these elements in order not to block the channels of the heat-exchange zone 21 which face the walls 25 of the channels of the distribution zone 22. Preferably, the first end 23 of the element 22 is arranged end to end with at least one part of the header 7, while the second end 24 is arranged end to end with at least one part of the structure 8. Preferably, the structure 8, the header 7 and/or the element 22 are connected by brazing to the plate 2 and are connected indirectly together via their respective connections to the plates 2. Advantageously, the element 22 is assembled on the plates 2 by brazing the support 27 to the plates 2, the support or bottom 27 comprising at least one face coated with a brazing agent. This face is positioned next to a plate 2 so as to form a connecting surface with said plate 2. Alternatively or in addition, the plate 2 entirely or partially have at least one face coated at least partially with a brazing agent layer.
In order to demonstrate the effectiveness of a distribution element 22 according to the invention for uniformly distributing the fluid, fluid flow simulations were carried out with a distribution element according to
The dimensional characteristics of the distribution element 22 were as follows:
As regards the fluid, the simulation parameters were as follows:
The results of these simulations are presented in
Of course, the invention is not limited to the particular examples described and illustrated in the present application. Other variants or embodiments within the competence of a person skilled in the art may also be considered without departing from the scope of the invention. For example, other directions and senses for the flow of the fluids in the heat exchanger are of course conceivable, without departing from the scope of the present invention. A distribution element according to the invention may thus be arranged in any distribution zone of the heat exchanger, in one or more series of passages 3, 4, 5 of the heat exchanger, upstream and/or downstream of one or more of the headers of the heat exchanger. For example,
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1757539 | Aug 2017 | FR | national |
This application is a 371 of International PCT Application No. PCT/FR2018/051804, filed Jul. 16, 2018, which claims priority to French Patent Application No. 1757539, filed Aug. 4, 2017, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/051804 | 7/16/2018 | WO | 00 |
