Patent Application
20200217596
The present invention relates to a fin body intended for being housed inside a heat exchange tube which is one from among heat exchange tubes showing a planar configuration.
The fin body is configured in the form of a plate, this plate being the one inserted into the heat exchange tube. The plate is configured from a metal sheet bent into a plurality of consecutive bends. Each of the bends extends along a longitudinal direction which will be identified as Z and is oriented, in the operating position, in the longitudinal direction of the exchange tube.
The invention is characterized by the configuration of the plate of the fin body according to a transverse section with respect to direction Z. Throughout the text, the term transverse will be understood to be synonymous to perpendicular.
According to the transverse section, the bends show a profile defining a periodic zigzag wavy path with a characteristic width s and a characteristic height h, both measured on said path.
The wavy path follows the midplane of the metal sheet having a thickness e, so the plate height will be h+e since on one of the faces of the plate the thickness contributes an amount of e/2 to the plate height with respect to the position of the path and another amount of e/2 on the opposite face of the plate. The total height of the plate will be identified as hout, and therefore verifies hout=h+e. In practice, the measurement that can be most readily measured is hout and the thickness e, and they both allow determining h.
Likewise, once the plate has been housed inside the heat exchange tube, the plate is supported on the inner faces thereof such that the bends form channels. The channel height will therefore be hch=h given that it corresponds with the plate height hout minus the thickness of the sheet reducing the amount e into the crest or trough, either when it is in the upper part or when it is in the lower part, respectively.
The same occurs with the characteristic width s. The channel width sch will be reduced by a value e because the channel becomes narrower by one amount e/2 on one side of the channel and by another amount e/2 on the other side of the channel. In other words, sch=s−e.
The characteristic width s used for determining sch is defined throughout this description as half the wavelength of the wavy path and the characteristic height h used for determining hch is defined as the distance between peaks of maximum amplitude of the wavy path.
Throughout the description, the properties of the plate expressed, for example, by means of correlations of efficiency or a pressure drop will be established from the channel width sch and plate height hout unless it is explicitly specified that they are other variables.
The invention is characterized by a range of the channel width sch to plate height hout ratio in the interval of 0.15-0.5, and according to more specific cases, in the lower subranges. As a result, the fin gives rise to a heat exchange tube with a higher efficiency than fins known in the state of the art without penalizing the pressure drop.
One of the fields of the art that has been subjected to the most intensive development is the field of heat exchangers, particularly those used in vehicles with internal combustion engines. There is very little space available in the engine compartment and the heat exchange requirements call for devices that are very compact and therefore offer an increasingly higher ratio between the heat that is exchanged and the volume taken up by the device.
One of the specific cases of interest are heat exchangers intended for reducing the temperature of hot exhaust gases by transferring heat to a liquid coolant. Heat exchangers of this type are found in exhaust gas recirculation (EGR) systems.
Another field of application of interest are heat recuperators where heat is transferred to a second fluid which allows making subsequent use of the heat extracted from the hot gas. Likewise, other applications are exchangers for acclimatizing or controlling the temperature of the vehicle.
To increase this ratio, heat exchange tube configurations which increase heat transfer between the hot gas circulating through the inside thereof and the liquid coolant circulating on the outside of the tube are being developed.
Various methods are known for generating turbulence inside the tube and at the same time increasing the area of contact with the gas, for example, by means of inwardly projecting fins or ribs on the surface of the tube.
Greater turbulence generates flow structures which increase convection between the tube surfaces and gas. The total heat flow will be greater if, in addition to higher heat convection, the available exchange area is increased.
Nevertheless, not just any configuration which increases turbulence and the exchange area will do because the inclusion of fins or elements projecting into the tube cause a pressure drop that may not be acceptable.
The technical problem to be solved is that of providing an exchange tube configuration and elements which increase heat exchange in the exchange tube without penalizing the pressure drop or with the pressure drop being minimal.
Another significant limitation in the configuration of a heat exchange tube is the manufacturability. The configuration of metal structures with multiple folds or deformations with very small characteristic dimensions may limit manufacturability. This is the case of the use of sheets with folds which require a very large number of folds and also with very small radii of curvature. The result can be a configuration which breaks during manufacture.
The present invention solves the technical problem being considered by proposing designs that are close to the limits of manufacturability which, although possible, are hard to achieve, and which a designer tends to not use. These designs are characterized by a wavy aspect ratio in a very narrow range of values where it has been experimentally proven that, far from what was expected, efficiency values that are surprisingly higher than those obtained in the state of the art and with low pressure drops have been obtained.
The invention relates to a fin body intended to be housed inside a heat exchange tube having a planar configuration. Once the fin body has been housed therein, the heat exchange tube is provided with fins considerably increasing the heat exchange area when hot gas flows through the inside thereof in the operating mode.
The configuration of the heat exchange tube is a constraint because by housing the fin body therein, the tube has walls closing the space where said fin body is housed and the attachment between both elements is established in these inner walls. Specifically, the attachment is established on the faces of the exchange tube which are shown as planar inner faces, parallel to and facing one another.
The heat exchange tube extends along a longitudinal direction which will be identified throughout the text as X-X′. As indicated, the exchange tubes have a planar configuration comprising two planar inner faces, parallel to and facing one another. In the preferred embodiment, the planar faces will have a pre-established constant width and are connected on the sides through a straight or curved wall.
The fin body is configured in the form of a plate and formed from a metal sheet having a thickness e, bent into a plurality of consecutive bends extending according to a direction Z, where the direction Z is intended for being parallel to the longitudinal direction X-X′ of the heat exchange tube housing it.
The fin body is a planar plate configured from a metal sheet with a specific width configured for enabling the housing thereof in the heat exchange tube and also a length suited to the length of the heat exchange tube. The plate height is achieved by means of folds of the metal sheet. By way of example, a method for manufacturing this sheet is by stamping between two molds, or according to a second example, the method is a continuous method, by rolling the metal sheet between two rollers with opposite or complementary configurations.
The bends of the sheet give rise to the fin plate height. The height is identified as defined in the description above as “hout” and is different from and strictly greater than the value of the thickness of the metal sheet which will be identified with the letter “e”.
The bends of the plurality of bends are parallel to one another, both when they are straight bends and when they are curved wavy shapes, and extend along a direction which has been identified as direction Z. This direction is the longitudinal direction of the tube when the fin body is operatively housed inside the tube. If the plurality of bends has a wavy generatrix, the direction Z is the direction in which said generatrix extends. A specific case of a wavy generatrix is a sine wave. The direction Z will be the axis around which the sine wave oscillates.
Additionally, the bends are configured by alternating between a first plane P1 and a second plane P2 parallel to the first plane P1, and with both planes being spaced from one another, wherein the first plane P1 and the second plane P2 are intended to coincide with the planar inner faces of the heat exchange tube, parallel to and facing one another;
The bends give rise to a constant height hout in the entire plate and are limited between two parallel planes identified as P1 and P2. This condition allows the plate to be housed inside the heat exchange tube having a planar configuration, such that the plate is in contact with its parallel inner faces. Once the fin body has been housed inside the tube, both components can be attached by means of welding, for example.
With respect to the configuration of the bends, according to a transverse section PT with respect to direction z, said bends show a periodic zigzag wavy path, wherein
Once the direction Z along which the bends extend has been established, this condition is applied to the configuration of the fin body considering the transverse section PT with respect to said direction Z. Transverse section PT is understood to be the section according to a plane perpendicular to direction Z.
The transverse section PT of the fin body formed by bends results in a wavy path. The two different wavy shapes that appear throughout the description must be differentiated:
To distinguish one wavy shape from another, the term “longitudinal wavy shape” will be used in the description for the first wavy shape, or it will be associated with direction Z. For the second wavy shape, either the term “longitudinal” is excluded or the wavy shape is associated with transverse section PT.
According to the invention, the fin body is characterized in that the wavy path according to the transverse section PT has a channel width sch to plate height hout ratio in the interval of [0.15-0.5], wherein sch=s−e and hout=h+e.
It has been found that in this range of values, the efficiency of heat transfer between the hot gas circulating through a planar heat exchange tube housing the fin body and a liquid coolant circulating on the outside of the same tube is higher than the efficiency of the same tubes when they incorporate fins configured according to the state of the art for the same conditions.
Efficiency (Eff) is defined as:
where Tog is the gas outlet temperature, Tig is the gas inlet temperature, and Tic is the liquid coolant inlet temperature.
Making use of this definition, in a series of experiments performed with a collection of tubes representing the state of the art, it has been verified that efficiency values of about 92% have been obtained under specific conditions, such as flow rate, temperature, and geometric parameters that are common to all the experiments, where this value is shown as a barrier that has not been overcome, and making use of a configuration according to the invention, these values increase at least by about 3% until reaching an increase of 5% giving rise to an efficiency of 97%, values which are not possible in any of the tubes of the state of the art while maintaining similar pressure drop values. It is observed that these increases mean surpassing even more than 50% of the percentage up to the theoretical limit of 100%. Exceeding by 3% the efficiency barrier established at 92% entails an efficiency improvement which was not expected by only modifying the shape of the fin body.
The foregoing and other features and advantages of the invention will become more apparent based on the following detailed description of a preferred embodiment given only by way of illustrative and non-limiting example in reference to the attached drawings.
According to the first inventive aspect, the present invention relates to a fin body suitable for being inserted in a heat exchange tube having a planar configuration. The heat exchange tube with the fin body is particularly suitable for heat exchangers which transfer heat energy between a hot gas and a liquid coolant. It is indicated as suitable because the use of the fin body is not limited to this application, such that the fluids transferring heat energy may be other fluids.
In the operating mode, the heat exchange tube is housed in a chamber through which the liquid coolant flows. The hot gas flows through the inside of the heat exchange tube and transfers part of the heat energy to the tube, and the heat exchange tube in turn transfers the same heat energy to the liquid coolant. Heat transfer from the hot gas to the tube is considerably increased due to the increase of the exchange surface due to the presence of the fin body.
The fin body, once inserted in the exchange tube and attached thereto, gives rise to a set of channels (CH) extending along the longitudinal direction X-X′ of the tube, guiding the hot gas flow, generating turbulence and offering a larger exchange area.
The configuration of the channels (CH) increases the area of exchange with the hot gas but also increases the pressure drop, so the configuration that these channels must have in order to increase efficiency without a significant pressure drop is not obvious.
The fin body (1) is in the form of a plate having a height hout, this height being obtained by means of a plurality of bends of the metal sheet. The front part, according to the orientation used in
This fist wavy shape according to the transverse section PT defines a path (T) having a zigzag configuration. The path (T) follows the midplane of the metal sheet, and it is shown in
The bends of the metal sheet are demarcated between a first plane P1 and a second plane P2 limiting the main faces of the fin body (1) in the form of a plate.
In the first embodiment, the fist wavy shape shows vertices (1.2) at the ends corresponding to the contact points of the sheet with the planes P1 and P2. The vertices (1.2) are connected by means of segments (1.1). These segments (1.1) have a straight central part perpendicular to planes P1 and P2, and the ends (1.3) of these segments (1.1) directly connecting with the vertices (1.2) are curved ends. A way of expressing that the straight central part is perpendicular to planes P1 and P2 is by asserting that such central parts are parallel to the normal to any of the planes P1 and P2.
As a result, the path (T) of the fist wavy shape is periodic and allows defining a characteristic distance which, in this description, is referred to as characteristic width (s), and corresponds to half the period of the path (T) of the fist wavy shape.
It can be observed in
The thickness reduces the characteristic width by an amount of e/2 on each of the sides of the channel (CH), giving rise to a smaller channel width sch. Although the configuration of the wavy path (T) of
The present invention is characterized by a first mode of configuring this first embodiment, where the channel width (sch) to plate height (hout) ratio is in the interval of [0.15-0.5]. It has been found that in this interval, efficiency exceeds the value by 3.7% with respect to the best designs of the state of the art.
A narrower range, i.e., the interval of [0.3-0.45], has been found, where the efficiency (Eff) of the exchange tube (2) to which there has been incorporated the fin body (1) configured according to this interval exceeds the value by 4.5% with respect to the best designs of the state of the art.
An even narrower interval of [0.35-0.36] has been found, where the efficiency (Eff) of the exchange tube (2) is maximum, even being 5% greater than that obtained by the best designs of the state of the art.
These conditions imposed on the channel width (sch) to plate height (hout) ratio are valid for any of the configurations of the fin body (1) that will be described based on other embodiments.
In this same
According to another embodiment, the fin body (1) only shows the first wavy shape given that the bends are straight according to direction Z.
According to another embodiment, a straight segment parallel to any of the planes (P1, P2) is placed in the position of the vertices (1.2) for increasing the welding area with the tube intended for housing the fin body (1).
The heat exchange tube (2) extends according to a longitudinal direction which is identified as X-X′. Once the fin body (1) has been housed, the direction Z along which the plurality of bends extends is parallel to direction X-X′ of the heat exchange tube (2).
The heat exchange tube (2) shows a first planar inner face (2.1) which is shown in the lower part according to the orientation of
In this same embodiment, the heat exchange tube (2) shows a plurality of punched spots (2.3) which assure the position of the fin body (1) with respect to the heat exchange tube (2) before carrying out the welding step. The punched spots (2.3) generate inner projections or protrusions which coincide with some channels (CH) of the bends of the fin body (1).
In this same
According to one embodiment, the longitudinal wavy path has an r/p ratio between the minimum characteristic radius (r) of the wavy shape, defined as the minimum radius of curvature measured in a projection according to a plane parallel to plane P1 or P2, and the pitch (p) that is smaller than 2, defined as the entire length of a wave of the wavy shape also measured on the same plane, more preferably in the interval of [0.2-1], and more preferably in the interval of [0.4 and 0.5]. Both measurements are depicted in
In the embodiment shown in
The wavy path (T) shows a periodic wave configuration formed by segments (1.1) connected by alternately located vertices (1.2). As a result, the bends of the plate of the fin body (1) are limited between an upper plane (P1) and a lower plane (P2), and where the wavy path (T) has in its intermediate part straight and oblique segments.
A rectangle has been depicted with a thick dotted line on the perspective view of the fin body (1), said rectangle identifying a portion of the drawing that has been enlarged in the top right part. The thickness e of the metal sheet and the manner in which the path (T) of the fist wavy shape is configured according to the transverse section according to the plane PT can be seen in this enlarged area. Given that the thickness e is small,
The path (T) is mainly formed by the straight and oblique intermediate parts of the segments (1.1) connected by vertices (1.2). These straight intermediate parts are connected at the vertex (1.2) by means of a curved portion (1.3). In the enlarged portion of
The trace of the midplane (PM) where the characteristic width (s) can be determined is identified with a discontinuous line both in the fin body (1) and in the enlarged area.
In this embodiment, the attachment between the fin body (1) and the inner face (2.1, 2.2) of the heat exchange tube (2) is performed through the generatrix that goes through the vertex of the bend (V) coinciding with the vertex (1.2) of the wavy path (T). The vertex of the bend (V) is distinguished from the vertex (1.2) of the path (T) as graphically shown in
The presence of the meniscus (M) gives rise to an increase of the contact area for improving attachment between the fin body (1) and the heat exchange tube (2), and also a higher heat transfer by conduction through said meniscus (M).
It has been found that this configuration gives rise to higher efficiency values, particularly when the channel width (sch) to plate height (hout) ratio is in the interval of [0.35-0.36], and to a minimum pressure drop.
Another aspect of the invention relates to a heat exchange tube (2) having a planar configuration and extending along a longitudinal direction X-X′ and with at least two planar inner faces (2.1, 2.2), parallel to and facing one another, said tube comprising a fin body (1) according to any of the embodiments described above housed therein, wherein the fin body (1) is oriented such that:
According to another embodiment, the tube (2) is formed by the consecutive stacking of stamped and stacked sheets (this configuration of heat exchangers is identified as stacked coolers). According to the invention, a tube configuration formed by the stacking of sheets gives rise to an inner space with planar faces parallel to and spaced apart from one another which is also occupied by the fin body (1) according to any of the described embodiments.
A specific way to perform attachment by brazing for any of the described examples of heat exchange tubes (2) and fin body (1) is by means of a nickel brazing sheet which is interposed between the fin body (1) and the inner face (2.1, 2.2) of the heat exchange tube (2) before being passed through the oven.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18382793.0 | Nov 2018 | EP | regional |
