Heat Exchanger for a High Inflow Velocity

The invention relates to a heat exchanger for cooling a hot fluid, particularly an exhaust or a fuel-cell cooling fluid, by means of a cooling fluid which is at a lower temperature relative to the hot fluid and has a high flow velocity, comprising a high-temperature grille for guiding the hot fluid, and a low-temperature grille for guiding the coolant.

It is a constant endeavor to produce aircraft engines with lower emissions. Conventional technologies have almost reached their limits. Only small steps are still possible; however, a major leap was made recently times by the simultaneous use of gears, which enabled the use of slower fans, and high-speed turbines. In order to further reduce emissions and increase efficiency, work is currently being done on systems for recovering water that rely on the use of heat exchangers and water recovery units to recover water from the exhaust gas. Previous systems relied on solutions with heat exchanger arranged outside the engine. The frontal surfaces of these heat exchangers on their cooling-air side would be much larger than, for example, the cross-section regions of the engine with which they are integrated. For this reason, the integration of such heat exchangers into the aircraft, according to the principle shown in, is difficult or impossible to implement. Increasing the inflow channel area required to reduce the speed would mean very large installation lengths. Furthermore, the required inflow surface of the heat exchangers would result in an increase in the displacement cross-section of the aircraft and thus a large increase in pressure and form resistances.

Cooling requirements are high even in fuel cells, an emerging technology in the field of aircraft engines. The solutions currently available can be further optimized so that a heat exchanger with small space requirements would be advantageous.

Also, heat exchangers operating with cooling fluids at high flow velocities and requiring less space can also be advantageous in other fields.

In this context, a high flow velocity is understood to mean a flow velocity that is typically encountered as inflow velocity in the aviation sector. One can safely assume a speed of greater than 50 m/s. If a heat exchanger is arranged in the bypass flow of the engine, significantly higher flow velocities, in the range of Mach 0.4 to Mach 0.5, can occur.

It is an object of the invention to propose a heat exchanger and a heat exchanger arrangement, which improve heat transfer through a rapidly flowing fluid and/or to minimize the installation space required.

This object is achieved by a heat exchanger having the features of independent claimand by a heat exchanger arrangement having the features of independent claim.

A heat exchanger according to the invention for cooling a hot fluid by means of a cooling fluid that has a lower temperature and a high flow velocity relative to the hot fluid comprises a high-temperature grille for guiding the hot fluid and a low-temperature grille for guiding the cooling fluid. According to the invention, a diffusor region to slow down incoming fluid is arranged in the at least one (preferably several) first low-temperature channel(s) of the low temperature grille through which the cooling fluid flows. Furthermore, according to the invention, the diffusor region and a first high-temperature channel of the high-temperature grille through which the hot fluid flows have at least one common wall for heat transfer. The diffusor region is already involved in the heat transfer because of the common wall, so that valuable installation space can be used in a thermally advantageous manner and in doing so, the size of the heat exchanger can be reduced.

According to one embodiment of the invention, the low-temperature channel can have a deflection region which is arranged upstream of the diffuser region and in which the cooling fluid gets deflected, but does not slow down. In other words, at first the cooling fluid can be deflected with an essentially constant or decreasing cross-sectional area before it enters the diffuser region, wherein the cross-sectional area of the low-temperature channel increases. This enables a change in the direction of the cold fluid flow from the inflow angle to the main slope angle of the low-temperature channel even before it enters the diffuser region. Preferably, the cooling fluid can be accelerated in the deflection region, that is, the cross-sectional area of the deflection region decreases in the flow direction. In a preferred development, the diffuser region can have essentially planar side walls, since the deflection has already taken place in the deflection region.

The heat exchanger can also be designed as a condenser for separating liquids from a gas flowing through the condenser, since the hot fluid can be, in particular, an exhaust gas from a turbomachine such as a gas turbine or an aircraft engine. The hot fluid can also be a coolant of a fuel cell, preferably to support the thermal management of a fuel cell and to be able to cool a fuel cell more efficiently. In particular, compressed air is preferably provided as the cooling fluid. Slowing down of the incoming cooling fluid means a reduction in its flow velocity, so that a cooling fluid flowing in at high speed can advantageously be slowed down to a reduced speed for the greatest possible absorption of heat, thereby reducing pressure losses. The high-temperature grille is, in particular, formed by a plurality of high-temperature channels, which at least comprise the first high-temperature channel. Furthermore, the low-temperature grille is preferably formed by a plurality of low-temperature channels, which comprise at least the first low-temperature channel.

Preferably, the high-temperature grille is arranged in a cross-flow and/or counter-flow configuration relative to the low-temperature grille, at least in sections. In a particularly preferred embodiment, the low-temperature channels and the high-temperature channels are arranged in a cross-flow configuration.

The diffusor region consists of one or more regions that extend into a cross-sectional area of the low-temperature grille through which flow takes place in an inlet cross-section or a minimal cross-section, in particular a minimal inlet cross-section of the diffuser region of the low-temperature channel, in particular a plurality of low-temperature channels, to a downstream cross-section, in particular the main cross-section, of the low temperature channel, which is larger than the inlet cross-section. This reduces the flow velocity of the cooling fluid in each of these regions.

The high-temperature grille and the low-temperature grille each represent a flow space for a fluid, whereby the two grilles, the high-temperature grille and the low temperature grille, can preferably jointly comprise an integral grille body with common walls of the two grilles or can have a grille body comprising common walls of the two grilles. The high-temperature channels and the low-temperature channels are arranged in the grille body. The common walls preferably have at least a minimal distance between the two flow spaces transverse to a respective wall extension. Furthermore, it can be envisaged that the walls have a constant wall thickness, at least in sections.

The common wall can thus be defined in such a way that its first wall side surface forms a part of the low-temperature grille and its second wall side surface facing away from the first wall side surface forms a part of the high-temperature grille. In this way, the first wall side surface extends into the diffuser region. This advantageously increases the heat flow.

In a first embodiment, the heat exchanger is further developed such that the at least one common wall for forming the diffuser region in the first low-temperature channel has a convexly curved first diffuser section. Preferably, the common wall downstream in the low-temperature grille has an adjoining straight main section for forming a main region of the first low-temperature channel with a constant cross section. This enables a change in direction of the cold flow from the inflow angle to the main slope angle of the low-temperature channel.

In another preferred embodiment, wherein a second common wall is arranged in the low-temperature channel opposite the first common wall, which is adjacent to the second high-temperature channel of the high temperature grille in the diffuser region on the wall side facing away from the first low-temperature channel, wherein it is envisaged that the second common wall in the diffusor region has a concavely curved second diffuser section. According to one embodiment, a curvature of the convexly curved first diffuser section may be smaller than a curvature of the second diffuser section or vice versa. The diffuser region and thereby the diffuser sections start, in particular, at the narrowest cross-sectional area of the low-temperature channel, preferably directly behind an inlet of the low-temperature channel.

Accordingly, in another preferred embodiment, an inlet for diverting the cooling fluid into the diffuser region can be arranged upstream of the diffuser region in the direction of flow of the cooling fluid. The inlet is used to direct the fluid from the flow channel into the low-temperature channel. An inlet surface facing away from the wind in the flow channel is advantageously extended, while an inlet surface facing the wind is bent by approximately 180°. The smallest cross-sectional area of the low-temperature channel is preferably located at the end of the bend of the inlet surface facing the wind in the low-temperature channel. At its other end of the bend, the inlet surface facing the wind merges into an inlet surface of an adjacent low-temperature duct facing away from the wind. Ideally, the diffuser region follows the inlet in the direction of flow in the low-pressure channel in order to slow down the flow. As a result, the flow direction of the cooling fluid is advantageously aligned with the flow direction in the diffuser area and the air resistance is reduced.

In order to achieve as ideal a flow as possible through the low-pressure channel, in another embodiment, an outlet region with a discharge nozzle for accelerating the cooling fluid is arranged in the heat exchanger downstream of the diffuser region.

Another aspect of the invention is a heat exchanger arrangement with heat exchanger, in particular, with a heat exchanger described above, comprising a flow channel for the flow of the cooling fluid to the heat exchanger. The heat exchanger is arranged in the flow channel for guiding the cooling fluid, and the low-temperature grille and the high-temperature grille form a first heat exchanger module of the heat exchanger. According to the invention it is envisaged that a plurality of common walls together form a first flow surface in the flow channel that borders the first heat exchanger module and is spanned by the common walls, the flow surface having an flow angle between 0° and 45°, advantageously between −3° and −15°, to a main channel direction of the flow channel. In this way, a particularly uniform flow (with a constant flow velocity) of the heat exchanger and the individual low-temperature channels can advantageously be achieved, which leads to a homogenous flow in each of the low-temperature channels and thus advantageously a homogenous heat flow from the hot fluid to the cooling fluid. The flow channel region in front of the heat exchanger can also be referred to as inflow region, with the main channel direction in this inflow region and the inflow surface forming an inflow angle. The inflow angle is preferably constant along at least part of the extension of the inflow surface. In a supplementary or alternative embodiment, the inflow surface can be curved or angled, with the inflow angle thereby assuming correspondingly different values. The inflow surface is formed by a surface spanned by the heat exchanger, i.e. enveloping it, whereby the surface borders the flow channel upstream and is an auxiliary construction for describing the boundaries of the heat exchanger.

The inflow surface can be planar, curved and/or contorted, in particular in sections, depending on the arrangement of the common walls. Viewed in space, an inflow surface design as a plane has a line contact with each common wall. In a cross-section through the heat exchanger, the contact is reduced to point contacts with the common walls. If the inflow surface is curved, the contact widens accordingly.

In a particularly preferred embodiment of the flow channel, the cross-section of the flow channel decreases in the flow direction in front of the inflow surface along the region occupied by the heat exchanger module. It can thus advantageously be envisaged that at a design point of the heat exchanger, which can be determined, for example, by a cruising speed of the turbomachine enclosing the heat exchanger, the cooling fluid is sucked into the low-temperature grille in layers from one low temperature channel to the next low-temperature channel. This is achieved in particular by the inlet cross-section of a first, more specifically, all low-temperature channel aligned with the main channel direction or perpendicular to it. Preferably, a second inlet of a second low-temperature channel adjacent to the first low-temperature channel and offset to it, can be arranged. As a result, barely any spatial flows arise along the flow in the flow channel, so that the heat exchanger arrangement works is especially efficient.

In a preferred development of the heat exchanger arrangement, a main section of the low-temperature channel with an extension axis borders the diffuser region downstream, particularly straight, wherein the direction of the extension axis, particularly a direction of a wall extension of the common wall in the main region, has a main slope angle of between 0° and 60°, preferably between 30° and 55°, to the flow of the heat exchanger. The extension axis of the main region is preferably a straight line and can, in particular, run parallel to an extension direction of the side surfaces of at least one of the common walls in the main region, in particular, in the flow direction. The main region can preferably have a uniform cross-sectional area along the extension axis perpendicular to the extension axis. In the main region, a large part of the heat transfer takes place between low-temperature grille and the high temperature grille. As the cross-sectional area is uniform along the longitudinal extension, an evenly distributed heat exchanger can be formed and advantageously contribute to the walls of the heat exchanger which is possible to design largely identically and thus cost-effectively. The design has a positive synergistic effect, particularly in a heat exchanger arrangement comprising a heat exchanger with a grille matrix of low and high temperature grilles, the low and high temperature channels, each of which is uniformly designed at least along an extension of the heat exchanger. Furthermore, calculations indicate that designing the main regions at an angle to the inflow surface, in particular, at an angle to the main channel direction, can lead to high flow losses. This is be advantageously avoided according to the invention with the slowing down in the diffuser.

In another embodiment, the heat exchanger arrangement can be developed in such a way that a plurality of common walls together form a first outflow surface in the flow channel that border the first heat exchanger module and is spanned by the common walls, the first outflow surface forming a first outflow angle between 0° and 45°, advantageously between 3° and 15°, to a main channel direction in the flow channel. Thereby, in an advantageous embodiment, the outflow angle of a heat exchanger module corresponds to the inflow angle of this heat exchanger module. However, it can be envisaged that the outflow angle is different from the inflow angle. In an advantageous embodiment, the outflow direction corresponds to the inflow direction and therefore the main channel direction. Preferably, the cross-section of the flow channel increases in the flow direction behind the outflow surface along the area occupied by the heat exchanger module, in particular, to the extent that the cross-section of the flow channel in the flow direction in the front of the inflow surface has decreased.

In addition, an embodiment of the heat exchanger arrangement can be envisaged, whereby the heat exchanger is formed from the first heat exchanger module and another second heat exchanger module, that a further plurality of low-temperature channels form the second heat exchanger module and that a further plurality of common walls together form a second flow surface in the flow channel which borders the second heat exchanger module and is spanned by the common walls, wherein the second flow surface forms a second flow angle between 0° and −45°, advantageously between 3° and 15°, to a main channel direction of the flow channel.

In a preferred embodiment of the heat exchanger arrangement, the additional plurality of common walls together form a second outflow in the flow channel which borders the second heat exchanger module upstream, wherein the second outflow surface forms a second outflow angle 0° and 45°, advantageously between 3° and 15°, to a main channel direction of the flow channel.

In a particularly preferred embodiment of the heat exchanger arrangement, it is envisaged that the first heat exchanger module and the second heat exchanger module are designed to be surface-symmetrical to a common surface between the first and second heat exchanger modules, the surfaces of which run parallel to the main channel direction of the flow channel.

Furthermore, the heat exchanger arrangement can be developed in a preferred embodiment in such a way that part of the flow channel forms a cold channel passing by the heat exchanger. This advantageously allows only part of the available cooling fluid to be used for cooling. In particular, the remaining air in an engine can thus be used immediately to generate thrust.

In a further aspect of the invention, a turbomachine with a bypass channel and a heat exchanger arrangement described above is envisaged, which is characterized by the fact that the flow channel is a bypass channel of the turbomachine and the low-temperature grille is in fluid connection with the bypass channel.

An advantageous development of the turbomachine also has a main flow channel, wherein the high-temperature grille is in fluid connection with a discharge of the main flow channel. This configuration can advantageously support water recovery from the exhaust gas of the turbomachine in a simple way.

Other advantages and features emerge from the following description of some of the preferred embodiments and the dependent claims.

Ina sectional view of a heat exchanger arrangementfrom the prior art is shown which has a heat exchangerwith a low-temperature grilleand a high-temperature grille. The heat exchangeris arranged in a flow channelbetween an inlet surfaceand an outlet surfaceof the flow channel.

The heat exchanger has low-temperature channels in the low-temperature grille, which are formed essentially parallel to the main channel direction, which results in a very large inflow surface. The high-temperature channels run into the plane of section. The large inflow surface, formed perpendicular to the flow direction, also results in high air resistance, in particular pressure resistance and form drag. Such configurations are disadvantageous in that they are usually too large to be effectively arranged in an actual engine, especially when very large cooling air flows are required.

The following are descriptions of the embodiments according to the invention. For the sake of simplicity, the same reference numbers are used in the description of the embodiments according to the invention that follow as in the description of the prior art, since the component names are the same.

shows the sectional view of a heat exchanger arrangementaccording to the invention with a flow channeland a heat exchangeraccording to the invention in the flow channel. The flow channelis arranged in a turbomachine. A cooling fluid flows through the flow channel, wherein the cooling fluid flows into the flow channelthrough an inlet surface, flows through the heat exchangerand, after flowing further through the rear flow channel, exits the flow channelagain at a discharge surface. A main channel directionis indicated by an arrow. In spatial terms, for example, the flow channelcan be rectangular in shape or have a circular ring section shape, wherein the flow channel can be laterally bounded by channel sides. The arrangement of the flow channelcan be repeated, in which case some common sides can also be removed or omitted, resulting in a heat exchanger arrangementhaving several heat exchangers. For example, such a heat exchanger arrangement can extend in the circumferential direction around a core of an engine.

The heat exchangeris formed from an inlet cowl, a grille matrix consisting of a low-temperature grilleand a high-temperature grille, and an outlet cowl. The grille matrix is also referred to below as a heat exchanger module. The low- and high-temperature grilles,described in more detail inare in a cross-flow configuration with respect to each other, i.e. a plurality of low-temperature channelsof the low-temperature grilleand a plurality of high-temperature channelsrun perpendicular to one another. The low-temperature channelsmostly run in the direction of the marked extension axis, while the high-temperature channelsrun in a direction into the drawing plane.shows a side view of the heat exchanger arrangementfrom, in which the directionof the high-temperature channelsis shown schematically with larger arrows. The outlet cowldirects the flow of the cooling fluid trailing downstream of the heat exchanger module.

In general, the heat exchangerhas an inflow surfacewhich is inclined at an angle αto the main channel direction. A more precise definition of the inflow surface is described with the help of. The heat exchangeralso has an outflow surfacewhich is inclined at an angle αto the extended main channel direction. The slope advantageously results in a large inflow surface. Within the heat exchanger, the low-temperature channelsin turn have a main slope angle β to the inflow surfacewhich differs from the angle α. This minimizes the total deflection of the cooling air when flowing through the heat exchanger; in this way the pressure losses are reduced.

The fluid flowing through the flow channelis neither decelerated nor accelerated in the inlet cowl region because—as can be seen from—the cross-sectional area, perpendicular to an axial direction Ax, remains the same in this region. Although the flow channelnarrows in an axial direction Ax inbecause the inlet cowlis already extending into the flow channel, the flow channelwidens in a radial direction R, as can be seen from, which together leads to essentially constant areas of the cross sections perpendicular to the axial direction Ax through the heat exchanger arrangement. While the radial boundary walls can be used to reduce the cross section in order to generate a nozzle flow.

In, the first embodiment of the heat exchanger arrangementfromis shown in a side sectional view, in particular in a meridian section. The flow directionof the high-temperature grille, already mentioned, is shown. In a rear area of the heat exchanger, cross ribsare indicated in the low-temperature grilleand the high-temperature grille, which is a means to provide an enlarged surface for heat exchange.

is an enlarged view of the detailed view A shown in, whereby the actual pathway of the grille matrix of the heat exchangercan be seen. The heat exchangercomprises the low-temperature grille, which consists of a plurality of low-temperature channels, and the high-temperature grille, which consists of a plurality of high-temperature channels. The low-temperature channelseach have an inlet, which serves to introduce and initially deflect the flow of the cooling fluid from the flow channel. In the present embodiment, the inletterminates at a downstream constriction, which serves as an inlet cross-sectioninto a downstream diffuser regionof the low-temperature channel. The size of a cross-sectional area in the diffuser regionincreases steadily along the longitudinal stretch of the diffuser regionup to a maximum cross-sectional areain the present embodiment. Downstream of the diffuser regionis a main regionwhose cross-section is constant along its longitudinal extent. Thus, the maximum cross-sectional area of a constant cross-sectional areais in the main region. Downstream of the main regionis a nozzle regionwhose cross-sectional area decreases from a uniform cross-sectional areato a discharge cross-sectional area, so that the cooling fluid flow accelerates. The speed of the flow of the cooling fluid increases along the flow through the low-temperature channeldue to the heat flow from the high-temperature channel, through which a hot fluid flows that has a higher temperature than the cooling fluid. This further accelerates the flow in the low-temperature channel.

A low-temperature channeland a first high-temperature channeleach have a first common wall. A high-temperature channelis enveloped by a common wall, while a low-temperature channelshares a common first wallwith a first adjacent high-temperature channeland a further second common wallwith a second adjacent high-temperature channel.

The course of the first and second wallsin the sectional plane shown inis described below using the first wall: Starting at the inflow surface, the wallin the inlet regionhas an inlet sectionfacing away from the wind. At the inlet sectionfacing away from the wind, the common wallin the diffuser regionhas a convex diffuser section. Adjoining the diffuser sectionis a first planar main sectionin the main region. Its wall extension is used to determine the main slope angle β. The parallelism of the wall extension in the main sectionand the main extensionof the main regionof the low-temperature channelis shown inby parallel signs. Adjoining the main sectionof the common wall is a concave outlet sectionwhich extends as far as the outflow surface. Facing the first common wall section, a further common wall section is arranged in the low-temperature channel, which has the following course: starting at the inflow surface, the second common wallhas a windward inlet sectionin the inlet region, wherein the windward inlet sectionis rounded and wherein the rounding can extend to the point of the smallest cross-section. Adjoining the inlet section, facing the wind direction, is a concave diffuser sectionin the diffuser section. The curvature of the convex diffuser sectionof the first common wallis greater than the curvature of the concave diffuser sectionof the second common wall, so that the diffuser regionwidens and thus has a continuously increasing cross-sectional area along its longitudinal extent, whereby the flow is advantageously slowed down. The concave diffuser sectionis followed by a second planar main sectionin the main region, which runs parallel to the extension of the first main sectionin the sectional view. The second main sectionis followed by a convex outlet sectionin the discharge region, which extends as far as the outflow surface. In the exemplary embodiment, a high-temperature channelis surrounded by a single common wallof sheet metal, wherein the concave outlet sectionand the convex outlet sectionof the single common wallabut one another and are welded or soldered and thus completely enclose the high-temperature channel.

shows a second embodiment of a heat exchanger arrangement, wherein the circumferential extension of the flow channel, here corresponding to the circumferential extension of the inlet surface, is larger than in the first embodiment, while the size of the heat exchangeris identical to the size in the first embodiment. This splits the flow, with part of the flow flowing into the heat exchangerand part being guided past the heat exchangeras a cold flow. Accordingly, a hot flow channelis created behind the outflow surface of the heat exchanger and a cold flow channelnext to the heat exchanger, the discharge surfaces of which contribute proportionately to a total mass flow.

shows a third embodiment of a heat exchanger arrangement, which in the embodiment is an inversion of the heat exchanger arrangementalong a reflecting surface, which spans in the radial direction R and an axial direction Ax. This creates a V-arrangement of the heat exchanger arrangement, wherein the heat exchanger arrangementhas a first heat exchanger moduleand a second heat exchanger module. The two heat exchanger modules,are connected at the front in the flow direction by a common inlet cowl, but each have their own outlet cowl. The inflow and outflow angles of the inflow and outflow surfaces,can vary depending on the installation situation. It can be envisaged that a first approach angle αof a first approach surfaceis smaller or larger than an approach angle αof a second approach surface. The same applies to the first outflow angle αof the first outflow surfaceand the first outflow angle αof the second outflow surface.

The hot flow channeloriginates from the two outflow surfacesandof the two heat exchanger modules,and traverses between them. The heated cooling gas expands between the outflow cowls. The cold flow channelis a channel section that is routed past the heat exchangeron both sides.

The heat exchanger arrangementdescribed inandcan also be arranged in a repeating pattern, which results, in particular, in a heat exchanger arrangementwith several alternating hot flow channelsand cold flow channels.