Patent Description:
Heat exchangers may be employed in conjunction with gas turbine engines. For example, a first fluid at a higher temperature may be passed through a first passageway, while a second fluid at a lower temperature may be passed through a second passageway. The first and second passageways may be in contact or close proximity, allowing heat from the first fluid to be passed to the second fluid. Thus, the temperature of the first fluid may be decreased and the temperature of the second fluid may be increased.

Counter-flow heat exchangers provide a higher efficiency than cross-flow type heat exchangers, and are particularly useful when the temperature differences between the heat exchange media are relatively small. Conventional heat exchangers with a plurality of tubes have drawbacks with regard to the connection and formation of numerous inaccessible tubes with small spacing.

The helical tubes must be arrayed without interruption in order to form a closed helical flow channel and to thereby ensure operation in true countercurrent flow with high efficiency. However, the assembly of tube bundles with contiguous helical tubes and their connection become particularly problematic as the number of tubes increases and were hitherto at best possible with a very small number of helical tubes.

As already mentioned, the manufacture of tube bundles of this type becomes particularly problematic when the number of tubes is increased inasmuch as the connection of the contiguous tubes becomes particularly difficult due to the inaccessibility of the tube ends and therefore is not possible with conventional connecting means. It is further particularly difficult to bend rigid tubes into exactly contiguous coils and to connect them by conventional connecting means.

<CIT> discloses a method of producing a multiple tube heat exchanger, on which the preamble of claim <NUM> is based.

The invention is defined by the subject-matter of the appended claims. A counter-flow heat exchanger is generally provided in accordance with claim <NUM>. In one embodiment, the counter-flow heat exchanger comprises: a first fluid path having a first supply tube connected to a first transition area separating the first fluid path into a first array of first passageways, with the first array of first passageways merging at a first converging area into a first discharge tube; and a second fluid path having a second supply tube connected to a second transition area separating the second fluid path into a second array of second passageways, with the second array of second passageways merge at a second converging area into a second discharge tube. The first passageways and the second passageways have a substantially helical path around the centerline of the counter-flow heat exchanger. Additionally, the first array and the second array are arranged together such that each first passageway is adjacent to at least one second passageway.

In one embodiment, the first transition area is positioned at one end of the helical path to supply a first fluid stream into the first array of first passageways, and wherein the second transition area is configured at an opposite end of the helical path to supply a second fluid stream into the second array of second passageways such that the first fluid stream and the second fluid stream circulate the helical path in opposite directions.

As used herein, a "fluid" may be a gas or a liquid. The present approach is not limited by the types of fluids that are used. In the preferred application, the cooling fluid is fuel, and the cooled fluid is oil. For example, the oil can be cooled from an initial temperature to a discharge temperature, with the discharge temperature being about <NUM>% of the initial temperature or lower (e.g., about <NUM>% to about <NUM>% of the initial temperature). The present approach may be used for other types of liquid and gaseous fluids, where the cooled fluid and the cooling fluid are the same fluids or different fluids. Other examples of the cooled fluid and the cooling fluid include air, hydraulic fluid, combustion gas, refrigerant, refrigerant mixtures, dielectric fluid for cooling avionics or other aircraft electronic systems, water, water-based compounds, water mixed with antifreeze additives (e.g., alcohol or glycol compounds), and any other organic or inorganic heat transfer fluid or fluid blends capable of persistent heat transport at elevated or reduced temperature.

A heat exchanger is generally provided that includes performance-enhancing geometries whose practical implementations are facilitated by additive manufacturing. Although the heat exchanger system described herein is broadly applicable to a variety of heat exchanger applications involving multiple fluid types, it is described herein for its high-effectiveness cooling of an engine oil (e.g., the hot stream) with a fuel (e.g., the cold stream).

Generally, the counter-flow heat exchanger features a pair of single inlet tubes transitioning to multiple helical passage ways then transitioning to single outlet tubes. The multiple passageways generally define non-circular geometries, so as to increase the surface area available for thermal exchange. Advantageously, the counter-flow heat exchanger is formed via additive manufacturing as a single component that requires no additional assembly.

Referring to <FIG> and <FIG>, an exemplary counter-flow heat exchanger <NUM> is generally shown. The heat exchanger <NUM> includes a first fluid path <NUM> and a second fluid path <NUM> that are separated from each other in that the respective fluids do not physically mix with each other. However, heat transfer occurs between the fluids within the first fluid path <NUM> and the second fluid path <NUM> through the surrounding walls as they flow in opposite directions, effectively cooling the hot stream by transferring its heat to the cold stream. It is noted that the first fluid path <NUM> is discussed as containing the hot stream therein, and the second fluid path <NUM> is discussed as containing the cold stream therein. However, it is noted that the first fluid path <NUM> or the second fluid path <NUM> can contained either the hot stream or the cold stream, depending on the particular use. Thus, the following description is not intended to limit the first fluid path <NUM> to the hot stream and the second fluid path <NUM> to the cold stream.

Referring now to the first fluid path <NUM>, a hot inlet <NUM> is shown supplying a hot fluid stream <NUM> into the first fluid path <NUM>. As it enters through the hot inlet <NUM>, the hot fluid stream <NUM> travels through the first supply tube <NUM> to a first transition area <NUM>. The first supply tube <NUM> is generally shown cylindrical (e.g., having a circular cross-section); however, the first supply tube <NUM> can have any suitable geometry for supplying the hot fluid stream <NUM> into the heat exchanger <NUM>.

<FIG> shows that the hot fluid stream <NUM> travels into the first transition area <NUM> and branches into a first array <NUM> of first passageways <NUM>. Specifically, the first transition area <NUM> defines a plurality of branches <NUM> that sequentially separate the first fluid path <NUM> from the first supply tube <NUM> into the first array <NUM> of first passageways <NUM>. The first transition area <NUM> is shown as being an anatomically inspired design in that a single supply tube <NUM> (i.e., an artery) is divided into a plurality of smaller passageways <NUM> (i.e., the veins) that have a different cross-sectional shape.

Referring again to <FIG> and <FIG>, the first array <NUM> of first passageways <NUM> generally follows a helical path around a centerline <NUM> of the heat exchanger <NUM>. Although shown making four passes around the centerline <NUM> (i.e., orbits) in the helical path, any number of orbits may form the helical path. Then, the first array <NUM> of first passageways <NUM> merge at a first converging area <NUM> after following the helical path around the centerline <NUM> into a first discharge tube <NUM>. The first converging area <NUM> is similar to the first transition area <NUM> in that the first array <NUM> of first passageways <NUM> converge back into a single tube that is the first discharge tube <NUM>. Thus, the first converging area <NUM> defines a plurality of merging areas <NUM>. Then, the hot stream <NUM> passes through the first discharge tube <NUM> and out of a first exit <NUM>.

Conversely, the second fluid path <NUM> defines a cold inlet <NUM> that supplies a cold fluid stream <NUM> into the second fluid path <NUM>. As it enters through the cold inlet <NUM>, the cold fluid stream <NUM> travels through the second supply tube <NUM> to a second transition area <NUM>. The second supply tube <NUM> is generally shown generally cylindrical (e.g., having a circular cross-section); however, the second supply tube <NUM> can have any suitable geometry for supplying the cold fluid stream <NUM> into the heat exchanger <NUM>. Similar to the first transition area <NUM> of the first fluid path <NUM>, the second transition area <NUM> of the second flow path <NUM> defines a plurality of forks that sequentially separated the second fluid path <NUM> from the second supply tube <NUM> into a second array <NUM> of second passageways <NUM>. The second array <NUM> of second passageways <NUM> generally follows a helical path around a centerline <NUM> of the heat exchanger <NUM>.

The second array <NUM> of second passageways <NUM> merge at a second converging area <NUM> after following the helical path around the centerline <NUM> into a second discharge tube <NUM>. The second converging area <NUM> is similar to the second transition area <NUM> in that the second array <NUM> of second passageways <NUM> converge back into a single tube that is the second discharge tube <NUM>. Thus, the second converging area <NUM> defines a plurality of merging areas <NUM>. Then, the cold stream <NUM> passes through the second discharge tube <NUM> and out of a second exit <NUM>. As shown, the second discharge tube <NUM> travels through the center of the heat exchanger <NUM> to carry the cold stream <NUM> down the centerline <NUM> prior to passing through the second exit <NUM>.

Through this configuration, the first fluid stream <NUM> and the second fluid stream <NUM> travel in opposite directions in their respective passageways <NUM>, <NUM> in order to have a counter-flow orientation with respect to the direction of flow of the first fluid stream <NUM> and the second fluid stream <NUM> in the helical section <NUM>. However, in an opposite embodiment, the heat exchanger <NUM> can be designed such that the first fluid stream <NUM> and the second fluid stream <NUM> travel in the same direction in their respective passageways <NUM>, <NUM>.

<FIG> and <FIG> show a cross-sectional view in a plane defined by the axial direction DA (that is in the direction of the centerline <NUM>) and the radial direction DR (that is in a direction perpendicular to the centerline <NUM>). This cross-sectional view includes the helical section <NUM> of the heat exchanger <NUM>. Generally, the first array <NUM> and the second array <NUM> are arranged together such that each first passageway <NUM> is adjacent to at least one second passageway <NUM> to allow for thermal exchange therebetween. In the specific embodiment shown, the first array <NUM> in the second array <NUM> are arranged together such that the first passageways <NUM> and the second passageways <NUM> are staggered and alternate moving outwardly in the radial direction (DR) from the centerline <NUM>.

The first passageways <NUM> and the second passageways <NUM> have an elongated shape. As shown, the first passageways <NUM> and the second passageways <NUM> have a length in the axial direction DA that is greater than its width in the radial direction DR. In certain embodiments, the first passageways <NUM> have a length in the axial direction DA that is at least about twice its width in the radial direction DR, such as at least about four times its width. For example, the first passageways <NUM> can have a length in the axial direction DA that is about <NUM> times to about <NUM> times its width in the radial direction DR, such as about <NUM> times to about <NUM> times its width. Similarly, the second passageways <NUM> have a length in the axial direction DA that is at least about twice its width in the radial direction DR, such as at least about four times its width. For example, the second passageways <NUM> can have a length in the axial direction DA that is about <NUM> times to about <NUM> times its width in the radial direction DR, such as about <NUM> times to about <NUM> times its width. As such, the relative contact area between the first passageways <NUM> and adjacent second passageways <NUM> can be maximized by an elongated, common wall therebetween.

The first passageways <NUM> generally define opposite side surfaces 120a, 120b extending generally in the axial direction DA and connected to each other by top wall <NUM> and a bottom wall <NUM>. The opposite side surfaces 120a, 120b have a generally variable radius from the inner centerline <NUM> of the first passageway <NUM>. In the embodiment shown, each of the opposite side surfaces 120a, 120b define a series of waves <NUM> having a peak <NUM> and a valley <NUM> with respect to their distance in the radial direction DR from the inner centerline <NUM> of the first passageway <NUM>. Although the opposite side surfaces 120a, 120b are shown having substantially the same pattern, it is to be understood that the opposite side surfaces 120a, 120b can have independent patterns from each other. In certain embodiments, the side surface 120a has a constantly varying distance in the radial direction DR from the inner centerline <NUM> of the first passageway <NUM>, and the side surface 120b has a constantly varying distance in the radial direction DR from the inner centerline <NUM> of the first passageway <NUM>.

Similarly, the second passageways <NUM> generally define opposite side surfaces 220a, 220b extending generally in the axial direction DA and connected to each other by top wall <NUM> and a bottom wall <NUM>. The opposite side surfaces 220a, 220b have a generally variable radius from the inner centerline <NUM> of the second passageway <NUM>. In the embodiment shown, each of the opposite side surfaces 220a, 220b define a series of waves <NUM> having a peak <NUM> and a valley <NUM> with respect to their distance in the radial direction DR from the inner centerline <NUM> of the second passageway <NUM>. Although the opposite side surfaces 220a, 220b are shown having substantially the same pattern, it is to be understood that the opposite side surfaces 220a, 220b can have independent patterns from each other. In certain embodiments, the side surface 220a has a constantly varying distance in the radial direction DR from the inner centerline <NUM> of the second passageway <NUM>, and the side surface 220b has a constantly varying distance in the radial direction DR from the inner centerline <NUM> of the second passageway <NUM>.

A divider wall <NUM> separates each first passageway <NUM> from adjacent second passageways <NUM>, and physically defines the respective side walls for the first passageway <NUM> and second passageways <NUM>.

Generally, the heat exchanger <NUM> is formed via manufacturing methods using layer-by-layer construction or additive fabrication including, but not limited to, Selective Laser Sintering (SLS), 3D printing, such as by inkjets and laser beams, Stereolithography, Direct Selective Laser Sintering (DSLS), Electron Beam Sintering (EBS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), Laser Net Shape Manufacturing (LNSM), Direct Metal Deposition (DMD), and the like. A metal material is used to form the heat exchanger in one particular embodiment, including but is not limited to: pure metals, nickel alloys, chrome alloys, titanium alloys, aluminum alloys, aluminides, or mixtures thereof.

The heat exchanger <NUM> is shown in <FIG> and <FIG> having an outer wall <NUM> that encases the first fluid path <NUM> and the second fluid path <NUM> of the heat exchanger <NUM>, with the respective inlets and outlet providing respective fluid flow through the outer wall. In one embodiment, the heat exchanger <NUM> is formed as an integrated component. For example, <FIG> and <FIG> show an exemplary heat exchanger system <NUM> formed from a single, integrated component, including the outer wall <NUM>, formed via additive manufacturing.

Claim 1:
A counter-flow heat exchanger (<NUM>) defining a centerline (<NUM>), the counter-flow heat exchanger (<NUM>) comprising:
a first fluid path (<NUM>), wherein the first fluid path (<NUM>) comprises a first supply tube (<NUM>) connected to a first transition area (<NUM>) separating the first fluid path (<NUM>) into a first array (<NUM>) of first passageways (<NUM>), and wherein the first array (<NUM>) of first passageways (<NUM>) merge at a first converging area (<NUM>) into a first discharge tube (<NUM>); and
a second fluid path (<NUM>), wherein the second fluid path (<NUM>) comprises a second supply tube (<NUM>) connected to a second transition area (<NUM>) separating the second fluid path (<NUM>) into a second array (<NUM>) of second passageways (<NUM>), and wherein the second array (<NUM>) of second passageways (<NUM>) merge at a second converging area (<NUM>) into a second discharge tube (<NUM>),
wherein the first passageways (<NUM>) and the second passageways (<NUM>) have a substantially helical path around the centerline (<NUM>) of the counter-flow heat exchanger (<NUM>), and wherein the first array (<NUM>) and the second array (<NUM>) are arranged together such that each first passageway (<NUM>) is adjacent to at least one second passageway (<NUM>), characterized in that the first passageways (<NUM>) and the second passageways (<NUM>) alternate moving outwardly in the radial direction from the centerline (<NUM>), wherein each first passageway (<NUM>) is separated from an adjacent second passageway (<NUM>) by a dividing wall (<NUM>), wherein the dividing wall (<NUM>) has a first surface that defines a side surface of the first passageway (<NUM>) and a second surface that defines a side surface of the second passageway (<NUM>), wherein the first fluid path (<NUM>) and the second fluid path (<NUM>) and an outer wall encasing (<NUM>) are additively manufactured as a single, integrated component.