Tube in cross-flow conduit heat exchanger

A heat exchanger that includes an input cavity defined by inlet cavity walls; a heat exchanger portion in fluid communication with the input cavity and defined between a first side and a second side, and wherein a plurality of baffles are positioned within the heat exchanger portion; and an outlet cavity in fluid communication with the heat exchanger portion and defined by outlet cavity walls. The heat exchanger portion comprises: a plurality of first fluid paths defined between the baffles and extending from the input cavity to the outlet cavity, and a plurality of tubes extending through the heat exchanger portion from the first side to the second side. Each tube extends through the baffles so as to define a second fluid path through the heat exchanger portion. Heat exchanger systems are also generally provided, along with methods for cooling a hot fluid input with a heat exchanger.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger system that uses a cooling fluid flowing in tubes with the hot fluid path flowing through a conduit and routed in cross-flow over the exterior of the tubes.

BACKGROUND OF THE INVENTION

In an aircraft design, a continuous flow of hot air is bled from one part of a gas turbine engine, cooled, and provided to a specific user application. A heat exchanger system may be used to cool the hot bleed air.

The preferred medium for cooling hot bleed air is engine bypass air that flows through the gas turbine fan duct. There are several limitations on the design of the heat exchanger system that exchanges heat between the bleed air and the bypass air. The inlet manifold that brings the hot bleed air to the heat exchanger, the heat exchanger itself, and the outlet manifold that transports the cooled bleed air away from the heat exchanger cannot together impose too great a pressure drop, or the cooled bleed air that reaches the user application will have insufficient pressure to perform properly. The heat exchanger itself cannot impose too great a pressure drop on the engine bypass air flowing through the fan duct, or the bypass air will have insufficient pressure to perform properly. Weight and size also impose tight limitations. As with all aircraft structures, it is important to keep the weight of heat exchanger system as low as possible. The heat exchanger system also cannot significantly increase the envelope size of the gas turbine engine, and desirably is as small as possible to leave installation space for other aircraft systems.

Deflections and dimensional changes are potential concerns in the heat exchanger. The deflections result from two sources. The components of the heat exchanger deflect due to the pressure and vibratory mechanical loadings that occur as the gas turbine engine is powered. The components of the engine and heat exchanger also change size as their temperatures vary during use. These dimensional changes must be accounted for in the heat exchanger structure, or otherwise the resulting stresses and strains would lead to premature failure of the heat exchanger unit. The thermally induced stresses and strains are particularly a concern for the heat exchanger system, where gases of different temperatures are in close proximity, and the relative temperature of the gases changes over time.

There is a need for a compact, lightweight heat exchanger system that cools the flow of hot bleed air.

BRIEF DESCRIPTION OF THE INVENTION

A heat exchanger is generally provided that includes, in one embodiment, an input cavity defined by inlet cavity walls; a heat exchanger portion in fluid communication with the input cavity and defined between a first side and a second side, and wherein a plurality of baffles are positioned within the heat exchanger portion; and an outlet cavity in fluid communication with the heat exchanger portion and defined by outlet cavity walls. The heat exchanger portion comprises: a plurality of first fluid paths defined between the baffles and extending from the input cavity to the outlet cavity, and a plurality of tubes extending through the heat exchanger portion from the first side to the second side. Each tube extends through the baffles so as to define a second fluid path through the heat exchanger portion.

Heat exchanger systems are also generally provided. In one embodiment, the heat exchanger system comprises at least two heat exchangers (such as described above) serially connected to each other with respect to the first flow path and serially connected to each other with respect to the second flow path.

Methods are generally provided for cooling a hot fluid input with a heat exchanger. In one embodiment, the method comprising: directing the hot fluid input into an input cavity defined by inlet cavity walls; directing the hot fluid input into a heat exchanger portion in fluid communication with the input cavity and defined between a first side and a second side; directing the hot fluid input into an outlet cavity in fluid communication with the heat exchanger portion and defined by outlet cavity walls; and directing a cooling fluid through a plurality of tubes extending through the heat exchanger portion from the first side to the second side. A plurality of baffles are positioned within the heat exchanger portion, with a plurality of first fluid paths defined between the baffles. Each tube extends through the baffles so as to define a second fluid path through the heat exchanger portion.

DETAILED DESCRIPTION OF THE INVENTION

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 air, and the cooled fluid is air. 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 hydraulic fluid, fuel, oil, 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 temperature.

A heat exchanger system 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 jet engine compressor bleed air flow by lower pressure fan duct air flow.

A recurring physics-based design challenge is that the prevailing thermodynamic state and flow conditions typically cause the external heat-sinking flow to be the heat transfer-limiting flow, not the hot pressurized bleed air which conventionally flows inside the heat exchanger. Because the fan air temperature and density are relatively low compared to the compressor bleed air, the fan air convection heat transfer coefficients tend to be relatively low, particularly at high altitude operating conditions, and there also tends to be more fan air temperature rise per unit of heat absorbed. The relatively greater temperature rise along the fan air flow reduces the differential temperature potential for cooling the compressor bleed air. Combined, both affects conspire to limit heat exchanger effectiveness per unit of surface area wetted by the fan air flow. Effectiveness increases with surface area, but the improvement diminishes asymptotically such that heat exchanger size increments become impractical and outlet pressure decrements become untenable.

However, the heat exchanger system described herein overcomes that limitation in a variety of ways. First, the heat exchanger has a geometric topology inversion in which the cooling air flow transits the heat exchanger interior within tubes while the cooled air flow is external to the tubes. Second, the heat exchanger is an additive-facilitated, fully open, well-regimented cellular geometry (see e.g.,FIG. 2B) characterized by high surface area to volume ratio with tailored flow constrictions. Combined, both of these features compensate for the relatively low heat sinking capacity of the fan flow by establishing a compact heat transfer surface array facilitating enhanced convection rates on both cooled and heated sides.

FIG. 1Aschematically represents a heat exchanger system5, according to one exemplary embodiment, including a heat exchanger10. Hot air input12enters the system10via an inlet manifold14and exits the system10via an outlet manifold16as cooled air output18. The hot air input12is typically bled from a portion of the engine core, where it is available at the temperature and pressure of interest. Generally, the pressure of the hot air flow through and out of the heat exchanger system10can be controlled so as to reduce the pressure drop of the hot air input12to the cooled air output18.

In the embodiment shown, the heat exchanger10includes an input cavity20in fluid communication with the inlet manifold14such that the hot air input12flows into the input cavity20upon entering the heat exchanger10. From the input cavity20, the hot air flows into and through a heat exchanger portion22to reduce the temperature of the hot air input. Then, the cooled air output18flows into an outlet cavity24before exiting the heat exchanger10via the outlet manifold16.

The heat exchanger portion22includes a plurality of high pressure paths26defined between baffles28and extending from the input cavity20to the outlet cavity24. The baffles28provide structural support for the heat exchange portion22including the conduit and the tubes42. The high pressure paths26allow the hot air input12to flow through the heat exchanger portion22to be converted to the cooled air output16. Cooling is achieved utilizing a cooling fluid30passing through the heat exchanger portion22via the low pressure cooling flow paths32(FIGS. 1B and 1C) that extend from a first side34to a second side36of the heat exchanger portion22. As such, the cooling fluid30flows through the heat exchanger portion22perpendicular to the high pressure paths26and the baffles28. The cooling air30can be from any source having a temperature and pressure that are lower than the hot air input12. For example, the cooling air30can be sourced from bypass air, FLADE air, or compressor air bleed (such as from a low pressure stage).

As shown inFIGS. 1B and 1C, the cooling flow paths32are defined from the tube inlet38defined in the first side34to an oppositely positioned tube outlet40defined in the second side36. A tube42extends from the tube inlet38defined in the first side34through the entire length of the heat exchanger portion22to the tube outlet40defined in the second side36. The tube42serves as a passage for the cooling fluid30to flow through the cooling flow path32from the tube inlet38to the tube outlet40.FIG. 1Cshows that the tube42extends through the internal baffles28defining the high pressure paths26. That is, the internal baffles28also define cavities allowing the tubes42to extend therethrough.

As stated, the high pressure paths26are defined by the internal space between the baffles28and extend from the input cavity20to the outlet cavity24with the tubes42extending through the high pressure paths26without preventing flow therethrough. Thus, the hot air passing through the high pressure paths26contacts the external surface of the tube wall44of the tubes42, allowing for heat exchange between the hot air of the high pressure path26and the cooling fluid30within the cooling flow path32defined by the tube42, while preventing any fluid mixing between the high pressure paths26and the cooling fluid30.

Referring toFIG. 1E, another embodiment of the heat exchanger portion22with variable diameter size tubes42. In the embodiment shown, the cooling flow paths32expand in average diameter from the tube inlet38defined in the first side34to the tube outlet40defined in the second side36. The expanding area of the tube42can, in particular embodiments, slow the flow of the cooling fluid30through the cooling flow paths32. Although shown as a constantly expanding tube42(e.g., having a conical shape), any suitable expansion shape can be utilized (e.g., stepped, piecewise linear, curvilinear, etc.). In alternative embodiments, the tubes42can change in average diameter from the tube inlet38defined in the first side34to the tube outlet40defined in the second side36, according to a continuously variable shape profile.

The embodiment shown inFIG. 1Ehas the tubes42expanding on its elongated, major axis (perpendicular to the cooling path30and parallel with the direction of flow of the high pressure path26from inlet manifold14to outlet manifold16) and optionally also on its minor axis (perpendicular to the cooling path30and to the direction of flow of the high pressure path26from inlet manifold14to outlet manifold16.

FIG. 1Fshows an embodiment of the heat exchanger portion22with variable diameter size tubes40and variable size baffles28with respect to their thickness. In the embodiment shown, the baffles28have an increasing thickness in the direction of the flow of the high pressure path26, thus decreasing the volume of the high pressure path26from the input cavity20to the outlet cavity24. That is, the flow cross-sectional area of the high pressure path26at the input cavity20does not equal the flow cross-sectional area of the high pressure path26at the output cavity24, which is smaller than the flow cross-sectional area of the high pressure path26at the input cavity20as shown in the embodiment ofFIG. 1F. As shown, each baffle28defines an inlet cross-section area at the inlet cavity and an outlet cross-section area at the outlet cavity, with the inlet cross-section area being different (i.e., larger) than the outlet cross-section area.

FIG. 1Falso shows that the heat exchanger portion22includes at least one composite baffle47formed from a core48and skin layers49. As such, different materials can be layered to form the baffles28as the composite laminate construction comprised of one or more heat-shunting, high thermal conductivity inner core layer(s)48sandwiched amongst outer skin layers49comprised of the same higher strength lower thermal conductivity material as the tube walls44. For example, the composite baffles47can be made of a bi-metallic composition. In addition, mass diffusion barriers may also be inserted between the skin layers49and the core layer(s)48. In addition to additive methods, the inner core layer may be established by a variety of film coating methods such as cold spray, thermal spray, plasma spray, chemical vapor deposition, sputtering, or plating. Material options include, but are not limited to, diamond, boron nitride, noble metals, bronze alloys, or mixtures thereof.

The tubes40can define a substantially straight cooling flow path32through the heat exchanger portion22. In other embodiments, the tubes40can define a non-straight cooling flow path32(e.g., bent, curved, looped, helical, serpentine, sinusoidal, etc.).

In one embodiment, as shown inFIG. 9, the cooling fluid30acan first enter an input cavity92via input supply94prior to flowing through cooling flow paths32defined within the tubes40. Additionally, the exiting cooling fluid30bcan first enter an output cavity96and exit via output supply98. Such embodiments are particularly useful when the cooling fluid is redirected into and through the heat exchanger portion22and/or for a liquid cooling fluid.

Generally, the heat exchanger10, and particularly the heat exchanger portion22, 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. Materials used to form the heat exchanger include (but are not limited to): pure metals, nickel alloys, chrome alloys, titanium alloys, aluminum alloys, aluminides, or mixtures thereof. As stated, the baffles28can be constructed from a material pairing(s) so as to enhance the heat exchange properties of the tubes42by augmenting the fin effect of the baffles

As stated, the cooling air26passing through the cooling flow paths32is at a pressure that is less than the pressure of the hot air passing through the high pressure paths26. The tubes42are reinforced by the integral baffles28to inhibit and prevent collapsing of the cooling flow paths32. The substantially oval shape of the tubes42(from the tube inlet38to the tube outlet40) enables higher surface area per unit pressure drop of the exterior flow. However, other shapes can be utilized to form the cross-section of the tubes42, including, but not limited to, circles, squares, rectangles, triangles, pentagons, hexagons, etc.

In particular embodiments, such as shown inFIG. 1D, a flow turbulating element46can be positioned on the internal and/or external surface of the tube wall44to turbulate fluid flow through, respectively, the low pressure cooling path32and/or the high pressure path26. The flow turbulating element46can be any suitable structure, such as a step, flange, swirler, spine, fin, concave dimple, convex dimple, vane, winglet, helical ridge, helical groove, etc.

In one embodiment, the heat exchanger10is formed from an integrated component. For example,FIGS. 2A and 2Bshow an exemplary heat exchanger system10formed from a single, integrated component50that includes each of the inlet manifold14, input cavity20, heat exchanger portion22, output cavity24, and outlet manifold16such that the hot air flow direction15is perpendicular to the low pressure cooling paths32defined by the tubes42. The heat exchanger10ofFIG. 2Ais shown as an integrated component50formed via additive manufacturing. As shown, the heat exchanger system10of this embodiment has a curved shape for use as a part of a gas turbine engine such as the annular FLADE™ bypass air duct. As such, bypass air can be utilized as the cooling air30. In other applications, the cooled fluid may be a liquid which flows within the conduit such that the bypass air also can be utilized as the cooling air30. In this embodiment, the hot air input12may be bleed air from the engine.

As used herein, the term “conduit” refers to the outer containment structure defined by the single, integrated component50through which, for example, the high pressure path26is routed in cross-flow over the exterior of the tubes40that contain the low pressure cooling path.

The embodiment ofFIG. 2Ashows an air-to-air example, where the inputs of both the high pressure paths26and the low pressure cooling paths30are gaseous. For example, the high pressure paths26is sourced from bleed air from the engine, while the low pressure cooling paths30is sourced from FLADE air.

The top surface52and the bottom surface54of the integrated component50are textured to define peaks56and valleys58that generally correspond to the positioning and pattern of the tubes42therein. The texture surfaces52,54(formed from the alternating peaks56and valleys58) serve two functions. First and foremost, the textured surfaces52,54reduce mal-distribution of the flow across the exterior surfaces of those tubes proximal to the conduit wall. That is, the textured surfaces52,54create a more uniform flow path around all of the tubes. Otherwise, there is a tendency for the hot air to flow along the shell walls and degrade performance of the heat exchanger. Second, the textured surfaces52,54provide a derivative benefit in that it supplementally reinforces (stiffens) the relatively large surfaces52,54against outward deflection caused by the relatively high internal pressure within the high pressure flow path26.

FIG. 2Cshows a cross-section of the exemplary heat exchanger system10ofFIG. 2A, according to one embodiment. As shown, at least one composite baffle47can be included, with a core48and skin layers49as discussed above. Additionally, to reduce weight, the cooling path32can be contracting in size from the first side34to the second side36. Due to this contracting size of the cooling paths32, and thus of the flow cross-sectional area of the tubes42, the baffles28can be spaced at an increasing distance apart from the first side34to the second side36in one embodiment such that the volume of the high pressure paths26can be controlled (e.g., made to be substantially equal) even though the tubes42are smaller and spaced closer nearer the second side36than the first side34.

FIGS. 3A and 3Bshow another exemplary embodiment of a heat exchanger system10formed from an integrated component60. In this embodiment, the external wall21of the input cavity20and the external wall25of the output cavity24are texturized with peaks56and valleys58. The textured nature of the external wall21and the external wall25reinforces the input cavity20and the output cavity24, respectively, against outward deflection caused by the relatively high internal pressure within the input cavity20and the output cavity24forming the high pressure flow path26.

FIG. 3Balso shows cavity baffles17in both the input cavity20and the output cavity24. The cavity baffles17define apertures19therein to allow fluid flow and mixing within the cavities20,24while still providing strength to the overall structures. In one embodiment, the cavity baffles17can be connected to and parallel with the baffles26as an extension thereof. Additionally, the cavity baffles17can be constructed to direct flow into and out of the heat exchanger portion22.

FIGS. 4A-4Cshow another exemplary embodiment of a heat exchanger system10formed from an integrated component70. The side wall72and side wall74define dimples74to create flow turbulation topology within the high pressure flow path26and to reinforce the relatively large side walls72,74against outward deflection caused by the relatively high internal pressure within the high pressure flow path26. Additionally, the dimples74also turbulate an external cool air flow around the side walls72,74for additional heat exchange between the high pressure flow paths26through the external walls of the integrated component70and the external cool air flow passing outside of the integrated component70. The external wall21of the input cavity20and the external wall25of the output cavity24include structural flanges78for reinforcement against outward deflection caused by the relatively high internal pressure within the input cavity20and output cavity24, respectively.

As seen from the various embodiments, the shape of the heat exchanger10can be varied, along with the orientation of the inlet manifold14into the input cavity20can be any suitable direction as long as the high pressure flow path26and the low pressure cooling path are perpendicular to each other. However, flow path crossing angles other than 90 degrees are not precluded. Additionally, the structural integrity of the exterior walls (of the input cavity, heat exchange portion, and/or the output cavity) can be reinforced through a variety of structural elements (e.g., dimples, alternating peaks and valleys, flanges, etc.) utilized alone or in various combinations.

The present approach is compatible with the use of only a single heat exchanger, or multiple heat exchangers with their respective high pressure flow path26in fluid communication with each other. For example,FIG. 5shows a heat exchange system5that includes two heat exchangers10(as inFIGS. 1A-1F) with the high pressure flow paths26connected in series through the connection manifold62such that the cooled air from the output cavity24of the first heat exchanger10passes through the connection manifold62to enter the input cavity20of the second heat exchanger for additional cooling.

Referring toFIG. 6, a jet engine air duct80is shown as an annular forward-looking-aft orientation for certain jet engines. The series of heat exchangers10are fluidly connected in series and aligned along the duct80in its annular orientation. Alternatively, the heat exchanger10form of an exemplary single, integrated component50shown inFIG. 2Ahas an annular orientation for inclusion within the duct80.

When multiple heat exchangers10are used in series, as shown inFIG. 6, the heat exchangers can be identical in composition in one embodiment. However, in an alternative embodiment, the heat exchangers10are different in terms of composition. For example, the first heat exchanger contacting the hot air input12at its highest temperature can be constructed of a relatively high temperature material (e.g., nickel-chromium based alloys such as available under the tradename Inconel® available from Special Metals Corporation, titanium, titanium alloys, etc.) due to the relatively high temperature of the hot air input12. Then, in the subsequent, downstream heat exchangers10with respect to the high pressure path26can be constructed of more lightweight, lower temperature materials (e.g., aluminum, aluminum alloys, etc.) as the hot air is cooled after passing through at least one of the upstream heat exchangers. In such embodiments, the connection manifold62can establish a boundary across which the material of the heat exchangers can change. As such, the material can be selected based on a combination of the required strength, working temperatures, and weight requirements while allowing optimization of the overall system.

FIG. 7shows yet another embodiment of an exemplary heat exchange system5where the heat exchanger10includes a plurality of heat exchanger portions22between the input cavity20and the output cavity24. The heat exchanger portions22are separated by a mixing cavity82such that the high pressure gas paths26of the first heat exchanger portion22A are fluidly connected in series to the mixing cavity82for mixing therein after passing through the first heat exchanger portion22A. The presence of the mixing cavity82restarts the thermal boundary layer in high pressure gas path26. Then, the mixed gas passes into the high pressure gas paths26of the second heat exchanger portion22B for further cooling therein.

Although shown as single pass systems with respect to the cooling fluid30, multipass variants are also generally provided. That is, the high pressure path26makes multiple transits (i.e., passes) through the cooling fluid30before exiting the heat exchanger system5. Such multi-pass arrangements can include co-flow and counter flow in the same system.

For example,FIG. 8shows an exemplary heat exchanger system5that is a multipass variant with respect to the cooling fluid30. In this embodiment, the hot air input12flows through the first heat exchanger10aand into the second heat exchanger10b. Thus, as shown, the heat exchangers10a,10bare serially connected to each other with respect to the flow path of the hot air. Additionally, the cooling fluid30aflows through the first heat exchanger portion22A to be a slightly warmer cooling fluid30bto flow through the second heat exchanger portion22B and exit as a slightly warmer cooling fluid30c. Thus, as shown, the heat exchangers are also serially connected with respect to the flow path of the cooling fluid.

In the shown embodiment, the hot air flow path (including the high pressure paths26a,26b) has two passes through the cooling fluid flow path (including the cooling flow paths32A,32B) with one being in each heat exchanger10a,10brespectively. Although shown as having two passes by the high pressure path26through the cooling fluid30, any number of passes can be utilized in the heat exchanger system5.