Patent Description:
Heat exchangers are made of many different types of materials. CMC heat exchangers are particularly useful in high temperature environments. However, CMC materials can have a low thermal conductivity, reducing the efficiency of CMC heat exchangers. Therefore, a method of augmenting and enhancing heat transfer in CMC heat exchangers is desired.

<CIT> teaches a method of manufacturing a heat exchanger core including parallel tubular regions from a glass ceramic matrix composite material including fibers, the method comprising wrapping the fibers around a mandrel (e.g. graphite, that may be removed by oxidation), infiltrating a glass material and removing the mandrel.

In one embodiment, a method of manufacturing a heat exchanger core from glass ceramic matrix composite is provided as defined by claim <NUM>.

In another embodiment, a heat exchanger is provided as defined by claim <NUM>.

This disclosure relates to a heat exchanger made from Ceramic Matrix Composite (CMC) materials, and in particular to heat exchangers formed of Glass Ceramic Matrix Composite (G-CMC) materials. The heat exchanger has surface features formed from G-CMC materials. The surface features can be protrusions or indentations either internally or externally which break up the flow boundary layer and increase flow turbulence, thereby increasing heat transfer in the heat exchanger. The heat exchanger will be discussed below with reference to <FIG>.

<FIG> is a perspective view of an embodiment of tube sheet heat exchanger <NUM> formed from G-CMC materials. Tube sheet heat exchanger <NUM> comprises tubular regions <NUM>, flat regions <NUM>, and passageways <NUM>. Passageways <NUM> comprises radially inner part surface <NUM> and radially outer part surface <NUM>.

Tube sheet heat exchanger <NUM> transfers heat from a first fluid to a second fluid. The first fluid can be at a higher temperature than the second fluid or vice-versa. The first fluid flows over radially outer part surface <NUM>. The second fluid flows through passageways <NUM> and contacts radially inner part surface <NUM>. The first fluid flows at an angle relative to the second fluid. The angle can be between <NUM> and <NUM> degrees. Tubular regions <NUM> are spaced apart from one another by flat regions <NUM> and form raised regions between flat regions <NUM>. In some embodiments flat regions <NUM> are wide. In alternative embodiments, flat regions <NUM> are substantially narrow. Alternatively, tubular regions <NUM> can directly abut each other, thus flat regions <NUM> would substantially not be present. Tubular regions <NUM> house passageways <NUM>. Tubular regions <NUM> are the regions where heat transfer from the first fluid to the second fluid primarily occurs. When present, some heat transfer occurs in flat regions <NUM>.

<FIG> each disclose a cross-sectional view of an embodiment of passageways <NUM> of tube sheet heat exchanger <NUM> and will be discussed together. <FIG> is a cross-sectional view of passageway <NUM> of tube sheet heat exchanger <NUM> of <FIG> taken along line A-A with protrusions <NUM>. <FIG> includes radially inner part surface <NUM>, radially outer part surface <NUM>, and protrusions <NUM>. <FIG> is a cross-sectional view of passageway <NUM> of tube sheet heat exchanger <NUM> of <FIG> taken along line A-A, except passageway <NUM> comprises grooved indentations <NUM>, <NUM>, or <NUM> instead of protrusions <NUM>. <FIG> includes radially inner part surface <NUM>, radially outer part surface <NUM>, and grooved indentations <NUM>, <NUM>, or <NUM>.

On radially inner part surface <NUM> of passageways <NUM> a first pattern is formed. In the embodiment of <FIG>, the first pattern is formed by protrusions <NUM>. In the embodiment of <FIG>, the first pattern is formed by grooved indentations <NUM>, <NUM>, or <NUM>. Grooved indentation <NUM> has a tight tread spacing whereas grooved indentation <NUM> has a wide tread spacing. Grooved indentation <NUM> has a tread spacing between the tight tread spacing of grooved indentation <NUM> and the wide tread spacing of grooved indentation <NUM>. In other embodiments, the first pattern can be a combination of grooved indentations <NUM>, <NUM>, and <NUM>. In other embodiments, the first pattern can be a combination of protrusions <NUM> and grooved indentations <NUM>, <NUM>, or <NUM> together in the same passageway <NUM>. The first pattern can further be any combination of protrusions and/or indentations which modulate a flow of a fluid through passageway <NUM>. Modulation of the flow of the fluid through passageway <NUM> increases heat transfer from radially inner part surface <NUM> into the G-CMC material with the heat then conducting to radially outer part surface <NUM>. Modulation of the flow can include breaking up the flow boundary layer and/or inducing mixing and turbulence within passageway <NUM>, thereby in some cases changing a substantially laminar flow to a substantially turbulent flow. Breaking up the flow boundary layer can lead to flow disruption and increased mixing. Further, if turbulent flow is induced heat transfer can occur even more readily as turbulent flow does not have an insulating layer along the radially inner part surface <NUM>.

Protrusions <NUM> create turbulent flow by protruding into a flow column in passageway <NUM> thereby interrupting the flow along radially inner part surface <NUM>. Grooved indentations <NUM>, <NUM>, or <NUM> also create turbulent flow within passageway <NUM> by altering flow nearest radially inner part surface <NUM>, thereby disrupting the overall flow column in passageway <NUM>. A tighter tread spacing can disrupt the overall flow column more than a wider tread spacing, however this further increases the pressure drop across the passageway <NUM> Both protrusions <NUM> and grooved indentations <NUM>, <NUM>, or <NUM> alter flow nearest radially inner part surface <NUM>, disrupting the insulation layer which forms in laminar flow. Additionally, both protrusions <NUM> and grooved indentations <NUM>, <NUM>, or <NUM> can be formed on radially outer part surface <NUM>.

<FIG> and <FIG> each disclose an embodiment of forming a G-CMC component and will be discussed together. <FIG> is flow diagram of G-CMC component being manufactured using mold <NUM> with injection sites <NUM> therein. The flow diagram of <FIG> includes the steps of providing mandrel <NUM>, forming fiber preform <NUM> around mandrel <NUM>, injecting fiber preform <NUM> with glass matrix material <NUM>, removing mandrels <NUM>, and providing the finalized G-CMC component. The flow diagram of <FIG> includes the steps of providing mandrel <NUM>, forming fiber preform <NUM> around mandrel <NUM>, infiltrating fiber preform <NUM> with glass matrix material <NUM>, hot pressing fiber preform <NUM> with die set <NUM>, removing mandrels <NUM>, and providing the finalized G-CMC component.

As shown in <FIG> and <FIG>, first step <NUM> in a possible embodiment of manufacturing the G-CMC component is providing mandrel <NUM> to a build surface. In some embodiments, the build surface can be mold <NUM>. In the embodiments of <FIG> and <FIG>, mandrel <NUM> is formed of graphite. In alternative embodiments, mandrel <NUM> can be formed of any material know to those of skill in the art to be chemically inert with chosen substate <NUM>. Mandrel <NUM> can have the first pattern discussed above with reference to <FIG> formed in negative on an outer tooling surface of mandrel <NUM>. The first pattern can include tooling surface protrusions or indentations which will form part surface indentations or protrusions, respectively, on radially inner part surface <NUM> of passageways <NUM>.

As shown in <FIG> and <FIG>, second step <NUM> of manufacturing the G-CMC component is forming fiber preform <NUM> around mandrel <NUM>. Fiber preform <NUM> provides a surface for glass matrix material <NUM> to adhere too. Fiber preform <NUM> also provides reinforcement and improves mechanical properties of the G-CMC component. Specifically, fiber preform <NUM> can increase a tensile strength of the G-CMC component and increase a heat transfer coefficient of the G-CMC component from radially inner part surface <NUM> to radially outer part surface <NUM>. In the embodiment of <FIG> and <FIG>, fiber preform <NUM> is formed of one or more ceramic fibers formed around the mandrel. In alternative embodiments fiber preform <NUM> can be formed of any fibers which are crystalline and compatible with to glass matrix material <NUM>. In alternative embodiments, fiber preform <NUM> can be silicon carbide, carbon, oxides, or combinations thereof. In alternative embodiments fiber preform <NUM> can be oriented in circumferential directions, linear directions, or random directions. In alternative embodiments fiber preform <NUM> can be formed from a plurality of chopped fibers. In alternative embodiments fiber preform <NUM> can be a single continuous thread wrapped and woven into layers.

As shown in <FIG> and <FIG>, third step <NUM> of the embodiment of <FIG> and <FIG> of manufacturing the G-CMC component is positioning mandrels <NUM> with fiber preform <NUM> thereon next to each other on the build surface, if there is more than one mandrel. Additional fiber preform <NUM> can be positioned between mandrels <NUM> to connect mandrels <NUM> together. As shown in <FIG>. glass matrix material <NUM> is then distributed in fiber preforms <NUM>.

In the embodiment of <FIG> glass matrix material <NUM> is glass. In alternative embodiments, glass matrix material <NUM> can be any material which hardens when cooled and which does not destroy fiber preform <NUM> and mandrels <NUM>. In alternative embodiments, glass matrix material <NUM> can include pure glass, silicone carbide, molten silicon, and combinations thereof. When hardened glass matrix material <NUM> and fiber preform <NUM> have a porosity of less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>%. Due to the low porosity, a distance between radially inner part surface <NUM> and radially outer part surface <NUM> can be reduced which improves heat transfer characteristics. Further, since the porosity is lower, increased control over surface roughness is possible. Specifically, surface roughness control with resolutions of less than <NUM>, less than <NUM>, and less than <NUM> are possible.

As shown in <FIG>, injection step <NUM> of the embodiment of <FIG> of manufacturing the G-CMC component is injecting molten glass matrix material <NUM> into mold <NUM> through injection sites <NUM>. Molten glass matrix material <NUM> infiltrates the spaces between fiber preform <NUM>, thereby forming an infiltrated core of the G-CMC component. Before injecting molten glass matrix material <NUM>, a pressure is applied to compact fiber preform <NUM>. Compacting fiber preform <NUM> reduces the space between fibers of fiber preform <NUM> thereby decreasing a porosity of the G-CMC component. A temperature of mold <NUM> is also increased. Increasing the temperature of mold <NUM> allows for glass matrix material <NUM> to flow more readily, thereby further decreasing a porosity of the G-CMC component. After the fiber preform <NUM> has been compacted and mold <NUM> has been heated, molten glass matrix material <NUM> is then injected into mold <NUM> through injection sites <NUM>. Injection sites <NUM> can be one-way valves to increase a pressure of the injected molten glass matrix material <NUM>. When glass matrix material <NUM> hardens, glass matrix material <NUM> and fiber preform <NUM> will take the shape of mold <NUM>. Mold <NUM> can be flat. Mold <NUM> can be textured. The texture on mold <NUM> can comprise protrusions or indentations. The plurality of protrusions can comprise a plurality of fins (not shown). The plurality of fins increases a surface area which interacts with the first fluid, breaks up the flow boundary, and/or induces turbulence in a flow of the first fluid. Mold <NUM> can be formed from graphite or any other material that does not destroy glass matrix material <NUM> and capable of handling the high temperatures of glass matrix material <NUM>.

As shown in <FIG>, pressing step <NUM> of the embodiment of <FIG> of manufacturing the G-CMC component comprises hot pressing infiltrated fiber preform <NUM> with die set <NUM>. Prior to hot pressing fiber preform <NUM>, a powdered version of glass matrix material <NUM> must be placed onto fiber preform <NUM>. Once the powdered version of glass matrix material <NUM> is placed onto fiber preform <NUM> a temperature is increased which melts the powdered version of glass matrix material <NUM>. After the glass matrix material <NUM> has been melted, then a pressure can be applied by die set <NUM>, thereby hot-pressing fiber preform <NUM>. The melting and applied pressure removes small bubbles in glass matrix material <NUM> between fibers of fiber preform <NUM> thereby decreasing a porosity of the G-CMC component.

Die set <NUM> can have a second pattern formed into contact surfaces of die set <NUM>. As shown in <FIG>, the second pattern can have tubular form 12F and flat form 14F. The second pattern as shown in <FIG> decreases a thickness between radially inner part surface <NUM> of passageway <NUM> and radially outer part surface <NUM>, increasing heat transfer. The second pattern also forms tubular portions <NUM> and flat portions <NUM> in outer part surface <NUM>. The second pattern can further include a textured surface. The textured surface can include protrusions or indentations. The protrusions can include a plurality of fins (not shown) which protrude from tubular region <NUM> and flat region <NUM>. The plurality of fins increases a surface area which interacts with the first fluid, breaks up the flow boundary, and/or induces turbulence in a flow of the first fluid. The textured surface can alternatively or in addition include a roughened surface. The roughened surface has a finer length scale than the textured surface. The roughened surface can be uniform. The roughened surface of radially outer part surface <NUM> has an RMS surface roughness of at least 3x, of least 5x, of at least 10X, or at least 20x of the surface prior to hot pressing with die set <NUM>. A possible embodiment comprises a surface which can be considered nominally smooth with. <NUM>" deviations, therefore a roughened surface after hot pressing with deviations of up to <NUM>" may have a surface roughness of 20X the surface prior to hot pressing. Protrusions <NUM> and grooved indentations <NUM>, <NUM>, or <NUM> can be larger than the deviations created by hot pressing with die set <NUM> or the texture created by mold <NUM>. Specifically, a height of protrusions <NUM> and grooved indentations <NUM>, <NUM>, or <NUM> can be greater than. <NUM>" (<NUM>), greater than. <NUM>" (<NUM>), greater than. <NUM>" (<NUM>), or greater than. <NUM>" (<NUM>) whereas the deviations created by hot pressing with die set <NUM> or the texture created by mold <NUM> have a height of up to <NUM>" (<NUM>), up to <NUM>" (<NUM>), and up to <NUM>" (<NUM>).

Die set <NUM> can be manufactured with additive manufacturing. Die set <NUM> can also be formed from graphite. Not shown in <FIG>, a chemical vapor deposition process can be applied to outer part surface <NUM> after hot pressing with die set <NUM>. The chemical vapor deposition process can increase a roughness of outer part surface <NUM>.

Reinforcement particles can be hot pressed into glass matrix material <NUM> and fiber preform <NUM> as part of fourth step <NUM>. The reinforcement particles can include local additions of secondary fibers, particulates, nanotubes, and a combination thereof. When secondary fibers are used, the secondary fibers can be at the same or different orientation as fiber preform <NUM>. The secondary fibers can be the same or a different material than fiber preform <NUM>. These reinforcement particles can improve the material characteristics of tube sheet heat exchanger <NUM> in the areas where the reinforcement particles are applied. The material characteristics which are increased include strength, stiffness, and thermal transfer characteristics. Die set <NUM> can be manufactured with additive manufacturing. Die set <NUM> can be formed from graphite.

Although injection step <NUM> and pressing step <NUM> are discussed here in separate figures, <FIG> and <FIG> respectively, injection step <NUM> and pressing step <NUM> can be used on the same G-CMC component. Specifically, a component can be formed via injection step <NUM> and a surface pattern can be imparted with pressing step <NUM>. Prior to fifth step <NUM>, glass matrix material <NUM> and fiber preform <NUM> can be heat treated. Heat treating glass matrix material <NUM> and fiber preform <NUM> can crystalize glass matrix material <NUM>. Crystalizing glass matrix material <NUM> can convert glass matrix material <NUM> to a ceramic and/or glass-ceramic material. Crystalizing glass matrix material <NUM> can increase a hardness of glass matrix material <NUM>. Crystalizing glass matrix material <NUM> can also decrease a porosity of the glass matrix material <NUM> further.

As shown in <FIG> and <FIG>, fifth step <NUM> in the embodiment of <FIG> and <FIG> is removing mandrels <NUM>. Mandrels <NUM> can be removed via chemical or mechanical means. Chemical removal can include oxidization. When mandrels <NUM> are formed of graphite, mandrels <NUM> can be oxidized away via a burning process. Mechanical removal of mandrels <NUM> can include sonication, electrical discharge machining, or a combination thereof. Mandrels <NUM> can be removed by any other method known to those of skill in the art of removing a sacrificial component from within another component.

As shown in <FIG> and <FIG>, after completion of fifth step <NUM>, manufacturing of the G-CMC component is completed, as represented by reference <NUM>. With completion <NUM> of the G-CMC component, the G-CMC component is ready for installation into any larger assembly. Specifically, any larger assembly where heat must be transferred from a first fluid to a second fluid.

The above steps <NUM>-<NUM> were described with reference to a G-CMC component. Steps <NUM>-<NUM> can likewise be utilized when forming tube sheet heat exchanger <NUM>. Steps <NUM>-<NUM> can further be utilized when forming shell and tube heat exchanger <NUM> (discussed below with reference to <FIG>) or any other heat exchanger with a first and a second passageway. The steps <NUM>-<NUM> can further be used for any other G-CMC components. The method described above with reference to steps <NUM>-<NUM> can be particularly useful for any G-CMC component which experiences high temperatures.

<FIG> disclose embodiments of mandrels <NUM> for forming a first pattern. <FIG> is a perspective view of an embodiment of mandrel <NUM> for forming protrusions <NUM> in passageways <NUM> of a heat exchanger. <FIG> is a perspective view of an embodiment of mandrel <NUM> for forming grooved indentations <NUM> in passageways <NUM> of a heat exchanger.

Mandrel <NUM> shown in <FIG> forms protrusions <NUM> in radially inner surface <NUM> of passageways <NUM>, hereinafter referred to as protrusion mandrel <NUM>. Protrusion mandrel <NUM> has a plurality of protrusions. Each protrusion is a circumferential protrusion from the tooling surface. Each protrusion has protrusion height <NUM>, protrusion width <NUM>, and protrusion spacing <NUM>. Protrusion height <NUM> is how far the protrusion extends from the tooling surface of protrusion mandrel <NUM>. Protrusion width <NUM> is an axial width of the circumferential protrusion. Protrusion spacing <NUM> is a distance between the each of the plurality of protrusions. Each of these distances can be varied for each and between each of the plurality of protrusions. When protrusion mandrel <NUM> is used in the formation of protrusions <NUM>, glass matrix material <NUM> infills between each of the plurality of protrusions. Protrusion spacing <NUM> is therefore the width of each of the of protrusions <NUM>. Protrusions <NUM> are discussed further above with reference to <FIG>. Protrusion mandrel <NUM> can be formed from graphite.

Mandrel <NUM> shown in <FIG> forms grooved indentations <NUM> in radially inner surface <NUM> of passageways <NUM>, hereinafter referred to as tread mandrel <NUM>. Tread mandrel <NUM> has a single protrusion. The single protrusion extends from a tooling surface of tread mandrel <NUM>. The single protrusion circumferentially wraps around the circumference of tread mandrel <NUM> a plurality of times. The single protrusion has tread height <NUM>, tread width <NUM>, and tread spacing <NUM>. Tread height <NUM> is how far the protrusion extends from the tooling surface of tread mandrel <NUM>. Tread width <NUM> is an axial width of the single protrusion. Tread spacing <NUM> is the distance between each of the plurality of circumferential wraps. When tread mandrel <NUM> is used in the formation of grooved indentations <NUM>, glass matrix material <NUM> infills between each of the plurality of circumferential wraps and each of the plurality of circumferential wraps presses into the radially inner surface <NUM> of passageway <NUM> forming grooved indentations <NUM>. A width of grooved indentations <NUM> is the width of tread width <NUM> and a depth of grooved indentations <NUM> is tread height <NUM>. Grooved indentations <NUM> are discussed further above with reference to <FIG>. Tread mandrel <NUM> can be formed from graphite.

<FIG> is a cross sectional view of an embodiment of shell and tube heat exchanger <NUM>. Shell and tube heat exchanger <NUM> includes shell <NUM> and tubes <NUM>. Each of tubes <NUM> includes passageway <NUM> with radially inner surface <NUM> and radially outer part surface <NUM>. Shell <NUM> has first and second entrances (<NUM>, <NUM>) and first and second exits (<NUM>, <NUM>).

Shell <NUM> surrounds a plurality of tubes <NUM>. A first fluid flows from first entrance <NUM> to first exit <NUM>. The first fluid flows over radially outer part surface <NUM> of each of tubes <NUM>. A second fluid fluids from second entrance <NUM> to second exit <NUM>. The second fluid flows through the plurality of passageways <NUM> inside of tubes <NUM>. Each of the plurality of passageways <NUM> can have a first pattern on radially inner surface <NUM>. The first pattern can be protrusions <NUM>, grooved indentations <NUM>, or any other combination of protrusions and indentations as discussed above with respect to <FIG>. Radially outer part surface <NUM> can have a second pattern. The second pattern can be a plurality of fins, a rough surface, or any combination of protrusions, indentations, and roughened surfaces as discussed above with respect to <FIG>. Shell <NUM> and tubes <NUM> can be formed from G-CMC through a manufacturing process similar to the process described above with reference to <FIG>.

Claim 1:
A method of manufacturing a heat exchanger core from glass ceramic matrix composite, wherein the method comprises:
placing one or more reinforcing fibers around one or more mandrels (<NUM>) into a mold cavity, wherein the one or more mandrels have one or more protrusions (<NUM>) which form a first surface texture, and one or more grooves (<NUM>, <NUM>, <NUM>) which form a second surface texture;
infiltrating the one or more reinforcing fibers with a glass matrix material to produce an infiltrated core, wherein the first surface texture forms a patterned feature on an interior surface of the infiltrated core, and the second surface texture forms a patterned feature on an interior surface of the infiltrated core; and
removing the one or more mandrels to create one or more passages passing through the infiltrated core.