RELATED APPLICATION

[0001] This application is related to and claims priority to PCT International Application No. PCT/US2022/026942, filed April 29, 2022, for “GRADED LATTICE STRUCTURES.”

BACKGROUND

[0002] Some operations produce heat. For example, computing device processors generate heat as transistors switch to execute instructions. Light emitting diodes (LEDs) produce heat while converting an electrical current into light. Batteries produce heat during charging and discharging due to internal resistance. Vehicle engines produce heat as fuel combusts. In some examples, heat and/or overheating may damage a device and/or may cause inefficient operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Figure 1 is a diagram illustrating a top-down internal view of an example of a heat exchanger;

[0004] Figure 2 is a diagram illustrating a cross-sectional view of an example of a heat exchanger;

[0005] Figure 3 is a diagram illustrating an example of a graph of temperature over dimensions of a flow channel; [0006] Figure 4 is a diagram illustrating an example of a graph of temperature over a surface of a heat exchanger;

[0007] Figure 5 is a block diagram of an example of an apparatus that may be used to manufacture a structure or structures described herein;

[0008] Figure 6 is a flow diagram illustrating an example of a method for manufacturing a structure;

[0009] Figure 7 is a diagram illustrating a first perspective view of an example of a heat exchanger;

[0010] Figure 8 is a diagram illustrating a second perspective view of the example of the heat exchanger;

[0011] Figure 9 is a diagram illustrating a cross-sectional view of an example of a heat exchanger;

[0012] Figure 10 is a diagram illustrating a perspective view of an example of an exchange structure;

[0013] Figure 11 is a diagram illustrating a perspective view of an example of an exchange structure;

[0014] Figure 12 is a diagram illustrating a perspective view of an example of a heat exchanger; and

[0015] Figure 13 is a diagram illustrating an example of a graph of temperature over a surface of a heat exchanger.

DETAILED DESCRIPTION

[0016] A heat exchanger is a device to transfer heat between mediums. For instance, a heat exchanger may be utilized to transfer heat from a heat source (e.g., processor, LED, combustion engine, battery, boiler, etc.) to a substance (e.g., fluid, water, air, etc.). In some examples, a heat exchanger may be utilized to cool a processor, engine, an LED light bulb, battery, etc. In some examples, a heat exchanger may be utilized to transfer heat from a substance (e.g., fluid, water, air, etc.) to an object (e.g., engine) or medium. In some examples, a heat exchanger may transfer heat from one fluid to another fluid. [0017] In some approaches, coolant may flow through a cold plate to absorb heat. In some cold plates, cooling structures (e.g., straight fins, pipes, and/or lattice structures, etc.) may be uniform throughout the entire cold plate. Because the coolant temperature may become higher along the flow path, the resulting temperature on the cold plate surface may be cooler at the inlet region and hotter at the outlet region. This may lead to a non-uniform temperature on the target object to be cooled. Non-uniform temperatures may degrade cooling performance, which may be evaluated based on a highest temperature.

[0018] Some examples of the techniques described herein may provide heat exchange structures that result in heat exchange with increased uniformity. For instance, a heat exchange structure may be graded. In some examples, a graded heat structure may have lower cooling performance at an inlet region than at an outlet region of a cold plate. Because the coolant temperature may be lower at the inlet region than at the outlet region, the resulting cooling temperature may be more balanced compared to other cold plates with uniform cooling structures. For instance, the highest cooling temperature may be reduced. The regions with lower cooling performance may have lower pressure drops than those with higher cooling performance. Accordingly, the resulting overall pressure drop of an enhanced graded structure may be reduced compared to that of a uniform structure. In some examples, a graded cooling structure may have different beam thicknesses, wall thicknesses, scales, surface areas, cross-sectional areas, and/or or topologies, etc., at different locations.

[0019] Some examples of the techniques described herein may provide heat exchangers that include exchange structures to transfer heat. For instance, a heat exchanger may include a flow channel with an exchange structure, where the exchange structure serves to transfer heat from a body of the heat exchanger to fluid flowing through the flow channel. An exchange structure is a structure to transfer (e.g., exchange, radiate, absorb, etc.) heat.

[0020] Some examples of exchange structures may include lattice structures. A lattice structure is an arrangement of a member or members (e.g., branches, beams, joists, columns, posts, rods, etc.). For example, a lattice structure may be structured along one dimension, two dimensions, and/or three dimensions. Examples of a lattice structure may include rods, two-dimensional grids, three- dimensional grids, gyroidal structures, cubic lattices, body-centered lattices, etc. In some examples, a lattice structure includes members disposed in a crosswise manner. For instance, two members of a lattice structure may intersect at a diagonal, perpendicular, or oblique (e.g., non-perpendicular and non-parallel) angle.

[0021] Some examples of exchange structures may include fins. A fin is a structure with a first dimension (e.g., width, thickness, x, etc.) that is less than a second dimension (e.g., length, y, etc.). In some examples, the first dimension (e.g., width, thickness, etc.) may be less than a third dimension (e.g., height, z, etc.). For example, a fin may have a relatively smaller thickness in relation to length. In some examples, a ratio of a first dimension (e.g., width, thickness, x, etc.) to a second dimension (e.g., length, y, etc.) may be less than 0.75 (e.g., 1/10, 1/20, 1/50, 1/100, etc.). In some examples, an exchange structure may include a plurality of fins. For instance, a set of fins may include fins disposed approximately in parallel with spacing between neighboring fins. In some examples, fins may not intersect.

[0022] In some examples, heat exchanger, lattice structure, fin(s), or a part(s) thereof may be manufactured by three-dimensional (3D) printing, another manufacturing technique(s), or a combination thereof. Some examples of 3D printing that may be utilized to manufacture some examples of the structures described herein may include Fused Deposition Modeling (FDM), Multi-Jet Fusion (MJF), Selective Laser Sintering (SLS), binder jet, Stereolithography (SLA), Selective Laser Melting (SLM), Electron Beam Melting (EBM), Metal Jet Fusion, metal binding printing, liquid resin-based printing, etc. For instance, a heat exchanger or a part thereof may be manufactured with metal 3D printing and/or another 3D printing technique.

[0023] In some examples, additive manufacturing may be used to manufacture 3D objects (e.g., geometries, lattices, fins, etc.). Some examples of additive manufacturing may be achieved with 3D printing. For example, thermal energy may be projected over material in a build area, where a phase change and solidification in the material may occur at certain voxels. A voxel is a representation of a location in a 3D space (e.g., a component of a 3D space). For instance, a voxel may represent a volume that is a subset of the 3D space. In some examples, voxels may be arranged on a 3D grid. For instance, a voxel may be cuboid or rectangular prismatic in shape. In some examples, voxels in the 3D space may be uniformly sized or non-uniformly sized. Examples of a voxel size dimension may include 25.4 millimeters (mm)/150 « 170 microns for 150 dots per inch (dpi), 490 microns for 50 dpi, 2 mm, 4 mm, etc. In some examples, voxels may be polygonal, polyhedral, irregularly shaped, curved, etc. The term “voxel level” and variations thereof may refer to a resolution, scale, or density corresponding to voxel size.

[0024] Some examples of the geometries and/or structures (e.g., lattice structures, fins, heat exchangers, etc.) described herein may be produced by additive manufacturing. For instance, some examples may be manufactured with a plastic(s), polymer(s), semi-crystalline material(s), metal(s), etc. Some additive manufacturing techniques may be powder-based and driven by powder fusion. Some examples of the geometries and/or structures (e.g., lattices) described herein may be manufactured with area-based powder bed fusionbased additive manufacturing, such as MJF, Metal Jet Fusion, metal binding printing, SLM, SLS, etc. Some examples of the approaches described herein may be applied to additive manufacturing where agents carried by droplets are utilized for voxel-level thermal modulation.

[0025] In some examples of additive manufacturing, thermal energy may be utilized to fuse material (e.g., particles, powder, etc.) to form an object (e.g., structure, geometry, lattice, etc.). For example, agents (e.g., fusing agent, detailing agent, etc.) may be selectively deposited to control voxel-level energy deposition, which may trigger a phase change and/or solidification for selected voxels.

[0026] In some examples of 3D printing, a binding agent (e.g., adhesive) may be printed onto material in a build volume to bind powder (e.g., particles) and form a precursor object (e.g., “green part”). The precursor object may be heated (in an oven or heating apparatus, for example) to sinter the precursor object and form a solid part.

[0027] Throughout the drawings, similar reference numbers may designate similar or identical elements. When an element is referred to without a reference number, this may refer to the element generally, with and/or without limitation to any particular drawing or figure. In some examples, the drawings are not to scale and/or the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples in accordance with the description. However, the description is not limited to the examples provided in the drawings.

[0028] Figure 1 is a diagram illustrating a top-down internal view of an example of a heat exchanger 120. For instance, the heat exchanger 120 may be a cold plate or may be included in a cold plate. The heat exchanger 120 may include a flow channel 112. A flow channel is a course (e.g., route, path, etc.) to carry a substance (e.g., fluid, water, air, and/or coolant, etc.). A flow channel may be bounded by a wall(s) and/or housing. For instance, the heat exchanger 120 includes the flow channel 112 bounded by a housing. In some examples, the flow channel 112 may be circular (e.g., tubular), rectangular, irregularly shaped, curved, prismatic, polygonal, or a combination thereof. In some examples, the housing may provide a wall or walls that contain the flow channel 112. In some examples, the housing may have a circular (e.g., tubular) shape, rectangular shape, irregular shape, or a combination thereof. In some examples, the flow channel 112 may follow a linear, non-linear, undulating, wrapping, helical, circular, curved, crenulated, crenellated, geometrical taxicab, and/or other path. In some examples, the flow channel 112 may be utilized to conduct the substance between an inlet and an outlet (e.g., for a part of a course traveled between an inlet and an outlet).

[0029] The heat exchanger 120 may include an exchange structure 122. In the example of Figure 1 , the exchange structure 122 is a lattice structure that includes members (e.g., beams) that intersect at a diagonal, perpendicular, or oblique (e.g., non-perpendicular and non-parallel) angle. In the example of Figure 1 , the members of the lattice structure intersect at varying (e.g., graded) angles. In other examples, the members of a lattice structure may intersect at a different angle or angles (e.g., 15°, 30°, 45°, 70°, 85°, 95°, 110°, 135°, a continuous range, etc.). In some examples, members of a lattice structure may be curved, gyroidal, interlaced, and/or intermeshed, etc. In some examples, the exchange structure 122 may include a fin(s) (e.g., graded fin(s)). For instance, a fin(s) may be utilized instead of a lattice structure. Examples of fins that may be utilized in some examples of the techniques described herein are described in relation to Figure 10, Figure 11 , Figure 12, and/or Figure 13. In some examples, some aspects of the description given herein relative to an exchange structure and/or lattice structure may apply to a fin(s) (e.g., graded fin(s)).

[0030] In some examples, the exchange structure 122 (e.g., a lattice structure and/or fin(s)) may be disposed in the flow channel 112. For instance, the exchange structure 122 may partially or fully span the flow channel 112. In some examples, the exchange structure 122 may be disposed within the housing. For instance, the exchange structure 122 may be included within the housing and/or may partially or fully span between walls of the housing. In some examples, the exchange structure 122 is a 3D lattice.

[0031] In some examples, the exchange structure 122 repeats in multiple directions. For instance, a lattice structure may repeat in two dimensions or three dimensions. A repeating structure may have the same or a similar shape(s) repeating spatially. For instance, a 3D lattice structure (e.g., a cell of a lattice structure) may repeat in three dimensions (e.g., along x, y, and z axes).

[0032] In some examples, the exchange structure 122 may permit flow. For instance, a substance (e.g., fluid, water, air, and/or coolant, etc.) may flow through the exchange structure 122 (e.g., around and/or between members of the exchange structure 122). In some examples, the heat exchanger 120 may be a single-flow heat exchanger or may be included in a single-flow heat exchanger. For instance, a heat source may be placed in contact with a heat exchanger (e.g., with a housing wall(s) of the heat exchanger 120). The heat may be conducted through the exchange structure 122. A substance flowing through the exchange structure 122 may absorb the heat from the exchange structure 122. Accordingly, the heat source may dissipate heat to the exchange structure 122, which may cool the heat source.

[0033] The exchange structure 122 (e.g., lattice structure and/or fin(s)) may be continuously graded between a first portion 124 of the flow channel 112 and a second portion 114 of the flow channel 112. Grading “between” portions may denote a comparison of gradings within portions and/or grading in a distance that separates the portions. A portion of a flow channel may be a point, part, region, area, and/or volume of a flow channel (e.g., point, part, region, area, and/or volume of a lattice structure and/or fin(s) in a flow channel). In some examples, portions may be a same size or a different size. For instance, the first portion 124 and the second portion 114 may have the same dimensions and/or may occupy the same quantity of volume.

[0034] Grading is a change in structure. For instance, grading may be a change in structure over a spatial range and/or distance. Continuous grading is a continuous change in structure (e.g., a gradual change in structure without a discrete and/or discontinuous change). In some examples, a continuous grading may vary linearly, may vary in accordance with a continuous function, and/or may vary with less than a threshold change over a distance (e.g., less than a threshold slope).

[0035] In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in thickness (e.g., member thickness, wall thickness, beam thickness, fin thickness, etc.). In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in geometrical scale (e.g., structure size and/or member spacing). In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in topology (e.g., shape, geometry type, etc.). In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in surface area. In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in density. In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in cross-sectional area. For instance, a structure may vary in thickness, geometrical scale, topology, surface area, density, and/or cross-sectional area. For instance, a continuously graded lattice structure and/or fin(s) may smoothly vary in thickness, geometrical scale, topology, surface area, and/or density over a spatial range. In the example of Figure 1 , the exchange structure 122 is continuously graded in geometrical scale between the first portion 124 and the second portion 114. For instance, the geometrical scale of the exchange structure 122 is linearly reduced from the first portion 124 to the second portion 114. In the example of Figure 1 , the spacing between members of the exchange structure 122 is gradually reduced over a distance between the first portion 124 and the second portion 114. In the example of Figure 1 , the density of the exchange structure 122 is gradually increased over a distance between the first portion 124 and the second portion 114. In some examples, the surface area of a structure (e.g., lattice structure) may gradually change between portions. In the example of Figure 1 , the surface area of the exchange structure 122 is gradually increased over a distance between the first portion 124 and the second portion 114.

[0036] In some examples, a structure (e.g., lattice structure and/or fin(s)) may be graded (e.g., continuously graded) between an inlet and an outlet of a flow channel and/or heat exchanger (e.g., heat exchanger 120). In some examples, an inlet and an outlet may be on a same side, on different sides, on opposite sides, on adjacent sides, etc., of a heat exchanger. For instance, some heat exchangers may have a height constraint that may limit placement of the inlet and the outlet to a side or sides of a heat exchanger. In some examples, a heat exchanger may have a width and/or length constraint(s) that may limit placement of the inlet and/or outlet on a top, bottom, and/or other side of the heat exchanger. Some examples of the techniques described here may enable increased temperature uniformity and/or decreased pressure drop with different inlet and/or outlet placements.

[0037] In some examples, a structure (e.g., lattice structure and/or fin(s)) may be continuously graded in one dimension, two dimensions, and/or three dimensions. For instance, thickness, geometrical scale, and/or topology may be continuously graded in one dimension, two dimensions, and/or three dimensions. Figure 1 illustrates an example of continuous grading in two dimensions. For instance, the geometrical scale of the exchange structure 122 gradually contracts in two dimensions (e.g., x and y dimensions) between the first portion 124 and the second portion 114. In some examples, continuous grading in one dimension may include a gradual spatial expansion or contraction in one dimension while remaining approximately constant in two other dimensions. In some examples, continuous grading in two dimensions may include a first gradual spatial expansion or contraction in a first dimension and a second gradual spatial expansion or contraction in a second dimension while remaining approximately constant in a third other dimension. In some examples, continuous grading in three dimensions may include a first gradual spatial expansion or contraction in a first dimension, a second gradual spatial expansion or contraction in a second dimension, and a third gradual spatial expansion or contraction in a third dimension. Variations between dimensions may be similar (e.g., expanding in two dimensions, etc.) or different (e.g., expanding in a first dimension while contracting in a second dimension, etc.).

[0038] In some examples, a flow channel may not be continuously graded. For instance, a flow channel may be bounded by parallel walls, walls with sharp (e.g., 90-degree) corners, uniformly distanced walls, and/or walls with abrupt (e.g., discrete) direction changes, etc. For instance, the flow channel 112 of Figure 1 is bounded by approximately parallel walls without an expansion or contraction in distance between the walls. In some examples, a flow channel may be graded and/or continuously graded.

[0039] An example of a flow direction 110 of a substance (e.g., fluid, coolant, air, etc.) is illustrated in Figure 1 . For instance, a substance may flow through the flow channel 112 (e.g., exchange structure 122). Figure 1 may provide an example of a top-down view of a cubic lattice structure (e.g., six-sided polyhedral cells that are approximately cubic-shaped in a diamond orientation, with opposite corners disposed along a height dimension of the flow channel 112, for instance). In this example, the cells of the cubic lattice structure vary in scale in width and length dimensions of the flow channel 112. The substance may flow through openings (e.g., channels or distances between beams) in a height dimension of the cubic lattice structure. In some examples, a heat source (or a region of a heat source) may be placed in contact with the heat exchanger 120. For instance, a processor, a battery cell, an LED, etc., may be disposed in contact with a wall of the heat exchanger 120. In some examples, a heat source may be disposed across a wall (e.g., a wall of the heat exchanger 120, a wall bounding the flow channel 112, etc.) from a graded structure (e.g., continuously graded exchange structure 122). The heat source may be uniform or non- uniform. The flow channel 112 may guide the substance through the heat exchanger 120, thereby allowing the substance to absorb heat being transferred to the exchange structure 122 from the heat source.

[0040] In some examples, the exchange structure 122 (e.g., lattice structure and/or fin(s)) may be 3D printed. For instance, the exchange structure 122 may be manufactured via 3D printing. In some examples, the exchange structure 122 and walls of the heat exchanger 120 may be printed concurrently (e.g., in the same build). In some examples, the exchange structure 122 may support the heat exchanger 120 (e.g., walls of the heat exchanger 120) during manufacturing. For instance, the exchange structure 122 may perform two functions: manufacturing support and heat dissipation. In some examples, the exchange structure 122 may be a non-sacrificial support to the heat exchanger 120. For instance, the exchange structure 122 may be maintained (e.g., not removed) after manufacturing. In some examples, the heat exchanger 120 may be utilized to facilitate removal of unprinted material. After printing, for instance, the heat exchanger 120 may allow for the passage of air (e.g., for vacuuming, for air blasting, etc.) for powder removal.

[0041] In some examples, a structure (e.g., the exchange structure 122) and a wall(s) of a heat exchanger (e.g., the heat exchanger 120) are a monolithic body. For instance, the exchange structure 122 and the walls of the heat exchanger 120 may have a same or similar material composition.

[0042] In some examples, a structure (e.g., the exchange structure 122) and a wall(s) of a heat exchanger (e.g., the heat exchanger 120) may be manufactured separately. For instance, the exchange structure 122 and walls of the heat exchanger 120 may be manufactured separately (e.g., independently) and/or may be assembled. For instance, the walls of the heat exchanger 120 may be manufactured with a separate technique (e.g. machining) and/or material(s).

[0043] In some examples, the heat exchanger 120 may be utilized to transfer (e.g., absorb or dissipate) heat. For instance, the heat exchanger 120 may be included within, mounted to, and/or disposed in contact with a heat source. For instance, the heat exchanger 120 (e.g., a housing wall of the heat exchanger 120) may be placed in contact with a processor, engine, LED lamp, lithium battery, computing device housing, and/or other heat source, etc., to cool the heat source. For instance, the heat exchanger 120 may be included in a processor liquid cooler. In some examples, the heat exchanger 120 may receive heated liquid and may cool the liquid (e.g., dissipate heat from the liquid).

[0044] Some examples of the techniques and/or structures described herein may provide enhanced cooling and/or performance. For instance, some examples may enhance temperature uniformity. For instance, a difference between a maximum temperature and a minimum temperature (e.g., temperature drop) of a heat exchanger may be reduced in some examples of the structures described herein. Some examples may reduce pressure drop. For instance, a pressure drop of a heat exchanger may be reduced in some examples of the structures described herein relative to other structures.

[0045] Some examples of the structures described herein may be relatively low-cost to fabricate. For instance, some examples of the techniques described herein may provide 3D manufacturing of a lattice structure and/or fin(s) (e.g., a heat exchanger, 3D printed cold plate, etc.), which may reduce manufacturing costs. Some examples of the structures described herein may include a variety of lattice structures and/or other heat exchange structures (e.g., fins, posts, pins, etc.). In some examples, skiving may or may not be utilized to manufacture a fin(s) described herein.

[0046] Figure 2 is a diagram illustrating a cross-sectional view of an example of a heat exchanger 226. The heat exchanger 226 may be an example of the heat exchanger 120 described in relation to Figure 1. In this example, the heat exchanger 226 includes a housing 230, flow channel 232, and a lattice structure 234. The heat exchanger 226 may be arranged in a cold plate design, where a heat source (e.g., uniform heat source) may be placed on top of the heat exchanger 226 and/or underneath the heat exchanger 226.

[0047] The heat exchanger 226 may include an inlet 238 to the housing 230. An inlet is a passage (e.g., duct, conduit, etc.) to a housing and/or wall of a heat exchanger to permit input of a substance (e.g., fluid, coolant, water, and/or air, etc.). In some examples, an inlet may include a protruding structure (e.g., sleeve, nipple, column, threaded protrusion, etc.) on the exterior of a heat exchanger. In some examples, an inlet may include a recess (e.g., threaded recess, socket, pressure fit recess, etc.) on the exterior of a heat exchanger. In some examples, an inlet may include a sealing mechanism(s) (e.g., gasket, O- ring, etc.). In the example of Figure 2, the inlet 238 is disposed on a first end of the housing 230 of the heat exchanger 226.

[0048] The heat exchanger 226 may include an outlet 240 from the housing 230. An outlet is a passage (e.g., duct, conduit, etc.) to a housing and/or wall of a heat exchanger to permit output of a substance (e.g., fluid, coolant, water, and/or air, etc.). In some examples, an outlet may include a protruding structure (e.g., sleeve, nipple, column, threaded protrusion, etc.) on the exterior of a heat exchanger. In some examples, an outlet may include a recess (e.g., threaded recess, socket, pressure fit recess, etc.) on the exterior of a heat exchanger. In some examples, an outlet may include a sealing mechanism(s) (e.g., gasket, O- ring, etc.). In the example of Figure 2, the outlet 240 is disposed on a second end of the housing 230 of the heat exchanger 226. In some examples, the inlet 238 and/or the outlet 240 may be hollow. For instance, the lattice structure 234 may not be included in the inlet 238 and/or the outlet 240.

[0049] In the example of Figure 2, the heat exchanger 226 includes a lattice structure 234. The lattice structure 234 may be a 3D lattice structure disposed in the housing 230. The lattice structure 234 is continuously graded within the housing 230 between the inlet 238 and the outlet 240. In this example, the geometrical scale of the lattice structure 234 is graded with a larger scale by the inlet 238 than by the outlet 240. For instance, the geometric scale in a first portion 236 is larger than the geometric scale in a second portion 252, with a continuous grading between the inlet 238 and the outlet 240. In some examples, the heat exchanger 226 may include a lattice structure 234 (e.g., cooling lattice structure) at scales within a range (e.g., 0.05 mm-3 mm, 0.001 inches-1 inch, etc.) for features and/or spacing. In some examples, the lattice structure 234 (e.g., the heat exchanger 226) may be capable of manufacturing through metal 3D printing.

[0050] In some examples, a first surface area of the first portion 236 of the lattice structure 234 adjacent to the inlet 238 may be less than a second surface area of the second portion 252 of the lattice structure 234 adjacent to the outlet 240. For instance, the first surface area of the first portion 236 may be less than the second surface area of the second portion 252, where the first portion 236 and the second portion 252 occupy same-sized volumes at different locations of the lattice structure 234 and/or flow channel 232. In some examples, a heat exchanger (e.g., heat exchanger 226) may provide increased heat exchange performance adjacent to an output relative to heat exchanger adjacent to an input. For instance, reduced scale, a different topology, reduced thickness, increased density, and/or increased surface area may provide increased heat exchanger performance.

[0051] In the example of Figure 2, a substance (e.g., fluid, coolant, water, and/or air, etc.) may flow into the heat exchanger 226 via the inlet 238, through the lattice structure 234, and out of the heat exchanger 226 via the outlet 240. For instance, fluid may pass from the inlet 238 through continuous grading of the lattice structure 234 to absorb heat (from the lattice structure 234, for instance) and pass to the outlet 240. Accordingly, the substance may flow through the lattice structure 234 of the heat exchanger 226 while absorbing heat from the lattice structure 234.

[0052] In some examples, a lattice structure may be attached to an interior wall or walls of a housing. For instance, the lattice structure 234 may be attached to top, bottom, and/or side interior walls of the housing 230.

[0053] Figure 3 is a diagram illustrating an example of a graph 354 of temperature over dimensions of a flow channel. For instance, the graph 354 illustrates temperature in Kelvin (K) over spatial dimensions of the flow channel 232 of Figure 2. In some examples, Figure 3 illustrates temperatures resulting from heat transfer due to a heat source (e.g., uniform heat source) placed on top of the heat exchanger 226.

[0054] Figure 4 is a diagram illustrating an example of a graph 456 of temperature over a surface of a heat exchanger. For instance, the graph 456 illustrates temperature in K over spatial dimensions of a surface of the heat exchanger 226 of Figure 2. In some examples, Figure 4 illustrates surface temperatures resulting from heat transfer due to a heat source (e.g., uniform heat source) placed on top of the heat exchanger 226. In the example of Figure 4, the temperature difference between the highest and the lowest temperatures is 0.8 K. The temperature distribution may be smaller (e.g., more even) in comparison with a heat exchanger having a uniform lattice structure. In this example, the highest temperature is 313.5 K and the pressure drop is 76.5 Pascals (Pa). The highest temperature and/or the pressure drop may be reduced in comparison with a heat exchanger having a uniform lattice structure. [0055] Figure 5 is a block diagram of an example of an apparatus 502 that may be used to manufacture a structure or structures described herein. The apparatus 502 may be a computing device, such as a personal computer, a server computer, a printer, a 3D printer, a smartphone, a tablet computer, etc. The apparatus 502 may include and/or may be coupled to a processor 504 and/or to a memory 506. The processor 504 may be in electronic communication with the memory 506. In some examples, the apparatus 502 may be in communication with (e.g., coupled to, have a communication link with) a manufacturing device (e.g., a 3D printing device). In some examples, the apparatus 502 may be an example of a 3D printing device. The apparatus 502 may include additional components (not shown) and/or some of the components described herein may be removed and/or modified without departing from the scope of this disclosure.

[0056] The processor 504 may be any of a central processing unit (CPU), a semiconductor-based microprocessor, graphics processing unit (GPU), field- programmable gate array (FPGA), an application-specific integrated circuit (ASIC), and/or other hardware device suitable for retrieval and execution of instructions stored in the memory 506. The processor 504 may fetch, decode, and/or execute instructions (e.g., manufacturing instructions 518) stored in the memory 506. In some examples, the processor 504 may include an electronic circuit or circuits that include electronic components for performing a functionality or functionalities of the instructions (e.g., manufacturing instructions 518). In some examples, the processor 504 may be utilized to manufacture one, some, or all of the structures described in relation to one, some, or all of Figures 1-2 and/or 7-12.

[0057] The memory 506 may be any electronic, magnetic, optical, or other physical storage device that contains or stores electronic information (e.g., instructions and/or data). Thus, the memory 506 may be, for example, Random Access Memory (RAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and the like. In some implementations, the memory 506 may be a non-transitory tangible machine- readable storage medium, where the term “non-transitory” does not encompass transitory propagating signals.

[0058] In some examples, the apparatus 502 may also include a data store (not shown) on which the processor 504 may store information. The data store may be volatile and/or non-volatile memory, such as Dynamic Random-Access Memory (DRAM), EEPROM, magnetoresistive random-access memory (MRAM), phase change RAM (PCRAM), memristor, flash memory, and the like. In some examples, the memory 506 may be included in the data store. In some examples, the memory 506 may be separate from the data store. In some approaches, the data store may store similar instructions and/or data as that stored by the memory 506. For example, the data store may be non-volatile memory and the memory 506 may be volatile memory.

[0059] In some examples, the apparatus 502 may include a communication interface (not shown) through which the processor 504 may communicate with an external device or devices (not shown), for instance, to receive and/or store information pertaining to an object or objects (e.g., geometry(ies), lattice(s), fin(s), heat exchanger(s), etc.) to be manufactured. The communication interface may include hardware and/or machine-readable instructions to enable the processor 504 to communicate with the external device or devices. The communication interface may enable a wired and/or wireless connection to the external device or devices. In some examples, the communication interface may further include a network interface card and/or may also include hardware and/or machine-readable instructions to enable the processor 504 to communicate with various input and/or output devices. Examples of input devices may include a keyboard, a mouse, a display, another apparatus, electronic device, computing device, etc., through which a user may input instructions into the apparatus 502. In some examples, the apparatus 502 may receive 3D model data 508 from an external device or devices (e.g., 3D scanner, removable storage, network device, etc.).

[0060] In some examples, the memory 506 may store 3D model data 508. The 3D model data 508 may be generated by the apparatus 502 and/or received from another device. Some examples of 3D model data 508 include a CAD file(s), a 3D manufacturing format (3MF) file(s), object shape data, mesh data, geometry data, etc. The 3D model data 508 may indicate the shape of an object or objects. For instance, the 3D model data 508 may indicate the shape of a geometry or geometries (e.g., regular and/or irregular geometries), a lattice structure or structures, a fin or fins, a housing or housings, and/or a heat exchanger or heat exchangers for manufacture. In some examples, the 3D model data 508 may indicate a shape of one, some, or all of the geometry(ies), lattice(s), fin(s), heat exchanger(s), etc., described herein.

[0061] In some examples, the processor 504 may execute the manufacturing instructions 518 to control a print mechanism (e.g., printhead, laser, nozzle, etc.) to print an exchange structure (e.g., lattice structure, fin(s), 3D lattice structure, etc.) with different grading (e.g., continuous grading, discrete grading, monotonically incremented grading, etc.) between a first portion of the exchange structure and a second portion of the exchange structure.

[0062] In some examples, the exchange structure (e.g., lattice structure, fin(s), etc.) may be continuously graded in thickness, geometrical scale, topology, surface area, cross-sectional area, and/or density, etc. In some examples, the exchange structure may be discretely graded between portions (e.g., between the first portion and the second portion). For instance, discretely graded portions of an exchange structure may have different thicknesses, geometrical scales, topologies, surface areas, cross-sectional areas, and/or densities. In some examples, a discontinuity may exist in thicknesses, geometrical scales, topologies, surface areas, and/or densities between discretely graded portions. In some examples, portions may be linked by a conduit or conduits. For instance, a first portion (e.g., first chamber, first region, etc.) with a first grading may be linked by a conduit(s) to a second portion (e.g., second chamber, second region, etc.) with a second grading. In some examples, the conduit(s) may not include (e.g., may not contain, may not house, etc.) an exchange structure (e.g., lattice structure and/or fin(s)). For instance, a conduit may be a passage, tube, or channel (different from a flow channel or housing, for example) that may not include an exchange structure (e.g., lattice structure and/or fin(s)). In some examples, a conduit(s) may not significantly affect pressure drop. In some examples, the exchange structure (e.g., lattice structure and/or fin(s)) may be discretized among different portions of the heat exchanger.

[0063] In some examples, the exchange structure (e.g., lattice structure and/or fin(s)) may be graded at monotonic increments in thickness, geometrical scale, topology, surface area, and/or density, etc. For instance, the exchange structure may have a monotonically incremented grading between portions (e.g., between the first portion and the second portion). For instance, monotonically incremented graded portions of an exchange structure may have different thicknesses, geometrical scales, topologies, surface areas, cross- sectional areas, and/or densities that monotonically change (e.g., monotonically increase or monotonically decrease) in accordance with an increment (e.g., 1% I 1 mm, 1 mm I 1 cm, 2 mm I cm, etc.). In some examples, an increment may exist in thicknesses, geometrical scales, topologies, surface areas, cross- sectional areas, and/or densities between monotonically incremented graded portions. In some examples, an exchange structure may be monotonically incremented over a distance (e.g., length, entire span, etc.) of the exchange structure and/or flow channel. In some examples, portions may be linked by a conduit or conduits. For instance, a first portion (e.g., first chamber, first region, etc.) with a first grading may be linked by a conduit(s) to a second portion (e.g., second chamber, second region, etc.) with a second monotonically incremented grading. In some examples, the conduit(s) may not include (e.g., may not contain, may not house, etc.) an exchange structure.

[0064] In some examples, the processor 504 may control a print mechanism and/or may send instructions to a 3D printer to print the exchange structure (e.g., lattice structure and/or fin(s)). For instance, the processor 504 (e.g., microprocessor) may control printing of the exchange structure in accordance with a 3D printing technique or techniques (e.g., SLM, EBM, FDM, and/or binder jet, etc.).

[0065] In some examples, the processor 504 may execute the manufacturing instructions 518 to control the print mechanism to print a housing, heat exchanger, a combination thereof, and/or a portion(s) thereof. In some examples, the exchange structure (e.g., lattice structure and/or fin(s)) and the housing and/or heat exchanger are printed concurrently. For instance, the lattice structure and the housing and/or heat exchanger may be printed concurrently as described in relation to Figure 1. For instance, the housing, exchange structure (e.g., lattice structure and/or fin(s)), and/or heat exchanger may be printed in a build. The housing may form a flow channel. For instance, the housing may include walls that contain a flow channel. In some examples, fluid (e.g., pressurized air, water, etc.) may be passed through the flow housing to remove binding agent residue and/or unfused powder.

[0066] In some examples, the exchange structure (e.g., lattice structure and/or fin(s)) may support the housing and/or heat exchanger during sintering. For instance, the exchange structure may support the housing and/or heat exchanger as described in relation to Figure 1 . In some examples of metal 3D printing, for instance, the exchange structure and the housing and/or heat exchanger may be printed as precursor objects and then sintered to join the metal particles and burn off the binding agent. During sintering, some structures may be prone to deformation, gravity slump, etc. In some examples of the techniques described herein, the exchange structure may support the housing and/or heat exchanger during sintering to reduce deformation and/or enhance object manufacturing accuracy. In some examples of oven sintering, the exchange structure may reduce (e.g., prevent) sagging in the housing and/or heat exchanger due to gravity. In some examples of laser sintering (e.g., SLM, EBM, etc.), the exchange structure may reduce (e.g., prevent) deformation in the housing and/or heat exchanger due to residue stress.

[0067] Figure 6 is a flow diagram illustrating an example of a method 600 for manufacturing a structure. The method 600 and/or an element or elements of the method 600 may be performed by an apparatus (e.g., electronic device). For example, the method 600 may be performed by the apparatus 502 described in relation to Figure 5.

[0068] The apparatus may determine 602 a continuous grading of an exchange structure (e.g., lattice structure and/or fin(s)). For example, the apparatus may store 3D model data representing an exchange structure. In some examples, the apparatus may determine 602 the continuous grading by scaling (e.g., continuously increasing or decreasing a scale of) a dimension or dimensions of a model representing an exchange structure. In some examples, the apparatus may determine 602 the continuous grading by adjusting a thickness (e.g., continuously increasing or decreasing a thickness) of a model representing an exchange structure. In some examples, the apparatus may determine 602 the continuous grading by morphing a first topology into a second topology (e.g., gradually transforming and/or interpolating a first exchange structure shape to a second exchange structure shape) of a model representing an exchange structure (e.g., lattice structure and/or fin(s)).

[0069] The apparatus may print 604 a heat exchanger by printing the exchange structure (e.g., lattice structure and/or fin(s)) with the continuous grading. For instance, the apparatus may be a 3D printer and/or may send instructions to a 3D printer to print the exchange structure (e.g., lattice structure, fin(s), 3D lattice structure, etc.). In some examples, the apparatus may utilize a geometrical model (e.g., CAD file(s), 3MF file(s), etc.) that specifies the shape (e.g., mesh, voxels, etc.) of the continuous grading. For example, the apparatus may control a printhead to print the exchange structure (e.g., lattice structure and/or fin(s)) according to the voxels representing the shape of the continuous grading. In some approaches (e.g., MJF), the exchange structure may be printed with fusing agent and fused using a thermal lamp to solidify the exchange structure. In some approaches (e.g., Metal Jet Fusion), the exchange structure may be printed with binding agent (e.g., glue) to form a precursor object (e.g., “green part”). The precursor object may be heated in an oven to solidify the exchange structure (and a housing, for instance). In some examples of binder jet printing, dimensions of the precursor object may be adjusted to account for consolidation that occurs during sintering.

[0070] Some examples of the techniques described herein may provide approaches to produce many types of exchange structures (e.g., lattice structures and/or fins) and/or other heat exchange features. For instance, some of the manufacturing approaches described herein may be executed on a computing device and/or 3D printer, which may provide relatively low design and/or manufacturing costs.

[0071] Figure 7 is a diagram illustrating a first perspective view of an example of a heat exchanger 758. Figure 8 is a diagram illustrating a second perspective view of the example of the heat exchanger 758. Figure 7 and Figure 8 are described together. The heat exchanger 758 may be an example of the heat exchanger 120 described in relation to Figure 1. In this example, the heat exchanger 758 includes a housing 760, a lattice structure 764, an inlet 768, and an outlet 770. The heat exchanger 758 may be arranged in a cold plate design, where a heat source may be placed on top of the heat exchanger 758 and/or underneath the heat exchanger 758. For instance, heat flux may be conducted through a top surface 766. In some examples, heat flux may or may not be uniform. In some examples, a lattice structure gradient may be designed to accommodate (e.g., compensate for) the heat flux distribution and/or produce an approximately uniform temperature and/or target temperature distribution.

[0072] In this example, the lattice structure 764 is continuously graded between the inlet 768 and the outlet 770. For instance, geometrical scale and wall thickness of the lattice structure 764 are gradually reduced over a distance of the heat exchanger 758, and surface area and density of the lattice structure 764 are gradually increased over a distance of the heat exchanger 758.

[0073] In this example, a substance (e.g., fluid, coolant, water, and/or air, etc.) may flow into the heat exchanger 758 via the inlet 768, through the lattice structure 764, and out of the heat exchanger 758 via the outlet 770. For instance, fluid may absorb heat from the lattice structure 764 (e.g., 3D lattice) and pass to the outlet 770. Accordingly, the substance may flow through the lattice structure 764 of the heat exchanger 758 while absorbing heat from the lattice structure 764.

[0074] Figure 9 is a diagram illustrating a cross-sectional view of an example of a heat exchanger 984. The heat exchanger 984 may be an example of the heat exchanger 120 described in relation to Figure 1. In this example, the heat exchanger 984 includes a housing 986, inlet 990, and/or outlet 992. The heat exchanger 984 also includes a lattice structure 994 (e.g., 3D lattice structure) in an internal flow channel. The heat exchanger 984 may be arranged in a cold plate design, where a heat source may be placed in contact with the heat exchanger 984. In the example of Figure 9, the lattice structure 994 is continuously graded between a first topology 974 (e.g., a trellis topology) and a second topology 976 (e.g., a wave topology).

[0075] In this example, a substance (e.g., fluid, coolant, water, and/or air, etc.) may flow into the heat exchanger 984 via the inlet 990, and out of the heat exchanger 984 via the outlet 992. For instance, fluid may pass into the inlet 990 to absorb heat from the lattice structure 994 and pass to the outlet 992.

[0076] In some examples of the techniques and/or structures described herein, different graded lattice structures may be produced for different objectives. For example, the overall scale of the graded lattice structure may be reduced so that the temperature may be further lowered. In some cases, the pressure drop may be increased to be higher than that of a uniform lattice structure. In another example, the overall scale of the graded lattice structure may be increased so that the pressure drop can be further lowered. In some cases, the highest temperature may be increased to be higher than that of the uniform lattice structure. [0077] Figure 10 is a diagram illustrating a perspective view of an example of an exchange structure 1001. In some examples, the exchange structure 1001 may be an example of the exchange structure 122 described in relation to Figure 1. In some examples, the exchange structure 1001 may be included a heat exchanger. For instance, the exchange structure 1001 may be included in the heat exchanger 120 described in relation to Figure 1 . In some examples, the exchange structure 1001 may be included in a cold plate.

[0078] In some examples, the exchange structure 1001 may be included in a flow channel as described in relation to Figure 1 . For instance, the exchange structure 1001 may be bounded by a wall(s) and/or housing. In some examples, the flow channel may be utilized to conduct the substance between an inlet and an outlet (e.g., for a part of a course traveled between an inlet and an outlet).

[0079] In the example of Figure 10, the exchange structure 1001 includes fins 1003. The fins 1003 are graded in thickness (e.g., increasing thickness) along a flow direction 1009 (e.g., along a y axis or length axis). In Figure 10, the fins 1003 are oriented vertically. In some examples, fins may be oriented vertically, horizontally, or at an oblique angle. In the example of Figure 10, fin thickness increases along the flow direction 1009 and fin spacing reduces along the flow direction 1009.

[0080] The exchange structure 1001 permits flow between the fins 1003. For instance, a substance (e.g., fluid, water, air, and/or coolant, etc.) may flow through the exchange structure 1001 (e.g., around and/or between the fins 1003 of the exchange structure 1001 ). In some examples, the exchange structure 1001 may be included in a single-flow heat exchanger. For instance, a heat source may be placed in contact with a heat exchanger (e.g., with a housing wall(s) of the heat exchanger). The heat may be conducted through the exchange structure 1001. A substance flowing through the exchange structure 1001 may absorb the heat from the exchange structure 1001. Accordingly, the heat source may dissipate heat to the exchange structure 1001 , which may cool the heat source.

[0081] In some examples, fin structures may provide high cooling efficiencies (e.g., enhanced cooling performance at a pressure drop). In the example of Figure 10, the exchange structure 1001 (e.g., fins 1003) is graded between a first portion 1005 and a second portion 1007. The first portion 1005 may be next to an inlet and/or the second portion 1007 may be next to an outlet. The exchange structure 1001 (e.g., fins 1003) may be continuously graded along the flow direction 1009. Grading may be structured on one side or both sides of a fin. In some examples, the exchange structure 1001 may be discretely structured transverse to the flow direction 1009 (e.g., perpendicular to the flow direction 1009). For instance, the exchange structure 1001 is (e.g., the fins 1003 are) graded in thickness and spacing along the flow direction 1009 (e.g., along the length of the fins 1003). In some examples, the exchange structure 1001 may result in a fluid velocity that is graded. For instance, fluid velocity may be lower at the first portion 1005, where the fins 1003 are thinner and more widely spaced, and fluid velocity may be higher at the second portion 1007, where the fins 1003 are thicker and more narrowly spaced. Cooling performance may be more efficient at thicker fins and narrower spacing. In some examples, the coolant temperature may increase along the flow path. By grading an exchange structure (e.g., fins 1003), the heat removed at different locations may be more balanced. Graded fins may produce a more uniform cold plate temperature (in comparison with a cold plate with uniform fins).

[0082] In some examples, an exchange structure (e.g., fins) may be graded (e.g., continuously graded) in thickness, geometrical scale, topology, surface area, density, and/or cross-sectional area. In some examples, graded thickness and graded scale may be independently structured and/or utilized. In some examples, grading may be applied to fins and/or pins. An example of fins graded in scale and surface area is described in relation to Figure 11.

[0083] Figure 11 is a diagram illustrating a perspective view of an example of an exchange structure 1111. In some examples, the exchange structure 1111 may be an example of the exchange structure 122 described in relation to Figure 1. In some examples, the exchange structure 1111 may be included in a heat exchanger. For instance, the exchange structure 1111 may be included in the heat exchanger 120 described in relation to Figure 1 . In some examples, the exchange structure 1111 may be included in a cold plate. [0084] In some examples, the exchange structure 1111 may be included in a flow channel as described in relation to Figure 1 . For instance, the exchange structure 1111 may be bounded by a wall(s) and/or housing. In some examples, the flow channel may be utilized to conduct the substance between an inlet and an outlet (e.g., for a part of a course traveled between an inlet and an outlet).

[0085] In the example of Figure 11 , the exchange structure 1111 includes fins 1113, 1121. The fins 1113, 1121 include first fins 1113 and second fins 1121. The first fins 1113 are graded in thickness (e.g., increasing thickness) along a flow direction 1119 (e.g., along a y axis or length axis). In Figure 11 , the first fins 1113 and second fins 1121 are oriented vertically. In the example of Figure 11 , the second fins 1121 are introduced (e.g., begin) between the first fins 1113 partway along a length of the first fins 1113. In some examples of the exchange structures described herein, an exchange structure may include a second fin(s) introduced between first fins partway along a flow channel and/or housing. In the example of Figure 11 , the first fins 1113 are disposed at an inlet and continue to an outlet. The second fins 1121 are disposed at the outlet.

[0086] In the example of Figure 11 , the thickness of the first fins 1113 decreases along the flow direction 1119 and the thickness of the second fins 1121 increases along the flow direction 1119. In the example of Figure 11 , the surface area (e.g., total surface area) of the fins increases along the flow direction 1119. Fin spacing increases between the first fins 1113 along the flow direction 1119 and decreases with the introduction of the second fins 1121.

[0087] The exchange structure 1111 permits flow between the first fins 1113 and second fins 1121. For instance, a substance (e.g., fluid, water, air, and/or coolant, etc.) may flow through the exchange structure 1111 (e.g., around and/or between the fins 1113,1121 of the exchange structure 1111 ). In some examples, the exchange structure 1111 may be included in a single-flow heat exchanger. For instance, a heat source may be placed in contact with a heat exchanger (e.g., with a housing wall(s) of the heat exchanger). The heat may be conducted through the exchange structure 1111 . A substance flowing through the exchange structure 1111 may absorb the heat from the exchange structure 1111. Accordingly, the heat source may dissipate heat to the exchange structure 1111 , which may cool the heat source.

[0088] In the example of Figure 11 , the exchange structure 1111 (e.g., first fins 1113 and/or second fins 1121 ) is graded between a first portion 1115 and a second portion 1117. The first portion 1115 may be next to an inlet and/or the second portion 1117 may be next to an outlet. In the example of Figure 11 , the cross-sectional area (e.g., area occupied by fins over a cross section of the exchange structure) may be approximately equal at the inlet and at the outlet. Fluid velocity may be lower at the first portion 1115, where the first fins 1113 are thicker and more widely spaced, and fluid velocity may be higher at the second portion 1117, where the first fins 1113 are thinner, the second fins 1121 are thicker, and where the first fins 1113 and second fins 1121 are more narrowly spaced. Cooling performance may be more efficient where surface area is increased. In some examples, fins may be graded in different (e.g., opposite) manners along a flow direction. For instance, the thickness of the first fins 1113 may be reduced along the flow direction 1119 and the thickness of the second fins 1121 (e.g., interior fins) may be increased along the flow direction 1119.

[0089] In some examples, when a fin structure is graded in scale, the surface area is also graded (e.g., smaller at larger scale regions, and larger at smaller scale regions). Heat exchange (e.g., cooling) may be more efficient at smaller scale areas. As the coolant temperature increases along the flow path, for instance, the heat taken away at different locations may be balanced.

[0090] Figure 12 is a diagram illustrating a perspective view of an example of a heat exchanger 1231. The heat exchanger 1231 may be an example of the heat exchanger 120 described in relation to Figure 1. In this example, the heat exchanger 1231 includes a housing 1233, graded fins 1235, an inlet 1239, and an outlet 1241. In some examples, the graded fins 1235 may be similar to the exchange structure 1001 described in relation to Figure 10. The heat exchanger 1231 may be arranged in a cold plate design, where a heat source may be placed on top of the heat exchanger 1231 and/or underneath the heat exchanger 1231. For instance, heat flux may be conducted through a top surface 1237. In some examples, heat flux may or may not be uniform. In some examples, a fin gradient may be designed to accommodate (e.g., compensate for) the heat flux distribution and/or produce an approximately uniform temperature and/or target temperature distribution.

[0091] In this example, the graded fins 1235 are continuously graded between the inlet 1239 and the outlet 1241. For instance, fin thickness of the graded fins 1235 is gradually increased over a distance of the heat exchanger 1231 , and fin spacing is gradually increased over a distance of the heat exchanger 1231. For instance, a thickness of the graded fins 1235 may range from 0.3-0.7 mm.

[0092] In this example, a substance (e.g., fluid, coolant, water, and/or air, etc.) may flow into the heat exchanger 1231 via the inlet 1239, through the graded fins 1235, and out of the heat exchanger 1231 via the outlet 1241. For instance, fluid may absorb heat from the graded fins 1235 and pass to the outlet 1241. Accordingly, the substance may flow through the graded fins 1235 of the heat exchanger 1231 while absorbing heat from the graded fins 1235.

[0093] Figure 13 is a diagram illustrating an example of a graph 1351 of temperature over a surface of a heat exchanger. For instance, the graph 1351 illustrates temperature in K over spatial dimensions of a surface of the heat exchanger 1231 of Figure 12. In some examples, Figure 13 illustrates surface temperatures resulting from heat transfer due to a heat source (e.g., a uniform heat source with a heat flux of 100,000 Watts/square meter) placed on top of the heat exchanger 1231. In the example of Figure 13, the temperature difference between the highest and the lowest temperatures is 0.6 K. The temperature distribution may be smaller (e.g., more even) in comparison with a heat exchanger having uniform fins. In this example, the temperature range is 312.6-313.2 K and a mass flow rate was 0.01 kilograms/second. The highest temperature and/or the pressure drop may be reduced in comparison with a heat exchanger having a uniform lattice structure.

[0094] While some of the examples described herein describe heat exchangers for absorbing heat, some examples of the techniques and structures described herein may be utilized to radiate heat and/or to warm an object or medium. For instance, heated fluid may be passed into a heat exchanger to radiate heat from the heat exchanger (to warm a cold engine, to heat air, for instance).

[0095] As used herein, the term “and/or” may mean an item or items. For example, the phrase “A, B, and/or C” may mean any of: A (without B and C), B (without A and C), C (without A and B), A and B (but not C), B and C (but not A), A and C (but not B), or all of A, B, and C.

[0096] While various examples of systems and methods are described herein, the systems and methods are not limited to the examples. Variations of the examples described herein may be implemented within the scope of the disclosure. For example, operations, functions, aspects, or elements of the examples described herein may be omitted or combined.