Coolant flow layer exchange-based heat management

Abstract

Systems and methods for coolant flow layer exchange-based heat management are provided. In one example, a conductive heat transfer apparatus (110) comprises a housing (112) that includes a first surface (113) and a second surface (114), and an interior pathway (115) defining a fluid flow path through the housing (112) and positioned between the first surface (113) and the second surface (114). The interior pathway (115) includes a three-dimensional flow layer inverting lattice (130) comprising a first inlet (131) oriented to receive a first flow layer (124) from the interior pathway and a second inlet (133) oriented to receive a second flow layer (126) from the interior pathway, and a plurality of passages forming a first fluid channel (132) and a second fluid channel (134) distinct from the first fluid channel (132), wherein the first fluid channel (132) and the second fluid channel (134) exchange a relative position of the first flow layer (124) and the second flow layer (126) with respect to the first surface (113) and the second surface (114).

Description

COOLANT FLOW LAYER EXCHANGE-BASED HEAT MANAGEMENTBACKGROUND OF THE INVENTION

[0001] Cooling devices, such as cold plates, are often used to cool electronic components by conductively absorbing thermal energy from the electronic components into a cooling liquid, and then transferring the thermal energy from the cooling liquid into a heat sink for dissipation to an ambient environment. The cooling liquid is circulated through the cooling device, for example by a pump, so that cooling liquid warmed by the absorbed thermal energy can be transported away from a location of the cooling device thermally coupled to the electronic components, and replaced with relatively cooler cooling liquid.BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The present technology is described in detail below with reference to the attached drawing figures, wherein:

[0003] FIG. 1 is a block diagram of an example conductive heat transfer apparatus, suitable for implementing aspects of the technology;

[0004] FIG. 2 is a block diagram of an example conductive heat transfer apparatus, suitable for implementing aspects of the technology;

[0005] FIGS. 3A and 3B illustrate examples of closed loop conductive heat transfer systems, according to aspects of the technology described herein;

[0006] FIG. 4 illustrates an example three-dimensional flow layer inverting lattice implemented using a walled gyroid lattice, according to an aspect of the technology described herein;

[0007] FIGs. 5 and 6 are example implementations of conductive heat transfer apparatuses, in accordance with an aspect of the technology described herein;

[0008] FIG. 7 is a flow diagram showing an example method for conductive heat transfer, in accordance with an aspect of the technology described herein;

[0009] FIG. 8 is a block diagram of an example operating environment, suitable for implementing aspects of the technology; and

[0010] FIG. 9 is a flow diagram showing an example method for generating a design file for a conductive heat transfer apparatus, in accordance with an aspect of the technology described herein.DETAILED DESCRIPTION OF THE INVENTION

[0011] Thermal management technologies provide solutions directed to preventing heat generating devices from overheating. Cooling devices, such as cold plates, are often used to cool electronic components by conductively absorbing thermal energy from the electronic components into a cooling liquid, and then transferring the thermal energy from the cooling liquid into a heat sink for dissipation to an ambient environment. The cooling liquid is circulated through the cooling device, for example by a pump, so that cooling liquid warmed by the absorbed thermal energy can be transported away from a location of the cooling device thermally coupled to the electronic components, and replaced with relatively cooler cooling liquid. While electronic device components, such as amplifiers, power supplies, batteries, and processing units, are non-limiting examples of heat generating devices where thermal management may be used to prevent overheating, other examples include mechanical devices (e.g., pumps, gearboxes) and / or electromechanical devices (e.g., motors).

[0012] Cold plates represent an example thermal management technology that utilizes the flow of a coolant (e.g., a liquid coolant) to transport heat absorbed from a heat generating device to a heat sink - which may dissipate the heat, for example, into an ambient environment.As an example, a heat generating device may be in contact with a surface of the cooling device,through which thermal energy is conducted from the heat generating device, through the surface of the cooling device, and into the coolant. As the liquid coolant absorbs the heat, it continues to increase in temperature - which also decreases its capacity to absorb additional heat. By circulating the liquid coolant through the cooling device, heated coolant is continuously replaced with relatively cooler coolant so that conductive transfer of heat from the heat generating device into the coolant continues.

[0013] Laminar flow of a cooling liquid is a phenomena that occurs where the coolant flowing through the channels of a cooling device stratifies into layers with minimal mixing of liquid between the layers. Heat exchange between layers within the context of laminar flow is limited. As a result, the layer(s) of the coolant liquid flowing closest to the surface receiving the thermal energy from the heat generating device more quickly lose capacity to absorb heat as compared to the layer(s) of liquid flowing farther from that surface, reducing the overall efficiency of the cooling device. One method for addressing laminar flow of the cooling liquid, and increasing cold plate efficiency, is to introduce structures into the flow path of the cooling liquid that mix the layers together to produce a more homogenous distribution of heat within the cooling liquid - thus increasing the total quantity of thermal energy absorbed into the cooling liquid (per unit volume) for dissipation to the ambient environment. However, the introduction of the mixing produces turbulence in the cooling liquid that can restrict the flow rate and lead to a higher pressure drop across the cooling device. In liquid cooling systems, a lower pressure drop is highly desired because it leads to lower energy consumption to maintain a desired flow rate and the potential use of lower power pumping components to circulate the coolant - with corresponding lower operational costs. As such, both laminar coolant flow and mixing induced turbulence present challenges with respect to designing and fabricating coolant based cooling devices.

[0014] In contrast to mixing laminar flow layers, one or more examples presented herein take advantage of the nature of laminar flow to increase the efficiency of coolant based cooling devices by exchanging laminar flow layer positions as the coolant flows through the cooling device. More specifically, a three-dimensional flow layer inverting lattice is inserted into a coolant flow path that, within the structure of the inverting lattice, swaps the relative position of the flow layers so that the layer of cooler liquid, previously closest to a colder second surface of the cooling device, is shifted to now flow along the first surface where heat is absorbed from the heat generating device. Similarly, the layer of hot liquid, previously flowing closest to the hotter first surface of the cooling device, is shifted to now flow along the second surface. Within the structure of the three-dimensional flow layer inverting lattice, separate flow channels separately carry the respective layers so that the exchange of the relative position of the layers does not result in mixing of the liquid between layers or thermal exchange between the layers. As a result, the liquid coolant layer shifted to contact with the first surface remains cooler and has a greater capacity to absorb heat from the electronic components than it would have if instead it were mixed with the hotter liquid. Correspondingly, the liquid coolant reaching the second side remains hotter than it would have if instead it were mixed with the cooler liquid, thereby carrying a greater quantity of thermal energy for dissipation to the ambient environment.

[0015] In some example implementations, the three-dimensional flow layer inverting lattice is implemented as a 3D-printed gyroid, such as a walled lattice form gyroid, for example. The geometry of a walled gyroid lattice separates its internal space into two oppositely congruent labyrinths of passages. Those passages can be used to define two distinct channels that orthogonally traverse the structure of the lattice to effect the exchange in the relative position of laminar flow layers, without mixing of the layers. The walled gyroid lattice may be formed from one or more walled gyroid lattice unit cells.

[0016] To realize the two distinct channels for the purpose of exchanging flow layers, the three-dimensional flow layer inverting lattice is structured so that a first face of the walled gyroid lattice, and an adjacent second face of the walled gyroid lattice, are both oriented to face into the incoming flow path for the liquid coolant. An infill is applied to the first face of the walled gyroid lattice so that the first face provides one or more inlet openings into a first of the two distinct channels, but not the second. An infill is applied to the second face of the walled gyroid lattice so that the second face provides one or more inlet openings into the second of the two distinct channels, but not the first. Incoming liquid coolant flows into either the inlet openings of the first and second faces of the walled gyroid lattice, but not otherwise around the walled gyroid lattice or through other faces of the walled gyroid lattice. Where a first laminar layer of fluid enters from the first face, and a second laminar layer enters from the second face, the first laminar layer will exit the walled gyroid lattice at a position within the coolant flow previously corresponding to the second layer, and the second laminar layer will exit the walled gyroid lattice the at a position within the coolant flow previously corresponding to the first layer.

[0017] In some examples, the three-dimensional flow layer inverting lattice may compose other geometries to perform the exchange of flow layers. For example, in some implementations, the liquid coolant may stratify into more than two laminar flow layers. Accordingly, in some such implementations, the internal geometry of the three-dimensional flow layer inverting lattice may include any number of two or more internal flow channels that facilitate flow position exchange for the two or more laminar flow layers. Where more than two laminar flow layers forms within the interior pathway, coolant flow layer exchange may be performed on the additional layers separate from the exchange of the first flow layer and the second flow layer. Corresponding additional fluid channels, each isolated from each other and from the first and second fluid channels, may be formed from the plurality of passages withinthe three-dimensional flow layer inverting lattice. In such example implementations, the flow layers flowing closer to the first surface may be channeled to instead flow closer to the second surface, and the flow layers flowing closer to the second surface may be channeled to instead flow closer to the first surface.

[0018] In some embodiments, the two, or more, internal flow channels of the three- dimensional flow layer inverting lattice may comprise geometries based on double-gyroid structures and / or other triply periodic minimal surface geometries, single helix, double helix, or higher order helical geometries, or other shaped channels arranged to invert the relative position of flow layers as described herein. Furthermore, the external geometry of the three- dimensional flow layer inverting lattice, in some examples, may comprise a geometry other than a set of adjacent first and second faces oriented to face into interior pathway carrying the incoming flow of liquid coolant. For example, the external geometry of the three-dimensional flow layer may comprise a conical shape, pyramidal shape, or other surface geometry, oriented towards the interior pathway carrying the incoming flow of liquid coolant - with inlet openings positioned to channel laminar flow layers into respective interior channels of the three- dimensional flow layer inverting lattice - without substantially introducing flow obstruction.

[0019] In order to inhibit heat transfer within the walled gyroid lattice between the coolant layers, the internal walls of the walled gyroid lattice that separate the two channels may be fabricated with a thickness that dampens heat transfer between the channels through the internal walls. In some examples, the internal walls are fabricated with a thickness that provides a thermal conductivity that is less than the thermal conductivity of the surface of the cooling device that interfaces with the heat generating device. That said, a relative increase in the thickness of the internal channel separating walls will result in a corresponding decrease in the cross-sectional area of the internal channels. The decreased cross-sectional area increases coolant flow resistance, decreases flow rate, and results in a greater coolant pressure dropacross the three-dimensional flow layer inverting lattice. As previously mentioned, in a liquid cooling system, a lower pressure drop is highly desired because it leads to lower energy consumption to maintain the desired flow rate and the potential use of lower power pumping components. As such, where the designer of the cooling device has established a design criterial based pressure drop specification for the cooling device, the interior wall thickness may be optimized to provide a target thermal conductivity between the internal channels that still meets the overall pressure drop design criteria for the cooling device. The first fluid channel and a second fluid channel thus are isolated by an interior wall of the three-dimensional flow layer inverting lattice that limits thermal conductivity between the first fluid channel and a second fluid channel. In some examples, thermal conductivity between the fluid channels may be controlled in other ways such as by introducing additives during the 3D printing process of the cooling device and / or controlling porosity and oxidation.

[0020] In various example implementations, multiple three-dimensional flow layer inverting lattice may be placed within the flow path of the cooling liquid, either with a distributed spacing within the flow path, or consecutively placed within the flow path. In some example implementations, the three-dimensional flow layer inverting lattice may be fabricated as a 3D-printed component during 3D-printing of the cooling device as a monolithic 3D printed object.

[0021] Referring now to FIG. 1, FIG. 1 is a diagram illustrating an example conductive heat transfer apparatus 110, in accordance with aspects of the technology of the present disclosure. Conductive heat transfer apparatus 110 is a cooling device that may be used to cool one or more heat generating devices by conductively absorbing thermal energy from the heat generating devices into a coolant (e.g., a cooling liquid), and then transferring the thermal energy from the coolant into a heat sink for dissipation to an ambient environment, as discussed in greater detail below.

[0022] In the example provided by FIG. 1, conductive heat transfer apparatus 110 comprises a housing 112 that includes a first surface 113 and a second surface 114. The housing also includes an interior pathway 115 that defines a fluid flow path through the housing 112 positioned between the first surface 113 and the second surface 114. In this example, the first surface 113 functions as a thermal interface for conductively receiving heat generated by one or more heat generating devices 140. The heat generating device(s) 140 may be mounted or otherwise securely coupled to the first surface 113. In some aspects, a thermally conductive paste may be applied between the heat generating device(s) 140 and the first surface 113 to enhance thermal conductivity. In operation, a coolant 120 is circulated through the interior pathway 115, entering the interior pathway 115 at an inflow port 116 of the housing 112 and exiting though an outflow port 117 of the housing 112.

[0023] The shape of the route taken by the interior pathway 115 through the housing 112 is not limited to any particular pattern and the shape may be selected based on factors such as, for example, the amount of heat that the apparatus 110 is designed to absorb from the heat generating device(s) 140. FIG. 2 illustrates two example routes for interior pathway 115, with a linear one -pass design illustrated at 200A, and a non-linear s-shaped multi-pass design illustrated at 200B. With the multi-pass design illustrated at 200B, the interior pathway 115 may interface with heat generating device(s) 140 for a greater distance. Therefore a coolant 120 flowing within the interior pathway may have a correspondingly longer pathway within which it can absorb heat from the heat generating device(s) 140 as compared to the relatively shorter distance of the interior pathway 115 from the linear one-pass design illustrated at 200A.

[0024] As previously discussed, in operation as the coolant 120 is circulated through the interior pathway 115, and heat is applied to first surface 113 by heat generating device(s) 140, a thermal gradient will appear within the coolant 120 between the first surface 113 and the second surface 114, and the coolant 120 will stratify into separate flow layers - aphenomena referred to as a laminar flow. Such is the case in FIG. 1 within laminar flow regions 122 and 123, where laminar flow of coolant 120 develops and the flow of coolant 120 stratifies into a first flow layer 124 and a second flow layer 126. Due to the nature of laminar flow, within laminar flow regions 122 and 123, there is very little mixing of coolant between the first flow layer 124 and the second flow layer 126, and moreover very little exchange of thermal energy between the first flow layer 124 and the second flow layer 126. In other words, absent a disturbance in the flow of coolant 120 caused by a structural feature within interior pathway 115, the first flow layer 124 and the second flow layer 126 are effectively isolated flow channels.

[0025] Referring to laminar flow region 122, within this region the first flow layer 124 flows within the interior pathway adjacent to the first surface 113 and absorbs the heat 142 that conducts through the first surface 113. In contrast, the second flow layer 126 flows within the interior pathway adjacent to the opposing second surface 114 and due to the thermal isolation produced by laminar flow, does not receive from the first flow layer 124 the heat 142 that conducts through the first surface 113. As the first flow layer 124 continues to absorb heat 142, its temperature will rise and its capacity to further absorb additional heat will begin to decline.

[0026] Accordingly, apparatus 110 further includes at least one three-dimensional flow layer inverting lattice 130. The three-dimensional flow layer inverting lattice 130 includes a first inlet 131 to receive the first flow layer 124 from the interior pathway 115 and a second inlet 133 to receive the second flow layer 126 from the interior pathway 115. The internal structure of the three-dimensional flow layer inverting lattice 130 comprises a plurality of labyrinth like passages that form a first fluid channel 132, and a second fluid channel 134 that is distinct and isolated from the first fluid channel 132 by interior walls. The first fluid channel132 and the second fluid channel 134 each traverse through the structure of the three-dimensional flow layer inverting lattice 130 such that the first fluid channel 132 and the second fluid channel 134 exchange a relative position of the first flow layer 124 and the second flow layer 126 with respect to the first surface 113 and the second surface 114 when those flow layers exit the three-dimensional flow layer inverting lattice 130. This inversion of the relative position of the first flow layer 124 and the second flow layer 126 is illustrated in laminar flow region 123 where the first flow layer 124 now flows within the interior pathway 115 adjacent to the second surface 114 and the second flow layer 126 now flows within the interior pathway 115 adjacent to the first surface 113. Because the second flow layer 126 was not substantially warmed by heat 142 as it flowed through laminar flow region 122, and did not substantially exchange heat with the first flow layer 124 within the structure of the three-dimensional flow layer inverting lattice 130, the second flow layer 126 arrives at the first surface 113 with a higher capacity for absorbing heat 144 than if it had been intentionally mixed with the first flow layer 124. Within laminar flow region 123, it is now the second flow layer 126 that flows within the interior pathway 115 adjacent to the first surface 113 and absorbs the heat 144 that conducts through the first surface 113. In contrast, the first flow layer 124 now flows within the interior pathway 115 adjacent to the opposing second surface 114 and due to the thermal isolation produced by laminar flow, does not receive from the second flow layer 126 the heat 144 that conducts through the first surface 113. In some instances, the first flow layer 124, by flowing adjacent to the opposing second surface 114, can dissipate through the second surface 114 at least a portion of the heat 142 that it previously absorbed from the first surface 113. That is, as the first flow layer 124 flows adjacent to the second surface 114 in laminar flow region 123, it can conductively transfer heat 145 to the housing 112 which dissipates through the second surface 114 into the ambient environment. In some examples, one or more heat sink devices (e.g., a plate fin heatsink) may be coupled to the second surface 114 to facilitate the exchange of heat from coolant 120 flowing adjacent to the second surface 114 (as shownat 143 and 145) through housing 112 and to the ambient environment, which may also function to increase the temperature gradient across the interior pathway 115 and encourage stratification of coolant 120 into the first flow layer 124 and second flow layer 126.

[0027] In some examples of the conductive heat transfer apparatus 110 described herein, the housing 112, three-dimensional flow layer inverting lattice 130, and interior pathway 115, among other structural components of the conductive heat transfer apparatus 110, may be fabricated using an additive manufacturing process, such as 3D printing, as a monolithic 3D printed object. During the additive manufacturing process, a build material is applied in sequential layers and energy applied to form a hardened material 160 that defines the material structure of the conductive heat transfer apparatus 110. As used herein, “build material” refers to the material and / or materials that are used to create a 3D object during additive manufacturing.

[0028] Referring now to FIG. 3A, as shown in FIG. 3A, coolant 120 may be circulated through a closed loop system 300 that includes at least the conductive heat transfer apparatus 110, a coolant circulator 310 (e.g., a pump) and a heat sink 315. The coolant circulator 310 establishes the flow of coolant 120 through the conductive heat transfer apparatus 110. The heated coolant 120 exiting from the outflow port 117 of conductive heat transfer apparatus 110 is carried though a conduit 305 to the heat sink 315, which may be positioned at a location remote from the conductive heat transfer apparatus 110. Within the heat sink 315, the thermal energy absorbed by the coolant 120 (e.g., absorbed from the heat generating device(s) 140) is removed from the coolant 120, for example dissipated into the ambient environment (e.g., through convective heat exchange), and / or exchanged via another cooling process. The cooled coolant 120 is received by the coolant circulator 310 and pumped back through a conduit 306 into the inflow port 116 of the conductive heat transfer apparatus 110 to complete the circuit.In this way heat generating device(s) 140 are efficiently cooled using the conductive heattransfer apparatus 110 by transporting heat generated by the heat generating device(s) 140 to a remotely located heat sink 314.

[0029] Referring now to FIG. 3B, as shown in FIG. 3B, in some examples, the positioning of the three-dimensional flow layer inverting lattice 130 within the interior pathway 115 may be coordinated with respect to the position of heat generating devices 140 it is intended to cool. For example, the in FIG. 3B the three-dimensional flow layer inverting lattice 130 is placed between heat generating device 140a and heat generating device 140b (or alternative between local hot points on a heat generating device 140 that spans across the three- dimensional flow layer inverting lattice 130). Such a configuration localizes the transfer of heat from the heat generating devices over the sections of the interior pathway 115 where laminar flow is occurring so that flow layer exchange techniques described herein can most efficiently can more effectively utilize the heat storage capacity of the coolant 120 to remove heat from the heat generating devices.

[0030] Referring now to FIG. 4, FIG. 4 is a diagram illustrating an example implementation of a three-dimensional flow layer inverting lattice 130 using a 3D-printed gyroid-based structure, such as a walled lattice form gyroid 400. In various examples, the walled gyroid lattice 400 may be formed from an array of one or more walled gyroid lattice unit cells 410. To realize the two distinct channels 132 and 134 of the three-dimensional flow layer inverting lattice 130 for the purpose of exchanging the position of flow layers 124 and 126, the three-dimensional flow layer inverting lattice 130 is structured so that a first external face 430 of the walled gyroid lattice 400, and an adjacent second external face 432 of the walled gyroid lattice 400, are both oriented to face into interior pathway 115 towards inflow port 116 so as to face into the incoming flow path for coolant 120.

[0031] An infill is applied to the first face 430 of the walled gyroid lattice 400 so that the first face 430 provides one or more inlet openings 440 into the first fluid channel 132, butnot the second fluid channel 134. An infill is applied to the second face 432 of the walled gyroid lattice 400 so that the second face 432 provides one or more inlet openings 442 into the second fluid channel 134, but not the first fluid channel 132. In some examples, the first face 430 may be angled to face towards the first surface 113 and the second face 432 may be angled to face towards the second surface 114. The incoming coolant 120 - stratified into the first flow layer 124 and the second flow layer 126 - is directed to flow into either the inlet openings 440 of the first face 430 of the walled gyroid lattice 400 or the inlet openings 442 of the second face 432 of the walled gyroid lattice 400, but not otherwise around the walled gyroid lattice 400 or through other faces of the walled gyroid lattice 400. Where the first flow layer 124 of coolant 120 enters walled gyroid lattice 400 from the first face 430 (e.g., facing the first surface113), it will exit the walled gyroid lattice 400 at an opposing third face 426 of the walled gyroid lattice 400 (e.g., facing the second surface 114). Where the second flow layer 126 of coolant 120 enters walled gyroid lattice 400 from the second face 432 (e.g., facing the second surface114), it will exit the walled gyroid lattice 400 at an opposing fourth face 424 of the walled gyroid lattice 400 (e.g., facing the first surface 113). In this way, the walled gyroid lattice 400 will have caused the first flow layer 124 and the second flow layer 126 to have effectively exchanged relative positions with respect to the first and second surfaces of the conductive heat transfer apparatus 110. Within the walled gyroid lattice 400, the internal structure comprises internal walls 415 that isolate the first fluid channel 132 from the second fluid channel 134 with respect to both fluid flow and thermal conduction. That is, internal walls 415 form physical barriers that prevent the mixing of the liquid coolant 120 between the first fluid channel 132 and the second fluid channel 134. Restricting the mixing of the liquid coolant 120 between the first fluid channel 132 and the second fluid channel 134 avoids turbulence that can produce an undesired level of pressure drop and also prevents the exchange of thermal energy between the flow layers that would be caused by mixing. Moreover, the thickness of the internal walls 415may be designed to control and / or limit the amount of thermal energy that is exchanged between the flow layers via conduction through the internal walls 415. In some example implementations, build material for fabricating at least the internal walls 415 of the walled gyroid lattice 400 may be selected based on limiting thermal conduction between the flow layers within the walled gyroid lattice 400.

[0032] Although the example of conductive heat transfer apparatus 110 illustrates an example where the interior pathway 115 includes a single three-dimensional flow layer inverting lattice 130, it should be understood that other implementations may include any number of one or more of the three-dimensional flow layer inverting lattice 130 located within the interior pathway 115 of conductive heat transfer apparatus 110. For example, as shown in FIG. 5, a conductive heat transfer apparatus 110 is shown at 500 that includes a plurality of three-dimensional flow layer inverting lattices 130 distributed along the length of the interior pathway 115. As another example, as shown in FIG. 6, a conductive heat transfer apparatus 110 is shown at 600 that includes a plurality of three-dimensional flow layer inverting lattices 130 consecutively placed and series connected within the interior pathway 115.

[0033] FIG. 7 is a flow chart illustrating an example method 700 for coolant flow layer exchange-based heat management, according to some aspects of the technology described herein. It should be understood that the features and elements described herein with respect to the method of FIG. 7 may be used in conjunction with, in combination with, or substituted for elements of, any of the other examples and implementations discussed herein and vice versa. Further, it should be understood that the functions, structures, and other descriptions of elements described with respect to FIG. 7 may apply to like or similarly named or described elements across any of the figures, aspects and / or examples described herein and vice versa. In some examples, elements of method 700 are implemented by components of a conductive heat transfer apparatus 110 such as illustrated with respect to any of FIGs. 1-6.

[0034] The method 700, at B702, includes channeling a cooling fluid flow through an interior pathway defining a fluid flow path of a conductive heat transfer device, the conductive heat transfer device comprising a first surface and a second surface, the cooling fluid flow comprising a first flow layer and a second flow layer. As illustrated in FIG. 1, one or more heat generating devices may have a thermal interface with the first surface of the conductive heat transfer device such that heat is conductively transferred through a wall of the conductive heat transfer device into the coolant flowing through the interior pathway. As the coolant is circulated through the interior pathway, and heat is applied to first surface by the heat generating device(s), a thermal gradient will appear within the coolant between the first surface and the second surface, and the coolant will stratify into separate flow layers - which include the first flow layer and the second flow layer. It should be understood that although the coolant is described herein as stratifying into two separate flow layers (e.g., the first flow layer and the second flow layer), an additional number of laminar flow layers may form within the interior pathway, which for the purpose of the coolant flow layer exchange-based heat management examples provided herein, may be considered component layers (e.g., sub-layers) within either the first flow layer or the second flow layer. In some examples where more than two laminar flow layers forms within the interior pathway, coolant flow layer exchange may be performed on the additional layers separate from the exchange of the first flow layer and the second flow layer.

[0035] The method 700, at B704, includes exchanging a relative position of the first flow layer and the second flow layer with respect to the first surface and the second surface based on channeling the cooling fluid flow through at least one three-dimensional flow layer inverting lattice within the fluid flow path. Within the three-dimensional flow layer inverting lattice, the first flow layer is channeled through a first fluid channel formed from a plurality of passages within the three-dimensional flow layer inverting lattice, and the second flow layer ischanneled through a second fluid channel formed from the plurality of passages within the three-dimensional flow layer inverting lattice, wherein the first fluid channel is isolated from the second fluid channel. The method may include restricting thermal conductivity between the first flow layer and the second flow layer while exchanging the relative position of the first flow layer and the second flow layer. For example, within the three-dimensional flow layer inverting lattice, the internal structure may comprise internal walls that isolate the first fluid channel from the second fluid channel with respect to both fluid flow and thermal conduction. That is, the internal walls form physical barriers that prevent the mixing of the liquid coolant between the first fluid channel and the second fluid channel. Restricting the mixing of the liquid coolant between the first fluid channel and the second fluid channel avoids turbulence that can produce an undesired level of pressure drop and also prevents the exchange of thermal energy between the flow layers that would be caused by mixing. The thickness of the internal walls may be designed to control and / or limit the amount of thermal energy that is exchanged between the flow layers via conduction through the internal walls. In some example implementations, build material for fabricating at least the internal walls of the three- dimensional flow layer inverting lattice may be selected based on limiting thermal conduction between the flow layers within the three-dimensional flow layer inverting lattice.

[0036] For implementations exchanging more than two flow layers, additional fluid channels, each isolated from each other and from the first and second fluid channels, may be formed from the plurality of passages within the three-dimensional flow layer inverting lattice. In such example implementations, the flow layers flowing closer to the first surface may be channeled to instead flow closer to the second surface, and the flow layers flowing closer to the second surface may be channeled to instead flow closer to the first surface.

[0037] In some examples, the three-dimensional flow layer inverting lattice includes a first inlet to receive the first flow layer from the interior pathway and a second inlet to receivethe second flow layer from the interior pathway, such as illustrated in FIGs. 1 and 3. The internal structure of the three-dimensional flow layer inverting lattice may comprise a plurality of labyrinth like passages that form a first fluid channel and a second fluid channel that is distinct and isolated from the first fluid channel. The first fluid channel and the second fluid channel each traverse through the structure of the three-dimensional flow layer inverting lattice such that the first fluid channel and the second fluid channel exchange a relative position of the first flow layer and the second flow layer with respect to the first surface and the second surface when those flow layers exit the three-dimensional flow layer inverting lattice.

[0038] The three-dimensional flow layer inverting lattice, in some examples, comprises a geometry based on a walled gyroid lattice. The walled gyroid lattice may be formed from an array of one or more walled gyroid lattice unit cells. The three-dimensional flow layer inverting lattice can be fabricated within the interior pathway of the conductive heat transfer device so that a first external face of the walled gyroid lattice, and an adjacent second external face of the walled gyroid lattice, are both oriented to face into the interior pathway so to face into the incoming flow path for the liquid coolant. The first external face may be oriented to face towards the first surface while the second face may be oriented to face towards the second surface. The incoming coolant - stratified into the first flow layer and the second flow layer - is directed to flow into either the inlet openings of the first face or the inlet openings of the second face (but not otherwise around the walled gyroid lattice or through other faces of the walled gyroid lattice). The first flow layer enters the walled gyroid lattice via the inlets of the first face (e.g., facing the first surface) and exits the walled gyroid lattice at an opposing third face of the walled gyroid lattice (e.g., facing the second surface). The second flow layer enters the walled gyroid lattice via the inlets of the second face (e.g., facing the second surface 114), and exits the walled gyroid lattice at an opposing fourth face of the walled gyroid lattice (e.g., facing the first surface). In this way, the walled gyroid lattice will have caused the first flowlayer and the second flow layer to have effectively exchanged relative positions with respect to the first and second surfaces of the conductive heat transfer apparatus.

[0039] As previously mentioned, a conductive heat transfer apparatus (such as conductive heat transfer apparatus 110), including the housing, the three-dimensional flow layer inverting lattice, interior pathway, and other structural features, may be fabricated using an additive manufacturing process, such as 3D printing, as a monolithic 3D printed object. During an additive manufacturing process, a build material is applied in sequential layers and energy applied to form a hardened material that defines the material structure of the conductive heat transfer apparatus. To fabricate a conductive heat transfer apparatus such as described herein, a build material comprising copper, aluminum, stainless steel, and / or other metallic or thermally conductive material may be used.

[0040] A conductive heat transfer apparatus as described herein may be fabricated using a metal printing (e.g., metal binding printing, binder jet, Metal Jet Fusion, etc.) 3D printing process. As an example, during metal printing, the conductive heat transfer apparatus may be printed layer-by-layer in a build volume.

[0041] In some examples, metal printing may include two phases. In a first phase, the printer (e.g., print head, camage, agent dispenser, and / or nozzle, etc.) may apply an agent or agents (e.g., binding agent, glue, latex, etc.) to loose metal powder layer-by-layer to produce a glued precursor (or “green”) object. For example, a build may begin by spreading powder. A scanning re-coater can lay down a uniform, thin layer of powdered metal (e.g., a build material) across the working area. The re-coater may be refilled from supply bins of metal powder and use bi-directional recoating for increased productivity. A print head applies a print agent, such as a metal jet binding agent, at precise locations onto the powder bed to define the geometry for one or more 3D objects undergoing fabrication. At one end of the scan, a print head service station may tests, cleans, and services the print heads for reliable operation. The liquidcomponents of the print agent evaporate. The powder bed is retracted based on the thickness of the next layer to be printed. The next layer is printed and the process repeats until the build (e.g., the structure of the conductive heat transfer apparatus) is completed. The powder bed with the 3D printed object(s) is heated to complete the evaporation of liquid components from the binding agent and to cure the polymers to achieve high strength in the green part(s). Once cooled, the green part(s) can be remove. Depowdering is the process of removing loose powder from around the 3D printed object(s) and from the surfaces of the part(s) during removal. Once loose powder has been removed, remaining powder can be processed and reused for economical consumables management. In a second phase, the precursor object may be sintered (e.g., heated) to produce an end object. In some implementations, the green parts are now moved into a furnace for sintering. Sintering may cause the metal powder to fuse, and / or may cause the agent to be burned off. At sintering temperatures, atomic diffusion at the surfaces of the metal particles binds them in a matrix that can exceed 96% solid density. During sintering the polymer from the metal jet binding agent also decomposes. The 3D printed object(s) resulting from the sintered green part(s) may now undergo post-processing to meet dimensional and surface finish requirements.

[0042] Example technologies that may be used in the additive manufacturing process for fabricating a conductive heat transfer apparatus such as described herein include, but are not limited to, selective laser melting (SLM) and electron beam melting (EBM) (both of which may be used to sinter metal parts), as well as stereo lithography (SLA), direct metal laser sintering (DMLS), bound metal deposition (BMD), fused deposition modeling (FDM), powder bed fusion, high-speed sintering, etc. Various metal powder build materials can be used during additive manufacturing of a conductive heat transfer apparatus, such as, but not limited to, aluminum, stainless steel, copper, cobalt, tungsten, titanium, platinum, gold, silver, palladium,Inconel, and nickel-based alloys.

[0043] As such, other example implementations may include a design file comprising instructions to control a three-dimensional (3D) printer to fabricate a 3D printed object comprising a conductive heat transfer apparatus according to the examples described herein. Referring now to FIG. 8, a block diagram is provided showing an operating environment 800 in which aspects of the present disclosure may be employed. Among other components not shown, example operating environment 800 includes a computing device 810 having a processor 812 and memory 814, and a 3D printer 830. Computing device 810 may be any form of computing device (other than the human mind) such as a personal computer, a server computer, a printer, a 3D printer, a smartphone, a tablet computer, a smart appliance, etc. The operating environment 800 and / or computing device 810 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.

[0044] The processor 812 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 814. Memory 814 may be any tangible non-transitory electronic, magnetic, optical, and / or other physical storage device that contains or stores electronic information (e.g., instructions and / or data), such as Random Access Memory (RAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), a storage device, an optical disc, and / or the like. In some implementations, the memory 814 may be a non-transitory machine-readable storage medium encoded with instructions executable by a processor, where the term “non-transitory” does not encompass transitory propagating signals or signals per se. The processor 812 may communicate with an external device or devices, for instance, to access and store the information pertaining to the manufacturing parameters of a 3D object through various inputand / or output devices, such as a keyboard, mouse, display, another apparatus, electronic device, computing device, computer, removable storage, network device, etc., through which a user may input instructions into and / or access data from the computing device 810.

[0045] In some examples, the memory 814 may store 3D model geometry data 816 for fabricating a conductive heat transfer apparatus comprising at least one three-dimensional flow layer inverting lattice such as described with respect to any of the examples discussed herein. The 3D model geometry data 816 may be generated by the computing device 810 and / or accessed from another device. Some examples of 3D model geometry data 816 include 3D model data, such as a 3D manufacturing format (3MF) file or files, a 3D computer-aided design (CAD) image, object shape data, mesh data, geometry data, etc. The 3D model geometry data 816 may indicate the geometry (e.g., shape) of the conductive heat transfer apparatus and its component parts. In some examples, the 3D model geometry data 816 may indicate a location of a conductive heat transfer apparatus with respect to a build volume, or the computing device may arrange a 3D object model represented by the 3D model geometry data 816 into a build volume.

[0046] In some examples, the memory 814 may store a design file 820 comprising manufacturing instructions to manufacture the conductive heat transfer apparatus and / or three- dimensional flow layer inverting lattice based on 3D model geometry data 816 through an additive manufacturing device, such as 3D printer 830. In some examples, the manufacturing instructions of the design file 820 interact with an application programming interface (API) of the 3D printer 830.

[0047] The design file 820 may be generated by the computing device 810, based on the 3D model geometry data 816 and manufacturing parameter data 805, by executing model generating instructions 818. While the 3D model geometry data 816 defines the general structure and geometry for the conductive heat transfer apparatus, the manufacturing parameterdata 805 includes user selected design specifications that affect the thermodynamic performance properties of the conductive heat transfer apparatus, such as a specified housing size, a cooling rating, a pressure drop rating, a coolant flow rate, a viscosity of the liquid coolant to be used in the conductive heat transfer apparatus and / or other parameters that affect the ability of the conductive heat transfer apparatus to remove heat from heat generating devices that the conductive heat transfer apparatus is designed to cool. Based on the 3D model geometry data 816 and manufacturing parameter data 805, the model generating instructions 818 may iteratively perform simulations, for example to optimize the cross-sectional area of the internal pathway of the conductive heat transfer apparatus, and the interior wall thicknesses of the three-dimensional flow layer inverting lattice located within the internal pathway, to derive dimensions for those features that provide for the target flow rates, pressure drop(s), and heat removal performance specified by the manufacturing parameter data 805. The design file 820 is transmitted to the 3D printer 830, or otherwise used by processor 812 to control 3D printer 830, to operate the 3D printer 830 to produce one or more instances of a conductive heat transfer apparatus that includes a three-dimensional flow layer inverting lattice such as described herein.

[0048] FIG. 9 is a flow chart illustrating a method 900 for a computer implement method for generating a design file that controls a 3D printer to fabricate a conductive heat transfer apparatus that comprises a three-dimensional flow layer inverting lattice according to any of the examples described herein. It should be understood that the features and elements described herein with respect to the method of FIG. 9 may be used in conjunction with, in combination with, or substituted for elements of, any of the other examples and implementations discussed herein and vice versa. Further, it should be understood that the functions, structures, and other descriptions of elements described with respect to FIG. 9 may apply to like or similarly named or described elements across any of the figures, aspects and / orexamples described herein and vice versa. In some examples, elements of method 900 are implemented by components of a computing device 810 such as illustrated with respect to FIG. 8. In some examples, instructions implementing method 900 may be encoded onto a non- transitory machine readable storage medium that may be read for execution by a processor.

[0049] The method 900, at B902, includes accessing manufacturing parameter data for a conductive heat transfer apparatus comprising an interior pathway defining a fluid flow path within an enclosure comprising a first surface and a second surface. The manufacturing parameter data includes user selected design specifications that affect the thermodynamic performance properties of the conductive heat transfer apparatus, such as a specified housing size, a cooling rating, a pressure drop rating, a coolant flow rate, a viscosity of the liquid coolant to be used in the conductive heat transfer apparatus and / or other parameters that affect the ability of the conductive heat transfer apparatus to remove heat from heat generating devices that the conductive heat transfer apparatus is designed to cool.

[0050] The method 900, at B904, includes generating, based on the manufacturing parameter data, a design file comprising instructions to control a three-dimensional (3D) printer to fabricate a 3D printed object comprising the conductive heat transfer apparatus, the instructions comprising directions to fabricate a three-dimensional flow layer inverting lattice within the interior pathway. As discussed herein, the at least one three-dimensional flow layer inverting lattice may comprise a plurality of passages forming a first fluid channel and a second fluid channel distinct from the first fluid channel. The first fluid channel and the second fluid channel are routed within the three-dimensional flow layer inverting lattice to exchange a relative position of a first flow layer and a second flow layer within the interior pathway with respect to the first surface and the second surface. The three-dimensional flow layer inverting lattice may include a walled lattice form gyroid, such as described with respect to FIG. 4. The walled gyroid lattice may be formed from an array of one or more walled gyroid lattice unitcells. In some examples, to realize the two distinct channels of the three-dimensional flow layer inverting lattice for the purpose of exchanging the position of first and second flow layers, the three-dimensional flow layer inverting lattice is structured so that a first external face of the walled gyroid lattice, and an adjacent second external face of the walled gyroid lattice, are both oriented to face into the interior pathway towards the inflow port so as to face into the incoming flow path for coolant. The internal geometry of the three-dimensional flow layer inverting lattice causes the first flow layer and the second flow layer of coolant flowing through the three-dimensional flow layer inverting lattice to exchange relative positions with respect to the first and second surfaces of the conductive heat transfer apparatus. In some example implementations, the design file may be generated by executing model generating instructions that inputs the manufacturing parameter data and 3D model geometry data, and performs iterative simulations to optimize dimensions of conductive heat transfer apparatus features to obtain thermodynamic performance properties corresponding to the manufacturing parameter data.

[0051] Referring now to FIG. 10, FIG. 10 illustrates simulation results for example flows of coolant liquid through example conductive heat exchangers (e.g., cold plates). In particular, FIG. 10 at 1010 illustrates simulation results for first simulation for a conductive heat transfer apparatus that includes a three-dimensional flow layer inverting lattice such as shown in FIG. 1, where the three-dimensional flow layer inverting lattice comprises a walled gyroid lattice. FIG. 10 at 1020 illustrates simulation results for a second simulation for a conductive heat exchanger that instead includes an embedded spiral structure that mixes the cooling liquid as it flows through the heat exchanger. For both simulations, the same middle temperature (312.6 K), coolant viscosity, flow rate, and structure was used, with the difference being that the first simulation at 1010 provided for laminar flow and use of the three- dimensional flow layer inverting lattice, and the second simulation at 1020 used the embeddedspiral structure to mix the coolant to eliminate any laminar flow from occurring. Where the first simulation 1010 with the three-dimensional flow layer inverting lattice demonstrated a 115 Pascal (Pa) pressure drop, the second simulation 1020 with the embedded spiral structure demonstrated a substantially higher 135 Pa pressure drop. In liquid cooling systems, a lower pressure drop is highly desired because it leads to lower energy consumption to maintain the desired flow rate and the potential use of lower power pumping components. Therefore, lower operational costs can be realized using the flow layer exchange techniques describe herein as compared to techniques that use coolant mixing. Also as shown in FIG. 10, a comparison of the temperature maps of the first simulation 1010 and the second simulation 1020 demonstrate that in this simulation, the three-dimensional flow layer inverting lattice produced the lower (e.g., more favorable) pressure drop while still achieving similar thermal performance as the embedded spiral structure.

[0052] Computer-storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVDs) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computing device. Computer storage media does not comprise signals per se.

[0053] The subject matter of aspects of the technology is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be practiced in other ways, to include different features or combinations offeatures similar to the ones described in this document, in conjunction with other present or future technologies. In addition, words such as “a” and “an,” unless otherwise indicated to the contrary, may also include the plural as well as the singular. Thus, for example, the constraint of “a feature” is satisfied where one or more features are present. Furthermore, the term “or” includes the conjunctive, the disjunctive, and both (a or b thus includes either a or b, as well as a and b).

[0054] While various examples of techniques are described herein, the techniques 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.

Claims

CLAIMSWhat is claimed is:

1. A conductive heat transfer apparatus, the apparatus comprising: a housing that includes a first surface and a second surface; and an interior pathway defining a fluid flow path through the housing and positioned between the first surface and the second surface, wherein the interior pathway includes a three-dimensional flow layer inverting lattice comprising: a first inlet oriented to receive a first flow layer from the interior pathway and a second inlet oriented to receive a second flow layer from the interior pathway; and a plurality of passages forming a first fluid channel and a second fluid channel distinct from the first fluid channel, wherein the first fluid channel and the second fluid channel exchange a relative position of the first flow layer and the second flow layer with respect to the first surface and the second surface.

2. The apparatus of claim 1, wherein the three-dimensional flow layer inverting lattice further comprises a geometry based on a walled gyroid lattice.

3. The apparatus of claim 1, wherein the three-dimensional flow layer inverting lattice comprises a walled gyroid lattice that includes a first external face, the first external face comprising the first inlet; wherein the walled gyroid lattice includes a second external face, the second external face comprising the second inlet; wherein the first external face includes a first infill that blocks access to the second fluid channel from the first external face; and wherein the second external face includes a second infill that blocks access to the first fluid channel from the second external face.

4. The apparatus of claim 3, wherein the first external face is oriented to face towards the first surface and the second external face is oriented to face towards the second surface.

5. The apparatus of claim 1, wherein the three-dimensional flow layer inverting lattice comprises a plurality of series connected three-dimensional flow layer inverting lattices within the fluid flow path.

6. The apparatus of claim 1, wherein the first surface, the second surface, the fluid flow path, and the three-dimensional flow layer inverting lattice, are integrated components of a monolithic 3D printed object.

7. The apparatus of claim 1, wherein the first fluid channel and a second fluid channel are isolated by an interior wall of the three-dimensional flow layer inverting lattice that limits thermal conductivity between the first fluid channel and the second fluid channel.

8. A non-transitory machine-readable storage medium encoded with instructions executable by a processor to: access manufacturing parameter data for a conductive heat transfer apparatus comprising an interior pathway defining a fluid flow path within an enclosure comprising a first surface and a second surface; and generate, based on the manufacturing parameter data, a design file comprising instructions to control a three- dimensional (3D) printer to fabricate a 3D printed object comprising the conductive heat transfer apparatus, the instructions comprising directions to fabricate a three-dimensional flow layer inverting lattice within the interior pathway, the three-dimensional flow layer inverting lattice comprising: a plurality of passages forming a first fluid channel and a second fluid channel distinct from the first fluid channel; and wherein the first fluid channel and the second fluid channel are routed within the three-dimensional flow layer inverting lattice to exchange a relative position of a first flow layer and a second flow layer within the interior pathway with respect to the first surface and the second surface.

9. The non-transitory machine-readable storage medium of claim 8, wherein the manufacturing parameter data includes: a housing size, a cooling rating, a pressure drop rating, a coolant flow rate, or a liquid coolant viscosity.

10. The non-transitory machine-readable storage medium of claim 8, the design file further comprising instructions to control the 3D printer to fabricate the three- dimensional flow layer inverting lattice based on a walled gyroid lattice.

11. The non-transitory machine-readable storage medium of claim 8, the instructions executable by the processor to further generate the design file based on iterative simulations to obtain thermodynamic performance properties corresponding to the manufacturing parameter data.

12. A method comprising: channeling a cooling fluid flow through an interior pathway defining a fluid flow path of a conductive heat transfer device, the conductive heat transfer device comprising a first surface and a second surface, the cooling fluid flow comprising a first flow layer and a second flow layer; and exchanging a relative position of the first flow layer and the second flow layer with respect to the first surface and the second surface based on channeling the cooling fluid flow through a three-dimensional flow layer inverting lattice within the fluid flow path.

13. The method of claim 12, further comprising: restricting thermal conductivity between the first flow layer and the second flow layer while exchanging the relative position of the first flow layer and the second flow layer.

14. The method of claim 12, further comprising: within the three- dimensional flow layer inverting lattice: channeling the first flow layer through a first fluid channel formed from a plurality of passages within the three-dimensional flow layer inverting lattice; and channeling the second flow layer through a second fluid channel formed from the plurality of passages within the three-dimensional flow layer inverting lattice, wherein the first fluid channel is isolated from the second fluid channel.

15. The method of claim 12, wherein the three-dimensional flow layer inverting lattice comprises a walled gyroid lattice that includes a first inlet that channels the first flow layer through a first fluid channel formed from a plurality of passages within the walled gyroid lattice; and wherein the walled gyroid lattice includes a second inlet that channels the second flow layer through a second fluid channel formed from the plurality of passages within the walled gyroid lattice, wherein the first fluid channel is isolated from the second fluid channel.

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