This invention is directed generally toward the field of heat exchangers, chemical reactors and recuperators employing a plurality of fluid flow channels; and more particularly to heat exchangers, chemical reactors and recuperators and methods of making heat exchangers, chemical reactors and recuperators using an additive process.
Often, an operating machine or electronic component or other system generates waste heat in the course of its normal operation. If this waste heat is not removed, degraded performance or damage to the system may result. Frequently, the operating temperature of a system needs to be precisely maintained in order to obtain optimal performance. For instance, analytical instruments may require that the sample to be analyzed be presented to the instrument at a precisely controlled temperature. Heat exchangers permit heat to be removed or added to the sample as may be desired. A common type of heat exchanger is referred to as a “heat sink;” also called a “single-sided heat exchanger”. A heat sink typically transfers heat between a solid object and some fluid media, which may be a liquid, air or other gasses. Computer microprocessors frequently employ heat sinks to draw heat from the processor to the surrounding air, thereby cooling the microprocessor. Fins are often provided to increase the surface area of the heat sink to the air thereby increasing the efficiency of the heat sink. Such a heat sink could also comprise a closed fluid system. For example, a recirculating liquid coolant might be used to transfer heat from that portion of the heat sink in contact with the heat-generating device to a remotely located radiator. Another type of heat exchanger employs at least two fluids. In this type of heat exchanger, heat is transferred from a first fluid to a second fluid without direct contact between the fluids. For example, a fluid-to-fluid heat exchanger for a blood processing machine may employ heated water to warm the blood to the desired temperature. The blood circulating path is completely separate from that of the water circulating path and dilution or contamination of the blood is thus avoided. Other types of heat exchangers include those designed to recover waste heat from systems that produce excess or otherwise unusable heat. Such systems are often referred to as recuperators. One example of a recuperator is a passenger compartment heater that derives heat from an automobile engine. Another example is a liquid rocket exhaust nozzle that employs a series of small fluid channels to pre-heat fuel or oxidizer. A chemical reactor might employ a similar structure of channels such that the reactants may be catalyzed and process heat removed in a combined heat exchanger/chemical reactor multi-channel device. In all of these examples it is desirable that the precise structure of the flow channels be controllable so the device may operate efficiently within the desired parameters.
Traditional methods of producing heat exchangers and the like typically involve assembly of a plurality of pre-formed specific components. A thermal radiator for an internal combustion engine may comprise inlet and outlet manifolds. Said manifolds being produced from metal or plastic and having been machined, formed or molded to the desired shape. A plurality of heat exchanging flow tubes is situated between these manifolds that provide a large surface area from which heat is removed typically through convection. Such designs include “tube and shell” heat exchangers. The flow tubes may be formed by welding, drawing, extrusion or any other suitable method. Fin structures may be added to further enhance heat transfer to a fluid heat transfer medium. Other components such as side caps and mounting brackets may also be attached to facilitate the utility of the device.
A known method for producing compact and highly efficient heat exchangers uses very precise and complex fluid flow structures comprising a plurality of stacked and bonded laminar elements. These types of compact heat exchangers are often referred to as Printed Circuit Heat Exchangers, or PCHE. In these structures, each layer of the stack is configured to a pre-determined shape and precisely aligned with other elements in the stack. Similar to the structure of a laminated padlock, through-holes or partial depth voids (channels) in the element of one layer may align with mating holes or voids in adjacent elements. By carefully controlling the relative position of the through holes and channels (or other voids) of each layer, intricate, three-dimensional channels and passages may be created within the stack structure. Frequently, such structures are produced in the following manner. A series of laminar elements, often referred to as shims, sheets, or platelets is produced in which a series of holes, slots, channels, or other shapes exist in the face(s) of, or through the element. The laminar element may be produced by sawing, punching, fine-blanking, coining, and water-jet or laser cutting or other means of material removal. A common method of producing very precise and complex through-hole and grooved-channel metal sheet laminar elements employs photochemical machining. In this process, acids or other chemicals are used to etch away material from a solid, thin plate to produce the desired holes and other shapes. The etching process may be 100% i.e. completely through the plate or, the process may be controlled to etch only partially through the plate, for example, 50% or halfway through the plate. When a series of these plates are stacked as previously described, a three-dimensional structure replete with complex fluid flow channels and other useful structures may be realized. Heat exchangers produced in this manner are sometimes referred to as Printed Circuit Heat Exchangers or PCHE. Joining the plates together may be accomplished by the use of adhesives, brazing or welding or other known bonding methods. A preferred bonding method, particularly for severe service structures which must operate under extreme temperature, pressure and corrosive environments, is that of diffusion bonding or variants such as transient liquid phase diffusion bonding (TLP DB) or diffusion brazing. The diffusion bonding process is well known and will not be elaborated upon.
Production processes using variously formed heat exchanger components require complex and expensive, special purpose tooling. Additionally, a number of unrelated fabrication and assembly processes must be employed. Since the tooling and processes required are often extremely part specific, it can be very expensive and time consuming to implement even a small design change. Additionally, since the production process usually relies on material removal, such as punching, or sawing, a considerable amount of waste material is created which must be recycled or discarded, potentially creating environmental issues. The process of using stacked, laminar elements as described previously, suffers from the same issues in that tooling is frequently very specific to a particular part and is not readily re-purposed. If photochemical machining is employed, less purpose-built tooling may be required as the etch pattern and exposure mask can be digitally generated. However, this flexibility is not without problems. The etching process employed uses corrosive materials, typically strong acids or bases. Further, effluent from the photomask development and removal and from etching and subsequent washing process contains not only strong chemicals but also dissolved metals that must be properly recovered, recycled or otherwise disposed of. This recycling/disposal is often complex and expensive.
The process of the instant invention overcomes many of the shortcomings of previous processes, particularly with respect to costly dedicated tooling and the generation of toxic waste materials. Significantly, an additive process variant enables reduced bonding process equipment costs and enables a multiple material selection at any useful place on the platelet surface. Multiple materials and multiple material forms are possible and useful in application.
An additive material process is employed to produce a structure that may find utility in heat sinks, heat exchangers, recuperators, chemical reactors and other systems requiring a plurality of pre-determined fluid passages. The processes of furnace bonding or diffusion bonding are well suited to the production of the laminar stacks previously described. The processes are precise, efficient and highly scalable. Additionally, these processes produce virtually no waste materials and employ a minimum of specialized fixturing. By utilizing an additive process in concert with conventional sheet stock to produce the laminar elements to be bonded, virtually all the waste materials of the entire process may be eliminated. Here the additive material is deposited on conventional sheet material in the pattern desired. The sheet stock is held flat and kept cool during the additive process by use of a vacuum or electrostatic or magnetic chuck or by another method. Additionally, the expensive and purpose-built tooling of previous production methods is not required. Further, since the exact geometry produced by many of the additive production processes is essentially software defined, design changes may be easily and quickly implemented. This is particularly useful if an iterative design process is being employed in which a series of different designs are to be produced and compared for efficacy. The resultant structures of additive processes suitable for production of devices such as heat exchangers and the like generally fall into two categories. The deposited structures may be dense or they may be less than fully dense and hence, more compliant and deformable than dense structures. In dense structures, the deposited structural material is at or very near its theoretical maximum density, having virtually no unintentional voids. In deformable structures, interstitial spaces will be present to some degree and tend to increase the compliance or plasticity of the structure. Dense structure additive processes that find application in the instant invention include, but are not limited to, ultrasonic 3-D deposition sometimes referred to as Ultrasonic Additive Manufacturing (UAM), Cold Spray, sometimes referred to as 3-D painting, Selective Laser Sintering (SLS), Alloy Tape Application, and Densified Silk Screening. In densified material application, such as by silk screening, a slurry of viscous material is deposited by screening. Other techniques of compliant material application include CNC extrusion, powdered tape application, or a similar process to produce a 3-dimensional structure. To be densified structures they may be fired in vacuum, reducing atmosphere or otherwise controlled atmosphere to yield the desired platelet pattern. Another method of producing dense structures employs “Solid Wire Plotting” in which a wire is simultaneously fed and bonded to a substrate while under computerized numerical control. The solid wire process is similar to Fused Deposition Modeling (FDM).
Non-densified deformable structure processes that find application in the instant invention include, but are not limited to, Silk Screening or CNC Extrusion without densification and die-cut powdered paste which may be a pure material, any alloy or a mixture of low melting point metals and a high melting point material, typically powdered. The degree of densification may be controlled by particle size, particle size distribution, percentage of any binder present, percentage of any filler alloy present, firing temperature and application of force during and after any sintering and bonding process. If desired, a porous structure may be created, through which fluids may flow. This may be desirable to increase surface area to improve heat transfer or increase active sites in a reactor. The degree of porosity may also be controlled by at least partially filling any interstitial spaces with an additional material either during or after the sintering process.
With the exception of the solid wire process, any of the other mentioned deformable additive processes may be employed to create a micro-porous structure if desired. The solid wire process may be used to create a macro-porous structure.
A beneficial feature of dense structures produced using any of the additive processes is that conventional and well-known diffusion bonding processes may be employed. Deformable structures produced by additive processes may be bonded using low force modified diffusion bonding or variations. Here again, the desirable features and benefits of diffusion bonding may be realized. In the case of liquid phase sintering, it is possible in some cases to combine the sintering process and the desired bonding to a sheet substrate in one operation or, at least, a ramped time and temperature operation.
A preferred structure of the invention comprises a substrate, which may or may not be planar, onto which is deposited the additive 3-D structure. The deformable nature of the structure is, through suitable processing, solidified and becomes dense and non-deformable. Diffusion bonding of conventional dense structures is well established. Heat exchangers using dense structures are processed through control of time, temperature and applied forces (pressure applied to faying surfaces) to complete bonding and hence create a suitably solid structure. Force application is a very costly portion of the entire processing costs due to the substantial force-distributing tooling (often used are large precision machined graphite or refractory metal or ceramic platens), and extra processing time to heat and cool tooling platens. The furnace utilized to apply force to the assemblies being bonded is costly in large part due to the extreme forces that need to be transmitted into the bonding furnace hot zone.
Deformable structures can be bonded without the expense of the large applied forces necessary in diffusion bonding of dense structures. The expense of creating extremely flat tooling and assembly components can be reduced due to the compliance of the screened or otherwise deformable platelet. Densification to any particular level required can be accomplished through appropriate time at temperature processing at significantly reduced applied forces.
Another benefit of the invention is that the composition of the screened or printed material can be tailored for the particular region of the platelet pattern where it may be best suited. For instance, if certain regions of the platelet structure require high corrosion resistance and other regions do not, a suitable low cost alternative material may be used accordingly side by side with a higher strength material. Additionally, structures that exhibit functionally gradient properties may also be created by the process of this invention. For example, a structure may be created in which the degree of thermal conductivity varies with respect to position in the structure. Similarly, a structure with positionally varying porosity could be created in structures that are non-dense. These functionally gradient features may be created by altering the formulation of the material to be deposited, altering any force applied to the material, altering the heat applied to the material and so forth.
Other objectives and further advantages and benefits associated with this invention will be apparent to those skilled in the art from the description, examples and claims which follow.
Referring to
While each layer of the deposition applied in
The size, shape and other characteristics of the first structure which provide a fluid flow channel 12A can be created by adding additional layers to the first layer 72. To build successive layers, at least one second material 74 is used to form additional components of said first structure which provides a fluid flow channel 12A. Material 74 may be the same as or a different material as material 70. The at least one second material 74 is placed or arranged in an predetermined orientation on, or next to the previously formed layer, layer 72. The at least one second material 74 is secured to layer 72 to form another layer 76, see
As shown in
The first material configured to form a second structure which provides a fluid flow channel can be arranged on the substrate 14 in a predetermined orientation, whereby the predetermined arrangement forms a component of the second structure which provides a fluid flow channel 12B. The first material configured to form a second structure which provides a fluid flow channel 82 can be secured by, for example, bonding, sintering or any other mechanism or procedure known to one of skill in the art which form a solid mass, to the substrate 14. This forms a first layer 84, see
The size, shape and other characteristics of the second structure which provides a fluid flow channel 12B can be created by adding additional layers to the first layer 84. To build successive layers, at least one second material configured to form a second structure which provides a fluid flow channel 86 is used to form additional components of the second structure which provides a fluid flow channel 12B. Material 86 may be the same as or a different material as those materials previously described. The at least one second material configured to form a second structure which provides a fluid flow channel 86 is placed or arranged in a predetermined orientation on, or next to the previously formed layer, layer 84. The at least one second material configured to form a second structure which provides a fluid flow channel 86 is secured to base layer 84 to form another layer 88, see
Depending on the forming processes, i.e. the sintering process and the characteristics of the material used, the structures can be created having different characteristics or properties. For example, the structure which provides a fluid flow channel 12 can be formed having a greater density than adjacent structures which provide a fluid flow channel 12 (i.e. 12A vs. 12B vs. 12C. Density of these structures can be controlled, for example, by the size of material used and by the manipulation of the formation process, i.e. degree of sintering. Moreover, since the structure which provides a fluid flow channel 12 is created layer by layer, an individual structure which provides a fluid flow channel 12 (i.e. 12A) may contain a first layer that is more or less dense than adjacent or successive layers. In addition, each fluid structure which provides a flow channel 12 (i.e. 12A vs. 12B vs. 12C) can be designed to have different porosities or percentage of void spaces. This may be accomplished by, for example, controlling or selecting the size and shape of the materials used. As described for density, an individual structure which provides a fluid flow channel 12 may be constructed so that each layer has a different porosity. Manipulation of these features allows for diverse structures, both internally, (i.e. layer by layer) and with respect to adjacent structures. Moreover, the diversity of the structures can be changed rapidly and easily.
Detailed embodiments of the instant invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific functional and structural details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representation basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.
One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.
In accordance with 37 C.F.R. 1.76, a claim of priority is included in an Application Data Sheet filed concurrently herewith. Accordingly, the present invention claims priority to U.S. Provisional Patent Application No. 61/906,746, entitled “METHOD OF USING ADDITIVE MATERIALS FOR PRODUCTION OF FLUID FLOW CHANNELS”, filed Nov. 20, 2013. The contents of which the above referenced application is incorporated herein by reference.
Number | Date | Country | |
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61906746 | Nov 2013 | US |