Patent Application
20180292146
The present disclosure relates generally to heat exchangers, and more specifically to a partially additively manufactured heat exchanger.
Heat exchangers, such as those utilized in aircraft or any similar application, typically include multiple layered channels with alternating hot and cold fluid passing through the channels. In such examples, a thin wall separating each channel from the adjacent channels is desirable as the thickness of the separating wall affects how efficiently heat can transfer from a hot channel to an adjacent cold channel through the wall separating the channels.
Existing additive manufacturing methods used to construct the heat exchanger structures limit the geometry capabilities and thickness capabilities of heat exchanger designs and prevent the utilization of some thin wall structures.
In one exemplary embodiment a heat exchanger includes a base structure, and a plurality of layers stacked on the base structure, each layer including a plurality of additively manufactured ribs extending from one of the base structure and an adjacent layer of the plurality of layers, and a foil layer disposed across the additively manufactured ribs such that a plurality of channels are defined within each layer.
In another example of the above described heat exchanger the plurality of additively manufactured ribs in at least one layer of the plurality of layers are skewed relative to the plurality of additively manufactured ribs in an adjacent layer.
In another example of any of the above described heat exchangers the plurality of additively manufactured ribs in at least one layer of the plurality of layers are aligned with the plurality of additively manufactured ribs in an adjacent layer.
In another example of any of the above described heat exchangers the foil layer has a thickness in the range of 15-35 microns.
In another example of any of the above described heat exchangers the foil layer has a thickness of approximately 25 microns.
In another example of any of the above described heat exchangers each of the additively manufactured ribs has a height in the range of 50-200 microns.
In another example of any of the above described heat exchangers each of the foil layers includes micro corrugations.
In another example of any of the above described heat exchangers each of the foil layers includes macro corrugations.
In another example of any of the above described heat exchangers each of the foil layers includes micro corrugations.
In another example of any of the above described heat exchangers the heat exchanger is one of an air-air heat exchanger, an air-fuel heat exchanger, an air-oil heat exchanger, and a fuel-oil heat exchanger.
In another example of any of the above described heat exchangers the additively manufactured ribs have a tapered cross section.
In another example of any of the above described heat exchangers a smallest width of each of the additively manufactured ribs is a base of the rib.
In another example of any of the above described heat exchangers a smallest width of the additively manufactured ribs is a top of the rib, relative to gravity during the manufacturing process.
In another example of any of the above described heat exchangers a smallest width of each of the additively manufactured ribs is at a mid-section of each of the ribs.
An exemplary method for constructing a partially additively manufactured heat exchanger includes building a first layer by additively manufacturing a plurality of first layer ribs on a base structure and applying a foil wall across the plurality of first layer ribs opposite the base layer, building at least one additional layer by additively manufacturing a plurality of additional layer ribs on a foil wall of an adjacent layer and applying a foil wall across the additional layers opposite the foil wall of the adjacent layer, and reiterating the step of building at least one additional layer by additively manufacturing a plurality of additional layer ribs on a foil wall of an adjacent layer and applying a foil wall across the additional layers opposite the foil wall of the adjacent layer a predetermined number of times, thereby creating a multi-layer heat exchanger.
In another example of the above described exemplary method for constructing a partially additively manufactured heat exchanger additively manufacturing a plurality of additional ribs comprises additively manufacturing additional ribs skewed relative to the ribs of the adjacent layer.
In another example of any of the above described exemplary methods for constructing a partially additively manufactured heat exchanger additively manufacturing a plurality of additional ribs comprises additively manufacturing additional ribs aligned with the ribs of the adjacent layer.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
Due to the nature of additive manufacturing technologies, certain thicknesses and three dimensional structures cannot reliably be achieved without the presence of too many flaws. One such structure is a thin wall boundary between heat exchanger channels. In order to create such a wall, the illustrated exemplary additive manufacturing machine further includes a foil roll 70. The foil roll 70 is configured to be automatically disposed on top of one or more layers of the additively manufactured component, thereby allowing for the creation of the thin wall. Once the foil layer is disposed on top of an additively manufactured layer, the next additively manufactured layer is constructed using the standard additive manufacturing techniques on top of the foil layer. The application of heat from the laser 50 bonds the foil layer to the previous additively manufactured layer, and to the new structure being created on top of the foil layer, integrating the foil layer into the additively manufactured component. This alternating additive manufacturing and foil layer application is referred to as partial additive manufacturing.
The hybrid approach described above includes the use of a foil, or other sheet material (referred to herein generally as foil), which is produced via a conventional rolling process and the use of an additive manufacturing process to successively join foils and additively manufactured layers to build up an intricate channel structure. The foil material is, in some examples, made from very high temperature, oxidation resistant alloys. The additively manufactured ribs are, in some examples, produced from the same material as the foil, or, in alternative examples, from a distinct material from the foil, depending on the specific requirements of a given heat exchanger.
Each layer 110 includes multiple ribs 130 protruding upwards from either the base structure 120 (in the case of the lowest layer 110) or from the immediately adjacent layer 110 (in the case of each subsequent layer 110.) As used herein “up” and “down” refer to the orientation of the heat exchanger 100 or other partially additively manufactured component, relative to gravity, during the partial additive manufacturing process. Applied across the ribs 130, opposite either the base structure 120 or the immediately preceding adjacent layer 110 is a foil layer 140. The foil layer 140 is adhered to the previous layer of ribs 130 via the additive manufacturing machine 10 (see
Defined by adjacent ribs 130 and adjacent foil layers 140 (or a foil layer 140 and the base structure 120) are multiple channels 150. During operation of the heat exchanger 100, hot and cold fluids flow through alternating layers and heat is transferred from a hot channel to an adjacent cold channel through the foil layer 140 defining the boundary. By utilizing the foil layer 140 as the wall separating adjacent channels, the thickness (width of the foil layer 140 normal to fluid flow through the channel 150) of the created wall is minimized, thereby increasing the efficiency of heat transfer. The foil layer 140 allows a thinner wall construction than could be achieved using a purely additive manufacturing technique.
With continued reference to
Multiple considerations are relevant to the construction process of the partially additively manufactured heat exchanger 100 of
In order to address these considerations, the cross sectional shape of each of the ribs 130 can be varied from the rectangular cross section illustrated in
The leftmost rib 332 has a trapezoidal cross section defined by a thinnest portion 302 at the connection to a base structure 320. In sequential layers, the thinnest portion 302 of the rib 332 is connected to a rib in the adjacent layer upon which the rib 332 is being constructed. The largest portion of the trapezoid is at the top, and provides a landing zone for aligning the rib in next layer sequentially. By providing the largest surface at the top, slight shifting in the alignment of the layers will still allow for construction of a properly constructed heat exchanger. One downside to this configuration, however, is that the connection between the rib 332 and the base 320 has a minimal contact area. As a result of the minimal contact area, heat dissipation from the rib 332 during the additive manufacturing process is limited, and can potentially lead to flaws in some examples.
The center rib 334 also includes a trapezoidal cross section, however the smallest thickness 304 of the rib 334 is positioned at the top edge of the layer 310. The cross sectional shape of the center rib 334 inverts the benefits and drawbacks of the leftmost rib 332, by providing minimal landing area for the next layer in the sequential construction, but providing maximal contact area for heat dissipation from creation of the rib 332 into the base plate 320.
In order to prevent either the landing area for the next rib from being too small, or the heat dissipation path during construction of the rib from being too small, an alternative rib shape that is a hybrid of the previous two ribs 332, 334 is utilized in some examples. The rightmost rib 336 illustrates one example hybrid shape. In the rightmost rib 336, the thinnest portion 306 of the rib 336 is positioned at, or near, the midpoint of the rib 336 height. In this way, the landing surface of the rib 336 at the top, and the heat dissipation of the rib 336 through contact with the base section 320 are both increased, but are not maximized. This configuration minimizes the detriments of the previously described ribs 332, 334, while still partially achieving the benefits of each previously described rib 332, 334.
In some example partially additively manufactured heat exchangers, it can be desirable to have fluid flowing in a first set of channels in one direction, and fluid flowing through a second set of channels in another direction. To accomplish this, sequential layers of the heat exchanger are rotated relative to previous layers. By way of example,
A further benefit that is achievable due to the partial additive manufacturing process for constructing the heat exchangers is that the foil layer can include corrugations which increase the surface area exposed to the fluid flowing through channels, and thereby increase the heat exchange through the channel wall defined by the foil layer.
Alternatively,
With reference to both
By incrementally building the heat exchanger using the partial additive manufacturing process described above, multiple materials can be utilized in the construction of the ribs, depending on the specific locational needs of the ribs within the heat exchanger. By way of example, the portion of the ribs at high corrosion potential locations can be constructed of specialty materials designed to mitigate corrosion. Alternatively, portions of the ribs can be made from slightly thicker materials, while materials and construction in other locations could be produced using lighter weight and thinner materials for high thermal conductivity.
While described herein as utilizing a powder bed manufacturing process, one of skill in the art will recognize that the process can be adapted to utilize powder feed, wire feed, or any other additive manufacturing process.
While illustrated and described herein using straight channels defined between two ribs, one of skill in the art will understand that the channels can be serpentine, include corners, or any other directional features, by altering the path of the corresponding ribs.
It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
