The subject matter disclosed herein generally relates to high temperature flow manifolds and, more particularly, to improved high temperature flow manifolds.
Flow manifolds may be used to collect, distribute, and/or enable the transfer of fluids within a system. Manifolds may be used for high temperature applications, such that high temperature fluids may be distributed into smaller channels, such as tubes, pipes, etc. For example, tube and shell heat exchangers may be used in high temperature applications because the channels can accommodate significant growth due to thermal expansion. Tube and shell heat exchanger designs utilize channels brazed into a hot inlet manifold such that the channel inlets are essentially flush with the inner surface of the manifold. The heat transfer coefficient in each channel may be much greater near the channel inlet (junction) than the developed heat transfer coefficient occurring a short distance into the channel. This design may result in a higher heat flux into the material of the channel near the channel inlet than into the adjacent manifold material, with resultant stresses in the channels at the channel-manifold junction when the channel and manifold materials are dissimilar or when the heat exchanger undergoes rapid thermal transients, i.e., the temperatures and/or flows through the heat exchanger vary rapidly with time. Undesirable stresses may be introduced in the channels at a channel-manifold junction when the material composition of the channel and the manifold constraining the channels are dissimilar.
According to one embodiment a manifold is provided. The manifold includes a body defining a chamber configured to receive a fluid, the body having a plurality of apertures passing therethrough and a plurality of channels engaged in the apertures and configured to receive the fluid from the chamber, each of the plurality of channels having an end defining an inlet that is in fluid communication with the chamber. Each channel defines a standoff defining a portion of the channel that is not in contact with the body such that the inlet is separated from the body by a standoff distance along the length of the channel. The standoff distance is a distance that is one or more times a hydraulic diameter of the inlet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include a plurality of shorteners, each shortener coupled with a respective inlet of a channel of the plurality of channels, each shortener configured to reduce the hydraulic diameter of the channel at the inlet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the plurality of shorteners are connected to form a sheet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that each shortener is integrally formed with the respective channel.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the standoff is a section of channel that extends the standoff distance from a surface of the body.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the standoff is at least partially defined by a standoff gap formed between an outer surface of the channel and the aperture.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the channel comprises a reduced width portion, wherein the reduced width portion has a width that is smaller than a width of a respective aperture and the length of the reduced width portion is the standoff distance, wherein the standoff gap is formed between the reduced width portion and the aperture.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the inlet of the channel is level with a surface of the body.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that each aperture defines a first portion having a first aperture width and a second portion having a second aperture width, wherein the first aperture width is larger than the outer surface of a respective channel, wherein the standoff gap is formed between the outer surface of the channel and the first portion.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first portion has a length equal to the standoff distance.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the outer surface of the channel and the aperture have the same geometric shape.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the standoff distance is a distance that is between three and six times a hydraulic diameter of the inlet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the body forms a manifold of a shell and tube heat exchanger and the channels form the tubes of the shell and tube heat exchanger.
According to another embodiment, a method of manufacturing a manifold is provided. The method includes providing a body defining a chamber configured to receive a fluid and having a plurality of apertures passing therethrough and installing a plurality of channels to engage with the apertures, each of the plurality of channels having an end defining an inlet that is in fluid communication with the chamber. As installed, each channel defines a standoff defining a portion of the channel that is not in contact with the body such that the inlet is separated from the manifold by a standoff distance along the length of the channel. The standoff distance is a distance that is one or more times a hydraulic diameter of the inlet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include installing a plurality of shorteners at the inlet of each channel, the shorteners configured to reduce the hydraulic diameter of the channel at the inlet.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the plurality of shorteners are each connected to form a sheet, the method comprising installing the sheet into the manifold.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the standoff is a section of channel that extends the standoff distance from a surface of the body.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the standoff is at least partially defined by a standoff gap formed between an outer surface of the channel and the aperture.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the inlet of the channel is level with a surface of the body.
In addition to one or more of the features described above, or as an alternative, further embodiments may include that the body is a manifold for a shell and tube heat exchanger and the channels are the tubes of the shell and tube heat exchanger.
Technical effects of embodiments of the present disclosure include reducing thermal stresses near a channel-manifold interface in a manifold. Further technical effects of embodiments include offsetting a channel inlet from a manifold interface and/or decreasing the hydraulic diameter of a channel at the channel inlet to reduce the length of offset.
The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
As shown and described herein, various features of the disclosure will be presented. Various embodiments may have the same or similar features and thus the same or similar features may be labeled with the same reference numeral, but preceded by a different first number indicating the figure to which the feature is shown. Thus, for example, element “a” that is shown in
As described herein, improved manifolds and characteristics thereof will be described with respect to a number of embodiments. However, those of skill in the art will appreciate that the various embodiments are non-limiting and the concepts and principles described may be applied to other configurations, devices, and/or systems. For example, described below are variations and embodiments of shell and tube heat exchangers. However, various concepts described with respect to the manifold of the heat exchanger may be applied to other manifolds, i.e., the application is not limited to heat exchanger manifolds.
As noted, the channels 106 are brazed into the body 102 and flush with the interface surface 108 at each aperture 104 such that inlets to the channels are flush with the interface surface 108 of the body 102. During operation, the heat transfer coefficient in each channel 106 may be much greater near the channel inlet, i.e., at the interface surface 108, than the developed heat transfer coefficient occurring a short distance into the channel 106, i.e., away from the interface surface 108. As a result, a high heat flux may be generated near the channel inlet with resultant stresses in the channels 106 at the interface surface 108, i.e., at a channel-manifold junction. If the channel and manifold materials are dissimilar and/or when the manifold undergoes rapid thermal transients, i.e., the temperatures and/or flows through the manifold vary rapidly with time, the stresses may be greatest. This may be further exacerbated due to a lower heat flux generated into the interface surface 108 and the body 102. That is, the heat flux of the channels 106 may be different than that of the material of the body 102, and thus thermal and mechanical stresses may arise based on the thermal expansion or contraction of either or both of the channels 106 and/or the body 102.
For example, if the channels 106 expand or contract at a faster rate than the material to which they are brazed, i.e., the interface surface 108 and body 102, the connection or brazing between the two elements may undergo stresses. Over time this may result in cracks and/or separation, of the braze material or the material of the channels and/or manifold, which may result in a leak, thus damaging the manifold 100.
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The standoff of the channels 206 may reduce thermal stresses near the channel/manifold interface, i.e., at the interface surface 208, by placing the channel inlet 210 far enough from the interface surface 208 to significantly reduce the heat flux into the material of the channels 206 at the interface surface 208. Although the heat transfer coefficient at the channel inlet 210 may remain high, the heat flux into the channel/manifold junction is reduced compared to the configuration shown in
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It will be appreciated by those of skill in the art that the manifold junction width 416 does not extend for the entire thickness of the body 402. Rather, a portion 420 of the aperture 404 through the body 402 will have a second aperture width 422 that is substantially the same as the outer width 418 of the channel 406. Substantially the same widths, as used herein, may mean that the widths are the same, or close enough to form an interference fit, or have a small separation between the two surfaces for brazing material, depending on the desired configuration. In some embodiments, a small air gap may be formed between the channel 406 and the body 402 such that a braze material may be supplied and the channel 406 and the body 402 may be brazed together. In some such embodiments, the braze material may not be supplied or at least may not interfere with the standoff gap 414. In some embodiments, the first aperture width 416 of the body 402 that is larger than the channel width 418 may be formed by a counter-bore or other machining.
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Similar to the embodiment of
In any of the above example embodiments, or variations thereof, the standoff distance (312, 412, 512) may be a function of the hydraulic diameter. In some embodiments, the standoff distance may be equal to one or more times the hydraulic diameter of the channel. Further, in some embodiments, the standoff distance may be equal to a length that is three to six times the hydraulic diameter of the channel. Due to increased weight and/or structural considerations, it may be desirable to minimize the standoff distance while maximizing the thermal benefits. Further, those of skill in the art will appreciate that variations or combinations of the non-limiting embodiments shown in
Further, those of skill in the art will appreciate that the standoff gap (414, 514) may not be a circumferential standoff gap. That is, in some embodiments, the channels may not be circular but rather may be square, rectangular, or have another geometric shape. As such, the above described “widths” may refer to a width or other dimension of the channel and/or aperture. As such, the standoff gap is not limited to a circumferential or circular gap, but rather, the standoff gap is a volume or space formed between an exterior or outer surface of the channel and an interior surface of an aperture that is formed in the manifold. In some non-limiting embodiments, the geometric shape of the channel and the geometric shape of the aperture may be the same, and in other non-limiting embodiments, the two geometric shapes may be different. Those of skill in the art will appreciate that additive manufacturing techniques may be used to form any desired configuration, while forming a gap between a surface of a channel and a surface of the manifold, without departing from the scope of the disclosure. The standoff gap may be any size, or distance, extending between the channel and the aperture. In some embodiments, the standoff gap may be configured to provide a volume between a surface of the channel and the aperture wherein a fluid within the manifold may enter the volume.
A flow recirculation zone may form at the channel inlet that may result in a high heat transfer coefficient region starting just beyond the recirculation zone instead of exactly at the channel inlet. This may result in a larger increased standoff distance to achieve optimal pressure drop and flow distribution across a hot inlet manifold to thus provide the thermal benefits described above. Because the length of the region with high heat transfer coefficient and the distance of this zone from the channel inlet due to recirculation are functions of the hydraulic diameter of the hot flow passages, the region of high heat transfer coefficient can moved or forced closer to the channel inlet, i.e., the standoff distance can be shortened by incorporating a feature that results in multiple flow channels for a short distance near the channel inlet, each with reduced hydraulic diameter.
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With the application of the shorteners, the length of heat transfer down the channel length extending beyond the manifold interface surface, and from the shortener to the channel, may be reduced by making the outer width of the shortener slightly smaller than the inner width of the channel with a resultant air gap between the shortener outer width and channel inner width. Other embodiments may employ, in the alternative or in combination with the air gap, thin material and/or material with a low conductivity, such as ceramic or metal alloys. Those of skill in the art will appreciate that the channels of the manifold may include one or more flow passages. As such, one or more shorteners may be applied to the flow passages of the channels. One example purpose of the shorteners is to minimize the hydraulic diameter of all possible passages. Further, as shown in
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At step 802, a manifold is provided. The manifold may include at least one manifold and a plurality of channels that are coupled to a body of the manifold. At step 804, a plurality of channels are installed into or with the manifold. The plurality of channels are positioned or set to have a standoff distance that is sufficient to minimize thermal stresses while minimizing the standoff. At step 806, the plurality of channels are provided with shorteners that are configured to enable the standoff distance to by minimal. The shorteners are provided to reduce the hydraulic diameters of the channels, thus enabling a shorter standoff distance. Although the process 800 is provided in a specific order, those of skill in the art will appreciate that the order may be varied or various steps may occur simultaneously and/or nearly simultaneously. Further, it will be appreciated that the various steps may define different techniques, such as described above. Moreover, additional steps may occur before, during, or after the above described process. For example, a step of depositing braze material and brazing the braze material to secure the channels to the manifold may be performed.
For example, step 804 may include installing a channel with an inlet having a reduced diameter, and thus the formation or manufacture of the channels may require a reduced diameter end, e.g., as shown in
Further, step 806 may include installing one shortener into each channel (e.g.,
Regardless of the order of steps or how the various steps are carried out, the end result of process 800 is a manifold with thermal stress reduction features in the form of a standoff of the channels and/or the addition of a shortener in the channel. Such manifolds may include features that are shown and described above, or may include variations thereon. For example, the standoff may be of any desired length, the channels may have any desired geometries and/or configurations, and the shorteners may be configured with any desired geometries and/or configurations.
Advantageously, embodiments described herein provide manifolds with reduced low cycle fatigue and increased life. Advantageously, the features of the standoff and/or shorteners described herein may reduce the stresses on the manifold at the manifold-channel interface/junction, and thus cracks and/or leaks due to thermal stresses may be prevented. This may be achieved, in accordance with various embodiments, by reducing the stresses and strains due to thermal gradients near the interface between the channel and manifold. For example, the heat flux in regions near the entrance of the channel may be reduced and/or high heat flux regions may be moved away from the manifold-channel interface/junction.
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.
For example, various geometries, configurations, distances, lengths, etc. may be used without departing from the scope of the present disclosure. Further, although some ratios and shapes are shown and described herein, these are provided as example and for illustrative purposes. Moreover, although shown and described with a standoff or a bore into the manifold, those of skill in the art will appreciate that any combination of standoff length and counter-bore depth may be used without departing from the scope of the present disclosure. Further, although shown with respect to a shell and tube heat exchanger, those of skill in the art will appreciate that embodiments described herein may be applied to any manifold, and may be applied to high-temperature manifolds as desired.
Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This invention was made with government support under Contract No. FA8650-09-D-2923 awarded by the United States Air Force. The government has certain rights in the invention.