US20240295369A1

US20240295369A1 - Heat exchangers with decongealing bypass and methods of decongealing the same

Info

Publication number: US20240295369A1
Application number: US18/177,519
Authority: US
Inventors: Christopher S. Elliott; Benjamin T. MATTHEWS; Steven W. J. HENDERSON
Original assignee: Meggitt Aerospace Ltd
Current assignee: Meggitt Aerospace Ltd
Priority date: 2023-03-02
Filing date: 2023-03-02
Publication date: 2024-09-05
Also published as: WO2024180343A1

Abstract

A heat exchanger comprising a matrix with an interior and an exterior. The matrix has an input face and an output face and one or more exterior surfaces that span between the input face and the output face. The primary media flows between the input face and the output face. The heat exchanger has a decongealing path that spans from an inlet across an entire length of the input face, spans the one or more exterior surfaces that span between the input face and the output face, and spans an entire length of the exterior output face to the outlet.

Description

FIELD

The present patent document relates to new designs for heat exchangers and in particular, better decongealing designs for heat exchangers.

BACKGROUND

For heat exchangers where there is a significant dependence between temperature and viscosity for the media (e.g., lubricating oil) there is a risk that at low temperatures, the media will congeal and a blockage will form within the heat exchanger matrix. In order to increase surface area and thus, efficiency, the matrix of a heat exchanger is often comprised of very small passages. When the viscosity of a liquid increases, the media is unable to flow freely through the small passages within the heat exchanger core.
A blockage in the core of a heat exchanger can cause a variety of related hazards. The primary issue is a significant back pressure that is created and may burst the heat exchanger core unless a relief valve is fitted. When the relief valve allows the media to bypass the heat exchanger core, the respective media will not be cooled or heated, as required. To this end, the performance if the heat exchanger is halted, or at a minimum seriously impaired, until the media in the heat exchanger core is decongealed.
If the media bypasses the heat exchanger core in a manner which permits persistent stagnation, then the media may fail to decongeal the core effectively in response to changes in demand. As a consequence, the media may be released back into the system without any thermal management (warming) occurring.
Typical conditions in which decongealing may be needed are when the associated hardware (i.e., an aircraft engine) is started under low temperature conditions where the media has high viscosity. It can also occur if there is a low ambient temperature and insufficient media temperature to prevent over cooling of the media in the heat exchanger core.
The heat exchanger core can be considered to have been decongealed when the flow of media through the heat exchanger core is free enough that the pressure drop across the core is low enough for the pressure relieving bypass valve to close.
The proposed heat exchanger designs and in particular the designs of the decongealing bypass is to enhance the natural decongealing of the heat exchanger core by means of distributing the heated primary media more effectively to promote decongealing of all layers. Preventing stagnation of the primary media will allow all the metal components to conduct heat through the heat exchanger core.

SUMMARY OF THE EMBODIMENTS

A novel heat exchanger is described and provided herein. In preferred embodiments, the heat exchanger comprises an input header and an output header. The input header is designed for intake of a fluid medium through an inlet. The inlet is located at a first distal end of the input header. The output header designed for expelling of the fluid medium through an outlet. The outlet is located at a second distal end of the output header.
The heat exchanger further comprises a matrix with an interior and an exterior wherein the exterior comprises an input face and an output face. One or more exterior surfaces of the heat exchanger spans between the input face and the output face.
The heat exchanger further includes a decongealing path that spans from the inlet across an entire length of the input face, spans at least one of the one or more exterior surfaces that span between the input face and the output face, and spans an entire length of the output face to the outlet.
In preferred embodiments, a bypass valve is located at an opposite end of the input header from the inlet. This ensures the entire length of the header is used for the decongealing path. Accordingly, in some embodiments, the decongealing path flows through an entire length of the input header and an entire length of the output header.
In some embodiments, the decongealing path spans all sides of the matrix but one.
In some embodiments, a bypass channel between the input face and the output face runs along the matrix exterior. In other embodiments, a bypass channel between the input face and the output face runs along a perimeter of the matrix interior.
In another aspect of the embodiments herein, a heat exchanger is provided that comprises an input header located at a first distal end; a bypass valve located on an opposite end of the input header from the inlet and an output header located at a second distal end. The heat exchanger further comprises a matrix with an interior and an exterior. The exterior of the matrix comprises an input face and an output face and one or more exterior surfaces that span between the input face and the output face. The heat exchanger further comprises a decongealing path that spans from an inlet across an entire length of the exterior input face, spans at least one of the one or more exterior surfaces that span between the input face and the output face, and spans an entire length of the output face to the outlet.
In another aspect of the embodiments herein, a heat exchanger is provided that comprises a matrix with a cross-section that comprises an input side and an output side and a perimeter that spans between the input side and the output side. The heat exchanger further comprises a decongealing path that spans an entire length of the input side and an entire length of the perimeter and an entire length of the output side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-section of a heat exchanger with a decongealing bypass according to the teachings herein;

FIG. 2 illustrates a cross-section of a heat exchanger core with a rectangular cross section and a decongealing bypass according to the teachings herein;

FIG. 3 illustrates a cross-section of a heat exchanger core with a hexagon shaped cross-section and a decongealing bypass according to the teachings herein;

FIG. 4 illustrates a cross-section of a heat exchanger core with a pentagon shaped cross-section and a decongealing bypass according to the teachings herein;

FIG. 5 illustrates a schematic cross-section of a multi-pass heat exchanger with a decongealing bypass setup according to the teachings herein; and

FIG. 6 illustrates a schematic cross-section of the multi-pass heat exchanger of FIG. 5 with the decongealing bypass open.

DETAILED DESCRIPTION OF THE DRAWINGS

It has been thought for a long time that the best way to decongeal a heat exchanger was to pass the hot media through the interior of the heat exchanger matrix. On its face, this seems to make sense. Get the heat as close to the area you want to heat up as possible. To this end, one can find endless heat exchanger designs where the decongealing bypass runs through the interior of the heat exchanger.
It turns out, physics sometimes works contrary to what is a first impression or would be obvious. The inventors of the heat exchanger designs and methods disclosed herein discovered that running the hot media through the interior is not the best way to decongeal a heat exchanger. In fact, and contrary to what is known in the art, the most efficient way to decongeal a heat exchanger matrix is to use the thermal conductivity of the matrix and run the fluid over as much of the matrix exterior surfaces as possible. The matrix itself will then distribute the heat throughout the interior via the conductive property of the matrix itself. To this end, a more efficient decongealing solution that spreads heat more evenly over the entire matrix can be achieved.
FIG. 1 illustrates a cross-section of a heat exchanger 10 with a decongealing bypass 25 according to the teachings herein. In FIG. 1 , the flow of the media in the decongealing bypass is illustrated by dashed line 25 from inlet 11 to outlet 12. In preferred embodiments, the inlet 11 to the upstream header 14, pressure relief valve 16 and bypass channel 18 are arranged such that the primary media has to flow past the input face 24 of the heat exchanger core 22 to reach the pressure relief valve 16 and bypass channel 18. In preferred embodiments such as the one shown in FIG. 1 , the primary media has to also flow past the output face 26 of the heat exchanger core 22 to reach the outlet 12. The input face 24 of the heat exchanger core 22 and the output face 26 of the heat exchanger core 22 are those through which the fluid that has a temperature controlled viscosity flows.
As may be appreciated, the difference between a channel in the heat exchanger core and a decongealing bypass 25 may be understood in terms of cross-sectional area. The increased cross-section area of the decongealing bypass 25 prevents the higher viscosity primary media from congealing. In preferred embodiments, the decongealing bypass 25 has a cross-sectional area that is 50% larger than the channels of the heat exchanger core. In even more preferred embodiments, the decongealing bypass 25 has a cross-sectional area that is 75% or more, 100% or more, 200% or more or 500% or more larger than the channels of the heat exchanger core.
In some embodiments, the decongealing bypass 25 may be distinguished from the heat exchanger core by the presence of a bypass valve 16 in its path. Such that a path between the inlet 11 and the outlet 12 that includes a bypass valve 16 is be considered a decongealing bypass. A bypass valve 16 is not technically required to define a decongealing bypass 25 but it is preferred to help force the liquid through the core 22 under normal back pressure.
As may be appreciated from FIG. 1 , the heat exchanger includes an input header 14 and an output header 20. In preferred embodiments, the input header 14 completely covers the input face 24 of the heat exchanger core 22. However, in other embodiments, more than one input header 14 may be used. In preferred embodiments, the decongealing bypass 25 extends over the entire length of the input face of the heat exchanger core from one side to the other. To this end, if more than one input header is used, at least one of the header designs should allow an extended path across the face of the heat exchanger core 22. The same is true for the output header 20.
As seen in FIG. 1 , the heat exchanger core 22 has other exterior surfaces 26 other than the input face 24 and output face 26. In the embodiment shown in FIG. 1 , an arced surface 26 extends between the input face 24 and output face 26. However, in other embodiments, any number of surfaces or sides may be used between the input face 24 and the output face 26 of the heat exchanger core 22.
FIG. 2 illustrates a cross-section of a heat exchanger core 22 with a rectangular cross section and a decongealing bypass 25 according to the teachings herein. In the embodiment of FIG. 2 , the decongealing bypass 25 wraps around all sides of the cross-section of the heat exchanger except one. Importantly, the decongealing bypass 25 passes over the entire length of both the input face 24 and the output face 26 of the heat exchanger core 22. The bypass valve 16 is on the opposite end of the input header from the inlet 11.
In the embodiment shown in FIG. 1 , in the congealed state where the relief valve 16 is open, the primary media would enter via the inlet 11, flow the length of the inlet header 14 washing the inlet face 24 of the heat exchanger core 22, pass through the relief valve 16 and bypass channel 18, then flow down the entire length of the outlet header 20 washing the outlet face 26 of the heat exchanger core 22.
As has been appreciated by the inventors herein, maximizing the contact of the primary fluid with the conductive material that makes up the matrix, especially on both ends of the flow path of the matrix, creates the most efficient decongealing path 25. The elimination of stagnant areas of primary media will force conduction of thermal energy to the metallic components of the core, promoting decongealing. This will ensure that all the heat exchanger layers are washed with warmer media as it flows from the inlet face 24 to the relief valve 16 and across the bypass channel 18 and over the length of the outlet face 26. The natural tendency for the primary media to flow through the core 22, will also mean that every layer is having the cold, high-viscosity media pushed out by warm, low-viscosity media until such point is reached where all channels in the matrix 22 have cleared.
When the layers have decongealed the pressure difference across the core 22 will drop and the relief valve 16 will close, causing all the primary media to flow through the core 22 exclusively. At this point the heat exchanger 22 will be isolated from the effects of the decongealing feature with all the core layers being equally efficient.
In the embodiment shown in FIG. 1 , the bypass path and in particular the bypass channel 18 are separate from the heat exchanger core 22. However, this is not required and especially not required for the bypass channel 18. In other embodiments, a portion of, or all of, the bypass path 25 may be integrated into the structure of the heat exchanger core 22. This may be done on the exterior of the matrix but be still part of the matrix or may pass through the matrix 22. The important aspect is that the bypass flow path 25 pass over the entire length of the input face 24 and output face 26 of the heat exchanger matrix 22.
As may be appreciated, one of the easiest ways to accomplish this is to use the input header 14 and output header 20 as part of the decongealing bypass path 25. However, embodiments may exist where other designs are used to affect the same decongealing bypass path 25. Any embodiment where the decongealing bypass path 25 does not reduce the efficiency of the heat exchanger core are preferred.
FIG. 3 illustrates a cross-section of a heat exchanger core 22 with a hexagon shaped cross-section 22 and a decongealing bypass 25 according to the teachings herein. In the embodiment of FIG. 3 , the decongealing bypass 25 wraps around all sides of the cross-section of the heat exchanger except one. In the embodiment of FIG. 3 , the input header and output header span two sides of the cross-section. It is to be understood that the heat exchanger cross-section can be any shape and the headers and bypass paths can span any number of sides. Importantly, the decongealing bypass 25 passes over the entire length of both the input face 24 and the output face 26 of the heat exchanger core 22. Accordingly, when the bypass valve 16 is open, the entire surface of both the input face 24 and the output face 26 of the matrix is washed with the warm fluid. In addition, at least one other exterior side of the matrix 22 is heated as the primary fluid flows through the bypass channel 25.
FIG. 4 illustrates a cross-section of a heat exchanger core 22 with a pentagon shaped cross-section 22 and a decongealing bypass 25 according to the teachings herein. In the embodiment of FIG. 4 , the decongealing bypass 25 wraps around only three of the five sides of the cross-section of the heat exchanger core 22. It is not required that the bypass 25 wrap around every single side of the heat exchanger or every single side but one. As may be appreciated, the decongealing bypass 25 passes over the entire length of both the input face 24 and the output face 26 of the heat exchanger core 22. Accordingly, when the bypass valve 16 is open, the entire surface of both the input face 24 and the output face 26 of the matrix 22 is washed with the warm fluid. In addition, at least one other exterior side of the matrix 22 is heated as the primary fluid flows through the bypass channel 25.
As should be understood from FIGS. 2-4 , the heat exchanger can be any shape and can have any shape cross-section. The sides of the heat exchanger core can be straight or curved. The key is to have the primary media (heated fluid) wash over as much of the conductive exterior surface of the heat exchanger core as possible as part of the decongealing bypass path 25. An important aspect of this is to have the decongealing path wash over the entire length of input face 24 and output face 26 of the heat exchanger core 22.
In operation, when a decongealing event occurs such as a blockage or an increased back pressure or some other indicator that decongealing is needed, the primary fluid will be routed down the decongealing path. This is typically done by the build up of pressure that activates a relieve valve and allows the primary medium to enter the decongealing path. The primary fluid then flows around the matrix and preferably, across the entire input face and output face of the matrix. The matrix conducts heat from the warm primary fluid from the input face and output face and any other locations of contact with the primary fluid in the decongealing path, into the interior of the matrix. In preferred embodiments, the heat is dispersed throughout the entire matrix as evenly as possible. This in turn heats the primary fluid in the matrix and decreases its viscosity thus allowing it to flow through the matrix more easily and removing the blockage. As the flow through the matrix improves, the back pressure is reduced and eventually the bypass valve closes and flow exclusively through the matrix resumes.
In the embodiments herein, emphasis is put on the decongealing path 18 spanning the entire length of the input face 24 and the output face 26 of the heat exchanger matrix 10. In preferred embodiments, the decongealing path 18 spans not just the entire length of the input face 24 and output face 26 but the entire input face 24 and output face 26 in all directions. For example, preferably, the decongealing path 18 spans the entire length and width (in 2-dimensional embodiments) of either the input face 24, output face 26 or both the input face 24 and the output face 26. In more complex geometries, the decongealing path 18 may span the entire surface of the input face 24 and/or output face 26 in more than one direction. As may be appreciated, the input header 14 and output header 20 are ideally suited to perform part of the decongealing path 18 because they typically already cover the input face 24 and output face 26 of the heat exchanger matrix 10.
FIG. 5 illustrates a schematic cross-section of a multi-pass heat exchanger 40 with a decongealing bypass setup according to the teachings herein. As may be appreciated by looking at FIG. 5 , the multi-pass heat exchanger has an inlet 11, outlet 12, core 22, input header 14 and output header 20. The direction of the cross-flow of the heat exchanger 40 is schematically shown by the large arrows above the heat exchanger 40.
The multi-pass heat exchanger 40 is so called due to the fact that the flow through the core can be thought of as making multiple passes. In normal operation, the fluid wraps around from the inlet 11 to outlet header 20 in a u-shaped flow path. The secondary fluid (usually air) passes straight through as shown by the large arrows. As may be seen in FIG. 5 , the fluid comes in inlet 11 and flows through the input header and through the input face 24 and into the core 22. The first pass is considered to be as the fluid moves from the input face through the core to the opposite side of the heat exchanger core 22. The second pass is considered to be as the fluid returns from the opposite end of the heat exchanger 42 back through the output face 26 into the output header 20 and exits the outlet.
As may be appreciated, multi-pass heat exchangers with an even number of passes, like the one shown in FIG. 5 , have their inlet 11 and outlet 12 on the same side. In contrast, multi-pass heat exchangers with an odd number of passes have their inlet 11 and outlet 12 on opposite sides of the heat exchanger.
As may be appreciated from the teachings herein, a key aspect to the embodiments taught herein is that when the bypass flow path is used, the liquid that needs to be decongealed is passed over the entire input face 24 and output face 26 of the matrix or core 22. In the specific case of the even numbered multi-pass heat exchanger 40, this can be accomplished by simply creating a decongealing path 18 that flows straight across the input face 24 and output face 26. This can be extremely simple in the case of an even number multi-pass heat exchanger 40.
FIG. 6 illustrates a schematic cross-section of the multi-pass heat exchanger 40 of FIG. 5 with the decongealing bypass open. As may be appreciated in FIG. 6 , the bypass channel 18 is a straight path from the inlet 11 to the outlet 12. In some embodiments, like the one shown in FIG. 6 , the decongealing path 18 can simply flow through the input header 14 and output header 20. In other embodiments, a separate bypass channel, separate from the headers, may be used.
In preferred embodiments, the inlet 11 and outlet 12 may be positioned on opposite distal ends of the input header 14 and output header 20 respectively in order to maximize the flow over the input face 24 and output face 26 when the bypass valve is open and the fluid is flowing through the decongealing path 18.

Claims

What is claimed is:

1. A heat exchanger comprising:

an input header designed for intake of a fluid medium through an inlet, wherein the inlet is located at a first distal end of the input header;

an output header designed for expelling of the fluid medium through an outlet, wherein the outlet is located at a second distal end of the output header;

a matrix with an interior and an exterior wherein the exterior comprises an input face and an output face and one or more exterior surfaces that span between the input face and the output face; and

a decongealing path that spans from an inlet across an entire length of the input face, spans at least one of the one or more exterior surfaces that span between the input face and the output face, and spans an entire length of the output face to the outlet.

2. The heat exchanger of claim 1, wherein the decongealing path comprises a bypass valve located at an opposite end of the input header from the inlet.

3. The heat exchanger of claim 1, wherein the decongealing path spans all sides of the matrix but one.

4. The heat exchanger of claim 1, wherein the decongealing path flows through an entire length of the input header and an entire length of the output header.

5. The heat exchanger of claim 1, wherein the decongealing path comprises a bypass channel that runs between the input face and the output face along the matrix exterior.

6. The heat exchanger of claim 1, wherein the decongealing path has a bypass channel that runs between the input face and the output face along a perimeter of the matrix interior.

7. A heat exchanger comprising:

an input header located at a first distal end;

an output header located at a second distal end;

a matrix with an interior and an exterior wherein the exterior comprises an input face and an output face and one or more exterior surfaces that span between the input face and the output face;

a decongealing path that spans from an inlet across an entire length of the input face, spans at least one of the one or more exterior surfaces that span between the input face and the output face, and spans an entire length of the output face to the outlet; and

a bypass valve located within the decongealing path.

8. The heat exchanger of claim 7, wherein the decongealing path spans all sides of the matrix but one.

9. The heat exchanger of claim 7, wherein the decongealing path flows through an entire length of the input header and an entire length of the output header.

10. The heat exchanger of claim 7, wherein the decongealing path comprises a bypass channel that runs between the input face and the output face along the matrix exterior.

11. The heat exchanger of claim 7, wherein the decongealing path comprises a bypass channel that runs between the input face and the output face along a perimeter of the matrix interior.

12. The heat exchanger of claim 7, wherein the bypass valve is located on an opposite end of the input header from the inlet.

13. A heat exchanger comprising:

a matrix with a cross-section that comprises an input side and an output side and a perimeter that spans between the input side and the output side;

a decongealing path that spans an entire length of the input side and an entire length of the perimeter and an entire length of the output side.

14. The heat exchanger of claim 13, further comprising:

an input header with an inlet located at a first distal end of the input header; and

an output header with an outlet located at a second distal end of the output header;

15. The heat exchanger of claim 14, wherein the decongealing path comprises a bypass valve.

16. The heat exchanger of claim 14, wherein the decongealing path spans all sides of the matrix but one.

17. The heat exchanger of claim 14, wherein the decongealing path flows through an entire length of the input header and an entire length of the output header.

18. The heat exchanger of claim 14, wherein the decongealing path comprises a bypass channel that runs between the input side and the output side along the matrix exterior.

19. The heat exchanger of claim 14, wherein the decongealing path comprises a bypass channel that runs between the input side and the output side along the perimeter of an interior of the matrix.

20. The heat exchanger of claim 15, wherein the bypass valve is located at an opposite end of the input header from the inlet.