Patent Grant
7017656
To improve the overall efficiency of a gas turbine engine, a heat exchanger or recuperator can be used to provide heated air for the turbine intake. The heat exchanger operates to transfer heat from the hot exhaust of the turbine engine to the compressed air being drawn into the turbine. As such, the turbine saves fuel it would otherwise expend raising the temperature of the intake air to the combustion temperature.
The heat of the exhaust is transferred by ducting the hot exhaust gases past the cooler intake air. Typically, the exhaust gas and the intake air ducting share multiple common walls, or other structures, which allows the heat to transfer between the two gases (or fluids depending on the specific application). That is, as the exhaust gases pass through the ducts, they heat the common walls, which in turn heat the intake air passing on the other side of the walls. Generally, the greater the surface areas of the common walls, the more heat which will transfer between the exhaust and the intake air.
As shown in the cross-sectional view of
Typically, during construction of such a heat exchanger, the plates 22 are positioned on top of one another and then compressed to form a stack 26. Since the plates are each separate elements, the compression of the plates 22 ensures that there are always positive compressive forces on the core 20, so that the plates 22 do not separate. The separation of one or more plates 22 can lead to a performance reduction or a failure by an outward buckling of the stack 26. As such, typically the heat exchanger is constructed such that the stack 26 is under a compressive pre-load.
Applying a high pre-load does reduce the potential for separation of the plates 22. However, this approach does have the significant drawback that all the components of the core 20 are placed under a much greater stress than they would be without the pre-loading. In addition, the pre-loading requires that the structure supporting the stack 26 must be much stronger and thus thicker. This pre-load assembly or support structure 40 collectively includes the strongbacks 28, the tie rods 30, as well as the shell 10 structure. This support structure 40 adds to both the weight and the cost of the heat exchanger.
The stack 26 can also be under a further compressive load, which is caused by differential thermal expansion between the core 20 and the support structure 40. As can be seen in
Differential thermal expansion between elements of the heat exchanger will cause a compression load to be applied to the quicker expanding sections (e.g. the core 20 and specifically the stack 26). As noted, a compression load is also applied to the stack 26 by the application of a pre-load. Compressive forces from pre-loading and differential thermal expansion can cause a variety of problems, such as fatigue failures, creep and buckling. Buckling is particularly problematic as it results in the slack 26 expanding outward (laterally) in one or more directions. This outward expansion causes the plates 22 to separate from one another, resulting in a nearly complete destruction of the heat exchanger.
An additional source of loading on the heat exchanger can be from the airflow in the core 20. When the inlet air in the core 20 is pressurized, an additional compressive load is applied to the stack 26. This compression loading can also contribute to the occurrence of buckling or other damage. Air pressure loads can further affect plumbing components in the core including the inlet duct 32 and the outlet duct 34. Loads are also created by the pressure of the air in the ducts that carry the air in and out of the core. The duct will carry this load and transfer it to the core 20. Since the core 20 is made of the thin plates 28, to avoid damage to the core 20, only very limited loads can be applied to the core 20.
In addition, the core 20 can also experience loads caused by external forces. Such forces include inertia loads, which occur in mobile applications, and loads transferred through the ducts from the attached plumbing, such as those caused by turbine vibrations. Inertia loads can be created by accelerations (such as changes in direction or speed) applied to a vehicle in which the heat exchanger is mounted. For example, a vehicle traveling over uneven terrain can cause various inertia loads to be applied to the heat exchanger. Inertia loads increase the likelihood of buckling by providing forces in a variety of directions including those which are aligned with, and perpendicular to, the compressive loads. The aligned inertia loads increase the potential for failure by being additive to the compressive loads. Whereas, the inertia loads directed perpendicular to the compressive loads, increase the likelihood of failure by encouraging the core to buckle to one side or the other. Similarly, the forces that are transmitted through the ducts have the potential to cause failures in the thin plates 20 at locations where the ducts contact the thin plates 28.
As shown in
Unfortunately, bellows typically have notable drawbacks, including that they are expensive, difficult to assemble and add additional leak paths to the heat exchanger. Such leaks greatly reduce the efficiency of the heat exchanger. Bellows also must be repaired or replaced frequently.
Therefore, a need exists for a heat exchanger that provides sufficient column stiffness for the core structure to prevent buckling and which can carry loads created is by the air pressure within the core. The heat exchanger's increased core column stiffness should significantly reduce the amount of pre-load applied to the core. This in turn will result in reduced structure needed to contain the core, as well as, reduced differential thermal expansion between the core and the shell. The heat exchanger should further be able to accommodate differential thermal growth without the use of a bellows system or other type of variable position linear force system. A heat exchanger with such increased column stiffness will enable the heat exchanger to withstand higher inertia loads. A need further exists for a heat exchanger that can distribute the loads from the ducting into the core structure without causing damage to, or a failure of, the core.
The present invention provides a heat exchanger with increased stiffness to prevent buckling of the core and which can carry air pressure, duct and inertia loads without damage to the core. In some embodiments, the present invention is a heat exchanger having a core with a heat exchange portion, and a shaft at least partly positioned in the core to increase the stiffness of the core. The shaft is positioned at least adjacent to the heat exchange portion of the core. The shaft is also located to limit movement of the heat exchange portion and to receive loads from the heat exchange portion. The shaft can be positioned through some, or all, of the heat exchange portion of the core.
The heat exchange portion can be a layering of heat exchange members, such that the shaft prevents the members from sliding out away from the core and causing the core to buckle. The shaft is permeable so that a passage in the shaft is in fluid communication with the heat exchange portion of the core. The heat exchanger can also include a load bearing member positioned adjacent the core. In this embodiment, the shaft is mounted to the load bearing member, so that the load bearing member can receive loads from the shaft.
In another embodiment, the heat exchanger includes a core, a duct in fluid communication with the core, a load bearing member positioned adjacent to the core, and a mount which attaches the duct to the load bearing member. By connecting the duct to the load bearing member, the duct can transfer loads to the load bearing member. This load transfer protects the core from being damaged by loads applied to the duct. The mount restrains the duct so to transfer, from the duct to the load bearing member, loads aligned substantially with the longitudinal axis of the duct as well as torsional and shear loads. These loads can include all mechanical loads caused by thermal differentials, air pressure, and other mechanical sources. The mount can also be adjustable to allow the duct to expand separately from the load bearing member. This keeps any differential thermal expansion, occurring between the duct and the load bearing member, from causing damage thereto. The mount can include a motion limiter, a limiter channel, a retainer and a retainer fastener. The duct can extend into the core, and as such, transfer loads over the length of the duct to the core.
In another embodiment of the present invention, the heat exchanger includes a core, a duct extending into the core, a load bearing member and a mount positioned between the duct and the load bearing member. The mount functions to transfer loads from the duct to the load bearing member. The heat exchange portion comprises layers of heat exchange members. The duct passes through at least some of the heat exchange members and can contact the heat exchange members to transfer loads to and from them over the length of the duct. The duct is in fluid communication with the core and is at least adjacent the heat exchange portion of the core. The duct is permeable so that a gas (e.g. air) may pass between the duct and the core. The mount attaches the duct to the load bearing member so that the load bearing member can receive loads from the duct.
a–d are side cut-away views of a portion of a heat exchanger in accordance with the present invention.
The present invention increases the stiffness and load carrying capability of a heat exchanger or other similar apparatus. As set forth herein, the present invention has several advantages over prior devices.
The Applicants' invention functions to reduce the potential for core buckling caused by the application of compressive forces as well as duct and inertia loads. Compressive forces can be created by pre-loading, differential thermal expansion, air pressure or other like sources. Whereas duct and inertia loads are typically a result of external forces such as accelerations and vibrations. The reduction in buckling provides the distinct advantage of not only greatly reducing the likelihood that the heat exchanger will be greatly damaged or destroyed, but also allows the heat exchanger to have a simpler structure. Such a simpler structure is cheaper, lighter, easier and potentially quicker to fabricate. In addition, such an improved structure will have a thermal response of the support structure (e.g. the shell, tie rods and strongbacks), which is much nearer to the response of the core. That is, by making the core stiffer, the supporting structure requires less material and the differential between the thermal expansion of the support structure and the core is reduced.
Further, the present invention's superior air pressure load carrying capability reduces loads being transferred to the core structure and allows the elimination of the use of a bellows system. This lack of a bellows results in a reduced potential for damage to the core structure as well as a lowered the possibility of air leaks. The lack of a bellows also reduces the cost and the complexity of the heat exchanger fabrication.
Therefore, the present invention provides a heat exchanger, or other similar apparatus, which is less expensive, easier to manufacture, lighter, less likely to fail (e.g. buckle), more durable, and, due to lower potential for leaks, one which can be much more efficient.
A heat exchanger apparatus which allows for differential thermal expansion of its elements without damage thereto is set forth in U.S. patent application Ser. No. 09/652,949 filed Aug. 31, 2000, entitled HEAT EXCHANGER WITH BYPASS SEAL ALLOWING DIFFERENTIAL THERMAL EXPANSION, by Yuhung Edward Yeh, Steve Ayres and David Beddome, which is hereby incorporated by reference in its entirety.
For the present invention, as shown in the cut-away views of
The core 110 is positioned within the shell 160. The core 110 functions to duct the inlet air past the exhaust gas, so that the heat of the exhaust gas can be transferred to the cooler inlet air. The core 110 performs this function while keeping the inlet air separated from the exhaust gas, such that there is no mixing of the air and the gas. Keeping the air and gas separate is important, as the mixing of the two will result in reduced efficiency, and potentially diminished engine performance.
As shown in
The heat exchange region 122 can be any of a variety of configurations that allow heat to transfer from the exhaust gas to the inlet air, while keeping the gases separate. However, it is preferred that the heat exchange region 122 be a prime surface heat exchanger having a series of layered plates 128, which form a stack 130. The plates 128 are arranged to define heat exchange members or layers 132 and 136 which alternate from ducting air, in the air layers 132 to ducting exhaust gases, in the exhaust layers 136. These layers typically alternate in the core 110 (e.g. air layer 132, gas layer 136, air layer 132, gas layer 136, etc.). Separating each layer 132 and 136 is a plate 128.
On either end of the stack 130 are a first end plate 142 and a second end plate 144. The first end plate 142 is positioned against the upper portion of the shell assembly 160 and the second end plate 144 is positioned against the lower portion of the shell assembly 160. Depending on the specific needs of the use of the heat exchanger 100 of present invention (e.g. required pre-loads, forces exerted on the stack 130, compression of the plates 128 of the stack 130, and the like), a series of tie rods 150 and an upper strongback or load bearing member 143 and a lower strongback or load bearing member 145, can be used to hold the stack 130 together and carry loads. On the outside of the shell 160 and above and below the core 110, are the upper strongback 143 and the lower strongback 145. The tie rods 150 and the strongbacks 143 and 145 (as well as the shell 160) carry compressive loads applied to the stack 130. These compressive loads can be from a variety of sources including pre-loading, differential thermal expansion, air pressure, and the like. The upper strongback 143, the lower strongback 145, the tie rods 150, as well as the shell 160, collectively form a support structure 155 which functions to apply the compressive force to the stack 130 of the core 110.
As can be seen, the plates 128 are generally aligned with the flow of the exhaust gas through the shell assembly 160. The plates 128 can be made of any well known suitable material, such as steel, stainless steel or aluminum, with the specific preferred material dependent on the operating temperatures and conditions of the particular use. The plates 128 are stacked and connected (e.g. welded or brazed) together in an arrangement such that the air layers 132 are closed at their ends 134. With the air layers 132 closed at ends 134, the core 110 retains the air as it passes through the core 110. The air layers 132 are, however, open at air layer intakes 124 and air layer outputs 126. As shown in
In contrast to the air layers 132, the gas layers 136 of the stack 130 are open on each end 138 to allow exhaust gases to flow through the core 110. Further, the gas layers 136 have closed or sealed regions 140 located where the layers 136 meet both the inlet manifold 116 and the outlet manifold 120. These closed regions 140 prevent air, from either the inlet manifold 116 or the outlet manifold 120, from leaking out of the core into the gas layers 136. Also, the closed regions keep the exhaust gases from mixing with the air.
Therefore, as shown in
With the stack 130 arranged as shown in
As the plates 128 and the connected structure of the core 110 heat up, they expand. This results in an expansion of the entire stack 130 and thus of the core 110. As noted, this expansion is faster than the expansion of the supporting structure 155 (the shell 160, strongbacks 143 and 145 and the tie rods 150). This differential expansion causes a compression force to be applied to the core 110. As noted in detail below, the inlet manifold tube 170 and outlet manifold tube 180, function to increase the stiffness of the core 110 and reduce the likelihood that the core 110 will buckle under compression forces caused by the differential expansion and by other sources.
Although the core 110 can be arranged to allow the air to flow through it in any of a variety of ways, it is preferred that the air is channeled so that it generally flows in a direction opposite, or counter, to that of the flow of the exhaust gas in the gas layers 136 (as shown in the cross-section of
The arrangement of the core 110 can be any of a variety of alternative configurations. For example, the air layers 132 and gas layers 136 do not have to be in alternating layers, instead they can be in any arrangement which allows for the exchange of heat between the two layers. For example, the air layers 132 can be defined by a series of tubes or ducts running between the inlet manifold tube 170 and the outlet manifold tube 180. While the gas layers 136 are defined by the space outside of, or about, these tubes or ducts. Of course, the heating of such a configuration of the core will still result in differential expansion between the core and the support structure. Therefore, the manifold tubes 170 and 180 are utilized to increase the stiffness of the core and in so doing reduce the chance of a buckling failure occurring.
The core 110 can also include secondary surfaces such as fins or thin plates connected to the inlet air side of the plates 128 and/or to the exhaust gas side of the plates 128. The core 110 and shell 160 can carry various gases, other than, or in addition to, those mentioned above. Also, the core 100 and shell 160 can carry any of a variety of fluids.
The shell assembly 160 functions to receive the hot exhaust gases, channel them through the core 110, and eventually direct them out of the shell 160. The shell 160 is relatively air tight to prevent the exhaust gas from escaping, or otherwise leaking out of, the shell 160. The shell 160 is large enough to contain the core 110.
The shell 160 also has openings 164 for the inlet manifold tube 170 and the outlet manifold tube 180. The shell assembly 160 can be made of any suitable well known material including, but not limited to, steel and aluminum. Preferably, the shell 160 is a stainless steel.
Because the shell assembly 160 can carry a variety of loads (both internally and externally exerted), and since the shell 160 does not need to transfer heat, its walls 162 are thick relative to the thin core plates 128. As previously noted, this greater thickness causes the shell 160 to thermally expand at a much slower rate than the core 110. This results in a significant amount of differential thermal expansion between the support structure 155 and the core 110, as the two are heated or cooled. The Applicants' present invention provides for this differential expansion by employing the manifold tubes 170 and 180 to increase the stiffness and load carrying capability of the core 110. As shown herein, the manifold tubes 170 and 180 can have any of a variety of embodiments.
As shown in
The manifold tubes 170 and 180 are continuous structural members, which run through all of the core plates 128. As such, in the event some plates 128 are forced or begin to move outwards, as would occur if the core 110 started to buckle, one or both of the manifold tubes 170 and 180 will carry the loads and prevent any of the plates 128 from moving from their original positions.
This load carrying ability of the manifold tubes 170 and 180 allows the core 110 to be subjected to significantly higher compressive loads than it otherwise would. As such, with use of the manifold tubes 170 and 180, the core 110 can be placed under higher air pressures and have a faster thermal expansion than that of the support structure 155. Further, because the core 110 can accommodate greater loads and has a higher stiffness, the amount of pre-load placed on the core 110 can be reduced. With less pre-loading necessary, the support structure 155 can be reduced in size. This results in a heat exchanger that is less expensive, lighter and easier to fabricate.
The manifold tubes 170 and 180 also function to carry and transfer loads applied to them. One such load is that generated by the airflow into and out of the core 110. For example, loads on one or both of the manifold tubes 170 and 180 can be generated by turning the airflow as it enters or exits the core 110. Changes in the speed and pressure of the airflow can also create loads on the tubes 170 and 180. These loads can be applied to the manifold tubes 170 and 180 in both longitudinal and lateral directions.
One problem with loads being applied to inlet and outlet ducting is that a transfer of some or all of the loads to the core 110 can easily result in significant damage to the core 110. As noted above, the plates 128 of the core 110 are kept very thin to facilitate the transfer of heat between the hot exhaust gas and the air. As such, the plates 128 lack the structure required to carry any significant load, and are therefore very susceptible to damage. Clearly, damage such as buckling or any deformation to the core 110 can greatly reduce the performance of the heat exchanger 100, or even cause its complete failure. Not only can the air or gas flows be disrupted or blocked, but also in the event of a separation or tear in the plates, the air and exhaust gas flows can mix together.
As noted above, prior devices attempted to alleviate airflow loads by using a bellows system, as shown in
In contrast, the manifold tubes of the Applicants' invention transfer loads without damaging the core of the heat exchanger. This load transfer can be accomplished in a variety of ways. As shown in
Nevertheless, the tubes 170 and 180 can also transfer loads directly to the core 110. The relatively long length of the tubes 170 and 180 allows loads to be transferred over a large area along the core 110. As such, the amount of force applied to any given area of the core 110 is minimized. In addition, the length of the tubes 170 and 180 creates a long moment arm, which acts to reduce the forces applied to the core 110. In this manner loads can be transferred to the core 110 without causing damage.
The manifold tubes 170 and 180 can also transfer loads to the core by being directly attached to the core 110. Specifically, by welding, brazing or otherwise attaching the tubes 170 and 180 to the core 110. In this manner, the core 110 can receive vertical loads (i.e. aligned with the longitudinal axis of the tubes 170 and 180), as well as horizontal loads (i.e. lateral to the longitudinal axis). The tubes 170 and 180 can be mounted to the core 110 in a variety of different ways and to various components of the core 110. For example, the tubes 170 and 180 can be brazed to the end plates 142 and 144 and/or to some or all of the core plates 128.
As shown in
As shown in
Many variations on the configuration, construction and arrangement of the manifold tubes 170 and 180 are possible. The tubes 170 and 180 can not only extend along the entire length of the manifolds 116 and 120 (as shown in
The manifold tubes 170 and 180 can be attached to the strongback 143 in any of a variety of embodiments to allow loads applied to the tubes 170 and 180 to be transferred to the strongback 143. As noted above, since the strongback 143 has a higher strength and stiffness relative to the core 110, transferring loads to the strongback 143 reduces or eliminates the likelihood that the core 110 will be damaged.
As shown in
The mount 190 functions both to transfer loads from the inlet tube 170 to the strongback 143 and to allow a limited amount of movement of the inlet tube 170 relative to the strongback 143. Allowing limited movement of the inlet tube 170 facilitates differential thermal expansion between the tube 170 and the strongback 143. Because the inlet manifold tube 170 is a very thin (relatively) sheet structure, when heated or cooled it will expand or contract much quicker than the substantially thicker structure of the strongback 143. By providing an expansion space 195 for this differential expansion, the mount 190 prevents the application of loads that could otherwise be generated by a mount that restrains the differential expansion. Such retraining can cause structural damage due to deformations, buckling, fatigue failures and creep. It is preferred that the inlet manifold tube 170 is welded to the first end plate 142.
As shown in
Configurations other than those shown in
The inlet limiter channel 194 is set into the strongback 143 and receives the inlet motion limiter 192. The limiter channel 194 functions to retain the motion limiter 192 while providing sufficient space for the differential thermal expansion, as noted above. The depth of the channel 194 preferably is sufficiently close to the thickness of the limiter 192 to retain the vertical movement of the inlet tube 170, but with enough clearance to allow substantially unrestricted horizontal movement of the inlet tube 170 due to thermal expansion. Such horizontal movement can be received by the expansion space 195. Alternative configurations of the limiter channel 194 are possible. For example, the limiter channel 194 can instead be on the surface of the strongback 143 and be defined by the inlet retainer 196 positioned about it.
As shown in
The inlet retainer fastener 198 functions to mount the inlet retainer 196 to the strongback 143. As shown in
Like the inlet mount 190, the outlet mount 200 functions to transfer loads from the outlet tube 180 to the strongback 143, while limiting vertical movement of the tube 180 and allowing for differential thermal expansion between the tube 180 and the strongback 143.
Many alternative configurations of the heat exchanger 100 exist. For example, instead of using both the inlet manifold tube 170 and the outlet manifold tube 180, the heat exchanger 100 can use just one of the two. Likewise, more than two manifold tubes can be used. In fact, in some embodiments, one or more of the manifold tubes function to direct the air with limited or no load bearing capability, while other manifold tubes function primarily as load bearing members.
As shown in the top cut-away view in
As shown in
Another embodiment of the present invention includes the use of a lower mount 210 on either or both of the manifold tubes 170 and 180. As shown in
As can be seen, many alternatives of the configuration of the mount 210 exist. For example, in
Another embodiment is the lower mount 210′, as shown in
c shows another embodiment of the lower mount. The mount 210″ includes sides 212″, a bottom 214″, an expansion space 216″ and a limiter 218″. In this embodiment, by being positioned along and close to the interior of the tube walls 174, the limiter 218″ functions to prevent lateral movement of the tube 170. In this manner the limiter 218″ also can carry lateral loads from the tube 170. By extending past the end of the tube 170, the limiter 218″ also allows for axial expansion of the tube 170. This allows the tube 170 to differentially expand relative to the core 110. Preferably, the mount 210″ includes an intermediate plate 220″ which is shaped to fit over the limiter 218″ of the second end plate 144″ to provide a seal against the passage of air and/or exhaust gas.
In still another embodiment of the mount, as shown in
Although not specifically shown in
While the preferred embodiments of the present invention have been described in detail above, many changes to these embodiments may be made without departing from the true scope and teachings of the present invention. The present invention, therefore, is limited only as claimed below and the equivalents thereof.
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