HEAT EXCHANGER UNIT AND METHOD FOR FLUID TO PASSIVELY BYPASSING A HEAT EXCHANGER

Abstract

The invention relates to a heat exchanger unit for an exhaust gas system. The heat exchanger unit comprises an inlet for a fluid flow to enter the heat exchanger unit and an outlet for a fluid flow to exit the heat exchanger unit. The heat exchanger unit comprises a heat exchanger having a heat exchanger conduit passing through the heat exchanger and at least one bypass conduit bypassing the heat exchanger, wherein the at least one bypass conduit comprises a bypass core having a plurality of channels arranged longitudinally along the bypass conduit.

Claims

1. Heat exchanger unit for an exhaust gas system, the heat exchanger unit comprising: an inlet for a fluid flow to enter the heat exchanger unit; an outlet for a fluid flow to exit the heat exchanger unit; the heat exchanger unit comprising a heat exchanger having a heat exchanger conduit passing through the heat exchanger and at least one bypass conduit bypassing the heat exchanger; wherein the at least one bypass conduit comprises a bypass core having a plurality of channels arranged longitudinally along the bypass conduit.

2. Heat exchanger unit according to claim 1, wherein the plurality of channels is arranged parallel to each other in the bypass core.

3. Heat exchanger unit according claim 1, wherein the bypass core comprises between 100 channels and 800 channels, preferably 200 channels to 600 channels, for example between 250 and 450 channels.

4. Heat exchanger unit according to claim 1, comprising an array of bypass conduits, each of the bypass conduits of the array of bypass conduits comprising a bypass core having a plurality of channels.

5. Heat exchanger unit according to claim 4, wherein at least some of the bypass conduits are arranged along a height of the heat exchanger.

6. Heat exchanger unit according to claim 4, wherein the array of bypass conduits comprises between two and 14 bypass conduits, preferably between three and ten bypass conduits, for example three, four or six bypass conduits.

7. Heat exchanger unit according to claim 1, wherein the plurality of channels in the bypass core is formed by corrugated sheet material.

8. Heat exchanger unit according to claim 7, wherein the plurality of channels is formed by rolled-up corrugated sheet material or corrugated plates arranged next to each other.

9. Heat exchanger unit according to claim 1, wherein the bypass core comprises or is made of steel, preferably stainless steel.

10. Heat exchanger unit according to claim 1, wherein the bypass core comprises a housing having a circular or rectangular cross-section.

11. Heat exchanger unit according to claim 1, comprising more than one heat exchanger core, for example two, three or four heat exchanger cores and at least a bypass conduit arranged in between neighbouring heat exchanger cores.

12. Heat exchanger unit according to claim 2, comprising an array of bypass conduits, each of the bypass conduits of the array of bypass conduits comprising a bypass core having a plurality of channels.

13. Heat exchanger unit according to claim 12, wherein at least some of the bypass conduits are arranged along a height of the heat exchanger.

14. Heat exchanger unit according to claim 2, wherein the plurality of channels in the bypass core is formed by corrugated sheet material.

15. Heat exchanger unit according to claim 14, wherein the plurality of channels is formed by rolled-up corrugated sheet material or corrugated plates arranged next to each other.

16. Heat exchanger unit according to claim 4, comprising more than one heat exchanger core, for example two, three or four heat exchanger cores and at least a bypass conduit arranged in between neighbouring heat exchanger cores.

17. Method for a fluid flow to passively bypass a heat exchanger, the method comprising separating an inlet fluid flow into a first flow portion and a second flow portion; letting the first flow portion to pass through a heat exchanger; and letting the second flow portion to bypass the heat exchanger via a bypass conduit; and combining the first flow portion after having passed the heat exchanger and the second flow portion after having bypassed the heat exchanger to an outlet fluid flow; wherein the second flow portion passes a plurality of channels arranged in the bypass conduit, such that a pressure drop of the second flow portion in the bypass conduit is adapted to a pressure drop of the first flow portion in the heat exchanger.

18. Method according to claim 17, therein dividing the second flow portion into several second sub-flows; letting the several second sub-flows bypass the heat exchanger and combining the second sub-flows with the first flow portion after the first flow portion has passed the heat exchanger.

19. Method according to claim 18, wherein each of the second sub-flows passes a plurality of channels when bypassing the heat exchanger.

20. Method according to claim 17, wherein a temperature of the outlet fluid flow is kept at a predefined temperature plus or minus 10 percent, with a temperature of the inlet fluid flow above 400 degree Celsius and a second flow portion between 40 percent and 85 percent of the inlet fluid flow.

Description

[0038] The heat exchanger according to the invention is particularly used in exhaust gas systems and the method according to the invention for a fluid flow being an exhaust gas. The exhaust gas may, for example, be exhaust gas of a diesel engine, a power plant or a fuel cell system. The fluid flow passing through and bypassing the heat exchanger may also be, for example, methane, hydrogen or other gas species. The invention is further described with regard to embodiments, which are illustrated by means of the following drawings, wherein:

[0039] FIG. 1 shows a heat exchanger unit;

[0040] FIGS. 2,3 show the heat exchanger unit in partially disassembled views;

[0041] FIG. 4 is a front view onto the heat exchanger unit of FIGS. 1 to 3;

[0042] FIG. 5 schematically shows a bypass unit;

[0043] FIGS. 6,7 are a perspective side view and a front view onto bypass conduits in a bypass unit;

[0044] FIGS. 8,9 show a perspective side view and a front view onto another embodiment of bypass conduits in a bypass unit;

[0045] FIG. 10 shows a bypass core;

[0046] FIG. 11 shows another embodiment of a bypass core;

[0047] FIG. 12 is a graph showing a difference between a state-of the art bypass (dashed line) versus a bypass according to the invention (solid line).

[0048] In the drawings, the same reference signs are used for the same or similar elements.

[0049] FIG. 1 and FIG. 2 show a heat exchanger unit 1 in a main housing 10. The heat exchanger unit comprises an inlet 12 for hot fluid, for example, exhaust gas of a combustion engine, to enter the heat exchanger unit. It also comprises an outlet 13 for fluid, for example cooled and hot gas, treated in the heat exchanger unit 1. Through the outlet 13, outlet fluid may leave the heat exchanger unit 1, for example to be led into another device, for example a fuel cell.

[0050] In FIG. 2 the front wall 11 of the main housing 10 is removed. It allows view onto three parallel arranged heat exchanger cores 2, for example heat exchanger stacks, and a downstream arranged mixing chamber 14. In the mixing chamber 14, the fluid flow having passed the three heat exchanger cores 2 and the fluid flow having bypassed the three heat exchanger cores 2 in bypass conduits is mixed before the so mixed fluid flow leaves the heat exchanger unit 1 via outlet 13.

[0051] In FIG. 3, some further elements of the main housing 10 have been removed, allowing view onto two side walls 15 of the housing 10 and the three heat exchanger cores 2 arranged in between the side walls 15. Two bypass conduits 3 are arranged in between the heat exchanger cores 2.

[0052] A part of the fluid flow, a first fluid flow, from a total inlet fluid flow entering the heat exchanger unit 1 via inlet 12, is made to pass any one of the three heat exchanger cores 2. By this, heat may be transferred from a hot gas to a cool fluid to be heated up. Another part of the fluid flow entering the heat exchanger unit 1 is made to bypass the heat exchanger cores 2. This second fluid flow is led through the bypass conduits 3 in between the heat exchanger cores 2.

[0053] As may be seen in the drawing of FIG. 3, as well as in FIG. 4 and FIG. 5, the bypass conduits 3 are mainly open spaces extending over the height of the heat exchanger cores 2 before and after passing through an array 30 of bypass conduits comprising a bypass core 33 having a plurality of channels as will be described further below. The bypass fluid flow is made to pass through the bypass cores 33.

[0054] The array 30 of bypass conduits 3 are fixedly mounted in a bypass housing 35. The bypass housing 35 may be premanufactured and mounted in the heat exchanger unit 1 in between the heat exchanger cores. By this, bypass units 1 may be adapted to a specific use and to specific heat exchanger conditions. Construction of a heat exchanger unit 1 suitable to different applications or operation condition may thus be realized. Also modification of an existing heat exchanger unit to different operation conditions may thus be realized, for example by exchanging such bypass units.

[0055] In the examples of FIG. 4 and FIG. 5, the array 30 of bypass conduits 3 comprises six circular tubes arranged in three horizontal rows of two bypass conduits each. The rows of bypass conduits of the array 30 are regularly arranged over the height of the heat exchanger stacks 2.

[0056] In the perspective view and the front view of FIG. 6 and FIG. 7, a bypass housing 35 comprising three bypass conduits 3 having a bypass core 33 is shown.

[0057] The three bypass cores 33 in the form of cylinders have a same size and are equidistantly arranged over the height of the heat exchanger cores 2. The longitudinal axes of the cylinders are arranged parallel to each other and along a general flow direction of the bypass fluid flow.

[0058] The bypass cores 33 comprise a plurality of channels 333 arranged longitudinally along the length of the bypass conduits. The bypass cores are embodied as cylinders formed by rolled-up corrugated sheet material. The corrugations of the sheet material, for example a sheet of corrugated stainless steel, automatically form the channels, when the sheet is rolled-up, wherein an outer winding of the sheet material touches an inner winding of the sheet material.

[0059] In the perspective view and the front view of FIG. 8 and FIG. 9, another example of a bypass housing 35 comprising three bypass conduits 3 each having a bypass core 33 is shown. The three bypass cores 33 are in the form of rectangular cuboids, have a same size and are equidistantly arranged over the height of the heat exchanger cores 2. A length of the rectangular cuboid is longer than its height and width.

[0060] The longitudinal axes of the rectangular cuboids are arranged parallel to each other and along a general flow direction of the bypass fluid flow.

[0061] The bypass cores 33 comprise a plurality of channels 333 arranged longitudinally along the length of the bypass conduits. The bypass cores 33 are formed by a plurality of corrugated plates, for example corrugated stainless steel plates. The plates may be welded to each other to prevent a displacement of the plates. The corrugations of neighbouring plates may be tilted against each other in order to prevent that neighbouring plates completely intertwine. By this, the plurality of channels extends into the longitudinal direction of the bypass cores 33, but deviate by a few degrees from being exactly parallel to a general flow direction in the bypass conduit 2.

[0062] The number of corrugates plates in a rectangular bypass core are preferably between 30 and 50 corrugates plates.

[0063] FIG. 10 shows a bypass core 33 in the form of a cylinder made by a densely rolled-up sheet of corrugated steel material. As may be seen in the figure, longitudinal channels 333 are formed by the corrugations between the individual windings of the roll.

[0064] In FIG. 11, a bypass core 33 in the form of a rectangular cuboid is shown. The bypass core 33 comprises a core housing 34. A plurality of parallel arranged plates 331 made of corrugated steel, preferably stainless steel, is arranged in the core housing 34. Channels 333 are formed by the corrugations of and in between the plates 331. The plates are preferably welded to each other and may also be welded to the core housing 34. The core housing 34 may also be made of steel and is preferably welded to the bypass housing 35 in a fluid-tight manner. In the embodiment as depicted in FIG. 11, a fluid flow would pass from the top of the bypass core 33, through the channels 333 in the plates 331 and out at the bottom of the bypass core 33.

[0065] In FIG. 12, bypass flow rates of a state-of the art bypass (dashed line) and bypass flow rates in a heat exchanger unit according to the invention (solid line) are shown.

[0066] For the measurements of FIG. 12, a bypass core was constructed with 200 channels per square inch.

[0067] It may be seen that both bypass solutions have a same percentage of about 68 percent of the flow that bypasses the heat exchanger at a flow rate of 0.008 kg/s.

[0068] However, at larger flows, only about 43 percent of the flow bypasses the heat exchanger at a flow rate of 0.040 kg/s for the state-of-the-art solution.

[0069] According to the invention, still 72 percent of the flow bypasses the heat exchanger also at a higher flow rate of 0.040 kg/s. The flow rate through the bypass according to the invention varies thus by only about 4 percent over the shown massflow range between 0.008 kg/s and 0.04 kg/s.

[0070] Examples of heat exchanger unit characteristics are: [0071] A bypass core having a size of 40 mm x 100 mm x 100 mm (width x length x height) comprises 300 channels [0072] A rectangular bypass core comprising 30 to 50 plates arranged in parallel [0073] In a fluid flow range between 0.01 kg/s and 0.04 kg/s a bypass flow is between [0074] 69 percent and 72 percent with a bypass core having 200 channels; [0075] 59 percent and 64 percent with a bypass core having 300 channels; [0076] 52 percent and 58 percent with a bypass core having 400 channels; [0077] 44 percent and 51 percent with a bypass core having 600 channels. [0078] A variation of pressure drop in the bypass channel is kept below 1 mbar, preferably below 0.5 mbar over the fluid flow range of 0.01 kg/s and 0.04 kg/s, in pressure drop ranges between 4 mbar and 7.2 mbar.