Patent Description:
In so-called shell-and-tube heat exchangers, for guiding one of the fluids tubes are arranged close to each other in a housing. The tubes may be U-tubes extending into a fluid collector. These collectors typically include plates and box-like shapes including several, typically long longitudinal, weld connections. Due to their construction, these devices are either massively built or not suitable for high pressure applications up to several hundred bar. For example, in the European patent application <CIT>, heat exchanger modules comprising a nested U-tube arrangement is shown. However, these modules are suitable for applications with a fluid pressure well below hundred bar. <CIT> discloses a tube-bundle heat exchanger according to the preamble of claim <NUM>.

Therefore, there is a need for a heat exchanger module and a tubular heat exchanger comprising such modules suitable for high pressure applications, in particular for pressure applications up to several hundred bar fluid pressure.

According to the invention, there is provided a heat exchanger module comprising several U-tubes for a first fluid flow, typically a pressurized fluid flow. The U-tubes have two straight sections connected by a U-shaped portion. Inlet ends of the several U-tubes are connected with an inlet collector tube and outlet ends of the several U-tubes are connected with an outlet collector tube.

Due to its construction, in particular using tubes as fluid collectors, the heat exchanger module is adapted and suitable for high pressure applications, for example pressure applications up to a maximum of <NUM> bar. It has been found that in particular heat exchanger modules for pressure applications up to <NUM> bar at temperatures between <NUM> degree Celsius and <NUM> degree Celsius, or even up to <NUM> degree Celsius, may be manufactured with low cost and weight.

Tubes have an intrinsic stability due to their circular cross section. In addition, tubes are generally manufactured in one piece, such that no welds need be present forming the collectors and making high pressure applications unavailable.

The U-tubes may be connected with the collector tubes in any suitable way and by any suitable means providing a fluid connection between the interior of the U-tubes and the interior of the collectors. For example, the U-tubes, respectively their inlet ends and outlet ends may be directly attached to the respective collector tubes.

Preferably, some or all ends of the U-tubes are embedded in tube walls of the inlet collector tube or outlet collector tube or in both the inlet collector tube and outlet collector tube.

Preferably, the inlet ends of the U-tubes are embedded in a tube wall of the inlet collector tube and outlet ends of the U-tubes are embedded in a tube wall of the outlet collector tube. This provides the advantage that the U-tubes and collectors may be positioned relative to each other. They may also at least partially be fixed to each other by a form-fit of the ends of the U-tubes and passages in the tube walls of the collector tubes.

Preferably, the inlet ends or the outlet ends of the U-tubes are connected with the tube wall of the respective collector tube over an entire wall thickness of the respective tube wall. More preferably, both, inlet ends and outlet ends are connected with the respective collector tubes over the entire tube wall of the respective inlet and outlet collector tube. Depending on a thickness of a tube wall, a connection between U-tubes and collector tubes generally extends over more than ten millimeters, for example up to <NUM> millimeters. This not only enhances stability of a joint to stand high forces or pressure but has also a favorable effect on leak tightness.

A tube wall thickness of inlet and outlet collector tube may be chosen and adapted, for example, to a pressure of a fluid the module is used with, tube materials or cost and space constraints. Tube wall thicknesses of inlet and outlet collector tubes are preferably in a range between <NUM> millimeters and <NUM> millimeters, more preferably in a range between <NUM> millimeters and <NUM> millimeters, for example between <NUM> millimeters and <NUM> millimeters.

In preferred embodiments, the tube wall of the inlet collector tube or the tube wall of the outlet collector tube is provided with through passages in the tube wall. The inlet ends or outlet ends of the U-tubes are arranged in the through passages, preferably drill holes or laser-cut holes. More preferably, the tube wall of the inlet collector tube and the tube wall of the outlet collector tube is provided with through passages. Thus, the inlet ends and the outlet ends of the U-tubes are arranged in the through passages.

Providing through passages in a tube wall bears the advantage that a collector tube as such may be provided as and remains a stable one-piece part. Passages for the fluid flow or for the U-tubes, respectively, may be provided only where required. Preferably, there are as many through passages in a tube wall of a collector tube as there are U-tubes to be connected to the collector tube.

While connections between metallic parts may typically be realized by welding, soldering or brazing, for elevated temperature and elevated pressure applications, such connections are realized by welding or brazing.

In the heat exchanger module, connections between U-tubes and collectors are preferably realized by brazing, for example vacuum brazing or diffusion bonding (also known as diffusion welding), but also by welding. In particular vacuum brazing with nickel-based brazing material allows to manufacture extremely stable and robust heat exchanger modules, which are suitable for applications in the mentioned high pressure and high temperature ranges.

Preferably, at least one of the inlet ends of the U-tubes or the outlet ends of the U-tubes comprises a brazed joint with the respective collector tube. More preferably, several inlet ends, most preferably, all inlet ends comprise a brazed joint with the inlet collector tube. More preferably, several outlet ends, most preferably, all outlet ends comprise a brazed joint with the outlet collector tube. By brazing, a length of a joint may be manufactured that extends over an entire wall thickness of the collector tube. Depending on the relative position of an inlet end or outlet end of a U-tube and a collector tube, joints may be manufactured that are even longer than a tube wall thickness.

Manufacturing brazing joints may be performed in a very efficient way and providing very stable connections. This will be described in more detail further below when referring to a method of manufacturing the heat exchanger modules according to the invention.

In the heat exchanger module, a longitudinal axis of the inlet collector tube and a longitudinal axis of the outlet collector tube are preferably arranged parallel to each other.

Preferably, a longitudinal axis of the straight sections of the U-tubes is arranged perpendicular to a longitudinal axis of an inlet collector tube or outlet collector tube.

An end of the inlet collector tube or an end of the outlet collector tube is closed, preferably, an end of the inlet collector tube and an end of the outlet collector tube is closed. Preferably, closed ends of inlet and outlet collector tubes are arranged on a same side of the heat exchanger module.

A closed end of the collector tubes may be realized, for example, by the provision of a bottom plate or similar. Such a bottom plate may be connected with the tube wall, for example by welding, brazing or by deep drawing of the collector tube including bottom wall. A closed end, in particular a bottom plate, may be plane or have a concave shape. A concave shape of a bottom wall may withstand elevated pressure compared to a plane shape and is known, for example from champagne bottles.

Inner and outer diameter of inlet collector tubes may be different or may be the same as inner and outer diameter of outlet collector tubes. Preferably, inner and outer diameters of an inlet collector tube and an outlet collector tube are the same. Preferably, inlet collector tube and outlet collector tube are identical with respect to size and material. This may simplify manufacture and construction of the collector tubes as well as of heat exchanger modules.

Preferably, the several U-tubes are arranged in a regular array in the heat exchange module. Preferably, the U-tubes are provided in nested arrangement, for example provided in rows, wherein the U-tubes of neighbouring rows are displaced versus each other.

Preferably, the inlet ends of the several U-tubes and the outlet ends of the several U-tubes are arranged in one or more rows, preferably linear rows. Preferably, the inlet ends of the several U-tubes and the outlet ends of the several U-tubes are each arranged in two to eight rows, preferably, in four to six rows. Preferably, the rows are equidistantly arranged to each other. Preferably, the one or more rows extend along a longitudinal direction of the collector tubes. Preferably, the one or more rows are arranged parallel to the longitudinal axis of the collector tube.

Preferably, the through passages for the inlet and outlet ends of the U-tubes and accordingly the inlet and outlet ends of the U-tubes are arranged in one half only of the collector tubes. Preferably, they are arranged in or extend over a maximum of a quarter of a circumference of a collector tube.

Preferably, the several U-tubes of a heat exchanger module are arranged parallel to each other, preferably equidistantly and preferably in one row.

A number of U-tubes in a heat exchanger module may be chosen and adapted to a user's need, cost or power requirement, space constraints etc. of the heat exchanger to manufactured from the heat exchanger modules.

A heat exchanger module may, for example, comprise between <NUM> and <NUM> U-tubes, preferably between <NUM> and <NUM> U-tubes, more preferably between <NUM> and <NUM> U-tubes, for example between <NUM> and <NUM> U-tubes.

A heat exchanger module may, for example, comprise between <NUM> to <NUM>, preferably nested, rows, each row comprising between <NUM> and <NUM> U-tubes, preferably between <NUM> to <NUM> rows, each row comprising between <NUM> and <NUM> U-tubes, more preferably between <NUM> to <NUM> rows, each row comprising between <NUM> and <NUM> U-tubes, for example four rows, each row between <NUM> and <NUM> U-tubes.

Under a 'nested arrangement of U-tubes' an arrangement of tubes is understood, wherein more than one row of U-tubes is arranged next to each other, wherein U-tubes of each row have a different bending radius and overall length, so that a row of U-tubes with small bending radius and length is at a closest possible distance to a row of U-tubes having larger bending radius and length.

The shape of the U-tubes of a heat exchanger module may be adapted to their position in the module. For example, if a U-tube is arranged in a more internal inner portion of the heat exchanger module or in a more external outer portion of the heat exchanger module, radii and sizes of U-shaped portions of the U-tubes, but also diameters are adapted accordingly.

In preferred embodiments of the heat exchanger module, the U-shaped portion of the several U-tubes have at least one of a different bend radius, a different size or a different diameter.

In the heat exchanger module, the two straight sections of the U-tubes have a different length. Different length of straight sections is advantageous as it allows for a more compact arrangement of the collector tubes and thus to a more compact design of the heat exchanger module. Preferably, all inlet straight sections of all U-tubes of a module have a same length and all outlet straight sections of all U-tubes of a module have a same length but different to the length of the inlet straight sections. This means that inlet collector tube and outlet collector tube are arranged at different heights with respect to the lengths of the two straight sections of the U-tubes. Accordingly, the two collector tubes may be positioned closer together compared to an exact parallel and inline positioning of two tubes allowing for a smaller set-up of the module. In particular, the longitudinal axis of the inlet and outlet collector tubes are arranged at different heights with respect to the length of the two straight sections and with respect to the height of the heat exchanger module, respectively.

A length of the outlet straight section of a U-tube may, for example, be between <NUM> percent and <NUM> percent of the length of the inlet straight section of a U-tube, more preferably between <NUM> percent and <NUM> percent, for example between <NUM> percent and <NUM> percent. Or vice versa, a length of an inlet straight section of a U-tube may, for example, be between <NUM> percent and <NUM> percent of the length of the outlet straight section of a U-tube, more preferably between <NUM> percent and <NUM> percent, for example between <NUM> percent and <NUM> percent. The heat exchanger module may further comprise fins, preferably longitudinal fins, arranged on an outside of the U-shaped tubes for guiding a second fluid flow in the direction of the fins along the outside of the heat exchanger module. Preferably, the fins are arranged parallel or perpendicular to a longitudinal axis of an inlet collector tube or outlet collector tube or both, arranged parallel and perpendicular to a longitudinal axis of the collector tubes.

Fins are provided to give the second flow that passes the U-tubes of the heat exchanger module on their outside some guidance, preferably to prevent a second flow to accumulate on a side of the heat exchanger module, for example on a top side or a bottom side. Preferably fins are longitudinal fins preferably extending over about an entire length of a heat exchanger module. Fins, for example arranged on a small side of a heat exchanger module, may interact with fins of neighbouring heat exchanger modules and form fins extending over some or all heat exchanger modules arranged in a tubular heat exchanger comprising a plurality of heat exchanger modules.

According to the invention, there is also provided a method for manufacturing a heat exchanger module according to the invention and as described herein. The method comprises providing a plurality of U-tubes and providing an inlet collector tube and an outlet collector tube with through passages in a tube wall of the inlet collector tube and with through passages in a tube wall of the outlet collector tube. The method further comprises accommodating inlet ends and outlet ends of the U-tubes in the through passages in the respective tube walls of the inlet collector tube and the outlet collector tube and connecting the inlet ends of the U-tubes to the inlet collector tube and connecting the outlet ends of the U-tubes with the outlet collector tube in a fluid tight manner, thereby forming a heat exchanger module.

The method further comprises applying brazing paste in the region of the through passages and heating the heat exchanger module above a melting temperature of the brazing paste, letting the brazing paste enter the through passages, thereby forming a brazed joint between the ends of the U-tubes and the respective collector tubes.

Through heating of the assembled module provide with brazing paste, the molten brazing paste enters the interstitial spaces between through passage and outer circumference of the ends of the U-tubes. The heating may be performed by putting the assembled U-tubes and collector tubes in a furnace. This allows to manufacture all U-tube connections in one step. No separate welding of individual connections is required. In addition, due to capillary forces, brazing paste enters the interstitial space between through passage and outer circumference of the ends of the U-tubes basically over the entire length of the through passages. By this, a very stable brazing joint may be formed, that preferably extends over the entire length of the through passage, which length corresponds to at least the thickness of the tube wall of a collector tube.

The brazing may be done, for example, in a vacuum furnace for vacuum brazing the U-tubes and collector tubes. It may also be done by diffusion bonding, wherein part of the brazing paste diffuses in the material of the tubes, in particular steel of the U-tubes and collectors. This may further improve a bond.

A brazing paste may be applied to the region of the through passages on the inside of the collector tubes or to the region of the through passages on the outside of the collector tubes. A brazing paste may also be applied to the region of the through passages to the inside and outside of the collector tubes.

Preferably, the heat exchanger module is heated in a vacuum furnace for connecting the connections between U-tubes and collector tubes. Preferably, the heat exchanger module is heated in a vacuum furnace for brazing, most preferably for brazing with a nickel-based brazing paste.

A material used for connecting individual parts of the heat exchanger module must be able to stand future operation temperatures of the heat exchanger module. For example, a brazing paste used for brazing connections of the heat exchanger module must in some embodiments be able to stand temperatures of up to <NUM> degree Celsius. Thus, a Nickel-based brazing paste must be heated above <NUM> degree Celsius to melt. Under such high temperature conditions oxidation of the materials involved occurs. Performing the brazing under vacuum may prevent or limit oxidation. By this potential degradation of the materials may be prevented and make the connections of the heat exchanger module stable also under high pressure and high temperature applications.

The method may comprise drilling or laser-cutting the through passages in the tube walls of the inlet collector tube and the outlet collector tube. Preferably, a same number of through passages are provided in a collector tube than a number of U-tubes are connected with the collector tubes.

Preferably, the method comprises providing a plurality of U-tubes in a nested arrangement, wherein inlet ends and outlet ends are arranged in parallel rows.

According to yet another aspect of the invention, there is provided a tubular heat exchanger. The tubular heat exchanger comprises a housing with a first fluid inlet and a second fluid inlet and a first fluid outlet and a second fluid outlet, wherein a plurality of heat exchanger modules according to the invention and as described herein are arranged in the housing. The plurality of heat exchanger modules are connected with each other, wherein the modules may be connected in series or in parallel or both in series and in parallel.

The first inlet of the tubular heat exchanger is connected with an inlet collector tube of a first heat exchanger module of the plurality of heat exchanger modules and the first outlet is connected with an outlet collector tube of a last heat exchanger module of the plurality of heat exchanger modules. The inlet collector tube may also be connected to inlet collector tubes of several first heat exchanger modules. For example, if the plurality of heat exchanger modules is arranged in two or more rows, the first inlet may be connected to two or more first heat exchanger modules, one of each row. Accordingly, the first outlet may be connected with two or more last outlet collector tubes of heat exchanger modules.

Depending on a desired power range or duty of the tubular heat exchanger, more or fewer heat exchanger modules may be provided in a housing. A plurality of heat exchanger modules accommodated in a housing of a tubular heat exchanger may, for example, comprise <NUM> to <NUM> modules, preferably <NUM> to <NUM> modules, such as, for example, <NUM> to <NUM> modules.

For example, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> modules may be arranged in series and in one row. The heat exchangers may, for example be arranged in two parallel rows in a housing, adding up to <NUM>, <NUM>, <NUM>, <NUM> or <NUM> modules in total.

Preferably, the plurality of heat exchanger modules is arranged in the housing in two or more parallel rows. Preferably, a first fluid inlet comprises a flow splitter, which flow splitter is connected with an inlet collector tube of a first heat exchanger module in each row of heat exchanger modules. By this, a first fluid, for example a pressurized supercritical fluid, is divided and distributed over the number of parallel rows of serially connected heat exchanger modules in the heat exchanger.

Preferably, the housing of the tubular heat exchanger is elongate having a longitudinal axis. Preferably, longitudinal axes of inlet collector tubes of the heat exchanger modules are arranged perpendicular to the longitudinal axis of the housing. In this arrangement a main first fluid flow flowing through the tubular heat exchanger is perpendicular to the first fluid flow in the collector tubes.

Preferably, the longitudinal axes of straight sections of U-tubes of the heat exchanger modules are arranged perpendicular to the longitudinal axis of the housing. In this arrangement a main first fluid flow flowing through the tubular heat exchanger is perpendicular to the first fluid flow flowing through the U-tubes.

The heat exchanger modules and the tubular heat exchanger are designed for use with pressurized fluid, such as for example a supercritical fluid, such as supercritical water or supercritical CO<NUM> or with organic fluids, such as, for example, oil.

The heat exchanger modules and the tubular heat exchanger stand pressures of the pressurized fluid up to <NUM> bar. Preferred pressures range between <NUM> bar and <NUM> bar, more preferred between <NUM> bar and <NUM> bar, for example between <NUM> bar and <NUM> bar.

The second fluid preferably has a low pressure, for example between <NUM> to <NUM> bar. The second fluid is a heat exchanger fluid, which is heated up by heat transfer from the first pressurized fluid to the second fluid. The second fluid may, for example, be thermal oil, for example silicone thermal oil or hot gas. Silicon oil may, for example, be in a pressure range of about <NUM> bar. The second fluid may also be used to cool down the first pressurized fluid, for example using cooling water. Water may, for example, be at atmospheric pressure or up to, for example, <NUM> bar.

An operation temperature range of the heat exchanger module and the tubular heat exchanger may be between <NUM> degree Celsius and <NUM> degree Celsius and is preferably between <NUM> degree Celsius and <NUM> degree Celsius. This temperature refers to the temperature of the first fluid, preferably measured at the inlet of the heat exchanger module or at the inlet of a heat exchanger, respectively.

A tubular heat exchanger according to the invention is typically used in megawatt power applications, for example between <NUM>. 5MW and <NUM> MW, preferably, between <NUM>. 5MW and 25MW, or between 1MW and 20MW, for example between 1MW to 15MW.

The heat exchanger module and tubular heat exchanger are adapted for high mass flows. A mass flow of a first, pressurized fluid, may, for example, be in a range between <NUM>/s and <NUM>/s, preferably in a range between <NUM>/s and <NUM>/s, for example between <NUM>/s and <NUM>/s.

With the present invention, heat exchanger modules may be manufactured using vacuum brazing in a vacuum furnace, preferably with high temperature brazing material, such as for example nickel-based brazing material. They are as such suitable for applications up to <NUM> bar and temperatures up to <NUM> degree Celsius. These modules may then be combined to form a heat exchanger of, for example, 10MW to 40MW heat exchange. The connection of the modules is preferably performed outside of the vacuum furnace, for example by welding.

Vacuum furnaces, in particular for vacuum brazing a heat exchanger module, have limited dimensions. It is technically not feasible to heat a vacuum volume of <NUM> to <NUM> cubic meters. Accordingly, large prior art heat exchangers cannot be vacuum brazed and as such are not suitable for high temperature, high pressure applications in the above given pressure and temperature ranges. Due to the individual manufacture of mechanically and thermally stable heat exchanger modules, also heat exchangers in the Megawatt range may be manufactured that are suitable for high temperature and high pressure applications.

In addition, the modularity of the heat exchanger of the present invention allows for serial production of the individual modules, which is advantageous in cost and time.

Further features and advantages of the method and tubular heat exchanger have been described relating to the heat exchanger module and are applicable also to the method and heat exchanger.

The invention is further described with regard to embodiments, which are illustrated by means of the following drawings, wherein:.

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

<FIG> shows a heat exchanger module <NUM> comprising an inlet collector tube <NUM> and an outlet collector tube <NUM>. Both collector tubes <NUM>, <NUM> have a circular cross section and an exemplary tube wall <NUM> thickness of about <NUM> to <NUM>. In a preferred embodiment, an outer diameter of the collector tubes is <NUM> and an inner diameter is <NUM> inner diameter, thus the tube wall thickness amounts to <NUM>.

The inlet collector tube <NUM> and outlet collector tube <NUM> comprise an open end <NUM> facing to the front in <FIG>. The inlet and outlet collector tubes <NUM>,<NUM> may comprise a closed opposite end <NUM> (not shown) if used as single module or possibly in serial arrangement with other heat exchanger modules. In other embodiments, the opposite end <NUM> may be open and for example attached to, in particular welded, to another inlet collector tube of another heat exchanger module. A pressurized first fluid may then transfer into the adjacent inlet collector tube and adjacent module.

As may be seen in more detail in <FIG> showing a partial view of the heat exchanger module of <FIG>, four times <NUM> U-tubes <NUM> are fluidly connected with the interior of the collector tubes <NUM>,<NUM> via the tube walls <NUM> of the collector tubes <NUM>,<NUM>.

The collector tubes <NUM>,<NUM> each comprise four rows of <NUM> through holes <NUM> in their tube walls <NUM>. All four rows are arranged in a lower half of the collector tubes. The four rows are arranged parallel to each other and along the length of the collector tubes <NUM>,<NUM> parallel to the longitudinal axis of the collector tubes. Through holes <NUM> in neighbouring rows are displaced by half the distance between through holes in a same row. This positioning allows for a nested arrangement of U-tubes with a distance between through holes of a few millimeter, for example <NUM> millimeter to <NUM> millimeter, and thus a very compact U-tube arrangement. An exemplary diameter of a through hole is <NUM> millimeter having a shortest distance to neighbouring through holes of <NUM> millimeter.

The U-tubes <NUM> comprise two straight sections <NUM>,<NUM> and a U-shaped portion <NUM> connecting the two straight sections to form the U-tubes <NUM>. The inlet ends <NUM> of the U-tubes and the outlet ends <NUM> of the U-tubes are arranged in the through holes <NUM> and are brazed to the tube walls <NUM>.

The through holes <NUM> are preferably drill holes or laser-cut holes, and drilled or cut into the tube walls <NUM> before inserting the ends <NUM>,<NUM> of the U-tubes <NUM> into the through holes <NUM>.

Preferably, the inlet ends and outlet ends <NUM>,<NUM> of the U-tubes form a brazed joint with the tube walls <NUM> of the inlet and outlet collectors <NUM>,<NUM>. This is preferably realized by vacuum brazing or diffusion bonding.

A length of a joint extends over an entire wall thickness of the collector tubes <NUM>,<NUM>, for example if the inlet ends <NUM> or outlet ends <NUM> are arranged exactly perpendicular to the circumference of the tube walls <NUM>. In more externally arranged U-tubes <NUM> and more internally arranged U-tubes <NUM> joints may be manufactured that ere even longer than the tube wall thickness.

The straight sections <NUM>,<NUM> of a U-tube have a different length. In <FIG> all inlet straight sections <NUM> of all U-tubes are longer than their respective outlet straight sections <NUM>. By this, the inlet collector tube <NUM> in <FIG> may be arranged at a different height than the outlet collector tube <NUM> when seen over a height of the heat exchanger module <NUM>. This allows to place inlet and outlet collector tubes <NUM>,<NUM> closer together in a width direction of the module and make the heat exchanger module <NUM> very compact. In the embodiment shown in <FIG> a length of the inlet straight sections <NUM> is, for example, between <NUM> to <NUM>, while a length of the outlet straight sections <NUM> is, for example, between <NUM> to <NUM> with an outer diameter of the U-tubes in a range between <NUM> and <NUM>. In another embodiment, a length of the inlet straight sections <NUM> is, for example, between <NUM> and <NUM>, while a length of the outlet straight sections <NUM> is, for example, between <NUM> and <NUM> with an outer diameter of the U-tubes in a range between <NUM> and <NUM>.

In <FIG> it may be seen that U-tubes in an interior portion of the heat exchanger module <NUM> are smaller in height and width than U-tubes in an exterior outer portion of the heat exchanger module <NUM>. The height of a U-tube is mainly defined by a length of the straight sections <NUM>,<NUM> of a U-tube. A width of a U-tube is defined by the size of the U-shaped portion.

Five longitudinal fins <NUM> in the form of strips are arranged on the outside of the U-tubes. The fins <NUM> extend parallel to the longitudinal axis of the collector tubes <NUM>,<NUM> and are provided for guiding a second fluid flow, which second fluid flow flows around the heat exchanger module <NUM>. The second fluid flow absorbs heat from a first highly pressurized fluid flow flowing in and through the collector tubes <NUM>,<NUM> and U-tubes <NUM>. The preferably equidistantly arranged fins <NUM> separate the outsides of the U-tubes into four to five sections, each section intended to guide about <NUM> percent or <NUM> percent of the total flow of the second fluid passing that side of the heat exchanger module <NUM>.

In the example of <FIG>, the fins on each of the four sides of the heat exchanger module <NUM> are embodied as plate of a sheet material, for example steel plate. One plate forms guiding fins on the outside and in the inside of the heat exchanger module <NUM>, wherein these fins are connected and preferably made in one piece. The plate extends in between the straight sections <NUM>,<NUM> of the U-tubes <NUM>.

The module as shown in <FIG> may be vacuum brazed in a vacuum furnace. Exemplary sizes of a vacuum furnace are from <NUM> up to <NUM> (diameter or extension), for example 700x650x300, 600x900x600, 1200x2000x1200, or (diameter) 250x340, (diameter)<NUM>×<NUM>. Preferred materials of a vacuum furnace are graphite or molybdenum. Preferred materials for brazing are Nickel or Chromium-Nickel containing brazing pastes, which require furnace temperatures above <NUM>, for example <NUM> to <NUM>. Typical vacuum in a vacuum furnace is <NUM>-<NUM> to <NUM>-<NUM> mbar.

<FIG> shows two heat exchanger modules <NUM> of <FIG> aligned and connected together. The inlet and outlet collector tubes <NUM>,<NUM> are fixed to each other, for example by welding.

A first fluid flow <NUM> is indicated by arrows <NUM> for the first fluid flow within the heat exchanger modules <NUM>. The first fluid flow <NUM> is guided into the inlet collector tubes <NUM> from both sides. There, the first fluid flow flows perpendicular to the longitudinal axis of the inlet collector tubes <NUM> through the U-tubes <NUM> of the heat exchanger modules <NUM>. Arrows <NUM> in dotted bold indicate an inlet flow in the U-tubes and in bold indicate an outlet flow in the U-tubes <NUM>.

It is also possible to guide the fluid from one side only into the inlet collector tubes <NUM> and to collect all first fluid from one outlet collector tube <NUM> only.

The collector tubes and U-tubes are made from a suitable metal, preferably, steel, more preferably stainless steel.

<FIG> shows a tubular heat exchanger <NUM>. In the housing <NUM> two rows of <NUM> heat exchanger modules <NUM>, for example the heat exchanger modules according to <FIG> are arranged in parallel (only front row visible), for example in a coupled arrangement as shown in <FIG>. The open ends <NUM> of the collector tubes <NUM>,<NUM> are connected with open ends of neighbouring collector tubes. Therein, an outlet collector tube <NUM> is connected with an inlet collector tube <NUM> of the neighbouring heat exchanger module <NUM> via connectors (not shown).

The housing <NUM> comprises a first inlet <NUM> and a first outlet <NUM> for a first high pressurized fluid <NUM> to enter the housing at the first inlet <NUM>, pass the heat exchanger modules <NUM> through the collector tubes <NUM>,<NUM> and U-tubes <NUM> and leave the housing via first outlet <NUM>.

The housing <NUM> comprises a second inlet <NUM> and a second outlet <NUM> for a second not or only low pressurized fluid <NUM> to enter the housing at the second inlet <NUM>, pass the heat exchanger modules <NUM> on their outside and leave the housing via second outlet <NUM>.

The housing <NUM> has a tubular shape with a tubular side wall <NUM> having a circular cross section and slightly convex shaped end walls <NUM>. The first inlet <NUM> and second outlet <NUM> are arranged in one of the side walls <NUM> and the second inlet <NUM> and first outlet <NUM> are arranged in the opposite side wall <NUM>. By this the first fluid flow <NUM> and the second fluid flow <NUM> pass the tubular heat exchanger in a main co-flow manner but in counter direction.

The second inlet and second outlet <NUM>,<NUM> are arranged in the center of the side walls <NUM>. The first inlet and first outlet <NUM>,<NUM> are arranged displaced to a lateral side of the housing <NUM>.

The fluid flow within the housing <NUM> is indicated by arrows <NUM> for the second fluid flow <NUM>. The second fluid flow <NUM> flows parallel to the longitudinal axis of the housing <NUM> essentially in a linear manner from the second inlet <NUM> to the second outlet <NUM> of the housing <NUM>.

The fluid flow within the housing <NUM> is indicated by arrows <NUM> for the first fluid flow <NUM>. The first fluid flow <NUM> is guided into the inlet collector tube <NUM> of a first heat exchanger module in a row. There, the first fluid flow flows perpendicular to the longitudinal axis of the housing <NUM> through the U-tubes <NUM> of the heat exchanger modules <NUM>. In the last heat exchanger module <NUM> in a row, the first fluid flow <NUM> is collected in the outlet collector tube <NUM> and leaves the heat exchanger via first outlet <NUM>. Again, arrows <NUM> in dotted bold indicate an inlet flow in the U-tubes and in bold indicate an outlet flow in the U-tubes <NUM>.

On, the front side of the heat exchanger module assembly five fins <NUM> may be seen extending in the longitudinal direction of the housing <NUM> and parallel to the second flow direction <NUM>. The fins <NUM> divide the space along the height of the U-tubes <NUM> in sections <NUM>. The second flow <NUM> remains in these sections <NUM> and a flow deviation into the direction of the collector tubes <NUM>,<NUM> or the U-shaped portions <NUM> of the U-tubes may be limited or prevented.

<FIG> show a longitudinal and a transversal cross-sectional view of the heat exchanger <NUM> of <FIG>.

Two times twelve modules, for example as in <FIG>, or <NUM> combined modules as shown in <FIG>, are arranged in series in the housing <NUM>. The housing <NUM> has a length <NUM> of about <NUM> (<NUM> including first inlet <NUM> and outlet <NUM>) and a diameter of about <NUM>.

The first inlet <NUM> and first outlet <NUM> are arranged in one line and on a same height with respect to a height of the heat exchanger and parallel and distanced to the second inlet and outlet <NUM>,<NUM>. The second inlet <NUM> and second outlet <NUM> are arranged on the central axis of the housing <NUM>.

The first inlet flow <NUM> entering the heat each exchanger <NUM> by the first inlet <NUM> is distributed via flow splitter <NUM> to the inlet collector tube <NUM> of the first heat exchanger modules <NUM> of each of the two rows of modules or to the two opposite ends of combined inlet collector tubes, respectively.

An inner diameter <NUM> of first inlet and outlet <NUM>,<NUM> is about <NUM>.

An outer diameter <NUM> of second inlet and outlet <NUM>,<NUM> is about <NUM>.

In the transverse view in <FIG>, the two rows of modules <NUM> are depicted one above the other. Neighbouring inlet collector tubes <NUM> and outlet collector tubes <NUM> are connected with each other by respective end connectors <NUM> connecting their open ends <NUM>.

In <FIG> a series of four heat exchanger modules <NUM> is shown. The modules <NUM> have a similar set-up as the modules of <FIG>. However, in the example of <FIG> adjacent modules <NUM> are flipped such that neighbouring straight sections <NUM>, <NUM> of adjacently arranged modules <NUM> have a same length.

Accordingly, adjacent modules <NUM> have a long and a short inlet straight section <NUM> and a long and a short outlet straight section <NUM>.

In <FIG>, an inlet collector <NUM> is not connected with its adjacent outlet collector <NUM> through an end connector <NUM> as shown in <FIG>. The collector tubes <NUM>,<NUM> comprise four radially, in the example shown in <FIG> horizontally, arranged interface tubes <NUM>. Each interface tube <NUM> of a collector <NUM>,<NUM> is connected to an interface tube <NUM> of an adjacent collector <NUM>,<NUM>. The connection of interface tubes <NUM> to each other may be performed by welding or brazing, preferably by welding.

The interface tubes <NUM> may be connected with the respective collector tube <NUM>,<NUM> in a same manner as the U-tubes are connected to the collectors <NUM>,<NUM>. Thus, preferably, through holes are provided in the tube walls of the collector tubes <NUM>,<NUM> and the interface tubes <NUM> are inserted into the through holes. A brazing joint between interface tube <NUM> and collector tube wall is preferably, realized in a same manufacturing step than the brazing of the ends of the U-tubes with the collector walls.

The modules <NUM> preferably comprise inlet collectors <NUM> and outlet collectors <NUM> having both ends closed.

The modules in the embodiment shown in <FIG> use longer or shorter inlet sections of the U-tubes in alternating succession. The modules <NUM> are identical, but every-other module of the series is flipped.

With radially arranged connector tubes <NUM>, equidistantly arranged over a length of a collector tube <NUM>,<NUM>, a fluid flow is homogeneously distributed over the length of the collector tubes <NUM>,<NUM> and thus over the length of the heat exchanger module <NUM>.

An example of a tubular heat exchanger comprises <NUM> heat exchanger modules arranged in two rows à <NUM> heat exchanger modules, with four times <NUM> U-tubes per heat exchanger module, preferably carbon dioxide (CO<NUM>) as pressurized fluid with a pressure between <NUM> bar and <NUM> bar and a mass flow of <NUM>/s.

Claim 1:
Heat exchanger module (<NUM>) comprising several U-tubes (<NUM>) for a first fluid flow, the U-tubes (<NUM>) having two straight sections (<NUM>, <NUM>) connected by a U-shaped portion (<NUM>), wherein the two straight sections (<NUM>, <NUM>) of the U-tubes (<NUM>) have a different length,
characterized in that inlet ends (<NUM>) of the several U-tubes (<NUM>) are connected with an inlet collector tube (<NUM>) and outlet ends (<NUM>) of the several U-tubes (<NUM>) are connected with an outlet collector tube (<NUM>),
and further characterized in that a longitudinal axis of the inlet collector tube (<NUM>) and a longitudinal axis of the outlet collector tube (<NUM>) are arranged at different heights with respect to a height of the heat exchanger module (<NUM>).