WO2012088613A1

WO2012088613A1 - Apparatus for measuring the flow of a fluid

Info

Publication number: WO2012088613A1
Application number: PCT/CH2010/000331
Authority: WO
Inventors: Felix Mayer; Mark Hornung; Martin GÖPPL
Original assignee: Sensirion Ag
Priority date: 2010-12-29
Filing date: 2010-12-29
Publication date: 2012-07-05

Abstract

An apparatus for measuring the flow of a fluid comprises a multi-channel section (3) for receiving the fluid. The multi-channel section (3) comprises at least two channels (34) separated by a guide (511). An outlet channel (4) is connected to the multi-channel section (3) for receiving the fluid supplied by the channels (34) of the multi-channel section (3). A flow sensor (1) for measuring the flow of the fluid is arranged in the outlet channel (4). The multi-channel section (3) supports reducing turbulences in the fluid.

Description

APPARATUS FOR MEASURING THE FLOW OF A FLUID

Technical Field

The invention relates to an apparatus for measuring the flow of a fluid, and to an associated use of such apparatus.

Background Art

In a state of the art arrangement for measuring the flow of a fluid, a bypass structure is suggested for enabling the measurement of large flows in a main path. In such arrangement, a small portion of the fluid is branched off from the main path into a bypass. By means of a flow sensor arranged in the bypass, a flow of the small fluid portion is measured. The measured flow allows for determining a flow of the fluid in the main path. Such arrangement is described in EP 1 443 314 A2.

It is aimed at directly measuring at least midsize flows in a main path without the need for a bypass structure. However, in such main path turbulences in the fluid constitute a disturbing factor for a precise measurement of the flow.

Disclosure of the Invention

Hence, it is a general object of the invention to provide an apparatus suited for directly measuring the flow of a fluid in a main path without the need for providing a bypass structure.

The problem is solved by an apparatus for measuring the flow of a fluid according to the features of claim 1. The apparatus comprises a multi-channel sec- tion for receiving the fluid. The multi-channel section comprises at least two channels separated by a guide. In addition, an outlet channel is provided which outlet channel is connected to the multi-channel section for re- ceiving the fluid supplied by the channels of the multichannel section. A flow sensor is arranged for measuring the flow of the fluid in the outlet channel.

It is observed that for enabling direct flow measurements a reduction of turbulences in the fluid is critical to obtain a precise flow measurement. A flow in any inlet/main channel is affected by such turbulences. By splitting the flow of the fluid to be measured and reunifying the resulting sub flows prior to measuring the flow, i.e. prior to a measurement location, the reunified flow may exhibit less turbulences and a more laminar property at the measurement location which in turn provides for better measurement results reflecting the real quantity of flow. Increasing the area of friction by introducing multiple channels supports reducing turbulences in the fluid and evoking a laminar flow property. Insofar, the apparatus may be understood as a device for reducing turbulences in the fluid and for improving a laminar flow of the fluid.

The channels of the multi-channel section are separated by a guide such guide being provided for guiding flows in at least two adjacent channels. As a result, the guide forms a wall for such adjacent channels for separating the channels and for guiding the fluid in the channels. For such purpose, the guide is responsible for splitting the inlet flow into sub flows and for maintaining such sub flows during travel through the individual channels. The one or more guides do not necessarily need to provide fully isolated channels where any fluid interaction is prevented between adjacent channels. The one or more guides may be embodied such that little exchange of fluid may occur between adjacent channels, as long as the maintenance of separate sub flows is supported. In an- other embodiment, the guide provides for fully isolated adjacent channels preventing any fluid interaction between the channels along their length.

The guide preferably is part of a component common to all channels of the multi-channel section. The common component may comprise multiple elements such as a body, a cover, and one or more guides between the channels. Some of its elements such as the body and the one or more guides may be formed integrally.

For other preferred embodiments of the present invention it is referred to the dependent claims which, for example, focus on the design of the multichannel structure, or on the design of the output channel.

Brief Description of the Drawings

The embodiments defined above and further em- bodiments, features and advantages of the present invention can be derived from examples of embodiments of the invention to be described hereinafter in connection with the following drawings:

FIG. 1 illustrates an apparatus for measuring the flow of a fluid according to an embodiment of the present invention, in diagram a) in a top view, in diagram b) in two longitudinal cuts long lines A-A and B-B, in diagram c) in two lateral cuts along lines C-C and D- D, and in diagram d) in a perspective transparent view,

FIG. 2 illustrates an apparatus for measuring the flow of a fluid according to another embodiment of the present invention, in diagram a) in a top view, in diagram b) in a longitudinal cut long line A-A, in diagram c) in a lateral cut along line B-B, and in diagram d) in a perspective transparent view,

FIG. 3 illustrates an apparatus for measuring the flow of a fluid according to a third embodiment of the present invention, in diagram a) in a top view, and in diagram b) in a perspective transparent view,

FIG. 4 illustrates an apparatus for measuring the flow of a fluid according to a fourth embodiment of the present invention, in diagram a) in a top view, in diagram b) in three longitudinal cuts long lines C-C, D-D and E-E, in diagram c) in two lateral cuts along lines A- A and B-B, and in diagram d) in a perspective transparent view,

FIG. 5 illustrates an apparatus for measuring the flow of a fluid according to a fifth embodiment of the present invention, in diagram a) in a top view, and in diagram b) in a perspective transparent view, and

FIG. 6 illustrates an apparatus for measuring the flow of a fluid according to a sixth embodiment of the present invention, in diagram a) in a top view, in diagram b) in a longitudinal cut long lines A-A, in diagram c) in two lateral cuts along lines B-B and C-C, and in diagram d) in a perspective transparent view.

Modes for Carrying Out the Invention

In the figures same or similar elements are referred to by the same reference signs across all figures .

FIG. 1 illustrates an apparatus for measuring the flow of a fluid according to an embodiment of the present invention, in diagram a) in a top view, in dia- gram b) in two longitudinal cuts long lines A-A and B-B, in diagram c) in two lateral cuts along lines C-C and D- D, and in diagram d) in a perspective transparent view.

The apparatus comprises a common component 5 which common component 5 comprises a body 51 made, for example, from metal such as aluminum or from plastics, and a cover not shown in any of the figures. The body 51 may preferably be manufactured by injection molding, or by any other molding technique. The common component 5 may be inserted into another component comprising inlet and outlet ports. For example, such other component may be made of metal as part of a duct system while the coiti- mon component 5 may be made from plastics.

In the body 51, there is arranged an input channel 2, connected to a multi-channel section 3, which multi-channel section 3 is connected to an outlet channel 4. The input channel 2, which takes the form of a single channel, supplies a fluid a flow of which fluid is to be measured to the multi-channel section 3 where the flow is split into two sub flows in the present example, guided by two channels 34 of the multi-channel section 3. A guide 511 is formed in the body 51 in between the chan- nels 34 in form of a bar for separating the two channels 34 from each other. The guide 511 preferably is formed integrally with the rest of the body 51. The two channels 34 in the multi-channel section 3 help to reduce turbulences in the fluid and make the flow become a laminar flow as far as possible. This effect is produced by having increased friction forces produced between the body 51 and the fluid by means of providing at least two channels 34 instead of one. The friction forces help reducing turbulences and support realignment of the flow. Insofar, it is preferred, that a length of the multi-channel section 3 is extended as far as the application allows.

The common component 5 preferably has a cuboid or similar form. Generally, the common component 5 may have a length x, a width y and a height/thickness z, see diagram d) . The length x typically is larger than the width y and the height z. An extension of the length x corresponds to a direction of a center line A-A of the outlet channel 4, which in turn corresponds to a flow direction at the outlet of the apparatus. The width y may primarily depend on the need for deflecting the flow in a lateral plane. The lateral plane generally is defined by the length x and the width y of the common component 5. This lateral plane also is denoted a horizontal plane. Any horizontal orientation refers to an orientation in the horizontal plane. A vertical orientation is aligned orthogonal to the horizontal plane which means that a vertical direction is aligned parallel to an extension of the height z of the common component 5.

Although it is apparent that the common component 5 may finally be installed in any orientation, for example with the horizontal plane being arranged in a vertical direction of installation, it is referred to the above definitions within the system of the common component 5 in order to define orientations relative to each other and with respect to the common component 5. Insofar, any channel section that may imply a flow direction with respect to the common component 5, such as a rising section to be defined later on, may not limit the claims since by altering the direction of installation, a flow in such rising section may, for example, no longer rise but fall. Still, such section is named as rising section according to the present naming convention, however, without limiting such section to rising flows only. It is understood that the above naming convention holds for all embodiments and the overall context of the present invention.

In the specific embodiment of the apparatus according to Figure 1, the multi-channel section 3 comprises a straight section 31 with two straight channels 34. For the upper channel in diagram a) a center line M-M is depicted. The center lines M-M of all channels 34 in the straight section 31 are parallel to a center line A-A of the outlet channel 4. In the present example, A-A also represents a center line of the inlet channel 2. In this respect, the center lines of all channels 2, 34, 4 in the common component 5 are aligned in parallel to each other, and all channels 2, 34, 4 are arranged in a common horizontal plane in the upper half of the body 51. There is no deflection of the flow neither in a lateral nor in a vertical direction except for a vertical/lateral deflection induced by an acceleration section 41 referred to in the following sections, and a lateral/vertical deflection occurring at the front edge of the guide 511 where the fluid supplied by the inlet section 2 meets the guide 511.

After the fluid having passed the multichannel section 3, the two sub flows are unified again for passing into the outlet channel 4. This implies that the fluid flows in a flow direction from the inlet channel via the multi-channel section 3 into the outlet chan^¬ nel 4. Supported by the multi-channel section 3, it is assumed that the flow shows a more homogeneous property at the exit of the multi-channel section 3 than at its entrance. At the exit of the multi-channel section 3, the two sub-flows exhibit a more or less uniform flow velocity for the reason that the two channels 34 provide for an identical length and an identical cross section which cross-section can be derived from diagram c) in cut C-C.

The outlet channel 4 comprises an acceleration section 41 and a measurement section 42. In the acceleration section 41, a cross section of the output channel 4 is narrowed, in the present example by reducing a width of the outlet channel 4 in flow direction as can be derived from diagram a) , and by reducing a height of the outlet channel 4 in flow direction by having the bottom wall rise as can be derived from diagram b) . The cross section can alternatively be reduced by amending only one these dimensions, or by other means. The reduced cross section in the acceleration section 41 evokes an acceleration of the flow which acceleration is beneficial for maintaining a laminar flow as produced in the multichannel section 3 and for reducing remaining turbulences in the fluid.

In the measurement section 42, the cross section of the outlet channel 4 remains constant. The cross- section of the outlet channel 4 in the measurement sec- tion can be derived from diagram c) in cut D-D. The cross-section preferably is of square shape. The cross- section of all channels in the common component 5 preferably is of rectangular or square shape. A flow sensor 1 is arranged in the measurement section 42 for measuring the flow of the fluid in the measurement section 42. The flow sensor 1 is arranged on top of the outlet channel 4. The flow sensor 1 may be embodied as a temperature sensing flow sensor which includes a heater between two tem- perature sensors. The heater heats the fluid such that a temperature measured upstream of the heater is different from a temperature measured downstream of the heater. A temperature difference between these two locations allows for determining the flow of the fluid.

An inlet and outlet port may be attached to the front ends of the common component 5 of Figure 1 for supplying and conveying away the fluid.

The idea allows for directly measuring the flow of a fluid in the fluid transmitting channel without requiring a bypass arrangement for the reason that turbulences are reduced by means of the multi-channel section 3. A subsequent arrangement of the flow sensor in the outlet section allows for measuring the reunified stabilized flow of the fluid.

FIG. 2 illustrates an apparatus for measuring the flow of a fluid according to another embodiment of the present invention. Diagram a) again illustrates the top view of such apparatus, diagram b) shows a longitudinal cut long line A-A, diagram c) a lateral cut along line B-B, and diagram d) a perspective transparent view. The multi-channel, section 3 of the embodiment of Figure 2 now includes three channels 34. As a result, the body 51 of the common component 5 includes two guides 511 in form of bars, preferably integrally formed together with the body 51.

Again, a straight section 31 of the multichannel section 3 is arranged in a common horizontal plane with the outlet channel 4. In the straight section 31, center lines M-M of the channels 34 - only one of which is illustrated for the bottom channel 34 in diagram a)- are aligned in parallel to the center line A-A of the outlet section 4. The channels 34 in the straight section 31 are arranged in parallel.

In addition to the straight section 31, the multi-channel section 3 includes a rising section 33 with three channels 34 connected to the straight section 31. The rising section 33 penetrates the height z of the body 51 and allows an inlet port to be arranged at the bottom side of the common component 5. In the multi-channel section 3, the sub flow of each channel 34 first rises and then will be deflected by 90° degrees for being dis- charged into the straight section 31.

The channels 34 in the rising section 33 are aligned in parallel. A center line R-R of each channel 34 in the rising section 33 is aligned orthogonal to the center line A-A of the outlet channel 4 and is aligned orthogonal to the center line M-M of the corresponding channel in the straight section 31.

Again, the outlet channel 4 may be formed integrally in the body 51 together with the multi-channel section 3. The outlet channel 4 provides an acceleration section 41 and a measurement section 42 identical to the embodiment illustrated in Figure 1. Any inlet port can be attached to an entrance of the multi-channel section 3 at the bottom side of the common component 5 whereas its top side may preferably be closed by a cover not shown.

Subject to the geometry and/or direction of external inlet and outlet ports, a measurement apparatus is provided which can interact with an inlet port being orthogonally arranged to an outlet port.

FIG. 3 illustrates an apparatus for measuring the flow of a fluid according to a third embodiment of the present invention. Diagram a) shows such apparatus in a top view and diagram b) in a perspective transparent view.

While the present outlet channel 4 is identical to the outlet channel 4 of the embodiments in Figures 1 and 2, the multi-channel section 3 now provides a different shape with three individual channels 34 arranged in a curved section 32 connected to the outlet channel 4. A rising section 33 is connected to the curved section 32. The curved section 32 including its three channels 34 is arranged in a common plane with the outlet channel 4 and claims an upper layer of the cuboid body 51. Each of the three channels 34 in the curved section 32 is bent by an angle a of 90 degrees in order to deflect the sub flow in each channel. In this respect, the guides 511 are bent, too, and provide deflection guidance for the fluid. The angle a preferably may be in a range between 80° and 100° degrees. The curved section 32 may be a preferred means for deflecting the flow within a small distance. The curved section 32 only takes little space while serv- ing the purpose of redirecting the flow such that the apparatus may be connected to inlet and outlet ports of given orientation.

In the curved section 32, the three channels 34 exhibit the same path length. This causes the exit points of the rising section 33 being offset by various distances dl, d2, d3 from the center line A-A of the outlet channel 4. The equal path length is beneficial for all sub flows now travelling the same distance between the inlet channel and the outlet channel which results in sub flows of similar velocity being merged at the end of the multi-channel section 3.

In another embodiment, the path length of the channels 34 in the curved section 32 is not identical but each channel 34 shows a different length. This may be beneficial in that the channels 34 of the rising section 33 may not need to be displaced but can be aligned in a row parallel to the center line A-A of the outlet channel 4. The problem of different velocities at the exit of the curved section 32 may then be tackled by various means: The cross section of the channels in the curved section or another subsequent section may be designed of differ- ent size such that, for example, the longest channel provides for the largest cross section, and the shortest channel may provide the smallest cross section. The cross section of a channel 34 is determined by its width and its height. Adjustments in its width and/or height may be made in order to achieve a uniform velocity across all sub flow components at the exit of the multi-channel section 3. In general, non-uniform velocities of sub flows at the exit of the multi-channel section 3 are not preferred since they may cause new turbulences not appreci- ated for measurement. Hence, it is preferred that at least two channels 34 in the multi-channel section 3 are designed with respect to their respective length and cross section such that the sub flows in these channels 34 show essentially the same velocity at a location where the sub flows from these channels 34 unite. Essentially the same velocity shall allow for a deviation of

plus/minus 15 per cent. In an embodiment, at least one of the length and the cross section of one of these channels is different to the length and the cross section respec- tively of the adjacent channel.

In this context, and provided that there are more than two channels in the multi-channel section 3, not all sub flows may need to be unified at the same location, but a first pair of sub flows may be unified first while a remaining sub flow may be unified with the first unified sub flows at a later location. Any sub flow merge may preferably be implemented at a location where the channel design assumes an equal flow velocity for the associated sub flows. Another scheme for unifying sub flows is unifying every two sub flows, unifying the resulting sub flows, and so on. FIG. 4 illustrates an apparatus for measuring the flow of a fluid according to a fourth embodiment of the present invention. Diagram a) shows a top view, dia^¬ gram b) three longitudinal cuts along lines C-C, D-D and E-E, diagram c) two lateral cuts along lines A-A and B-B, and diagram d) a perspective transparent view.

Except for the outlet channel 4, the present embodiment is identical to the embodiment of Figure 3. In addition to Figure 3, there are shown multiple longitudi- nal cuts in diagram b) which illustrate each channel 34 in the rising section 33 and the curved section 32.

As to the outlet channel 4, the acceleration section 41 and the measurement section 42 still are embodied in the apparatus of Figure 4. However, in addition a recess section 43 is provided. As can best be derived from diagrams c) and d) , the recess section 43 comprises recesses 433 arranged laterally in the outlet channel 4. Given that two side walls 432 limit the extension of the outlet channel 4 in lateral direction, the recesses 433 are arranged with respect to and/or in these side walls

432. Each side wall 432 includes a recess 433 at its vertically upper end close to the flow sensor 1. Given that the wall defined by the flow sensor 1 or to which the flow sensor is mounted to is denoted as sensor wall 431, the two side walls 432 adjoin the sensor wall 431. Insofar, the side walls 432 define a lateral extension of the outlet channel 4 at least in its measurement section 43. A regular width of the outlet channel 4 is denoted by width wl. Compared to the regular width wl, the recesses 433 in the side walls 432 result in an extended width w2 of the outlet channel 4 in its measurement section 43. A portion of the outlet channel 4 with the extended width w2 is arranged between the flow sensor 1 and a portion of the outlet channel 4 with the regular width wl in a ver- tical direction.

In a longitudinal direction, the recesses 433 start prior to an arrangement of the flow sensor 1, and terminate at the end of the flow sensor 1 or, as shown in Figure 4, beyond the end of the flow sensor 1.

It was found that such recesses 433 support stabilizing a flow of the fluid in lateral sections of the outlet channel 4, and in particular in regions close to the flow sensor 1. In this context, stabilizing the flow shall include reducing turbulences and supporting a laminar flow. For this reason, it is preferred that the outlet channel 4 is widened laterally close to the flow sensor 1. For the reason that the flow may need some distance in the outlet channel 4 for being stabilized, it is advantageous that the recess section 43 starts in a sufficient distance from the flow sensor 1, i.e. prior to the flow sensor 1 in flow direction.

In the above embodiment, the recesses 433 are formed in the body 51 of the common component 5. In other embodiments and subject to the mechanical setup of the common component 5, the recesses 433 may be arranged in a cover or in another element. It is preferred, that the recesses 433 are arranged in the side walls 432 of the outlet channel 4. However, it is generally advantageous that the flow to be measured may laterally expand prior to the measurement location. Preferably, means for implementing such lateral expansion is arranged at a vertical position close to the flow sensor 1, and especially in the upper half of the outlet channel 4 in vertical direction.

In a preferred embodiment, a height of each recess in vertical direction may be at least a tenth of the height of the outlet channel 4 in the measurement section 42. A preferred height of the channel 4 may be between 1 mm and 1.5 mm. In another embodiment, a height of each recess in vertical direction may be at least 0.1 mm, or at least 0.2 mm. A recess 433 may be manufactured by cutting off material from the body 51, or by providing a mold for the body 51 such that the one or more recesses 433 are implemented. FIG. 5 illustrates an apparatus for measuring the flow of a fluid according to a fifth embodiment of the present invention, in diagram a) in a top view, and in diagram b) in a perspective transparent view. The pre- sent embodiment may be understood as a variant of the embodiment of Figure 4. The multi-channel section 3 again comprises a curved section 32 connected to the outlet channel 4. The outlet channel 4 is connected to another multi-channel section 6 integrated into the common compo- nent 5 comprising another curved section 61, and comprising another rising section 62 as can be derived from diagram b) . The outlet section 4 is connected to the other multi-channel section 6 by means of a deceleration section 44 in which deceleration section 44 the cross- section of the outlet channel 4 widens such that a velocity of the fluid becomes reduced. The recess section 43 preferably partly extends over both, the acceleration section 41 and the deceleration section 44. In doing so, the channel structure in the common component 5 is a sym- metrical structure in which the fluid can be supplied to the measuring section 43 either via the multi-channel section 3 or via the other multi-channel section 6. Irrespective of the flow direction the measurement conditions are the same. In another scenario, where there is a pre- ferred flow direction through the measurement apparatus, temporary back flows can easily be measured by the present apparatus. In this respect, it is preferred that the channel structure is mirrored with respect to the flow sensor such that for both flow directions the same meas- urement conditions apply.

It is apparent, that the symmetry between the multi-channel section 3 and the other multi-channel section 6 is not limited to the embodiment of the multichannel section 3 comprising a curved section 32 con- nected to a rising section 33. Any other design of the multi-channel section 3 may be applicable. The multichannel section 3 and the other multi-channel section 6 preferably are arranged in symmetry to each other with respect to an axis orthogonal to the center line of the outlet channel 4. In this respect, it is also preferred that the outlet channel 4 is designed symmetrically in itself with respect to such axis.

FIG. 6 illustrates an apparatus for measuring the flow of a fluid according to a sixth embodiment of the present invention, in diagram a) in a top view, in diagram b) in a longitudinal cut long lines A-A, in dia- gram c) in two lateral cuts along lines B-B and C-C, and in diagram d) in a perspective transparent view. The present embodiment may be understood as a variant of the embodiment of Figure 1. The present embodiment differs from the embodiment of Figure 1 in that the guide 511 of the multi-channel section 3 is extended into the outlet channel 4. In the present example, the guide 511 not only is extended into the outlet channel 4 but is also reduced in height compared to the guide 511 of Figure 1. This allows for the flow sensor 1 in the outlet channel 4 to measure the complete flow and not only a sub flow from one of the channels 34 of the multi-channel section 3. Hence, the flow sensor 1 is exposed to the entire flow supplied via the inlet channel 2 to the measurement section 42. Such arrangement of the guide 511 may support a laminar flow in the outlet channel 4.

In any of the embodiments according to Figures 2 to 5, an inlet port may be aligned orthogonally with respect to the outlet channel 4, and may be directly connected to the multi-channel section 3. However, in an- other embodiment, the inlet port may be integrated into the body 51 in form of an inlet channel 2, and preferably may be aligned in a plane parallel to the horizontal plane defined by the outlet channel 4, however, at a lower level. In an alternative embodiment, such inlet channel 2 may be arranged in an additional plate attached to the body 51. The inlet channel 2 preferably is formed as a single channel for supplying the fluid to the multichannel section 3.

Any of the embodiments introduced may be used for measuring the flow of a fluid directly in a main channel without the need of a bypass structure. A flow of 10 liters per minute may, for example, be measured by such apparatus. The fluid can be any one of a liquid or a gas .

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. Apparatus for measuring the flow of a fluid, comprising

a multi-channel section (3) for receiving the fluid, the multi-channel section (3) comprising at least two channels (34) separated by a guide (511),

an outlet channel (4) connected to the multi- channel section (3) for receiving the fluid supplied by the channels (34) of the multi-channel section (3), and a flow sensor (1) for measuring the flow of the fluid in the outlet channel (4) .

2. Apparatus according to claim 1, wherein the multi-channel section (3) comprises a straight section (31) in which the channels (34) are aligned in parallel and center lines (M-M) of the channels (34) are aligned in parallel to a center line (A-A) of the outlet channel (4) .

3. Apparatus according to claim 1 or claim 2, wherein the multi-channel section (3) comprises a curved section (32) for deflecting a flow in each channel (34) by an angle (a) between 80° and 100° degrees, and

wherein the curved section (32) and the outlet channel (4) are arranged in a common plane.

4. Apparatus according to any one of the preceding claims,

wherein the multi-channel section (3) com- prises a rising section (33) in which the channels (34) are aligned in parallel and center lines (R-R) of the channels (34) are aligned orthogonal to a center line (A- A) of the outlet channel (4).

5. Apparatus according to claim 2 in combina- tion with claim 4, wherein the straight section (31) is arranged between the rising section (33) and the outlet channel (4) .

6. Apparatus according to claim 3 in combina- tion with claim 4,

wherein the curved section (32) is arranged between the rising section (33) and the outlet channel (4) .

7. Apparatus according to claim 6, wherein the channels (34) in the curved section (32) are designed of equal length such that the center line (R-R) of each channel (34) in the rising section (33) is offset by a different distance (d) from the center line (A-A) of the output channel (4) .

8. Apparatus according to any one of the preceding claims,

wherein the multi-channel section (3) and the outlet channel (4) are formed in a common component (5), wherein the common component (5) comprises a body (51) forming the walls of each channel (34) and the outlet channel (4) except for a top wall, and

wherein the common component (5) comprises a cover (52) for forming the top wall of each channel (34) and the output channel (4) when being attached to the body (51) .

9. Apparatus according to any one of the preceding claims,

comprising a guide (511) between two

neighboring channels (34) for separating the channels (34) and for guiding the fluid in the channels (34),

wherein the channels (34) are designed of equal length.

10. pparatus according to claim 8, comprising an inlet channel (2) connected to the multi-channel section (3) for supplying the fluid to the multi-channel section (3) , wherein the inlet channel (2) is formed in the common component (5) .

11. Apparatus according to any one of the preceding claims,

wherein the outlet channel (4) comprises an acceleration section (41) with a narrowing cross section in flow direction.

12. Apparatus according to claim 11,

wherein the acceleration section (41) is con- nected to a measuring section (42) at its narrow end, wherein the measuring section (42) comprises a constant cross section, and

wherein the flow sensor (1) is arranged in the measuring section (42) for measuring the flow of the fluid in the measuring section (42) .

13. Apparatus according to any one of the preceding claims,

wherein the flow sensor (1) is arranged at a sensor wall (431) of the outlet channel (4), and

wherein the outlet channel (4) comprises a recess section (43) in which a recess (433) in one or both side walls (432) adjoining to the sensor wall (431) provide for an extended width (wl) of the outlet channel (4) compared to a regular width (w2) .

14. Apparatus according to claim 13,

wherein along a length of the outlet channel (4) the recess section (43) starts prior to the flow sensor (1) and extends to at least an end of the flow sensor (1) in flow direction.

15. Apparatus according to any one of the preceding claims,

wherein the outlet channel (4) is arranged between the multi-channel section (3) and another multichannel section (6), and

wherein the multi-channel section (3) and the other multi-channel section (6) are arranged symmetrically.

16. Apparatus according to any one of the preceding claims,

wherein at least two channels (34) of the multi-channel section (3) are designed with respect to their respective length and cross section such that the sub flows in these channels 34 show essentially the same velocity at a location where these sub flows unite.

17. Use of an apparatus according to any one of the preceding claims for directly measuring the flow of a fluid without using a bypass for determining the flow of a fluid in a main path connected to such bypass.