Device for suppressing disturbances of a physical flow which traverses a shaft containing a liquid medium

Abstract

The invention relates to a device (10) for suppressing disturbances of a physical flow which traverses a shaft (12) containing a liquid medium (20). The device (10) has a built-in module (22) which can be placed on the inner side of the shaft in a sealed manner. The built-in module (22) is provided with an upper cover element (24) and a lower base element (26). Both elements have the same number of through-openings (30). Furthermore, the built-in module (22) has a plurality of hollow rods (34), each of which is sealingly connected at one end to one of the through-openings (30) of the cover element (24) and is hydraulically sealingly connected at the opposite other end to one of the through-openings (30) of the base element (26). Lastly, the built-in module (22) also has at least one examination space (38) between the plurality of hollow rods (34) for receiving an examination unit (28) for examining the flow (50) traversing the shaft (12). Flow movements (52) of the liquid medium (20) that occur in the shaft (12) and are directed along the shaft (12) and thus substantially at right angles to the flow (50) to be examined traversing the shaft (12) or that have flow components directed in such a way can be conducted past the at least one examination space (38) through the hollow rods (34), whereby the hollow rods (34) have a bypass function.

Description

[0001] SCHÖTTLER, M.

[0002] Device for suppressing disturbances of a physical flow traversing a shaft containing a liquid medium

[0003] The invention relates to a device for suppressing disturbances of a physical flow that traverses a shaft containing a liquid medium, in particular a shaft, e.g. in the ground, with a substantially round and preferably circular cross-section, such as in a drilled well.

[0004] Shafts in the ground, such as groundwater monitoring wells, wells, and shafts filled with liquid media, are important access points to the groundwater body and other liquid media. They are used, for example, for conducting groundwater hydraulic investigations and for taking samples for water analysis. These shafts, installed in the ground, have walls permeable to the surrounding material (e.g., porous material like sand or gravel, fractured / disturbed solid material like rock, or liquid material like water or oil). The inside of such shafts is typically lined with perforated pipes. An installation module containing testing and measuring equipment is inserted into these pipes to analyze the liquid medium. Examples of such built-in modules are described in DE-A10 2017 113 189 , WÖ-A-2014 / 174014 and CN-A-1 19 434 949.

[0005] The flow crossing such a permeable shaft, which needs to be investigated, is generally distorted, particularly in well-constructed boreholes, due to the geometry and the change in hydraulic resistance (e.g., the material outside the shaft, i.e., the sediment) towards the shaft interior (free flow). This distortion does not reflect the flow conditions upstream of the shaft. Typically, flow in a shaft containing a liquid medium occurs both horizontally and vertically, and is usually laminar. The mixing of horizontal and vertical flow therefore usually results in a chaotic (flow) system.

[0006] From DE-A-198 26 265 a method and a borehole probe for investigating soils are known, wherein the probe inserted into the borehole has a vertically continuous channel.

[0007] The object of the invention is to create a device for suppressing disturbances of a physical flow (in the sense of unbundling, i.e., separating horizontal flow from vertical flow and thus defining flow paths) that crosses a shaft containing a liquid medium, with which it is possible to keep flow components directed axially to the shaft axis away from the investigation space of an installation module with an investigation unit for investigating the flow crossing the shaft perpendicular to the shaft axis.

[0008] To solve this problem, the invention proposes a device for suppressing disturbances of a physical flow that traverses a shaft containing a liquid medium, in particular a shaft e.g. in the ground, with

[0009] - an installation module that can be inserted into the shaft under a hydraulically sealed system on the inside of the shaft, i.e. on the inside of the shaft wall,

[0010] - the installation module is equipped with

[0011] - an upper cover element that has a multitude of through-holes,

[0012] - a lower base element which has a number of through-holes equal to the number of through-holes of the cover element,

[0013] - a plurality of hollow bars, each of which is hydraulically sealed at one end to one of the through-openings of the cover element and at its opposite end hydraulically sealed to one of the through-openings of the bottom element, and SCHÖTTLER, M. - at least one investigation space between the plurality of hollow bars for receiving an investigation unit for investigating the flow crossing the shaft perpendicular to its axis,

[0014] wherein flow movements of the liquid medium occurring in the shaft, which are directed along the shaft and thus essentially perpendicular to the flow to be investigated, which crosses the shaft perpendicular to its axis, or which have flow components directed in this way, can be guided past the at least one investigation chamber by the hollow bars, whereby the hollow bars have a bypass function.

[0015] The invention proposes a device which, on the one hand, results in a uniform, regulated, controlled and stabilized flow, running essentially perpendicular to the shaft axis, across the entire shaft cross-section in the area of ​​the installation module, and, on the other hand, hydraulically short-circuits existing flow movements in the shaft that run essentially axially to the shaft axis, so that these do not have any disturbing effects on the horizontal flow passages in the installation module or in the examination space of the installation module.

[0016] For this purpose, the device according to the invention comprises the aforementioned installation module, which can be inserted into the shaft on the inside under a hydraulically sealed connection. The installation module itself has an upper cover element and a lower base element. Both elements have a plurality of through-openings and are connected to each other via a plurality of hollow rods. The two ends of each hollow rod are hydraulically sealed to a through-opening in the cover element and a through-opening in the base element. Within the arrangement of hollow rods is the actual test chamber of the installation module, which serves to accommodate a test unit for investigating the flow crossing the shaft. SCHÖTTLER, M.Due to the large number of hollow bars running along the length of the shaft, the portion of the flow within the shaft that flows essentially perpendicular to the direction of the horizontal flow under investigation (which essentially crosses the shaft perpendicularly) flows past the investigation space (bypass function) at a large number of local positions across the shaft's cross-section and does not disturb the horizontal flow actually being investigated.

[0017] In the arrangement according to the invention, the hollow bars primarily fulfill the bypass function. However, they also serve, to a certain extent, to connect the cover element and the base element, thus contributing to the stability of the installation module. Furthermore, the hollow bars also smooth the flow and, in this respect, also serve to "calm" or harmonize (stabilize) the flow under investigation.

[0018] Additionally, it can be advantageously provided in the device according to the invention that

[0019] - that the cover element has supports between adjacent through-openings,

[0020] - that the floor element has supports between adjacent passageways and

[0021] - that flow compensating bars causing flow division and / or flow dispersion are arranged between each of the supports of the lid element and each of the supports of the base element, having opposite ends which are held by the supports,

[0022] - in the latter case, the flow comparability bars can be hollow, so that the flow components axially directed along the shaft can also be guided past the investigation space.

[0023] In an advantageous further development of the above variant, the supports of the cover element and the base element can be designed as receiving bores, e.g., in the form of blind holes or receiving spigots, for receiving the ends of the flow equalization rods. SCHÖTTLER, M.

[0024] It may be advantageous if the through-openings of the lid element and the base element are arranged along, in particular, concentric circles, and if the through-openings of two adjacent circles are spaced apart from each other.

[0025] In a further advantageous embodiment of the invention, it can be provided that the supports of the lid element and the base element are arranged radially aligned with the through openings of the lid element and the base element along a circular line with through openings, which are arranged radially outwards to a radially inwards adjacent circular line with through openings.

[0026] Furthermore, it can be advantageous if

[0027] - the cover element has a plate-shaped body which has the through-openings as well as, if present, the supports and furthermore at least one receiving opening,

[0028] - the base element has a plate-shaped body which has the through-openings as well as, if present, the supports and furthermore at least one receiving opening,

[0029] - between the receiving openings of the lid element and the base element, at least one examination chamber is arranged and

[0030] - the housing of a probe can be hydraulically and tightly received from the receiving openings of the cover element and the base element.

[0031] In a further advantageous embodiment of the invention, it can be provided that: - the cover element has a circumferential wall projecting from its plate-shaped body in a direction away from the arrangement of the hollow bars and, if present, the flow equalization bars, to form a hydraulically tight seal on the inside of the shaft, and SCHÖTTLER, M. - the bottom element has a circumferential wall projecting from its plate-shaped body in a direction away from the arrangement of the hollow bars and, if present, the flow equalization bars, to form a hydraulically tight seal on the inside of the shaft.

[0032] Furthermore, it may be advantageous if the perimeter walls of the cover element and the bottom element have external grooves with sealing rings or brackets for receiving sealing elements in order to seal against the inside of the shaft.

[0033] In an advantageous further embodiment of the invention, the plate-shaped bodies of the lid element and the bottom element can be disc bodies and, in particular, circular disc bodies, and the circumferential walls can be cylindrical.

[0034] To further stabilize the installation module, connecting struts can be provided between the cover element and the base element, in addition to the hollow bars and the flow equalization bars. For this purpose, it can be advantageous to include:

[0035] - that the circumferential wall of the cover element has at least one inwardly projecting projection which is aligned with one of the through-openings of the cover element,

[0036] - that the perimeter wall of the floor element has at least one inwardly projecting projection which is aligned with one of the passage openings of the floor element, and

[0037] - that at least one connecting strut is arranged between the projections of the lid element and the base element, extending through the hollow bar that connects the two through-openings with which the projections are aligned.

[0038] In a further advantageous embodiment of the invention, at least one axially extending blocking element can be arranged between the cover element and the base element in the circumferential region of the installation module for the purpose of blocking a flow movement passing through the shaft between the installation module and the shaft wall at right angles. This measure allows horizontally circumferential flow movements around the installation module between it and the shaft wall to be suppressed. This improves the measurement result, as such flow components of the horizontal flow under investigation are now also detected.

[0039] The aforementioned at least one blocking element advantageously extends from the cover element to the base element and can be attached to at least one of these elements, but preferably to both. Additionally or alternatively, the at least one blocking element can also be attached to one of the hollow bars and / or flow equalization bars arranged around the perimeter of the installation module, projecting outwards. Furthermore, it is advantageous if several blocking elements are arranged evenly or unevenly distributed around the perimeter of the installation module.

[0040] For example, an elastomer is suitable as a material for the blocking elements. Any other material suitable for a hydraulic seal against the shaft wall can also be used, at least in the end-face area of ​​the blocking element where it should seal against the shaft wall.

[0041] It may also be expediently provided that at least one of the hollow bars has an inner and / or outer coating to function as a passive sampler, and / or that at least one of the flow smoothing bars and / or the at least one connecting strut, if present, has an outer coating to function as a passive sampler. Passive sampler coatings are generally known and serve to "capture and bind" substances in the flow under investigation. Activated carbon, for example, is suitable as a coating. The substances accumulating on the passive sampler are used for subsequent analysis for various investigative purposes. If the flow smoothing bars (SCHÖTTLER, M.) are present and hollow, they can also have the aforementioned passive sampler coating on their inner surface.Such a coating can also be present on the outside of the at least one blocking element, if one is provided.

[0042] The hollow bars and, if present, the flow equalization bars may have a circular cylindrical or otherwise cylindrical, elliptical or polygonal circumference.

[0043] The invention is explained in more detail below with reference to an exemplary embodiment and the drawing. Specifically, the drawing shows:

[0044] Fig. 1 shows in longitudinal cross-section a shaft, for example, laid in the ground with an installation module arranged in it,

[0045] Figures 2 to 5

[0046] Various views of the installation module with cover element and base element, as well as the hollow rods connecting these two elements, and / or flow equalization rods,

[0047] Fig. 6 schematically shows the installation module in its structure and when arranged in the shaft.

[0048] Fig. 7 shows the installation module according to Fig. 6 with additional connecting struts and

[0049] Fig. 8(a), (b)

[0050] Flow diagrams in cross-section and longitudinal section through the shaft without installation module,

[0051] Fig. 9(a), (b)

[0052] Flow diagrams in cross-section and longitudinal section through the shaft with the installation module according to Fig. 6 and

[0053] Fig. 10(a), (b)SCHÖTTLER, M. Flow diagrams in cross-section and longitudinal section through the shaft with the installation module according to Fig. 7.

[0054] Figures 1 to 5 show different views of a device for suppressing disturbances (in the sense of separating / unbundling horizontal and vertical flow movements and homogenizing the horizontal flow movement under investigation) in a physical flow in a shaft, with the installation module also shown schematically in Figure 6, while Figure 7 shows an extension of the installation module according to Figure 6.

[0055] The device 10 is arranged in a shaft 12, as shown in Fig. 1, which is embedded in a substrate, such as soil 14. The shaft 12 can, for example, be a drilled well. The shaft wall 16 is formed, for example, by a slotted pipe, between which and the soil 14, gravel 18 or sand is present in this embodiment. The soil 14 is permeated, for example, by groundwater, which, as the liquid medium 20 to be investigated, is also contained in the shaft 12. Of interest for the investigation of the groundwater (liquid medium 20) is, for example, its horizontal flow 50, its velocity, and any contamination.

[0056] For the investigation of the flow 50 running perpendicular to the shaft axis, it is advantageous if a region exists within the device 10 in which this flow is calm, uniform, and as laminar as possible. In principle, the flow conditions within the shaft 12 are quite chaotic; they consist of a superposition of flows in various directions, in particular of horizontally flowing flows 50 and vertical flow movements 52.

[0057] The device 10 has an installation module 22 comprising an upper cover element 24 and a lower base element 26. Both elements are hydraulically sealed against the shaft wall 16. In the cover element 24 and in the base element 26, there is a centrally located opening 24a, 26a, through which a test unit 28 is inserted into the installation module 22. The test unit 28 is, for example, an optically operating unit for visualizing and recording flow patterns (reference is made, for example, to the test units or probes described in DE 10 2017 131 189 A1 and WO 2014 / 174014 A1).

[0058] The upper cover element 24 and the lower base element 26 are provided with a plurality of through- and receiving openings 30, 32 (better seen in Figures 6 and 7), which are arranged opposite and aligned with one another and between which both hollow bars 34 and flow equalization bars 36, which need not be hollow, are located. The latter bars are not strictly necessary, but increase the stability of the installation module 22 as well as the harmonization / equalization of the flow 50. The receiving openings 32, which receive the flow equalization bars 36, are preferably designed as blind receiving openings.

[0059] The hollow rods 34 are inserted at both ends into the through-openings 30 of the cover and bottom elements 24 and 26 and positioned hydraulically tight within them. Above the through-openings 30 of the cover element 24 and below the through-openings 30 of the bottom element 26, both elements are open, allowing potential vertical flows 52 in the shaft 12 to flow through the hollow rods 34 without entering the space between the cover element 24 and the bottom element 26. Within the arrangement of hollow rods 34 and flow equalization rods 36, surrounded by these, is the actual test chamber 38, in which the measuring device of the test unit 28 is located.

[0060] As described above, the potential vertical flow 52 within shaft 12 does not interfere with the horizontal flow 50, which runs across shaft 12 between the various rods and thus also moves through the investigation chamber 38. SCHÖTTLER, M.

[0061] Figures 2 to 6 show various views of the installation module 22. Figures 4 and 5 illustrate the through- and receiving opening arrangements in the cover and base elements 24 and 26. The larger diameter through-openings 30 accommodate the ends of the hollow bars 34, while the smaller diameter receiving openings 32, which could also be designed as blind holes, accommodate the ends of the flow equalization bars 36, which are typically made of solid material and also serve, among other things, to increase the stability of the installation module 22.

[0062] Figures 2 to 4 also show that both the cover element 24 and the bottom element 26 are made in two parts and each has an annular cap 40 or 42 with circumferential wall 41 or 43 and a plate body 44, 46, e.g. designed as a disc, which has the passage and receiving openings 30, 32.

[0063] Figure 6 shows a schematic representation of the installation module 22. The reference numerals for the individual elements are taken from Figures 1 to 5. It can be seen that sealing elements 48 are provided for the hydraulic sealing of the cover element 24 and the bottom element 26 against the shaft wall 16. These sealing elements are held, for example, in external grooves 49 of the circumferential walls 41, 43 by a cover element 24 and a bottom element 26, which project from the respective disc-shaped plate bodies 44, 46 and are, for example, part of the caps 40, 42 (see also Figures 1 to 4). Figure 6 also shows the flow arrows for the horizontal flow 50 to be investigated and for vertical flow movements 52 within the shaft 12, which flow past the test chamber 38 through the hollow bars 34 (bypass function).

[0064] Figure 7 shows an extension of the installation module 22 from Figure 6. It can be seen that, for further stabilization of the installation module 22, the cover element 24 and the base element 26 are mechanically connected by connecting struts 54. These connecting struts 54 run inside at least some of the hollow bars 34 and are attached at their ends to internal projections 56 of the cover element 24 and the base element 26.

[0065] Figures 8 to 10 show the cross-sectional and longitudinal sections through shaft 12, illustrating the flows that may potentially occur there.

[0066] Figure 8 illustrates these conditions without the installation module 22 being arranged in shaft 12. The horizontal flow 50 is shown in Figure 8(a), while the vertical flow 52 is shown in Figure 8(b).

[0067] Figure 9 shows the flow situation when the installation module 22 is arranged in the shaft 12. It can be seen that the horizontal flow 50 (see Figure 9(a)) flows essentially undisturbed, laminar and homogenized through the installation module 22, while the vertical flow 52 (see Figure 9(b)) flows through the hollow bars 34 without disturbing the horizontal flow 50.

[0068] The same constellation is shown in Fig. 10 for the case that the installation module 22 has the extension according to Fig. 7.

[0069] With reference to Figs. 8(a), 9(a) and 10(a), a further advantageous embodiment of the device 10 according to the invention will be discussed below.

[0070] As can be seen particularly from the flow examples in the aforementioned figures, horizontal flow movements exist in the inner circumferential region of the shaft wall 16. These movements may potentially flow around the outside of the installation module without entering the area between the hollow bars 34 and / or the flow equalization bars 36, and thus potentially without reaching the test chamber 38. The aim is to prevent such circumferential flow movements, in particular those that, as illustrated in Fig. 8(a), enter the shaft from the left in the central region of the shaft wall 16 and, instead of passing through the hollow bars 34 and the flow equalization bars 36, and thus also through the test chamber, flow around the outside of the installation module. This is prevented by the blocking elements 58, which in this embodiment are arranged evenly distributed around the circumference of the installation module. Fig.Figure 9(a) shows that these blocking elements 58, for example, project outwards from the outer hollow bars 34 or the outer flow equalization bars 36. This is also shown, among other things, in the figures.

[0071] Figures 4 and 5, as well as Figures 2 and 3, show these blocking elements 58 extending between the cover element 24 and the bottom element 26, forming a hydraulically tight seal against the inside of the shaft wall 16. SCHÖTTLER, M.

[0072] REFERENCE MARK LIST

[0073] device

[0074] Shaft

[0075] soil

[0076] shaft wall

[0077] gravel

[0078] liquid medium

[0079] Installation module

[0080] Cover element

[0081] an opening in the lid element

[0082] floor element

[0083] an opening in the base element examination unit

[0084] Intake openings

[0085] Intake openings

[0086] Hollow rods

[0087] Flow compensating rods, investigation room

[0088] cap

[0089] Perimeter wall of the lid element

[0090] cap

[0091] Perimeter wall of the floor element panel body

[0092] plate body

[0093] sealing elements

[0094] Outer groove for sealing rings

[0095] Flow perpendicular to the shaft axis; flow parallel to the shaft axis; connecting struts

[0096] Protrusions

[0097] Blocking element

Claims

SCHÖTTLER, M. REQUIREMENTS 1. Device for suppressing disturbances of a physical flow that traverses a shaft containing a liquid medium, in particular a shaft, e.g. in the ground, with a substantially round and preferably circular cross-section, such as in the case of a drilled well, with - an installation module (22) which can be inserted into the shaft (12) under a hydraulically sealed system on the inside of the shaft, - wherein the installation module (22) is equipped with - an upper cover element (24) which has a plurality of through-openings (30), - a lower base element (26) which has a number of through-holes (30) equal to the number of through-holes (30) of the cover element (24), - a plurality of hollow bars (34), each of which is hydraulically tight connected at one end to one of the through-openings (30) of the cover element (24) and at its opposite other end to one of the through-openings (30) of the bottom element (26), and - at least one examination space (38) between the plurality of hollow rods (34) for receiving an examination unit (28) for investigating the flow crossing the shaft (12), - wherein flow movements (52) of the liquid medium (20) occurring in the shaft (12), which are directed along the shaft (12) and thus essentially perpendicular to the flow (50) to be investigated crossing the shaft (12) or have flow components directed in this way, through which hollow rods (34) can be guided past the at least one examination space (38).

2. Device according to claim 1, characterized in that, - that the cover element (24) has supports between adjacent passage openings (30), SCHÖTTLER, M. - that the base element (26) has supports between adjacent passage openings (30) and - that between each of the supports of the lid element (24) and each of the supports of the bottom element (26) flow compensating bars (36) are arranged which cause flow division and / or flow dispersion and which have opposite ends which are held by the supports.

3. Device according to claim 2, characterized in that the holders of the cover element (24) and the base element (26) are designed as receiving bores and / or openings (32) and / or as blind bores and / or as receiving nozzles and / or as through openings for receiving the ends of the flow equalization rods (36), wherein in the latter case the flow equalization rods (36) may be hollow.

4. Device according to one of claims 1 to 3, characterized in that the through-openings (30) of the lid element (24) and the bottom element (26) are arranged along, in particular, concentric circles and that the through-openings (30) of two adjacent circles are spaced apart from each other.

5. Device according to claims 2 and 4 or according to claim 3, characterized in that the supports of the lid element (24) and the base element (26) are arranged along a circular line with through openings (30) which are arranged radially outwards to a radially inwards adjacent circular line with through openings (30), and are arranged radially aligned with the through openings (30) of the lid element (24) and the base element (26) along the radially inwards adjacent circular line.

6. Device according to one of claims 1 to 5, characterized in that the cover element (24) has a plate-shaped body (44) which has the through-openings (30) and, if present, the supports and furthermore at least one receiving opening (24a), - that the base element (26) has a plate-shaped body (46) which has the through-openings (30) and, if present, the supports and furthermore at least one receiving opening (26a), - that at least one examination chamber (38) is arranged between the receiving openings (24a, 26a) of the cover element (24) and the base element (26) and - that the housing of the examination unit (28) can be hydraulically sealed from the receiving openings (24a, 26a) of the cover element (24) and the base element (26).

7. Device according to claim 6, characterized in that, - that the cover element (24) has a circumferential wall (41) projecting from its plate-shaped body (44) in a direction away from the arrangement of the hollow bars (34) and, if present, the flow equalization bars (36) to form a hydraulically tight system on the inside of the shaft (12) and - that the bottom element (26) has a circumferential wall (43) projecting from its plate-shaped body (46) in a direction away from the arrangement of the hollow bars (34) and, if present, the flow equalization bars (36) to form a hydraulically tight system on the inside of the shaft (12).

8. Device according to claim 7, characterized in that the circumferential walls (41, 43) of the cover element (24) and the base element (26) have external grooves (49) with sealing rings or holders for receiving sealing elements (48) for sealing to the inside of the shaft (12). SCHÖTTLER, M.

9. Device according to claims 6 and 7 or according to claim 8, characterized in that the plate-shaped bodies (44, 46) of the lid element (24) and the bottom element (26) are disc bodies and in particular circular disc bodies and that the circumferential walls (41, 43) are cylindrical.

10. Device according to claim 7 or according to one of the preceding claims, insofar as it relates to claim 7, characterized in that - that the circumferential wall (41) of the cover element (24) has at least one inwardly projecting projection (56) which is aligned with one of the through-openings (30) of the cover element (24), - that the circumferential wall (43) of the base element (26) has at least one inwardly projecting projection (56) which is aligned with one of the passage openings (30) of the base element (26), and - that at least one connecting strut (54) is arranged between the projections (56) of the cover element (24) and the base element (26), which extends through the hollow rod (34) which connects the two passage openings (30) with which the projections (56) are aligned.

11. Device according to one of claims 1 to 10, characterized in that at least one axially extending blocking element (58) for hydraulically tight fit on the inside of the shaft (12) is arranged between the cover element (24) and the bottom element (26) in the circumferential area of ​​the installation module (22) for the purpose of blocking a flow movement through the shaft (12) in the circumferential area of ​​the installation module (22).

12. Device according to one of claims 1 to 11, characterized in that the at least one blocking element (58) extends from the cover element (24) to the base element (26). SCHÖTTLER, M.

13. Device according to one of claims 1 to 12 characterized by several blocking elements (58) which are arranged uniformly or unevenly distributed in the circumferential area of ​​the installation module (22).

14. Device according to one of claims 11 to 13, characterized in that the at least one blocking element (58) is arranged on the cover element (24) and / or the bottom element (26) and / or on a hollow rod or flow equalization rod (36), if present, located in or near the circumferential area of ​​the installation module (22).

15. Device according to one of claims 1 to 14, characterized in that at least one of the hollow rods (34) and / or at least one of the flow equalization rods (36), if present and hollow, has an inner or outer coating for functioning as a passive collector and / or that at least one of the flow equalization rods (36) and / or the at least one connecting strut (54), if each present, has an outer coating for functioning as a passive collector and / or that the at least one blocking element (58), if present, has an outer coating for functioning as a passive collector.

16. Device according to one of claims 1 to 15, characterized in that the hollow rods (34) and, if present, the flow equalization rods (36) have a circular cylindrical or otherwise cylindrical or elliptical or polygonal circumference.

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