THERMOMETERS FOR CRYOGENIC APPLICATIONS

Description

[0001] The present invention relates to an arrangement for determining and / or monitoring a temperature of a medium in a measuring tube.

[0002] Thermometers in a wide variety of designs have become known from the state of the art, and their underlying measuring principles have also been described in detail. For example, there are thermometers that use the expansion of a liquid, gas, or solid with a known coefficient of expansion to measure temperature, or those that relate the electrical conductivity of a material to temperature, such as when using resistance elements or thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a substance to determine its temperature.

[0003] A temperature sensor in the form of a so-called thin-film sensor, particularly a resistance temperature detector (RTD), uses a sensor element provided with connecting wires and applied to a carrier substrate. The back of the carrier substrate is usually coated with metal. The sensor elements used are so-called resistance elements, which are provided, for example, by platinum elements, and are also commercially available under the designations PT10, PT100, and PT1000, among others.

[0004] With temperature sensors in the form of thermocouples, the temperature is determined by a thermoelectric voltage that arises between the thermocouple wires made of different materials that are connected at one end. Thermocouples according to DIN standard IEC584, e.g. thermocouples of type K, J, N, S, R, B, T or E, are usually used as temperature sensors for temperature measurement. However, other material pairs, in particular those with a measurable Seebeck effect, are also possible. The temperature sensors are often part of a measuring insert, which can be inserted, for example, into an immersion body immersed in the medium or a protective tube. The protective tube then essentially fulfills the function of a housing that protects the measuring insert from the environment, e.g. aggressive media, forces and / or high pressures and / or temperatures in the respective process. The protective tubes, in turn, are typically inserted into a pipe socket of a container or a measuring tube.

[0005] Thermometers in pipelines are fundamentally exposed to the flow of the respective medium, which can give rise to various problems. The specific installation situation plays a role, among other things. For example, thermometers are often installed in straight sections of the respective pipeline in such a way that a longitudinal axis through the thermometer runs essentially perpendicular to the direction of flow of the medium. Alternatively, it has also become known to arrange thermometers in a curved section of the pipeline. The flow of the medium is then responsible for different mechanical forces acting on the thermometer, e.g. shear forces or forces induced by vortex shedding, which can cause vortex-induced oscillation of the thermometer.

[0006] In fluid mechanics, vortex formation is also known as a "Kärman vortex street." It is a repeating pattern of swirling eddies in different directions caused by the discontinuous separation of the flow of a medium around a body, causing this body to oscillate. The closer the frequency of the oscillations is to the natural frequency of the body around which the medium flows, the more oscillations are induced. The frequency of the oscillations is determined by process parameters such as the physical properties of the medium, the flow velocity, and the shape of the thermometer.

[0007] In the worst case, vortex shedding can damage the thermometer. At the very least, however, it will reduce its operating life or service life. Therefore, the possibility of vortex formation must be duly considered when developing a thermometer for use in a flowing medium. Standard methods are available today, such as ASME PTC 19.3 TW-2010 or DIN43772, which define various design rules for thermometers. These methods can also be used to check the thermometer design for its sensitivity to vortex formation. However, the available methods are always limited to specific thermometer designs and / or process conditions.

[0008] Fundamentally, the natural frequency of the thermometer and the natural frequency of vortex shedding must be separated from each other. This minimizes the probability of the occurrence of the dangerous condition of resonant vortex-induced oscillations of the thermometer. To achieve such a separation of frequencies, the geometry of the thermometer can be varied, for example, by reducing the length of the thermometer, increasing its diameter, and / or by using a comparatively thicker wall thickness for the thermowell.

[0009] Alternatively, when functional constraints do not permit certain changes to the dimensions of the thermometer, mechanical mounts or absorbers are sometimes used to reduce the thermometer's sensitivity to vortex shedding. These mechanical mounts or absorbers are usually installed in a gap between the pipe socket or the pipe and the outer surface of the thermometer. The mounts or absorbers then increase the thermometer's natural frequency by reducing the thermometer's free length. However, it is difficult to mount the mounts or absorbers in such a way that a high degree of coupling and thus the desired effect can be achieved. A further problem is that a fixed position of the mount or absorber is not possible.The absorber's position within the process cannot be guaranteed due to the different thermal expansion coefficients of the various thermometer components. For this reason, a corresponding design of a thermometer with a holder or absorber, for example, does not currently meet the requirements of the ASME PTC 19.3 TW-2010 standard. DE 102005 002 383 A1 discloses a mounting insert that is pushed into a pipe socket such that a pin is locked in an opening in the pipe socket, preventing the mounting insert from rotating in the pipe socket.

[0010] DE 102011 089 942 A1 discloses a mounting device for a measuring insert for temperature measurement. The mounting device has a molded part for attaching the mounting device to a pipeline. A spring element presses the measuring insert into the mounting device.

[0011] DE 35 16815 A1 discloses a thermometer for a reaction chamber operating at elevated temperature and pressure. Using a handwheel, the thermometer can be moved toward and out of the reaction chamber.

[0012] For cryogenic applications, i.e., for use at low temperatures, it is advantageous for the thermometer to be long and have the smallest possible diameter, both in terms of its thermal properties and its measurement accuracy, as well as to reduce heat dissipation errors. It is also advantageous to design the walls of the thermowell used as thin as possible. However, as described above, such a design is particularly disadvantageous with regard to vortex-induced oscillations of the thermometer.

[0013] The invention is based on the object of addressing this problem and providing a thermometer which is also ideally suited for measuring low temperatures of flowing media.

[0014] This object is achieved by the arrangement according to claim 1. Advantageous embodiments are specified in the dependent claims.

[0015] With regard to the arrangement, the object underlying the invention is achieved by an arrangement for determining and / or monitoring a temperature of a medium in a measuring tube, comprising a thermometer for cryogenic applications, wherein the thermometer has a measuring insert with a temperature sensor and a protective tube for receiving the measuring insert, and a fastening insert, wherein the fastening set is designed for fastening the thermometer in a pipe socket of a measuring tube, comprising- a holding element for fastening the thermometer to the fastening insert, and- a locking device which is designed to prevent a rotational movement relative to the measuring tube.

[0016] According to the invention, at least one component of the fastening insert is designed and / or arranged such that the fastening insert is movable in the direction of a longitudinal axis of the pipe socket such that temperature effects due to different thermal expansion coefficients of different components of the thermometer can be compensated.

[0017] The mobility of the fastening insert parallel to the longitudinal axis compensates for temperature effects due to different expansion coefficients.

[0018] At the same time, the holding element is rigidly connected to the thermometer so that there is always a sufficient mechanical coupling to reduce the probability of vortex-induced vibrations occurring. It is an advantage of the present invention that sufficient stability can be achieved with regard to the fastening insert while simultaneously compensating for any temperature effects that occur. The use of a fastening insert according to the invention therefore allows the respective thermometer to be optimized with regard to its thermal properties. For example, the thermometer can be made long and a thin wall for the protective tube can be selected. The fastening insert is therefore preferably suitable for use in the cryogenic, i.e. low, temperature range.

[0019] In one embodiment, the fastening insert further comprises a base body with a through-opening for receiving the thermometer, wherein an outer wall of the base body is adapted to the geometric dimensions of an inner wall of the pipe socket. The base body serves as an adapter between the pipe socket and at least one further component of the fastening unit. Preferably, the base body is designed such that it can be inserted into a defined position relative to an inner wall of the pipe socket. It is advantageous if the base body can be connected to the container socket in a force-fitting and / or material-fitting manner. For example, the base body can be attached to the inner wall of the pipe socket by means of a weld or similar means.

[0020] It is also advantageous if the base body is designed in the form of a hollow cylinder. This allows the symmetry of the pipe socket, which is usually also cylindrical, to be maintained.

[0021] In one embodiment, the fastening insert comprises an annular spring element which can be inserted, in particular detachably, into the pipe socket or into the base body.

[0022] The spring element is specifically dimensioned so that it can be inserted into the pipe socket or the base body with a predefined spring tension. The spring element can thus adapt to different expansions or contractions of different components of the fastening insert, the thermometer, and / or the pipe socket depending on the temperature conditions and can accordingly compensate for different mechanical expansions or contractions of the different components due to different thermal expansion coefficients.

[0023] In a further embodiment of the fastening insert, the locking device comprises an elongated guide element, which is attached to a wall of the pipe socket or the base body, and which locking device engages with a component of the fastening insert when the fastening insert is inserted into the pipe socket. The locking device is preferably connected to the wall of the pipe socket or the base body by force and / or material bonding; for example, the locking device is welded to the respective wall.

[0024] At least one component of the fastening insert, which is inserted into the pipe socket or into the base body, then has, for example, a recess, a slot, or a receptacle into which the locking device engages when the fastening insert is mounted.

[0025] Thus, in one embodiment of the invention, it is advantageous if the spring element has an elongated slot, wherein the guide element is fastened to a wall of the pipe socket or the base body in such a way that the guide element engages in the slot when the spring element is arranged in the pipe socket or in the base body. The guide element is preferably fastened in the pipe socket or in the base body in such a way that a longitudinal axis of the guide element is parallel to a longitudinal axis of the pipe socket. A length of the guide element is adapted in particular to the respective thermal expansion coefficients and / or to the expected mechanical expansions and / or contractions of the various components as a result of temperature changes.

[0026] An alternative embodiment includes a locking device comprising a threaded bolt. The threaded bolt has at least a first portion with a thread, which serves for attachment to the base body or the pipe socket, and a second, threadless portion. The threaded bolt is preferably aligned parallel to a longitudinal axis of the pipe socket. However, the threaded bolt can also optionally comprise a third portion, which is also provided with a thread. The first and third portions are then preferably arranged in the two end regions of the threaded bolt.

[0027] At least the component of the fastening insert which is designed and / or arranged such that the fastening insert is movable in the direction of a longitudinal axis through the pipe socket then comprises a through-opening through which the threaded bolt is guided and which is arranged in the second partial region of the threaded bolt.

[0028] In a configuration with a locking mechanism comprising a threaded bolt, the base body has an annular base surface, to which base surface a socket with an internal thread is attached for receiving the threaded bolt. In this case, the threaded bolt is screwed into the threaded bolt, for example, with the first portion. In this specific configuration, the locking mechanism against rotational movements of the thermometer is achieved by means of the screw connection to the base body.

[0029] In one embodiment of the fastening insert, the holding element has an annular element in which the thermometer can be fastened.

[0030] To fasten the thermometer in the annular element, all fastening methods known to the person skilled in the art can be considered, for example a screw connection with corresponding threads or using an adjusting screw.

[0031] In an alternative embodiment of the fastening insert, the holding element is designed in the form of a cylindrical element with a, in particular central, first through-bore, in which first through-bore the thermometer can be fastened, and wherein an outer diameter of the cylindrical element is adapted to an inner diameter of the pipe socket or the base body. The first through-bore is in particular a central through-bore with respect to a cross-sectional area of ​​the cylindrical element, the inner diameter of which is adapted to an outer diameter of the thermometer.

[0032] For the design of the holding element in the form of a cylindrical element, it is advantageous if the holding element comprises at least one second through-bore for establishing fluidic contact between an internal volume of the measuring tube and an internal volume of the thermometer. The second through-bore is an eccentric through-bore relative to a cross-sectional area of ​​the cylindrical element.

[0033] Another embodiment involves the retaining element being connected to the pipe socket, the base body, or the annular spring element in a force-fitting and / or material-fitting manner. In this context, both a detachable and a non-detachable connection are possible.

[0034] In the case where the fastening insert has an annular spring element, one embodiment includes the retaining element comprising a web, which web connects the retaining element and the spring element. In this embodiment, the retaining element and the spring element are preferably rigidly and firmly connected to one another. For example, the web can be connected to the spring element and the retaining element by means of two welded joints.

[0035] In the event that the fastening insert has a base body and that the holding element has the shape of a cylindrical element, an alternative embodiment includes that the base body and the holding element can be connected to one another by means of a screw connection, in particular the holding element comprises at least one third through-bore, wherein the holding element and the base body can be connected to one another by means of the threaded bolt of the locking device, by means of a screw, or by means of a further threaded bolt.

[0036] In one embodiment, the arrangement includes a pressure tapping port. The pressure tapping port can also be used to determine the pressure of the medium in the measuring tube. Particularly in the case of a cryogenic application, this avoids the need for an additional connection to the process by providing vacuum insulation of the measuring tube, which would otherwise be necessary for an additional measuring point.

[0037] It should be noted that the embodiments described in connection with the fastening insert according to the invention are also applicable mutatis mutandis to the arrangement according to the invention and vice versa.

[0038] The invention and its advantageous embodiments are explained in more detail with reference to the following figures. They show: Fig. 1 the origin of vortex-induced vibrations, Fig. 2 a thermometer with a protective tube and a mechanical holder, Fig. 3 a first embodiment of a thermometer with a fastening insert according to the invention, and Fig. 4 a second embodiment of a thermometer with a fastening insert according to the invention.

[0039] In the figures, identical elements are given the same reference numerals.

[0040] Fig. 1 illustrates the origin of vortex shedding w on a cylindrical, conically tapered thermometer 1, which is exposed to a flowing medium M in a tube 2. The tube 2 is shown here by its walls. In the flow direction v of the medium M, a comb-like pattern of the flow profile develops behind the thermometer 1. Depending on the flow velocity v of the medium M, this can lead to vortex shedding, which in turn can cause the thermometer 1 to oscillate.

[0041] These vibrations are mainly caused by two forces acting on thermometer 1: a shear force in the y-direction and a lifting force in the x-direction, which add up to the total flow-related force F flow. The shear force causes oscillations with a frequency fs, while the lifting force causes oscillations with a frequency of 2fs. The frequency fs depends on the flow velocity v of the medium M and on various physical or chemical properties of the medium M, such as its viscosity and density, as well as on the geometry of thermometer 1, such as its diameter, its length and the thickness of the walls of the protective tube. The closer the frequency fs is to the natural frequency of thermometer 1 and the higher the flow velocity v of the medium M, the greater the resulting vibration-generating forces. The effect of these forces orThe occurrence of vortex shedding can damage thermometer 1. In the worst case, it can even lead to a complete failure of thermometer 1. This is referred to as the so-called resonance condition.

[0042] To reduce the sensitivity of thermometers to such vortex formation, the design of the thermowell can be adapted, as described in the introduction. However, the measures required to optimize the geometry of thermometer 1 with regard to vortex shedding and those required to optimize thermometer 1 with regard to temperature effects, particularly those caused by unwanted heat dissipation, are fundamentally contradictory.

[0043] Another possibility to avoid vortex-induced vibrations of the thermometer 1 is to use a mechanical support 4, as shown in Fig.2 illustrated. The holder 4 is inserted into a pipe socket 3 of the measuring tube 2 and increases the natural frequency of the thermometer 1 by reducing the free length of the thermometer 1.

[0044] However, the problem with such mechanical mounts 4 is that they cannot ensure sufficient mechanical coupling to the thermometer 1 at all times. In particular, mechanical expansion of the various components of the respective arrangement as a result of different thermal expansion coefficients that occur during temperature changes have made such solutions unreliable.

[0045] The present invention solves this problem by a fastening insert 6, which is movable parallel to a longitudinal axis L through the pipe socket 3. This movement in the direction of the longitudinal axis allows temperature effects to be compensated without affecting the mechanical coupling to the thermometer 1.

[0046] In the figures Fig. 3 and Fig. 4 Two particularly preferred embodiments for a fastening insert 6 according to the invention and for arrangements 7 according to the invention are shown. The measuring tube 2 and the pipe socket 3 are each designed, for example, for use at low temperatures T and have, for example, a vacuum insulation not shown separately here.

[0047] For the design according to Fig. 3 the fastening insert 6 has a locking device 8 in the form of an elongated guide element which is welded to the inner wall of the pipe socket 3, as for example in Fig. 3a The fastening insert 6 further comprises an annular spring element 9, the geometric dimensions of which are also adapted to the dimensions of the pipe socket 3. The spring element 9 has a slot 9a into which the locking device 8 engages when the spring element 9 is arranged in the pipe socket 3. The spring element 9 is further connected via the web 10 to the annular holding element 11, which serves to fasten the thermometer 1. The locking device 8 prevents any rotational movement of the fastening insert 6 relative to the pipe socket.

[0048] A movement S therm in the direction of a longitudinal axis L of the pipe socket is possible and serves to compensate for temperature effects, which lead to thermally induced forces F therm acting on the thermometer 1 and the fastening insert 6, as shown in Fig. 3b illustrated. Such forces F therm result from different expansion coefficients of the respective components and the associated different mechanical expansions due to temperature changes. The forces F hold caused by the wall of the pipe socket 3 and the spring element serve to attach the holding element 11 to the thermometer 1, which in turn, due to the holding element 11, has a reduced sensitivity to the forces F flow caused by the flow, as in connection with Fig. 1 has been described.

[0049] A second exemplary, particularly preferred embodiment of a fastening insert 6 according to the invention or an arrangement 7 according to the invention is shown in Fig. 4 shown in two views rotated by 90°. As can be seen from Fig. 4a As can be seen, the fastening insert has a base body 13 in the form of a hollow cylinder, which is firmly inserted into the pipe socket 3, for example, the base body 13 is welded into the pipe socket 3. The base body 13 also has an annular bottom surface 14, to which bottom surface 14 a socket 15 with an internal thread for receiving the threaded bolt 16, which is part of the locking device 8. By means of the threaded bolt 16, the base body 13 is non-positively connected to the holding element 11, which is designed here in the form of a cylindrical element. The holding element 11 has, as in Fig. 4b visible, via a first through-bore 12a for receiving the thermometer 1, via a second through-bore 12b for establishing fluidic contact between an internal volume of the measuring tube 2 and an internal volume of the thermometer 1, and a third through-bore 12c for fastening the holding element 11 to the base body 13 by means of the threaded bolt 15.

[0050] For the variant of a fastening insert shown here, a movement in the longitudinal direction of the pipe socket 3 is also possible, while a rotational movement is prevented by the locking device 8. Accordingly, just as in the case of the design according to Fig. 3 , forces F therm resulting from temperature effects and flow-related forces F flow are compensated.

[0051] In the design according to Fig. 4the arrangement 7 further comprises a pressure tapping nozzle 17 for determining a pressure of the medium M. This is made possible by the fluidic contact between an internal volume of the measuring tube 2 and an internal volume of the thermometer 1, which is ensured for the illustration shown here by the second through-bore 12b.

Claims

1. An arrangement (7) for determining and / or monitoring a temperature of a medium (M) in a measuring tube (2), comprising a thermometer (1) for cryogenic applications, wherein the thermometer (1) has a measuring insert with a temperature sensor and a protective tube for mounting the measuring insert, and a mounting insert (6), wherein the mounting insert is configured to mount the thermometer (1) in a tube adapter (3) of the measuring tube (2), comprising • a retaining element (11) for mounting the thermometer (1) on the mounting insert (6), and • a locking mechanism (8), which is configured to prevent a rotational movement relative to the measuring tube (2), wherein at least one component of the mounting insert (6) is configured and / or arranged in such a way that the mounting insert (6) can be moved toward a longitudinal axis of the tube adapter (3) in such a way that it is possible to compensate for temperature effects caused by different components of the thermometer having different coefficients of thermal expansion.

2. The arrangement (7) as claimed in claim 1, wherein the mounting insert (6) comprises a basic body (13) with an opening for mounting the thermometer (1), wherein an outer wall of the basic body (13) is adapted to the geometric dimensions of an inner wall of the tube adapter (3).

3. The arrangement (7) as claimed in at least one of the preceding claims, wherein the mounting insert comprises an annular spring element (9), with it being possible to insert said spring element (9) into the tube adapter (3) or into the basic body (13), in particular such that it can be detached again.

4. The arrangement (7) as claimed in at least one of claims 1 to 3 or 2 to 3, wherein the locking mechanism (8) has an elongated guide element, which is mounted on a wall of the tube adapter (3) or the basic body (13), and said locking mechanism (8) engaging in a component of the mounting insert (6) when the mounting insert (6) is inserted into the tube adapter (3).

5. The arrangement (7) as claimed in claims 3 and 4, wherein the spring element (9) has an elongated slot (10), and wherein the guide element (8) is mounted on a wall of the tube adapter (3) or the basic body (13) in such a way that the guide element engages in the slot (10) when the spring element (9) is arranged in the tube adapter (3) or in the basic body (13).

6. The arrangement (7) as claimed in at least one of claims 1 to 3, wherein the locking mechanism (8) comprises a threaded bolt (16).

7. The arrangement (7) as claimed in claim 6, wherein the basic body (13) has an annular base area (14), to which base area (14) a connector (15) with an internal thread for mounting the threaded bolt (16) is fitted.

8. The arrangement (7) as claimed in at least one of the preceding claims, wherein the retaining element (11) has an annular element in which the thermometer (1) is mounted.

9. The arrangement (7) as claimed in at least one of claims 1 to 7, wherein the retaining element (11) is configured in the form of a cylindrical element with a first, in particular centric, through-hole (12a), in which first through-hole (12a) the thermometer (1) is mounted, and wherein an external diameter of the cylindrical element (11) is adapted to an internal diameter of the tube adapter (3) or the basic body (13).

10. The arrangement (7) as claimed in claim 9, wherein the retaining element (11) comprises at least a second through-hole (12b) for establishing fluidic contact between an internal volume inside the measuring tube (2) and an internal volume of the thermometer (1).

11. The arrangement (7) as claimed in at least one of claims 1 to 10, at least one of claims 2 to 10, or at least one of claims 4 to 10, wherein the retaining element (11) is connected to the tube adapter (3), the basic body (13), or the annular spring element (9) by means of a force-fit connection and / or a permanent material bond.

12. The arrangement (7) as claimed in claims 3 and 11, wherein the retaining element (11) comprises a bar (10), said bar (10) linking the retaining element (11) and the spring element (9).

13. The arrangement (7) as claimed in claims 2, 9, and 11, or 2, 6, 9, and 11, wherein the basic body (13) and the retaining element (11) can be connected to each other by means of a screw connection, in particular the retaining element (11) comprises at least a third through-hole (12c), wherein the retaining element (11) and the basic body (13) can be connected to each other by means of the threaded bolt (16) of the locking mechanism (8), by means of a screw, or by means of an additional threaded bolt.

14. The arrangement as claimed in at least one of the preceding claims, comprising a pressure relief connection (17).