Thermometers for cryogenic applications

Abstract

The invention relates to a fixing insert (6) for fixing a thermometer (1) in a tubular connection (3) of a measuring tube (2), comprising: a retaining element (11) for fixing the thermometer (1) to the fixing insert (6); and a locking device (8) designed to prevent rotational movement relative to the measuring tube (2). The invention also relates to an assembly comprising: a thermometer (1); and a fixing insert (6) according to the invention. According to the invention, at least one component of the fixing insert (6) is designed and / or arranged such that the fixing insert (6) can be moved in the direction of the longitudinal axis of the tubular connection (3).

Description

Technical Field

[0001] The invention relates to a fixing insert for fixing a thermometer in a connection of a pipe, and to a device for determining and / or monitoring the temperature of a medium in a container. Background Art

[0002] Thermometers are known in the prior art in various embodiments, and their basic measuring principles are also well described in the literature. For example, there are thermometers that utilize the expansion of liquids, gases, or solids with known expansion coefficients to measure temperature, or thermometers that correlate the electrical conductivity of a material with the temperature, such as with resistors or thermocouples. In contrast, radiation thermometers, especially pyrometers, utilize the thermal radiation of a substance to determine its temperature.

[0003] In the case of temperature sensors in the form of so-called thin-film sensors, such as resistance temperature detectors (RTDs), a sensor element is used that is provided with a connecting cable and applied to a substrate, the back of which is usually coated with metal. In this case, the sensor element is a so-called resistance element, for example in the form of a platinum element, which is commercially available, for example, under the designations PT10, PT100, and PT1000.

[0004] In the case of temperature sensors in the form of thermocouples, the temperature is determined by the thermovoltage that occurs between the thermocouple wires, which are connected on one side and made of different materials. For temperature measurement, thermocouples according to DIN standard IEC 584 are usually used as temperature sensors, for example thermocouples of types K, J, N, S, R, B, T, or E. However, other material pairs can also be used, in particular those with a measurable Seebeck effect.

[0005] The temperature sensor is usually part of a measuring insert, which can be inserted into an immersion body or protective tube, for example, and thus extends into the medium. The protective tube thus essentially fulfills the function of a housing, protecting the measuring insert from environmental influences in the process, such as aggressive media, excessive forces, and / or high pressures and / or temperatures. The protective tube is then typically inserted into a connection of a container or pipe.

[0006] Thermometers in pipelines are exposed to the flow of the medium, which can lead to various problems. In this case, among other things, the specific installation plays a role. Thermometers are usually installed in straight sections of pipelines, for example, in such a way that the longitudinal axis of the thermometer extends essentially perpendicular to the flow direction of the medium. Alternatively, it is also possible to arrange the thermometer in a bend in the pipeline. In either case, the flow of the medium is responsible for different mechanical forces acting on the thermometer, such as shear forces or forces caused by vortex shedding. Vortex shedding can cause oscillations of the thermometer.

[0007] Vortex formation in a fluid flow can take the form of a "Kármán vortex street." This involves a recurring pattern of vortices swirling in different directions, caused by discontinuous separations of the medium flow around a body and resulting in oscillations of the body. The closer the oscillation frequency is to the eigenfrequency of the body around which the medium flows, the greater the resulting oscillations. The frequency of the oscillations is determined, for example, by process parameters such as the physical properties of the medium, the flow rate, and the shape of the thermometer.

[0008] In the worst case, the shedding of these vortices can damage the thermometer. At the very least, the lifespan of the thermometer is reduced. Therefore, the potential for vortex formation must be fully considered when developing thermometers for use in flowing media. Currently, standard methods exist, such as ASME PTC 19.3TW-2010 or DIN 43772, which define various design rules for thermometers. These methods can be used to examine the sensitivity of thermometer designs to vortex formation. However, the available methods are limited to specific thermometer types and / or process conditions.

[0009] Essentially, efforts are made to separate the natural frequencies of the thermometer and the natural frequencies of vortex shedding. This way, the likelihood of the thermometer experiencing dangerous resonances and vortex-induced oscillations can be minimized. For example, to achieve this frequency separation, the thermometer's geometry can be modified, for example by reducing its length, increasing its diameter, and / or using a relatively thick protective tube.

[0010] Alternatively, when functional limitations do not allow a specific change in the dimensions of the thermometer, mechanical supports or dampers are sometimes also used in order to reduce the sensitivity of the thermometer to vortex shedding. These mechanical supports or dampers are usually installed in the gap between the joint or pipe and the outside of the thermometer. The supports or dampers increase the natural frequency of the thermometer by reducing the free length of the thermometer. However, it has proven difficult to install the supports or dampers so as to be able to achieve a high degree of coupling and the resulting desired effect. Another problem is that due to the different thermal expansion coefficients of the different components of the thermometer, it is not possible to ensure the fixed position of the supports or dampers in the process. For this reason, at present, corresponding embodiments of thermometers with supports or dampers do not, for example, meet the requirements of standard ASME PTC 19.3TW-2010.

[0011] Therefore, for cryogenic applications, it is advantageous to make the thermometer as long and as small in diameter as possible to reduce heat conduction errors, both in terms of the thermometer's thermal characteristics and its measurement accuracy. Furthermore, it is advantageous to make the walls of the protective tube as thin as possible. However, such structures, such as those described above, are particularly detrimental to the thermometer's vortex-induced oscillations. Summary of the Invention

[0012] The object of the present invention is to solve this group of problems and to provide a thermometer which is also particularly suitable for recording low temperatures of flowing media.

[0013] This object is achieved by the fixing insert and the device according to the invention, advantageous embodiments of which are explained below.

[0014] With regard to the fixing insert, the object of the present invention is achieved by a fixing insert for fixing a thermometer in a pipe joint, the fixing insert comprising a retaining element for securing the thermometer to the fixing insert and a stop designed to prevent rotational movement relative to the pipe. According to the invention, at least one component of the fixing insert is designed and / or arranged such that the fixing insert is movable in the direction of the longitudinal axis of the joint.

[0015] The movability of the fixing insert parallel to the longitudinal axis allows compensation for temperature effects caused by different expansion coefficients. At the same time, the retaining element is rigidly connected to the thermometer, ensuring a constant mechanical coupling that effectively reduces the likelihood of vortex-induced oscillations. An advantage of the present invention is that sufficient stability of the fixing insert can be achieved while simultaneously compensating for the resulting temperature effects. Consequently, the use of the fixing insert according to the present invention allows optimization of the thermometer's thermal properties. For example, the thermometer can be long, while the protective tube can have thin walls. Consequently, the fixing insert is preferably usable in the cryogenic area, i.e., at low temperatures.

[0016] In an embodiment, the fixing insert further comprises a base body having a channel for receiving the thermometer, wherein the exterior of the base body is adapted to the geometry of the interior of the connector.The base body effectively acts as an adapter between the connector and the at least one additional component of the fixing insert.

[0017] The base body is preferably designed so that it can be introduced into a defined position relative to the interior of the joint. Advantageously, the base body can be connected to the receiving joint by force, such as friction, fixation, and / or material bonding. For example, the base body can be fixed to the interior of the joint by welding or the like.

[0018] Furthermore, it is advantageous if the base body is realized in the form of a hollow cylinder, so that the symmetry of the joint, which is usually also cylindrical, can be matched.

[0019] In an embodiment, the fixing insert comprises a circular spring element that can be inserted, in particular releasably inserted, into the connector or the base body. The spring element is particularly dimensioned such that it can be inserted into the connector or the base body with a predeterminable spring tension. Thus, the spring element can adapt to different expansions or contractions of various components of the fixing insert, the thermometer, and / or the connector depending on temperature conditions and accordingly compensate for any mechanical expansions or contractions of the various components due to different coefficients of thermal expansion.

[0020] In another embodiment of the fixing insert, the stop comprises an elongated guide element that is fixed to the wall of the connection piece or the base body, and the stop engages in a part of the fixing insert when the fixing insert is introduced into the connection piece. Preferably, the stop is connected to the wall of the connection piece or the base body by force, such as friction, fixation, and / or material bonding; for example, the stop is welded to the wall.

[0021] At least one component of the fixing insert introduced into the connection piece or into the basic body then comprises, for example, a cavity, a groove or a seat in which the stop engages when the fixing insert is inserted.

[0022] Therefore, in an embodiment of the present invention, it is advantageous if the spring element comprises an elongated groove, wherein the guide element is fixed to the wall of the connecting piece or base body in such a manner that the guide element engages in the groove when the spring element is arranged in the connecting piece or base body. Preferably, the guide element is fixed to the connecting piece or base body in such a manner that the longitudinal axis of the guide element extends parallel to the longitudinal axis of the connecting piece. The length of the guide element is particularly adapted to the thermal expansion coefficients of the various components and / or to anticipated mechanical expansion and / or contraction as a result of temperature fluctuations.

[0023] An alternative embodiment includes the stopper comprising a threaded bolt. This threaded bolt comprises at least a first portion having threads for fastening to the base body or the joint, and a second portion lacking threads. Preferably, the threaded bolt is oriented parallel to the longitudinal axis of the joint. However, the threaded bolt can also optionally comprise a third portion, also provided with threads. Preferably, the first and third portions are then arranged at the two end regions of the threaded bolt.

[0024] At least the part of the fixing insert which is realized and / or arranged such that it is movable in the direction of the longitudinal axis of the joint then comprises a channel through which the threaded bolt passes and which is arranged on the second portion of the threaded bolt.

[0025] In an embodiment with a stopper comprising a threaded bolt, the base body has a circular base plate, onto which is mounted a tube having an internal thread for receiving the threaded bolt. In this case, the threaded bolt is screwed into the internally threaded tube, for example, together with the first portion. In this embodiment, the stopper effectively prevents rotational movement of the thermometer by virtue of its threaded connection to the base body.

[0026] In an embodiment of the fixed insert, the retaining element comprises a circular element in which the thermometer can be fixed.

[0027] For fixing the thermometer in the round element, all fixing means known per se to the person skilled in the art can be used, for example a screw connection with mutually corresponding threads or the use of fixing screws.

[0028] In an alternative embodiment of the fixing insert, the retaining element is realized in the form of a cylindrical element having a first, in particular central, channel in which the thermometer can be fixed, and wherein the outer diameter of the cylindrical element is adapted to the inner diameter of the adapter or the base body. The first channel is in particular the central channel of the cross-sectional area of the cylindrical element, and its inner diameter is adapted to the outer diameter of the thermometer.

[0029] In the case of an embodiment in which the retaining element is in the form of a cylindrical element, the retaining element advantageously comprises at least a second channel for creating fluid contact between the inner volume of the tube and the inner volume of the thermometer.The second channel is an eccentric channel of the cross-sectional area of the cylindrical element.

[0030] Another embodiment comprises, and holding element is fixed by force, for example friction fixation and / or by material bonding, is connected with joint, matrix or circular spring element.In this respect, can use releasable or non-releasable connection.

[0031] For the case where the fixing insert comprises a circular spring element, an embodiment provides that the retaining element comprises a strut connecting the retaining element and the spring element. In this embodiment, the retaining element and the spring element are preferably rigidly connected together by a material bond. For example, the strut can be connected to the spring element and the retaining element by means of two welded joints.

[0032] For the case in which the fixing insert has a base body and the retaining element has the form of a cylindrical element, alternative embodiments include that the base body and the retaining element are connectable to one another by means of a threaded connection, in particular, the retaining element has at least a third channel, wherein the retaining element and the base body are connectable to one another by means of a threaded bolt of a stop, by means of a screw or by means of an additional threaded bolt.

[0033] Furthermore, the object of the present invention is achieved by a device for determining and / or monitoring the temperature of a medium in a container, comprising: a measuring insert having a temperature sensor for determining and / or monitoring the temperature of the medium; and a protective tube for receiving the measuring insert. According to the invention, the device also comprises an inventive fixing insert according to at least one of the described embodiments.

[0034] In an embodiment, the device includes a pressure tapping connection. Furthermore, via this pressure tapping connection, it is possible to determine the pressure of the medium in the pipe. In particular, for cryogenic applications, this avoids the need for an additional connection to the process, which would otherwise be required for additional measuring points, by insulating the pipe against vacuum, if present.

[0035] It should be noted here that the embodiments described in conjunction with the fixing insert according to the invention can also be applied mutatis mutandis to the device according to the invention and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention and its advantageous embodiments will now be explained in more detail based on the accompanying drawings, which show the following:

[0037] Figure 1 Showing the origin of vortex-induced oscillations,

[0038] Figure 2 A thermometer is shown with a protective tube and a mechanical support,

[0039] Figure 3 A first embodiment of a thermometer with a fixed insert according to the invention is shown, and

[0040] Figure 4 A second embodiment of a thermometer with a fixed insert according to the invention is shown.

[0041] In the drawings, identical elements are provided with identical reference numerals. DETAILED DESCRIPTION

[0042] Figure 1 The figure shows how vortices w are shed from a cylindrical, conically tapering thermometer 1 exposed to a medium M flowing in a tube 2. The tube 2 is shown here by its wall. A comb-like pattern of flow profiles forms along the flow direction v of the medium M 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.

[0043] The vibrations are mainly caused by the following two forces acting on the thermometer 1: the shear force in the y direction and the lifting force in the x direction, which add up to form the total force F determined by the flow rate flow . The shear forces cause oscillations with a frequency of fs, while the lifting forces cause oscillations with a frequency of 2fs. The frequency fs depends on the flow velocity v of the medium M and various physical or chemical properties of the medium M, such as its viscosity and density, as well as the geometry of the thermometer 1, such as its diameter, its length and the thickness of the wall of the protective tube. The closer the frequency fs is to the natural frequency of the thermometer 1 and the higher the flow velocity v of the medium M, the greater the oscillations of the forces generated thereby. The thermometer 1 can be damaged by the action of these forces and the occurrence of vortex shedding. In the worst case, the thermometer 1 can fail completely. This is known as the so-called resonance condition.

[0044] In order to reduce the sensitivity of the thermometer to such vortex formation, the design of the protective tube can be modified, as described above. However, the actions for optimizing the geometry of the thermometer 1 with respect to vortex shedding and the actions for optimizing the thermometer 1 with respect to temperature effects, in particular those caused by undesirable heat removal, run essentially in opposite directions.

[0045] Another way to prevent vortex-induced oscillations of the thermometer 1 is to use a mechanical support 4, such as Figure 2 The support 4 is introduced into the joint 3 of the tube 2 and increases the eigenfrequency of the thermometer 1 by reducing its free length.

[0046] However, with this mechanical support 4 there is the problem that an effective mechanical coupling to the thermometer 1 cannot always be ensured. In particular, the mechanical expansion of the various components of the device during temperature changes due to different thermal expansion coefficients makes this solution unreliable at this point in time.

[0047] The invention solves this problem using a fixed insert 6 that is movable parallel to the longitudinal axis L of the joint 3. Thanks to this movement in the direction of the longitudinal axis, temperature effects can be compensated without affecting the mechanical coupling to the thermometer 1.

[0048] Figure 3 and 4Two particularly preferred embodiments of the inventive fixing insert 6 and the inventive device 7 are shown. The pipe 2 and the connection 3 are each implemented, for example, for low temperature T applications and, for example, comprise vacuum insulation (not shown separately).

[0049] exist Figure 3 In the case of the embodiment of the embodiment, the fixing insert 6 comprises a stop 8 in the form of an extended guide element, which is welded to the inside of the joint 3, for example Figure 3 The fixing insert 6 also includes a circular spring element 9, the geometry of which is also adapted to the dimensions of the connector 3. The spring element 9 has a groove 9a in which the stopper 8 engages when the spring element 9 is arranged in the connector 3. The spring element 9 is also connected to a circular retaining element 11 for fixing the thermometer 1 via a strut 10. The stopper 8 prevents the fixing insert 6 from rotating in the connector.

[0050] On the contrary, the movement S in the direction of the longitudinal axis L of the joint therm is possible and serves to compensate for temperature effects in the form of thermally induced forces F that otherwise act on the thermometer 1 and the fixing insert 6 therm This is Figure 3 As a result of the temperature change, the force F therm The force F is generated by the different expansion coefficients of the different components and the associated different mechanical expansions. hold For fixing the holding element 11 on the thermometer 1 so that the thermometer 1 is then subjected to the flow-induced force F flow The reduced sensitivity, such as above combined Figure 1 As stated.

[0051] A second example of a particularly preferred embodiment of the fixing insert 6 of the invention and of the device 7 of the invention is Figure 4 The figures are shown in views rotated 90° relative to each other. Figure 4 As shown in FIG. a, the fixing insert comprises a base body 13 in the form of a hollow cylinder, which is fixed in the joint 3. For example, the base body 13 is welded to the joint 3. The base body 13 also has a circular bottom plate 14 in which an internally threaded tube 15 is mounted for receiving a threaded bolt 16 as part of the stop 8. By means of the threaded bolt 16, the base body 13 is connected to the retaining element 11, which in this case is realized in the form of a cylindrical element, by force fixing (for example friction fixing). Figure 4 As shown in FIG. 2 , the retaining element 11 has a first channel 12 a for receiving the thermometer 1 , a second channel 12 b for creating fluid contact between the inner volume of the tube 2 and the inner volume of the thermometer 1 , and a third channel 12 c for fixing the retaining element 11 to the base body 13 by means of a threaded bolt 15 .

[0052] Also for the second variant of the fixing insert, a movement in the longitudinal direction of the joint 3 is possible, while a rotational movement is prevented by the stop 8. Accordingly, as in Figure 3 In the case of the embodiment, the force F generated by the temperature effect therm and flow-related force F flow can be compensated.

[0053] exist Figure 4 In the embodiment shown, the device 7 further comprises a pressure take-off connection 17 for measuring the pressure of the medium M. This is achieved by fluid contact between the inner volume of the tube 2 and the inner volume of the thermometer 1 , which in the case shown is ensured by the second channel 12 b.

[0054] Reference numerals

[0055] 1 thermometer

[0056] 2 tubes

[0057] 3 connectors

[0058] 4 Mechanical supports

[0059] 5 Vacuum insulation

[0060] 6 Fixing insert

[0061] 7 Devices

[0062] 8 Stopper

[0063] 9 Spring element

[0064] 10 Pillars

[0065] 11. Retaining element

[0066] 12 channels

[0067] 13 Matrix

[0068] 14 Base plate

[0069] 15 tubes

[0070] 16 thread bolt

[0071] 17 Pressure take-off connector

Claims

1. A device (7) for determining and / or monitoring the temperature of a medium (M) in a pipe (2), said device comprising a thermometer (1) for cryogenic applications, said thermometer comprising: - a measuring insert having a temperature sensor for determining and / or monitoring the temperature of the medium; as well as - a protective tube for receiving said measuring insert, The device further comprises a fixing insert (6) for fixing the thermometer (1) in the joint (3) of the pipe (2), wherein the fixing insert (6) comprises - a retaining element (11) for securing the thermometer (1) to the fixing insert (6), and a stop (8) realized to prevent rotational movement relative to the tube (2), It is characterized by: At least one component of the fixing insert (6) is realized and / or arranged such that the fixing insert (6) is movable in the direction of the longitudinal axis of the joint (3), such that the movability of the at least one component can compensate for temperature effects caused by different expansion coefficients of different components of the thermometer.

2. The device (7) according to claim 1, wherein the fixed insert (6) further comprises a base (13) having a channel for receiving the thermometer (1), wherein The exterior of the base body (13) is adapted to the geometric dimensions of the interior of the joint (3).

3. The device (7) according to claim 2, in, The base body (13) is realized in the form of a hollow cylinder.

4. The device (7) according to claim 2, The fixing insert (6) further comprises a circular spring element (9), which can be inserted into the joint (3) or the base body (13).

5. The device (7) according to claim 4, in, The spring element (9) can be releasably inserted into the connection (3) or the base body (13).

6. The device (7) according to claim 4, in, The stop (8) comprises an elongated guide element which is fixed to the wall of the joint (3) or the base body (13) and which engages in a part of the fixing insert (6) when the fixing insert (6) is inserted into the joint (3).

7. The device (7) according to claim 6, in, The spring element (9) comprises an elongated slot (10), and Therein, when the spring element (9) is arranged in the joint (3) or the base (13), the guide element is fixed to the wall of the joint (3) or the base (13) in such a way that the guide element engages in the groove (10).

8. The device (7) according to claim 2, in, The stop member (8) comprises a threaded bolt (16).

9. The device (7) according to claim 8, in, The base body (13) has a circular base plate (14) on which a tube (15) with an internal thread for receiving the threaded bolt (16) is mounted.

10. The device (7) according to one of claims 1 to 9, in, The holding element (11) comprises a circular element in which the thermometer (1) can be fixed.

11. The device (7) according to one of claims 1 to 9, in, The retaining element (11) is realized in the form of a cylindrical element having a first channel (12a) in which the thermometer (1) can be fixed, and wherein the outer diameter of the cylindrical element (11) is adapted to the inner diameter of the connector (3) or the base body (13).

12. The device (7) according to claim 11, in, The first channel (12a) is a central first channel.

13. The device (7) according to claim 11, in, The retaining element (11) comprises at least a second channel (12b) for creating fluid contact between the inner volume of the tube (2) and the inner volume of the thermometer (1).

14. The device (7) according to claim 4, in, The retaining element (11) is connected to the connection (3), the base body (13) or the circular spring element (9) by force fastening and / or by material bonding.

15. The device (7) according to claim 14, in, The retaining element (11) is connected to the connection (3), the base body (13) or the circular spring element (9) by friction fixing.

16. The device (7) according to claim 4, in, The retaining element (11) includes a support (10) connecting the retaining element (11) and the spring element (9).

17. The device (7) according to claim 8, in, The base body (13) and the retaining element (11) can be connected to one another by means of a threaded connection, wherein the retaining element (11) and the base body (13) can be connected to one another by means of the threaded bolt (16) of the stop (8), by means of a screw or by means of an additional threaded bolt.

18. The device (7) according to claim 17, in, The retaining element (11) has at least a third channel (12c).

19. The device according to claim 1, further comprising a pressure take-off connection (17).

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