Thermowell for temperature sensor

Abstract

The invention relates to the field of measuring technology and can be used in oil refining, power engineering, metallurgy and other branches of industry to prevent damage to temperature sensors when measuring the temperature of flowing liquid and gaseous media. A thermowell for a temperature sensor comprises a mounting part for attachment to an object, and an immersion part in the shape of a solid of revolution having a blind hole, said immersion part having flow modifying elements on the outer surface thereof, which are provided in the form of longitudinal ribs divided into sections, wherein the sections on adjacent ribs are offset from one another. The technical result is that of adapting a thermowell for use across a wider range of flow rates by more efficiently reducing vortex formation and oscillation amplitude.

Description

[0001] Protective sleeve for temperature sensor.

[0002] The claimed invention relates to measurement technology and can be used to measure the temperature of moving liquid and gaseous media to prevent damage to temperature sensors. It can be used in oil refining, energy, metallurgy, and other industries. Technological processes implemented in these industries are often characterized by high flow rates of the medium being measured, along with high temperatures and pressures. Under such conditions, protecting temperature sensors with thermowells is essential.

[0003] Temperature sensor thermowells with various geometric shapes are known in the art. A straight thermowell has a uniform diameter along the entire length of the immersion section—the portion of the thermowell from the mounting point to the end of the thermowell located in the medium being measured (the stem). Stepped thermowells are designed with a decreasing diameter toward the end of the stem. The reduced surface area reduces flow resistance and improves the sensor's response to temperature changes. Conical thermowells have a diameter that gradually decreases along the immersion section. They offer greater strength due to the change in angle of attack, as well as a faster response time to temperature changes. The application of thermowells is limited by the flow rates of the medium being measured.Thus, for protective sleeves of straight and conical shapes with an immersion depth of 400 mm, according to the strength calculation method of MRP YUNKZH-13, approved by JSC VNIINEFTEMASH [1], as well as the criteria of the international standard ASME RTS 19.3 [2], the recommended application rate is at a medium density of 54 kg / m3. 3 no more than 7 m / s.

[0004] The speed limitation is explained by the fact that the sleeve, immersed in the flow of the medium being temperature-measured, experiences a complex stress state. This stress state is created by the external pressure of the medium, acting over the entire surface of the immersed portion of the sleeve, and the directed force of the flow. The force of the flow on the rod, as a rod element, is considered the primary loading factor. Due to viscosity, the boundary layer of the flow near the surface of the rod separates from its main body. This separation results in the formation of a vortex (hydrodynamic) wake behind the rod, causing hydroelastic oscillations of the sleeve rod. The higher the flow velocity, the greater the vortex formation and the greater the oscillations. Significant frequency and amplitude of rod oscillations can lead to the risk of its failure due to fatigue and resonance phenomena.

[0005] To prevent destruction and / or reduce the impact of the described phenomenon on reliability, thermopocket sleeves were developed, the design of which reduces vortex formation and, consequently, the vibration load on the sleeve rod.

[0006] Thus, a protective sleeve produced by the company Daily Thermetrics, model Daily Helix Thermowell DHTW [3], with a design that reduces vortex formation is known. The design elements of the sleeve use the technical solutions specified in the Eurasian patent EA 50 015862 B1 of the company ENDET LTD. (GB). The thermowell according to patent EA 015862 B1 contains an elongated tube with flow-modifying elements in the form of one or more helical / spiral fins longitudinally wound along and around at least a part of the outer surface of said tube. The thickness of the fins is from 0.005D to 0.2D, and the height 55 of the fins is from 0.05D to 0.5D, where D is the outer diameter or thickness of the tube. In this case, the tube is closed at one end and provided with a connecting element at the other end, which allows for attachment to the wall of a pressure vessel, pipeline, etc. Such a device is typically designed to accommodate a temperature sensor, such as a thermocouple, within the thermowell tube.Thus, the thermowell ensures sufficiently close thermal contact between the sensor and the fluid medium whose temperature needs to be measured, and the thermowell also protects the sensor from direct contact with the fluid medium, thereby preventing mechanical damage to the sensor.

[0007] Also known is a design of a protective sleeve in the form of a twisted square, patent RU 2575136 C1 of the company ROSEMOUNT INC (US). The design includes a section of contact with the process fluid for installation in a process vessel; an elongated section extending from the section of contact with the process fluid to a hermetically sealed end, wherein the elongated section includes a twisted section, which is twisted around a longitudinal axis; wherein the section of contact with the process fluid and the elongated section form a channel for a sensor, configured to accommodate a sensor therein; and wherein the twisted section has a cross-section that includes at least three walls of equal dimensions that form a polygon, and wherein the walls form spirals along the longitudinal axis of the twisted section.

[0008] The spiral shape of the above-mentioned designs helps suppress harmful vibrations, thereby significantly reducing the dynamic loads to which the thermowell is subjected. This thermowell design significantly reduces the risk of thermowell failure and allows operation in flow velocity ranges inaccessible to cylindrical thermowells and thermowells with variable diameters. Indeed, a numerical analysis of the flow process characteristics conducted by Daily Thermetrics in Autodesk CFD software using physical and mathematical methods confirms the effectiveness of the spiral shape. According to the results obtained, specified in the White Paper - CFD Analysis of Helix Thermowell Design Doc: # DTC-WP-1003 Rev B [4], the oscillation amplitude of the stem tip of a thermowell with a spiral shape and an immersion length of 400 mm in a medium with a density of 54 kg / m 3and a flow velocity of 7 m / s, is 10 times smaller than the oscillation amplitude of a straight cylindrical cylinder under the same conditions. A comparison of the oscillation amplitude of the piston rod tip of a spiral-shaped cylinder and a straight cylindrical cylinder is shown in Fig. 1, where the amplitude of the straight cylindrical cylinder is significantly higher than that of the spiral-shaped cylinder.

[0009] The Applicant's evaluation of the dynamic load calculation results, specifically the flow-induced oscillation frequency, in ANSYS software using the ASME PTS 19.3 international standard methodology confirmed the limitations of using straight cylindrical protective sleeves, as well as the effectiveness of spiral-shaped designs. According to the standard, the dynamic load calculation is performed taking into account the damping coefficient—the Scruton number—Nsc, which is directly proportional to the permissible relative frequency r, calculated as the ratio of the induced oscillation frequency f s to the natural frequency of oscillations fn The relative frequency r can be used as the limit of the permissible load on the thermowell material, depending on the applied load under resonance conditions. The maximum relative frequency value according to the standard is 0.8. The calculation was performed for thermowells with an immersion length of 400 mm and a medium density of 54 kg / m3. 3 and a flow rate of 7 m / s. The calculation results are shown in Table 1 and Fig. 2 and Fig. 3, which show that the spiral-shaped sleeve has a double safety factor from the limit of the permissible dynamic load, on the contrary, the relative frequency value for the cylindrical-shaped sleeve exceeded the limit and it is not recommended for use. Table 1

[0010] Frequency Frequency

[0011] own induced Relative Form Conclusion of oscillations oscillation frequency, g

[0012] (fn), Hz (fs), Hz

[0013] Not

[0014] Cylindrical 83 PO 1.3

[0015] Recommended: Spiral 34 0.4

[0016]

[0017] 88 Recommended

[0018] There are known technological processes in which the flow velocity of the temperature-measured medium is significantly higher than 7 m / s. For example, in a flare collector installation for sulfur production or in an electric desalination plant with a medium density of 1-2 kg / m3. 3 speeds of up to 150 m / s can be achieved.

[0019] The disadvantage of a spiral-shaped thermowell / protective sleeve is that its application area is limited to a flow rate of the temperature-measured medium of up to 100 m / s at a medium density of 1-2 kg / m3. 3. The speed limits were obtained during the analysis of the characteristics of flow processes using physical and mathematical methods with the help of Ansys software. According to the Applicant's document - CFD analysis of helical strakes thermowell [5] - a sleeve with a spiral shape and an immersion length in the medium of 600 mm, with a density of 1.3 kg / m 3 and a flow rate of 100 m / s experiences oscillations that are non-uniform in amplitude and period, as shown in Fig. 4. OOO NPP RITM (https: / / nppritm.ru / products / gz / gz-hs / ), a manufacturer of protective thermowells for the GZ-HS spiral-shaped model, also limits the operating range for flow rates to no more than 100 m / s.

[0020] The proposed invention solves the technical problem of eliminating vibration load from the flow of the measured medium.

[0021] The technical result is an increase in the range of application of the sleeve in terms of flow speed due to a more effective reduction in vortex formation, a reduction in the amplitude of oscillations up to 10 times, while the amplitude profile and the period of oscillations remain uniform, which expands the range of possible application speeds to 150 m / s at a medium density of 1.3 kg / m3. 3 immersion length in the environment 600 mm.

[0022] To achieve the stated technical result, a protective sleeve is proposed, comprising a mounting section for attachment to the wall of a pressure vessel, and a connected immersion section in the form of a rotating body with a blind hole, the outer surface of which contains flow-modifying elements. A distinctive feature of the proposed device is that the flow-modifying elements are designed as longitudinal ribs divided into sections, i.e., they have a discrete shape. Furthermore, the sections on adjacent ribs are offset relative to one another. The immersion section can be constructed from two or more rotating bodies. The protective sleeve design allows for sensor replacement without removing the protective sleeve from the object, as well as the ability to position the sensor terminal head outside the pipeline or apparatus insulation.

[0023] Fig. 5 and Fig. 6 show a general view of a protective sleeve with a cylindrical immersion part and view A - the displacement of sections of adjacent ribs, where:

[0024] 1 - mounting part; 2 - immersion part; 3 - blind hole; 4 - rib; 5 - rib section; 6 - displacement of sections of adjacent ribs.

[0025] When using flow-modifying protective elements with a discrete shape on the surface of the liner, vortex formation in the flow around the liner is significantly minimized, and the value of the turbulence kinetic energy index (TKE) is reduced.

[0026] In fluid dynamics, turbulent kinetic energy (TKE)—the average kinetic energy per unit mass—is one of the important characteristics. High turbulent kinetic energy causes the formation of vortices, which oscillate the liner. According to the Applicant's data obtained during the analysis of flow process characteristics using physical and mathematical methods using Ansys Performance software, a comparison of helical strakes, a thermowell, and a discrete thermowell using CFD [6], the value of kinetic energy near the body of a discrete-shaped liner at a flow velocity of 100 m / s and a medium density of 1.3 kg / m 3 and the length of the immersion part of 600 mm is significantly lower (up to 4 times) than the value in the case of a spiral shape (9.5 10 -2 m 2 ·With -2 – spiral shape, 2.4 10 -2 m 2 ·With -2- discrete shape). No vortex formation occurs. Fig. 7 and Fig. 8 show the turbulence kinetic energy profiles for sleeves with a spiral and discrete shape, respectively.

[0027] Thus, a significant reduction in the amplitude of oscillations is achieved - up to 10 times (5.9 ·10 -2 mm – spiral shape, 5.1 10 -3 mm - discrete form). Fig. 9 and Fig. 10 show the maximum amplitude of oscillations of the tip of the sleeve rod for sleeves with spiral and discrete forms, respectively.

[0028] Thus, the profile of the amplitude and period of oscillations remains uniform for a sleeve with a discrete shape, as shown in the graph of Fig. 11.

[0029] A significant change in the above parameters reduces vortex formation and, consequently, the vibration load on the sleeve rod, the risk of structural failure due to fatigue and resonance phenomena, which increases the reliability of the discrete protective sleeve and expands its range of application to 150 m / s flow velocity.

[0030] The Applicant's evaluation of the dynamic load calculation results, specifically the flow-induced oscillation frequency, in ANSYS software using the ASME PTS 19.3 international standard methodology also confirmed the limitations of spiral-shaped protective sleeves and the effectiveness of discrete-shape designs. The calculation was performed for sleeves with a 600 mm immersion length and a medium density of 1.3 kg / m3. 3and a flow velocity of 150 m / s. The calculation results are presented in Table 2 and in Fig. 12 and Fig. 13, which show that the discrete-shaped sleeve has a safety factor of two times the permissible dynamic load limit; on the contrary, the relative frequency value for the spiral-shaped sleeve exceeded the limit and it is not recommended for use.

[0031] Table 2

[0032] Frequency Frequency

[0033] own induced Relative Form Conclusion of oscillations oscillation frequency, g

[0034] (fn), Hz (fs), Hz

[0035] Not Spiral 55 62 1.1

[0036] recommended

[0037]

[0038] Discrete 60 25 0.4 Recommended

[0039] Table 3 lists the design variants of protective sleeves that were manufactured and tested at one of the refineries. A general view of the sleeves is shown in Fig. 14, which corresponds to one of the variants of the claimed device. The sleeve design comprises a mounting part for attachment to the tank wall in the form of a flange, connected to it by a submersible section in the form of two bodies of revolution—a cone and a cylinder. The submersible cylindrical section with a diameter D is provided with flow-modifying elements in the form of ribs divided into sections of height H and thickness c, with the sections of adjacent rows offset by a distance s relative to one another, as shown in Fig. 15 and Fig. 16.

[0040] Table 3

[0041] Immersion length, mm 250 260

[0042] Discrete diameter 28 28

[0043] parts, mm

[0044] Speed, m / s 50 150

[0045] Density, kg / m3 20 1.4

[0046] Viscosity, kg / m-s (10*-5) 1.6 0.8

[0047]

[0048] Temperature, °C 350-400. Operating conditions are provided according to the process parameters specified in the temperature control instrument data sheets. The sleeves have been manufactured and installed for operation, and there have been no customer complaints.

[0049] Fig. 14, Fig. 15 and Fig. 16 show a sleeve with a submersible part made of two bodies of revolution with flow-modifying elements in the form of ribs divided into sections, made on one of them, a section of the submersible part and the displacement of the rib sections in adjacent rows, where:

[0050] 1 - mounting part;

[0051] 2 - immersion part;

[0052] 3 - blind hole;

[0053] 4 - rib;

[0054] 5 - rib section;

[0055] 6 - displacement of sections of adjacent ribs;

[0056] D - diameter;

[0057] H - height of ribs.

[0058] The protective sleeve is installed on the object using the mounting part (1), while a blind hole (3) is made in the immersion part (2), consisting of a conical and cylindrical part, intended for installing a temperature sensor. When the flow passes around the immersion part of the sleeve (2) with flow-modifying elements (4) made in the section located directly in the flow, in the form of ribs divided into sections (5), each of the sections forms its own separate vortex wake as a result of flow separation from it. The directions and structures of these vortex wakes are differently directed in space, due to the arrangement of the sections of the flow-modifying elements at different angles to the oncoming flow. As a result, instead of one large vortex wake having a part directed opposite to the flow and capable of creating oscillations of the sleeve rod, a multitude of multidirectional small vortex flows are created that are incapable of creating oscillations. Bibliography:

[0059] 1. Electric sleeves for thermoelectric converters and resistance temperature converters: strength calculation method for MRP YUNKZh-13 / Obninsk, OOO PK Tesey, 2013. - 11 pp.

[0060] 2. ASME RTS 19.3 TW-2016. Thermowells. Performance Test Codes - 62 pages.

[0061] 3. Daily Helix Thermowell (DHTW) - URL:

[0062] http: / / www.dailyinst.com / roducts / thermowells /

[0063] 4. CFD Analysis of DHTW utilizing VE Technology. A Helix Thermowell Design White Paper - URL:

[0064] http: / / www.dailyinst.com / roducts / thermowells /

[0065] 5. CFD analysis of helical strakes thermowell, 2024 - 11 pages.

[0066] 6. Performance comparison of helical strakes thermowell and discrete thermowell using CFD, 2024 - 16 pp.

Claims

Invention formula A protective sleeve for a temperature sensor, including a mounting part for fastening to an object, an immersion part in the form of a body of revolution with a blind hole, on the outer surface of which flow-modifying elements are made, characterized in that the flow-modifying elements are made in the form of longitudinal ribs divided into sections, wherein the sections on adjacent ribs are offset relative to each other.

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