A method for calculating theoretical sealing pressure of a magnetic fluid sealing device considering temperature

Abstract

The application discloses a kind of theoretical sealing pressure calculation method of magnetic fluid sealing device considering temperature, belong to magnetic fluid sealing device sealing pressure evaluation field.The purpose is to solve the problem of accurate calculation of theoretical sealing pressure of magnetic fluid sealing device at any temperature.The principle is to determine the mechanical structure size of magnetic fluid sealing device and its pole shoe, permanent magnet, magnetic conducting sleeve and magnetic liquid material performance parameters first, establish numerical model to simulate magnetization process, obtain the magnetic field result of magnetic fluid sealing device under different temperature conditions;Then, according to the magnetic field intensity in the sealing gap of magnetic fluid sealing device and the number of pole teeth under different temperature conditions obtained by numerical calculation, the saturation magnetization intensity of magnetic fluid sealing device and the total difference of magnetic induction intensity in the sealing gap of magnetic fluid sealing device are calculated respectively;Finally, the theoretical sealing pressure is calculated.The method establishes the correlation between temperature and magnetic field intensity of magnetic fluid sealing device, and can efficiently and accurately evaluate the theoretical sealing pressure.

Description

Technical Field

[0001] This invention relates to a method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device that takes temperature into account, and belongs to the field of sealing pressure evaluation of magnetohydrodynamic sealing devices. Background Technology

[0002] The core working structure of a magnetohydrodynamic (MHD) sealing device mainly includes key components such as pole shoes, permanent magnets, magnetically conductive bushings, and magnetic fluid. This unique structure allows the permanent magnet's magnetic field to create a special magnetic field gradient difference within the sealing gap of the device. Under the combined effect of this magnetic field gradient difference and the pressure of the sealing medium, the magnetic fluid is adsorbed within the sealing gap, forming a continuous MHD sealing ring and achieving a sealing effect. Currently, researchers have developed MHD sealing devices suitable for various applications; however, there are few reports on how to accurately calculate the theoretical sealing pressure generated by these devices.

[0003] Xihua University disclosed a magnetohydrodynamic sealing device with enhanced sealing performance, including a sealing body with a hollow sealing shell. The sealing shell is sleeved on a rotating shaft, and a sealing cavity is formed between the inner wall of the sealing shell and the rotating shaft. A first sealing component, a stationary ring, and a second sealing component are sequentially arranged along the axial direction within the sealing cavity (Publication No.: CN119196313A). This invention significantly improves the sealing performance of the magnetohydrodynamic sealing device by forming a multi-layered sealing structure along the axial direction through the first and second sealing components. Tsinghua University disclosed a magnetic powder sealing liquid device with fluid dynamic pressure reverse transport (Publication No.: CN113833858A), including a main shaft, a left retaining ring of the shaft sleeve, an outer sleeve, an end face sealing O-ring, a left pole shoe, a pole shoe O-ring, a spiral groove shaft sleeve, a right pole shoe, a magnetic isolation ring, a left bearing, a right bearing, a threaded sealing cover, a bearing elastic retaining ring, a right retaining ring of the shaft sleeve, and a permanent magnet for the magnetic source. The trapezoidal teeth on the pole shoe have an opposite rotation direction to the helical teeth on the bushing. This allows the sealing fluid to fill the pores of the magnetic powder, while the magnetic force on the magnetic powder increases the fluid pressure in the gap, achieving zero leakage of the sealed fluid. The aforementioned patents all disclose a magnetic fluid sealing structure suitable for different temperature conditions, but none of them address the method for calculating the theoretical sealing pressure generated by the magnetic fluid sealing device. Furthermore, the theoretical sealing pressure is a key factor in the mechanical structure design and sealing performance evaluation of magnetic fluid sealing devices. Accurately and efficiently evaluating the theoretical sealing pressure is fundamental to ensuring the safe, reliable, and efficient operation of the magnetic fluid sealing device. Summary of the Invention

[0004] To address the problems of low efficiency and accuracy in calculating the theoretical sealing pressure of existing magnetohydrodynamic (MHD) sealing devices and overcome the shortcomings described in the background art, this invention provides a method for calculating the theoretical sealing pressure of MHD sealing devices that considers temperature. The method includes the following steps:

[0005] (1) Determine the mechanical structure dimensions of the magnetic fluid sealing device and the performance parameters of its pole shoes, permanent magnets, magnetic bushings and magnetic fluid materials, establish a numerical model to simulate the magnetization process, and obtain the magnetic field results of the magnetic fluid sealing device under different temperature conditions;

[0006] (2) Based on the magnetic field strength B and the number of pole teeth i in the sealing gap of the magnetic fluid sealing device under different temperature conditions obtained by numerical calculation, the magnetic fluid saturation magnetization M of the magnetic fluid sealing device is calculated respectively. s The total difference in magnetic induction intensity ΔB in the sealing gap of the magnetohydrodynamic sealing device;

[0007] (3) The theoretical sealing pressure of the magnetic fluid sealing device is calculated according to the following formula:

[0008] ΔP=M s (1-k0T / mH)ΔB (1)

[0009] In the formula, k0 is the Boltzmann constant; T is the absolute temperature; m is the magnetic moment of the particle; and H is the magnetic field strength of the permanent magnet.

[0010] Furthermore, the magnetic fluid is an incompressible fluid; the magnetic fluid is isothermal.

[0011] Furthermore, the magnetic fluid saturation magnetization M of the magnetic fluid sealing device s Calculate according to the following formula:

[0012] M s =B0 / μ0 (2)

[0013] In the formula, B0 is the saturation magnetic induction intensity of the magnetic fluid in the sealing gap of the magnetic fluid sealing device; μ0 is the vacuum permeability.

[0014] Furthermore, the total difference in magnetic induction intensity ΔB of the magnetic fluid sealing device is calculated according to the following formula:

[0015]

[0016] In the formula The maximum value of the magnetic induction intensity under the i-th pole tooth in the sealing gap of the magnetohydrodynamic sealing device; It represents the minimum magnetic induction intensity of the i-th pole tooth in the sealing gap of the magnetohydrodynamic sealing device.

[0017] Furthermore, the absolute temperature T should be the average temperature of the magnetic fluid in the magnetic fluid sealing gap, and the maximum value of the absolute temperature T should not exceed the failure temperature of the magnetic fluid.

[0018] Furthermore, the magnetic field strength H of the permanent magnet is the average magnetic field strength of the permanent magnet corresponding to the absolute temperature T.

[0019] The advantages of this method are: first, it establishes the correlation between temperature and magnetic field strength of the magnetic fluid sealing device, which can accurately assess the theoretical sealing pressure; second, it uses numerical simulation to calculate the magnetization process of the magnetic fluid sealing device, which saves costs and greatly improves the efficiency of theoretical sealing pressure calculation. Attached Figure Description

[0020] Figure 1 A flowchart illustrating a method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device that takes temperature into account.

[0021] Figure 2 This is a schematic diagram of the mechanical structure dimensions of a certain type of magnetohydrodynamic sealing device.

[0022] Figure 3 This is the demagnetization curve for a permanent magnet;

[0023] Figure 4 Magnetic field cloud diagrams of a magnetohydrodynamic sealing device under different operating temperature conditions;

[0024] Figure 5 The magnetic flux density at a certain section under different operating temperatures;

[0025] Figure 6 The theoretical sealing pressure of the magnetohydrodynamic sealing device at different operating temperatures. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] The following is an example of calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature, but the scope of protection of this invention is not limited to the following implementation example.

[0028] The mechanical structure dimensions of a certain type of magnetohydrodynamic sealing device are as follows: Figure 2 As shown in Table 1, the performance parameters of the pole shoes, permanent magnets, magnetic bushings, and magnetic fluid materials of a certain type of magnetohydrodynamic sealing device are presented. Nd-Fe-B permanent magnets of model N42SH are used, and their demagnetization curves are shown in [the table below]. Figure 3 As shown.

[0029] Table 1 Parameters of Permanent Magnet Materials

[0030]

[0031] The permeability parameters of common electromagnetic pure iron materials are shown in Table 2 below. The pole shoes and magnetic bushings of this invention are made of ordinary electromagnetic pure iron.

[0032] Table 2. Magnetic permeability parameters of commonly used electromagnetic pure iron materials

[0033]

[0034] This invention uses specially prepared refined synthetic oil as the base liquid, and finally obtains a magnetic liquid with a relative permeability of 1.1 and a saturation magnetic induction intensity B0 of 0.03T.

[0035] according to Figure 3 The demagnetization curve of the permanent magnet N42SH is shown. The relationship between temperature and the magnetic field of the magnetic fluid sealing device was studied at six operating temperatures: 20℃, 60℃, 80℃, 100℃, 120℃, and 150℃. The magnetic field cloud diagrams of the magnetic fluid sealing device under different operating temperatures are shown below. Figure 4 As shown.

[0036] This invention selects a representative cross-section as the research object. The length of this cross-section is consistent with the total length of the magnetically conductive bushing, and the cross-section is located 0.1 mm above the axis (which is exactly at the center of the sealing gap). The simulation calculation results of the magnetic induction intensity on the cross-section under different temperature environments are obtained, as shown below. Figure 5 As shown.

[0037] The magnetic fluid saturation magnetization M of the magnetic fluid sealing device is calculated according to the following formula. s according to:

[0038] M s =B0 / μ0 (1)

[0039] In the formula, μ0 is taken as 4π×10 -7 H / m, then the magnetic fluid saturation magnetization M of the magnetic fluid sealing device s It equals 23.9 kA / m.

[0040] Table 3 Calculated theoretical sealing pressure values ​​at different temperatures

[0041]

[0042] The total difference ΔB in magnetic induction intensity of the magnetohydrodynamic sealing device under different operating temperatures is calculated according to the following formula:

[0043]

[0044] The calculation results are shown in Table 3.

[0045] Finally, the theoretical sealing pressure of the magnetohydrodynamic sealing device at different operating temperatures is calculated according to the following formula:

[0046] ΔP=M s (1-k0T / mH)ΔB (2)

[0047] In the formula, k0 is the Boltzmann constant, which is taken as 1.38 × 10⁻⁶. -23J / K; T is absolute temperature in K; m is the magnetic moment of the particle, taken as 1.25 × 10⁻⁶. -20 A·m 2 H represents the magnetic field strength of the permanent magnet, measured in A / m. The theoretical sealing pressure of the magnetohydrodynamic sealing device at different temperatures is shown below. Figure 6 As shown.

Claims

1. A method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature, characterized in that... The method includes the following steps: Step 1: Determine the mechanical structure dimensions of the magnetic fluid sealing device and the performance parameters of its pole shoes, permanent magnets, magnetic bushings, and magnetic fluid materials; establish a numerical model to simulate the magnetization process and obtain the magnetic field results of the magnetic fluid sealing device under different temperature conditions; Step 2: Based on the magnetic field strength in the sealing gap of the magnetic fluid sealing device under different temperature conditions obtained by numerical calculation... With the number of pole teeth Calculate the saturation magnetization of the magnetic fluid in the magnetic fluid sealing device. The total difference in magnetic induction intensity in the sealing gap of the magnetohydrodynamic sealing device ; Step 3: The theoretical sealing pressure of the magnetohydrodynamic sealing device is calculated according to the following formula: (1) In the formula Boltzmann's constant; Absolute temperature; For the particle's magnetic moment; The magnetic field strength of the permanent magnet.

2. The method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature as described in claim 1, characterized in that... In step one, the magnetic fluid is an incompressible fluid; The magnetic fluid is isothermal.

3. The method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature as described in claim 1, characterized in that... In step two, the magnetic fluid saturation magnetization intensity of the magnetic fluid sealing device is... Calculate according to the following formula: (2) In the formula The saturation magnetic induction intensity of the magnetic fluid in the sealing gap of the magnetic fluid sealing device; is the vacuum permeability.

4. The method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature as described in claim 1, characterized in that... In step three, the total difference in magnetic induction intensity of the magnetic fluid sealing device Calculate according to the following formula: (3) In the formula The first in the sealing gap of the magnetic fluid sealing device The maximum value of the magnetic induction intensity under the pole teeth; The first in the sealing gap of the magnetic fluid sealing device The minimum value of magnetic induction intensity under the first-stage pole teeth.

5. The method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature as described in claim 1, characterized in that... In step three, the absolute temperature The absolute temperature should be the average temperature of the magnetic fluid in the magnetic fluid sealing gap. The maximum value does not exceed the failure temperature of the magnetic fluid.

6. The method for calculating the theoretical sealing pressure of a magnetohydrodynamic sealing device considering temperature as described in claim 1, characterized in that... In step three, the magnetic field strength of the permanent magnet... The absolute temperature The corresponding average magnetic field strength of the permanent magnet.

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