RU2030661C1 - Method of sealing shaft of rotor machine - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: ring rotating flow of sealing fluid undergoes outer hydrothermal effects and negative density gradient is created along the ring radius. If kinematical viscosity of fluid does not exceed 5·10^-6 m²/s the value of the density gradient is maintained at a level defined by a relationship available in the invention description. EFFECT: simplified method. 4 dwg

Description

 The invention relates to a sealing technique and can be used mainly in rotary machines (pumps, centrifuges, mixers) to reduce fluid leaks from the chambers being sealed along a rotating shaft when there are no conditions to reduce the guaranteed clearance.

 There is a method of non-contact sealing of a rotating shaft of a rotary machine using labyrinth-slot elements installed on the stator and rotor by creating hydraulic resistance in the path of the flowing fluid, for example, by reducing the clearance between the stator sleeve and the shaft, installing “antennae” in grooves, grooves, brushes, turbulization of the flow [1].

 The known method provides the appropriate sealing effect with small gaps and nominal (design) modes, while reducing the shaft speed, turbulizers and screw cuts worsen their effectiveness; it is not always possible to reduce the guaranteed clearance in shaft seals, which are prone to vibration and bending deformations.

 There is also known a method of sealing the shaft, according to which the reduction of fluid leaks is achieved due to additional external physical (hydrodynamic, thermal, electromagnetic, acoustic, etc.) effects on the annular rotating flow of the sealing medium in the throttle channel, which uses the external thermal effect on the flow - freezing - in order to increase the efficiency of the seal [2].

 The known method, based mainly on the effect of reducing fluid leakage by reducing the gap between the stator and the rotor ("freezing"), cannot be used in rotary machines whose shafting is subject to vibration or large bending deformations, and therefore requires increased guaranteed sealing gaps.

 The purpose of the invention is to increase the efficiency of compaction due to the optimization of operational parameters.

≅ 5Ω² где Δ ρ - изменение плотности уплотняющей среды вдоль радиуса кольцевого потока, кг/м³;
Δ r - толщина кольцевого потока, м;
Ω - частота вращения вала, 1/с;
6,53^.10^-7 - эмпирическая константа для уплотняемых сред с кинематической вязкостью ν ≅ 5^.10^-6 м²/с.The technical result is achieved by the fact that according to the method of sealing the shaft of a rotary machine using throttle labyrinth-slit elements of the stator and rotor by external hydrothermal action on the annular rotating flow of the sealing medium in the throttle channel and creating along the radius of the ring a negative density gradient of the sealing medium, the average absolute value of which support within the limits defined by the ratio

≅ 5Ω ² where Δ ρ is the density change of the sealing medium along the radius of the annular flow, kg / m ³ ;
Δ r is the thickness of the annular flow, m;
Ω - shaft rotation frequency, 1 / s;
6.53 ^. 10 ^-7 - empirical constant for sealed media with kinematic viscosity ν ≅ 5 ^. 10 ^-6 m ² / s.

 Figure 1 shows a diagram of a first embodiment of a seal with a heater in the stator; figure 2 is the same, but with a refrigerator in the stator; figure 3 - varieties of tubular probes located in section A of a rotary groove trapezoidal cut, in section B of the comb seal of the "antennae" type, in section B of a simple gap seal; figure 4 is a diagram of a second variant of the seal.

In figure 1, 2 and 4 are indicated: r ₁ - the largest radius of the annular gap; r ₂ is the smallest gap radius; Δr = r ₁ - r ₂ is the thickness of the annular gap.

The first variant (Fig. 1) of the device (designed to reduce the groove of the “cold” coolant from the sealable chamber 1) contains a throttle channel 2 formed by an annular surface of radius r _{1 of the} stator 3 and a counter surface of radius r _{2 of the} rotor 4. An adjustable heater 5 is built into the stator e.g. electric type. The hollow tube probes 6 and 7, with their tips equipped with temperature sensors 8, border the stator and rotor surfaces of the throttle channel, respectively. The throttle channel 2 itself can be a simple slotted (Fig. 3) or "cluttered" with screw threads (Fig. 3A) and crests of the "antennae" type (Fig. 3B).

The same version of the device (figure 2), but designed to reduce leakage of the "hot" coolant from the chamber 9, contains a similar throttle channel 10 formed by a cylindrical radius r _{2 by the} surface of the stator 11 and the response radius r _{1 by the} surface of the groove groove on the rotor 12, however , an adjustable refrigerator 13 is integrated in the stator, for example, a coil for circulating cold coolant. By analogy with figure 3, the throttle channel 10 can be a simple slotted or "cluttered" with helical grooves or crests of the "antennae" type, but it must be equipped with hollow flowing tubular probes with tips adjacent to the annular stator surface of radius r ₂ and similar probes, bordering on a rotor surface of radius r ₁ . Inside the probe tips are installed similar temperature sensors 8.

The second variant of the device (Fig. 4) comprises a sealable chamber 14 and a throttle channel 15 formed by cylindrical surfaces of radius r _{1 of the} stator 16 and radius r _{2 of the} rotor 17. The portion of the stator surface 18 is permeable, and therefore hydraulically (through micropores) connected to the chamber 19 for external gas pressurization (permeability is ensured by the manufacture of bushings 18 from porous fluoroplastic or metal powder - granules by powder metallurgy).

 The seal works as follows (figure 1).

> 0 , но отрицательный градиент плотности среды (жидкости)
▽ρ =

< 0 , где ρ₁ - плотность при t₁; ρ₂ - при t_2; t₁>t_2; ρ₁ > ρ₂ .The cooled medium (liquid) flows from the chamber 1 through the throttle channel 2. The surface of the rotor 4 of radius r _{2 is} cooled to temperature t ₂ , the counter surface of the stator 3 with radius r ₁ , heated by thermocouple 5, has a temperature t ₁ > t ₂ . A positive temperature gradient is created along the radius of the ring with a thickness Δr = (r ₁ -r ₂ )> 0:
▽ t =

> 0, but a negative gradient in the density of the medium (liquid)
▽ ρ =

<0, where ρ ₁ is the density at t ₁ ; ρ ₂ - at t _2; t ₁ > t _2; ρ ₁ > ρ ₂ .

 In a ring flow rotating with a frequency Ω, under the influence of ▽ ρ <0 and centrifugal forces C, a complex, unstable, vortex (turbulent) movement arises, which increases the hydraulic resistance and therefore reduces the resultant outflow of the medium.

 The mechanism of flow instability: heavy (cold) fluid particles bordering the rotor, under the influence of the forces C, tend to move to the stator, and light (heated) particles to the rotor. As a result of such external energy impact, developed turbulence arises in the annular flow, the self-energy of which is clearly not enough for the generation of turbulent pulsations. In the case of + ▽ ρ, the flow, under the influence of the forces of C, stabilizes on the contrary, the pulsations are damped, and the hydraulic resistance decreases.

As experiments have shown, hydraulic resistance increases only if a certain condition is met, i.e. for a certain combination of Ω, Δ ρ, Δ r. Therefore, to create optimal operating conditions of the seal, it is important to measure the temperatures t ₁ and t ₂ and determine ρ ₁ and ρ _{1 from them} . For this, suction tube probes 6 and 7 are used, in the tips of which thermal sensors 8 are installed.

In the event of the flow of the heated medium from the chamber 9 (Fig. 2) through the channel 10, the surface of the rotor 12 of radius r _{1 is} heated to t ₁ , the counter surface of the stator 12 of radius r _{2 is} cooled to t ₂ <t ₁ (thanks to the refrigerator 13), along the radius of the ring Δr = (r ₁ - r ₂ )> 0, a negative density gradient is also created.

< 0 (t₁>t₂, ρ₁< ρ₂).▽ ρ =

<0 (t ₁ > t ₂ , ρ ₁ <ρ ₂ ).

 The second embodiment of the device works similarly (Fig. 4).

< 0 , где ρ₁ - плотность аэрированной жидкости возле поверхности 18 радиуса r₁; ρ₂ - плотность жидкости у роторной поверхности радиуса r₂; ρ₁ < ρ₂.The liquid flows from the chamber 14 through the throttle channel 15. The surfaces of the rotor 17 of radius r ₂ and the stator 16 of radius r ₁ have the same temperature. A negative density gradient - ▽ ρ along the radius of the ring Δr = (r ₁ -r ₂ )> 0 is created by blowing dispersed gas from the chamber 19 through the permeable surface 18 of the stator into the annular flow
▽ ρ =

<0, where ρ ₁ is the density of the aerated liquid near the surface 18 of radius r ₁ ; ρ ₂ is the fluid density at the rotor surface of radius r ₂ ; ρ ₁ <ρ ₂ .

The values ρ ₁ and ρ ₂ can be estimated by knowing the flow rate of the injected gas Q ^" , the porosity ϑ of the permeable septum, and the amount of fluid leakage Q ^I : ρ ₁ ≈ (1- ϑ) ρ ^* ˙ ρ ₂ = [1 - Q ^II / (Q ^II + Q ^I )] ρ ^* , where ρ ^{* is the} density of a clean (without gas) liquid.

PRI me R. The shaft is sealed D ₂ = 2r ₂ = 180 mm using the labyrinth-slot element of the stator type B (Fig. 3) D ₁ = 2r ₁ = 200 mm, the ring thickness Δr = r ₁ - r ₂ = 100 mm, the gap between the crest and the shaft δ = 0.5 mm, the pitch of the ridges h = 10 mm, the number of ridges z = = 10 pcs. Characteristics of sealing medium: water at ⁴⁵ ° C and a pressure of ^2. 10 ⁵ Pa (2 kg / cm ² ) has a density of 900 kg / m ³ . The differential pressure ΔP of 0.4 ^. 10 ⁵ Pa.

1. With isothermal water flow through the throttle channel at ΔР = 0.4 ^. 10 ⁵ Pa temperature of the stator t ₁ = 45 ^о С and rotor t ₂ = = 45 ^о С, leakage rate G = 0.5 l / s at shaft rotation frequency Ω = 50 1 / s and G = 0.6 l / s at Ω = 25 1 / s.

=

=

= 0 .The density gradient of water along the radius of the ring
▽ ρ =

=

=

= 0.

=

= 65,3

<

= 5·10

<

5Ω²= 5·50²=12500

3. Снизили частоту вращения вала до Ω= 25 1/с, сохранив температуры статорных и роторных элементов уплотнения t₁ = 120^о С ( ρ₁= 940 кг/м³) и t₂ = 45^о С ( ρ₂ = 990 кг/м³), протечки увеличились до G = 0,6 л/с, т.е. до величины, соответствующей случаю, когда Ω= 25 1/с и ▽ ρ = 0. Хотя отрицательный градиент плотности и сохранился прежним Δ ρ / Δ r = -5^.10³ кг/м⁴, определенное условие нарушилось, работа уплотнения не улучшилась: (режимные параметры не оптимальны):

= 65,3

<

= 5·10

>

5Ω²= 5·25²= 3125

4. При прежней частоте вращения вала Ω= 25 1/с снизили температуру поверхности r₁ статорного элемента до t₁ = 90^о С ( ρ₁= 965,3 кг/м³), сохранив температуру поверхности r₂ ротора t₂ = 45^о С ( ρ₂ = 990 кг/м³), протечки сократились с 0,6 л/с до G^* = 0,41 л/с, так как определенное условие снова восстановилось: (965,3-990)/10^-2 = -2500 кг/м⁴ и

= 65,3

<

= 2500

<

5Ω²= 5·25²= 3125

Работа уплотнений снова улучшилась (режимные параметры оптимальны).2. Heated the surface r _{2 of the} stator element to t ₁ = 120 ^о С (water density ρ ₁ = 940 kg / m ³ ), preserving the rotor surface temperature t ₂ = 45 ^о С (ρ ₂ = 990 kg / m ³ ), consumption water leakage decreased from 0.5 l / s to G ^* = 0.33 l / s, the density gradient along the radius of the ring became negative Δ ρ / Δ r = (940-900): 10 ^-2 = -5 ^. 10 ⁺³ kg / m ⁴ and a certain condition of the method is fulfilled (operating parameters are optimal):

=

= 65.3

<

= 5 · 10

<

5Ω ² = 5 · 50 ² = 12500

3. Reduced the shaft speed to Ω = 25 1 / s, while maintaining the temperature of the stator and rotor seal elements t ₁ = 120 ^о С (ρ ₁ = 940 kg / m ³ ) and t ₂ = 45 ^о С (ρ ₂ = 990 kg / m ³ ), leaks increased to G = 0.6 l / s, i.e. to the value corresponding to the case when Ω = 25 1 / s and ▽ ρ = 0. Although the negative density gradient remained unchanged Δ ρ / Δ r = -5 ^. 10 ³ kg / m ⁴ , a certain condition was violated, the compaction work did not improve: (operating parameters are not optimal):

= 65.3

<

= 5 · 10

>

5Ω ² = 5 · 25 ² = 3125

4. At the same shaft rotation frequency Ω = 25 1 / s, the surface temperature r _{1 of the} stator element was reduced to t ₁ = 90 ^о С (ρ ₁ = 965.3 kg / m ³ ), while maintaining the surface temperature r _{2 of the} rotor t ₂ = 45 ^о С (ρ ₂ = 990 kg / m ³ ), leakages decreased from 0.6 l / s to G ^* = 0.41 l / s, as a certain condition was restored again: (965.3-990) / 10 ^{- 2} = -2500 kg / m ⁴ and

= 65.3

<

= 2500

<

5Ω ² = 5 · 25 ² = 3125

Seals performance improved again (operating parameters are optimal).

Claims (1)

METHOD FOR SEALING A ROTARY MACHINE SHAFT using throttle labyrinth-slit elements of the stator and rotor by external hydro-thermal action on the annular rotating flow of the sealing medium and creating a negative density gradient along the radius of the ring, characterized in that for media with kinematic viscosity not more than 5 · 10 ^{- 6} m ² / s the average absolute value of the density gradient is maintained in accordance with the ratio

where Δρ is the change in the density of the sealing medium along the radius of the annular flow, kg / m ³ ;
Dr is the thickness of the annular flow, m;
Ω - shaft rotation frequency, s ^{- 1} ;
6.53 · 10 ^{- 7} is the empirical constant for sealing media with kinematic viscosity ψ ≅ 5 · 10 ^-6 m ² / s.

Images