Oleksandr Pozovnyi1 , Andriy Zahorulko1, Jan Krmela2,3, Artem Artyukhov1, Vladimíra Krmelová3 1Faculty of Technical Systems and Energy Efficient Technologies, Sumy State University. RymskogoKorsakova st.,2, 40007, Sumy. Ukraine. E-mail: aleksandrpozovnyi@gmail.com, a.zagorulko@omdm.sumdu.edu.ua, a.artyukhov@pohnp.sumdu.edu.ua 2Faculty of Mechanical Engineering, J. E. Purkyně University in Ustí nad Labem. Pasteurova 3334/7, 400 01 Ustí nad Labem. Czech Republic. E-mail: jan.krmela@ujep.cz 3Faculty of Industrial Technologies in Púchov, Alexander Dubček University of Trenčín. I. Krasku 491/30, 02001 Púchov. Slovak Republic. E-mail: jan.krmela@tnuni.sk, vladimira.krmelova@tnuni.sk

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Calculation of the Characteristics of the Multi-gap Seal of the Centrifugal Pump, in Depend-ence on the Chambers' Sizes

Higher parameters of centrifugal machines are constantly required, such as the pressure of the medium to be sealed and the speed of rotation of the shaft. However, as the parameters increase, it becomes more and more difficult to ensure the effectiveness of sealing. In addition, sealing systems affect the overall safety of equipment operation, especially vibration. In order to harmonize the sealing functions and increase the dynamic rigidity of the rotors of centrifugal machines, a method for modeling complex sealing systems has been developed. Non-contact seals are considered as hydrostatic–dynamic bearings that can effectively dampen rotor oscillations. A general approach to the analysis of non-contact seals as automatic control systems and an algorithm for constructing their dynamic characteristics at the design stage were proposed for the first time. Models of “rotor-gap seal”, impulse seal and “rotor–hydraulic face” systems, and seal-supports of a shaftless pump have been studied to assess the effect of these seal systems on the oscillatory characteristics of the rotor. Analytical dependencies are obtained for calculating the dynamic characteristics and stability limits of seals as hydromechanical systems. The directions for improving the safety of operation of critical pumping equipment due to a targeted increase in the rigidity of non-contact seals are determined, which leads to an increase in the vibration resistance of the rotor and the environ-mental safety of centrifugal machines. The paper proposes a method for designing sealing systems based on the configuration of sealing components in order to achieve harmonization between sealing and vibration reliability, taking into account oscillatory processes due to hydrodynamic sealing characteristics.

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Methodology of Designing Sealing Systems for Highly Loaded Rotary Machines

Composite materials have a wide range of functional properties, which is ensured by using various technological methods of obtaining both the matrix or fillers and the composition as a whole. A special place belongs to the composition formation technology, which ensures the necessary structure and properties of the composite. In this work, a computer simulation was carried out to identify the main dependencies of the behavior of composite materials in the process of the main technological operations of their production: pressing and subsequent sintering. A polymer matrix randomly reinforced with two types of fillers: spherical and short cylindrical inclusions, was used to construct the finite element models of the structure of composites. The ANSYS Workbench package was used as a calculation simulation platform. The true stress–strain curves for tension, Poisson’s ratios, and ultimate stresses for composite materials were obtained using the finite element method based on the micromechanical approach at the first stage. These values were calculated based on the stretching diagrams of the matrix and fillers and the condition of the ideality of their joint operation. At the second stage, the processes of mechanical pressing of composite materials were modelled based on their elastic–plastic characteristics from the first stage. The result is an assessment of the accumulation of residual strains at the stage before sintering. The degree of increase in total strain capability of composite materials after sintering was shown.

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Computer Simulation of Composite Materials Behavior under Pressing

There is a constant demand for higher equipment parameters, such as pressure of a sealing medium and shaft rotation speed. However, as the parameters rise it becomes more difficult to ensure hermetization efficiency. Moreover, sealing systems affect the overall operational safety of the equipment, especially vibratory. Non-contact seals are considered as hydrostatodynamic supports that can effectively damp rotor oscillations. Models of an impulse and a groove seals, models of rotor-seals system and rotor-auto-unloading system, model of a shaftless pump are studied to evaluate an effect of these sealing systems on oscillatory characteristics of rotor. Analytical dependencies for computation the dynamic characteristics of impulse seals, hydromechanical systems rotor-seals and rotor-auto-unloading, as well as shaftless pumps are obtained. These dependencies describe the radial-angular vibrations of a centrifugal machine rotor in seals-supports. Equations for computation the amplitude-frequency characteristics are given. The directions of improving the оperational safety of critical pumping equipment by purposefully increasing the rigidity of non-contact seals that leads to higher rotor vibration stability have been determined.

https://doi.org/10.15407/pmach2022.01.032

General Approach to Modeling of Non-Contact Seals and Their Effect on the Dynamics of a Centrifugal Machine Rotor

The basics of sealing and its connection with the dynamics of centrifugal machines are described. Modeling, calculation and construction of packing and mechanical seals are presented. Designs, models and calculation methods of non-contact seals, as well as analysis of their infl uence on the vibration state of centrifugal machine rotors, are considered. Directions for improving seals are proposed. The general principles of the construction of complex sealing systems are presented. 

Sealing systems and dynamics of centrifugal machines

Using the finite volume method, the problem of a three-dimensional fluid flow through a three-shaft seal of a high pressure centrifugal pump at different values of radial shaft displacements has been solved. Numerical calculations were carried out without taking into account deformation of seals under the influence of uneven pressure distribution. Pressure distributions, leakage values and hydrodynamic radial forces were obtained depending on the magnitude of the eccentricity. As a result of numerical calculations, the dependences of the radial forces on the radial shaft displacement were constructed and the hydrostatic stiffness coefficient was determined. These dependencies were also obtained using analytical equations. The obtained numerical results differ from the theoretical ones less than 5%. It should also be noted that the application of the three-gap seal significantly reduces leakage compared to homogeneous and double-layer seals, as well as increases the radial force stiffness, which in its turn provides a low level of rotor vibration.

Oleksandr Pozovnyi

Papers

Calculation of Hydrostatic Forces of Multi-gap Seals and Its Dependence on Shaft Displacement