Simona Fialová

Identification and Experimental Verification of the Adhesive Coefficient of Hydrophobic Materials

This work presents a methodology for the determination of adhesive coe cient of a liquid ow over a hydrophobic surface. The starting point for this work was a study, which describes the general boundary condition for shear stress on a general curvilinear surface depending on the adhesive coe cients. The adhesive coe cient is determined on the basis of an experiment that utilizes the motion of a droplet on an inclined plane.

Study of the Adhesive Coefficient Effect on the Hydraulic Losses and Cavitation

The article is focused in three areas. In the first part there are analyzed the adhesion forces at the liquid and solid surface interface. There are shown the measured values of surface energy for different types of surfaces. The value of surface energy is decisive for determining the extent of the surface wettability by the liquid.The second part points to the possible negative effects of partly wettable surfaces, showing susceptibility to cavitation. The third section describes the practical aspects of surface wettability by the liquid. Under the new boundary conditions bases, expressing the effect of adhesion forces, there are determined the centrifugal pump characteristics.

Assessment of cavitation creation depending on the surface wettability

The flow of fluids near the slide surface is analyzed in the work introduction. Surface is considered as partly hydrophobic, depending on the surface energy for different types of material surfaces. There is point out the relationship of the adhesion force to liquid/surface interaction. This creates a new boundary condition, different from the adhesion conditions. On the adhesion force basis is assessing the conditions of cavitation creation, depending on the surface energy change.

Bearing with magnetic fluid and hydrophobic surface of the lining

This work focuses on the setting of the stiffness and damping matrix of the long cylindrical bearing. Additional effects of the electrically conductive fluids are determined on the magnetic induction dependence. The new boundary conditions are used, which express the effect of the adhesion forces between the liquid and the solid surface. The boundary condition allows the definition of the transition from a hydrophobic surface to the hydrophilic one.

Tensors of added damping, stiffness and mass in a thin gap of hydrodynamic machine

The methodology of determining the additional effects of a liquid acting on hydrodynamic machine rotor is presented in the paper. Special attention is paid to the force effects of the liquid inside the hydrodynamic sealing gap. A new mathematical model is derived from which is evident an influence of different parameters of the liquid bond on the additional stiffness, mass and damping.

Analysis of the effect of hydrophobic properties of surfaces in the flow part of centrifugal pumps on their operational performance

The results of experimental studies focused on evaluating the effect of different conditions of wetting of functional surfaces in flow parts of centrifugal pumps (specifically, impellers) used in heat- and watersupply systems on their operational performance are presented. The conditions of interaction of the pumped medium with the impeller surfaces were altered through hydrophobization of functional surfaces that was implemented using the techniques developed at the Moscow Power Engineering Institute and the Brno University of Technology. It is demonstrated that this hydrophobization produced a considerable positive effect and raised the efficiency of pump units based on centrifugal KM pumps of three different form factors produced by ZAO Pompa (Shchelkovo) and a K centrifugal pump produced by Sigma. The efficiency was increased by 2–6% depending on the pump model. The results of experimental studies of the effect of hydrophobization of the surface of a canonical plate-type domain with a working medium flowing longitudinally along it in a hydrodynamic bed (Moscow Power Engineering Institute) are detailed. Two flat plates with a length of 250 mm and a width of 252 mm were studied. The surfaces of these plates had different roughness values, since one of the plates was polished prior to hydrophobization. Different wetting conditions, which were monitored by measuring the contact angle with a KRUSS MobileDrop goniometer, were established after hydrophobization. The obtained experimental data showed that the surface friction of the modified plate with a higher initial roughness (unpolished plate) was reduced by as much as 23%. This result agrees completely with the Cassie hypothesis.

The Cavitation Effect on the Electromagnetic Field

It is generally known, that liquids, including water, are electrically conducting. The electric conductivity magnitude among others depends on the minerals concentration. Using the additives it is possible to increase the electric conductivity.

Flow of Newtonian and non-Newtonian fluid through pipe with flexible wall

This paper solves fluid-structure interaction between flexible wall and two types of fluid. Wall was considered as aorta and was described as hyperelastic material by 5-parameters Mooney-Rivlin model. Fluids and structure were set as incompressible. First fluid was Newtonian and has dynamic viscosity of the blood. Second was non-Newtonian and its viscosity was defined with Carreau rheology model. The aim of this paper is to show a comparison between Newtonian and non-Newtonian fluid flow in pliable vessel.This paper solves fluid-structure interaction between flexible wall and two types of fluid. Wall was considered as aorta and was described as hyperelastic material by 5-parameters Mooney-Rivlin model. Fluids and structure were set as incompressible. First fluid was Newtonian and has dynamic viscosity of the blood. Second was non-Newtonian and its viscosity was defined with Carreau rheology model. The aim of this paper is to show a comparison between Newtonian and non-Newtonian fluid flow in pliable vessel.

Influence of Eccentricity and Angular Velocity on Force Effects on Rotor of Magnetorheological Damper

This article presents the evaluation of force effects on squeeze film damper rotor. The rotor is placed eccentrically and its motion is translate-circular. The amplitude of rotor motion is smaller than its initial eccentricity. The force effects are calculated from pressure and viscous forces which were measured by using computational modeling. Damper was filled with magnetorheological fluid. Viscosity of this nonNewtonian fluid is given using Bingham rheology model. Yield stress is not constant and it is a function of magnetic induction which is described by many variables. The most important variables of magnetic induction are electric current and gap width between rotor and stator. The simulations were made in finite volume method based solver. The motion of the inner ring of squeeze film damper was carried out by dynamic mesh. Numerical solution was solved for five different initial eccentricities and angular velocities of rotor motion.

Application of heterogeneous blading systems is the way for improving efficiency of centrifugal energy pumps

The results of independent research implemented by the teams of authors representing the Brno University of technology (Czech Republic) and Moscow Power Engineering Institute National Research University (Russia) are presented and compared. The possibilities for improving the energy efficiency of slow-speed centrifugal pumps (with a specific speed coefficient ns < 80) widely used in power engineering—in thermal power stations, in heat electric-power stations, in nuclear power plants, and in boiler rooms—were investigated. These are supply pumps, condensate pumps, precharge pumps, etc. The pumps with such values of ns are widely used in some technological cycles of oil-and-gas and chemical industries too. The research was focused on achieving the shape of the pump efficiency characteristics providing a significant extension of its effective working zone and increasing its integrated efficiency. The results were obtained based on new approaches to the formation of a blading system of an impeller of a slow-speed centrifugal pump different from the traditional blading system. The analytical dependences illustrating the influence of individual geometry of a blading system on the efficiency were presented. The possibilities of purposeful changing of its structure were demonstrated. It was experimentally confirmed that use of the innovative blading system makes it possible to increase the pump efficiency by 1–4% (in the experiments for the pumps with ns = 33 and 55) and to extend its efficient working zone approximately by 15–20% (in the experiment for the pumps with ns = 33 and 66). The latter is especially important for the supply pumps of NPP power units. The experimental results for all investigated pumps are presented in comparison with the characteristics of the efficiency provided by the blading systems designed by traditional methods.