Milada Kozubková

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.

Dispersion of Light and Heavy Pollutants in Urban Scale Models: CO2 Laser Photoacoustic Studies

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO2 laser photoacoustic spectroscopy in the region of the atmospheric window (9–10 μm). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

Methods of experimental investigation of cavitation in a convergent - divergent nozzle of rectangular cross section

Abstract Cavitation is a phenomenon with both positive and negative effects and with dynamic manifestations in hydraulic, food, chemical and other machinery. This article deals with the detection and dynamic behavior of cavitation clouds in water flows through a rectangular cross-section convergent-divergent nozzle. Cavitation was measured by methods applicable in engineering practice. Pressure, flow rate, noise, vibration, and amount of air dissolved in the liquid were measured and cavitation region was recorded with a high-speed camera. Evaluation of acquired images in connection with measured pressure pulsations and mechanical vibrations was performed with the use of the FFT method. In certain cases, dimensionless parameters were used to generalize the measurements. The results will be used to specify multiphase mathematical cavitation model parameters.

Methodology of Cavitation Modelling in Diffusers

Cavitation is undesirable phenomenon occurring mainly in the flow of water in pumps and turbines, and therefore it is necessary to pay attention to it. The purpose is to explore the possibility of the mathematical modelling of the cavitation using Singhal cavitation model, which solves the multiphase flow of water and vapour. The issue can be solved taking into account the non-condensable gas (air). Singhal cavitation model was selected on the basis of good experience in the modelling of dynamic cavitation changes in the Laval nozzle [2], [10]. This article presents two alternatives. The first variant is testing a mathematical model for flow in a simple geometry of the cone. The second variant resolves the formation of cavitation rope behind vortex generator and the results are compared with experiment.

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.

Experiments and mathematical models of methane flames and explosions in a complex geometry

The paper focuses on the application of mathematical modeling of methane turbulent combustion in a complex geometry and on the choice of parameters of one-step and two-step chemical kinetics models. Parameters of chemical kinetics have a profound influence on the correct implementation of the combustion mathematical model used in the CFD (computational fluid dynamics) simulation of the methane-air mixture explosion in a family house. Results are compared with experimental measurements.

Urban Air Pollution and Its Photochemistry Studied by Laser Spectroscopic Methods

This work compares approaches both of mathematical and physical modelling of pollutant dispersion in simulated atmospheric boundary layer (ABL) with results of remote sensing of atmospheric pollutants. Measurements were performed over a highway outside a city and in an urban street canyon with extensive traffic under different meteorological conditions (autumn versus summer period). Time-resolved spatial distributions of pollutants (NO2 and O3) were measured by the combined DIAL (differential absorption light detection and ranging)/SODAR (sound detection and ranging) method and using spot analyzers appropriately located on the leeward and windward sides near the urban street canyon bottom. Qualitative agreement was found between the results obtained by remote sensing in the real atmosphere and those obtained by physical modelling in the simulated atmosphere of a wind tunnel for the autumn period. On the other hand, the analysis of the monitoring results and outputs of the physical modelling shows disagreement for the summer period. Besides neglecting the thermal effect during the sunny period, chemical reactions or photochemical processes taking place in the street canyon can affect the dispersion and distribution of pollutants very significantly. To improve the description of the system investigated, the Computational Fluid Dynamics (CFD) environment was tested for a basic implementation of photochemical reactions into the commonly used mathematical models of turbulence and dispersion processes as well.

Diagnostics of Resistance Coefficients and Cavitation of Flow Control Valve

The paper deals with the determination of characteristic as dependence of the valve pressure drop on the flow rate, flow characteristic and cavitation conditions in case of water flow in the flow control valve. Emphasis is put on the utilization of simple, available relationships and measuring for identification of the basic valve coefficients, e.g. loss coefficient, flow rate coefficient and cavitation factor. These coefficients are used for designing of pipe circuits. In this paper there is defined methodology for determining those coefficients and is applied to the modified cone of flow control valve for verification the linear flow characteristic. It is necessary to consider the fact that in various countries the modifications of coefficients are preferred and it is therefore necessary to specify them.

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

Abstract The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fluoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin film deposition. Specifically, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fluoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fluoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fluence profile. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fluoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.