Krzysztof Wieja

Determination of physicochemical properties of diacylglycerol oil at high pressure by means of ultrasonic methods.

The purpose of the paper is to address, using ultrasonic methods, the impact of temperature and pressure on the physicochemical properties of liquids on the example of diacylglycerol (DAG) oil. The paper presents measurements of sound velocity, density and volume of DAG oil sample in the pressure range from atmospheric pressure up to 0.6GPa and at temperatures ranging from 20 to 50°C. Sound speed measurements were performed in an ultrasonic setup with a DAG oil sample located in the high-pressure chamber. An ultrasonic method that uses cross-correlation method to determine the time-of-flight of the ultrasonic pulses through the liquid was employed to measure the sound velocity in DAG oil. This method is fast and reliable tool for measuring sound velocity. The DAG oil density at high pressure was determined from the monitoring of sample volume change. The adiabatic compressibility and isothermal compressibility have been calculated on the basis of experimental data. Discontinuities in isotherms of the sound speed versus pressure point to the existence of phase transitions in DAG oil. The ultrasonic method presented in this study can be applied to investigate the physicochemical parameters of other liquids not only edible oils.

Propagation of ultrasonic Love waves in nonhomogeneous elastic functionally graded materials

This paper presents a theoretical study of the propagation behavior of ultrasonic Love waves in nonhomogeneous functionally graded elastic materials, which is a vital problem in the mechanics of solids. The elastic properties (shear modulus) of a semi-infinite elastic half-space vary monotonically with the depth (distance from the surface of the material). The Direct Sturm-Liouville Problem that describes the propagation of Love waves in nonhomogeneous elastic functionally graded materials is formulated and solved by using two methods: i.e., (1) Finite Difference Method, and (2) Haskell-Thompson Transfer Matrix Method. The dispersion curves of phase and group velocity of surface Love waves in inhomogeneous elastic graded materials are evaluated. The integral formula for the group velocity of Love waves in nonhomogeneous elastic graded materials has been established. The effect of elastic non-homogeneities on the dispersion curves of Love waves is discussed. Two Love wave waveguide structures are analyzed: (1) a nonhomogeneous elastic surface layer deposited on a homogeneous elastic substrate, and (2) a semi-infinite nonhomogeneous elastic half-space. Obtained in this work, the phase and group velocity dispersion curves of Love waves propagating in the considered nonhomogeneous elastic waveguides have not previously been reported in the scientific literature. The results of this paper may give a deeper insight into the nature of Love waves propagation in elastic nonhomogeneous functionally graded materials, and can provide theoretical guidance for the design and optimization of Love wave based devices.

Evaluation of viscoelastic parameters of surface layers by ultrasonic Love waves

Simultaneous determination of the rheological parameters of viscoelastic surface layers is very important in many applications such as: sensors, geophysics, seismology, and in the NDT of materials. Love wave energy is concentrated near the waveguide surface, so that Love waves are especially suited to study the material properties of surface layers. In this work, the Direct Sturm-Liouville Problem for the Love wave propagation in a layered viscoelastic waveguide have been presented and solved. Next, the Inverse Problem was created and solved as an Optimization Problem. The adequately formulated objective function that depends on the elastic and viscoelastic parameters of a waveguide of the Love wave and the experimental data was used. The solution of the Inverse Problem allows to determine unknown values of the viscosity and shear elasticity of a viscoelastic medium from measurements of the dispersion curves of Love waves.

Ultrasonic investigation of physicochemical properties of liquids under high pressure

High pressure research of the physicochemical properties of liquids has been stimulated by the fast development of such technologies as biodiesel production, high-pressure food processing and conservation, modification of biotechnological properties. Monitoring and studying liquid viscosity and ultrasonic wave velocity in liquids as a function of pressure and temperature enable to evaluate many important physicochemical parameters of liquids. These methods allow also insight into the phenomena governing the microstructural modifications occurring in treated substances, i.e. phase transitions. The knowledge of physicochemical properties (e.g. density, relaxation time, internal pressure or free volume) of pressurized substances is essential for understanding, design and control of the process technology. Measurements were conducted on the example of diacylglycerol oil (DAG oil), that is an important constituent of oils and fats.

The influence of rheological parameters of viscoelastic liquids on the propagation characteristics of ultrasonic Love waves

Progress in materials engineering has led to development of new materials with improved functional characteristics. One of the new types of materials introduced into industrial practice are plastics and polymers. These materials exhibit rheological (viscoelastic) properties, which combine simultaneously the properties of liquids and solids. Due to their attractive features, such as low specific weight, high resistance to chemical agents, cost effectiveness etc. these materials are widely used in chemical, automotive, aviation and space industry. Thus, it is very important to develop new, robust and accurate methods to measure the rheological parameters (viscosity η, elasticity μ and density ρ) of plastics and polymers. The conventional mechanical methods used so far to this end are outdated, time consuming, and cumbersome. To overcome this problems, the authors propose the use of ultrasonic methods that employ surface Love waves, what is a novelty.

Investigation of high-pressure phase transitions in biofuels by means of ultrasonic methods

The fundamental goal of this work is to verify the hypothesis of the existence of high-pressure phase transitions in biofuel components on the example of rapeseed fatty acid methyl esters (RME), by using ultrasonic methods. in a wide range of pressures (from atmospheric pressure to 300 MPa) and for various temperatures from 5 to 20 °C. Investigation of phase transitions in biofuels at high pressures is of great importance in the design of injection systems in modern diesel engines (common rail). Direct examination of phase transitions in liquids under high pressure, using classical methods, is very difficult. To overcome this disadvantage, the authors applied ultrasonic methods (viscosity measurement), which in contrast to the classical methods allow in a relatively simple way the investigation of high-pressure properties of liquids. Viscosity was measured by the original method that uses ultrasonic surface waves of the Bleustein-Gulyaev type, developed by the authors at the Institute of Fundamental Technological Research in Warsaw. From the measured viscosity isotherms, the occurrence of high-pressure phase transitions in methyl esters were evaluated.

Inverse Method for Determining Profiles of Elastic Parameters in the Functionally Graded Materials using Love Waves

This paper presents the use of SH (Shear Horizontal) surface Love waves to determine the distributions of elastic parameters in nonhomogeneous Functionally Graded Materials. The advantage of Love waves applied to investigate the elastic properties of materials is that the Love wave energy (in contrast to the other types of waves, e.g., plate Lamb waves) is concentrated in the vicinity of the surface layer. The penetration depth of the SH surface Love waves depends on the frequency. Therefore, Love waves are particularly suitable for investigating the profiles of the mechanical properties in nonhomogeneous Graded Materials. Direct Problem (Direct SturmLiouville Problem) that describes the propagation of Love waves in nonhomogeneous graded materials has been formulated and solved numerically by applying the Transfer Matrix Method. The Inverse Procedure (Inverse Sturm-Liouville Problem) for determining the distribution of elastic properties versus depth in the nonhomogeneous materials has been developed. Love wave dispersion curves in nonhomogeneous graded materials were evaluated numerically (synthetic data). Using the evaluated dispersion curves of Love waves and a developed Inverse Procedure the distributions of elastic shear coefficient as a function of depth (distance from the surface of the material into the bulk) in a heterogeneous surface layer deposited on a homogeneous substrate have been evaluated. Power type profiles (i.e., root square, linear and quadratic) of the shear elastic coefficient in the surface layer were considered. The results of this study can be useful in the investigation of elastic properties of Graded Materials in electronics as well as in geophysics and seismology.

Inverse method for evaluation of elastic parameters in functionally graded materials using ultrasonic Love wave

The aim of this study was to evaluate the inverse procedure to determine profiles (as a function of depth) of the mechanical properties of inhomogeneous FGM resulting from the application of various technological processes of surface treatment. First, the Direct Sturm-Liouville Problem for Love waves propagating in elastic graded materials with various profiles of the shear stiffness as a function of the distance from the surface, has been solved using the Finite Difference Method and Transfer Matrix Method (Haskell-Thompson method). Love wave dispersion curves were evaluated in the frequency range from 4 to 23 MHz. The Inverse Problem was formulated as an Optimization Problem with appropriately constructed objective function that depended on the material properties of an elastic waveguide of the Love wave and the experimental data. To minimize the considered objective function, optimization procedures of the Nelder-Mead type from Scilab software package were employed.

Ultrasonic studies of physicochemical parameters of biofuels in a broad range of pressures and temperatures

The aim of the study was to investigate the phase transitions in biofuel components by using ultrasonic methods on the example of methyl esters of fatty acids, in a wide range of pressures (from atmospheric pressure to 400 MPa) and for various temperatures from 5 to 20 °C. Investigation of phase transitions in biofuels at high pressures is of great importance in the design of injection systems in modern diesel engines (common rail). Direct examination of phase transitions in liquids under high pressure, using classical methods, is very difficult. To overcome this disadvantage, the authors applied ultrasonic methods (viscosity measurement), which in contrast to the classical methods allow in a relatively simple way the investigation high-pressure properties of liquids. Viscosity was measured by the original method that uses ultrasonic surface waves of the Bleustein-Gulyaev type, developed by the authors at the Institute of Fundamental Technological Research in Warsaw. From the measured viscosity isotherms, the occurrence and kinetics of high-pressure phase transitions in methyl esters were evaluated.

Density and viscosity of liquids determination using an inverse method for Love wave propagation

The aim of this work was to establish an inversion procedure for the simultaneous determination of the viscosity and density of liquids. To this end, measurements of dispersion curves of the phase velocity and attenuation of shear horizontal Love waves were applied. Love waves propagate in an elastic layered waveguide covered on its surface with an investigated viscous (Newtonian) liquid. Firstly, the Direct Sturm-Liouville Problem of the Love wave propagation in a such waveguide was formulated and solved. Subsequently, the Inverse Problem was formulated and solved as an Optimization Problem. The appropriately constructed objective function that depends on the material properties of a waveguide of the Love wave, material properties of an investigated liquid (viscosity and density), and the experimental data was employed. The simultaneous determination of both liquid density and viscosity is important in the monitoring of technological processes in many industries (e.g. chemical, petroleum, pharmaceutical industry) as well as in geophysics.