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Abstract:
In many technological processes (e.g., in the chemical, petrochemical, food, and plastics industries), liquids are subjected to high pressures and temperatures. Therefore, knowledge of their thermodynamic properties is essential for understanding, design, and control of the process technology. Direct evaluation of the thermodynamic parameters of liquids under high pressure, using conventional methods, is very difficult. Therefore, the application of these methods in industrial conditions, particularly in on-line control of the technological parameters of liquids, is practically impossible. Ultrasonic methods (e.g., sound speed measurements) are very suitable for this purpose because of their simplicity and accuracy. The sound velocity is closely related to numerous thermodynamic properties of liquids. The objective of this paper is to address the influence of temperature and pressure on the thermodynamic parameters of liquids, using the example of diacylglycerol (DAG) oil, employing ultrasonic methods. In this paper, we present ultrasonic velocity and density measurements (performed by the authors) in DAG oil over a range of pressures and temperatures. On the basis of experimental results (the sound velocity and liquid density versus pressure and temperature) a series of DAG oil thermodynamic parameters such as specific heat ratio, intermolecular free path length, Van der Waals constant b, surface tension, and effective Debye temperature were evaluated as functions of pressure and temperature.

Keywords:
Thermodynamical properties of liquid, High pressure food processing, ultrasonic methods, sound velocity, surface tension

Abstract:
High-pressure processing is a powerful technology for food preservation. The knowledge of foods properties in the high-pressure range is important to develop and optimize such processes by means of mathematical modeling and simulation. Ultrasonic methods are rapid, non-invasive and can be used to characterize foods like edible oils (e.g., composition, purity, and quality assessment). In this paper, they were applied for the investigation of physicochemical properties of olive oil at high pressure at different temperatures. The sound wave velocity was measured by the pulse-transmission method and the corresponding oil density was additionally determined from the monitoring of sample volume change. Measurements were conducted in the pressure range up to 600 MPa, for temperatures from 20 to 50°C. Intermolecular free length, isothermal and adiabatic compressibility versus pressure were calculated using measured sound speed and density isotherms. Discontinuities in the measured isotherms of sound speed and density versus pressure indicate the presence of liquid-to-solid phase transitions. The kinetics of the liquid-to-solid phase transition was also investigated. The transformation times of olive oil augment with increasing temperature. This study can be broadened to other liquid foodstuffs to investigate the influence of temperature on their physicochemical properties at high pressure.

Keywords:
Physicochemical properties, Intermolecular free length, Ultrasonic velocity, High-pressure food processing, Olive oils

Abstract:
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 0.6 GPa 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.

Keywords:
Ultrasonic methods, Sound velocity, Phase transitions, High pressure food processing, Physicochemical parameters

Abstract:
The nonlinearity parameter B/A is a measure of the nonlinearity of the equation of state for a fluid. The nonlinearity parameter B/A is a physical parameter often used in acoustics, from underwater acoustics to biology and medicine. It can provide information about structural properties of the medium, internal pressure and inter-molecular spacing. The thermodynamic method has been applied for determination of B/A parameter in diacylglycerol (DAG) oil as a function of pressure at various temperatures. Isotherms of the density and phase velocity of longitudinal ultrasonic wave as a function of pressure have been measured. Using the thermo- dynamic method along with measured isotherms of sound speed and density, the nonlinearity parameter B/A (for DAG oil) was evaluated as a function of pressure (up to 220 MPa) at various temperatures ranging from 20 to 50◦C.

Keywords:
Nonlinearity parameter B/A, thermodynamic method, high pressure, longitudinal ultrasonic wave velocity

Abstract:
The influence of high pressure on viscosity and compressibility of diacylglycerol (DAG) oil has been presented in this paper. The investigated DAG oil was composed of 82% of DAGs and 18% TAGs (triacylglycerols). The dynamic viscosity of DAG was investigated as a function of the pressure up to 400 MPa. The viscosity was measured by means of the surface acoustic wave method, where the acoustic waveguides were used as sensing elements. As the pressure was rising, the larger ultrasonic wave attenuation was observed, whereas amplitude decreased with the liquid viscosity augmentation. Measured changes of physical properties were most significant in the pressure range near the phase transition. Deeper understanding of DAG viscosity and compressibility changes versus pressure could shed more light on thermodynamic properties of edible oils.

Keywords:
DAG viscosity, compressibility, phase transitions, transmitted and scattered light

Abstract:
In this paper, phase transitions in diacylglycerol (DAG) oil are investigated by using an ultrasonic method for measuring viscosity. Viscosity of diacylglycerol (DAG) oil is measured over a wide range of hydrostatic pressures up to 500 MPa, and at temperatures ranging from 10 to 40 °C. The observed discontinuities in the viscosity versus pressure curves (isotherms) indicate phase transitions. An original ultrasonic method that uses the surface acoustic Bleustein–Gulyaev (B–G) wave was employed to measure the viscosity of DAG oil at high pressure range. This method allows for fast and reliable measurement of DAG oil viscosity along various isotherms. Moreover, the kinetics of the observed phase transformations at various temperatures was analyzed. The results of the study are a novelty, and can be helpful in evaluating the physicochemical properties of edible oils.

Keywords:
Edible oils, Ultrasonic methods, Diacylglycerols, Viscosity, Phase transitions, High pressure

Abstract:
In this work, the variation of sound velocity with hydrostatic pressure for oleic acid is evaluated up to 350MPa. During the measurement, we identified the phase transformation of oleic acid and the presence of the hysteresis of the dependence of sound velocity on pressure. From the performed measurements, it can be seen that the dependence of sound velocity on pressure can be used to investigate phase transformations in natural oils. Ultrasonic waves were excited and detected using piezoelectric LiNbO3(Y-36 cut) 5MHz transducers. The phase velocity of the longitudinal ultrasonicwaveswas measured using a cross-correlation method to evaluate the time of flight.

Keywords:
Sound velocity, oleic acid, high pressure, phase transition

Abstract:
A new ultrasonic method of viscosity measurement at a high-pressure condition has been presented. The method is based on the Love wave amplitude measurement. The same electronic setup as in the Bleustein– Gulyaev (B–G)wave method applied by the authors recently for a high-pressure measurementwas adopted. The new transducers were made of metallic materials which make them more reliable at high-pressure conditions. The method has been successfully applied for the viscosity measurement of some triglycerides at high-pressure conditions up to 1GPa. The results have been compared with the earlier results obtained using B–G waves. This comparison has shown that Love wave method sensors are more reliable than B–G wave sensors and cheaper in fabrication, although the sensitivity of Love wave sensors was lower. During the measurement, the phase transitions in the investigated liquids were observed.

Keywords:
Love SH waves, viscosity, phase transitions, sensors

Abstract:
In this paper, a new method for measuring the viscosity of liquids at high pressure is presented. To this end the authors have applied an ultrasonic method using the Bleustein-Gulyaev (BG) surface acoustic wave. By applying the perturbation method, we can prove that the change in the complex propagation constant of the BG wave produced by the layer of liquid loading the waveguide surface is proportional to the shear mechanical impedance of the liquid. In the article, a measuring setup employing the BG wave for the purpose of measuring the viscosity of liquids at high pressure (up to 1 GPa) is presented. The results of high-pressure viscosity measurements of triolein and castor oil are also presented. In this paper the model of a Newtonian liquid was applied. Using this new method it is also possible to measure the viscosity of liquids during the phase transition and during the decompression process hysteresis of the dependence of viscosity on pressure.

Keywords:
Bleustein-Gulyaev (B-G) waves, high pressure, viscosity measurements, phase transitions

Abstract:
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.

Keywords:
High pressure phase transitions, physicochemical parameters of biofuels, ultrasonic viscosity measurements, rapeseed methyl esters

Abstract:
In many technological processes (e.g. in chemical, petrochemical, food and plastics industry) liquids are subjected to high pressures and temperatures. Therefore knowledge of their thermodynamic properties is essential for understanding, design and control of the process technology. Direct evaluation of thermodynamic parameters of liquids under high pressure, using conventional methods, is very difficult. Therefore, these methods are useless in industrial conditions, particularly in on-line control of the technological parameters of liquids. Ultrasonic methods (e.g., sound speed measurements) due to their simplicity and accuracy are very suitable for this purpose. The sound velocity is closely related with numerous thermodynamic properties of liquids. In this paper we report ultrasonic velocity and density measurements (performed by the authors) in diacylglycerol (DAG) oil over a range of pressures and temperatures. On the basis of experimental results (the sound velocity and liquid density versus pressure and temperature) the thermal expansion coefficient, specific heat capacity at constant pressure, isothermal and adiabatic compressibility of DAG oil were calculated as a function of pressure and temperature.

Keywords:
Themodynamic parameters of liquids, high pressure, ultrasonic velocity, density, compressibility

Abstract:
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.

Keywords:
Physicochemical parameters of liquids, high pressure, ultrasonic velocity, viscosity of liquids, DAG oil

Abstract:
The nonlinearity parameter B/A is a measure of the nonlinearity of the equation of state for a fluid. It plays a significant role in acoustics, from underwater acoustics to biology and medicine. The nonlinearity parameter is important because it determines distortion of a finite amplitude wave propagating in the fluid. Moreover, it can be related to the molecular dynamics of the medium and it can to provide information about structural properties of medium, internal pressures, clustering, intermolecular spacing, etc. Importance of the B/A parameter increases with the development of high-pressure technologies. The thermodynamic method has been applied for determination of B/A parameter in diacylglycerol (DAG) oil as a function of pressure at various temperatures.

Keywords:
Nonlinearity parameter B/A, Thermodynamic method, ultrasoniv velocity, high pressure

Abstract:
Monitoring and studying the pressure effect on liquid properties are becoming increasingly important in food, chemical, cosmetic and pharmaceutical industry as well as in laboratory practice. Accurate thermodynamic data in liquids as a function of pressure are required for studies the structure of liquids as well as for various engineering applications. Direct measurement of thermodynamic parameters is very difficult. The velocity of sound is related to many thermodynamic parameters and can be measured relatively simple. In this work the variation of sound velocity and isothermal compressibility with hydrostatic pressure for triolein is evaluated up to 650 MPa. During the measurement we stated the phase transformation of triolein and the presence of the hysteresis of the dependence of sound velocity on pressure. To the authors' knowledge, the measurement of the sound velocity of liquids under high pressure during the phase transition is the novelty. From the performed measurements it results that the dependence of sound velocity on pressure can be used to investigate phase transformations in natural oils.

Keywords:
Vegetable oils, Velocity measurement, Phase measurement, Ultrasonic variables measurement, Thermodynamics, Liquids, Pressure measurement, Chemical industry, Monitoring, Pressure effects

Abstract:
The high-pressure properties of triolein, a subject of extensive research at the Faculty of Physics of Warsaw University of Technology (WUT) has been enhanced by the results of viscosity measurements within the pressure range up to 0.8 GPa. For the measurement the authors have adopted a new ultrasonic method based on Bleustein-Gulyaev waves, successfully developed earlier for the low pressures in the Section of Acoustelectronics of the Institute of Fundamental Technological Research. The measurements have shown: 1) Exponential rise of viscosity with pressure up to 0.5 GPa. 2) Extraordinary increment of viscosity at constant pressure during phase transition. 3) Further exponential rise of viscosity with pressure of the high-pressure phase of triolein. 4) The pressure exponents of the viscosity of both phases were different (the high-pressure phase had much smaller exponent). 5) The decomposition of the high-pressure phase due to the slow-decompression has shown very large hysteresis of viscosity on pressure dependence.

Keywords:
Bleustein-Gulyaev (B-G) waves, high-pressure phase transitions, viscosity measurements, triolein

Abstract:
The pressure change of viscosity of castor oil have been measured by ultrasonic method within the range of pressure up to 0.9 GPa. For the measurement, the authors have applied a new ultrasonic method based on Bleustein-Gulyaev (B-G) waves. For the lower pressures (up to 0.3 GPa) the results have been compared with earlier results obtained by falling body method, whereas for the higher pressure range results were compared with those obtained by the flow type viscometer. The measurements have shown: 1. Exponential rise of viscosity with pressure up to 0.4 GPa according to the Barus formula. 2. Extraordinary increment of viscosity at constant pressure during phase transition. 3. The decomposition of the high pressure phase during the decompression process have shown very large hysteresis of viscosity on pressure. 4. After the decompression process the viscosity lasts higher then a initial value for several hours.

Keywords:
Bleustein-Gulyaev (B-G) waves, high pressure, phase transitions, viscosity measurements