Search

The present article summarizes experimental and theoretical considerations required for a proper use of dynamic light scattering (DLS) for the measurement of transport properties of fluids. It addresses not only recent advancements of the method, but also aims to provide recommendations to researchers who intend to apply the technique in the future. As outlined in this study, DLS is based on the analysis of scattered light governed by microscopic statistical or periodic fluctuations that originate from the thermal movement of molecules and/or particles at macroscopic thermodynamic equilibrium. The dynamics of these hydrodynamic fluctuations in the bulk of fluids or at their phase boundaries are related to the underlying diffusive processes and, thus, to the associated transport properties, and are reflected by the time-dependent correlation function of the scattered light intensity. The fundamentals of this type of detection, known as photon correlation spectroscopy (PCS), will be discussed in the present contribution in some more detail. It is emphasized that the experiments need to be designed carefully in accordance with theory in order to assign the measurement signals to the corresponding hydrodynamic fluctuations. If the necessary conditions are fulfilled, DLS allows the accurate determination of several transport properties including kinematic and dynamic viscosity, thermal diffusivity, mutual diffusivity, and sound attenuation, which may be accessed together with other thermophysical properties such as speed of sound and surface or interfacial tension. In some instances, also the simultaneous determination of several transport properties is possible. With the exception of the sound attenuation, expanded uncertainties for the mentioned transport properties down to 1 % can be achieved for various types of fluid systems over a wide range of thermodynamic states up to elevated temperatures and pressures as well as in the vicinity of critical points. This performance and versatility of the DLS technique is documented in the present study by highlighting measurement examples from recent thermophysical property research on different classes of working fluids relevant for process and energy technology. [ABSTRACT FROM AUTHOR]

This review deals with the investigation of the ultrasonic velocity in organic liquids on the saturation curve and with analysis of the results obtained at the Kursk State University - KGU (before that, Kursk State Pedagogical Institute - KGPI) during the period from 1969 to the present day. Much attention is given to the description of the procedure of measurement of the sound velocity by the pulse-phase method developed at the Laboratory of Molecular Acoustics of the KGU and to the estimation of measurement errors. The data on the sound velocity along the saturation curve in a wide temperature range for three classes of organic liquids (saturated hydrocarbons, aliphatic alcohols, and aromatic hydrocarbons) are given in the form of tables. Characteristic features of the behavior of the sound velocity and adiabatic compressibility of liquid in the vicinity of the critical point are investigated, and the possibility of using the acoustic data for the calculation of the thermodynamic properties of liquids is studied. [ABSTRACT FROM AUTHOR]

The interaction of light and matter leads to the scattering of light and the scattered light carries information about the thermodynamic properties of the matter. The light scattered on dilute gases carries far more information about the gas than is comprised within the Navier-Stokes-Fourier theory of gases. It takes extended thermodynamics of many moments to satisfactorily describe the characteristic features of such light quantitatively. [ABSTRACT FROM AUTHOR]

In this paper I place physics teaching, and the inclusion of the history of physics into teaching, within a wide context. I start from the conviction that there are considerable changes ahead in the life circumstances of people in western industrial societies. This expectation should influence our aims of education generally, and in particular the aims of physics teaching. The paper does not offer final solutions, but analyses the situation and thereby argues for a change in perspective in physics teaching. The main idea is that physics teaching has to solve the problem of balancing seemingly incompatible needs, for example, conveying a stock of stable, dependable physics knowledge to students, and on the other hand to train them to see their physics knowledge within varying contexts of change. It is argued that the history of physics can be of high value in solving this problem. [ABSTRACT FROM AUTHOR]