Friedrich-Alexander-Universität Erlangen-Nürnberg

Dynamic Light Scattering Lab (DLS)

Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP)

The Dynamic Light Scattering Labs located in the SAOT building are part of the Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP) headed by Prof. Dr.-Ing. habil. Andreas Paul Fröba.

One of the major prerequisites for optimum apparatus and process design in energy and process engineering is the knowledge of exact thermophysical properties, especially of transport coefficients. The working unit of Prof. Fröba provides modern methods for the scientific and industrial determination of thermophysical properties. Dynamic light scattering (DLS) techniques allow for high-accuracy and, in some cases, simultaneous determination of a large number of thermophysical properties of transparent fluids over a wide range of conditions without applying macroscopic gradients. For the determination of binary diffusion coefficients of gases, a Loschmidt cell combined with holographic interferometry is also available. Other conventional measurement devices used in the working unit are a guarded parallel plate instrument developed for the determination of thermal conductivity, a vibrating tube densimeter as well as equipment for measuring surface tension, surface free energy, and the refractive index.

Further topics of the working unit mainly focus on the investigation and development of methods for heat transfer enhancement in technical systems. Thus, the efficiency of whole processes can be significantly improved. One example is the experimental and theoretical investigation of condensation heat transfer on tubes and in tube bundles as well as the promotion of dropwise condensation of steam. Furthermore, a new modelling approach with respect to the effective thermal conductivity of nanofluids has been developed recently. Other technical applications studied in the working unit in finished projects are water separation systems in air conditioning as well as seawater desalination systems.

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Lab History

The first Dynamic Light Scattering (DLS) experiments representing the origin of the current activities within the DLS-Lab were initiated by Prof. Leipertz at the Ruhr-University Bochum. Since 1989, when Prof. Leipertz founded the Chair of Engineering Thermodynamics (LTT), these activities have been continued at the University of Erlangen-Nuremberg. After the excellence cluster SAOT had been initialized in 2006, the DLS setups were used for SAOT research in the labs at LTT until they could be moved to the new SAOT buildings at the Röthelheim-Campus in January 2009. The DLS equipment was continuously improved to the state of the art. Nevertheless, equipment used in 1989 is still available to give access to the basics and the very beginning of DLS experiments.

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Main scope

Besides a continuous improvement of the DLS measurement technique, the DLS-Lab located at SAOT concentrates on the property analysis for media and working fluids which are of interest for energy and chemical engineering. It is the intention of the DLS Group to realize interdisciplinary studies by improving and applying the DLS method for, e.g.,

  • ionic liquids
  • bio-medical tissue
  • liquid-gas systems
  • near-critical systems or
  • crude oil - asphaltenes.

 

These studies are the basis for durable collaborations with manifold industrial and academic partners such as the Petroleum Institute (PI) in Abu Dhabi, Solvay GmbH or the Institute of Chemical Reaction Engineering (CRT) in Erlangen.

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DLS - DYNAMIC LIGHT SCATTERING

DLS provides unique options for the absolute determination of a large number of transport and other thermophysical properties with a single experimental setup. This non-invasive method is suitable for analyzing fluids in thermodynamic equilibrium. Research performed in the DLS-Lab within the past 15 years significantly contributed to the development of the method with respect to applicability and accuracy. Today, DLS is a standard technique for the determination of thermophysical properties of dense fluids.

Conventional DLS analyzes Rayleigh and Brillouin light scattering processes governed by microscopic fluctuations in bulk fluids. Thermophysical properties which can directly be accessed by DLS are thermal diffusivity, sound speed, sound attenuation, mutual diffusivities for binary mixtures, and the Landau-Placzek ratio.

Addition of spherical particles with defined diameter allows the determination of the particle diffusion coefficient and the dynamic viscosity of the liquid. Vice versa, mean particle sizes and particle size distributions can be measured for stable dispersions with known viscosity.

Applying DLS for phase boundaries or liquid surfaces (Surface Light Scattering, SLS), the kinematic viscosity and - with available density data - the surface tension can be probed simultaneously. In current efforts to advance the SLS technique, the analysis of the properties of opaque liquids is of interest.

WATCH THE BROWNIAN MOTION

Further thermophysical properties which can be derived from DLS results are, e.g., isochoric and isobaric heat capacities, bulk viscosity, isentropic compressibility, and the isentropic exponent. DLS is used at SAOT for analyzing dense fluids in a wide temperature range from –40°C to +500°C at pressures up to 200 bar. Nevertheless, this non-invasive technique can also be applied for more extreme conditions such as high temperature melts.

Literature

A. P. Fröba, A. Leipertz, Diffusion measurements in fluids by dynamic light scattering, Diffusion Fundamentals 2, 63.1-63.25 (2005).

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