The research fields at AOT-TP are strongly interlinked. Nevertheless, the corresponding topics can be structured as follows.
Experimental determination of thermophysical properties
Several optical, but also conventional methods are applied to obtain reliable thermophysical property data for a wide range of thermodynamic states. A certain focus lies on the measurement of transport properties including mass diffusion coefficients, thermal diffusivity, thermal conductivity, viscosity, and Soret coefficients. Equilibrium properties accessible with the instrumentation available at AOT-TP are densities, interfacial tensions, speed of sound and sound attenuation, refractive index, and wetting parameters such as contact angles. In addition, the determination of the hydrodynamic size of different kinds of small particles (e.g., solid nanoparticles or droplets in nano- or microemulsions) in heterogeneous systems is possible via the measurement of their translational diffusion coefficient. For a more detailed overview on the measurement methods available at AOT-TP as well as on the accessible thermophysical properties and thermodynamic states, please download our Thermophysical Properties Flyer.
Theoretical determination of thermophysical properties
The theoretical determination of several transport and equilibrium properties of fluids of interest for process and energy engineering is currently focused on the application and further development of MD simulations. Here, available molecular models in the form of force fields are used, but also modified and tested regarding their transferability within specific substance families. The application of MD simulations helps to identify and quantify structure-property relationships which can be used in a next step for the development of prediction methods for specific properties and fluid classes. This development always implies the challenge of keeping the balance between a good applicability in engineering practice and the necessary accuracy.
Development and application of novel measurement methods
Closely associated with its name, the Institute of Advanced Optical Technologies – Thermophysical Properties (AOT-TP) is certainly active in the development and optimization of several – mainly optical – methods for the accurate determination of thermophysical properties also under harsh conditions. In addition to Dynamic Light Scattering (DLS), which has been continuously further developed by the research team of Andreas P. Fröba for its application in the bulk of fluids (also called “conventional DLS”) and to interfaces (also called Surface Light Scattering, SLS), further techniques are currently being established at the institute. They include, e.g., Shadowgraphy for the simultaneous measurement of several transport properties in fluid mixtures as well as Laser-Induced Gratings (LIG, also called Forced Rayleigh Scattering, FRC) applied to the bulk of fluids and interfaces. Furthermore, Raman spectroscopy is used for the determination and monitoring of mixture compositions, while the Beam Deflection Method and other approaches are used to determine the refractive index. Current conceptual studies also prepare the development of industrially applicable sensors based on light scattering methods. In connection with the development and application of optical measurement methods, funding of the major instrumentation “Setup for the Optical Measurement of Transport Properties and Further Thermophysical Properties of Fluids” by DFG (details) is greatfully acknowledged.
Heat Transfer
Recent research activities related to heat transfer comprise different directions. Measurements on an apparatus allowing for a systematic investigation of the condensation of hydrocarbon-based refrigerant mixtures on horizontal tubes and corresponding bundles contribute for the development of respective heat-transfer models. Furthermore, an analytic model for the effective thermal conductivity of heterogeneous systems such as nanofluids has been developed and undergoes further refinements. Additional research aims at a fundamental investigation of heat transfer for dropwise condensation of working fluids with low surface tension on suitable surface modifications and modeling the heat transfer in the complex microscopic contact situation of tool and workpiece in hot stamping.