Focus and Strategy
The main focus of the research activities at AOT-TP lies on the development and application of various methods for the accurate determination of thermophysical properties of fluids of interest for chemical and energy engineering. This includes both experimental and theoretical approaches where our strategy is to combine the benefits of the different methods. At AOT-TP, experimental research includes the application and development of several conventional and optical methods with the aim of accessing broad ranges of thermodynamic states and minimizing experimental uncertainties. The obtained measurement results are used as a reference database for the validation of theoretically determined thermophysical property data, where the current focus lies on the application and further development of modecular dynamics (MD) simulations for this purpose. One benefit of the theoretical methods is that they can also be applied for thermodynamic states that are difficult to access in experiments. As MD simulations also provide information on molecular interactions between the involved species, they can be employed for finding or corroborating explanations for specific behaviors of experimentally determined property data. By a systematic selection of fluid systems to be studied, experimental and theoretical results are combined to derive structure-property relationships with the aim of developing predictive models for thermophysical properties of arbitrary systems which should be suitable for their application in engineering practice. Current efforts also aim at opening new research fields related to heat transfer. This area is already closely linked to the competences available at AOT-TP owing to the extensive investigation of thermal transport properties and wetting behavior as well as previous activities of institute members in experimental investigation and modelling of condensation heat transfer.
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.
Recent research activities related to heat transfer comprise different directions. For example, an analytic model for the effective thermal conductivity of heterogeneous systems such as nanofluids has been developed and undergoes further refinements. In addition, current efforts aim at checking the feasibility of the promotion of dropwise condensation of working fluids with low surface tension by suitable surface modifications. Last but not least, heat transfer modelling activities for different applications such as condensation on tubes as well as processes where contact resistances between solids are important are in preparation.
In the following, some selected ongoing and finished projects representing the research activities are summarized. Links to the project summaries providing more detailed information are included.
- Thermophysical properties of long-chained hydrocarbons, alcohols, and their mixtures with dissolved gases (funded by DFG; details)
- Development of a high-speed shadowgraph for the accurate and simultaneous determination of multiple transport properties of fluid mixtures under high pressures and high temperatures (funded by DFG; details)
- Characterization of molecular diffusion in liquids with dissolved gases (funded by DFG; details)
- Accurate determination of binary gas diffusion coefficients by using laser-optical measurement methods and molecular dynamics simulations (funded by DFG; details)
- Characterization of microemulsions by dynamic light scattering and Raman spectroscopy (funded by BMWi; details in German)
- Diffusion coefficients in mixtures related to surrogate fuels containing biogenic compounds (part of a project funded by AiF; details in German for the complete project)
- Model-based analysis of diffusion experiments in binary gas mixtures in a Loschmidt cell (funded by DFG; details)
- Lubricant-refrigerant mixtures: Wetting behavior and interfacial tension (funded by FKT)
- Diffusion coefficients of gas mixtures using a Loschmidt cell combined with holographic interferometry (funded by DFG; details)
- Diffusion coefficients of refrigerant-lubricant mixtures by dynamic light scattering (funded by FKT; details in German and English, click “hier” on linked website)