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 molecular 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. New research fields have recently been opened in the area of 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. Here, current projects focus on the experimental investigation and modeling of condensation heat transfer of hydrocarbon mixtures on tubes and tube bundles, dropwise condensation of fluids with low surface tension, and the heat transfer between the contacting surfaces of tool and workpiece in hot stamping.
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.
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.
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.
- Experimental investigation of viscosity, interfacial tension, and thermal conductivity of oil-refrigerant mixtures by light scattering and conventional techniques (funded by DFG within the Research Unit (FOR 5595) “Oil-refrigerant multiphase flows in gaps with moving boundaries – Novel microscopic and macroscopic approaches for experiment, modeling, and simulation
- Influence of dissolved hydrogen on the thermophysical properties of organic liquids (funded by DFG; details)
- Influence of the material properties of blowing agent loaded melts on the formation and structure of polymer foams (funded by DFG; details)
- Dropwise condensation heat transfer of fluids with low surface tension (funded by DFG; details)
- Modeling of heat transfer in hot stamping (funded by DFG; details)
- Moderating effects of alcohols on the interfacial tension of multi-phase systems consisting of carbon dioxide and organic solvents (funded by DFG; details)
- Condensation of binary hydrocarbon mixtures on horizontal tubes and tube bundles (funded by BFS; for details visit the BFS website and search for “Kohlenwasserstoffgemischkondensation” (in German only))
- Diffusion in mixtures of water, brine, hydrogen, and methane (contracted research with Shell Global Solutions International BV)
- Effective thermal conductivity of dispersions with a liquid continuous phase (funded by DFG; details)
- Characterization of molecular diffusion in electrolyte systems (funded by DFG; details)
- Development of the shadowgraph method for the accurate determination of diffusivities of fluid mixtures under high pressures and high temperatures (funded by DFG; details)
- Properties of the gas/liquid interface of Interface-enhanced SILP systems (funded by DFG within the Collaborative Research Centre (SFB 1452) “Catalysis at liquid interfaces”; details)
- Characterization of diffusion of nanoparticles (funded by DFG within the Collaborative Research Centre (SFB 1411) “Design of particulate products”; details)
- Thermophysical properties of LOHC systems under conditions relevant for hydrogen release (as a sub-contractor of HI ERN within the LOHC-train project funded by StMWi; details in German and English)
- Thermophysical properties of long-chained hydrocarbons, alcohols, and their mixtures with dissolved gases (completed, 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 (completed, funded by DFG; details)
- Characterization of molecular diffusion in liquids with dissolved gases (completed, funded by DFG; details)
- Accurate determination of binary gas diffusion coefficients by using laser-optical measurement methods and molecular dynamics simulations (completed, funded by DFG; details)
- Characterization of microemulsions by dynamic light scattering and Raman spectroscopy (completed, funded by BMWi; details in German)
- Diffusion coefficients in mixtures related to surrogate fuels containing biogenic compounds (completed, 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 (completed, funded by DFG; details)
- Lubricant-refrigerant mixtures: Wetting behavior and interfacial tension (completed, funded by FKT; details)
- Diffusion coefficients of gas mixtures using a Loschmidt cell combined with holographic interferometry (completed, funded by DFG; details)
- Diffusion coefficients of refrigerant-lubricant mixtures by dynamic light scattering (completed, funded by FKT; details)
Further information on AOT-TP and research activities can be accessed via the FAU current research information system (CRIS).