Fundamental theoretic/experimental characterization of fluw morphology and local heat transfer in wiped film evaporators

• Applicants: Professor Dr.-Ing. Jens-Uwe Repke; Professor Dr.-Ing. Stephan Scholl
• Subject Area: Process Systems Engineering ; Chemical and Thermal Process Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 561285967

The distribution of liquid films on heated surfaces, allows the purification of highly viscous, thermally sensitive and high-boiling substances. This is made possible in so-called wiped film evaporators. They enable purification and recycling processes possible that are gentle on products and resources. However, due to the mechanical influence on the liquid film, the interdependencies between flow morphology, fluid dynamics and heat transfer are very complex and therefore not sufficiently understood. In practice this is an inhibitor to the application and further development of wiped film evaporators. This research project addresses this issue by investigating the flow morphology and its influence on single-phase heat transfer on wiped surfaces. The liquid distribution and flow state in the bow wave, gap zone and film region will be evaluated experimentally and simulatively as a function of operating conditions and fluid properties. The aim of the project is to gain an in-depth understanding of how the flow processes affecting heat transfer at wiped surfaces in order to optimize and understand wiped film evaporators. Ultimately, this will make their operation more efficient. The objectives of the project are to systematically study the fluid dynamics in the bow wave in the wiped film evaporator and to resolve the local heat transfer in space and time, taking into account the fluid dynamics. The results will be used to develop a mechanistic model capable of describing the fluid dynamics and the main heat transfer mechanisms in the wiped film evaporator. Numerical simulations will be combined with experiments. A wiped film evaporator made of glass will be used to investigate the fluid dynamics and to experimentally determine the residence time distribution and the fluid hold-up. In addition, optical observations with a high-speed camera are used to record and evaluate the flow morphology. A full energy balance is performed to determine the single-phase heat transfer on the product side. The experimental data are complemented by simulation data from a comprehensive numerical simulation of a wiper segment. In the numerical simulations, the bow wave geometry and the interactions between the film zone and bow wave are investigated and the mixing between these two zones is characterized. The single-phase heat transfer on the product side is determined. The simulation and experimental data will be continuously compared throughout the project in order to identify any invalid assumptions in the simulation at an early stage and to ensure an optimal experimental design.

• DFG Programme: Research Grants