"Tube-in-Tube Principle": Kaiserslautern researchers optimize the wetting and sliding behavior of pipelines

Fluid should flow resistance-free through narrow pipes, such as in production facilities. This is usually achieved through applied coatings. A research team at the Technical University of Kaiserslautern (TUK) is now rethinking the flow behavior: The starting point is an additional, internally located pipe with a functional surface, which not only optimizes wetting and sliding behavior according to the lotus effect but also stabilizes air inclusions needed for it. Using laser technology, these structures can be transferred onto practical pipelines. The German Research Foundation (DFG) is funding the project with around 740,000 euros.

Two departments at TUK and a Kaiserslautern institute are pooling their expertise for the project "Wetting and Transport Behavior of Substrate-Free Planar and Curved Hierarchical Stripe Structures": Junior Professor Clarissa Schönecker (Microfluidics), Prof. Dr. Egbert Oesterschulze (Physics and Technology of Nanostructures), and Privat-Dozent Dr. Johannes L’huillier (Photonics Center Kaiserslautern e.V.).

"In contrast to a conventional pipe, the flow is deliberately influenced by introducing an additional perforated inner pipe to reduce friction resistance," explains Oesterschulze. "A second medium at the perforated points interacts with the medium inside the inner pipe and influences its wetting and flow behavior. This new wetting state derives from the well-known 'Cassie-Baxter state' in the literature and is extended in this interdisciplinary research project to the 'substrate-free Cassie-Baxter state.' "Additionally, we want to specifically influence the wetting on the inner pipe through a hierarchical surface structure, i.e., a combination of nano- and microstructures," says the physicist.

Oesterschulze's working group investigates these wetting and flow processes on silicon structures manufactured with micro-technology, making them very precise.

He receives support from mechanical engineering and process engineering: "I consider the developed structures from a flow engineering perspective and provide impulses through fluid dynamic calculations on how the desired functions, such as roughness or wettability, can be realized," adds Schönecker. "Ultimately, this results in surfaces that are more applicable and more stable. I am generally thinking about application perspectives where liquids are transported under pressure or load through thin pipelines—such as in process engineering or microsystems," explains Schönecker.

To test the desired practical suitability, the Photonics Center is involved. "Using highly precise laser processing, we can transfer the hierarchical surface structures onto conventional metal pipes," says L’huillier. "In other words, together we provide the design and the necessary basic research for our functionally optimized component in terms of flow behavior and are already building the bridge to application."

Questions answered:

Junior Professor Clarissa Schönecker
Tel.: 0631 205-5971
Email: schoenecker@mv.uni-kl.de

Prof. Dr. Egbert Oesterschulze
Tel.: 0631 205-2680
Email: oester@rhrk.uni-kl.de

Priv.-Doz. Dr. Johannes L’huillier
Tel.: 0631 415 575 - 12
Email: johannes.lhuillier@pzkl.de