Research

Research Summary

Technological relevance of transport and wetting processes. Image: Peter Stephan
Technological relevance of transport and wetting processes. Image: Peter Stephan

In many technologies the dynamic wetting or dewetting of surfaces by liquids plays a prominent role, for instance in printing or coating technologies, in phase-change heat transfer processes, in microfluidics and lab-on-a-chip technologies, as well as in numerous reactor geometries or other process industry installations. Frequently the wetting and dewetting phenomena are closely coupled to the transport of momentum, energy (heat) or mass occurring in close proximity to the advancing or receding three-phase contact line (liquid/gas/solid). Typically, the determining physical phenomena involved are restricted to a very small region around the contact line, at the nano- or microscale. Nevertheless, these phenomena often determine the overall effectiveness and efficiency of the entire technology or production, occurring at much larger macroscales.

Examples would be the maximum speed of printing or coating and corresponding defects, the maximum achievable heat transfer with pool boiling, the transition from very efficient drop condensation to less efficient film condensation, or the optimal transfer of crop protection agents onto plant surfaces.

The big questions

Interaction of transport and wetting. Image: Peter Stephan
Interaction of transport and wetting. Image: Peter Stephan

The fundamental mechanisms involved in the interaction between wetting and transport processes are in many respects not yet understood. To date research in this area has focused on the dependence of the wetting process on the local fluid velocity at the contact line, i.e. wetting coupled with momentum transport. However serious deficits exist in our understanding when, parallel to momentum transport, also heat and mass transport are involved, as is the case in almost all of the above-mentioned applications. These deficits become even more blatant when complex fluids are involved, e.g. suspensions or mixtures, or when complex surfaces are examined, e.g. rough or porous.

The intention of the CRC is to successively address and remove these very relevant knowledge deficits. To achieve this goal the fundamental processes and phenomena involved must be examined over a wide range of length scales (nano-micro-macro) and the transfer of basic research to applications must be ensured. This necessitates the use of very diverse methods and expertise from very different disciplines.

Generic configurations and common software

The generic configurations "Immersed Body" (left) and "Sessile Drop" (right) incorporate special features allowing them to also act as validation cases for simulation models. Image: Sebastian Keuth
The generic configurations “Immersed Body” (left) and “Sessile Drop” (right) incorporate special features allowing them to also act as validation cases for simulation models. Image: Sebastian Keuth

The SFB comprises 18 subprojects grouped into three research areas: Generic Experiments; Modelling and Simulation; New and Improved Applications. As an overarching and integrating factor two generic configurations have been specified. Furthermore, OpenFOAM has been selected as a common software platform. The generic configurations Immersed Body and Sessile Drop act not only as experimental platforms with which specific scientific hypotheses can be tested, but incorporate special features allowing them to also act as validation cases for simulation models.