Local fouling investigations as basis for describing the integral fouling behavior

• Applicant: Professor Dr.-Ing. Stephan Scholl
• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398352126

The research project aims at an in-depth understanding of the influences of the crystalline structure of a fouling deposit on local fluid dynamics and heat transfer and its consolidation to an interpretability of the integral fluid dynamic and heat transfer-related equipment performance. This shall be reached through targeted local and integral experimental investigations in combination with an improvement of the modelling concept according to Schlüter. Besides a determination of the local (segmental) pressure drop, especially the investigations on local flow velocities and the fluid dynamic conditions in the vicinity and within the highly porous outer layer of the crystalline structure are of specific relevance. Results from phase 1 show that the crystal layer has significant axial gradients with respect to quantity and structure. These axial differences in quantity and morphology influence local flow conditions as well as heat transfer. The influence of the local crystal structures on flow conditions shall be monitored using a Stereo µPIV. The investigations are based on the following research hypotheses: • The three-layered structured of the crystalline deposit, with compact base, tight needle tangle and open needle tops, together with their gradual axial distribution induce differences in local flow and heat transfer processes. • A locally resolved modelling of fouling and flow conditions accounting for roughness and constriction effects can capture this behaviour quantitatively. • The local description of fluid dynamic and heat transfer conditions may be integrated to a holistic picture of the integral equipment behaviour. Based on these hypotheses, the following insight targets may be formulated: • Local flow velocities, pressure drop and heat fluxes may be determined through segmental measurements. • Structure and morphology of the crystal layer at the inner surface of the tube may be replicated on flat probe plates. • Based on the three-layered structure of the crystal deposit, local thermal and mass-based fouling resistances may be calculated. • The developed modelling concept may be transferred to other crystalline systems provided that their temperature dependence of solubility is known. Besides the direct investigation of the grown crystal structures, a method shall be developed that allows for a physical replication of the structures. This will allow for further experiments without interfering with or destroying the fragile structures. Fragility of the crystals has presented major challenges in the first project phase. The method to develop shall conserve the local structure of the crystalline layer and allow for subsequent structural characterization.

• DFG Programme: Research Grants