Cleanability of Aged-Fouling Deposits

• Applicant: Professor Dr.-Ing. Stephan Scholl
• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 442905766

Fouling of heat transfer surfaces has significant economic and environmental impacts. The severity of the impacts of fouling is affected by the ageing of adhered deposit. Ageing is a sub-process of fouling and can be defined as changes in the mechanical and/or thermal properties of a deposit. During Phase 1 of the DFG project, “Alterung von Foulingbelägen”, the ageing properties (i.e., thermal conductivity and mechanical hardening) of a whey protein fouling deposit are defined as a function of the deposit thickness and the temperature of fouling formation. The investigations in Phase 1 applied a custom-built laminar flow channel (LFC) for the monitoring of continuous changes in the thermal fouling resistance during ageing. The results of Phase 1 illustrated an increase in thermal conductivity with an increase in fouling thickness and an increase in mechanical hardening with an increase in the temperature of fouling formation. The terminal properties of an aged fouling deposit, such as those characterized in Phase 1, determine the starting point for subsequent cleaning processes. Cleaning processes are needed to remove aged fouling deposits and restore process efficiency. The cleaning effort required for removal depends on the ageing properties of the soil. The proposed follow-up project (Phase 2) aims to understand ageing through the removal of deposits during cleaning. Phase 2 is motivated by new research questions generated from the results of Phase 1 and comments from reviewers of the project proposal from Phase 1 which suggested an increased emphasis on the study of the cleaning of aged deposits in following research. In Phase 2, model aged soils will be generated using a special baking mold with gradients in the concentration of compositional components (e.g., mineral and protein) and baking time along the thickness of the deposit. The chemical and mechanical removal properties of model soils will be quantified under quiescent and continuous flow conditions. The results will be summarized by dimensionless numbers (DN) to describe the functional relationship between ageing properties and cleaning properties. The relationship described by the DNs will be validated using a real aged soil. The methods associated with Phase 2 involve upgrades to the LFC applied in Phase 1 and construction of a millimanipulation device. Together, the results of Phase 1 and 2 will provide a better understanding of the interplay between fouling and cleaning as a basis for an integrated optimization of fouling mitigation and cleaning.

• DFG Programme: Research Grants