Influence of surface modification on the composition of a calcium phosphate-rich whey protein deposit in a plate heat exchanger
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The unwanted formation of deposits during the thermal treatment of milk and milk products is an unresolved problem for the dairy industry. A method to reduce fouling on heat transfer surfaces is the defined modification of the energetic surface properties. However, an anti-fouling surface, approved for use in the food industry, easy to clean, that is resistant in operation, and stays effective over the lifetime of a plant is still a challenge. The present work aims to investigate the influence of diamond-like carbon (DLC, a-C:H) and Si-doped DLC (a-C:H:Si and a-C:H:Si:O) coatings with particular high mechanical hardness, wear resistance, and chemical inertness, against milk fouling. Experiments were conducted using a pilot-scale plate heat exchanger with a calcium phosphate-rich whey protein solution as model fluid. The results showed that surface modification directly affected the formation of deposits, their composition, as well as their adhesive strength. Lower protein content on DLC and SICAN (a-C:H:Si) and lower mineral deposition on SICAN were measured. Further analysis showed that original energetic properties were changing during several fouling and cleaning cycles. Furthermore, the electron–donor component (γ−) was the main differentiating factor determining the extension of fouling. A quadratic relationship between the deposit protein content respectively the final fouling resistance and γ− was found, suggesting an optimum value of γ− for which fouling is minimal. The results should lead to a better understanding of the fouling process and demonstrates the potential of the DLC coatings to enhance operational effectiveness.
KeywordsMilk fouling Model fluid Deposit composition DLC coating Surface energy
The authors gratefully acknowledge the funding of C. Boxler’s Ph.D. grant by the Friedrich-Ebert-Stiftung and the preparation of the DLC coatings at Fraunhofer Institute for Surface Engineering and Thin Films, Braunschweig. Heat exchanger plates have been provided by GEA Ecoflex GmbH, Sarstedt, and WPI by Arla Foods Ingredients Group P/S, Viby.
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