Mineral Formation in Heat Exchangers

Heat exchangers are everywhere in society, but they are prone to mineral formation on inner surfaces, causing loss of efficiency. The LINX team at Aarhus University studied the impact of anti-fouling coatings on the unwanted mineral formation in simulated heat exchangers.

Heat exchangers pass heat from one medium to another without the two media mixing. Many households that rely on district heating have heat exchangers to provide hot tap water; heat from the hot district water is transferred to cold consumption water as the latter flows through the unit, providing “on-demand” hot tap water without the need for a boiler.

Heat exchangers are made of metal, and rely on carefully engineered internal surfaces to pass the heat efficiently from one medium to the other. However, when operating with water (as in the household case) unwanted mineral formation (called “fouling”) may occur on the hottest surfaces. The effect is identical to the minerals forming inside an electric kettle, requiring an occasional descaling. A heat exchanger, however, is a closed system, which often operates 24-7 and cannot be cleaned easily. Ultimately, the mineral deposits are responsible for decreased efficiency and energy losses. By understanding what materials interactions lead to degradation, the lifetime of heat exchangers may be improved. For Grundfos Holding A/S (Grundfos), this understanding is crucial and Grundfos has committed significant effort in to studying and understanding surface-fouling.

The LINX team at Arhus University (AU) supplemented these ongoing efforts with materials characterization; AU used X-ray diffraction to assess the impact of anti-fouling surface modifications in simulated heat exchangers.

Read the interesting one pager from this project: Mineral formation in heat exchangers (a collaboration between Grundfos and Aarhus University).

Techniques and Methods

Fouling is the deposition of unwanted material (organic or inorganic) on surfaces of components working in wet environments, which can lead to severe degradation in performance and integrity. As a world leader in pumping solutions and water pump technology, understanding how fouling occurs and how to suppress it therefore is crucial for Grundfos Holding A/S (Grundfos).

In this LINX project, the LINX team at Aarhus University (AU) investigated fouling in simulated heat exchangers. AU used position resolved X-ray diffraction to map distributions of inorganic fouling across steel surfaces from simulated heat exchangers. The degree of surface fouling as well as the crystal structure distributions of, e.g., aragonite and calcite, were investigated as a function of operating conditions.

Furthermore, AU evaluated the anti-fouling capacity of promising coatings. This was done by comparing the mineral formation on coated as well as non-coated surfaces, which had been exposed to heat exchanger environments for the same amount of time. X-ray diffraction data were collected in a position resolved manner in order to determine and compare the spatial distributions of inorganic fouling on the different surfaces. By means of these investigations certain anti-fouling coatings were found to be quite effective.

Project Information

Participants: Grundfos, Aarhus University.
Materials degradation in wet environments – fouling (FP08.003, Materials at operating and processing conditions).