Hard water scale formation and mitigation at higher temperatures

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Electrically powered heat pump systems will play a key role in providing hot water and heating in domestic and commercial installations as the UK moves away from fossil fuels: these systems are already widely used in locations without ready access to natural gas. Heat pumps rely on efficient heat transfer in condensers, which is compromised by the formation of fouling layers (water scale) arising from hardness salts present in the water. Scale formation increases with water temperature: the next generation of heat pump systems aim to deliver water at 85-90C, so sustainable mitigation methods are required that do not require the use of chemical dosage. The key aims of the research are:(i) to develop quantitative models of scale formation in plate heat exchangers under heat pump operating conditions, so that these can be designed to minimise the rate of growth of fouling layers; (ii) to quantify the impact of surface treatment and water pretreatment strategies on fouling rates at these higher temperatures, and (iii) to determine the effectiveness of post-exchanger passive capture technologies to prevent detached scale or fouling precursors from the heated water.