ANS:B - excessive corrosion

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid excessive corrosion. When cooling water temperatures exceed certain thresholds, it can accelerate corrosion within the heat exchanger system. Higher temperatures can promote chemical reactions between the water and the materials of construction, leading to corrosion and degradation of the equipment. This corrosion can cause structural damage, decrease system efficiency, and ultimately result in costly maintenance and repairs. By limiting the outlet temperature of the cooling water to 50°C or below, industries aim to mitigate the risk of corrosion and extend the lifespan of their heat exchanger systems.