Problem 8.2: Explain why CaCO often precipitates on
From Chapter 8 Problem Set. Level 1: Conceptual Mastery.
Question
Explain why CaCO₃ often precipitates on heat-transfer surfaces even when the bulk water looks stable.
Answer
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CaCO₃ exhibits inverse solubility - its solubility decreases as temperature rises. Heat-exchange surfaces are the hottest points in the system. Additionally, boundary layers at the surface concentrate ions, local pH can rise at cathodic sites, and the metal surface provides nucleation and anchoring points. Bulk water may be below saturation while the surface microenvironment is above it.