Abstract:

Calcium carbonate fouling has a higher thermal resistance, and deposition of calcium carbonate on the heat exchange surface will lead to the reduction of heat exchanger efficiency, thus the formation and suppression of calcium carbonate are the focus of heat exchanger design. In this work, molecular dynamics method was adopted to analyze the adsorption and dehydration behavior of calcium carbonate on the copper metal surface in supersaturated calcium carbonate solution. The results showed that Ca—C coordination number firstly increased and then approached a constant value during the adsorption process of calcium carbonate to the surface, while the ion hydration number firstly decreased and then approached a constant value. The structure of calcium carbonate adsorbed on the metal surface did not changed significantly, and calcium carbonate was an amorphous structure with a certain hydration number. Increasing the surface temperature, the dehydration of the calcium carbonate was more complete, coordination numbers of Ca—C and Ca—O become higher, and the calcium carbonate adsorbed on the high-temperature surface transforms from a hydrated structure to anhydrous crystals. When the surface temperature was 800K, the ion hydration number was close to 0, and the Ca—O coordination number was approximate 6, which was close to the Ca—O coordination number of anhydrous calcium carbonate crystals at the macro scale.

Key words: calcium carbonate, adsorption, dehydration, simulation, surface

摘要：

碳酸钙污垢具有较高的热阻，换热壁面碳酸钙的沉积会导致换热器效率显著下降，因此，换热壁面碳酸钙的形成机理与抑制是换热器设计研究的重点。本文采用分子动力学方法模拟分析过饱和溶液中碳酸钙在高温铜金属壁面上的吸附与脱水行为。模拟结果表明，在碳酸钙向壁面吸附过程中Ca—C配位数先增加后趋近于定值，离子的水合数先减少后趋近于定值。吸附在金属壁面的碳酸钙内部结构未发生明显变化，碳酸钙为具有一定水合数的非晶体结构。壁面温度越高，吸附的碳酸钙脱水越完全，Ca—C和Ca—O的配位数越高，高温壁面吸附的碳酸钙从水合结构向无水晶体转化。当壁面温度提高到800K，离子水合数接近于0，Ca—O配位数约为6，与宏观尺度下无水碳酸钙晶体的Ca—O配位数相接近。

关键词: 碳酸钙, 吸附, 脱水, 模拟, 表面