Effect of temperature on composite fouling deposition characteristics of silica particle and calcium carbonate: A molecular dynamics study

Abstract

In heat exchangers, silica (SiO₂) and calcium carbonate (CaCO₃) often coexist to form composite fouling, and temperature is a key factor that changes dynamically. To investigate the influence of temperature on SiO₂ particle and CaCO₃ composite fouling, this paper employs two composite fouling models of SiO₂ particle and CaCO₃. Molecular dynamics (MD) simulation methods are used to study the deposition characteristics of composite fouling under different system temperatures and wall temperatures, as well as the influencing laws on the formation of composite fouling. The results showed that, compared with the 323 K system, the thermal motion of atoms in the 363 K system is more intense, and the kinetic energy of ions in the system increases, which accelerates the deposition of composite fouling and shortens the deposition time by 50 %. Meanwhile, the number density of Ca²⁺ ions near the wall increases, and the peak number density of water molecules decreases, leading to a reduction in the compactness of water molecules at the wall. This results in a denser formation of composite fouling clusters on the wall. Compared with a wall temperature difference of 20 K, when the wall temperature difference is higher (100 K), the temperature near the wall is higher, and the diffusion coefficient of ions is larger at the same moment. The peak number density of water molecules on the high-temperature wall is lower, allowing the particle and ions to more easily overcome the barrier posed by the water molecules on the Cu surface, resulting in faster deposition on the high-temperature surface. The deposition time is reduced by a maximum of 55.6 %, while the number of ions adsorbed on the high − temperature wall increases by a maximum of 9 %. The research results help to reveal the influence laws of system temperature and wall temperature differences on composite fouling. It provides important theoretical support for the design or maintenance strategies of heat exchangers and the design of scale inhibitors.