Molecular Dynamics Simulation Of The Growth Characteristics Of CaCO₃ In Solution On Its Fouling Surface

Scale has always been a major problem in daily life and industrial production,especially in industrial heat exchange equipment,the problem of heat exchange equipment fouling caused by reduced efficiency or even irreversible equipment failure can lead to a lot of economic losses.Many scholars have already started to conduct a lot of research on how to inhibit the fouling of heat exchange equipment and remove the fouling of heat exchange equipment.The main component of scale is Ca CO₃,and the root cause of scale growth is the intermolecular force of attraction of scale facing free Ca²⁺and CO₃^2-in solution.In this paper,using a molecular dynamics approach,simulations were carried out by modelling a mixed system of calcite crystalline surfaces,water molecules,Ca²⁺and CO₃^2-,under static working conditions and a constant concentration solution capable of maintaining a constant amount of Ca²⁺and CO₃^2-in the solution,respectively.The results of the calculations were varied by changing the concentration of Ca²⁺and CO₃^2-in the solution and changing the set temperature.The equilibrium determination of the calculation results was carried out,the relevant data concerning the fouling growth characteristics were analysed and the law of fouling growth was summarised.In the stationary condition,the total energy of the system decreases more rapidly with increasing temperature to reach the equilibrium position during the calculation,and a small portion of the free Ca²⁺and CO₃^2-in solution are attracted to each other to form clusters without being adsorbed on the calcite crystal surface.The binding energy of Ca²⁺,CO₃^2-to the fouling surface was calculated and it was found that the growth of the binding energy decreased between the concentration of the solution of 55.56 mg/L and 66.67 mg/L,when the growth of the calcium carbonate fouling surface was poor;the effect of temperature on the binding of Ca²⁺and CO₃^2-to the calcite crystal surface was a disordered effect,with 310.5K The growth of the fouling surface is poor at 310.5K.The radial distribution function plot between the relevant components reveals that the fouling surface has difficulty in aggregating CO₃^2-,generally by aggregating Ca²⁺,which in turn attracts CO₃^2-thus generating the growth of the fouling surface,and that the calcite crystalline surface aggregates more readily with Ca²⁺and CO₃^2-with CO₃^2-at a distance of about 2（?）.The self-diffusion coefficient of each particle revealed that Ca²⁺and CO₃^2-diffuse more easily at solution degrees between 55.56 mg/L and 66.67 mg/L.An increase in temperature makes it easier for water molecules to diffuse and hinders fouling growth,and temperature affects CO₃^2-self-diffusion in stages,and the effect is greater in low concentration solutions than in in highly concentrated solutions.For the calculation results of the constant concentration solution,the original fouling surface becomes structurally unstable during the fouling growth process and the newly generated fouling surface is an ACC.The average fouling growth rate was calculated and it was found that when the set solution concentration was less than 33.33 mg/L,the average fouling growth rate gradually increased as the set concentration increased;when the set solution concentration was greater than 33.33 mol/L,the average growth rate of fouling decreases as the set concentration increases;when the temperature is between 285.5K and 298K,310.5K and 335.5K,the average growth rate of fouling increases;when the temperature is between298K and 310.5K,348K and 360.5K,the average growth rate of fouling decreases.The single point free energy and binding energy between the original fouling surface and the newly formed fouling surface were analysed and it was found that at smaller concentrations,the change in concentration had a greater effect on the original fouling surface,but allowed the newly formed fouling to grow stronger;at larger solubilities,the concentration of the solution had a greater effect on the newly formed fouling surface,but allowed the original fouling surface and the newly formed fouling surface to bond less well.By using the radial distribution function of Ca²⁺on the original and new fouling surfaces,it was found that the ability of the fouling surface to collect Ca²⁺was strongest at the set concentration of 33.33 mg/L.The temperature change had a greater effect on the original fouling surface than the newly generated fouling surface.By calculating the mean square displacement of the new fouling surface,it was found that temperature shifted the growth position of the fouling surface more in the low concentration solution than in the high concentration solution.By using the concentration profiles of free Ca²⁺and CO₃^2-,the distribution of free Ca²⁺and CO₃^2-was found to be more dispersed in the horizontal direction with increasing concentration and temperature,and the distribution of free Ca²⁺and CO₃^2-was more dispersed in the vertical direction than in the horizontal direction.