Research On The Effect Of Applied Electric Field On The Formation And Structure Of Calcium Carbonate Clusters

The existence of fouling on the heat exchanger surface will increase the thermal resistance and the flow resistance,reducing the heat transfer efficiency,which will cause heat transfer deterioration,resulting in damage to the heat exchanger and economic losses,affecting the safe operation of the equipment.In order to solve this problem,a large number of scale inhibition methods have been proposed in recent years,mainly divided into chemical scale inhibition method and physical scale inhibition method.Chemical scale inhibition method,through the addition of chemical reagents to the medium to inhibit the formation of surface fouling,the operation process is simple,but likely to cause secondary pollution of the environment.The physical scale inhibition method,through the application of electric field and magnetic field or high frequency acoustic wave,etc.to change the motion characteristics of the dissolved scale ions in the medium to achieve the purpose of scale inhibition,where the applied electric field can also be sterilized and corrosion inhibition of fluid media at the same time,which has received wide attention in recent years,but the current mechanism of electric field scale inhibition is still unclear,resulting in the optimization of the electric field scale inhibition process is limited.In order to investigate the early process of scale formation under the action of electric field at microscopic level,this paper uses molecular dynamics method to simulate the early formation process of calcium carbonate fouling in industrial fields under the action of uniform and non-uniform electric field to reveal the influence of electric field on the process and provide theoretical basis for the application of electric field scale inhibition in industrial fields.The agglomeration and dehydration of calcium carbonate under the action of electric field can be divided into three stages,namely,the spontaneous growth stage of pre-nucleated clusters,the agglomeration stage between pre-nucleated clusters,and the internal structural rearrangement stage of cluster aggregates.The homogeneous electric field promotes the spontaneous growth of preformed nucleated clusters,resulting in a closer average Ca²⁺-CO₃^2-distance and higher Ca²⁺-CO₃^2-coordination number.At the same time,the electric field promoted the agglomeration of pre-nucleated clusters,and the fastest agglomeration of calcium carbonate was observed when7 500 V/cm electric field was applied,which was 33%faster than that without electric field,while the average coordination number of Ca²⁺was increased by 21%.In the cluster aggregate structural rearrangement stage,the cluster aggregate structure was more compact under the electric field,the number of[Ca（CO₃）₂（H₂O）₅]local structures decreased and the number of[Ca（CO₃）₃（H₂O）₄]local structures increased,which was favorable to the subsequent transformation to the anhydrous crystalline phase,and the calcium carbonate cluster aggregate possessed the most compact structure when 7 500 V/cm electric field was applied.When the temperature of the system was increased to 400 and 440 K,the higher the temperature,the tighter the structure of the calcium carbonate cluster aggregates when no electric field was applied,which is consistent with the relevant experimental findings.When the uniform electric field applied,the characterization is same as 360 K,but the cluster aggregate structure was tighter and the water molecule content was lower under the coupling effect of electric field and high temperature.Compared with the uniform electric field,the alternating electric field has different effects on the agglomeration and dehydration of calcium carbonate clusters.When the amplitude of the alternating electric field is fixed,the higher the frequency the faster the spontaneous growth rate of calcium carbonate pre-nucleated clusters.The average coordination number of Ca²⁺-CO₃^2-in the agglomeration stage of pre-nucleated clusters tends to increase with the increase of the alternating electric field frequency and then decreases,and the average coordination number is the largest when 40 GHz alternating electric field is applied,which is 28.5%higher than that without the electric field.When the frequency of the alternating electric field was fixed and the amplitude was increased,the average coordination number of Ca²⁺-CO₃^2-in the spontaneous growth phase of the pre-nucleated clusters first increased and then decreased,with the fastest agglomeration rate in the alternating electric field with an amplitude of 1 570 V/cm.In the agglomeration phase of the pre-nucleated clusters,the Ca²⁺average coordination number increases and then decreases with the increase of amplitude.In the internal rearrangement stage of the cluster aggregates,the aggregates were the most compact with an applied alternating electric field of 1 570 V/cm.Compared with the uniform electric field,the average coordination number of Ca²⁺is higher and the hydration number is lower after the application of the alternating electric field,and the structure of the cluster aggregates is tighter,which is favorable to the formation of the anhydrous crystalline phase.