Study On Factors Affecting Fouling Growth Characteristics Of CaCO₃ In Smooth Pipes

Heat exchanger fouling phenomenon is common in industrial production,studying the influencing factors of heat exchanger fouling can provide a theoretical basis for reducing the formation of fouling on the heat exchange surface.Ca CO₃ fouling is the most common crystallization fouling in heat exchange equipment,so this paper takes Ca CO₃ fouling as the research object and studies the influencing factors of Ca CO₃ fouling in smooth heat exchanger tube through experiment and numerical simulation.Firstly,the fouling thermal resistance method was used to study the casing heat exchanger,and 316L stainless steel tube was selected as the test tube.The growth of Ca CO₃fouling in the test tube was studied when the concentration of Ca CO₃ solution was 375 mg/L,the inlet temperature of solution was 45±1℃,the inlet temperature of heating circulating water was 80±0.5℃,and the flow rates were 0.72,0.9,1.08,and 1.26 m/s,respectively.The experimental results show that the smaller the flow rate,the more serious the Ca CO₃ fouling on the wall surface of the test tube;the thermal resistance of Ca CO₃ fouling increased gradually with time,and the total heat transfer coefficient of the test tube decreased with time.Secondly,a Ca CO₃ fouling growth prediction model was established to calculate the growth of Ca CO₃ fouling under experimental conditions and compared with the experimental results,and the effects of solution inlet temperature,wall temperature,solution flow rate and solution concentration on Ca CO₃ fouling growth were systematically studied by the established Ca CO₃ fouling growth prediction model.The results show that the experimental results and the calculated results have the same trend,which verifies the accuracy of the model;the fouling thermal resistance show a gradual growth trend with time;the higher the solution inlet temperature,wall temperature and solution concentration,the larger the net fouling deposition rate and the larger the fouling thermal resistance;under the turbulent flow condition,the flow rate has little effect on the fouling deposition rate,and the flow rate mainly affects the fouling stripping rate by influencing the wall shear stress,the larger the flow rate,the larger the fouling stripping rate,the smaller the net fouling deposition rate and the smaller the fouling thermal resistance.Finally,the effects of pipe shape,pipe diameter and pipe built-in twisted band on Ca CO₃fouling were investigated.It was found that when the pipe cross-sectional area,heat transfer area and operation period were the same,elliptical pipe scaling was the most serious,followed by round pipe,rectangular pipe again,and square pipe scaling was the least.The greater the ratio between the long axis and short axis of elliptical tube,the greater the thermal resistance of fouling;the larger the length to width ratio of the rectangular tube,the greater the thermal resistance of its fouling;the larger the diameter of the round tube,the smaller the fouling thermal resistance;the built-in twisted belt of the pipe can not only improve the heat transfer performance of the test tube,but also effectively prevent the deposition of fouling on the heat exchange surface,and the smaller the width of the twisted belt when the twisted belt pitch is certain,the more serious the fouling,and the larger the twisted belt pitch when the twisted belt width is certain,the more serious the fouling.