方形螺旋管中CaSO4污垢特性的数值模拟

摘要

Starting with the heat and mass transfer, the mathematical model for forming process of CaSO4 crys-tallization fouling within square spiral tubes was built to analyze influences of CaSO4 concentration, pitch of helical pipe and inlet velocity on the fouling deposit rate, denudation rate and the fouling resistance in spiral tubes. Basing on temperature field, velocity field and CaSO4 concentration field and the fouling model simula-ted, the CaSO4 scale deposition rate, erosion rate, net deposition rate and fouling resistance’ s variation with time were calculated. Analysis results show that, rise of CaSO4 concentration can increase fouling’ s mass dep-osition rate and denudation rate and resistance;the bigger pitch of square spiral tube can reduce tube fouling’ s mass deposition rate and denudation rate and resistance;and increase of inlet velocity can decrease fouling’ s mass rate and resistance in the tube. Analyzing the variation trend of dirt’ s net deposition rate in spiral tubes with different pitches indicates that in a certain stage, the fouling rate in the tube is negative, and that is to say the square spiral tube has a certain anti-scale effect in a certain time. Smaller CaSO4 concentration and bigger pitch of the square screw tube as well as higher inlet velocity can bring about better scale inhibition effect.%从传热传质的角度建立了方形螺旋管内CaSO4析晶污垢形成过程的数学模型，通过对数学模型进行数值模拟计算，得到了CaSO4浓度、螺距及入口速度等参数对管内污垢的沉积率、剥蚀率、净沉积率和污垢热阻的影响。根据模拟得到的方形螺旋管管内的温度场、速度场和CaSO4浓度场，进而结合污垢模型，计算出CaSO4污垢的沉积率、剥蚀率、净沉积率和污垢热阻随时间的变化规律。通过分析计算数值模拟结果，得到CaSO4浓度的增加会增加污垢的质量沉积率和剥蚀率，同时也会增加污垢热阻；方形螺旋管螺距的增加会降低管内的污垢质量沉积率和剥蚀率，并且会降低管内污垢热阻；入口速度的增大，会减小管内的污垢的质量速率和热阻。通过分析不同螺距的方形螺旋管中污垢净沉积率的变化趋势发现，在一定阶段内，污垢在管中的污垢净沉积率为负值。也就是说，方形螺旋管在一定时间内具有一定的阻垢效果。并且当CaSO4浓度越小、方形螺旋管螺距越大、入口速度越大时，这种阻垢效果越好。