电磁场抑制换热面析晶污垢的形成

Inhibition of the formation of crystallization fouling on heat transfer surface by electromagnetic field

为研究电磁场对换热表面析晶污垢的抑垢情况,该研究以电磁水处理动态试验台为依托通过一系列变工况的试验,获取了不同磁场强度、流速和入口温度下碳酸钙污垢热阻热阻曲线,又通过电磁场、流场及温度场之间的正交分析得出了各因素对析晶污垢生长的具体影响。结果表明,试验磁感应强度范围内污垢热阻随磁感应强度的增大呈减小趋势;不加磁场湍流状态下,流速越大污垢热阻越小;磁场与流速共同作用可以强化阻垢效果。随着入口温度的增加,热阻渐近值先增大后减小,在入口温度为30℃时出现极大值;电磁场处理产生的热阻减小的效果要大于入口温度增加引起的热阻增加的效果。通过正交分析,得出了影响污垢生长的主次因素由强到弱依次为磁感应强度、流速、入口温度。同时计算出了该试验台在试验工况下的最优运行工况,在入口温度30℃,流速0.4m/s,磁感应强度20 mT情况下抑垢效果最好。研究结果可为工业循环水除垢抑垢提供一定的参考。

Crystallization fouling, one of the most common fouling types, mostly forms on heat transfer surfaces in water pipe system. The crystallization fouling is inevitable to cause low efficiency of heat transfer in various equipment, and the short service life. Recently, the perception of fouling removal and suppression has been familiar, while the anti-fouling technology has developed greatly. Compared with the current fouling treatment method, the electromagnetic water treatment has become one of the main physical anti-fouling methods due to its cost-saving, convenient installation, simple operation, remarkable fouling suppression effect and environmentally friendly. Therefore, this study aims to investigate the effect of electromagnetic field on the crystallization fouling of heat transfer surface under various working conditions based on the electromagnetic scale suppression platform that modified by tube-shell heat exchanger. A sodium carbonate method was used to prepare calcium carbonate supersaturated solution according to the sodium carbonate and calcium chloride molar mass 1:1, while the thermal resistance of calcium carbonate fouling was obtained under different magnetic induction intensity, flow rate and inlet temperature. Specifically, the influence of inlet temperatures and inlet flow rates on the thermal resistance of calcium carbonate crystallization fouling was also discussed in magnetic treatment. The effect of working conditions and magnetic induction intensity on thermal resistance was clarified systematically, as well the coupling relationship between the working parameters, using the collected variation curve of fouling thermal resistance under different operating conditions. The results show that the thermal resistance of fouling decreases with the increase of magnetic induction intensity. The fouling thermal resistance and induction period decrease as the flow velocity increases in turbulence without magnetic field. The inhibition effect of fouling can be enhanced by the interaction between magnetic fields and flow rates. As the inlet temperature increases, the approximate value of thermal resistance increases first and then decreases, finally the maximum appears when the inlet temperature is 30 ℃. The interaction between the electromagnetic field and the inlet temperature depends on the change of the thermal resistance subjected to magnetic field. The decrease of the thermal resistance that caused by the electromagnetic field treatment can be greater than that by the increase of the inlet temperature. According to the operating range of the experimental platform, three factors were selected, including three levels of magnetic induction intensity, inlet velocity and inlet temperature for each treatment. Through orthogonal analysis, the primary and secondary factors affecting the formation of fouling from strong to weak are magnetic induction intensity, flow rate and inlet temperature. The optimal operating conditions are the inlet temperature of 30 ℃, the flow rate of 0.4 m/s, and the magnetic induction intensity of 20 mT, on the experimental platform. This finding can provide a sound theoretical guidance for crystallization fouling in the water treatment system during industrial production.