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

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.