Magnetic water treatment

Abstract

INTRODUCTION The buildup of scale deposits inside cooling water pipes and boilers presents a very costly problem in many industrial processes. Scale deposits significantly reduce heat transfer efficiency and can lead to partial or even complete blockage of the water flow passage inside the pipes. Several techniques can be used to remove scale deposits, ranging from washing the pipes and boiler walls with acid, to actually chipping away the scale with a chisel. Over the past 50 years, magnets have been marketed as devices for prevention of scale buildup. Magnetic water treatment consists of passing water through a strong permanent magnet installed in or on a feed pipeline. Later, when the water is heated in a boiler or heat exchanger, it presumably loses its tendency to deposit scale on the hot surfaces. The deposits that do form are reported to have a loose, non-adhering texture and to be easy to remove [i]. The manufacturers of these devices admit that they are not always effective, and almost all research groups that have evaluated magnetic water treatment devices in a controlled setting have concluded that the technique does not affect scale deposition [2,3]. Despite general skepticism about whether magnetic treatment works, the devices continue to be manufactured by hundreds of different companies and are fairly popular. If magnetic water treatment is indeed a real phenomenon and if the conditions which are necessary for it to work could be elucidated, it would be a very inexpensive alternative to conventional chemical water treatment techniques. Our research goal is to determine the most likely mechanisms whereby magnetic water treatment may work and to test these hypotheses experimentally. Most scale deposits consist of salts that become less soluble with increasing temperature. The most common is calcium carbonate (CaC03). CaCO 3 can occur in several crystalline forms calcite, aragonite, or vaterite. Calcite is thermodynamically more stable than aragonite or vaterite but precipitation of aragonite relative to calcite can be kinetically favored at elevated temperatures [4]. Depending on the pH, the types of ions present, and the temperature, aragonite may transform to calcite over time. We think it very unlikely that a magnetic field of only a few thousand gauss can affect Ca 2+ and CO32ions directly since the interaction energies are too small compared to kT; however, an interaction via iron is plausible. One way would be for the iron to act as a poison for growth of scale deposits. We have investigated this possibility and here report that ferrous iron at low concentrations is indeed a poison to calcite growth. It appears to have little or no effect on aragonite growth.