A study of physical water treatment technology to mitigate the mineral fouling in a heat exchanger.

摘要

The objectives of the present study were to investigate the fundamental mechanism of physical water treatments for hard water—bulk precipitation—and specifically to investigate how electromagnetic fields alter the characteristics of scale deposits—particulate fouling—on the surface of a heat exchanger. In an attempt to understand the role of these electromagnetic fields, the present study examined how the performance of the PWT (i.e., permanent magnets or solenoid-coil induction technology) was affected by various parameters such as flow velocity, concentration, geometric arrangement, etc. All experimental studies were conducted in a heat exchanger with circulating cooling-tower water, and the fouling resistance was estimated over a period of time.; PWT technology uses a magnetic or electric field to treat hard water physically. It is hypothesized that the external magnetic or electric field precipitates dissolved mineral ions in bulk water to form clusters (i.e., colloidal particles of submicron size).{09}The clusters grow in size as the solubility of the mineral ions drops due to an increased temperature of the water inside the heat transfer equipment. As the clusters compete for dissolved mineral ions with heat transfer surfaces, the fouling at the heat-transfer surfaces is significantly reduced.; The present study was conducted to validate this hypothesis. As a direct method, a particle-size analyzer was used to provide supporting data for the bulk precipitation hypothesis. In addition, surface tension measurement and water analysis were used together with one of the PWT technologies to further provide supporting data for the hypothesis.; Fouling resistances, which indicated the performance degradation of a heat exchanger, were experimentally measured through heat transfer tests. Real-time microscopy, SEM photographs, and X-ray diffraction were performed to characterize scale deposits. Various key parameters such as flow velocity, water concentration, the arrangement of permanent magnets, and the frequency and strength of the current signal in a solenoid-coil device were examined to determine the optimum conditions for maximum efficiency of physical water treatment methods.