Physical Water Treatment Using Oscillating Electric Fields to Mitigate Scaling in Heat Exchangers

Abstract

This chapter presents an environment-friendly method to mitigate scaling in heat exchangers. A new physical water treatment (PWT) using high-frequency oscillating electric fields produced directly in water was used to mitigate scaling of heat transfer surfaces. The new method of using high-frequency oscillating electric fields directly in water is a major improvement over the previous PWT methods (i.e., low electric field strength, about ~1 mV/cm, and low allowable frequency, ~2 kHz). Both artificial and natural hard water at varying calcium carbonate hardness were used. Different combinations of voltages and frequencies were investigated to get the optimum values for the mitigation of scaling. It is hypothesized that the oscillating electric fields in the present PWT method precipitate the dissolved mineral ions such as calcium to mineral salts in bulk water. As the mineral ions continue to precipitate and adhere on the surfaces of the suspended particles, the particles grow in size and adhere to the solid heat transfer surface in the form of soft sludge or particulate fouling. This type of fouling is believed to be easily removed by shear forces created by flow than those deposits produced from the precipitation of mineral ions directly on the solid heat transfer surface, i.e., precipitation fouling. The new PWT method using oscillating electric fields presents a valid tool to mitigate scaling in heat exchangers from cooling water. The work in this book is based from the PhD dissertation of the first author at the Division of Mechanical Design Engineering at Chonbuk National University. Section 3.1 presents an overview of mineral fouling and the different methods to mitigate the fouling formation in heat exchangers, focusing on physical water treatment. Sections 3.2, 3.3, 3.4 and 3.5 give in detail the experimental work and discussion of the use of oscillating electric fields as a means to mitigate mineral fouling in a double-pipe heat exchanger. Section 3.6 summarizes the present study.