首页|A study of electronic descaling technology to control precipitation fouling
A study of electronic descaling technology to control precipitation fouling
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The objective of the present study is to study the fundamental mechanism of an electronic descaling (ED) technology, an innovative technique to control precipitation fouling in a heat exchanger. The ED technology utilizes a time-varying signal to create ionic agitation, resulting in the precipitation of the scale-causing ions into insoluble crystals, such that fouling can be prevented. The ED technology involves basically three different disciplines, which are water chemistry, electromagnetic theory, and heat exchanger knowledge. The present study proposed a theory of the ED technology and examined various parameters which influence the performance of this technology. In order to prove the hypothesis of the ED technology, the crystal growth of $\rm CaCO\sb3$ in water samples (both untreated and treated) was observed using a microscope. The untreated water sample showed a large number of small crystals within a range of 1 to 10 $\mu$m in diameter, whereas the water sample treated by the ED technology showed a small number of large crystals ranging from 10 to 20 $\mu$m in diameter. Large crystals are more likely to move with bulk flow, instead of adhering onto a heat transfer surface. Tests were also conducted to examine the feasibility of reducing hardness of water by removing precipitated $\rm CaCO\sb3$ particles by a filtration method. The batch test results showed that when the ED treatment was used without mixing, the total reduction of alkalinity was only 3%. When the ED treatment was applied together with mechanical mixing, an 18% reduction of total alkalinity was found. Such results indicated that the ED treatment greatly promoted $\rm CaCO\sb3$ precipitation from water when mixing was present. Fouling reduces pipe opening, increases pressure drop across a heat exchanger, and decreases heat transfer coefficient. A series of tests were also conducted in a single-tube heat exchanger to confirm whether the ED technology can prevent fouling or not. Artificial hard water of 1,000 ppm as $\rm CaCO\sb3$ was used throughout the tests. The pressure drop obtained with the ED treatment was approximately 51% less than that without the ED treatment, and the asymptotic heat transfer coefficient obtained with the ED treatment was approximately 12% larger than that without the ED treatment. When the ED treatment was used together with a filter, precipitation fouling was almost completely prevented even for the harsh fouling conditions tested in the present study.
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