Won Tae Kim’s research while affiliated with Drexel University and other places

The purpose of the present study is to investigate the effect of a physical water treatment (PWT) technology on fouling mitigation in a simulated cooling tower operating at high cycles of concentration. Hard water was produced by evaporating pure water in a circulating open cooling tower, where dissolved calcium carbonate ions became concentrated with time. Heat transfer tests were conducted in a rectangular channel by varying the cycle of concentration (COC) from 5 to 10, and fouling resistances were measured over 270 hrs for each case with and without the PWT treatment. Another test was conducted with no blowdown case with and without the PWT treatment. The fouling resistance at 5 cycles with the PWT treatment was about 70% less than that in the case without the PWT treatment at the end of 270-hr tests. Even at 10 cycles, the PWT treatment reduced the fouling resistance by 60% from the value for the no treatment case. Thus, one can conclude that the PWT technology can help circulating cooling-tower water at relatively high COC for significant freshwater conservation, while keeping fouling resistances below industry standards.

The present study introduces a new experimental method to visualize the fouling process of CaCO3. A mini-channel heat exchanger system with a microscopic imaging technique was developed for real-time visualization of the fouling process. The present study discussed how scale started initially, how scale formed thick layers, and how a small crystal grew into a large one, touching the adjacent one. Detail microscopic images of scale crystals and corresponding fouling resistances were obtained over the entire fouling process. The microscopic observation indicated that the fouling process could be divided into three stages: an induction period, a period of uniform generation of nuclei, and a period of uniform growth of scale. Sudden appearance of numerous small nuclei indicated the end of the induction period, a key event before the rapid increase in the fouling resistance. The present experimental method using microscopic images of the wet fouling process provides a valuable insight on the fouling mechanism.

The purpose of the present study was to investigate the effect of an air bubble on scale formation. Artificial hard water was used, whose hardness was equivalent to 1,000 ppm as CaCO3. Photographs of scaled heat-transfer surfaces showed the distribution of CaCO3 crystals around the bubble and in divergent tail-like areas downstream of the bubble. It was speculated that nucleation seeds were created around the bubble due to the release of CO2 gas at the interface from water to the air bubble. The seeds were carried downstream along streamlines around the bubble. The bubble affected the scale-deposition area approximately forty times larger than the bubble size. In the study, the local temperature effect did not significantly affect the formation of scale deposition.

The purpose of the present study was to investigate the effect of electronic antifouling (EAF) technology on fouling mitigation in a heat exchanger in an open, cooling-tower system. Two tests were performed in a rectangular heat-transfer channel at 5 cycles of concentration: one without the EAF treatment and the other with the EAF treatment. The fouling resistance in the case with the EAF treatment was about 70% less than that in the case without the EAF treatment at the end of 270-hr tests. (C) 2001 Elsevier Science Ltd.

The objective of the present study was to investigate the behavior of CaCO3 crystal formation at the very beginning stage of fouling. This article describes an experimental method which employs a light microscope system to visualize crystal growth behavior during the fouling process inside a transparent rectangular channel. Crystal visualization data are presented to examine the crystal growth behavior of calcium carbonate crystallizing from hard-water fouling. The present study provides crystal growth data as a function of time, which includes crystal creation, crystal growth, the number of crystals, and removal process. Both the rate and location of crystal growth were found to be dictated by small seed crystals formed in the early stage of fouling. The removal rate was found to be almost negligible compared to the deposition rate.