REDUCING SCALE DEPOSITION BY PHYSICAL TREATMENT Sungmin Youn and Professor X. Si, Calvin College REDUCING SCALE DEPOSITION BY PHYSICAL TREATMENT Sungmin Youn and Professor X. Si, Calvin College Scale deposition on metal surfaces from salt- containing water considerably reduces the efficiency and performance of heat transfer equipments. Scale depositions could be reduced through physical or chemical methods. However, in some cases chemical methods are unpractical due to cost and contamination issues, rendering the physical methods the only feasible options. The objective of this study was to evaluate the effectiveness of two physical treatments in reducing scale depositions. One is to decrease the surface energy of the heat exchanger wall through surface modification; the other one is to change the crystallography of the small solid particles formed in the solution by applying a magnetic field. For the first method, Copper and stainless steel surfaces were modified by micro-scale (μm thickness) PTFE (Poly-Tetrofluorethylene) films and nano-scale (nm thickness) thiolate SAMs. To study the magnetic treatment effect on the formation of the calcium carbonate scale, a magnetic field up to 0.6 T was implemented in a simulated recirculation cooling water system. The experiments showed that the formation rate of the calcium carbonate scale was decreased on modified surfaces and the induction period was prolonged with the decrease of the surface energy. The study also showed that the nucleation and nucleate growth of calcium carbonate particles were enhanced through magnetic water treatment. In addition, using a higher flow rate and/or filtration of suspended calcium carbonate particles achieves a longer induction period. IntroductionResults The deposition of calcium carbonate scale will increase with higher surface temperature, higher flow velocity, and higher calcium carbonate concentration due to higher reaction rate. When hard water was exposed to strong magnetic field, the nucleation of calcium carbonate scale was enhanced in the fluid. The resulting crystals are mainly soft aragonites that are easier to remove by flow shear. The calcium carbonate fouling behavior on surfaces with various surface energy levels was also studied, which include Cu, Cu-SAMs, Cu- PTFE, Stainless steel, and electro-polished stainless steel surfaces. The results showed that when surface energy was decreased, the growing rate of fouling and the ultimate fouling resistance were reduced and the induction period was elongated. Thank Mr. Sidney Jansma for financial supporting on this project. In this experiment, the preheated tap water in the tank was kept at constant temperature (40 o C). Three valves were used to control the flow rate passing through either a, b, or c route, depending on the requirement of the tests. The heat flux onto the STU was controlled by a voltage meter. The temperatures measured by the thermometers. After 2 to 3 hours, the temperatures became constant values. Then the NaHCO3 and CaCl2 solutions were added into the natural water in the tank. The temperatures measured by the thermometers will be read every 5 minutes until they became steady. In order to investigate the dependence of fouling behavior on the surface properties, copper, Cu-PTFE, Cu-Thiolate SAM, stainless steel, and electro-polished stainless steel. Before these pipes were used for fouling tests, the surface energy of the pipe walls was measured. Procedures Figure 1 shows a schematic diagram of the test facility, which consists of a water circulating loop, a reservoir tank filled with hard water, a centrifugal pump, a filter, a permanent magnet (0.6T), and a Scaling Testing Unit (STU). The STU is composed of a heated pipe and a glass tube. The fluid flows between the two pipes, while the scale grows and deposits onto the surface of the heated pipe. Designed with the principles of dynamic thermal resistance, the STU is used to measure the thermal resistance of the scale. Figure 2 shows the cross-sectional view of the STU. Figure 1. Diagram of the test facility Figure 2. Cross-Sectional view of STU Experimental Apparatus Conclusions Figure 3. The influence of flow rate on fouling rateFigure 4. The influence of concentration on fouling rate Figure 5. The influence of thermal power on fouling rate Figure 6. The influence of magnetic field on fouling rate when the solution was not filtered Figure 7. The influence of magnetic field on fouling rate when the solution was filtered Acknowledgment