• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.272-277
• /
• 2005

The discharge gap clearly is to order and to promote the improvement of processing feature of die-sinking electro discharge machining(EDM). If creation carbon, which generated by pyrolysis of EDM oil and processing pace power which is generated in between an electrode and a workpiece, are overproduced, they will lower the processing speed and roughness of the surface. Therefore, it is gone through the .flow analysis of EDM oil in order to improve the treatment of processing chips, which is an important problem by contriving a new flushing method. The condition of an electric discharge is not considered to be a progressing of processing. It is assumed that the flow of processing fluid is equal to the flow of processing chip, which is remaining in the discharge gap, and analyzing its correlation.

• Journal of dental hygiene science
• /
• v.15 no.5
• /
• pp.659-665
• /
• 2015

A wide variety of methods have been used to control Dental Unit Waterline (DUWL) contamination. Among the methods, flushing is mainly used because it is simple and easy to use. Generally, flushing of DUWL for 20 or 30 sec before using high speed handpieces or scalers is recommended. However, the appropriateness of flushing time was not investigated thoroughly. The purpose of this study was to check the effective time of flushing for decreasing bacterial contamination. Seven dental unit chairs were randomly selected in student clinical simulation laboratory for this experiment. DUWLs were continuously flushed and water samples were collected at an interval of 30 seconds for 15 minutes. From five dental unit chairs, water samples were collected every 10 seconds for 1 minute. Bacterial levels in water samples were examined by the culture method on R2A plates. After 10 second flushing of DUWLs, the number of bacteria significantly reduced and decreased continuously up to 40 seconds. However, even after the water was flushed for 15 minutes, the bacterial contamination level was not reduced below recommended bacteria level, 200 CFU/ml. In addition to flushing, the periodic chemical disinfection is required to control the DUWL water to the recommended level.

• Journal of Soil and Groundwater Environment
• /
• v.14 no.2
• /
• pp.17-25
• /
• 2009

The applicability of soil washing/flushing to treat a contaminated soil with cadmium (Cd) and copper (Cu) using a mixture of organic/inorganic extractant was evaluated in laboratory-scale batch and column tests. Citric acid was the effective extractant to remove Cd and Cu from the soil among various organic acids except EDTA. Carbonic acid was chosen as inorganic extractant which was not only low toxicity to environment, but also increasing soil permeability. Moreover, the optimum ratio of organic and inorganic extractant to remove Cd and Cu was 10 : 1, and this ratio of organic and inorganic extractant achieved removal efficiencies of Cd (46%) and Cu (39%), respectively. The increasing flow rate of extractant could explain the phenomena of soil packing when carbonic acid was used with organic extractant (i.e. EDTA and citric acid). Therefore, a mixture of organic extractant with inorganic extractant, especially carbonic acid, could resolve a problem of soil packing when this extractant was applied to a field application to remove Cd and Cu using in-situ soil flushing process.

• The Journal of Korean Academy of Prosthodontics
• /
• v.36 no.1
• /
• pp.64-80
• /
• 1998

The risk of cross-contamination in dental clinic is very high. Those who are engaged in dental clinic are exposed to various microorganisms in saliva and blood of patient. Potential possibility of cross-contamination of patient to patient, patient to dentist, dentist to laboratory technician always exist, which is important in the view of public health. It is well known that microorganisms may cause cross-contamination by suck-back of microorganisms into the water supply line or air supply line of dental unit and sprayed back into the next patient's oral cavity. The majority of microorganisms coming from dental unit are water microorganisms from the main water supply which have colonized the tube within the units and multiplied in the relatively warm and stagnant conditions. The purpose of this study is to measure the extent of microbial contamination of dental unit and ultrasonic scaler, to evaluate that dental unit water supply is suitable for drinking water, and to assess the effect of flushing on reduction of microbial contamination of dental unit and ultrasonic scaler. In the first experiment, water samples(50ml) from 20 dental units and 10 ultrasonic scalers in Seoul National Univ. Hosp. were tested for the presence of coliform. The samples were filtered by membrane filtration technique.(Microfil system, Millipore Co. U. S. A.) The filter was then placed onto MacConkey agar plate and the plates with filter on it were incubated aerobically at $37^{\circ}C$ for 5 days. The colors and shapes of colonies were examined if those were coliform. To verify the presence of coliform, the colonies were inoculated into phenol red lactose broth and incubated aerobically at $37^{\circ}C$ for 2 days. The fomation of gas was observed. In the second experiment, water samples from 20 handpieces, 10 ultrasonic scalers and 30 A/W syringes after 0, 2, 4, 6 min. flushing respectively were taken. $200{\mu}l$ water samples were spreaded on Brain Heart Infusion agar plate and the plates were incubated aerobically at $37^{\circ}C$ for 5 days. The number of colony was counted. The results obtained were summarized as follows 1. The water from dental unit and ultrasonic scaler was not suitable for drinking water. 2. No coliform was founded in dental unit and ultrasonic scaler water supply. 3. The number of colony of dental unit and ultrasonic scaler was highest in the group of o min. flushing(p<0.05). 4. There was no statistically significant difference in the extent of microbial contamination among handpiece, ultrasonic scaler and A/W syringe (p>0.05). 5. The number of colony was lowest in the group of 4 min. flushing, but there was no statistically significant difference among 2, 4, 6 min. flushing groups.(p>0.05) 6. It is recommended to flush dental unit water line for 4 min. after use on each patient.

• Membrane Journal
• /
• v.21 no.2
• /
• pp.127-140
• /
• 2011

The effects of $TiO_2$ photocatalyst coating bead concentration, water-back-flushing period (FT), and back-flushing time (BT) were investigated in hybrid process of ceramic ultrafiltration and photocatalyst for advanced drinking water treatment in this study. Photocatalyst coating bead concentration was changed in the range of 10~40 g/L, FT in 2~10 min and BT in 6~30 sec. Then, we observed the effects on resistance of membrane fouling $(R_f)$, permeate flux (J) and total permeate volume $(V_{\Upsilon})$ during total filtration time of 180 min. As decreasing photocatalyst coating bead concentration, $R_f$ increased and J decreased. $V_{\Upsilon}$ was the highest value of 8.85 L at 40 g/L of photocatalyst coating bead concentration. At FT change experiment, $R_f$ decreased and J increased as decreasing FT. Then $R_f$ decreased and J increased according to increasing BT at BT change experiment. Because at NBF (no back-flushing) dramatic membrane fouling reduced membrane pore size, turbid and dissolved organic matters ($UV_{254}$ absorbance) could be removed efficiently. Therefore, treatment efficiencies of turbidity and dissolved organic matters were the highest at NBF. Then by cleaning effect of photocatalyst coating bead, the treatment efficiencies of turbidity and dissolved organic matters increased as decreasing FT and increasing BT.

• Journal of Korea Water Resources Association
• /
• v.42 no.10
• /
• pp.845-855
• /
• 2009

In this study, changing characteristics of bed materials downstream of Daecheong Dam by flushing flow was investigated. Flushing flow affected the downstream environment in such a way that the mean diameter of bed material was increased and the standard deviation was decreased. The vertical sorting of bed materials composed of mixed sediment in the sediment box was observed. The surface layer was composed of gravels, and uniform sand material was buried below it. Relative fractions (Di/D50) of the bed material trapped in the box was nearly 1.0 for the bed material coarser than D$_{50}$ at Hyundo gauging station, and was between two values on the bed surface before and after the flushing flow at Bugang gauging station. Ratio of driving force to resisting force for each fraction ($\tau_i^*$) with the faction size maintained constant for the bed material coarser than D$_{50}$ at Hyundo station. At Bugang station, however, it was rapidly decreased. It means that pavement of the surface layer of bed material at Bugang station was developed, with the sediment particles moving downstream uniformly by flushing flow.

• Membrane Journal
• /
• v.26 no.4
• /
• pp.301-309
• /
• 2016

The effects of water back-flushing time (BT) and photocatalyst-coated polypropylene (PP) beads were investigated in hybrid water treatment process of alumina microfiltration and the PP beads in this study, and compared with the previous study with alumina ultrafiltration membrane and the same PP beads. The BT was changed in the range of 6~30 s with fixed 10 min of back-flushing period (FT). Then, the BT effects on resistance of membrane fouling ($R_f$), permeate flux (J) and total permeate volume ($V_T$) were observed during total filtration time of 180 min. As longer BT, $R_f$ decreased and J increased dramatically; however, $V_T$ was the maximum at BT 10 s. The treatment efficiency of turbidity was high beyond 99.0%, and the BT effect was not shown. The treatment efficiency of organic matters was the highest value of 89.0% at no back-flushing (NBF), and increased as longer BT. The optimum input concentration of the PP beads was 20 g/L in the viewpoint of membrane fouling; however, the optimum PP beads of the previous study was 40 g/L. The treatment efficiency of turbidity and organic matters were the maximum at 30 g/L of the PP beads; however, those of the previous study with alumina ultrafiltration membrane and the same PP beads were the highest at 40 g/L.

• Membrane Journal
• /
• v.18 no.1
• /
• pp.26-34
• /
• 2008

In this study, periodic water-back-flushing using permeate water was performed to minimize membrane fouling and to enhance permeate flux in advanced water treatment system by ceramic microfiltration. We investigated effect of water-back-flushing period (FT) and time (BT), and tried to find the optimal operating conditions. BT was fixed at 3 sec and FT was changed in $30{\sim}120$ sec to inspect effect of FT. Also, FT was fixed at 120 sec and BT was changed as $3{\sim}12$ sec at experiment of BT effect. At both two experiments, TMP was fixed at 1.52 bar, water-back-flushing pressure at 0.98 bar, feed flow rate at 0.5 L/min, and feed water temperature at $20^{\circ}C$. As the result, optimal FT was 30 sec at fixed BT 3 sec in our experimental range. It means that the more frequent back-flushing was the more effective to reduce membrane fouling. However, there were not large effects of FT due to a short BT. Then, increasing BT at fixed FT 120 sec could decrease resistance of membrane fouling ($R_f$) and increase permeate flux (J) and dimensionless permeate flux ($J/J_o$), and the most total permeate volume ($V_T$) could be produced at the maximum BT 12 sec.

• Journal of Environmental Impact Assessment
• /
• v.29 no.3
• /
• pp.219-229
• /
• 2020

This study evaluated the applicability of the convergence technology by deriving the optimum conditions about operating factors of electrical resistance heating to enhance the soil flushing effect on soil contaminated with bunker C oil in the coastal landfill area. As a result of the batch scale experiment, the flushing efficiency of the VG-2020 was higherthan that of the Tween-80, and the flushing efficiency increased by about 1.4 times at 60℃ compared to room temperature. As a result of the electrical resistance heating box experiment, soil temperature rose to 100℃ in about 40~80 minutes in soil with water content of 20~40%, and it was found that the heat transfer efficiency is excellent when the pipe-shaped electrode rod with STS 316 material is located in a triangular arrangement in saturated soil. In addition, it was confirmed that the interval between the electrode rods to maintain the soil temperature above 60℃ under the optimum conditions was 1.5 m, and the soil flushing box experiment accompanying electrical resistance heating showed TPH reduction efficiency of about 55% at 5 Pore Volume, and satisfied the Korean standard for the conservation of soil (less than TPH 2,000 mg/kg) at 10 Pore Volume.

• Membrane Journal
• /
• v.22 no.3
• /
• pp.171-177
• /
• 2012

Effect of humic acid (HA), photo-oxidation and adsorption with periodic $N_2$ back-flushing was investigated in hybrid process of ceramic ultrafiltration and photocatalyst for drinking water treatment. It was compared and investigated with the previous result at water back-flushing in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). As decreasing HA, $R_f$ decreased dramatically and J increased, and finally $V_T$ was the highest at HA 2 mg/L. As HA concentration increased from 2 to 10 mg/L, the membrane fouling resistance after 180 mins' operation ($R_{f,180}$) improved 0.8 times more than that of water back-flushing. Therefore, HA concentration should affect on the membrane fouling at $N_2$ back-flushing than water back-flushing. Turbidity treatment efficiencies were almost constant independent of HA concentration, but HA treatment efficiency was the maximum at HA 2 mg/L. This means that adsorption and photo-oxidation of photocatalyst beads could removed HA at HA 2 mg/L, but it was not enough at 4 mg/L. Beyond HA 6 mg/L, UF could effectively treat HA by thick cake layer on membrane surface and severe inner membrane fouling.