• Korean Journal of Materials Research
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• v.30 no.12
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• pp.693-700
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• 2020

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.65-65
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• 1999

Dry etching technique provides more easy controllability on the etch profile such as anisotropic etching than wet etching process and the results of lots of researches on the characterization of various plasmas or ion beams for semiconductor etching have been reported. Chlorine-based plasmas or chlorine ion beam have been often used to etch several semiconductor materials, in particular Si-based materials. We have studied the effect of He flow rate on the Si and SiO2 dry etching using chlorine-based plasma. Experiments were performed using reactive ion etching system. RF power was 300W. Cl2 gas flow rate was fixed at 58.6 sccm, and the He flow rate was varied from 0 to 120 sccm. Fig. 1 presents the etch depth of si layer versus the etching time at various He flow rate. In case of low He flow rate, the etch rate was measured to be negligible for both Si and SiO2. As the He flow increases over 30% of the total inlet gas flow, the plasma state becomes stable and the etch rate starts to increase. In high Ge flow rate (over 60%), the relation between the etch depth and the time was observed to be nearly linear. Fig. 2 presents the variation of the etch rate depending on the He flow rate. The etch rate increases linearly with He flow rate. The results of this preliminary study show that Cl2/He mixture plasma is good candidate for the controllable si dry etching.

• The KSFM Journal of Fluid Machinery
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• v.1 no.1 s.1
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• pp.24-31
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• 1998

Aerodynamic performance tests and flow measurement were carried out for several radial impellers of NACA 65-810 airfoil. The data base obtained are to be used for verifying the methods of flow analysis and CFD codes. The effects of numbers and span of blades on the performances, efficiency and impeller exit flow are investigated in the present study. The flow rate on the performance curve is proportional to the span of the blade for the same value of fan pressure rise. The magnitude of radial velocity component at the impeller exit gradually decreases from the hub to shroud side. The magnitude of tangential velocity component gradually increases from the hub to shroud side. The way of variations of velocity is the same at the diffuser exit, however, becomes more uniform. The pressure rise performance increases with blade number at the small flow coefficients, however, decreases with the number of blade at the large flow coefficients. This shows that flow guidance in important at the low flow rate and the friction becomes significant at the high flow rate.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.141-146
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• 1999

An experimental investigation on the leakage characteristics of a labyrinth seal, high-low seal, is studied. Pressure distribution and leakage flow rate are measured along with the shaft speed and the pressure difference between the entrance and the exit. Pressure distribution vanes almost linearly along the seal and the leakage flow rate increases as the increase of the pressure difference. Furthermore, it is found that both the shaft speed and the shaft vibration have no influence on the leakage of the labyrinth seal.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.311-317
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• 2005

Hybrid rocket had many advantage with compared to solid and liquid rockets. In this study, swirl flow hybrid motor was designed and manufactured. And the methods of regression rate improvement were considered. Thrust was calculated with pressure of the combustion chamber and the regression rate was measured in low flow rate of oxidizer. Several problems and solutions of operating hybrid rocket was presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.70-73
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• 1988

Influence of Velocity and Temperature on Streaming Electrification of Insulating Oil is investigated by injection method. Leakage current is increased slightly with increasing temperature in the temperature range 20 to $80^{\circ}C$ at low flow rate, however, it show a peak in the temperature 40 to $60^{\circ}C$ at high flow rate. Leakage current is also increased linearly with increasing flow rate in the flow rate range 1 - 31/min but thereafter, it is increased abruptly with increasing flow rate.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.10
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• pp.487-491
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• 2003

The low-cost, simple structured micropump which is actuated by piezoelectric-discs, is fabricated with polydimethylsiloxane (PDMS) and the performances of the micropump, such as pump rate and backpressure, are characterized. The PDMS micropump with diffusers instead of passive check valves as a flow-rectifying element was fabricated. The deflection of glass diaphragm measured by atomic force microscope (AFM) is about 0.4$\mu\textrm{m}$ when applying a 150V square wave voltage at 300Hz across a 300${\mu}\ell$ thick piezoelectric disc. While the square wave driving voltage is applied to the piezoelectric disc of the actuator, the flow rate is measured by fluid displacement variation of the outlet tube. The flow rate of micropump increases with enhancing the applied voltage due to the increase of diaphragm deflection. The flow rate and the backpressure of the micropump with diffusers are about 32.9${\mu}\ell$/min and 173Pa respectively for the above mentioned deflection conditions.

• Electrical & Electronic Materials
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• v.7 no.3
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• pp.206-212
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• 1994

In this paper, We discuss the $POCI_3$ doping process according to the variation of deposition temperature, gas flow rate and doping time. The factors acted with $POCI_3$ doping are gas flow rate deposition temperature and time etc. Among them the temperature is the most important factor. For the $POCI_3$ flow rate, it should not exceed the resistivity saturation point developed on poly surface by annealing treatment. Therefore, this study suggests the optimum conditions of Poly-silicon treatments with the $POCI_3$ flow rate.

• Corrosion Science and Technology
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• v.12 no.2
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• pp.85-92
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• 2013

This work is concerned with an evaluation of dynamic boric acid corrosion (BAC) of low alloy steel for reactor pressure vessel of a pressurized water reactor (PWR). Mockup test method was newly established to investigate dynamic BAC of the low alloy steel under various conditions simulating a primary water leakage incident. The average corrosion rate was measured from the weight loss of the low alloy steel specimen, and the maximum corrosion rate was obtained by the surface profilometry after the mockup test. The corrosion rates increased with the rise of the leakage rate of the primary water containing boric acid, and the presence of oxygen dissolved in the primary water also accelerated the corrosion. From the specimen surface analysis, it was found that typical flow-accelerated corrosion and jet-impingement occurred under two-phase fluid of water droplet and steam environment. The maximum corrosion rate was determined as 5.97 mm/year at the leakage rate of 20 cc/min of the primary water with a saturated content of oxygen within the range of experimental condition of this work.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.243-244
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• 2014

The opposed flow flame in a mesoscale channel was constructed to observe the flame stabilization behaviors at low strain rate conditions (<$10s^{-1}$). The purpose of this study is to get the overall flame behaviors of partially premixed flames with oxygen enhanced conditions at low strain rates. The oxygen ratio in oxidizer was changed from 18 to 30 %. Conclusively, the flame extinction limit approached to about $1s^{-1}$, and divided into three representative regimes corresponding to self propagating flame, transitional flame, quenching flame regimes.