• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.75-80
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• 2005

Study for toner adhesion is known as an important role in electrophotography. In this research, a centrifugal detachment method was used to measure the adhesion force of several hundred particles simultaneously and to determine its sensitivity to particle size. For uncharged toner particles, we estimated the van der Waals force based on the centrifugal farce experiments. Then for charged toner particles, the centrifugal force experiments were carried out. The difference between the results for charged toner particles and the results for uncharged toner particles was compared with the image force calculated from a model which assumed that the toner charge was located at the center of the particle. In the calculations, experimental data obtained by E-SPART (Electrical- Single Particle Aerodynamic Relaxation Time) analyzer were used. The adhesion force of micro-sized toner particles deposited on the DR surface was found to be approximately 1${\~}$3 nN.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.51-57
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity As the pressure waves are propagating between the pumping station and the distributing reservoir, the pressure inside the pipe drops to the liquid vapor pressure with the pipeline profile, at which time a vapor cavity forms, and finally the column separation occurs. If the pressure in the pipe is less than the atmospheric pressure, the pipe can be collapsed and destroyed after the water columns separated by the vapor cavity rejoin. During the reverse flow, the pressure is so abnormally increased at the pumping station that the accident of flooding may happen due to the failure of system. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations, in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• International Journal of Fluid Machinery and Systems
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• v.8 no.1
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• pp.1-12
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• 2015

In cardiopulmonary support systems with a membrane oxygenation such as a percutaneous cardiopulmonary support (PCPS) or an extracorporeal membrane oxygenation (ECMO), blood pumps need to generate the pressure rise of approximately 200mmHg or higher, due to the high hydraulic resistances of the membrane oxygenation and of the cannula tubing. In order to realize the blood pump with higher pressure rise, higher anti-hemolysis and thrombosis performances, the development of novel centrifugal blood pump composed of two-stage has been conducted by the authors. In the present paper, effective attempts to decrease the wall shear stress and to suppress the stagnation are introduced for the prevention of hemolysis and thrombosis in blood pumps. The hemolysis test was also carried out and it was clarified that the decrease of wall shear stress is effective as a guideline of design of blood pumps for improving the anti-hemolysis performance.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.91-100
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• 2016

Efficiency characteristics of centrifugal turbopumps for a liquid rocket engine were investigated. Predicting the performance of pumps for a turbopump assembly test, the variation on pump efficiency by working fluids was analyzed from pump component tests. Water and liquid nitrogen (LN2) were used for the component test, kerosene (Jet A-1) and liquid oxygen (LOX) were adapted for the turbopump assembly (TPU) test as working fluids. Overall performance of the pumps was investigated covering design/off-design operating points and the pump efficiency on the environment of real media (LOX/kerosene) could be modified from the pump component tests.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.38-45
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• 2016

A study was conducted on the effect of leading edge location for the performance characteristics of a centrifugal compressor impeller. Five impellers with different leading edge location were selected for numerical analysis. The impeller with leading edge located 10% away from the inlet about meridional distance from entrance to exit showed the best total pressure ratio and efficiency. Also, this case showed relatively uniform flow distribution because of a weak intensity of the separation region at impeller exit. The impeller with leading edge located far from this location showed lowest total pressure ratio and efficiency. Performance of compressor also decreased due to non-uniform flow distribution at impeller exit.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.28-34
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• 2014

This paper presents the performance enhancement of a double-inlet centrifugal blower by the shape optimization of an impeller. Two design variables, a number of blade and a length of chord, are introduced, and analyzed by a response surface method. Three-dimensional compressible Navier-Stokes equations are used to analyze the blower performance and the internal flow of the blower. Throughout the numerical simulation of the blower, blower efficiency can be increased by reducing separation flow generating from the blade leading edge of a blade pressure surface. It is noted that recirculation flow observed inside the blade passage induces low velocity region, thus increases pressure loss. Efficiency and pressure of the optimum blower are successfully increased up to 3% and 3.9% compared to those of reference blower at the design flow condition, respectively. Detailed flow field inside the blower is also analyzed and compared.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.81-85
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• 2015

The purpose of this study is to evaluate energy savings for inverter driving multi-stage centrifugal pump. Variable speed driving pump system has high efficiency compared with constant speed driving pump system. Because of difficulty to estimate operating efficiency of variable speed driving pump system, energy saving rates are used to replace operating efficiency. energy saving rates are calculated from pump input power and pump duty cycle. But another researches have used pump duty cycles of each season for energy saving rate. In this study, for estimating energy saving rate more high accuracy, pump duty cycles are measured for 1 year. pump duty cycles, depending on the season and be classified according to the weekday/weekend or during the week day. By this pump duty cycles, Energy saving rate is calculated appropriately.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.209-216
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• 2011

The flow upstream of a centrifugal pump impeller has been investigated by both experimental test and numerical simulation. For experimental study, the flow field at four sections in the pump suction is measured by using PIV method. For calculation, the three dimensional turbulent flow for the full flow passage of the pump is simulated based on RANS equations combined with RNG k-$\varepsilon$ turbulence model. From those results, it is noted that at both design lo ad and quarter load condition, the pre-swirl flow whose direction is the same as the impeller rotation exists at all four sections in suction pipe of the pump, and at each section, the pre-swirl velocity becomes obviously larger at higher rotational speed. It is also indicated that at quarter load condition, the low pressure region at suction surface of the vane is large because of the unfavorable flow upstream of the pump impeller.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.170-178
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• 1999

In general, an impeller of centrifugal turbomachinery is designed at isolated condition without considering the presence of a volute, but when the impeller is operating with its volute, the performance of impeller can be different. This is largely caused by the interaction between the impeller and volute flow fields. The magnitude of distortion is increased as the operating point is away from the design point and, as a result, the interaction between the impeller and volute is stronger. In the present calculation, the flow through the impeller is simulated using coarse grids. The flow within the impeller and the volute is naturally unsteady, but the flow is assumed to be steady across the interface between the volute and impeller flow fields. Under the assumption of steady three-dimensional incompressible turbulent flow, the time averaged N-S equations involving standard k-$\epsilon$ turbulent model was solved by the F.V.M. The calculation results are compared with the experimental results obtained for an industrial fan by Sakai etc. and the Hood agreement is demonstrated. And the effects of the impeller-volute interaction are studied.

• The KSFM Journal of Fluid Machinery
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• v.18 no.2
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• pp.67-72
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• 2015

The purpose of this study is to achieve energy saving effect of inverter driving multistage centrifugal pump. For determining the operation points in the pump system, the system curves should be obtained experimentally. To get the system curves, three pumps combined in parallel and one pump operated with different rotational speeds. But for variable speed pump system, energy saving rates can not be evaluated from operation efficiencies. That is why operation efficiencies, system curves, duty cycles, and input powers of the pump system were measured by the constructed experimental apparatus. The duty cycle segmented into different flow rates and weighting the average value for each segment by the interval time. The system was operated with two different periods. The mean duty cycles were collected from apartment and found that the system operated at 40% and at 50% or below capacity. Measured energy saving rate was 58.16%. Estimating method of energy saving rate could be more effective operation index than that of operation efficiency.