• The KSFM Journal of Fluid Machinery
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• v.5 no.1 s.14
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• pp.42-48
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• 2002

In this study, the instability of a centrifugal compressor with vaned diffuser was investigated. During unstable operation of the test compressor, pressure fluctuations at different diffuser radius ratios were measured by using high frequency pressure transducers. Two different types of stall, mild and deep stalls, were observed alternately and irregularly at some flow rates where the compressor performance was steeply deteriorated. In this transient zone, the size of rotating stall cell was estimated through the wavelet transform analysis. It was about 45 percents of rotor circumferential space at 300 rpm and not dependent on flow rate.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.143-147
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• 2008

Numerical analysis is performed to find flow and heat transfer characteristics for ring type heat exchanger. 3-D numerical predictions are carried out for the ring type heat exchanger system with Reynolds number varying in the range of 1,000 and 10,000. From the prediction, streamwise velocity, pressure drop, flow rate and heat transfer coefficient are analyzed. It is also found that characteristics of pressure drop and heat transfer generally follow well proportional variations of Re$m^$for the wide range of Reynolds number considered in this study.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.17-17
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• 2010

This paper address technical issues in calibrating discharge coefficients of sonic nozzles used to measure the volume flow rate of low vacuum dry pumps. The first challenging issue comes from the technical limit that their calibration results available from the flow measurement standard laboratories do not fully cover the low vacuum measurement range although the use of sonic nozzles for precision measurement of gas flow has been well established in NMIs. The second is to make an ultra low flow sonic nozzlesufficient to measure the throughput range of 0.01 mbar-l/s. Those small-sized sonic nozzles do not only achieve the noble stability and repeatability of gas flow but also minimize effects of the fluctuation of down stream pressures for the measurement of the volume flow rate of vacuum pumps. These distinctive properties of sonic nozzles are exploited to measure the pumping speed of low vacuum dry pumps widely used in the vacuum-related academic and industrial sectors. Sonic nozzles have been standard devices for measurement of steady state gas flow, as recommended in ISO 9300. This paper introduces two small-sized sonic nozzles of diameter 0.03 mm and 0.2 mm precisely machined according to ISO 9300. The constant volume flow meter (CVFM) readily set up in the Vacuum center of KRISS was used to calibrate the discharge coefficients of the machined nozzles. The calibration results were shown to determine them within the 3% measurement uncertainty. Calibrated sonic nozzles were found to be applicable for precision measurement of steady state gas flow in the vacuum process. Both calibrated sonic nozzles are demonstrated to provide the precision measurement of the volume flow rate of the dry vacuum pump within one percent difference in reference to CVFM. Calibrated sonic nozzles are applied to a new 'in-situ and in-field' equipment designed to measure the volume flow rate of low vacuum dry pumps in the semiconductor and flat display processes.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1159-1167
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• 2000

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration. The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to $78{\mu}m$. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2079-2084
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• 2007

A small-scale thermoelectric cooling system was built in an effort to enhance the performance of the refrigeration system by utilizing the water-cooled jacket which was attached on the hot side of the thermoelectric module. Considered design parameters for the water-cooled jacket included the geometry of the flow passage inside the jacket and the flow rate of cooling water. The higher flow rate of cooling water in the jacket resulted in a better performance of the refrigeration system. The introduction of geometrical complexity of the cooling water flow passage to the cooling jacket also showed significant improvement on the performance of the thermoelectric refrigeration system such as the cooling capacity and the COP of the refrigeration system.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.10-16
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• 2003

To investigate the jet effect on circulation control, a segment of model was prepared and inserted horizontally across the test section of the cavitation tunnel. The hydrodynamic forces acting on the model were measured under the 2 dimensional flow behavior. Circulation flow control requires higher flow rate of water jet than boundary layer control does. Jet injection is effective in increasing lift coefficient and the increments reach to 160% in a certain combination of parameters such as an angle of attack, jet flow rate and flap angle. The blown water jet not only reduces form drag but also thrust effect, which is sometimes greater than the form drag in specific conditions.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.427-427
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• 2021

During the rainy season, heavy downpours are always a source of concern for the world. Flooding and heavy rains can devastate communities, disrupt agriculture, and contribute to traffic accidents.. Weir and flow hall effect sensors are the conventional analytical methods for measuring flow rate; in this paper, we analyzed manhole flowrate statistics. The measurement of the flow rate of a notch/weir is a time-consuming task that necessitates continuous mathematical analysis. . We created three types of IoT sensors in this study: (HC-SR04 ultrasonic, YF-S201 magnetic, and HB100 radar), which take the sensor's real-time input signal and estimate the flow using a notch equation and a previously calibrated optimized coefficient of discharge. The proposed systems are cost-effective, but in terms of accuracy, we found that the HC-SR04 ultrasonic sensor is the best of the three systems

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.323-326
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• 2005

In this study, experimental studies were performed the combustion characteristics of end- burning hybrid propulsion system. PMMA, PE were used as fuel and gas oxygen as oxidizer. The regression rate depend on oxidizer flow rate also on thermodynamic properties of fuel. as result, empirical formula for regression rate was deduces with oxidizer flow rate and mass transfer coefficient B number.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.368-372
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• 2005

The variation of regression rate of single port hybrid rocket was studied with various fuel. As fuel, PE, PMMA were used and gas oxygen as oxidizer. The regression rate depends on but flow rates of oxidizer also thermodynamic properties of fuel. In this study, the empirical relation for regression rate of solid fuel were found with mass transfer coefficient(B number) and oxidizer flow rate.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.172-177
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• 2005

The object of this experiment is comparing heat transfer performance and pressure drop characteristics by baffle cut rate, fluid velocity and heating temperature. Experiments were carried out in cross flow heat exchanger with water as a working fluid. In this experiment, baffle cut rate is 30%, 40%, 50%, velocity is 0.5m/s, 1.0m/s, 1.5m/s, and heating temperature is $30^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$. An experimental device to measure the heat transfer coefficient was constructed. The experimental result were obtained for the fully developed turbulent flow of water in tube on the condition of uniform heat flux.