• Proceedings of the KSME Conference
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• 2002.08a
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• pp.775-778
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• 2002

In order to analyse the mechanism of a flow tone around a cavity, the correlations between the flow in the cavity and the boundary layer flow in front of the cavity are studied experimentally in this paper. The instability In the boundary layer forms the vortex at the front edge of the cavity and the flow tone is occurred by the vortex breakdown at the rear edge of the cavity Therefore, the boundary layer measurement is important in the cavity flow control. We measure the velocity of the boundary layer at the entrance of the cavity using hot-wire anemometry and the flow tone around the cavity by microphone. The boundary layer characteristic is changed by the various angle of the flap on the front edge of the cavity, while it is less influenced by the ratio of length and depth of the cavity.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1037-1042
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• 1990

The air-fuel ratio of an internal combustion engine must be controlled with accuracy for the improvements of exhaust emission and fuel consumption. Therefore, it is necessary to measure the exact instantaneous amounts of fuel and suction air, so we carried out the experiments for measuring the air flow velocity in a suction pipe of an internal combustion engine using three types of instantaneous air flowmeter. The results obtained can be summarized as follows: (1) The laminar-flow type flowmeter is able to measure both the average and the instantaneous flow rate, but it is necessary to rectify the pulsating air flow in the suction pipe. (2) The a spark-discharge type flow velocity meter is able to measure the instantaneous air velocity, but it is necessary to choose the suitable electrode form and the spark character. (3) The tandem-type hot-wire flow velocity meter indicates the instantaneous flow velocity and its flow direction.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.6
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• pp.82-89
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• 1991

In order to investigate the characteristics of flow around the intake around the intake valve exit, discharge coefficient and the velocity near the valve exit in steady state were measured using X-type hot-wire. Valve and valve seat insert used in experiment were constructed as the same shape of production engine and the flow characteristics at various flow rates and valve lifts were investigated. From the results of discharge coefficient measurements, it is observed that there exists a similarity between the flow characteristics around the production engine valve and the typical poppet valve. Measurement of the velocity at the valve exit shows that the normalized radial velocity between the primary direction of flow and the valve angle is large, but the difference becomes smaller as the flow rate increases.

• Journal of the korean Society of Automotive Engineers
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• v.10 no.5
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• pp.42-53
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• 1988

The effects of ignition position on combustion in a chamber with swirl flow were investigated by use of hot wire anemometer, high speed schlieren photography, and chamber pressure measurement. In experiments, the closed-constant volume combustion chamber was used, and the swirl was formed unsteadily by suction of external fluid after reducing pressure in the chamber. Results show that the effect of ignition position on combustion depends on the flow state and the flame propagation distance corresponding to each ignition position. Also, the effect of combustion promoting increases as an ignition position moves from the center of chamber to the outside, but maximum burning pressure was obtained at the position that is the shortest flame propagation distance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.3
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• pp.161-167
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• 1991

This paper presents the results of some measurement of the fluctuating velocity field in the turbulent boundary layer disturbed by a triangular prism and discusses the discovery of the disturbed boundary layer. A prism of height 8mm was used for experiments. The streamwise location of the prism was fixed at 1200mm downstream from the leading edge and the space between the prism center and the wall was set at three different values, 6, 15 and 33.5mm. The results show that the near-wall region of the disturbed boundary layer recovers original state much more quickly than the outer region. In the case h=6mm the recovery is faster than the other cases. Moreover, it was found that peak of fluctuating velocities moves outwards somewhat rapidly with increasing ${\times}$ mainly due to the turbulent diffusion of the fluctuating velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.275-283
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• 1996

The turbulence in the engine cylinder is generated by intake pressure and inertia effects during intake stroke, and is generated and decreased by piston compression effect during the compression stroke. The classified needed to generate high turbulence flow at vicinity of ignition timing. Therefore, A single-shot Rapid Intake Compression Expansion Machine (RICEM), which is able to realize the intake, compression, expansion or intake-compression stroke under high piston speed respectively, was manufactured and evaluated in order to find methods to generate high turbulence at around spark timing. It was found that the characteristics of RICEM such as reapperance, leakage, piston displacement with crank angle was corresponding to those of real engine and RICEM simulates not only high temperature and high pressure field but also flow patterns of the actual engine by increasing of pressure in intake line.

• Mass Spectrometry Letters
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• v.12 no.1
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• pp.26-30
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• 2021

The impurity concentration is a crucial parameter for semiconductor thin films. Evaluating the impurity distribution in silicon thin film is another challenge. In this study, we have investigated the doping concentration of boron in silicon thin film using time of flight secondary ion mass spectrometry in dynamic mode of operation. Boron doped silicon film was grown on i) p-type silicon wafer and ii) borosilicate glass using hot wire chemical vapor deposition technique for possible applications in optoelectronic devices. Using well-tuned SIMS measurement recipe, we have detected the boron counts 101~104 along with the silicon matrix element. The secondary ion beam sputtering area, sputtering duration and mass analyser analysing duration were used as key variables for the tuning of the recipe. The quantitative analysis of counts to concentration conversion was done following standard relative sensitivity factor. The concentration of boron in silicon was determined 1017~1021 atoms/㎤. The technique will be useful for evaluating distributions of various dopants (arsenic, phosphorous, bismuth etc.) in silicon thin film efficiently.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3_1spc
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• pp.537-543
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• 2013

A water-$Al_2O_3$ nanofluid was manufactured, and its thermal conductivity was measured in this study. The measurement was performed at volumetric concentrations of 0.5%, 1%, 2%, and 3%, and the nanoparticle sizes were 20 nm and 70 nm. Experimental test equipment, using the transient hot wire method, was installed to measure the thermal conductivity of the nanofluid, and the measured results were confirmed by measuring pure water with a measurement error of 0.92% at $20^{\circ}C$. The thermal conductivity enhancement ranged from 4.8% to 13.6% for the 20 nm particle size, and from 3.1% to 8.8% for the 70 nm particle size at a concentration range of 0.5% to 3%. The enhancement increased with a decrease in particle size and an increase in concentration. With the elapse of time after manufacturing the nanofluid, the thermal conductivity enhancement decreased significantly from 5 to 9 h, and this trend was measured under all of the measurement conditions. After 24 h, the enhancement ranged from 1.2% to 3.5% for the 20 nm particles, and from 0.6% to 2.3% for the 70 nm particles. The enhancement trends with the elapse of time were almost identical with and without stirring the nanofluid. SDBS (Sodium Dodecyl Benzene Sulfonate) was added as a dispersing agent, and the decrease in the thermal conductivity enhancement was delayed.

• Journal of the Korean Society of Combustion
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• v.13 no.2
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• pp.1-6
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• 2008

An experimental study of the flame response in a turbulent premixed combustor has been conducted with room temperature, atmospheric pressure inlet conditions using premixed natural gas. The fuel is premixed with the air upstream of a choked inlet to avoid equivalence ratio fluctuations. Therefore the observed flame response is only the result of the imposed velocity fluctuations, which are produced using a variable speed siren. Measurements are made of the velocity fluctuation in the nozzle using hot wire anemometry and of the heat release fluctuation in the combustor using chemiluminescence emission. The results are analyzed to determine the phase and gain of the flame transfer function as a function of the modulation frequency. Of particular interest is the effect of flame structure on the flame response predictions and measurements. The results show that both the gain and the phase of flame transfer function are closely associated with the flame length and structure, which is dependent upon the upstream flow perturbation as well as equivalence ratio in the current study.

• Journal of Mechanical Science and Technology
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• v.14 no.11
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• pp.1305-1318
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• 2000

The local wall shear stress in transitional boundary layer was estimated from the near-wall mean velocity data using the principle of Computational Preston Tube Method(CPM). The previous DNS and experimental databases of transitional boundary layers were used to demonstrate the accuracy of the method and to provide the applicable range of wall unit y(sup)+. The skin friction coefficients predicted by the CPM agreed well with those from previous studies. To reexamine the applicability of CPM, near-wall hot-wire measurement were conducted in developing transitional boundary layers on a flat plate with different freestream turbulence intensities. The intermittency profiles across the transitional boundary layers were reasonably obtained from the conditional sampling technique. An empirical correlation between the representative intermittency near the wall and free parameter K$_1$of the extended wall function of CPM has been newly proposed using the present and other experimental data. The CPM has been verified as a useful tool to measure the wall shear stress in transitional boundary layer with reasonable accuracy.