• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.2171-2180
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• 1991

An analysis model for off-design performance of radial inflow turbines with or without variable area guide vane is developed, where two important factors in loss models, total pressure ratio between variable area guide vane exit and scroll casing inlet and rotor loss coefficient are determined without experimental data. The analysis results show that the predicted trends with or without variable area guide vane are consistent with the experimental observations. The comparison of present method with the well-known NASA off-design performance analysis program shows that the mass flow rate and static efficiency by present analysis are in good agreement with those by the NASA program. Therefore, this method can be used to predict off-design performance of radial inflow turbines with validity of the loss models used by present analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.8
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• pp.671-676
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• 2014

The vortex cup is proposed as a method to transport sensitive products such as silicon wafers in manufacturing. Air through the inlet nozzle located at the top of the vortex cup flows to form a swirl in the cylinder. The flow located in the lower part of the thin gap between the vortex cup and the bottom surface escapes and generates a negative pressure that can lift objects. In this research, three-dimensional numerical simulation of the air flow field in a vortex cup is performed, and a comparison of the simulation and experimental results shows very good agreement. In addition, the vortex cup length and shape that affect the negative pressure were applied to the analysis. Through the simulation results, optimum conditions for the vortex cup shape were proposed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.367-375
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• 2013

In this study, the characteristics of the heat transfer coefficient and pressure drop were numerically analyzed according to the axis ratio (AR), pitch, location of vortex generator, and bump phase of the tube surface about an elliptical fin-tube heat exchanger. The boundary condition for CFD analysis was decided as a tube surface temperature of 348 K and inlet air velocity of 1-5 m/s. RSM 7th turbulent model was chosen as the numerical analysis for the sensitivity level. The analysis results indicated that the AR and transverse pitch decreased whereas the heat transfer coefficient increased. On the other hand, there was little difference in the longitudinal pitch. Furthermore, the heat transfer rate was more favorable when the vortex generator was located in front of the tube. Also, the bump phase of the tube surface indicated that the pressure drop and heat transfer were more favorable with the circle type than with the serrated type.

• Journal of Energy Engineering
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• v.12 no.4
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• pp.259-266
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• 2003

Load reduction ring (LRR) was installed on the ABB-Atom sparger to reduce the oscillatory loadings due to the air bubble clouds in the water pool in case of safety relief system operations. In order to investigate the effect of LRR on the pressure field, a numerical simulation on the behavior of air bubble clouds discharging into a water pool through a ABB-Atom sparser without LRR was performed by using a commercial thermal hydraulic analysis code, FLUENT 4.5. Among the multi-phase models contained in the code, the VOF (Volume Of Fluid) model was used to simulate the interface of water, air and steam flows. By comparing the analysis results with the previous ones, the load reduction ring has an effect on reducing the oscillatory loads at the wall. It also includes the effect of air mass and inlet boundary conditions of the pipe on the pressure oscillations at the wall.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.251-258
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• 1990

Optimal design of heat exchanger for closed CO$_{2}$ gas turbine plant of three processes selected from the result of cycle analysis have been discussed previously paper(I) has been carried out under specified inlet and outlet conditions. Independent variables such as number of parallel connection, tube diameter, shell side and tube side pressure loss as well as dependent variables such as shell diameter, number of tubes, number of serial connections were all characterized according to the standardization or so. Search method was used to construct a computer simulation together with the calculation of heat transfer rate by logarithmic mean temperature difference method. Strength analysis of major parts was carried to examine their dimensions satisfying heat transfer and pressure loss requirements.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1824-1827
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• 2005

For application to micro fluid control systems such as ${\mu}TAS$ (Micro Total Analysis Systems) and DDS (Drug Delivery Systems), it is very significant to handle precise and minute flow rates with low pressure pulsation. In this study, a novel valveless piezoelectric pump using peristaltic motion with three disk type PZT actuators is presented. The newly devised pump with an effective size of $70mm{\times}60mm{\times}55mm$ has three actuator layers connected in series from inlet to outlet. The PZT actuator has a maximum displacement of 240 ${\mu}m$ and a maximum force of 1.6 N. When the driving voltage for PZT actuators is sequentially applied with a certain phase shift, the pumping is performed by peristaltic motion of liquid volume. The working fluid is shut off without the driving voltage. Three methods for sequential driving are proposed and experimentally investigated. First and second methods utilize an intermittent sinusoidal waveform with phase shift of $90{\circ}\;and\;120^{\circ}$, respectively. Third method uses a rectangular waveform with phase shift of $90^{\circ}$. A controller with multi-phase shifter is designed and fabricated. Then, frequency and voltage-flow rate characteristics and load pressure-flow rate characteristics are experimentally investigated to verify the validity of the developed pump.

• Journal of the Korean Institute of Gas
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• v.21 no.5
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• pp.9-15
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• 2017

Natural gas fuel has known to be very promising in terms of abundancy and economic value. Therefore it is widely treated as research topics in a variety field of production, storage and utilization. Natural gas has become one of the major sources for the power generation by using internal combustion engines(ICE). Development of natural gas fuel injection device should be preceded to realize a reliable natural gas fuel supply system for a MW class power generation reciprocating ICE. In this research, an injection valve which consists of solenoid and body part with a moving plate was designed and its dynamic performance was experimented in the engine-like environment. Displacement length and diameter of an armature and diameter of a solenoid coil were tested at former study. In this research the effect of materials of solenoid core, size of main housing inlet and supply gas pressure are examined.

• Journal of the Korean Institute of Gas
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• v.13 no.1
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• pp.28-33
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• 2009

Natural gas is the world's most plentiful combustible fuel, abundantly acailable in all continent. A fuel injector designed specifically for low energy density gaseous fuels has been developed. The injector incorporates design features that are necessary to optimize the performance for fuels such as CNG, LNG. Gaseous fuel injectors have a decisive influence upon starting performance, driveability, fuel consumption and exhaust emissions. A gaseous fuel injector has been developed to cope with the considerably larger volume flow rates and the developed gaseous fuel injector could be used at heavy duty natural gas engine. The static flow of injectors at various inlet pressure was directly proportional and the controllability showed great performance.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.573-580
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• 2005

This study was to investigate the removal characteristics of toluene in a gas stream by using a biotrickling filter packed with zeolite-contained polyethylene media. The specific surface area and the void fraction of the media were $500\;m^2/m^3$ and 82%. The surface roughness of the media was higher than that of pure polyethylene media. The toluene removal efficiency decreased with increasing the inlet toluene concentration and gas flow rate. The maximum elimination capacity of toluene in the biotrickling filter was $64\;g/m^3{\cdot}hr$. During 200 days operation, toluene removal efficiency was maintained from 90% to 98% until 167 days, hereafter, it was rapidly reduced with a rise in pressure drop due to an excess proliferation of biomass on the media. Pressure drop and removal capability of the biotrickling filter was fully recovered after backwashing.

• Korean Journal of Agricultural Science
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• v.42 no.1
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• pp.53-61
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• 2015

Development of highly efficient and energy-saving tractors has been one of the issues in agricultural machinery. For design of such tractors, measurement and analysis of load on major power transmission parts of the tractors are the most important pre-requisite tasks. Objective of this study was to perform pre-processing procedures before effective analysis of load data of agricultural tractors (30, 75, and 82 kW) during major field operations such as plow tillage, rotary tillage, baling, bale wrapping, and to select the suitable pre-processing method for the analysis. A load measurement systems, equipped in the tractors, were consisted of strain-gauge, encoder, hydraulic pressure, and radar speed sensors to measure torque and rotational speed levels of transmission input shaft, PTO shaft, and driving axle shafts, pressure of the hydraulic inlet line, and travel speed, respectively. The entire sensor data were collected at a 200-Hz rate. Plow tillage, rotary tillage, baling, wrapping, and loader operations were selected as major field operations of agricultural tractors. Same or different farm works and driving levels were set differently for each of the load measuring experiment. Before load data analysis, pre-processing procedures such as outlier removal, low-pass filtering, and data division were performed. Data beyond the scope of the measuring range of the sensors and the operating range of the power transmission parts were removed. Considering engine and PTO rotational speeds, frequency components greater than 90, 60, and 60 Hz cut off frequencies were low-pass filtered for plow tillage, rotary tillage, and baler operations, respectively. Measured load data were divided into five parts: driving, working, implement up, implement down, and turning. Results of the study would provide useful information for load characteristics of tractors on major field operations.