• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.238-246
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• 2004

This paper reports an experimental study around a module about forced air flow by blower (35${\times}$35${\times}$6㎣) in a portable personal computer model(200${\times}$235${\times}$10㎣). Experimental report is to know three data to investigate thermal resistance, adiabatic wall temperature and visualized fluid flow around the module by combination of the moving number and the arrangement method of blower. The channel inlet flow velocity has been varied between 0.26, 0.52 and 0.78㎧, and input power ( $Q_{p}$) to the module is 4W. To investigate thermal resistance. the heated module is mounted on two boards(110${\times}$110${\times}$1.2㎣, k=20.73, 0.494W/ $m^{\circ}C$) in parallel-plate channel to forced air flow. The temperature distribution were visualized by heated module on acrylic board(k=0.262W/ $m^{\circ}C$) using liquid crystal film. Fluid flow around the module were visualized using particle image velocimetry system.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.84-92
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• 2010

In this study a numerical analysis has been conducted for the flow characteristics and pumping performance of a piezoelectric-based micropump with electromagnetic resistance exerted on electrically conducting fluid. Here, electromagnetic resistance is alternately applied at the inlet and outlet with alternately applied magnetic fields in association with the reciprocal membrane motion of the piezoelectric-based micropump. A model of Prescribed Deformation is used for the description of the membrane motion. The internal flow characteristics and pumping performance are investigated with the variation of magnetic flux density, tube size, displacement of membrane and the frequency of the membrane. It turns out that the current micropump has a wide range of pumping flow rate compared with diffuser-nozzle based micropumps.

• Tribology and Lubricants
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• v.32 no.5
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• pp.166-171
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• 2016

Electric vehicle ownership is expanding for two reasons: its technology features have enhanced fuel economy, and the number of vehicle emissions regulations is increasing. Battery performance has a large influence on the capability of electric vehicles, and even though battery thermal management has been actively researched, specific technological improvements to battery performance are not being presented. For instance, many industrial applications utilize vortex tubes as components for refrigeration machines because of their numerous intrinsic benefits. If electric vehicles incorporate vortex tubes for battery cooling, performance and efficiency advancements are possible. This study uses a counter-flow vortex tube to investigate its temperature separation characteristics, based on the back pressure of the cold air exit and the difference between the inlet and back pressures. The experiment uses a vortex tube with the following parameters: six nozzle holes, a 20 mm inner vortex diameter (D), a 14D tube length, a 0.7D cold exit orifice diameter, and a nozzle area ratio of 0.142. The measurements prove that the temperature difference between the hot air and cold air decreased because of the flow resistance of the hot air and the backflow phenomenon at the cold air exit. The flow resistance causes the temperature difference to decrease, and the back pressure of the cold air exit influences the flow resistance. The results show that the back pressure significantly influences the efficiency of temperature separation.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.2
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• pp.73-81
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• 2003

The performance of heat exchanger using oscillating heat pipe (OHP) for low temperature waste heat recovery was evaluated. OHP used in this study was made from low finned copper tubes connected by many turns to become the closed loop of serpentine structure. The OHP heat exchanger was formed into shell and tube type. R-22 and R-141b were used as the working fluids of OHP with a fill ratio of 40 vol.%. Water was used as the working fluid of shell side. As the experimental parameters, the inlet temperature difference between heating and cooling water and the mass velocity of water were changed. The mass velocity of water was changed from 30 kg/$m^2$s to 92 kg/$m^2$s. The experimental results showed that the heat recovery rate linearly increased as the mass velocity and the inlet temperature difference of water increased. Finally, the performance of OHP heat exchanger was evaluated by $\varepsilon$-NTU method. It was found that the effectiveness would be 80% if NTU were about 1.5.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.7-15
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• 2009

The aim of this study was to survey the effects of the beachface gradient on 3-D currents around the open inlets of submerged breakwaters. First, the numerical model was validated by a comparison with existing experimental data. This model is able to consider the flow through a porous medium with inertial, laminar, and turbulent resistance terms, i.e. simulate directly WAve?Structure?Seabed/Sandy beach interaction, and can determine the eddy viscosity with a LES turbulent model in a 3-Dimensional wave field (LES-WASS-3D). Using the numerical results of this model, the 3-D currents around the open inlets of submerged breakwaters were examined in relation to the beachface gradient. Moreover, the wave height distribution and mean flow around them are also discussed, as well as the distribution of the wave breaking points over the crest.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.4
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• pp.21-30
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• 1997

This paper describes the experimental method of a pod-type waterjet propulsion system in a towing tank and shows the experimental analysis and test results of a designed waterjet propulsion system to be used for a hybrid high speed craft. The cruising performance of this craft is estimated from the results of the hull resistance test and waterjet test under the assumption that the interaction between the hull and the inlet pod is very small. A pod-type waterjet system with an axial pump was designed and a stand-alone waterjet experimental system was developed. Useful data such as the pump performance, the jet efficiency, the losses of inlet duct and nozzle were obtained. Test results show a good agreement with the design requirement.

• International Journal of Automotive Technology
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• v.2 no.2
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• pp.39-45
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• 2001

Hydrogen is seen as one of the important energy vectors of the next century. Hydrogen as a renewable energy source, provides the potential for a sustainable development particularly in the transportation sector. Hydrogen driven vehicles reduce both local as well as global emissions. The laboratory of transporttechnology (University of Gent) converted a GM/Crusader V-8 engine for hydrogen use. Once the engine is optimised, it will be built in a low-floor midsize hydrogen city bus for public demonstration. For a complete control of the combustion process and to increase the resistance to backfire (explosion of the air-fuel mixture in the inlet manifold), a sequential timed multipoint injection of hydrogen and an electronic management system is chosen. The results as a function of the engine parameters (ignition timing. injection timing and duration, injection pressure) we given. Special focus is given to topics related to the use of hydrogen as a fuel: ignition characteristics (importance of electrode distance), quality of the lubricating oil (crankcase gases with high contents of hydrogen), oxygen sensors (very lean operating conditions), noise reduction (configuration and length of inlet pipes). The advantages and disadvantages of a power regulation only by the air to fuel ratio (as for diesel engines) against a throttle regulation (normal gasoline or gas regulation) are examined. Finally the goals of the development of the engine are reached: power output of 90 kW, torque of 300 Nm, extremely low emission levels and backfire-safe operation.

• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1154-1161
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• 2016

The heat transfer characteristics between liquid lead bismuth eutectic (LBE) and helium are of great significance for the two-loop cooling system based on an accelerator-driven system (ADS). This paper presents an experimental study on the resistance characteristics and heat transfer performance in a LBE-helium experimental loop of ADS. Pressure drops in the LBE loop, the main heat transfer, and the coupled heat transfer characteristics between LBE and helium are investigated experimentally. The temperature of LBE has a significant effect on the LBE thermo-physical properties, and is therefore considered in the prediction of pressure drops. The results show that the overall heat transfer coefficient increases with the increasing helium flow rate and the decreasing inlet temperature of helium. Increasing the LBE Reynolds number and LBE inlet temperature promotes the heat transfer performance of main heat transfer and thus the overall heat transfer coefficient. The experimental results give an insight into the flow and heat transfer properties in a LBE-helium heat exchanger and are helpful for the optimization of an ADS system design.

• Journal of Power System Engineering
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• v.22 no.1
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• pp.11-17
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• 2018

The steady-state, incompressible and three-dimensional numerical analysis was carried out to evaluate the internal flow fields characteristics of wind tunnel contractions made by Morel's curve equations. The turbulence model used in this study is a realizable ${\kappa}-{\varepsilon}$ well known to be excellent for predicting the performance of the flow separation and recirculation flow as well as the boundary layer with rotation and strong back pressure gradient. As a results, when the flow passes through the interior space of the analytical models, the flow resistance at the inlet of the plenum chamber is the largest at $Z_m=300$, 400 mm, but the smallest at $Z_m=700mm$. The maximum turbulence intensity in the test section is about 2.5% when calculated by the homogeneous flow, so it is improved by about 75% compared to the 10% turbulence intensity at the inlet of the plenum chamber due to the contraction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1390-1398
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• 1999

A numerical analysis for ROT sparger of PWR(Pressurized Water Reactor) is carried out. Computation is performed to investigate the flow characteristics as the change of design factor. As the result of this study, RDT sparger's flow resistance coefficient is K=3.53 at the present design condition if engineering mar&in is considered with 20%, and flow ratio into branch pipe is $Q_s/Q_i=0.41$. Velocity distribution at exit is not uniform because of separation in branch pipe. In the change of inlet flow rate and section area ratio of branch pipe for main pipe, flow resistance coefficient is increased as $Q_s/Q_i$ decreasing, but in the change of branch angle and outlet nozzle diameter of main pipe, flow resistance coefficient is decreased as $Q_s/Q_i$ decreasing. As the change rate of $Q_s/Q_i$ is the larger, the change rate of flow resistance coefficient is the larger. The change rate of pressure loss is the largest change as section area ratio changing. The optimal design condition of sparger is estimated as the outlet nozzle diameter ratio of main pipe is $D_s/D_i=0.333$, the section area ratio is $A_s/A_i=0.2$ and the branch angle is ${\alpha}=55^{\circ}$.