• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.5
• /
• pp.457-464
• /
• 2010

Representative methods for removing spilled oil include mechanical skimming, chemical treatment, burning at the surface of the spilled oil, and microbiological degradation. Among these methods, mechanical skimmer is the most efficient. Mechanical skimming can be classified into the following categories: belt-type, disk-type, weir-type, drum-type. We designed models with a submerged orifice for use in our experiments, for an objective and systematic evaluation of the recovery efficiency of mechanical skimming. Basically, oil is lighter than seawater and hence tends to float on the surface of the latter if there is sufficient time for floating. The present skimmer is kind of wear-type with the submerged orifice for seawater to be squeezed through, minimizing water content in the tank. From the experimental results, we identify the parameters that influence the oil recovery rate and recovery efficiency. The recovery efficiency can be enhanced by increasing the thickness of the oil layer in the first oil accumulative tank.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.6
• /
• pp.1539-1544
• /
• 1995

Copper blow test to measure the forging capability of 35 ton counterblow hammer and upset of plasticine on the model hammer to investigate the change of the blow efficiency during the forging process have been performed together with finite element analyses of these experiments. The blow efficiency of the hammer has been found to be dependent on the friction and on the contact area between the die and the workpiece. The effects of the volume and the aspect ratio of the billet have not been found. Inferring from the experimental results and Schey's empirical formula on the forging load, we expect that the efficiency also varies with the flow stress of the workpiece material and with the shape complexity of the forging product.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.5
• /
• pp.30-35
• /
• 2013

In order to increase cell efficiency in crystalline silicon solar cell, reduction of light reflection is one of the essential problem. Until now silicon wafer was textured by wet etching process which has random patterns along crystal orientation. In this study, high aspect ratio patterns are manufactured by nano imprint process and reflectance could be minimized under 1%. After that, screen printed solar cell was fabricated on the textured wafer and I-V characteristics was measured by solar simulator. Consequently cell efficiency of solar cell fabricated using the wafer textured by nano imprint process increased 1.15% than reference solar cell textured by wet etching. Internal quantum efficiency was increased in the range of IR wave length but decreased in the UV wavelength. In spite of improved result, optimization between nano imprinted pattern and solar cell process should be followed.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.11
• /
• pp.1564-1570
• /
• 1998

In-situ particle monitors(ISPMs) are widely used for monitoring contaminant particles in vacuum-based semiconductor manufacturing equipment. In the present research, the performance of a Particle Measuring Systems(PMS) Vaculaz-2 ISPM at subatmospheric pressures has been studied. We created uniform upstream conditions of particle concentration and measured the detection efficiency, the lower detection limit, and the size response of the ISPM using uniform sized methylene blue aerosol particles. The effect of particle size, particle velocity, particle concentration, and system pressure on the detection efficiency was examined. Results show that the detection efficiency of the ISPM decreases with decreasing chamber pressure, and with increasing mass flow rate. The lower detection limit of the ISPM, determined at 50 % of the measured maximum detection efficiency, was found to be about $0.15{\sim}0.2{\mu}m$, which is similar to the minimum detectable size of $0.17{\mu}$ given by the manufacturer.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.5
• /
• pp.1200-1210
• /
• 1990

Conventional efficiencies of the adiabatic compression process such as isentropic efficiency and polytropic efficiency can be explained as exergetic efficiencies replacing the reference atmospheric temperature with the temperature which can be determined in the process itself. So that, other efficies such as maximum isentropic efficiency can be defined by giving proper reference temperatures. By applying the same logical principles, exergetic and other rational efficiencies for the non-adiabatic compression process are also defined and discussed for their physical meanings and reasonable engineering applications.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.4
• /
• pp.351-358
• /
• 2006

This paper presents analytical results of a rotary vane compressor performance when the compressor is used for air supply from underwater. Compression characteristics such as pressure and temperature in a compression chamber are analyzed. Volumetric and adiabatic efficiencies are calculated. Vane dynamics are also performed to give reaction forces on the vane from the cylinder inner surface and from vane slots. Compressor efficiency is about 34.9%, and about 55% of the compressor loss is produced by the friction between the vane nose and the cylinder wall. Volumetric efficiency is about 79.5%, and indicated efficiency is about 77.1%, which are comparable to other displacement type compressors. When roller was introduced between housing inner wall and vane tips, mechanical efficiency could be improved by as much as 24.9%, depending on the roller friction.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.1
• /
• pp.95-101
• /
• 2014

In this study, an ISM (immersed solid method) was used for investigating the mass flow rate and efficiency of an involute-gear pump featuring very high rotational speed. For considering circulation flow at the gear pump and housing, fluid flow was assumed as turbulent, and the rotational speed of the gear pump increased under the condition of constant pressure at both the inlet and outlet. The efficiency and mass flow rate of the gear pump were studied by varying its rotational speed and the clearance between the gear tip and the housing. In the simulation results, as the rotational speed were increased, the average mass flow rate and efficiency increased. Furthermore, as the clearance between the gear tip and the housing was increased, the average mass flow rate and efficiency decreased. The efficiency was 85.11, 90.94, and 93.62 at rotational speeds of 6,000 rpm, 8,000 rpm, and 10,000 rpm, respectively, under the condition that there was no clearance. In addition, the efficiency was 93.62, 93.29, and 92.74 at clearances of 0 m, 0.00001 m, and 0.00003 m respectively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2004.03a
• /
• pp.577-587
• /
• 2004

A coaxial pulsed plasma thruster (PPT) with a Teflon cavity was designed, and its performance characteristics were examined varying stored energy, cavity length and capacitance. The PPT was tested as the entire system including the discharge circuit, and the results were explained with both the transfer efficiency and the acceleration efficiency. The transfer efficiency is defined as the fraction of energy in capacitors supplied into plasma, and the acceleration efficiency as the fraction of energy supplied into plasma converted to thrust energy. To estimate these efficiencies, the equivalent plasma resistance was defined and calculated using energy conservation during discharge. The equivalent plasma resistance proportionally increased with cavity length, and therefore the current peak increased with decreasing cavity length. The energy density calculated by the transfer efficiency was increased with decreasing cavity length. As a result, higher acceleration efficiency and lower transfer efficiency were obtained with shorter cavity length. Accordingly, there was an optimal cavity length for the thrust efficiency. The specific impulse and the impulse bit per unit stored energy ranged from 390 s and 50 $\mu$ Ns/J for a cavity length of 34 mm to 825 s and 11 $\mu$ Ns/J for a cavity length of 4 mm when the stored energy was fixed to 21.4J. Thus, it was showed that the performance of this PPT approached that of electromagnetic-acceleration-type PPT with decreasing cavity length. The PPT achieved thrust efficiencies of 10-12% at 21.4 J and 6-7% at 5.35 J at cavity lengths between 14 mm and 29 mm.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.5
• /
• pp.401-410
• /
• 2019

The operating conditions greatly impact the efficiency and performance of polymer electrolyte membrane (PEM) fuel cell systems and must be properly managed to ensure better performance and efficiency. In particular, small variations in operating conditions interact with each other and affect the performance and efficiency of PEM fuel cell systems. Thus, a systematic study is needed to understand how small changes in operating conditions affect the system performance and efficiency. In this paper, an automotive fuel cell system (including cell stack and balance of plant [BOP]) with a turbo-blower was modeled using MATLAB/Simulink platform and the sensitivity analyses of main operating parameters were performed using the developed system model. Effects of small variations in four main parameters (stack temperature, cathode air stoichiometry, cathode pressure, and cathode relative humidity) on the system efficiency were investigated. The results show that cathode pressure has the greatest potential impact on the sensitivity of fuel cell system efficiency. It is expected that this study can be used as a basic guidance to understand the importance of achieving accurate control of the fuel cell operating conditions for the robust operation of automotive PEM fuel cell systems.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.1
• /
• pp.52-61
• /
• 2009

This experiment was conducted in attempt of improving hydrodynamic efficiency of the propulsion mechanism by installing a spring to the wing so that the opening angle of the wing in one stroke can be changed automatically, compared to the existing method of fixed maximum opening angle in Weis-Fogh type ship propulsion mechanism. Average thrust coefficient was almost fixed with all velocity ratio with the prototype, but with the spring type, thrust coefficient increased sharply as velocity ratio increased. Average propulsive efficiency was larger with bigger opening angle in the prototype, but in the spring type, the one with smaller spring coefficient had larger value. In the range over 1.0 in velocity ratio where big thrust can be generated, spring type had more than twice of propulsive efficiency increase compared to the prototype.