• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.3
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• pp.73-82
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• 2006

Wind energy is one of the promising renewable energies that could provide electricity and other mechanical power. Wind energy market is dramatically growing in many European countries, but wind power is only 0.2% of the total renewable energy uses that is only about 2% of the primary energy consumption in Korea. It is widely accepted that wind resources fur power generation are only limited in some areas including coastal regions and mountainous areas in Gangwon province in Korea, particularly in terms of large scale wind power developments. In this study, wind velocity data were analyzed with respect to the potential utilization. The data provided from National Weather Service were used for the analysis. In addition, field wind data were also collected and analyzed for the comparison between the national data. The comparison showed that there were significant differences between the experimental station and the national station that are about 5km away. Annual average wind speed at the experimental station was less than 2 m/s, which is not enough fur wind power generation. It seemed that the topographic condition resulted in a significant difference in wind speed. When 600 W and 2.5 kW wind turbines were used, annual power productions were only 186 kWh and 598 kWh, respectively. When the average wind speed is lower, wind pumping is an alternative use of wind. At the experimental station, the average pumping rate of $3m^3/h$ at the head of 3 m was expected at a 2.5 m rotor under the conditions that efficiencies of the rotor and the pump were 40% and 80%, respectively. It did not seem that the wind pumping was not applicable at the station either. A higher wind speed was required to install the wind machines. Meanwhile, wind pumping would be applicable in conditions with lower pumping heads. Other applications were introduced far further wind energy utilization, including wind powered ventilation and friction heat generation in greenhouses.

• Advances in concrete construction
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• v.10 no.4
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• pp.357-367
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• 2020

The impulse of this paper is to examine the influence of unsteady flow comprising of Eyring-Powell nanofluid over a stretched surface. This work aims to explore efficient transfer of heat in Eyring-Powell nanofluid with bio-convection. Nanofluids possess significant features that have aroused various investigators because of their utilization in industrial and nanotechnology. The influence of including motile microorganism is to stabilize the nanoparticle suspensions develop by the mixed influence of magnetic field and buoyancy force. This research paper reveals the detailed information about the linearly compressed Magnetohydrodynamics boundary layer flux of two dimensional Eyring-Powell nanofluid through disposed surface area due to the existence of microorganism with inclusion the influence of non- linear thermal radiation, energy activation and bio-convection. The liquid is likely to allow conduction and thickness of the liquid is supposed to show variation exponentially. By using appropriate similarity type transforms, the nonlinear PDE's are converted into dimensionless ODE's. The results of ODE's are finally concluded by employing (HAM) Homotopy Analysis approach. The influence of relevant parameters on concentration, temperature, velocity and motile microorganism density are studied by the use of graphs and tables. We acquire skin friction, local Nusselt and motil microorganism number for various parameters.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.76-80
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• 2010

Oil hydraulic piston pumps are being extensively used around the world, because of their simple design, light weight, effective cost, etc. An oil hydraulic pump is likely to have the serious problems of high leakage, friction, and low energy efficiency after a long period of use. In an oil hydraulic piston pump, the clearance between the valve block and piston plays an important role for volumetric and overall efficiency. In this study, the wear property of the SACM645 material with DLC coating used for a hydraulic piston pump was determined by experimentation with variable heat treatment. To investigate the effect according to the piston surface condition, five different types of specimens were prepared. The maximum tensile strengths of the QT and QT Nitration specimens had similar values of about 800 MPa, but the strains indicated a big difference. In a wear test, the wear characteristic of the DLC coating specimen was shown to be excellent. The QT, QT + IH, QT + Nitration, and matirx specimen showed similar wear characteristics. In the case of a dry condition without oil, the DLC coating specimen had good wear resistance, with no wear shown.

• Journal of the Korean earth science society
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• v.26 no.1
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• pp.66-77
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• 2005

Aerological observation at Heuksando located in south-western part of Koran Peninsula has been started at 1 June 2003. In order to clarify the improvement of meteorological prediction quality. it is necessary to compare between aerological data observed at Gawngju and Heuksando and to make clear the influence of Heuksando data assimilation. Therefore numerical simulations were carried out with High resolution meterological prediction system based on MM5(The 5th Generation Mesoscale Model). The pattern of wind and temperature field observed at Heuksando and Gwangju are different due to land surface friction End Sensible heat flux at surface and the wind field Simulated With Gwangju and Heuksando aerological data agree well with observation wind field. Although the amount of precipitation in these experiments is underestimated. the area and starting time of precipitation around Honam province in case with Heuksando data is more reliable that without the data.

• Atmosphere
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• v.22 no.2
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• pp.209-219
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• 2012

Extreme heavy snowfall episodes have been investigated in case of accumulated snowfall amount larger than 50 cm during the past ten years, in order to understand the association of low-level stability with heavy snowfall in the Yeongdong region. In general, the selected 4 events have similar synoptic setting such as the Siberian High extended to East Sea along with the Low passing by the southern Korean Peninsula, eventually inducing easterly in the Yeongdong region. Specifically moist-adiabatically neutral layer has been observed during the heavy snowfall period, which was easily identified using vertical profiles of equivalent potential temperature observed at Sokcho, whereas convective unstable layer has been formed over the East sea due to relatively warm sea surface temperature (SST) about $8{\sim}10^{\circ}C$ and lower temperature around 1~2 km above the surface, obtained from RDAPS. Difference of equivalent potential temperature between 850 hPa and surface as well as difference between air and sea temperatures altogether gradually increased before the snowfall period. Instability-induced moisture supply to the atmosphere from the East sea, being cooled and saturated by the upper cold surge, would make low-level ice cloud, and eventually move inland by the easterly flow. Heavy snowfall will be enhanced in association with low-level convergence by surface friction and upslope wind against Taebaek mountains. This study emphasizes the importance of low level stability in the Yeongdong region using the radiosonde sounding and RDAPS data, which should quantitatively be examined through numerical model as well as heat and moisture supply from the ocean.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.461-467
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• 2012

An experimental study was carried out to measure frictional pressure drop in flow boiling to deionized water in a microchannel having a hydraulic diameter of $500{\mu}m$. Tests were performed in the ranges of heat fluxes from 100 to $400kW/m^2$, vapor qualities from 0 to 0.2 and mass fluxes of 200, 400 and $600kg/m^2s$. The frictional pressure drop during flow boiling is predicted by using two models; the homogeneous model that assumes equal phase velocity and the separate flow model that allows a slip velocity between two phases. From the experimental results, it is found that the two phase multiplier decreases with an increase in mass flux. Measured data of pressure drop are compared to a few available correlations proposed for macroscale and mini/microscale. The homogeneous model well predicted frictional pressure drop within MAE of 29.4 % for the test conditions considered in this work.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1245-1252
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• 2001

The condensation pressure drop for pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube was investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and coolant flowing in the annulus. The test section consists of 1220 [mm] length with horizontal copper tube of 3.38 [mm] outer diameter and 1.77 [mm] inner diameter. The refrigerant mass fluxes ranged from 450 to 1050 [kg/(㎡$.$s)] and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main experimental results were summarized as follows : In the case of single-phase flow, the pressure drop of R-134a is much higher than that of R-22 and R-410A for the same Reynolds number. The friction factors for small diameter tubes are higher than those predicted by Blasius equation. In the case of two-phase flow, the pressure drop increases with increasing mass flux and decreasing quality. The pressure drop of R-134a is much higher than that of R-22 and R-410A for the same mass flux. Most of correlations proposed in the large diameter tube showed enormous deviations with experimental data. However, the correlation predicted by Honda et al showed relatively good agreement with experimental data for R-134.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.4
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• pp.463-470
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• 2016

In this paper, the characteristics analysis of LMD track, such as including track structure, track wear resistance and track thickness, were analyzed to enhance the deposition efficiency using a diode-pumped disk laser. SKD61 hot work steel plate and Fe based AISI M2 alloy were used as a the substrate and powder for the LMD process, respectively. The laser power, track pitch and powder feed rate among LMD parameters were adopted to estimate the deposition efficiency. As the laser power is increased, heat input and melting pool on the substrate is grown also increases, so resulting in the increased LMD track thickness was increased. Through EPMA mapping analysis of the cross-section in the LMD track, it was observed that all the elements are evenly distributed inside. Therefore, the entire hardness in the LMD track is expected to be almost uniform regardless of location. The characteristics of the LMD specimen were excellent compared to the STD11 specimen in terms of the wear track width and the wear rate as well as the coefficient of friction. Especially the wear rate of LMD specimen has been significantly reduced by 60 % or more. From Based on the experimental results, the prediction formula of LMD thickness was calculated by using laser power, track pitch and powder feed rate.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.2
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• pp.259-266
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• 2020

Magnetic gears have the same characteristics as mechanical gears, and each rotor does not come in contact, which is advantageous over mechanical gears in friction noise, heat generation, and maintenance. In addition, when the rotor using the coil-winding is applied, it is possible to control the output of the gear as well as to cut off its own drive in the emergency situation and to change its gear ratio. So the application of the magnetic gear is infinite. However, when the coil-winding rotor is used, cogging torque due to the attraction force between the permanent magnet and the iron core appears, which leads to an increase in the torque ripple component causing the rotor vibration. Therefore, in this paper, various shapes of the coil-winding rotor are analyzed to reduce the torque ripple of the rotor, and the optimum shape for reducing the torque ripple of the magnetic gear is presented.

• Journal of Environmental Science International
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• v.16 no.10
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• pp.1169-1177
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• 2007

The main objective of this research was to evaluate the effects of process variables which were forming ability, flow displacement, effective stress, effective strain, fluid vector and products defects on manufactured artificial lightweight aggregate made of both incinerated sewage sludge ash and clay by means of the numerical analysis of a rigid-plastic finite element method. CATIA (3D CAD program) was used for an extrusion metal mold design that was widely used in designing aircraft, automobile and metallic molds. A metal forming analysis program (ATES Co.) had a function of a rigid-plastic finite element method was used to analyze the program. The result of extrusion forming analysis indicated clearly that a shape retention of the manufactured artificial light-weight aggregate could be maintained by increasing the extrusion ratio (increasing compressive strength inside of extrusion die) and decreasing the die angle. The stress concentration of metal mold was increased by increasing an extrusion ratio, and it was higher in a junction of punch and materials, friction parts between a bottom of the punch and inside of a container, a place of die angle and a place of die of metal mold. Therefore, a heat treatment as well as a rounding treatment for stress distribution in the higher stress concentration regions were necessary to extend a lifetime of the metallic mold. A deformity of the products could have made from several factors which were a surface crack, a lack of the shape retention and a crack of inside of the products. Specially, the surface crack in the products was the most notably affected by the extrusion ratio.