• 설비공학논문집
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• 제27권3호
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• pp.146-151
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• 2015

The heat transfer performance of heating medium oil fluidized bed heat exchanger was measured. The operation variables were air flow rate, air inlet temperature, moisture content, water flow rate and water inlet temperature. The outside heat transfer coefficient was determined from the heat exchanger experiment and its experimental correlation was determined as a function of air velocity and viscosity of heating medium oil. Effect of viscosity was well agreed with the previous studies. Errors of the correlation equation was less than about 10% for outside heat transfer coefficient developed in this study when compared with the measured value. Hot water with the temperature greater than $77^{\circ}C$ could be produced by using the heating medium oil fluidized bed heat exchanger.

• International Journal of Fluid Machinery and Systems
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• 제10권3호
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• pp.218-226
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• 2017

Severe radial thrust under off-design operating conditions can be a harmful factor for centrifugal pumps. In the present work, effects of geometry of a double volute casing on the hydrodynamic performance of a centrifugal pump have been investigated focusing on off-design conditions. Three-dimensional steady Reynolds-averaged Navier-Stokes analysis was carried out by using shear stress transport turbulence model. Numerical results for the hydrodynamic performance of the centrifugal pump were validated compared with experimental data. The hydraulic efficiency and radial thrust coefficient were used as performance parameters to evaluate the hydrodynamic characteristics of the centrifugal pump. The cross-sectional area ratio of the volute casing, the expansion coefficient of the rib structure, the distance between the rib starting point and volute entrance, and radius and width of the volute entrance, and length of the rib structure, were selected as geometric parameters. Results of the parametric study show that the performance parameters are significantly affected by the geometric variables and operating conditions. Optimal configurations of the double volute casing based on the design of experiments technique show outstanding performance in terms of the efficiency and radial thrust coefficient.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.11-24
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• 2017

The present work focuses multi-objective optimization of blade sweep for a Wells turbine. The blade-sweep parameters at the mid and the tip sections are selected as design variables. The peak-torque coefficient and the corresponding efficiency are the objective functions, which are maximized. The numerical analysis has been carried out by solving 3D RANS equations based on k-w SST turbulence model. Nine design points are selected within a design space and the simulations are run. Based on the computational results, surrogate-based weighted average models are constructed and the population based multi-objective evolutionary algorithm gave Pareto optimal solutions. The peak-torque coefficient and the corresponding efficiency are enhanced, and the results are analysed using CFD simulations. Two extreme designs in the Pareto solutions show that the peak-torque-coefficient is increased by 28.28% and the corresponding efficiency is decreased by 13.5%. A detailed flow analysis shows the separation phenomena change the turbine performance.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.158-160
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• 2005

Zener coefficient on cubic shaped particle was proposed. Most previous researches about Zener coefficient were developed on the assumption that the shape of particle is spherical. But, some particle has other shape, and modification of Zener coefficient needs with shape of particle. In this research, TiN particle that has a cubic shape was considered. A Zener coefficient of a cubic shape TiN was theoretically calculated with appropriate assumptions. And, using a semi-empirical method, Zener coefficient was also measured. Finally, the proposed Zener coefficient was proved by comparing with experimentally measured data.

• 전기전자학회논문지
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• 제22권2호
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• pp.480-483
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• 2018

Wireless power transfer (WPT) is the technology that forces the power to transmit electromagnetic field to an electrical load through an air gap without interconnecting wires. This technology is widely used for the applications from low power smartphone to high power electric railroad. In this paper, the model of wireless power transfer circuit for the low power system is designed for a resonant frequency of 13.45 MHz. Also, a feedback WPT circuit to improve the power transfer efficiency is proposed and shown better performance than the original open WPT circuit, and the methodology for power efficiency improvement is studied as the coupling coefficient increases above 0.01, at which the split frequency is made.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.28-33
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• 2001

Screw conveyors are used extensively in industrial for conveying and elevating materials. Despite their apparent simplicity, the mechanics of the conveying action is very complex. so many engineers depend on experiential data. Capacities of screw are pumping, steady flow of polymer melts, steady volumetric throughput etc. they are affected by geometry of screw, heat flux, pressure on inside barrel, rotating velocity, friction coefficient at screw surface etc. by computation volumetric efficiency increases as rotating velocity increases and decreases as friction coefficient increases. also it decreases with short pitch length. and double flight screw is more effective than single flight screw. The temperature of polymer melts by heating pad and injection pressure play a very important role in the injection molding machine. so in this paper we analyze thermal distortion and stress of screw includes pressure and temperature distributions by finite element analysis to understand what design factors influence on volumetric throughput efficiency of the screw and thermo-mechanical characteristics of screw.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.787-790
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• 2002

In this work, numerical experiments ave conducted to find out the optimal shape of flapping-airfoil using thickness variation airfoils. In the previous study of flapping-airfoil, we had found that the thrust efficiency of thicker airfoil is better than thinner one, but the latter has higher thrust coefficient. Therefore, we have combined thin(NACA0009) and thick(NACA0015)airfoil to overcome these demerits of each airfoil. Using this combined airfoil, we can achieve acceptable aerodynamic performances from thrust efficiency and coefficient points of view. In order to computational study, we have used parallel-implemented incompressible Wavier-Stokes solver. Computational results show how to design leading and trailing edge shapes.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2003년도 추계학술발표회
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• pp.497-500
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• 2003

If ground water levels of a confined fractured rock aquifer fluctuate with sea tides, individual values of hydrogeologic parameters can be determined. Tidal efficiency and time lag are first calculated from the water level data recorded at an observation device situated inland from the sea. The tidal efficiency factor of the aquifer at the seacoast is then determined from the observation in monitoring wells and used to calculate storage coefficient. Tidal efficiency factor and the tidal time lag are utilized to calculate storage coefficient and the results are compared. This method is tested in the southeastern coastal area of Busan, Korea. This is a simple and inexpensive way to test confined aquifer but the analysis should be performed according to the coastal environment.

• 한국경영과학회지
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• 제37권1호
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• pp.29-43
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• 2012

We design a DEA-AR model using multiple regression analysis with new methods which limit weights. When there are multiple input and single output variables, our model can be used, and the weights of input variables use the regression coefficient and coefficient of determination. To verify the effectiveness of the new model, we evaluate the efficiency of the Regional Corporations in Korea. Accordance with statistical analysis, it proved that there is no difference between the efficiency value of the DEA-AR using AHP and our DEA-AR model. Our model can be applied to a lot of research by substituting DEA-AR model relying on AHP in the future.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.69-79
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• 2000

Falling film rectification involves simultaneous heat and mass transfer between vapor and solution film. In the present work, the adiabatic rectification process of ammonia-water vapor by the falling solution film on the vertical plate was investigated. The continuity momentum, energy and diffusion equations for the solution film and the vapor mixture were formulated in integral forms and solved numerically, The model could predict the film thickness, the pressure gradient, and the mass transfer rate. The effects of Reynolds number and ammonia concentration of solution and vapor mixture, rectifier length, and the enhancement of mass transfer coefficient in each phases were investigated. The stripping of water in vapor mixture occurred near the entrance of ammonia solution, which imposed the proper size of an adiabatic rectifier. Rectifier efficiency increased as film Reynolds number increased and as vapor mixture Reynolds number decreased. The improvement of rectifier efficiency was significant with the enhancement of mass transfer coefficient in falling film.