• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2385-2394
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• 1992

Granular solid propellants having energy and fast burning rate produce great thrusts within extremely short time intervals. Thus numerical researchs prevailed rather than experimental. Using a 2-phase fluid dynamics model among 1-dimensional 2-phase models, a numerical program was set up to describe reacting flow fields, moving boundary with oscillating pressure waves and constitutive laws research. It deserves special emphasis that correlations of convective heat transfer coefficient and viscous drag force among constitutive laws are tested and discussed because slight variations of their constants make a large influence on their results. In this calculations, some of correlations make the large difference in results. Therefore constitutive laws for convective heat transfer coefficient and viscous drag force need more considerations with experiments.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.134-140
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• 1999

A three-dimensional CSCM upwind flux difference splitting Navier-stokes code with two-equation turbulence models was developed to predict the transonic flows in centrifugal compressor diffuser. The k-$\epsilon$ model of Abe et al. performed well in predicting the pressure distribution in the shock wave/turbulent boundary-layer interaction. Three turbulence models predicted the similar distribution of static pressure through the diffuser and showed a good agreement with the experimental results. The secondary flows in the corner were predicted well by these turbulence models. The pressure increase before the throat of the diffuser vane is important for the overall pressure recovery. As the mass flow rate increased the blockage decreased at the throat. The pressure coefficient distribution through the diffuser depended on the throat blockage not on the rotational speed of the impeller.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.70-75
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• 2021

Recently, several efforts have been made to improve the thermal efficiency of a refrigerant compressor. In this study, we attempted to improve energy efficiency ratio (EER) performance by reducing the superheat of the linear compressor. To this end, heat generated inside the compressor must be effectively dissipated. Therefore, heat dissipation was improved by processing ribs in the gap-flow region generated owing to the vibration of the compressor body. The results showed that the convective heat transfer coefficient becomes significantly high when ribs are used, increasing the heat dissipation rate. This helps improve EER by reducing the superheat of the compressor.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1974-1979
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• 2007

In this study, Ice slurry generator heat transfer characteristics are experimentally investigated for the ice slurry generating system with scraper which is pneumatically operated. The ice slurry generator has the same shape as the vertical double tube type heat exchanger. Refrigerant is flowing in the outside tube and ethylene glycol solution in the inside tube. Refrigerant and solution water are parallel flow type which entering bottom of generator and leaving top of generator. The experimentations are conducted under the various test conditions such as compressor speed and cooling water temperature. For the above experimental conditions, heat transfer characteristics of the ice slurry generating system are evaluated in terms of the overall heat transfer coefficient and the heat transfer rate. And the experimental results show that the heat transfer rate of the system is increased as the compressor speed increases and the cooling water temperature decreases.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.5
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• pp.77-86
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• 2010

Hydrologic Simulation Program-Fortran (HSPF) coupled with PEST which is optimization program was calibrated and validated at Bochung watershed by using monitoring data of water quantities and nutrient loading. Although the calibrated data were limited, model parameters of each land use type were optimized and coefficient of determinations were ranged from 0.94 to 0.99 for runoff, from 0.89 to 1.00 for TN loading, and from 0.92 to 1.00 for TP loading. The optimized hydrological parameters indicated that the forested land could retain rainfall within soil layer with high soil layer depth and infiltration rate compared with other land use type. Hydrological characteristics of paddy rice field are low infiltration rate and coefficient of roughness. The calibrated parameters related to nutrient loading indicated generation of nutrient pollution from agricultural area including upland and paddy rice field higher than other land use type resulting from fertilizer application. Overall PEST program is useful tool to calibrate HSPF automatically without consuming time and efforts.

• The Korean Journal of Rheology
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• v.7 no.3
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• pp.181-191
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• 1995

점탄성유체의 물성치들 중 정압열팽창계수 및 밀도는 자연대류 열전달 연구에 전단 속도 0에서의 점도는 점탄성유체에 대한 모델들 사용 시 필요하다. 본 연구에서는 점탄성유 체이며 마찰 감소 첨가제, 유전자 분리용액동으로 사용하는 Separan AP-273 용액의 정압열 팽창계수, 밀도 및 전단속도 0에서의 점도에대한 농도 및 온도의 영향을 조사하였다. 작동유 체의 물성치들은 10~6$0^{\circ}C$의 온도범위와 100~20,000wppm의 농도범위에서 측정되었다. 작 동유체의 물성치들에 미치는 열주기와 노화의 영향을 조사하기 위해서 정압열팽창계수와 전 단속도 0에서의 점도를 교대로 두 번씩 측정했다. 정압열팽창계수 및 밀도를 측정하는 장치 의 측정 정밀도는 증류수에 대한 측정치와 문헌에 나타난 자료를 비교하여 얻었고 이는 $\pm$ 2%이내였다. Separan AP-273용액의 정압열팽창계수 및 밀도는 증류수의 값들로 대치될수 있다. 작동유체의 정압열팽창계수와 밀도는 열주기와 노화의 영향을 받지 않았다. 낙하식 점 도계를 사용해 측정한 겉보기점도 값들을 나타내느 flow curve에서 전단속도가 0이 되는방 향으로 겉보기점도를 외삽시켜 Separan AP-273용액에 대한 전단속도0에서의 점도를 얻었 다. 정압열팽창계수 측정 전후에 측정한 작동유체에 대한 전단속도 0에서의 점도는 열주기 와 노화로 인해 퇴화되었다.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.347-352
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• 2005

The objectives of this paper are to study the characteristics of heat transfer and pressure drop in plate heat exchangers for absorption applications, and to quantify the effect of mass flow rate, solution concentration, and geometric conditions such as chevron angle on the heat transfer coefficient and pressure drop in the plate heat exchangers. The working fluid is $H_2O$/LiBr solution with the LiBr concentration range of 53.2 - 62.5 % in mass. The results show that the overall heat transfer coefficient increases linearly with increasing Re. The heat transfer rate increases with increasing the chevron angle while it does not significantly depend on the LiBr concentration. The pressure drop also increases with increasing the chevron angle. The effect of the chevron angle on the pressure drop is more significant than that of the concentration.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.410-423
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• 2019

Fire suppression using a water mist nozzle directly above an n-Heptane pool in a fire compartment with a door opening was numerically investigated using the Fire Dynamics Simulator (FDS) for the purpose of application in nuclear power plants. Input parameters for the numerical simulation were determined by experimental measurements. Water mist was activated 10 s after the fire began. The sensitivity analysis was conducted for three input parameters: total number of cubic cells of 6032-2,926,400, droplets per second of 1000-500,000, and extinguishing coefficient of 0-100. In a new simple calibration method of this study, the extinguishing coefficient yielding the fire suppression time closest to that measured by experiments was found for use as the FDS simulation input value. When the water mist jet flow made contact with the developed fire, the heat release rate instantaneously increased, and then rapidly decreased. This phenomenon occurred with a displacement of the flame near the liquid fuel pool. Changing the configuration of the door opening with different aspect ratios and opening ratios had impact on the maximum value of the heat release rate due to the flame displacement.

• Journal of Computational Design and Engineering
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• v.3 no.4
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• pp.349-362
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• 2016

The numerical solutions of unsteady hydromagnetic natural convection Couette flow of a viscous, incompressible and electrically conducting fluid between the two vertical parallel plates in the presence of thermal radiation, thermal diffusion and diffusion thermo are obtained here. The fundamental dimensionless governing coupled linear partial differential equations for impulsive movement and uniformly accelerated movement of the plate were solved by an efficient Finite Element Method. Computations were performed for a wide range of the governing flow parameters, viz., Thermal diffusion (Soret) and Diffusion thermo (Dufour) parameters, Magnetic field parameter, Prandtl number, Thermal radiation and Schmidt number. The effects of these flow parameters on the velocity (u), temperature (${\theta}$) and Concentration (${\phi}$) are shown graphically. Also the effects of these pertinent parameters on the skin-friction, the rate of heat and mass transfer are obtained and discussed numerically through tabular forms. These are in good agreement with earlier reported studies. Analysis indicates that the fluid velocity is an increasing function of Grashof numbers for heat and mass transfer, Soret and Dufour numbers whereas the Magnetic parameter, Thermal radiation parameter, Prandtl number and Schmidt number lead to reduction of the velocity profiles. Also, it is noticed that the rate of heat transfer coefficient and temperature profiles increase with decrease in the thermal radiation parameter and Prandtl number, whereas the reverse effect is observed with increase of Dufour number. Further, the concentration profiles increase with increase in the Soret number whereas reverse effect is seen by increasing the values of the Schmidt number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.11
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• pp.450-457
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• 2016

While many studies on the heat transfer effect of an impinging jet have been published, most studies focus on the downward impinging jet. This study investigates the impinging jet heat transfer phenomenon when water at a temperature of $24^{\circ}C$ impinges on the downward isothermal circular plate at 60, 70, and $80^{\circ}C$ and when the upward round jet nozzle is 4, 6, and 8 mm diameter with a flow rate 3.6, 4.6, and 5.6 L/min, respectively, and when the ratio of the nozzle clearance/nozzle diameter (H/D) is 1. The results showed that, as the nozzle diameter decreases, the heat transfer coefficient increases at a constant flow rate. The correlation equation of $Nu_r$, $Pr_r$, and $Re_{jg}$ is obtained in the impinging and constant velocity flow region $(Nu_r/Pr^{0.4}_r)Dr=4.6[Re_{jg}(r/R_c)Dr]^{0.8}$ at all flow rates, in the deceleration and falling flow regions $(Nu_r/Pr^{0.4}_r)Dr=42.7{\mid}Re_{jg}(r/R_c)Dr-345.7{\mid}^{0.3}$ at 3.6 L/min, $(Nu_r/Pr^{0.4}_r)Dr=92.4{\mid}Re_{jg}(r/R_c)Dr-16.8{\mid}^{0.2}$ at 4.6 L/min, and $(Nu_r/Pr^{0.4}_r)Dr=322.4{\mid}Re_{jg}(r/R_c)Dr-536.2{\mid}^{0.01}$ at 5.6 L/min.