• 설비공학논문집
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• 제21권11호
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• pp.629-635
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• 2009

In this study, fin surface temperature and frost properties, i.e., frost thickness and frost surface temperature on a heat exchanger, were experimentally analyzed with different fin thicknesses, fin sizes and thermal conductivities of fin. As a result, it is found that fin thickness and thermal conductivity of fin should be considered in order to design an efficient heat exchanger fin. Correlations of dimensionless average frost properties were proposed as functions of dimensionless air temperature, dimensionless fin base temperature, dimensionless fin thickness, absolute air humidity, Reynolds number and Fourier number. The correlations predicted well the average frost thickness with a maximum error of 10.5% and frost surface temperature with a maximum difference of $0.89^{\circ}C$, respectively.

• 설비공학논문집
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• 제11권5호
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• pp.700-708
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• 1999

The optimum dimple shape and arrangement in the channel of a plate heat exchanger with staggered dimples are proposed in this study. Four important geometric parameters are selected as design variables, the pressure drop and heat transfer characteristics are examined in the channel of plate heat exchangers. The optimization is accomplished by minimizing the global criterion function which consists of the correlations of Nusselt number and pressure drop. The optimum geometric parameters were found at the dimensionless dimple distance (L) of 0.272, the dimensionless dimple angle ($\beta$) of 0.44, the dimensionless dimple volume (V) of 0.106 and the dimensionless dimple pitch (G) of 0.195. It is found that the heat transfer and pressure drop of the optimum model are increased by approximately 227.9% and 32.9%, respectively, compared to those of the base model.

• 한국초전도ㆍ저온공학회논문지
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• 제21권3호
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• pp.1-5
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• 2019

The superconductor stability theories are consistently described by the integral formula. If the defined stability function is a simple decreasing function, it becomes a cryogenic stability condition. If the stability function has a maximum value and a minimum value, and the maximum value is less than 0, then it is a cold-end recovery condition. If the maximum value is more than 0, it can be shown that the unstable equilibrium temperature, that is, the MPZ (minimum propagation zone) temperature distribution can exist. The MPZ region is divided into two regions according to the current ratio. At the low current ratio, the maximum dimensionless temperature is greater than 1, and at the relatively high current ratio, the maximum dimensionless temperature is less than 1. In order to predict the minimum quench energy, the dimensionless energy was obtained for the MPZ temperature distribution. In particular, it was shown that the dimensionless energy can be obtained even when the MPZ maximum temperature is 1 or more.

• 대한설비공학회지:설비저널
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• 제16권5호
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• pp.504-515
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• 1987

This study conducts an analysis for the heat diffusion of an annular fin considering con-vection phenomena at the fin edge as well as along the fin perimeter. When the temperature of the fin base is given with an increasing exponential function, the exact series solutions of tem-perature distribution are obtained by laplace transformation in terms of dimensionless para-meters. From these solutions heat flux and fin efficiency can be obtained. These exact solu-tions converge rapidly for large values of dimensionless time, but slowly for small ones. To avoid this convergence difficulty, approximate solutions of the temperature distribution and heat flux for small values of dimensionless time are also presented. Substituting the variations of dimensionless parameters into the these exact solutions, the characteristics of these response are investigated.

• 설비공학논문집
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• 제4권4호
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• pp.243-252
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• 1992

A mixed convection heat transfer from two vertical parallel plates has been studied numerically by the finite difference method. Effects of the Grashof number, the relative length, $L_2/L_1$. the dimensionless temperature ratio, ${\Phi}_2/{\Phi}_1$ and the dimensionless plate spacing, $b/L_1$ are examined for the heat transfer. Independent of the Grashof numbers and $L_2/L_1$, the dimensionless vertical velocity distributions skewed on the left plate as ${\Phi}_2/{\Phi}_1$ decreased. The dimensionless vertical velocity distribution for $Gr/Re^2=1$ and ${\Phi}_2/{\Phi}_1=1.0$ is skewed to the right plate $L_2/L_1=0.5$, symmetric at $L_2/L_1=1.0$ and skewed to the left plate at $L_2/L_1=1.5$. But for $Gr/Re_2=10.0$ and ${\Phi}_2/{\Phi}_1=1.0$ reversed velocity patterns are obtained. Regardless of the Grashof numbers and $L_2/L_1$, the mean Nusselt nembers on the inside surface of the left plate decreases and those of the right inside surface increases as ${\Phi}_2/{\Phi}_1$ increases. Temperature, velocity and mean Nusselt number distributions are apparently not affected by $L_2/L_1$.

• 한국수자원학회논문집
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• 제43권7호
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• pp.657-666
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• 2010

본 연구에서는 하도준설 및 골재채취에 의한 교란하천의 적응과정을 정량적으로 파악하기 위하여 이동상 실내실험을 수행하였으며, 하상경사 및 골재채취를 위한 준설 규모의 변화에 따른 하도의 응답 특성을 분석하였다. 웅덩이의 되메우기가 진행 중일 때에는 웅덩이의 이동속도는 일정하지만, 되메우기가 완료된 후에는 웅덩이(pit)의 이동속도가 빠르게 진행된다. 또한 웅덩이가 되메워지는 동안에 웅덩이의 수중 안식각은 일정하게 유지되었다. 하상경사가 급할 경우에, 웅덩이가 되메워지는 시간과 이동속도가 증가하였다. 골재채취에 의한 하천준설의 규모가 증가하게 되면, 웅덩이의 되메워지는 시간이 증가하게 되며, 웅덩이의 규모가 증가할수록 적응시간이 증가하였다. 무차원 마찰속도가 증가하면 무차원 웅덩이 깊이는 감소하고 무차원 웅덩이 이동속도가 증가하였다. 웅덩이 이동속도가 증가하면 무차원 웅덩이 깊이가 감소하였다. 무차원 사주의 이동속도가 증가하면, 웅덩이의 이동속도가 증가하였다. 상류에서 발달한 사주의 이동이 편향되면, 흐름이 집중되는 사주의 선단부의 위치에 따라 웅덩이의 형상이 변형되어 하류로 이동하였다.

• 에너지공학
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• 제6권2호
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• pp.119-128
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• 1997

수평배관의 열성층 유동을 완화하기 위하여 아래부분에 Heat Tracing을 한 수평배관의 외부 가열에 의한 열성층 유동과 열전달 특성을 수치적으로 해석하기 위하여 비정상 2차원 모델을 이용하였다. 무차원 지배방정식은 제어체적방법과 SIMPLE 알고리즘을 사용하여 해를 구하였다. Heat Tracing이 있는 수평배관 내부 열성층 유동의 등온선, 유선분포, Nusselt수, 온도 분포를 해석하였다. 무차원 시간 1,500에서 최대 무차원 온도차가 0.424로 계산되어졌고 무차원 시간 9,000 이후에는 열성층 현상이 없어졌다.

• 대한기계학회논문집B
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• 제29권2호
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• pp.189-196
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• 2005

The physical model considered here is a horizontal layer of fluid heated below and cold above with a conducting body placed at the center of the layer. The body has dimensionless thermal conductivities to the fluid of 0.1, 1 and 50. Two-dimensional solution for unsteady natural convection is obtained using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers. Multi-domain technique is used to handle a square-shaped conducting body. The results for the case of a conducting body are also compared to those of adiabatic and neutral isothermal bodies. When the dimensionless thermal conductivity is 0.1, a pattern of fluid flow and isotherms and the corresponding time-averaged surface Nusselt number are almost the same as the case of an adiabatic body. When the dimensionless thermal conductivity is 50, a pattern of flow and isotherm and the corresponding surface and time-averaged Nusselt number are similar to those of neutral body. The results for the case of dimensionless thermal conductivity of unity are also compared to those of pure natural convection.

• Ecology and Resilient Infrastructure
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• 제4권4호
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• pp.245-254
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• 2017

본 연구에서는 실내실험을 통해 위어의 설치 각도 변화에 대한 위어 상하류에서 흐름특성 변화와 하도 변화를 정량적으로 분석하였다. 위어의 설치 각이 증가함에 따라 위어의 길이는 증가하지만, 위어의 유효길이는 감소하였다. 위어 상류에서는 유사가 퇴적되어 배수가 형성되는 지점에서 델타가 발달하고, 하류로 이동하였다. 델타의 이동속도는 위어에 가까워질수록 감소하며, 크기는 증가하였다. 무차원 위어의 길이가 증가함에 따라, 무차원 사주의 파장이 감소하고, 무차원 사주의 파고는 증가하였다. 무차원 사주의 파장이 증가함에 따라 무차원 사주의 파고는 감소하였다.

• 한국운동역학회지
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• 제26권1호
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• pp.1-9
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• 2016

Objective: The aim of this study is to investigate the association between dance experience and smoothness of hand trajectory during dance by using three jerk-based quantitative methods (integrated squared jerk, mean squared jerk, and dimensionless jerk). Methods: Eleven Korean traditional dancers whose experience of dancing ranged from 5 years to 20 years participated in this study. Dancers performed the Taeguksun motion in Korea traditional dance. Six infrared cameras were used to capture the movement of the hands of the dancers. The smoothness of hand movement was calculated using three jerk-based methods. Results: With regard to the smoothness of the right hand, dance experience was significantly correlated with dimensionless jerk (r=0.656, p=0.028), while dance experience was not significantly correlated with integrated squared jerk (r=0.581, p=0.552) and mean squared jerk. With regard to the smoothness of the left hand, there was no correlation between dance experience and any of the three jerk values. Conclusion: Our results showed that individuals with more dance experience performed the task more smoothly. This study suggests that dimensionless jerk should be used as a predictor for smoothness in dance movement. Thus, our results support the idea that smoothness is an aspect of movement quantity distinct from speed and distance.