• 대한기계학회논문집B
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• 제26권2호
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• pp.253-260
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• 2002

It is known that frost formation on surfaces of the heat exchanger seriously affects the performance of the refrigeration system. Accordingly, defrosting should follow, and effective defrosting is possible only when both analytic tools and comprehensive experimental data on frost formation are assailable. An experimental investigation was undertaken to characterize the effect of environmental parameters on frost formation on a horizontal cylinder in cross uniform flow. Several experiments were carried out with various environmental parameters such as inlet air temperature, inlet air humidity, air velocity and cooling surface temperature. Frost thickness, mass, surface temperature and cylinder inner and outer temperature were measured at front and rear positions of the cylinder. Thickness, mass, density, and effective thermal conductivity of the frost layer were obtained from measured data and effects of environmental parameters on the frost formation were analyzed. Data from experiments were correlated using dimensionless variables.

• Nuclear Engineering and Technology
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• 제44권6호
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• pp.639-652
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• 2012

A three-dimensional discrete fracture network model was developed in order to simulate the hydraulic characteristics of a granitic rock mass at Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The model used a three-dimensional discrete fracture network (DFN), assuming a correlation between the length and aperture of the fractures, and a trapezoid flow path in the fractures. These assumptions that previous studies have not considered could make the developed model more practical and reasonable. The geologic and hydraulic data of the fractures were obtained in the rock mass at the KURT. Then, these data were applied to the developed fracture discrete network model. The model was applied in estimating the representative elementary volume (REV), the equivalent hydraulic conductivity tensors, and the amount of groundwater inflow into the tunnel. The developed discrete fracture network model can determine the REV size for the rock mass with respect to the hydraulic behavior and estimate the groundwater flow into the tunnel at the KURT. Therefore, the assumptions that the fracture length is correlated to the fracture aperture and the flow in a fracture occurs in a trapezoid shape appear to be effective in the DFN analysis used to estimate the hydraulic behavior of the fractured rock mass.

• 오토저널
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• 제4권3호
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• pp.40-47
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• 1982

Heat transfer on packed bed is considered to be important for the effective designs of chemical reaction equipment, air conditioning system, and storage type heat exchanger, etc. Currently studies are being carried out quite actively in this field in order to increase the heat transfer efficiency. The effect of heat transfer is closely relater to materials, shapes, porosities and packing states of packed bed as well as mutual dimensional relations between particles and the container. Investigation shows that heat transfer results appear to be influenced by such parameters as fluid velocity through packed bed, mass flow, and thermal properties. It is noted that viscosity is also considered to be an important factor in this problem. In this study, effective thermal conductivities on packed bed, effects of thermal conductivity (Ke) and friction factor (Fk) according to change of porosity(.epsilon.) and Reynolds number(Reh(, and pressure loss of the fluid, are experimentally investigated. Results show that the effective thermal conductivity increases and the friction factor decreased, as against the increase of Reynolds number. But as the increase of porosity increase them both.

• 지질공학
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• 제32권1호
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• pp.41-57
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• 2022

본 연구는 부산 기장지역에 분포하는 백악기 흑운모 화강암에 대한 사례연구를 통하여 DFN(discrete fracture network) 유동해석 기반의 REV(representative elementary volume) 크기 및 삼차원 수리전도텐서 추정을 위한 워크플로우를 제시하였다. 연구지역을 대표하는 이차원 DFN에 대하여 절리텐서의 일차불변량을 이용하여 절리의 빈도 및 길이가 보정되었다. 현장수압시험을 수행하여 선형의 등가유로관으로 취급된 현장의 절리에 대한 유효수리간극이 추정되었다. 연구지역의 이차원 DFN 블록에 대한 REV의 크기는 블록 크기에 따른 지향적 블록수리전도도의 변화를 분석하여 20 m × 20 m으로 결정하였다. 연구지역의 이차원 DFN에 대하여 산정된 지향적 블록수리전도도는 현장의 수리적 거동과 관련하여 강한 이방성을 지시한다. 다양한 방향으로의 이차원 DFN에서 산정된 지향적 블록수리전도도를 바탕으로 연구지역의 절리성 암반에 대한 삼차원 수리전도텐서가 추정되었다. 삼차원 수리전도텐서의 주성분 방향은 현장에서 구분된 주 절리군의 방향과 일치한다.

• Geomechanics and Engineering
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• 제14권5호
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• pp.467-477
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• 2018

Estimation of hydraulic parameters is a critical step during design of foundation dewatering works. When many piles are installed in an aquifer, estimation of the hydraulic conductivity should consider the blocking of groundwater seepage by the piles. Based on field observations during a dewatering project in Shanghai, hydraulic conductivities are back-calculated using a numerical model considering the actual position of each pile. However, it is difficult to apply the aforementioned model directly in field due to requirement to input each pile geometry into the model. To develop a simple numerical model and find the optimal hydraulic conductivity, three scenarios are examined, in which the soil mass containing the piles is considered to be a uniform porous media. In these three scenarios, different sub-regions with different hydraulic conductivities, based on either automatic inverted calculation, or on effective medium theory (EMT), are established. The results indicate that the error, in the case which determines the hydraulic conductivity based on EMT, is less than that determined in the automatic inversion case. With the application of EMT, only the hydraulic conductivity of the soil outside the pit should be inverted. The soil inside the pit with its piles is divided into sub-regions with different hydraulic conductivities, and the hydraulic conductivity is calculated according to the volume ratio of the piles. Thus, the use of EMT in numerical modelling makes it easier to consider the effect of piles installed in an aquifer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1546-1551
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• 2004

This paper presents a mathematical model to predict the frost properties and heal and mass transfer within the frost layer formed on a cold plate. The laminar flow equations for the air-side are analyzed. and the empirical correlations of local frost properties are employed in order to predict the frost layer growth. The correlations of local frost density and effective thermal conductivity of frost layer, obtained from various experimental conditions, are derived as functions of various frosting parameters (Reynolds number, frost surface temperature, absolute humidity and temperature of moist air, cooling plate temperature, and frost density). The numerical results are compared with experimental data and the results of various models to validate the present model, and agree well with experimental data within a maximum error of 10%. The heat and mass transfer coefficients obtained from the numerical analyses are presented, as the results, it is found that the model for frost growth using the correlation of heat transfer coefficient without solving air flow have a limitation in its application.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.163.1-163.1
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• 2014

Electron-electron interactions bear important information on fundamental electronic properties such as electron effective mass, conductivity, and charge mobility. By using angle-resolved photoemission spectroscopy, here we address unusual electron self-energy in graphene induced by the electron-electron interactions, which are distinguished from those of an ordinary Fermi liquid. Our findings provide a new route for two-dimensional electron systems toward device applications.

• 설비공학논문집
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• 제8권2호
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• pp.299-306
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• 1996

This work presents an analytical model, so called modified LMTD method, to predict the thermal performance of finned-tube heat exchanger under frosting conditions. In this model, the total heat transfer coefficient and effective thermal conductivity of the frost layer were defined as a function of frost surface temperature. The surface temperature of the frost layer formed on the heat exchanger was calculated through the analysis of the heat and mass transfer process in the air and frost layer. To examine the validity of this analytical model, the computed results from the present model, such as heat transfer rate, frost mass and thickness of frost, were compared with the ones of the expermental work and LMED method.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제11권1호
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• pp.95-105
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• 2007

A mathematical modeling for the drying process of hygroscopic porous media, such as wood, has been developed in the past decades. The governing equations for wood drying consist of three conservation equations with respect to the three state variables, moisture content, temperature and air density. They are involving simultaneous, highly coupled heat and mass transfer phenomena. In recent, the equations were extended to account for material heterogeneity through the density of the wood and via the density variation of the material process, capillary pressure, absolute permeability, bound water diffusivity and effective thermal conductivity. In this paper, we investigate the drying behavior for the three primary variables of the drying process in terms of control volume finite element method to the heterogeneous transport model on one-dimensional grid.

• 한국수소및신에너지학회논문집
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• 제26권5호
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• pp.469-476
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• 2015

The purpose of this work is to investigate main factors to design a solid-state hydrogen stroage system with magnesium hydride with 10 wt% graphite using numerical simulation tools. The heat transfer characteristic of this material was measured in order to perform the highly reliable simulation for this system. Based on the measured effective thermal conductivity, a transient heat and mass transfer simulation revealed that the total performance of hydrogen storage system is prone to depend on heat and mass transfer behaviors of hydrogen storage medium instead of its inherent kinetic rate for hydrogen adsorption. Furthermore, we demonstrate that the thermodynamic aspect between equlibrium presssure and temperature is one of key factor to design the hydrogen storage system with high performance using magnesium hydride.