• Journal of Power System Engineering
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• v.12 no.5
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• pp.54-58
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• 2008

최근 열교환기의 향상을 위해 발포다공성매체의 적용이 증가하고 있다. 열교환기의 적용에 있어서 발포다공성매체의 이점을 살펴보기 위해 본 연구에서는 2가지 실험을 수행하였다. 첫 번째는 수력의 관점에서 투과계수 및 내부계수를 결정하는 것이고, 두 번째는 열교환의 관점에서 다공성매체의 유효전도율을 측정하는 것이다. 본 실험에서는 기공도는 거의 같으나 기공의 크기가 각각 20 ppi와 40 ppi인 구리 다공성매체를 사용하였다. 실험의 결과는 40 ppi 크기의 다공성매체가 수력과 열교환, 두가지 관점 모두에서 보다 높은 저항 효율을 나타낸다는 것을 보여준다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.189-198
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• 2004

We consider the problem of whether the three-dimensional checkerboard has the connectivity. For this purpose, we first consider the problem of determining the effective conductivity of a checkerboard-shaped composite material by the Brownian motion simulation method. Specifically, we use the efficient first-passage-time technique. Simulation results show that the effective conductivity of the three-dimensional checkerboard increases faster than the two-dimensional counterpart as the contrast between the phase conductivities increases. This implies that the three-dimensional checkerboard's connectivity is stronger than the two-dimensional checkerboard's and thus each phase material of the three-dimensional checkerboard is more likely to be connected than not to be connected.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.910-932
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• 1996

A problem of determining the effective conductivity of a useful model of sphere-matrix type, disordered three-phase composite media is considered. Specifically, a three-phase media in which two-phase composite spheres, consisting of spheres of conductivity $k_2$((phase 2) and concentric shells of conductivity $k_3$(phase 3), are randomly distributed in a matrix of conductivity $k_1$( (phase 1) is considered. As for the structure models configuring three-phase composite media, three different structure models of PCS, PS-1 and PS-2 models are defined, which are analogous to well-established PCS, PS structure models of two-phase composite media. Futhermore, a generalized PS-PCS structure model is proposed to incorporate thesee three different models in one. Effective condectivity $k^{\ast}$of multiphaes composite media is greatly influenced by the phase connectivity of each disspersed phase material, as well as phase conductivities and phase volume fractions. Phase connectivity of three-phase PCS, PS-1, PS-2 composite media is quantified by the impentrability parameter $\lambda$. Mathematically rigorous first-order cluster bounds on $k^{\ast}$ are derived for these models of three-phase composite media, and as computation examples, first-order cluster bounds on $k^{\ast}$ for three-phase composites consisting of largely different phase conductivities are computed and compared as function of concnectivity parpmeter $\lambda$. Results and discussions are given.

• Solar Energy
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• v.10 no.2
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• pp.10-17
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• 1990

Short-term tests were conducted on a house at KIER, Daejon for its thermal performance evaluation. The test procedure and data analysis were made according to the PSTAR method. Each test period was 3 days during which the building was unoccupied. The data measured with 8 channels were used to renormalize an audit based simulation model of the house. The following are the key parameters obtained in the present analysis: 1) the building loss coefficient(skin conductance plus infiltration conductance during coheating period); 2) the effective building heat capacity; and 3) the effective solar gain. An estimation of total heat required to maintain a standard level of comfort during a typical winter season is also calculated on the basis of the renormalized simulation model and typical long term weather data.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.411-414
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• 2006

This study was examined to determine hydraulic conductivity of vadose zone($K_s$) and effective porosity(${\phi}_e$) of undisturbed soil profiles collected at each vadose zone of 6 study areas in South Korea. Effective porosity was approximately 19% of total porosity for each soil profile. Applied to Ahuja's equation, the correlation between $K_s$ and ${\phi}_e$ showed $y=1.3{\times}10^{-7}x^{2.15}(r^2=0.37)$ for total soil profiles. Although the small numbers of soil profile were used for this study, the result of this study might be used for other soil hydraulic studies as reasonable data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.1 no.1
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• pp.33-36
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• 2000

Auto DOME-reversing system had been installed in a vacuum coating chamber which decreased the coating time, the electric energy spending and the contamination by rotating and revilving substance. Auto multi coating with dual electron beam was accomplished and effective coating area was increased. The coating duration was decreased with 30%. the production efficiency were increased with 50%. Also the surface conductivity the coated film uniformity and anti-reflection capablity were also improved.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.16-22
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• 2013

A general characterization procedure based on the extraction of a 2n-port admittance matrix corresponding to n uniform coupled lines on the multi-layered substrate using the Finite-Difference Time-Domain (FDTD) technique is presented. In this paper, the frequency-dependent normal mode parameters are obtained from the 2n-port admittance matrix to analyze multi-layered asymmetric coupled line structure, which in turn provides the frequency-dependent propagation constant, effective dielectric constant, and line-mode characteristic impedances. To illustrate the technique, several practical coupled line structures on multi-layered substrate have been simulated. Especially, embedded conductor structures have been simulated. Comparisons with Spectral Domain Method are given, and their results agree well. It is shown that the FDTD based time domain characterization procedure is an excellent broadband simulation tool for the design of multiconductor coupled lines on multilayered PCBs as well as thick or thin hybrid structures.

• Geophysics and Geophysical Exploration
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• v.12 no.4
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• pp.328-337
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• 2009

To investigate the relation between pore fluid conductivity and bulk resistivity of a rock sample it is assumed that electrolyte solution perfectly substitute the pore fluid that occupied the pore space within the sample in general. In this study, it is investigated that how much can the electrolyte solution substitute the pore fluid by repeating the same saturation process. Four kinds of NaCl solutions of 8, 160, 3200, 64000 ${\mu}S$/cm are used. The saturation process has repeated four times for each electrolyte in increasing conductivity order first then four times each in decreasing order. The more the saturation process repeated with the same electrolyte, the more electrolyte solution substitute the pore fluid. Geometric mean of bulk resistivity in increasing and decreasing orders with the same electrolyte solution is assumed to be mostly close to the bulk resistivity with perfect substitution. Bulk resistivity measurements for both increasing and decreasing order differs within 10% to the geometric mean when repeating the saturation process 4 times while maximum 40% difference is observed when single saturation process for each electrolyte solution with increasing order. The modified parallel resistant model can generally represent the relations between pore fluid resistivity and bulk resistivity in the experiment, but more experimental data with various rock samples with different porosity is needed to generalize the model.

• Solar Energy
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• v.12 no.3
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• pp.28-36
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• 1992

The performance of a latent heat storage system using a thermosyphon as the heat transfer device between the heat source and the phase change material was investigated experimentally. In order to increase the effective conductivity of the phase change material, layers of copper wire mesh were immersed in the paraffin wax(Sunoco P-116) in such a way that they also may be considered as fins of the thermosyphon. The important results are as follows : (1) The void space of the wire mesh allowed the convection to occur, thus enhanced the performance of the system : (2) The increase of the number of layer of wire mesh increased the conduction heat transfer. However, it also had adverse effect of subduing convective motion of liquid wax : and (3) Overall heat transfer coefficient and thermosyphon conductance increased with the increase of the number of layer of wire mesh, whereas the heat transfer coefficient between the thermosyphon and the wax decreased.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.125-125
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• 2000

백금 스퍼터 증착시 아르곤에 산소와 같은 첨가 가스를 사용할 경우 산화막에 대한 접착력이 좋아지며 백금 박막의 우선배향성을 조절할 수 있음이 알려져 있다. 이러한 첨가 가스는 백금 박막에 상당량 포함되며 스퍼터링 후 열처리 과정에서 탈착되는 것으로 알려져 있다. 후열처리 도중 첨가 가스의 탈착 거동이 백금 박막의 미세구조, 조성 및 전기 전도도 등과 같은 제반 물성에 영향을 미칠 것이라 추정된다. 본 연구에서는 백금의 스퍼터링 시 질소를 첨가하여 질소가 포함된 백금 박막을 증착한 후 질소 탈착 거동을 연구하기 위해 실시간 타원해석기(in situ ellipsometer)를 이용하여 진공열처리(15mTorr)하면서 온도변화에 따른 유효굴절율(n)과 소광계수(k) 값을 구하였다. 또한 산소를 첨가하여 얻은 백금 박막의 결과와 비교하여 백금 박막내에 포함된 산소와 질소의 탈착 거동의 차이를 조사하였다. 산소를 이용하여 우선배향성이 (200)으로 조절된 박막의 경우 n과 k의 급격한 변화가 관찰되었으며 이로부터 55$0^{\circ}C$ 온도에서 산소가 급격히 빠져나감을 추측할 수 있었으며 열처리 후에는 백금 bulk 값에 가까운 값을 가짐을 알 수 있었다. 한편, 질소를 사용하여 (200)으로 우선배향성이 조절된 박막의 경우 n,k 값의 후열처리 도중의 변화 양상은 스퍼터링 압력에 크게 의존하는 것으로 나타났다. 22mTorr에서 스퍼터링한 박막의 경우 23$0^{\circ}C$ 부근에서 굴절률과 미세구조의 변화가 있음을 관찰할 수 있었으나, 10mTorr에서 스퍼터링한 시편의 경우 굴절률의 변화양상은 산소를 상요한 경우와 매우 유사한 거동을 나타내지만 열처리 후에는 상대적으로 낮은 n,k 값을 나타내고 있었다. 또한 열처리 시편의 미세구조 변화에 대한 분석 결과 산소 사용의 경우는 측정온도 범위내에서는 후 열처리 후에도 박막내에 hole이나 hillock 등이 관찰되지 않아 bulk 값에 가까운 n, k 값을 가지지만, 질소 사용의 경우는 hole, 표면 거칠기, 혹은 스퍼터링 중에 인입된 질소의 탈착이 완전히 이루어지지 못해 bulk 값과 다르게 나온 것으로 생각된다.