• 에너지공학
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• 제8권2호
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• pp.224-232
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• 1999

캡슐형 잠열재를 이용한 열저장 시스템은 바닥 난방 및 건물 난방에서 매우 효과적인 시스템이다. 이러한 시스템 개발에 필수적인 요소가 열유동 매체가 순환하는 파이프 주변의 캡슐내 온도 분포와 열유동 매체의 유량 등이다. 그러므로 본 연구에서는 3차원 비정상 상태에서 Navier-Stokes 방정식, 난류모델을 비롯한 스칼라 보존 방정식을 적용하여 캡슐 블록의 온도 분포 및 파이프 내의 유동장 해석을 수행하였다. 또한 본 연구와 같이 계산 영역이 특별한 기하학적 현상을 형상(circle+square)인 문제 해결하는데 적용할 수 있는 새로운 격자 생성 기술(MBFGE/CCM)을 개발하였다. 격자계는 파이프에서 원형 격자를 이용하였고, 캡슐 블록에서 사각 격자를 이용하여 다중격자와 미세격자를 결합하여 사용하였다. 본 연구의 목적은 컴퓨터를 이용한 수치해석적 방법을 미세 캡슐을 이용한 축열보드에 적용하여 2종류의 열경계 상태에 대하여 속도와 온도분포를 계산하여 비교분석을 하는 것이다. 온도는 축열 보드의 한 쪽면은 대류면이고 다른 한쪽면은 단열면인 경우(Case 2)보다 양면 모두 단열인 경우(Case 1)일 때 더 높게 상승하였다. 온수 파이프 중심선인 Y=0 에 가까운 영역에서 Case 1과 Case 2사이에 축열 보드 내에서 온도 차이는 확연하게 나타났다. 향후 수치해석의 정확도를 높이고 축열 보드의 열전달 현상을 보다 정확히 계산하기 위해서는 위치 및 시간에 따른 정밀한 온도 측정값이 필요하고 특히 잠열재인 미세 캡슐이 상변화를 하므로 온도 변화에 따른 물질의 비열(C$_{p}$)과 열전달율(λ)을 고려한 방정식이 요구된다.

• Journal of Mechanical Science and Technology
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• 제16권8호
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• pp.1127-1134
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• 2002

The effects of pressure and temperature on the autoignition of propane and n-butane blends were investigated using a rapid compression machine (RCM) , which is widely used to examine the autoignition characteristics. The RCM was designed to be capable of varying the compression ratio between 5 and 20 and minimize the vortex formation on the cylinder wall using a wedge-shaped crevice. The initial temperature and pressure of the compressed gas were varied in range of 720∼900 K and 1.6∼ 1.8 MPa, respectively, by adjusting the ratio of the specific heat of the mixture by altering the ratio of the non-reactive components (N$_2$, Ar) under a constant effective equivalence ratio (ø$\_$f/= 1.0) The gas temperature after the compression stroke could be obtained from the measured time-pressure record. The results showed a two-stage ignition delay and a Negative Temperature Coefficient (NTC) behavior which were the unique characteristic of the alkane series fuels. As the propane concentration in the blend were increased from 20% and 40% propane, the autoignition delay time increased by approximately 41 % and 55% at 750 K. Numerical reduced kinetic modeling was performed using the Shell model, which introduced some important chemical ideas, represented by the generic species. Several rate coefficients were calibrated based on the experimental results to establish an autoignition model of the propane and n-butane blends. These coefficients can be used to predict the autoignition characteristics in LPG fueled Sl engines.

• 한국전자통신학회논문지
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• 제18권6호
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• pp.1049-1056
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• 2023

대기경계층 고도는 지면의 가열로 인해 발생한 난류가 경계층 내의 열, 수증기 등을 혼합하면서 생성되는 꼭대기로 일반적으로 열역학적 방법을 통해 결정한다. 윈드프로파일러는 대기 중으로 보낸 신호의 산란 정보로 대기의 정보를 산출한다. 윈드프로파일러 관측으로 대기경계층 깊이를 결정하기 위해 난류 성분의 스펙트럼 및 난류운동에너지 소산율, 굴절지수구조계수를 산출하는 방법을 제시하였다. 라디오존데 자료를 기반으로 산출한 온위와 비습의 연직 분포 특징과 비교하여 윈드프로파일러 산출물 기반의 대기경계층 고도 결정 방법이 매우 유용한 것으로 평가되었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.17-22
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• 2002

A conventional silica gel/water adsorption chiller has been analyzed numerically. A novel non-dimensional mathematical model has been presented to analyze the design effect of different components of an adsorption chiller. The design parameters of this system are characterized by the number of transfer unit, NTU, of different components and the inert material alpha number, ${\alpha}$of different components of the systems. Results show that condenser NTU$\sub$a/ has the most influential effect on the system performance, which is fellowed by absorber NTU$\sub$e/. It is also seen that coefficient of performance (COP) and non-dimensional specific cooling capacity increases with the increase of NTU$\sub$a/ and NTU$\sub$e/, but decreases with the increase of inert material alpha number. A thermo-economic data of the adsorption chiller and some other heat pump systems those are in practical operation are also presented.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 춘계학술대회 논문집
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• pp.108-113
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• 1993

The material for the machine tool structure should have high static stiffiness and damping in its property to improve both the static and dynamic performances. The static stiffness of a machine tool can be inceased by using either higher modulus material in the structure of a machine tool. However, the machine tool structrue with high stiffness but low damping is vulnerable to vibration at the resonance frequencies of the structure . For the high precision and highsped machine tool structure, therefore, the high damping capacity is most important in order to suppress vibration. The damping of a machine tool can not be increased by increasing the static stiffness. The best way to increase the damping capacity of the machine tool structure is to use a composite material which is composed of on material with high stiffness with low damping and another material with low stiffness with high damping. Therefore, in this paper, the bed of the ultra high precision grinding machine for mirror surface machining of brittle materials such as ceramics and composite materials was designed and manufactured with the epoxy concrete material. The epoxy concrete material was prepared by mixing epoxy resin with different size sands and gravels. The modulus, compressive strength, coefficient of thermal expansion, specific heat, and damping factor were measured by varying the compaction ratio, sizes and contents of the ingredients to assess the effect of the processing parameters on the mechanical properties of the material. Based of the measured properties, the prototype epoxy resin concrete bed for the mirror surface CNC grinding machine was designed and manufactured.

• 한국연초학회지
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• 제18권2호
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• pp.150-159
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• 1996

In this study, to obtain the basic data for the optimum moisture control system, moisture adsorption characteristics, adsorption isotherms models for water and surface physical characteristics of burley and flue-cured tobacco were investigated. By the hypothesis' the phenomenon of moisture adsorption of tobacco is the same as the first order reaction, the wetting constant (k) and equilibrium moisture content were obtained. And activation energy, frequency factors were also calculated by applying its data to Arrhenius equation. The Kamei's empirical formula of moisture adsorption isotherms showed the best agreement with the experimental data and its correlation coefficient (r) was 0.997. It can be seen that specific surface area of burley is 157 m2/g, that of flue-cured is 152 m2/g, -△H1 of adsorbed monolayer is 45,972 J/mol, 45,486 J/mol, respectively, and the condensation heat (40,595 J/mol) being caught in adsorbed multilayer is less than that of monolayer.

• 한국세라믹학회지
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• 제43권12호
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• pp.865-871
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• 2006

In order to examine and compare the characteristics of two vitrified forms (AG8W1 and DG2) simulated for the operation of a commercial vitrification facility being constructed in Ulchin nuclear power plant, the vitrified forms were cooled by the natural cooling and annealing methods respectively. And the Product Consistency Test (PCT), compressive strength, thermal conductivity, specific heat, phase stability, softening point and Coefficient of Thermal Expansion (CTE) of the vitrified farms were experimented. Consequently, it was shown that there were no significant differences on the physiochemical properties of the vitrified forms performed the natural cooling and annealing.

• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 2009년도 춘계학술논문발표회 논문집
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• pp.557-563
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• 2009

FMVSS 302 수평 연소 시험법을 통과한 자동차 내장재의 열적 특성을 평가하기 위해서 콘칼로미터를 이용하여 시험을 수행하였다. 화재 위험과 관련된 착화시간(time to ignition), 열방출률(heat release rate), 질량감소율(specific mass loss rate), 감쇠계수(extinction coefficient) 그리고 연기요소(smoke factor)와 같은 여러 가지 요소들을 분석하였다. 최대 열방출률값은 시험편에 따라 232${\sim}$635kW/$m^2$으로 큰 편차를 보였으며, 연기요소 또한 99${\sim}$551MW/$m^2$로 큰 편차를 보였다. 보조매트의 최대 열방출률은 다른 시험편에 비해서 상대적으로 낮은 값을 보였지만, 총연기 발생이 다른 시험편에 비해서 상당히 높았다. 따라서 최대 열방출률과 총 연기발생을 함께 고려한 연기요소값은 상대적으로 다른 시험편에 비해서 높게 나타났다.

• 한국세라믹학회지
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• 제32권4호
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• pp.507-515
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• 1995

The monolithic dry gels of the Li2O-Al2O3-TiO2-SiO2 system were prepared by the sol-gel technique using metal alkoxides as starting materials to obtain monolithic glass-ceramics at low temperature without melting. Activation energy for the crystal growth of the gel with 6.05% TiO2, nucleating ageng, for the preparation of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was 101.14kcal/mol. As a result of the analysis of DTA & XRD, it was confirmed that the crytallization of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was the most efficient when 6.05% TiO2, nucleating agent, was added. $\beta$-eucryptite solid solution crystals and $\beta$-spodumene solid solution crystals were detected in the sample heat treated above 85$0^{\circ}C$. The sintered gel heat treated at 85$0^{\circ}C$ had the specific surface area of 185$m^2$/g, the pore volume of 0.19cc/g and the average pore radius of 20.8$\AA$. This shows that the sintered gel is also comparatively porous material. In temperature range of 25~85$0^{\circ}C$ thermal expansion coefficient of the specimen which was crystallized for 10hrs at 85$0^{\circ}C$ was 6.7$\times$10-7/$^{\circ}C$, which indicated that the crystallized specimen was turned out to be the glass-ceramic with low thermal expansion.

• 한국분말재료학회지
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• 제13권5호
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• pp.313-320
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• 2006

The present study is to analyze the thermoelectric properties of $Bi_{0.4}Sb_{1.6}Te_3$ thermoelectric materials fabricated by the mechanical grinding process. The $Bi_{0.4}Sb_{1.6}Te_3$ powders were prepared by the combination of mechanical milling and reduction treating methods using simply crushed pre-alloyed $Bi_{0.4}Sb_{1.6}Te_3$ powder. The mechanical milling was carried out using the tumbler-ball mill and planetary ball mill. The tumbler-ball milling had an effect on the carrier mobility rather than the carrier concentration, whereas, the latter on the carrier concentration. The specific electric resistivity and Seebeck coefficient decreased with increasing the reduction-heat-treatment time. The thermal conductivity continuously increased with increasing the reduction-heat-treatment time. The figure of merit of the $Bi_{0.4}Sb_{1.6}Te_3$ sintered body prepared by the mechanical grinding process showed higher value than one of the sintered body of the simply crushed powder.