• 대한기계학회논문집A
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• 제40권2호
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• pp.139-145
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• 2016

본 연구에서는 나노클레이 함량에 따른 나노클레이-에폭시 나노복합재료의 흡습 특성 및 기계적 특성을 실험을 통해 분석하였다. 나노복합재료의 흡습 시험, 인장시험 및 접착조인트를 나노클레이 함량에 따라 구성하였으며 이를 통해 수분 포화도, 수분 확산 계수, 인장 강도 및 접착 강도와 같은 특성을 파악 할 수 있었다. 또한 나노클레이 및 에폭시 재료를 분자단위로 모델링하여 재료의 흡습 특성변화의 매커니즘을 분석할 수 있는 분자동역학 시뮬레이션을 수행하였으며 그 결과를 실험결과와 비교하여 고찰하였다. 본 연구에서 제안된 분자동역학 시뮬레이션 기법은 흡습특성의 변화를 성공적으로 예측할 수 있었으며, 추후 다른 나노-복합재료의 연구에도 널리 활용될 것이라 기대된다.

• 한국구조물진단유지관리공학회 논문집
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• 제24권1호
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• pp.142-147
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• 2020

본 연구의 목적은 콘크리트 재료 및 구조물의 균열 특성 평가에 활용되고 있는 확산초음파 기법의 적용 가능성을 검토하는데 있다. 이를 위한 첫 단계로 외부 환경에 따라 변화하는 콘크리트의 수분 함유량 변화를 묘사하여, 확산초음파 파라미터와 콘크리트 수분 함유량 사이의 상관관계 분석을 수행하였다. 실험실 환경에서 완전 건조된 실험체를 수중에서 포화시켜가며 콘크리트 함수율의 차이를 묘사하였으며, 콘크리트 내부에서 초음파의 산란 현상이 충분히 발생하는 500 kHz 주파수 대역대의 신호를 가진 및 분석하여 확산초음파 파라미터인 초음파 확산계수와 초음파 에너지 소산계수를 산정하였다. 콘크리트의 수분 함유량은 확산초음파 실험 시 실험체의 무게 변화를 통해 추정하였으며, 수분 함유량 증가에 따라 실험체에서 무게가 약 2.5 % 가량 증가한 것으로 나타났다. 콘크리트 실험체의 포화정도에 따라 초음파 확산계수는 지속적으로 증가하는 것으로 나타났으나, 변화율은 확산초음파 기법의 계측 오차 범위 내에 있었다. 반면에, 초음파 에너지 소산계수는 완전 포화된 콘크리트에서 완전 건조된 콘크리트 대비 약 120 % 증가하여, 수분함유량에 대해 민감한 것으로 나타났다. 따라서, 추후 확산초음파 기법을 활용하여 콘크리트 재료 및 구조물의 균열 특성 평가 시 함수율에 대한 고려가 필요할 것으로 사료된다.

• 마이크로전자및패키징학회지
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• 제29권3호
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• pp.37-42
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• 2022

최근 반도체 패키지 구조는 점점 더 얇아지고 복잡해지고 있다. 두께가 얇아짐에 이종 계면에서 물성차이에 의한 박리는 심화될 수 있으며 따라서 계면의 신뢰성이 패키징 설계에 중요한 요소라 할 수 있다. 특히, 반도체 패키징에 많이 사용되는 폴리머는 온도와 수분에 영향을 크게 받기 때문에 환경에 따른 물성 변화 고려가 필수적이다. 따라서, 본 연구에서는 다양한 온도조건에서 수분의 흡습과 탈습을 모두 고려한 패키지 구조의 계면 박리 예측을 유한 요소 해석을 통해 수행하였다. 확산계수와 포화 수분 함량과 같은 재료의 물성은 흡습 실험을 통해 확보하였으며, 흡습 이후 TMA 와 TGA 를 통하여 각 재료의 수분 팽창 계수를 확보하였다. 각 계면의 접합 강도 평가를 위해 수분의 영향을 고려하여 다양한 온도 조건에서 마이크로 전단 실험을 수행하였다. 이러한 물성을 바탕으로 온도와 수분에 의해 발생하는 변형을 모두 고려한 패키지 박리 예측 해석을 수행하였으며, 결과적으로 리플로우 공정 동안의 실시간 수분 탈습 거동을 고려한 계면 박리 예측을 성공적으로 수행하였다.

• 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.

• Journal of Biosystems Engineering
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• 제18권1호
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• pp.48-59
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• 1993

Pepper is considered as one of main crops not only in the agricultural production but also in farmer's income. Red-pepper is much consumed by Koreans everyday in the form of powder, but its processing processes such as drying and grinding cause many problems. Consequently, it is required to improve the quality of red-pepper powder for high dietary life. This study was conducted to investigate the heat and mass transfer characteristics of red-pepper powder by convection and radiation conditioning. Physical and thermal properties such as specific heat, thermal conductivity and thermal diffusivity were also determined in terms of moisture content of the powder.

• Computers and Concrete
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• 제15권2호
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• pp.183-198
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• 2015

Chloride ingress implies a complex interaction between physical and chemical process, in which heat, moisture and chloride ions transport through concrete cover. Meanwhile, reinforced concrete structure itself undergoes evolution due to variation in temperature, relative humidity and creep effects, which can potentially change the deformation and trigger some micro-cracks in concrete. In addition, all of these process show time-dependent performance with complex interaction between structures and environments. In the present work, a time-dependent behavior of chloride transport in reinforced concrete beam subjected to flexural load is proposed based on the well-known section fiber model. The strain state varies because of stress redistribution caused by the interaction between environment and structure, mainly dominated by thermal stresses and shrinkage stress and creep. Finally, in order to clear the influence of strain state on the chloride diffusivity, experiment test were carried out and a power function used to describe this influence is proposed.

• Journal of Ginseng Research
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• 제9권2호
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• pp.248-255
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• 1985

In order to investigate the optimal drying condition of white ginseng by using bulk air drier(130 x 62 x 65cm), drying curves, diffusion coefficient at various drying temperature, the energy of activation, variation of color intensity and chemical components during drying of white ginseng were studied. Fick's second low of diffusion for diffusion out of spheres was successfully applied to describe the drying of white ginseng. It was found that the diffusion coefficient of water was 2.2x107, 9.0x107 cm2/sec at drying temperature 4$0^{\circ}C$, 55$^{\circ}C$, respectively. An Arrhenius type temperature dependency of moisture diffusivity was found, the energy of activation being 18.8 Kcal/g mol. Color intensity of white ginseng dried at various drying temperature was increased with an increase in drying temperature. The contents of crude protein, reducing sugar and crude saponin during drying of white ginseng were gradually decreased as increasing of drying time. And with the sensory evaluation by multiple comparison difference analysis, the optimal drying temperature of white ginseng was between 45$^{\circ}C$ and 5$0^{\circ}C$.

• Advances in materials Research
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• 제13권3호
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• pp.161-171
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• 2024

This study aimed to investigate the effect of physicochemical properties and mix ratios of iron ore (oxide feed): coke (reductant) on the carbothermic reductions of iron ore. Coke size was fixed at ≤63 ㎛ while iron ore size varied between 150-63 ㎛ and ≤63 ㎛ respectively. Mix ratios were changed from 100:0 (reference) to 80:20 and 60:40 while the temperature, heating rate and soaking duration in muffle furnace were fixed at 1100 ℃, 10 ℃/min and 1 hour. Particle size analyzer, XRF, CHNS and XRD analyses were used for determination of raw feed characteristics. The occurrence of phase transformations from various forms of iron oxides to iron during the carbothermal reductions were identified through XRD profiles and supported with weight loss (%). XRF analysis proved that iron ore is of high grade with 93.4% of Fe₂O₃ content. Other oxides present in minor amounts are 2% Al₂O₃ and 1.8% SiO₂ with negligible amounts of other compounds such as MnO, K₂O and CuO. Composite pellet with finer size iron particles (≤63 ㎛) and higher carbon content of 60:40 exhibited 45.13% weight lost compared to 32.30% and 3.88% respectively for 80:20 and 100:0 ratios. It is evident that reduction reactions can only occur with the presence of coke, the carbon supply. The small weight loss of 3.88% at 100:0 ratio occurs due to the removal of moisture and volatiles and oxidations of iron ore. Higher carbon supply at 60:40 leads into better heat and mass transfer and diffusivity during carbothermic reductions. Overall, finer particle size and higher carbon supply improves reactivity and gas-solid interactions resulting in increased reductions and phase transformations.

• 한국토양비료학회지
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• 제17권1호
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• pp.12-17
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• 1984

토양개량제(土壤改良劑) 처리(處理)가 토양중(土壤中)에서 수분(水分)의 이동(移動)에 미치는 영향(影響)을 구명(究明)코져 사양토(砂壤士)와 미사질양토(微砂質壤土)에 친수성(親水性)인 Uresol과 소수성(疎水性)인 Bitumen을 처리(處理)하여 습윤각(濕潤角), 침투성(浸透性) 및 확산계수(擴散係數) 변화(變化)를 측정(測定)하였는 바 그 결과(結果)를 요약(要約)하면 다음과 같다. 1. Uresol 처리(處理)에 의하여 사양토(砂壤土) 습윤각(濕潤角)이 $10^{\circ}$이상(以上) 감소(減少)되어 친수성(親水性)이 증대(增大)되었으나 미세질양토(微砂質壤土)는 큰 변화(變化)가 없었다. 2. Bitumen 처리(處理)로 미세질양토(微砂質壤土)의 습윤각(濕潤角)은 무처리(無處理) $76.0^{\circ}$에서 $84.9^{\circ}$로 증가(增加)되었으며 사양토(砂壤土)는 소수성(疎水性)으로 변하였다. 3. 침투성(浸水性)(Penetrability)과 흡수성(吸水性)(Sorpotivity)은 Uresol 처리(處理)에 의하여 사양토(砂壤土)에서는 2배이상(倍以上) 증가(增加)되었고 미세질양토(微砂質壤土)에서는 큰 차이가 없었으나, Bitumen 처리(處理)는 두 토양의 침투성(浸水性)을 반이하(半以下)로 억제(抑制)시켰다. 4. 수분(水分)의 침투성(浸水性)은 습윤각(濕潤角)의 여현(餘弦)(cos ${\alpha}$)과 정비례(正比例)하였다. 5. 수분(水分)의 확산계수(擴散係數)는 토양개량제(土壤改良劑) 처리(處理)로 크게 변화(變化)되었으며, 그 차이(差異)는 토양수분함량(土壤水分含量)이 적을수록 심(甚)하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.2-11
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• 2006

In the processes of hydrological cycle, when precipitation reaches the ground surface, water may become surface runoff or infiltrate into soil and then possibly further percolate into groundwater aquifer. A part of the water is returned to the atmosphere through evaporation and transpiration. Soil moisture dynamics driven climate fluctuations plays a key role in the simulation of water transfer among ground surface, unsaturated zone and aquifer. In this study, a one-layer canopy and a four-layer soil representation is used for a coupled soil-vegetation modeling scheme. A non-zero hydraulic diffusivity between the deepest soil layer modeled and groundwater table is used to couple the numerical equations of soil moisture and groundwater dynamics. Simulation of runoff generation is based on the mechanism of both infiltration excess overland flow and saturation overland flow nested in a numerical model of soil moisture dynamics. Thus, a comprehensive hydrological model integrating canopy, soil zone and aquifer has been developed to evaluate water resources in the plain region of Huaihe River basin in East China and simulate water transfer among precipitation, surface water, soil moisture and groundwater. The newly developed model is capable of calculating hydrological components of surface runoff, evapotranpiration from soil and aquifer, and groundwater recharge from precipitation and discharge into rivers. Regional parameterization is made by using two approaches. One is to determine most parameters representing specific physical values on the basis of characterization of soil properties in unsaturated zone and aquifer, and vegetations. The other is to calibrate the remaining few parameters on the basis of comparison between measured and simulated streamflow and groundwater tables. The integrated modeling system was successfully used in the Linhuanji catchment of Huaihe plain region. Study results demonstrate that (1) on the average 14.2% of precipitation becomes surface runoff and baseflow during a ten-year period from 1986 to 1995 and this figure fluctuates between only 3.0% in drought years of 1986, 1988, 1993 and 1994 to 24.0% in wet year of 1991; (2) groundwater directly deriving from precipitation recharge is about 15.0% t of the precipitation amount, and (3) about half of the groundwater recharge flows into rivers and loses through evaporation.