• Tribology and Lubricants
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• 제37권5호
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• pp.195-202
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• 2021

This paper presents a numerical analysis of the lubrication characteristics of condensed water molecules on a solid surface by conducting molecular dynamics simulations. We examine two models consisting of a simple hexahedral substrate with and without water molecules to reveal the lubrication mechanism of mono-layered water molecules. We perform a sliding simulation by contacting and translating a single asperity on the substrate under various normal loads. During the simulation, we measure the friction coefficient and atomic stress. When water molecules were interleaved between solid surfaces, atomic stress exerted on individual atom and friction coefficient were smaller than those of model without water molecule. Particularly, at a low load, the efficacy of water molecules in the reduction of atomic stress and friction is remarkable. Conversely, at high loads, water molecules rarely lubricate solid surfaces and fail to effectively distribute the contact stress. We found a critical condition in which the lubrication regime changes and beyond the condition, significant plastic deformation was created. Consequently, we deduce that water molecules can distribute and reduce contact stress within a certain condition. The reduced contact stress prevents plastic deformation of the substrate and thus diminishes the mechanical interlocking between the asperity and the substrate.

• 한국농촌건축학회논문집
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• 제23권4호
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• pp.63-71
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• 2021

The purpose of this study was to investigate whether the standard models for rural housing and wooden housing model have performance for hygrothermal and to propose a way of improvement relevant to hygrothermal performance for those models. All of the models to be analyzed were found to have some parts that were absent of stability in terms of performance for hygrothermal. In the process of analyzing the causes and proposing improvement measures, the following conclusions were derived. Fist, The exterior surface of the structure should be composed of a structure with good moisture permeability, and for the interior surface, a variable vapor retarder paper should be applied in consideration of the reverse condensation phenomenon in summer. Second, in terms of performance for hygrothermal, applications of external insulation plaster finish to the exterior wall or of ventilation method using a rafter vent on the roof should be avoided. Third, a rain screen method with a ventilation layer should be applied to the exterior wall, and a method of constructing ventilation layer separated from the insulation layer with a vapor retarder paper should be applied to the roof. Fourth, the application of insulation materials having capillary action, such as wood fiber insulation board or cellulose insulation board, contributes to more stable performance for hygrothermal.

• 대한기계학회논문집 C: 기술과 교육
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• 제2권1호
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• pp.47-55
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• 2014

본 연구에서는 태양열에 의해 증발된 해수면에서의 수증기를 응축의 원리를 이용하여 담수의 생산이 가능한 친환경 담수장치(Eco-friendly Desalination System)를 고안하고, 가능성을 판단하는데 연구의 목적을 두고 있다. 응축 열전달 공식을 이용하여 습공기의 물성변화에 따른 연간 응축수 생산량을 예측하였으며, 항온항습챔버의 실험을 통해 실제 습공기조건 변화에 따른 응축량을 측정하였다. 습공기의 이론 응축률과 실험을 통해 측정한 실제 응축률의 오차율을 산출하였으며, 오차의 원인을 분석하고 응축률 보정계수인 응축계수와 점성계수를 구하여 보정된 이론 응축률 공식에 도출하였다. 보정된 응축률 식을 이용하여 설계된 규모의 풍력터빈연간 생산 가능한 담수량을 산출한 결과 최대 연간 약 2,927톤 정도의 담수를 생산할 수 있다는 사실을 알 수 있었다.

• 한국균학회지
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• 제40권4호
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• pp.215-223
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• 2012

느타리버섯 수출력 증진방안을 모색하기 위하여 선적전 고농도 $CO_2$ 및 흡습지 처리가 모의 수출과정에서 버섯의 품질에 미치는 영향을 조사하였다. 수출과정의 온도 변화는 표장용기 내부에 응축수를 만들어 품질을 떨어뜨리는 원인이 되며 흡습지는 경도 유지, 갈변 예방 등에서 효과적이었다. 그러나 모의소매과정에서의 고온($15^{\circ}C$) 노출은 그 효과를 크게 감소시켰다. 선적전 고농도의 $CO_2$ 처리는 경도에 대한 영향은 뚜렷하지 않았지만 버섯의 색택변화를 지연시켰다. 총당, 페놀 등 내적성분은 처리간 일정한 경향을 보이지 않았다. 전반적 수출잠재력은 현행 수출용 규격인 작은 버섯에서 높았다. 수출용 버섯의 품질저하는 포장용기내 응축수 발생과 온도변화의 영향을 크게 받아 이를 개선하기 위한 노력이 필요하다.

• 청정기술
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• 제28권3호
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• pp.249-257
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• 2022

Grand canonical Monte Carlo 전산모사 방법에 의하여 77.16 K에서 국부분자배향 모델을 가지는 나노 기공 탄소 흡착제에 대한 질소의 평형 흡착량을 계산하였다. 국부분자배향 모델은 일정한 공간을 가지는 규칙적인 격자에 동일한 크기를 배열하였다. 국부분자배향 영역의 연속적인 평면의 직교(out-of-plane)의 제거에 의해 미세기공을 도입하였고, 기본구조단위의 기울임을 통해 기울어진 기공을 도입하였다. 이런 기공 구조는 틈새형 기공 구조보다 나노기공을 가지는 탄소계 흡착제의 흡착 연구에 보다 현실적인 모델이 된다. 또한 이들 기공 구조에 대해 기공도, 표면적 그리고 제한된 비선형 최적화 기법을 활용하여 기공크기분포에 구하였다. 또한 참고 자료로써 틈새형 기공에서의 등온 평형흡착량도 계산하였다. 틈새형 기공에서는 질소분자의 5배 이상의 기공에서 hysteresis 루프가 관찰되었고, 모세관 응축과 응축의 역과정인 증발이 한 압력에서 한 번에 일어났다. 국부분자배향 기공모델에서는 질소분자의 크기의 6배 큰 기공에서 기저 슬립면, armchair 슬립면 그리고 상호연결된 채널에서 각각 세 가지 연속적인 응축이 관찰되었다. 탈착 과정의 hysteresis 루프에서는 단일 또는 두 압력에서 응축의 반대인 증발이 관찰되었다.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2553-2559
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• 2012

The adsorption properties of benzene, toluene, p-xylene in MCM-41 with heterogeneous and cylindrical pore were studied using grand canonical ensemble Monte Carlo simulation. The simulated isotherms were compared with experimental ones, and the different adsorption behaviors in MCM-41 with pore diameters of 2.2 and 3.2 nm were investigated. The simulated adsorption amounts above the capillary-condensation pressure agreed with the experimental ones. The simulation results showed that most molecular planes were nearly parallel to the pore axis. This orientation was not affected by the molecular position in the pore. The molecular planes were nearly parallel to the pore surface for the adsorbate molecules close to the pore wall, and the molecules in the MCM-41 with the pore diameter of 3.2 nm were ordered along the pore axis.

• Applied Microscopy
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• 제47권3호
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• pp.176-186
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• 2017

Two-dimensional (2D) materials have been studied widely owing to their outstanding properties since monolayer graphene was isolated in 2004. Especially, among 2D materials, phosphorene, a single atomic layer of black phosphorus (BP), has been highlighted for its electrical properties. This material can serve as a substitute for graphene, which has been revealed as a "semi-metal", in next-generation semiconductors. However, few-layer BP is prone to degradation under ambient conditions owing to its reactivity with oxygen and water, which results in the condensation of water droplets on the surface of the BP flakes. This causes charge transfer from the phosphorus atom to oxygen, resulting in the formation of phosphoric acid (oxide) and degrades the various properties of BP. Therefore, it is necessary to find passivation methods to prevent BP flakes from being degraded under ambient conditions. This review article deals with recent studies on passivation methods for BP and their performance against oxygen and water, effects on the electrical properties of BP, and the extent to how they protect BP.

• 한국세라믹학회지
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• 제56권6호
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• pp.521-525
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• 2019

A study was conducted to investigate the possibility of a composite material containing a composite resin as a matrix and hydroxyapatite (HAp) powder as a substitute material for tooth repair. As the content of HAp increased, hardness value (111.9 HV at 9%) increased and flexural strength (73.3 MPa at 9%) decreased. Observation of the microstructure after immersion in a simulated body fluid (SBF) solution confirmed a dense structure due to mutual coagulation and curing. It was thought that fine HAp recrystals were formed with the lapse of time, and they were entangled to form a condensation structure and had a dense structure. In addition, since the activity was shown by the ion migration on the surface of a tooth, it was highly likely that a biocompatible bond occurred during tooth contact. Therefore, it could be used as a substitute material for tooth repair.

• Current Photovoltaic Research
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• 제5권2호
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• pp.43-46
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• 2017

Large absorption band shift has been observed for the azo-dye (disperse red-13, DR-13) attached on the surface of silica spheres. Urethane linkage has been utilized to form covalent bond between azo-dye (-OH) and 3-isocyanatopropyltriethoxysilane (ICPTES, -N=C=O). The synthesized ICPTES-DR-13 (ICPDR) molecules were attached to the silica spheres by the hydrolysis and condensation reaction. Although the absorption peak of DR-13 in methanol is at 510 nm, the absorption peak of the ICPDR-silica spheres shifts to 788 nm. The large absorption peak shift is due to the formation of intramolecular charge-transfer band with large aggregated ICPDR.

• 한국세라믹학회지
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• 제30권6호
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• pp.485-491
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• 1993

Porous glass in the ZrO2.SiO2 system containning up to 30mol% zirconia were prepared by the sol-gel method from metal alkoxides and their pore characteristics with reaction parameters were investigated. The gels were made by hydrolyzing and condensation of the mixed metla alkoxides and were converted into the porous glass by heating up to $700^{\circ}C$. As a results, the mean pore radius became larger with increasing contents of HCl, H2O and hydrolysis temperature, and an alcohol with a large molecular weight for making the porous glass. In the case of 20ZrO2.80SiO2 porous glass with heated at $700^{\circ}C$, HCl and H2O content was 0.3mol and 4mol, the specific surface area was 284$m^2$/g, average mean pore radius was about 19.4$\AA$, porosity was 22.55% and pore characteristics depended on heating temperature.