• 제목/요약/키워드: hard sphere

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Calculation of the Entropies and Chemical Potentials of Hard-Sphere Solutes Solvated in Hard-Sphere Solids Using the Radial Free-Space Distribution Function

  • 윤병집
    • Bulletin of the Korean Chemical Society
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    • 제20권10호
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    • pp.1209-1212
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    • 1999
  • The entropies and chemical potentials of hard-sphere solutes solvated in hard-sphere solids were calculated by Monte Carlo method using the radial free-space distribution function. This method is based on calculating the entropy by comparing the free volume of a molecule with that of an ideal gas, and is applicable even when the size of solute is very large and the solvent is a solid. When the diameter of hard-sphere solute is small the solute molecule behaves as like as a fluid in solid structures, but when the diameter of solute becomes large, a fluid-to-solid phase transition takes place. The fluid-to-solid phase transition occurs at the region of the smaller size of solute with the more increase of solvent density. The least square fit values of analytical form of the radial free-space distribution functions of solute molecules are presented for future uses.

The Interaction Potential Functions in an Electrolyte Protein Solution

  • Jee, Nam-Yong;Kim, Jae-Jun
    • Macromolecular Research
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    • 제14권6호
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    • pp.654-658
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    • 2006
  • Recent developments in equations of state for molecular fluids have demonstrated the feasibility of using the hard-sphere equation to describe the effects of repulsive forces in simple fluids. By including a suitable term for attractive forces, most conveniently a uniform background potential, the properties of bio-macromolecular interaction can be roughly calculated. However, the choice of the potential used in perturbed hard-sphere chain (PHSC) theory for describing the attractions between macromolecules is rather complicated. For hard-sphere chains, the prediction accuracy from each model strongly depends on the choice of potential function.

Equations of State for Hard-Sphere Chains: Effect of Attractive Contribution

  • Kim Jae-Jun
    • Macromolecular Research
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    • 제14권2호
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    • pp.220-229
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    • 2006
  • Several equations of state for hard-sphere chains with various perturbation terms are reviewed. For each model, three characteristic parameters are required to represent phase equilibria of normal fluids and obtained from thermodynamic properties of pure saturated liquids. The models are then compared with computer simulation data to show the effect of attractive contribution forms employed. Calculated values of vapor-liquid equilibria (VLE) of hydrocarbons that can be reproduced for each model are also compared with experimental results. An additional parameter, ${\zeta}_{KB}$, is required to represent the VLE of pure water, which is ascertained to have a strong influence on the theoretical coexistence curve.

Phase Transition and Approximated Integral Equation for Radial Distribution Function

  • Yoon, Byoung-Jip;Jhon, Mu-Shik
    • Bulletin of the Korean Chemical Society
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    • 제7권1호
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    • pp.20-23
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    • 1986
  • A reduced condition for liquid-gas phase transition from the singularity of compressibility is derived using diagrammatic approach and is examined in the hard sphere system. The condition turns out that the Percus-Yevick and the Hyper-Netted-Chain approximation never conceive the idea of phase transition, and explains that the liquid-gas transition does not exist in hard sphere system. The solid-fluid transition is considered on the viewpoint of correlation function and diagrammatic analysis.

Computer Simulations of two kinds of Polydisperse Hard-Sphere Systems; Atomic Systems and Colloidal Suspensions

  • Shimura Tsutomu;Yamazaki Hiroyuki;Terada Yayoi;Tokuyama Michio
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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    • pp.21-22
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    • 2003
  • We perform two kinds of computer simulations on polydisperse hard-sphere systems; a molecular-dynamics simulation on atomic systems and a Brownian-dynamics simulation on colloidal suspensions. Analyses of the mean square displacement, the radial distribution function, and the pressure suggest that there exist three phase regions, a liquid phase region, a metastable phase region, and a crystal phase region, where the freezing and melting points are shifted to the values higher than in monodisperse case. It is also shown that the long-time behavior of colloidal suspensions is exactly the same as that of atomic systems.

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Electrostatic Adsorption of Uniformly Charged Electrolytes within Like-charged Electrodes

  • Jang, Seanea;Shin, Ghi Ryang;Kim, Soon-Chul
    • Journal of the Korean Physical Society
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    • 제73권9호
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    • pp.1315-1323
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    • 2018
  • The classical-fluids density functional theory has been developed for studying the structural and the electrical properties of electrolyte solutions containing uniformly charged hard-spherical ions. The modified fundamental-measure theory has been used to evaluate the hard-sphere contribution. The mean-field approximation has been employed to calculate the cross correlation between the hard sphere contribution and the Coulomb interaction. The Poisson equation for ions carrying charges that are spatially separated has been solved. The present theory shows reasonably good agreement with the corresponding Monte Carlo simulation results. The calculated results show that the attraction between like-charged planar surfaces is the result of the intra-ionic correlation and depends strongly on the ion size, valence, mole fraction, and charge distribution of electrolytes.

원판형 드래그펌프내의 희박기체유동 (Rarefied Gas Flows in Spiral Channels of a Disk-Type Drag Pump)

  • 황영규;허중식
    • 유체기계공업학회:학술대회논문집
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    • 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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    • pp.82-87
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    • 2000
  • The direct simulation Monte Carlo (DSMC) method is applied to investigate the flow field of a disk-type drag pump. The pumping channels are cut on both sides of a rotating disk. The rotor has 10 Archimedes' spiral blades. In the present DSMC method, the variable hard sphere model is used as a molecular model, and the no time counter method is employed as a collision sampling technique. For simulation of diatomic gas flows, the Larsen-Borgnakke phenomenological model is adopted to redistribute the translational and internal energies.

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Non-equilibrium Monte Carlo Simulations for Critical Flux of Hard Sphere Suspensions in Crossflow Filtration

  • Kim, Albert S.
    • 한국막학회:학술대회논문집
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    • 한국막학회 2008년도 춘계 총회 및 학술발표회
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    • pp.33-47
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    • 2008
  • Non-equilibrium (irreversible) themodynamics is used to investigate colloidal back-diffusion during crossflow membrane filtration. The chemical potential is generalized as a superposition of equilibrium and irreversible contributions, originating from Brownian and shear-induced diffusion, respectively. As a result, an effective drag force is derived using the irreversible thermodynamics for a particle undergoing both Brownian and shear-induced diffusion in a sheared concentrated suspension. Using the drag force, a hydrodynamic force bias Monte Carlo method is developed for crossflow membrane filtration to determine the critical flux of hard sphere suspensions. Effects of shear rate and particle size on the critical flux are studied, and results show a good agreement with experimental observations reported in the literature.

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침투성 구형 모델에 관한 분자 전산 연구: II. 충돌 특성 (Molecular Simulation Studies for Penetrable-Sphere Model: II. Collision Properties)

  • 김춘호;서숭혁
    • 폴리머
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    • 제35권6호
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    • pp.513-519
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    • 2011
  • 침투 가능한 구형 모델 유체의 충돌 특성을 고찰하고자 분자 동력학 방법을 이용한 전산 모사를 수행하였다. 이로부터 다양한 범위의 입자 충전 분율 ${\phi}$ 및 척력적 에너지 ${\varepsilon}^*$ 조건에 대한 충돌 빈도수, 평균 자유 행로, 강체형 반사 충돌각 및 연체형 침투 충돌각의 분포도, 유효 충전 분율 등을 계산하였다. 낮은 척력적 에너지 조건에서는 연체형 충돌이 주된 특성이나, 반면 높은 척력적 에너지 조건에서는 강체형 충돌이 주된 요인이었다. 매우 흥미롭게도, 전체 충돌 빈도수에 대한 연체형 충돌비(또는, 강체형 충돌비)는 정준 앙상블의 몬테카를로 전산 모사에서 받아들임 확률(또는, 되돌림 확률)로 표시되는 볼쯔만 인자와 직접적으로 관계되었다. 이와 같은 거동 입자들의 동적 충돌 특성들은 ${\varepsilon}^*{\geqq}3.0$${\phi}{\geqq}0.7$ 범위의 높은 척력적 에너지 및 높은 충전 분율 조건에서 제한적이었으며, 이는 침투성 구형 모델에서 나타나는 클러스터 형성 구조를 함축하고 있다.