• 한국응용과학기술학회지
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• 제18권4호
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• pp.325-331
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• 2001

The critical micelle concentration (CMC) at which micelles start to form from a surfactant solution is usually measured in terms of conventional concentration units. However, the thermodynamic potentials are expressed in terms of mole fraction $X_{CMC}$ and $X_{CMC}$ cannot be directly measured experimentally. The Gibbs free energy, ${\Delta}G^{\ast}_{mic}$, in particular is related to $X_{CMC}$ through ${\Delta}G^{\ast}_{mic}$ = $RTlnX_{CMC}$. When it comes to CMC, the molar CMC, $C_{CMC}$, differs only by the proportionality $C^{-1}_{w}$ with $C_{w}$ being the molarity of water. Hence, $C_{CMC}$ is found to be a proper representation of CMC. However, in calculation of ${\Delta}G^{\ast}_{mic}$ and other thermodynamic potentials from the CMC, $X_{CMC}$ or $C_{CMC}/C_{w}$ should be used.

• Bulletin of the Korean Chemical Society
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• 제17권8호
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• pp.735-744
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• 1996

We present results of molecular dynamic (MD) simulations for the thermodynamic and structural properties of liquid n-alkanes, from n-butane to n-heptadecane, using three different models Ⅰ-Ⅲ. Two of the three classes of models are collapsed atomic models while the third class is an atomistically detailed model. Model Ⅰ is the original Ryckaert and Bellemans' collapsed atomic model [Discuss. Faraday Soc. 1978, 66, 95] and model Ⅱ is the expanded collapsed model which includes C-C bond stretching and C-C-C bond angle bending potentials in addition to Lennard-Jones and torsional potentials of model Ⅰ. In model Ⅲ all the carbon and hydrogen atoms in the monomeric units are represented explicitly for the alkane molecules. Excellent agreement of the results of our MD simulations of model Ⅰ for n-butane with those of Edberg et al.[J. Chem. Phys. 1986, 84, 6933], who used a different algorithm confirms the validity of our algorithms for MD simulations of model Ⅱ for 14 liquid n-alkanes and of models Ⅰ and Ⅲ for liquid n-butane, n-decane, and n-heptadecane. The thermodynamic and structural properties of models Ⅰ and Ⅱ are very similar to each other and the thermodynamic properties of model Ⅲ for the three n-alkanes are not much different from those of models Ⅰ and Ⅱ. However, the structural properties of model Ⅲ are very different from those of models Ⅰ and Ⅱ as observed by comparing the radial distribution functions, the average end-to-end distances and the root-mean-squared radii of gyrations.

• International Journal of Automotive Technology
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• 제5권4호
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• pp.287-295
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• 2004

A performance simulator for the fuel cell hybrid electric vehicle (FCHEV) is developed to evaluate the potentials of hybridization for fuel cell electric vehicle. Dynamic models of FCHEV's electric powertrain components such as fuel cell stack, battery, traction motor, DC/DC converter, etc. are obtained by modular approach using MATLAB SIMULINK. In addition, a thermodynamic model of the fuel cell is introduced using bondgraph to investigate the temperature effect on the vehicle performance. It is found from the simulation results that the hybridization of fuel cell electric vehicle (FCEV) provides better hydrogen fuel economy especially in the city driving owing to the braking energy recuperation and relatively high efficiency operation of the fuel cell. It is also found from the thermodynamic simulation of the FCEV that the fuel economy and acceleration performance are affected by the temperature due to the relatively low efficiency and reduced output power of the fuel cell stack at low temperature.

• 한국세라믹학회지
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• 제49권1호
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• pp.48-55
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• 2012

Degradation of performance and life time of a functional material or device thereof is induced, to a great extent, by mass transfer in the material that is driven by various thermodynamic forces imposed intentionally or accidentally during its operation or service. The forces are any gradient of intensive thermodynamic variables, component chemical potentials, electrical potential, temperature, stresses, and the like. This paper reviews electric-field induced degradation phenomena in ionic solid compounds including insulation resistance degradation, crystal shift, microstructural alterations, compositional unmixing, and compound decomposition. Their inner workings are also discussed qualitatively.

• 설비공학논문집
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• 제11권1호
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• pp.125-132
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• 1999

Studies are being done to replace conventional refrigerants with alternatives that have low or no ozone depletion and greenhouse warming Potentials, yet possess appropriate pro perties for a refrigeration cycle. To achieve this goal, a consistent set of thermodynamic properties of the working fluid is required. A common problem with the possible alternative refrigerants is that sufficient experimental data do not exist, thus making it difficult to develp complete equations of state that can predict properties in all regions including the vapor-liquid equilibrium. One solution is the use of the generalized equation of state correlations that can predict thermodynamic properties with a minimum number of characteristic parameters. Characteristic parameters required for the generalized equation of state are, in general, critical temperature, critical pressure, critical volume and normal boiling temperature. In this study, estimation of these characteristic parameters of refrigerants by group contribution method is developed.

• 한국세라믹학회지
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• 제49권1호
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• pp.11-18
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• 2012

The characteristic features of solid oxide fuel cells are reviewed from the viewpoint of the thermodynamic variables to be developed inside cells/stacks particularly in terms of gradients of chemical potential, electrical potential and temperature and corresponding flows of air, fuel, electricity and heat. Examples of abrupt destruction of SOFC systems were collected from failures in controlling their steady flows, while continuous degradation was caused by materials behaviors under gradients of chemical potentials during a long operation. The local equilibrium approximation has been adopted in NEDO project on the durability/reliability of SOFC stacks/systems; this makes it possible to examine the thermodynamic stability/reactivity as well as mass transfer under the thermodynamic variable gradients. Major results of the NEDO project are described with a focus on degradation/deterioration of electrolyte and electrode materials.

• Macromolecular Research
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• 제11권1호
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• pp.53-61
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• 2003

A molecular-thermodynamic model is developed for the salt-induced protein precipitation. The protein molecules interact through four intermolecular potentials. An equation of state is derived based on the statistical mechanical perturbation theory with the modified Chiew's equation for the fluid phase, Young's equation for the solid phase as the reference system and a perturbation based on the protein-protein effective two body potential. The equation of state provides an expression for the chemical potential of the protein. In a single protein system, the phase separation is represented by fluid-fluid equilibria. The precipitation behaviors are simulated with the partition coefficient at various salt concentrations and degree of pre-aggregation effect for the protein particles. In a binary protein system, we regard the system as a fluid-solid phase equilibrium. At equilibrium, we compute the reduced osmotic pressure-composition diagram in the diverse protein size difference and salt concentrations.

• Nuclear Engineering and Technology
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• 제10권3호
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• pp.127-136
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• 1978

온도종속 Thomas-Fermi 이론을 적용하여 금속의 일종인 Na에 대한 상태방정식, chemical potential, % ion 화도, 엔트로피, 원자당운동에너지 및 총에너지 등을 포함한 제열학적동을 산출하였다. $\rho$$_{0}$를 Na의 비등점에서의 정상밀도라 할 때 0.1$\rho$$_{0}$ ~ 10$\rho$$_{0}$ 까지의 밀도영역에서, 또한 Na이 기체 또는 액체상태로 존재할 것으로 기대되는 $textsc{k}$T=60.88Ryd.~0.0216Ryd 까지의 온도영역에 대하여 이들 양을 산출하였다. 본 연구에서는 고온 및 고압상태에서의 물리양 산출하는 것을 주목적으로 하고 있으나 Thomas-Fermi 근사가 기대되는 것처럼 그렇게 조잡하지 않음을 보이기 위하여 극저온 및 극저밀도에서의 물리양들도 산출하였다. 특히 고온에서의 상태방정식, 운동에너지, chemical potential 및 엔트로피를 ideal Fermi gas의 이들 양과 비교하였다. 그 결과, 산출한 chemical potential은 서로 잘 일치하나 엔트로피, 원자당운동에너지 및 상태방정식은 $textsc{k}$T=60.88Ryd.의 고온에서도 상당한 차이가 있음을 발견하였다.

• Carbon letters
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• 제28권
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• pp.87-95
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• 2018

This study examined the influence of operating parameters on the electrosorptive recovery system of lithium ions from aqueous solutions using a spinel-type lithium manganese oxide adsorbent electrode and investigated the electrosorption kinetics and isotherms. The results revealed that the electrosorption data of lithium ions from the lithium containing aqueous solution were well-fitted to the Langmuir isotherm at electrical potentials lower than -0.4 V and to the Freundlich isotherm at electrical potentials higher than -0.4 V. This result may due to the formation of a thicker electrical double layer on the surface of the electrode at higher electrical potentials. The results showed that the electrosorption reached equilibrium within 200 min under an electrical potential of -1.0 V, and the pseudo-second-order kinetic model was correlated with the experimental data. Moreover, the adsorption of lithium ions was dependent on pH and temperature, and the results indicate that higher pH values and lower temperatures are more suitable for the electrosorptive adsorption of lithium ions from aqueous solutions. Thermodynamic results showed that the calculated activation energy of $22.61kJ\;mol^{-1}$ during the electrosorption of lithium ions onto the adsorbent electrode was primarily controlled by a physical adsorption process. The recovery of adsorbed lithium ions from the adsorbent electrode reached the desorption equilibrium within 200 min under reverse electrical potential of 3.5 V.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.155-155
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• 2014

The oxide film was formed in hydrogen induced cracking (HIC) environment by potentio-dynamic method. Corrosion potentials and rates of the X-65 and X-80 line pipe steels were -0.3495 $V_{SHE}$, $2.833{\times}10^{-3}A/cm^2$ and 0.2716 $V_{SHE}$ and $2.533{\times}10^{-3}A/cm^2$, respectively. Surface composition analysis of the oxide film contained sulfur. Thermodynamic analysis of the HIC solution chemistry suggested that the oxide phase consisted of iron sulfate. Dynamic nano-indentation method applied to determine nano-hardnesses of the oxide film and base metal hardness.