• 공업화학
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• 제25권1호
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• pp.96-102
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• 2014

입상활성탄에 대한 metanil yellow의 흡착은 흡착제의 양, pH, 초기농도, 접촉시간과 흡착온도를 조작변수로 선택하여 회분식 실험으로 연구되었다. 흡착평형자료는 Langmuir와 Freundlich 흡착등온식에 대한 적합성을 평가하였다. 흡착평형은 Freundlich 흡착등온식이 더 잘 맞았으며, 계산된 분리계수 값으로부터 입상활성탄이 metanil yellow를 효과적으로 처리할 수 있다는 것을 알 수 있었다. 동력학적 실험으로부터, 흡착공정은 유사이차반응속도식에 잘 맞으며, 속도상수($k^2$) 값은 초기농도가 증가할수록 감소하였다. 활성화 에너지, 엔탈피, 엔트로피 및 Gibbs 자유에너지 변화와 같은 열역학 파라미터들은 흡착공정의 특성을 평가하기 위하여 298~318 K의 온도 범위에서 조사하였다. 활성화 에너지의 계산 값은 23.90 kJ/mol로 입상활성탄에 대한 metanil yellow의 흡착이 물리적 공정임을 나타냈다. Gibbs 자유에너지 변화의 음수값(${\Delta}G=-2.16{\sim}-6.55kJ/mol$)과 엔탈피 변화의 양수값(${\Delta}H=+23.29kJ/mol$)은 각각 흡착공정이 자발적 공정 및 흡열과정임을 나타냈다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1122-1127
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• 2004

an isolated droplet combustion exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous air. Results show that the operating pressure and driving frequency have an important role in determining the amplitude and phase lag of a combustion response. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Phase difference between pressure and evaporation rate decreases due to the reduced thermal inertia at high pressure. In addition to this, augmentation of perturbation frequency also enhances amplification of vaporization rate because the time period for the pressure oscillation is much smaller than the liquid thermal inertia time. The phase of evaporation rate shifts backward due to the elevated thermal inertia at high acoustic frequency.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.23-32
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• 2002

Combustion and flame propagation characteristics of the liquid phase LPG injection (LPLI) engine were investigated in a single cylinder optical engine. Lean bum operation is needed to reduce thermal stress of exhaust manifold and engine knock in a heavy duty LPG engine. An LPLI system has advantages on lean operation. Optimized engine design parameters such as swirl, injection timing and piston geometry can improve lean bum performance with LPLI system. In this study, the effects of piston geometry along with injection timing and swirl ratio on flame propagation characteristics were investigated. A series of bottom-view flame images were taken from direct visualization using an W intensified high-speed CCD camera. Concepts of flame area speed, In addition to flame propagation patterns and thermodynamic heat release analysis, was introduced to analyze the flame propagation characteristics. The results show the correlation between the flame propagation characteristics, which is related to engine performance of lean region, and engine design parameters such as swirl ratio, piston geometry and injection timing. Stronger swirl resulted in foster flame propagation under open valve injection. The flame speed was significantly affected by injection timing under open valve injection conditions; supposedly due to the charge stratification. Piston geometry affected flame propagation through squish effects.

• 한국환경과학회지
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• 제26권3호
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• pp.363-371
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• 2017

This study evaluates the adsorption properties of Sr ions in an aqueous solution of the synthetic zeolite (Z-Y1) prepared using coal fly ash generated from a thermal power plant. In order to investigate the adsorption characteristics, the effects of various parameters such as the initial concentrations of Sr ion, contact time, and solution pH were investigated in a batch mode. The Langmuir and Redlich-Peterson model fitted the adsorption isotherm data better than the Freundlich model. The maximum adsorption capacity of Sr ions, as determined the Langmuir model, was 181.68 mg/g. It was found that by varying the Sr ion concentration, pH, and temperature, the pseudo-second-order kinetic model describes the adsorption kinetics of the Sr ion better than the pseudo-first-order kinetic model. The calculated thermodynamic parameters of ${\Delta}H^0$ and ${\Delta}G^0$ showed that the adsorption of Sr ions on Z-Y1 was occurred through a spontaneous and an endothermic reaction. We found that the adsorption of Sr ions by Z-Y1 was more affected by pH than by temperature and Sr ion concentration.

• 한국수소및신에너지학회논문집
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• 제19권6호
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• pp.537-544
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• 2008

In this paper, flow characteristics of an adiabatic capillary tube in a transcritical $CO_2$ have been investigated employing the homogeneous model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously. Two friction factors(Churchill) and viscosity(McAdams) are comparatively used to investigate the flow characteristics. Supercritical and subcritical thermodynamic and transport properties of $CO_2$ are calculated employing EES property code. Flow characteristics analysis of $CO_2$ adiabatic capillary tube is presented to offer the basic design data for the operating parameters. The operating parameters considered in this study include inlet temperature and pressure of an adiabatic capillary tube, evaporating temperature and inner diameter tube. The main results were summarized as follows : inlet temperature and pressure of an adiabatic capillary tube, evaporating temperature, mass flowrate and inner diameter of $CO_2$ adiabatic capillary tube have an effect on length of an adiabatic capillary tube.

• 전기화학회지
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• 제15권1호
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• pp.54-66
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• 2012

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift ($90^{\circ}{\geq}-{\varphi}{\geq}0^{\circ}$) vs. potential (E) behavior for the optimum intermediate frequency ($f_o$) and the fractional surface coverage ($0{\leq}{\theta}{\leq}1$) vs. E behavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and the related electrode kinetic and thermodynamic parameters. At Ni/0.5 M $H_2SO_4$ and 0.1M LiOH aqueous solution interfaces, the Frumkin and Temkin adsorption isotherms (${\theta}$ vs. E) of H for the cathodic hydrogen ($H_2$) evolution, interaction parameters (g), equilibrium constants (K), standard Gibbs energies (${\Delta}G^0_{\theta}$) of H adsorption, and rates of change (r) of ${\Delta}G^0_{\theta}$ with ${\theta}$ have been determined using the phase-shift method and correlation constants. A lateral repulsive interaction (g>0) between the adsorbed H species appears. The value of K in the alkaline aqueous solution is much greater than that in the acidic aqueous solution.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.35-38
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• 2007

액체로켓엔진(Liquid Rocket Engine) 의 천이성능 예측을 위해 선행연구 되었던 LRE 시스템 모듈화 프로그램의 결과를 살펴보고, 일본의 로켓엔진 동적 해석 프로그램(Rocket Engine Dynamic Simulator)의 엔진 시스템 동적 해석 방법과 모델링에 대해 고찰하였다. LRE 시스템 모듈화 프로그램에서는 각 구성품에 대한 설계 인자를 수학적으로 모델링하였고 구성품 간의 유량과 압력을 매칭시켜 통합하여, 로켓엔진 시스템의 요구조건을 만족하는 각 구성품에 대한 주요 설계 파라미터를 도출하는 과정에 관하여 논의하였다. 로켓엔진 시스템을 유한한 배관요소들의 연결로 모델링하고, 시간의 함수로 표현되는 보존방정식을 적용하여 터보펌프, 밸브, 오리피스，추력실 등 유체기기의 작동 특성을 모사하는 동특성 설계 과정에 관하여 고찰한다.

• 한국자동차공학회논문집
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• 제2권5호
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• pp.121-134
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• 1994

Shock tube investigation of ethylene oxide-$0_{2}-N_{2}$ mixture have been performed to reveal detonation characteristics of the mixture in terms of detonation pressure and speed. Theoretical calculation of thermodynamic parameters at the Chapmann-Jouguet detonation of the mixture has been also performed. A comparision of the observed results with the calculated ones can lead us to predict the detonation parameters of ethylene oxide in an artificial air. In addition, we have observed ignition delay times of ethylene oxide mixtures. The best fit of the observed delay times to Arrhenius gas kinetic relation gives : ${\tau}=10^{-144}{e{xp}}(E_a/RT)[C_{2}H_{4}O]^{-4.8}[O_{2}]^{-12.4}[N_{2}]^{-14.1}$ $E_a=3.67kcal/mole$ The observed activation energy is markedly reduced, compared with the case of ethylene oxide diluted in Ar. It could be due to the factor that $N_2$ play a role as detonation promoter yielding very reactive NOx radicals.

• 한국주조공학회지
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• 제29권4호
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• pp.181-186
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• 2009

The interrelationship between new parameter ${\sigma}$ and maximum diameter $D_{max}$ is elaborated and discussed in comparison with four other glass forming ability (GFA) parameters, i.e. (1) super-cooled liquid region ${\Delta}T_x (=T_x - T_g)$, (2) reduced glass transition temperature $T_{rg} (=T_g/T_l)$, (3) K parameter $K (=[T_x-T_g]/[T_l -T_x])$, and (4) gamma parameter ${\gamma}(=[T_x]/[T_l+T_g])$ in Ca-based bulk metallic glass (BMG) systems. The ${\sigma}$ parameter, defined as ${\Delta}T^*{\times}P^'$, has a far better correlation with $D_{max}$ than the GFA parameters suggested so far, clearly indicating that the liquid phase stability and atomic size mismatch dominantly affect the GFA of Ca-based BMGs. Thus, it can be understood that the GFA of BMGs can be properly described by considering structural aspects for glass formation as well as thermodynamic and kinetic aspects for glass formation.

• Bulletin of the Korean Chemical Society
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• 제4권3호
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• pp.115-119
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• 1983

The ionic association constants (K) of 2, N-dimethyl pyridinium iodide (2NDMPI) in 95 volume percentage ethanol-water mixture were determined by a modified UV and conductance method at $20^{\circ}C{\sim}50^{\circ}C$ under 1 to 2000 bars. The K values increase with increasing pressure and decrease with temperature. The total partial molar volume change (${\Delta}V$) has relatively small negative value and the absolute ${\Delta}V$ value decrease with increasing pressure and temperature. The ion size (a) and solvation number (n) of 2NDMPI were about 5 $\AA$ and changed from 1 to 3 with decreasing temperature. Other thermodynamic parameters such as enthalpy (${\Delta}H^{\circ}$) and entropy (${\Delta}S^{\circ}$) for the equilibrium of the 2NDMPI were evaluated. From all the parameters mentioned above, we came to conclusion that the electrostriction effect of 2NDMPI in the ethanol-water mixture is enhanced with increasing pressure and decreasing temperature.