• Title/Summary/Keyword: molecular diffusion

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Analysis of Influential Factors on Wax Deposition for Flow Assurance in Subsea Oil Production System (해저 석유생산시스템에서 유동안정성 확보를 위한 왁스집적 영향요소 분석 연구)

  • Jung, Sun-Young;Kang, Pan-Sang;Lim, Jong-Se
    • Journal of Advanced Marine Engineering and Technology
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    • v.39 no.6
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    • pp.662-669
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    • 2015
  • There has been an increased interest in the mitigation of wax deposition because wax, which usually accumulates in subsea oil-production systems, interrupts stable oil production and significantly increases the cost. To guarantee a required oil flow by mitigating wax deposition, we need to obtain a reliable estimation of the wax deposition. In this research, we perform simulations to understand the major mechanisms that lead to wax deposition, namely molecular diffusion, shear stripping reduction, and aging. While the model variables (shear reduction multiplier, wax porosity, wax thermal conductivity, and molecular diffusion multiplier) can be measured experimentally, they have high uncertainty. We perform an analysis of these variables and the amount of water and gas in the multiphase flow to determine these effects on the behavior of wax deposition. Based on the results obtained during this study for a higher wax porosity and molecular diffusion multiplier, we were able to confirm the presence of thicker wax deposits. As the shear reduction multiplier decreased, the thickness of the wax deposits increased. As the amount of water increased, there was also an increase in the amount of wax deposits until 40% water cut and decreased. As the amount of gas increased, the amount of wax deposits increased because of the loss of the light hydrocarbon component in the liquid phase. The results of this study can be utilized to estimate the wax deposition behavior by comparing the experiment (or field) and simulation data.

Separation of Hydrogen-Nitrogen Gases by PTMSP/PDMS-Borosilicate Composite Membranes (PTMSP/PDMS-Borosilicate 복합막에 의한 수소-질소 기체 분리에 관한 연구)

  • Lee, Suk Ho;Lee, Hyun Kyung
    • Membrane Journal
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    • v.25 no.2
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    • pp.123-131
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    • 2015
  • The PTMSP/PDMS graft copolymer were synthesized from the PTMSP[poly(1-trimethylsilyl-1-propyne)] and the PDMS[poly(dimethylsiloxane)] and then the PTMSP/PDMS-borosilicate composite membranes were prepared by adding the porous borosilicates to the PTMSP/PDMS graft copolymer. The number-average molecular weight (${\bar{M}}_n$) and the weight-average molecular weight (${\bar{M}}_w$) of PTMSP/PDMS graft copolymer were 460,000 and 570,000 respectively, and glass transition temperature ($T_g$) of PTMSP/PDMS graft copolymer appeared at $33.53^{\circ}C$ according to DSC analysis. According to the TGA measurements, the addition of borosilicate to the PTMSP/PDMS graft copolymer leaded the decreased weight loss and the completed weight loss temperature went down. SEM observation showed that borosilicate was dispersed in the PTMSP/PDMS-borosilicate composite membranes with the size of $1{\sim}5{\mu}m$. Gas permeation experiment indicated that the addition of borosilicate to PTMSP/PDMS graft copolymer resulted in the increase in free volume, cavity and porosity resulting in the gradual shift of the mechanism of the gas permeation from solution diffusion to molecular sieving surface diffusion, and Knudsen diffusion. Consequently, the permeability of $H_2$ and $N_2$ increased and selectivity ($H_2/N_2$) decreased as the contents of borosilicate increased.

Antimicrobial Activity of Extracted by Supercritical Fluid from Origanum vulgare, Cinnamomum cassia, Chamaecyparis obtusa and Scutellariae baicalensis (오레가노, 육계, 편백 및 황금의 초임계 유체 추출물의 항균 활성)

  • Kim, Woo-Jin;Cho, Jun-Young;Choi, Chang-Suk;Yoon, Gee-Sun;Lee, Won-Kyu;Ryu, Yeon-Woo
    • KSBB Journal
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    • v.23 no.2
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    • pp.147-152
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    • 2008
  • The variety of functional plants has an attention for new natural food preservation and natural antiseptic development. The extracts from functional plants with various methods (ethanol extraction, hot water extraction and supercritical fluid extraction) tested antimicrobial activity against 10 strains including the pathogenic and food poisoning bacteria, the yeast and fungi. The antimicrobial activities of supercritical fluid extracts were shown higher than ethanol extract and hot water extract when tested with disc-diffusion method and minimum inhibitory concentration (MIC). Antimicrobial activity of supercritical fluid extract was two times higher than ethanol extract in Cinnaonomum cassia. In addition, the supercritical fluid extractions of Chamaecyparis obtuas and the C. cassia showed the higher yield than Origanum vulgare and Scutellariae baicalensis. The supercritical fluid extract of C. cassia showed an antimicrobial activity against all strains tested. The supercritical fluid extract of S. baicalensis showed strong antimicrobial activity on Listeria monocytogenes. Supercritical fluid extraction of O. vulgare and C. obtuas showed strong antimicrobial activity on Salmonella typhimuriium. In MIC test, C. obtuas was shown the best natural material for the preparation of natural antimicrobial agent by supercritical fluid extraction. In conclusion, these results suggest that supercritical fluid extraction technique was effective to obtain functional ingredient with higher antimicrobial activity in the development of new antimicrobial reagent from natural materials.

Prediction of Chloride Profile considering Binding of Chlorides in Cement Matrix

  • Song, Ha-Won;Lee, Chang-Hong;Ann, Ki Yong
    • Corrosion Science and Technology
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    • v.8 no.2
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    • pp.81-88
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    • 2009
  • Chloride induced corrosion of steel reinforcement inside concrete is a major concern for concrete structures exposed to a marine environment. It is well known that transport of chloride ions in concrete occurs mainly through ionic/molecular diffusion, as a gradient of chloride concentration in the concrete pore solution is set. In the process of chloride transport, a portion of chlorides are bound in cement matrix then to be removed in the pore solution, and thus only the rest of chlorides which are not bound (i.e. free chlorides) leads the ingress of chlorides. However, since the measurement of free/bound chloride content is much susceptible to environmental conditions, chloride profiles expressed in total chlorides are evaluated to use in many studies In this study, the capacity of chloride binding in cement matrix was monitored for 150 days and then quantified using the Langmuir isotherm to determine the portions of free chlorides and bound chlorides at given total chlorides and the redistribution of free chlorides. Then, the diffusion of chloride ion in concrete was modeled by considering the binding capacity for the prediction of chloride profiles with the redistribution. The predicted chloride profiles were compared to those obtained from conventional model. It was found that the prediction of chloride profiles obtained by the model has shown slower diffusion than those by the conventional ones. This reflects that the prediction by total chloride may overestimate the ingress of chlorides by neglecting the redistribution of free chlorides caused by the binding capacity of cement matrix. From the evaluation, it is also shown that the service life prediction using the free chloride redistribution model needs different expression for the chloride threshold level which is expressed by the total chlorides in the conventional diffusion model.

Addition Effect of the Deposition and Buoyancy Terms in Modeling Turbulence Diffusion of Hazardous Air Pollutants (유해 대기오염물질의 난류확산 수치모의에서 침적한과 부력항 추가에 따른 효과)

  • Won, Gyeong-Mee;Lee, Hwa-Woon;Ji, Hyo-Eun;Kim, Cheol-Hee;Song, Chang-Keun
    • Journal of Korean Society for Atmospheric Environment
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    • v.22 no.1
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    • pp.73-84
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    • 2006
  • Hazardous Air Pollutants (HAPs) are characterized by being relatively heavier and denser than that of ambient air due to the various reasons such as higher molecular weight, low temperature and other complicated chemical transformations (Witlox, 1994). In an effort to investigate transport and diffusion from instantaneous emission of heavy gas, Lagrangian Particle Dispersion Model (LPDM) coupled with the RAMS output was employed. Both deposition process and buoyancy term were added on the atmospheric diffusion equations of LPDM, and the locations and concentrations of dense gas particle released from instantaneous single point source (emitting initially for 10 minutes only) were analyzed. The result overall shows that adding deposition process and buoyancy terms on the diffusion equation of LPDM has very small but detectable effect on the vertical and horizontal distribution of Lagrangian particles that especially transported for a fairly long traveling time. Also the slumping of dense gas can be found to be ignored horizontally compared to the advection by the horizontal wind suggesting that it was essential to couple the Lagrangian particle dispersion model coupled with the RAMS model in order to explain the dispersion of HAPs more accurately. However, during the initial time of instantaneous emission, buoyancy term play an important role on the vertical locations of dense particles for near surface atmosphere and around source area, indicating the importance of densities of HAPs in the beginning stage or short duration for the risk assessment of HAPs or management of heavy vapors during the explosive accidents.

A Study on Transport Characteristics of Hydrochloric Acid in an Anion Exchange Membrane (음이온 교환막에서 염산의 이동특성 연구)

  • 강문성;오석중;문승현
    • Membrane Journal
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    • v.8 no.3
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    • pp.148-156
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    • 1998
  • Diffusion dialysis is a membrane process driven by concentration difference using ion-exchange membranes and has been employed for many years for the acid recovery from acidic waste generated in steel, metal-refining and dectro-plating industries. Theoretically acid flux increases in propomon to the acid concentration difference. At acid concentrations higher than 3 N HCl, however, the acid flux had not increased linearly with the concentration difference. In this paper the effects of acid concentrations on diffusion dialysis for hydrochloric acid recovery and the acid transport mechanism in an anion exchange membrane were studied by membrane sorption tests and diffusion clialysis cell tests. The experimental results showed that the molecular diffusion was a major transport mechanism in a low acid concentration range and the proton leakage through an anion exchange membrane played an important role at higher acid concentrations. Also osmotic water transport and membrane dehydration retarded the transport of protons and caused the permeate flux to decrease.

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스테인레스강 Overlay 용접부의 Disbonding에 관한 연구 1

  • 이영호;윤의박
    • Journal of Welding and Joining
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    • v.1 no.2
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    • pp.45-52
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    • 1983
  • Many pressure vessels for the hot H$\sub$2//H$\sub$2/S service are made of 2+1/4Cr-1Mo steel with austenitic stainless steel overlay to combat agressive corrosion due to hydrogen sulfide. Hydrogen dissolves in to materials during operation, and sometimes gives rise to unfore-seeable damages. Appropriate precautions must, therefore, be taken to avoid the hydrogen induced damages in the design, fabrication and operation stage of such reactor vessels. Recently, hydrogeninduced cracking (or Disbonding) was found at the interface between base metal and stainless weld overlay of a desulfurizing reactor. Since the stainless steel overlay weld metal is subjected to thermal and internal-pressure loads in reactor operation, it is desirable for the overlay weld metal to have high strength and ductility from the stand point of structural safety. In section III of ASME Boiler and Pressure Vessel Code, Post-Weld Heat Treatment(PWHT) of more than one hour per inch at over 1100.deg. F(593.deg. C) is required for the weld joints of low alloy pressure vessel steels. This heat treatment to relieve stresses in the welded joint during construction of the pressure vessel is considered to cause sensitization of the overlay weld metal. The present study was carried out to make clear the diffusion of carbon migration by PWHT in dissimilar metal welded joint. The main conclusion reached from this study are as follows: 1) The theoretical analysis for diffusion of carbon in stainless steel overlay weld metal does not agree with Fick's 2nd law but the general law of molecular diffusion phenomenon by thermodynamic chemical potential. 2) In the stainless steel overlay welded joint, the PWHT at 720.deg. C for 10 hours causes a diffusion of carbon atoms from ferritic steel into austenitic steel according to the theoretical analysis for carbon migration and its experiment. 3) In case of PWHT at 720.deg. C for 10 hours, the micro-hardness of stainless steel weld metal in bonded zone increase very highly in the carburized layer with remarkable hardening than that of weld metal.

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The Effect of the Molecular Weight of PEG on Diffusion Though Cellulose (PEG 분자량에 따른 셀룰로오스에서의 확산거동)

  • 우종형;서영삼;윤기종
    • Proceedings of the Korean Fiber Society Conference
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    • 2003.04a
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    • pp.421-422
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    • 2003
  • 면섬유를 가공할 때 가공효과는 면섬유 미세기공에의 가공제 흡착량에 의존한다. 흡착량에 영향을 주는 것은 화학적으로는 가공제와 면섬유 간의 친화력이고, 물리적으로는 가공제의 물 속에서의 크기 즉, hydrodynamic volume이다. 기존 면섬유 가공제의 경우 낮은 분자량을 사용하였으나, 최근 들어 높은 분자량의 가공제를 사용 하는 경향이 있다. 고분자량 가공제의 경우에는 앞서 언급한 것과 같이 가공제의 크기가 가공제의 가공효과에 영향을 미칠 수 있으나, 이에 관련된 연구는 많지 않다. (중략)

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A MODIFIED SOLUTION PROCEDURE FOR THE ELLIPTIC-TYPE CONDITIONAL MOMENT CLOSURE MODEL IN NONPREMIXED TURBULENT REACTING FLOW

  • Liu, Tao;Huh, Kang-Yul
    • 한국연소학회:학술대회논문집
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    • 1997.06a
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    • pp.113-122
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    • 1997
  • The conditional moment closure formulation considering the molecular and turbulent diffusion is derived. A simplified solution procedure is proposed to reduce the computational burden due to the increased dimensionality of the conditionally averaged variables. A conditionally averaged variable is expressed as a linear weighted average of the two extremes, 'no reaction' and 'equilibrium' states. The modified elliptic-type conditional moment closure formulation is implemented to simulate a two dimensional nonpremixed mixing layer reacting flow. Results show good agreement for the conditional averages of the species concentration in Bilger et al.

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A Molecular Neural Network Based on Synaptic Transmission (시냅스 전위활동에 기반한 분자 신경망)

  • 정호진;조동연;장병탁
    • Proceedings of the Korean Information Science Society Conference
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    • 2003.04c
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    • pp.416-418
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    • 2003
  • 해마 뉴런의 시냅스에서 발생하는 전류는 후시냅스의 생화학적 반응을 통해 다음 뉴런으로 전달된다. 즉, 시냅스는 정보를 전달하는 매개로서 전시냅스에서 입력된 정보에 의거하여 후시냅스로 보내는 전류량을 조절하게 된다. 본 논문에서 제안하는 시냅스 기전 신경망 모델은 기존의 신경망과는 달리 시냅스에서 일어나는 반응-확산(reaction-diffusion) 모델에 의하여 입력과 출력의 관계를 결정한다. 제안된 신경망을 분류 문제에 적용한 결과 은닉 뉴런층 없이도 좋은 성능을 보였으며, 이 신경망은 앞으로 뇌에서의 생화학적 뉴런 학습 양상을 연구하는 모델로 사용될 수 있다.

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