• Title/Summary/Keyword: Convection-diffusion

Search Result 226, Processing Time 0.024 seconds

Preliminary Studies on Double-Diffusive Natural Convection During Physical Vapor Transport Crystal Growth of Hg2Br2 for the Spaceflight Experiments

  • Ha, Sung Ho;Kim, Geug Tae
    • Korean Chemical Engineering Research
    • /
    • v.57 no.2
    • /
    • pp.289-300
    • /
    • 2019
  • We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide ($Hg_2Br_2$) crystals in 1 g and microgravity (${\mu}g$) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), $1{\leq}AR{\leq}10$. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than $10^{-2}g$ make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.

Chloride Penetration into Concrete in Tidal Zone by Diffusion-Convection Analysis (확산과 이송을 고려한 콘크리트의 염소이온 침투해석)

  • Kim, Ki-Hyun;Cha, Soo-Won;Jung, Hyung-Mok
    • Journal of the Computational Structural Engineering Institute of Korea
    • /
    • v.22 no.6
    • /
    • pp.607-615
    • /
    • 2009
  • Analysis of chloride penetration into concrete is performed considering the repeated wetting and drying conditions of tidal zone, by means of the developed finite element program which enables the diffusion-convection analysis to be conducted. Heat conduction and moisture diffusion are also included in the finite element analysis program in order that their effects to chloride penetration may be considered. For the efficiency of calculation, the analyses of temperature, relative humidity and free chloride concentration are conducted successively in that order, by treating the convection of chloride due to moisture diffusion as an source or sink term. By comparing the analysis result from finite element analysis, where main variable is a wetting and drying period, with the chloride profiles from ACI Life-365 method, it is shown that the Life-365 method gives an accurate result for the submerged zone but does not consider the differences of wetting and drying period. To obtain an accurate chloride profile in the tidal zone, it is confirmed that the diffusion-convection finite element analysis should be applied.

Temperature Dependent Self-Diffusion Coefficients of Valinomycin and the Potassium-Valinomycin Complex

  • Kim, Su-Deuk;Lee, Yun-Jung;Joo, Hyun-Hye;Ahn, Sang-Doo
    • Journal of the Korean Magnetic Resonance Society
    • /
    • v.12 no.1
    • /
    • pp.51-59
    • /
    • 2008
  • Convection effect in liquids has been one of the main targets to be overcome in pulsed-field-gradient NMR measurements of self-diffusion coefficients since the temperature gradient along the sample tube generated by the heating and/or cooling process causes the effect, resulting in additional diffusion. It is known that the capillary is the most appropriate tube type for diffusion experiments at variable temperatures since the narrower tube suppresses convection effectively. For evaluating the properties of hydrogen bonding, diffusion coefficients of the $K^+$-complexed and free valinomycin in a micro tube have been determined at various temperatures. From the analysis of the obtained diffusion coefficient values, we could conclude that the intramolecular hydrogen bonding in both of the $K^+$ complexed and free valinomycin in a non-polar solvent is preserved over the observed temperature range, and the temperature dependence of hydrogen bonding is more pronounced in free valinomycin. It is also thought that there is no big change in the radius of the $K^+$-complexed as temperature is varied, and the ratio of overall radius, $r_{complex}/r_{free}$ is slightly decreased as temperature rises.

HIGH-ORDER WEIGHTED DIFFERENCE SCHEMESTHE CONVECTION-DIFFUSION PROBLEMS

  • Choo, S.M.;Chung, S.K.;Kim, Y.H.
    • Communications of the Korean Mathematical Society
    • /
    • v.14 no.4
    • /
    • pp.815-832
    • /
    • 1999
  • High-order weighted difference schemes with uniform meshes are considered for the convection-diffusion problem depending on Reynolds numbers. For small Reynolds numbers, a weighed cen-tral difference scheme is suggested since there is no boundary layer. For large Reynolds numbers, we propose a modified up wind method with an artificial diffusion in order to overcome nonphysical oscilla-tion of central schemes and obtain good accuracy in the boundary later. Existence and corresponding error estimates of the solution for the difference scheme have been shown. Numerical experiments are provided to back up the analysis.

  • PDF

A Study on Etching Patterns of Copper Surface by Chemical Corrosion (동(銅) 표면(表面)의 화학부식(腐蝕)에 의한 식각(蝕刻) 패턴 연구)

  • Kim, Min-Gun;Seo, Bong-Won
    • Journal of Industrial Technology
    • /
    • v.20 no.B
    • /
    • pp.77-86
    • /
    • 2000
  • In order to observe the pattern forming of copper plate and chemical corrosion reaction, a study on the effect of the process parameters on the formation of micro-pattern by a photochemical etching of copper plate was carried out. The results are as follows : 1) Etching rate increases as the concentration of etchant increases under the regular condition of the temperature by the increasing of diffusion rate to surface. 2) Etching rate increases as the temperature of etchant increases by the fast acting of the material delivery of diffusion to surface under the regular condition of concentration. 3) It was found that etching speed increases as the material delivery of convection rising increased when the aeration speed of etchant increases. This result was from the fact acted by the material delivery of convection rising rather than material delivery of diffusion to the surface.

  • PDF

An Investigation of the Sample Rotation Effects on Suppression of Convective Flows in PGSE Diffusion NMR Experiments

  • Kim, Minkyoung;Chung, Kee-Choo
    • Journal of the Korean Magnetic Resonance Society
    • /
    • v.20 no.2
    • /
    • pp.61-65
    • /
    • 2016
  • Undesirable convective flow in an NMR tube inhibits the accurate measurement of diffusion coefficients by NMR spectroscopy. To minimize the convection effects, various methods have been suggested, and it has been known that the use of sample rotation can be useful. However, it has not been clearly examined that the convection suppressing effect of the sample rotation under the different spinning speeds. In this study, the relation between convective flow and the sample rotation was investigated using PGSE NMR diffusion experiments to reveal the feasibility for controlling the convective flow in an NMR tube by sample rotation itself. The viscosity effect was also examined using solvents with four different viscosities, acetone-$d_6$ chloroform-d, pyridine-$d_5$, and $D_2O$. The sample rotation showed apparent convection suppressing effects at all temperature range for the low viscosity solvents, acetone-$d_6$ and chloroform-d, even at the faster than 5 Hz spinning rate. The similar patterns were also observed for pyridine-$d_5$ and $D_2O$, which have higher viscosity. This effect was observed even at high temperatures where convective flow arises conspicuously.

FINITE DIFFERENCE SCHEMES FOR A GENERALIZED CALCIUM DIFFUSION EQUATION

  • Choo, Sang-Mok;Lee, Nam-Yong
    • East Asian mathematical journal
    • /
    • v.24 no.4
    • /
    • pp.407-414
    • /
    • 2008
  • Finite difference schemes are considered for a $Ca^{2+}$ diffusion equations with damping and convection terms, which describe $Ca^{2+}$ buffering by using stationary and mobile buffers. Stability and $L^{\infty}$ error estimates of approximate solutions for the corresponding schemes are obtained using the extended Lax-Richtmyer equivalence theorem.

  • PDF

A mathematical model of blood flow and convective diffusion processes in constricted bifurcated arteries

  • Chakravarty S.;Sen S.
    • Korea-Australia Rheology Journal
    • /
    • v.18 no.2
    • /
    • pp.51-65
    • /
    • 2006
  • Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Wavier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.

AN OVERLAPPING SCHWARZ METHOD FOR SINGULARLY PERTURBED THIRD ORDER CONVECTION-DIFFUSION TYPE

  • ROJA, J. CHRISTY;TAMILSELVAN, A.
    • Journal of applied mathematics & informatics
    • /
    • v.36 no.1_2
    • /
    • pp.135-154
    • /
    • 2018
  • In this paper, an almost second order overlapping Schwarz method for singularly perturbed third order convection-diffusion type problem is constructed. The method splits the original domain into two overlapping subdomains. A hybrid difference scheme is proposed in which on the boundary layer region we use the combination of classical finite difference scheme and central finite difference scheme on a uniform mesh while on the non-layer region we use the midpoint difference scheme on a uniform mesh. It is shown that the numerical approximations which converge in the maximum norm to the exact solution. We proved that, when appropriate subdomains are used, the method produces convergence of second order. Furthermore, it is shown that, two iterations are sufficient to achieve the expected accuracy. Numerical examples are presented to support the theoretical results. The main advantages of this method used with the proposed scheme are it reduce iteration counts very much and easily identifies in which iteration the Schwarz iterate terminates.