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Diffusion and Thermodiffusion in Hydrocarbon Mixtures
Published in Devrim Balköse, Ana Cristina Faria Ribeiro, A. K. Haghi, Suresh C. Ameta, Tanmoy Chakraborty, Chemical Science and Engineering Technology, 2019
Cecília I. A. V. Santos, Valentina Shevtsova, Ana C. F. Ribeiro
Mutual diffusion refers to the fluxes of solution components caused by composition differences and the resulting chemical potential gradient driving forces, in contrast to self-diffusion, which occurs without mass transport in systems of uniform chemical composition. It is very common in the scientific literature to find misunderstandings concerning the meaning of the parameter frequently just denoted by D and referred to as “diffusion coefficient.”56 It is necessary to distinguish between two distinct processes: self-diffusion D* (also named as intradiffusion, tracer diffusion, single ion diffusion, or ionic diffusion) and mutual diffusion D (also known as interdiffusion, concentration diffusion, or salt diffusion). Methods such as those based in nuclear magnetic resonance (NMR), polarography, and capillary-tube techniques with radioactive isotopes measure self-diffusion coefficients, not mutual diffusion. However, for bulk substance transport, the appropriate parameter is the mutual diffusion coefficient, D. Theoretical relationships derived between self-diffusion and mutual diffusion coefficients, D* and D, respectively, have had limited success for estimations of D (as well as theoretical formulae for the calculation of D), and consequently, experimental mutual diffusion coefficients are absolutely necessary. In the two infinite dilution limits of a binary mixture, the Fickian diffusion coefficients coincide with the intradiffusion coefficient of the diluted component.
Fructose And Its Impact On The Diffusion Of Electrolytes In Aqueous Systems
Published in A. K. Haghi, Lionello Pogliani, Devrim Balköse, Omari V. Mukbaniani, Andrew G. Mercader, Applied Chemistry and Chemical Engineering, 2017
Ana c. F. Ribeiro, luis M. P. Verissimo, M. Luisa ramos, daniela F. S. L. Rodrigues, miguel A. Esteso
There are two markedly distinct processes of diffusion, self-diffusion, D* (also named as intradiffUsion, tracer diffusion, single ion diffusion, or ionic diffusion), and mutual diffusion, D, (also known as interdiffusion, concentration diffusion, or salt diffusion).1−4 Methods such as those based on NMR, polarography, and capillary tube techniques with radioactive isotopes measure self-diffusion coefficients, not mutual diffusion. However, for bulk matter transport, the appropriate parameter is the mutual diffusion coefficient, D. Theoretical relationships derived between self-diffusion and mutual diffusion coefficients, D* and D, respectively, have had limited success for estimation of D (as well as theoretical models for the calculation of D) and consequently experimental determination of mutual diffusion coefficients is absolutely necessary.
Mathematical Hydrocarbon Fate Modeling in Soil Systems
Published in Edward J. Calabrese, Paul T. Kostecki, Principles and Practices for Petroleum Contaminated Soils, 2019
Edward J. Calabrese, Paul T. Kostecki
Molecular diffusion in solution is the process whereby ionic or molecular constituents move under the influence of their kinetic activity in the direction of their concentration gradient. The process of diffusion is often known as self-diffusion, molecular diffusion, or ionic diffusion. The mass of diffusing substance passing through a given cross section per unit of times is proportional to the concentration gradient (Fick’s first law).
Molecular Dynamics Study of CO2 Phase Change Transport in the Near-Critical Region: Model Parameter Optimization
Published in Heat Transfer Engineering, 2023
Zi-Yu Liu, Lin Chen, Haisheng Chen
After discussing the accuracy of optimized results, another common property of CO2-self-diffusion coefficient (D) [39] in different regions is analyzed. Figure 4 shows the 3D surface diagram of CO2 self-diffusion coefficient at different temperatures and pressures from OPLS-AA forcefield. It can be observed that self-diffusion coefficient increases when temperature increases while self-diffusion coefficient decreases with the increase of pressure. For example, the D value is 143.55 × 10−8 m2/s in 305 K, 1.08 MPa while the value is 148.30 × 10−8 m2/s in 320 K, 1.08 MPa. The D value is 9.47 × 10−8 m2/s in 298 K, 5.8 MPa while the value is 9.02 × 10−8 m2/s in 298 K, 6.06 MPa. And this phenomenon does not change even CO2 condition is from gas phase to supercritical region. The self-diffusion coefficient is 143.55 × 14−8 m2/s in 305 K, 1.08 MPa (gas phase) while the D value is 4.12 × 10−8 m2/s in 305 K, 7.27 MPa (supercritical phase). It is worth noting that the CO2 self-diffusion coefficient gradually decreases from sub-critical phase to supercritical phase although the angle value we optimized has a dramatic transition. Besides that, the CO2 self-diffusion coefficient has just a slight increase with the increase of temperature in supercritical region when angle is fixed at 179.63°. The self-diffusion coefficient ranges from 4.06 × 10−8 m2/s to 4.48 × 10−8 m2/s when the temperature changes from 304.2 K to 320 K, pressure is from 7.12 MPa to 11.09 MPa. However, for gas phase, CO2 self-diffusion coefficient has an obviously increase with the increase of temperature when angle is also fixed at 179.63°. The self-diffusion coefficient ranges from 12.56 × 10−8 m2/s to 0.16 × 10−8 m2/s when the temperature increases from 304.2 K to 320 K, pressure shows decrease trend from 6.81 MPa to 1.18 MPa. In other words, angle value has a more sensitive change in supercritical region than gas phase for simulating CO2 self-diffusion coefficient, and the complexity of CO2 properties in the near-critical region may be the cause.