Comsol negative concentration. how to avoid negative concentration.

Comsol negative concentration To start a new discussion with a link back to this one, click here. Comsol includes a lot of frustration :(Till Ivar KJELBERG COMSOL Multiphysics(r) fan, retired The benefit is that C The problem with this model is that the concentration of B on the surface can reach negative concentration. Also, Oct 5, 2014 · Negative concentration values in Transport of Diluted Species Study Posted 2014年10月5日 GMT-4 03:36 Fluid & Heat, Computational Fluid Dynamics (CFD), Microfluidics 2 Feb 2, 2012 · Hello. Hence, the first-order rate constant has units m s-1, representing an During the discharge simulation the concentration in the negative electrode decreases and that in the positive electrode increases. I am relatively new to COMSOL so I Oct 17, 2019 · There is a zone of negative concentration above the surface where the flux is set; Change the mesh. I'm modeling creeping flow and transport of dilute species through a series of ribs, with an electrochemical reaction occuring at 10 mA/sqcm on the bottom surface if you check the boundary equations: inflow fixed the concentration on the boundary to the one of a fictitious reservoir on the external side. how to avoid negative concentration. PDT Version 4. 3a 2 When setting up user-defined kinetics expressions, avoid evaluating negative concentrations by using expressions such as max(c, eps^2), where eps is the machine epsilon Nov 8, 2015 · when the initial concentration is 1mol/m^3, the negative value is about -0. m. When explicitly including mass transport in a model, this dependence is typically described by a concentration dependent kinetics expression as Use negative values for reactants and positive values for products in the modeled reaction. (which is equal to the concentration of C on the surface going over the initial The concentration will locally be slightly negative at t=0, as shown in the figure. I used the standard mesh from comsol and two custom quad meshes . 01mm) when ever I increase the particle radius, the concentration of one of the reactants The stationary model converges, but with the negative concentration region. cells move in the direction of the electric field or deviates from the field. Figure 1: Solutions to the time-dependent diffusion problem with a boundary condition at the left (c=1) that creates With the Use logarithm formulation for electrolyte salt concentration functionality enabled the interface will solve for the logarithm of the electrolyte salt concentration. I'm currently exploring the possibility of using a conditional statement to set these concentrations Is there any difference between Concentration dependent Butler-Volmer equation and Normal Butler-Volmer equation? I have built a PEM fuel cell model,and my results didn't I am running simulation containing a node of flow through free and porous media and a node for electrostatics and one node for transportation of dilute species but i m not erro：Log of negative. I want to know whether the COMSOL software is suitable for the calculation Feb 26, 2015 · The issue of negative concentrations has appeared on this forum repeatedly, and there seems to be no easy solution to that problem. Low potentials at the negative electrode are harmful to the battery, since this may result in accelerated solid-electrolyte-interphase (SEI) 4 | PROCESS CONTROL USING A PID CONTROLLER of the convective flow. 1, 0. This can occur when the model involves reactions or Jun 27, 2012 · I'm working on a vapor intrusion model in which the contaminant is moving in soil. Posted 10. There is a similar example The problem with this model is that the concentration of B on the surface can reach negative concentration. The boundary conditions for the mass balance are: Negative concentration values - transport of diluted species + Darcy's law (transport in porous bed) Posted 09. When simulating with the SCD+TDS with Butler-Volmer kinetics, I am getting unrealistic concentrations (both negative Jan 22, 2010 · It helped, but at last the concentration doesn't reach zero. Now I try to simulate the mixing in the microchannel without reactions. I'm currently exploring the possibility of using a conditional statement to set these concentrations Convergence problems are often the underlying issue when negative concentrations are observed in high convection regimes (high Péclet number) and with large reaction terms or fast kinetics Mar 9, 2019 · At the time to run the model just with the application of Transport of diluted species, applying the semi-empirical kinetic model, the model works properly and the concentrations Convergence problems are often the underlying issue when negative concentrations are observed in high convection regimes (high Péclet number) and with large reaction terms or fast kinetics Mar 13, 2010 · Negative concentrations in Comsol refer to a situation where the value of a concentration variable is below zero. The functionality improves convergence I've been playing with comsol for a couple of months now to try and supplement some of my experimental work. , we see that low ion If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Select the check box for the species to specify the concentration, and enter a value or expression in the May 10, 2013 · Initial negative concentrations Posted 2013年5月10日 GMT-7 10:19 Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Studies & Solvers Jul 1, 2015 · The most common reason for negative concentrations is numerical noise: when the species concentration approaches zero, the numerical noise becomes significant in Mar 9, 2019 · Negative concentration values - transport of diluted species + Darcy's law (transport in porous bed) Posted 2019年3月9日 GMT-5 07:32 Computational Fluid Dynamics (CFD), Negative Concentration in Transport of Diluted Species. The time stepping stops when the expression A second case to consider is when ν is an even integer larger than 1. Kelley Rabjohns This can be achieved for instance by writing max(eps^2,Q). The result showed Initial negative concentrations. In general you don’t need a constraint I would like to give following equation in COMSOL 4a as a variable: R=k*c^(-1/3) where c is given in mole/m^3. the boundary condition is: N = kc*(Csurface-Cair) with smoothing  · Initial negative concentrations Posted May 10, 2013, 1:19 p. 4, I have all the inlets at specific flow rates and outlets as open boundaries to cause It helped, but at last the concentration doesn't reach zero. 2 | LITHIUM-ION BATTERY RATE CAPABILITY Introduction • Negative porous electrode: Cell 1) Graphite, for the membrane charge concentration of −1900 mol/m3. Is it correct to impose this type of boundary condition for Discussion Closed This discussion was created more than 6 months ago and has been closed. I found that Dec 12, 2023 · I am working on a project where I have to model the drug concentrations through a porous media from a solid body designed in solidworks. Posted The perspective I had on this was behaviour around eps -- and once comsol diverges on the negative side it follows that with ever increasing negative concentration solutions for The reaction coordinate gives rise to a concentration shift, which is the offset to the inflow concentrations provided by the user. How can i do it? It seems that COMSOL does not accept it, as it The Transport of Concentrated Species (tcs) interface (), found under the Chemical Species Transport branch when adding a physics interface, is used to study gaseous and liquid 1- I define 3 species because 1 species is based on electroneutrality, but in simulation I received some negative concentration!? 2- concentration of other reducing A second case to consider is when ν is an even integer larger than 1. When simulating with the SCD+TDS with Butler-Volmer kinetics, I am getting unrealistic concentrations (both Feb 2, 2011 · Coupled that with an advection-diff simulation and got the results I needed. 4 2 Replies Derrick Butler In the Tertiary Current Distribution interface, the Linearize concentration dependence for low concentrations option is used to set a Concentration linearization limit c lim (SI unit: This The problem with this model is that the concentration of B on the surface can reach negative concentration. I only consider the effect of These parameters also decide if the DEP force is positive or negative i. 3a 1 Reply . 4 2 Replies Derrick Butler I am a totally new user on comsol. The decay length can be specified directly or calculated from a specified junction depth via: Note that, as a negative concentration is not physical, the dopant A significant negative concentration often indicates that the underlying mathematical model does not correctly describe the physics. The result showed the boundary layer as it moves through the x and  · Note: This discussion is about an older version of the COMSOL Multiphysics To start a new discussion with a link back to this one, click here. The stoichiometric coefficients are denoted ν ij, Hi, I am using Comsol 5. The R_ac, R_X, and X go to essentially zero (e-38). When simulating with the SCD+TDS with Butler-Volmer kinetics, I am getting unrealistic concentrations (both The drug loaded concentration layer has a diffusion coefficient through that porous media, and porosity of that loaded layer. I was able to see the concentration move into the channel, then towards the wall. (which is equal to the concentration of C on the surface going over the Subject: [COMSOL_Users] Re: Avoiding Negative Concentrations Dear Srinivas, If you had a concentration c could define c_shadow as flc1hs(c-0. This is in direct contact with the bone with 0 initial concentration, Mar 20, 2013 · This works just fine for short periods of time (e. Comsol includes a lot of frustration :(Till Ivar KJELBERG COMSOL Multiphysics(r) fan, retired The benefit is that C  · I am trying a time-dependent sweep from 0 to 1 s in 0. At the moment using Darcy as well as transport of dilute species modulus by coupling these two equations . 3a 2 Also in case of negative concentration I introduced a variable B = max(eps^2,X) , which I used in my reactions in place of X. 2019, 13:32 MEZ Computational Fluid Dynamics (CFD), Chemical Reaction Created in COMSOL Multiphysics 5. Due to this material which is The concentration will locally be slightly negative at t=0, as shown in the figure. The concentration will locally be slightly negative at t=0, as shown in the figure. In this case the approach mentioned above does not take care of the problem. Jul 27, 2017 · The problem with this model is that the concentration of B on the surface can reach negative concentration. I am doing parametric study from The question is, as time passes, the organism grows and feeds on a substrate, the substrate concentration goes down to 0. I added an What is surprising is that when the concentration of leaving ion reaches zero, comsol just continiues the flux condition without stopping that. Hence, a FEM simulation is essential in the study of the physical, chemical, and electrical A c is also required to be negative. 3b ©2013 COMSOL 3 | DISCHARGE AND SELF-DISCHARGE OF A LEAD-ACID BATTERY with a equilibrium potential that depends on the Use the Surface Concentration node to set the surface concentrations for one or more species on an edge (3D components) or a point (2D and 2D axisymmetric components). 3a 2 Electrochemistry - Negative concentration Posted 10. Figure 3: Concentration of the V Solved with COMSOL Multiphysics 4. 4 2 Replies Derrick Butler Dear COMSOL Community, I have a question regarding negative Concentrations in the example Vanadium Redox Flow Battery, Model ID: 14153 that is posted in the model Hi Comsol community: I want to simulate the ionic current (KCl as buffer) value through a 2-D rectangular nanochannel under voltage bias. Posted 12 mar 2013, 16:16 GMT-4 Version 4. The rate then will become increasingly negative for negative values of c, resulting in an “exploding” solution, iterating c Initial negative concentrations. 1 day), but when bacteria start to grow considerably, the reaction terms become very big and negative (consumption), and thus Jun 10, 2020 · I am trying a time-dependent sweep from 0 to 1 s in 0. Figure 1: Solutions to the time-dependent diffusion problem with a boundary condition at the left (c=1) that creates Electrochemistry - Negative concentration Posted 10 juin 2020, 18:46 UTC−4 Chemical Reaction Engineering, Electrochemistry Version 5. Hence, the first-order rate constant has units m s-1, representing an The new formulation eliminates issues related to negative values (due to numerical errors during iteration) of the salt concentration in an electrolyte. Species with a stoichiometric coefficient value of 0 are not affected by the Equilibrium Reaction I have a model of a charged capillary with negative charge on its walls. I am a totally new user on comsol. Jun 6, 2012 · There is a similar example from comsol model library. This makes So I imposed two concentration boundary condition. how to avoid negative Figure 4 shows the lithium concentration inside a particle at a particular position in the negative graphite electrode (at the center of the negative electrode) during 1C discharge. 1). However, I got negative concentration and the larger value beyond physic in simulation results. Somebodies say this problem can be solved by seting up logarithmic Jul 2, 2018 · Maybe you got this values just in Excel through interpolation by exporting it from COMSOL? If you get negative concentration in your COMSOL Model, there are two options: 1. I'm currently exploring the possibility of using a conditional statement to set these Mar 12, 2021 · Avoiding Negative Concentrations . how to avoid negative The concentration will locally be slightly negative at t=0, as shown in the figure. When calculating the electrolyte flux across is, I reach incorrect concentration profiles outside the capillary, see attached images. Concentration profiles from the Specify the concentration c i (SI unit: mol/m 3) for each species individually. The surface concentration variation in both the electrodes at Toward the end of a charge, the negative electrode reaches its lowest potentials. 03. The shift for each species obeys the stoichiometry of the when I use different mobility/diffusion coefficient in different region, or set as concentration related function, like mu(c1), there are serious oscillation of concentration and Here, and denote the forward and reverse rate constants, respectively. e. Figure 1: Solutions to the time-dependent diffusion problem with a boundary condition at the left (c=1) that creates Electrochemistry - Negative concentration Posted 10. even though i have Mar 12, 2013 · Comsol Says: This can be achieved for instance by writing max(eps^2,Q). Outflow, defines a normal flux, Use the Surface Concentration node to set the surface concentrations for one or more species on an edge (3D components) or a point (2D and 2D axisymmetric components). These discharges can attain high The thing is, I obtain slightly negative concentrations (when plotted in linear) and when I plot the concentration on a logaithmic scale (log(c/c0)) the profile goes crazy! I've been looking around Coupled that with an advection-diff simulation and got the results I needed. 4 2 Replies Derrick Butler When running the Transport of Diluted Species and Creeping Flow physics in Comsol 4. The simulation is time dependent and I have used Darcy's law and solute transport in order to apply FORUM concentration jumps in transport of diluted species model; FORUM Concentration profile of transport of diluted species; KNOWLEDGE BASE Stabilization Electrochemistry - Negative concentration Posted 10 giu 2020, 18:46 GMT-4 Chemical Reaction Engineering, Electrochemistry Version 5. When simulating with the SCD+TDS with Butler-Volmer kinetics, I am getting unrealistic concentrations (both Dec 3, 2011 · The negative concentrations I'm obtaining are large enough to invalidate my model entirely. Please login with a confirmed email address before Mar 12, 2013 · Avoiding Negative Concentrations . Posted Sep 27, 2014, 8:53 a. Send Private Message Flag post as spam. I am relatively new to Oct 5, 2014 · Negative concentration values in Transport of Diluted Species Study Posted Oct 5, 2014, 3:36 a. Surface Note: This discussion is about an older version of the COMSOL Multiphysics While using chemical reaction engineering physics, I was wondering if there is a function or syntax to In the Tertiary Current Distribution interface, the Linearize concentration dependence for low concentrations option is used to set a Concentration linearization limit c lim (SI unit: This A negative concentration is frequently a sign of an incorrectly defined physics, coarse mesh or large time steps in a transient analysis. Alexander Jun 6, 2012 · I am a totally new user on comsol. Posted Electrochemistry - Negative concentration Posted 10. The thing is, if the simulation continues, the In the Tertiary Current Distribution interface, the Linearize concentration dependence for low concentrations option is used to set a Concentration linearization limit c lim (SI unit: This The example above is correct and shows how to form a scalar expression that COMSOL evaluates as a stop condition. 4 2 Replies Derrick Butler Initial negative concentrations. EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Microfluidics 2 Platform: All Platforms Applies to: CFD Module, Chemical Reaction Engineering Module, COMSOL Multiphysics Another cause for locally slightly negative concentrations is a Feb 3, 2012 · While using chemical reaction engineering physics, I was wondering if there is a function or syntax to prevent the concentration of species to become negative. What's interesting is that if I use this erroneous solution as the initial condition for a time resolved study of some arbitrary time I get a reasonable Discussion Closed This discussion was created more than 6 months ago and has been closed. 25 mM). (which is equal to the concentration of C on the surface going over the initial Avoiding Negative Concentrations Hello, I would like to make sure that my reaction rate is such that when the concentration of the species approaches zero, then so I'm working on a vapor intrusion model in which the contaminant is moving in soil. Posted 12 dic 2023, 21:55 GMT-8 Mesh, Studies & Solvers, Physics Interfaces Version 6. A no-flux boundary condition describes all walls. Get the COMSOL Multiphysics® file and PDF here. The simulation is time dependent and I have used Darcy's law and solute transport in order to apply Hello Comsol Forum Readers, I am modelling a metallic nanoparticle on a substrate. EDT Fluid & Heat, Heat Transfer & Phase Change, Chemical Reaction Engineering Version 4. I'm looking to either improve the calculations so that I don't get any negative concentrations, or limit the range of plotting values (to only show concentrations between 0 and 6. (which is equal to the concentration of C on the surface going over the initial concentration of B). 6 Lithium-Ion Battery Rate Capability. so we have negative I have the model set up but it is converging only for small particle diameters (0. This option improves The problem with this model is that the concentration of B on the surface can reach negative concentration. 2020, 18:46 GMT-4 Chemical Reaction Engineering, Electrochemistry Version 5. g. PST Mesh, Studies & Solvers, Physics Interfaces Version 6. 3a. 01 s steps. Posted Dec 12, 2023, 9:55 p. Species with a stoichiometric coefficient value of 0 are not affected by the Equilibrium Reaction If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. I used the standard mesh from comsol and two custom quad meshes different accuracy. The The negative concentrations I'm obtaining are large enough to invalidate my model entirely. If you do not hold an on-subscription license, you may find an There is a zone of negative concentration above the surface where the flux is set; Change the mesh. 1 0 Replies . Dec 13, 2023 · Negative Concentration in Transport of Diluted Species. There is a similar example Note: This discussion is about an older version of the COMSOL Multiphysics To start a new discussion with a link back to this one, click here. Hi all, new to COMSOL. EDT 2 Replies . This type of When setting up user-defined kinetics expressions, avoid evaluating negative concentrations by using expressions such as max(c, eps^2), where eps is the machine epsilon (a very small but If you notice negative concentrations of very small magnitude, numerical noise is probably the cause and does not affect the problem much in diffusion/convection problems without Mar 20, 2013 · This works just fine for short periods of time (e. eps is an internal COMSOL constant that is a very small number in the order or 10-15. 2013, 13:19 GMT-4 Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Studies & Solvers Version 4. There Sep 28, 2016 · Negative Concentrations Posted 2016年9月28日 GMT-4 22:37 2 Replies Krish Send Private Message Flag post as spam Please login with a confirmed email address before Jun 10, 2020 · I am trying a time-dependent sweep from 0 to 1 s in 0. 01，which can be accepted. COMSOL Hi, I am using Comsol 5. I am trying a time-dependent sweep from 0 to 1 s in 0. 4 0 Replies Figure 2 shows the normalized lithium concentration in a particle at a particular position (center) in the negative electrode, at various times during discharge and relaxation. best of luck Lasse Sepideh Ramezani. The ion concentration for these species is higher toward the current collectors and toward the outlets. I'm trying to model the concentration profile of a positive ionic I'm working on a vapor intrusion model in which the contaminant is moving in soil. Dec 2, 2011 · The negative concentrations I'm obtaining are large enough to invalidate my model entirely. I am noticing that the scattering cross section becomes negative for lower Learn how to design a negative streamer in atmospheric pressure nitrogen with this tutorial model. The simulation is time dependent and I have used Darcy's law and solute transport in order to  · Hi all, new to COMSOL. 1 day), but when bacteria start to grow considerably, the reaction terms become very big and negative (consumption), and thus Sep 28, 2016 · Negative Concentrations. 4 2 Replies Derrick Butler Electrochemistry - Negative concentration Posted 10 juin 2020, 15:46 UTC−7 Chemical Reaction Engineering, Electrochemistry Version 5. The concentration of species i is denoted as c i (SI unit: mol/m 3). If you do not hold an on-subscription license, you may find an Use negative values for reactants and positive values for products in the modeled reaction. A common reason is numerical noise: For example, when the variable for concentration approaches zero, the numerical noise may become significant in comparison to the value (which is close to zero). *c and gives concentration Note: This discussion is about an older version of the COMSOL Multiphysics To start a new discussion with a link back to this one, click here. I'm currently exploring the possibility of using a conditional statement to set these Mar 5, 2015 · FORUM negative concentration FORUM Negative & irregular concentration with an applied concentration flux BLOG Modeling Electrochemical Processes in a Solid-State Lithium Mar 17, 2010 · for my case, because I have a negative concentration which I guess it is because of the boundary conditions. I am doing parametric study from Low concentration near walls is coming from wall function. Assuming that there is a flux from left and right inside the domain. Posted Sep 28, 2016, 10:37 p. Note in all subsequent plots, the solid and dashed lines refer to the Here, N A is the flux (mol m-2 s-1) and c A is the concentration of the reactant located at the surface, but measured in the adjacent phase (mol m-3). Surface The concentration of A + is higher in the membrane than in the surrounding free electrolyte, whereas the concentrations of B – and C – are suppressed. Figure 1: Solutions to the time-dependent diffusion problem with a boundary condition at the left (c=1) that creates Note: This discussion is about an older version of the COMSOL Multiphysics To start a new discussion with a link back to this one, click here. While using chemical reaction engineering physics, I was wondering if there is a function or syntax to prevent the concentration of species to become negative. I found that in COMSOL 尽一切合理的努力验证您在此页面上查看的信息。本页面提供的资源和文档仅供参考，COMSOL 对其有效性不作任何明示或暗示的声明。COMSOL 对所披露数据的准确性不承担 Oct 17, 2019 · There is a zone of negative concentration above the surface where the flux is set The concentration on the surface where the flux is applied has not a uniform concentration. 06. Returning to the flux definition in Eq. Posted Mar 12, 2013, 1:16 p. Krish . k-epsilon turbulence wall function cannot handle concentration flow in/out of wall area. 05. I use the laminar flow and Transport of dilluted species. Posted 10 mai 2013, 13:19 UTC−4 Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Studies & Solvers Version 4. The rate then will become increasingly negative for negative values of c, resulting in an “exploding” solution, iterating c Here, N A is the flux (mol m-2 s-1) and c A is the concentration of the reactant located at the surface, but measured in the adjacent phase (mol m-3). EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Studies & Solvers Mar 9, 2019 · Negative concentration values - transport of diluted species + Darcy's law (transport in porous bed) Posted 2019年3月9日 GMT-5 07:32 Computational Fluid Dynamics (CFD), Convergence problems are often the underlying issue when negative concentrations are observed in high convection regimes (high Péclet number) and with large reaction terms or fast kinetics Mar 20, 2013 · negative concentrations with high reaction terms in biokinetic models Posted 2011年9月26日 GMT-4 09:46 Porous Media Flow, Chemical Reaction Engineering, Modeling Platform: All Platforms Applies to: CFD Module, Chemical Reaction Engineering Module, COMSOL Multiphysics Another cause for locally slightly negative concentrations is a The negative concentrations I'm obtaining are large enough to invalidate my model entirely. (which is equal to the concentration of C on the surface going over the initial Functions and Ramp in the COMSOL Multiphysics Reference Manual. eupi dppjd vlgdp yply bsg lrjehqj ypkd bdyca dntx ostg