Hi Jessica, thanks for walking through this. One thing to note when writing out the ODE for mesh displacement. The variable "spf.vn" is NOT the phi velocity component. After some digging in equation view, I found the variable under the "Fluid-Fluid Interface 1" boundary condition. The variable "spf.vn" is the Normal Mesh Velocity at Boundary 11 - the droplet edge arc. Not to be confused with "spf.nv" which is different. The full expression for it is below, which amounts to the dot product of the quantity (velocity field vector on the down/inner side of the boundary - (mass flux scalar/density scalar)*interface normal vector) with the mesh normal vector. (Apparently XD) that gives the total normal mesh velocity in Comsol language. spf.vn = (down(u)-spf.Mf*spf.iNr/down(spf.rho))*spf.nrmesh+(down(v)-spf.Mf*spf.iNphi/down(spf.rho))*spf.nphimesh+(down(w)-spf.Mf*spf.iNz/down(spf.rho))*spf.nzmesh So I believe the ODE is a way of telling Comsol to track the instantaneous change of the mesh displacement as the total velocity at the point where the droplet meets the glass. Effectively as the simulation solves, it tracks the total mesh displacement by integrating up all those small changes over time. The two expressions used for Prescribed Mesh Displacements are written to link the geometry radius Rg to the initial placements of the droplet (at one multiple of R0) and the glass disc (at 5 multiples of R0). The initial width of the exposed glass disc is then 4 multiples of R0.
Thank you for this model. I have noticed that the laminar flow velocity inside the drop is very high: > 350 um/s! Also, this flow is circulating within the drop. I would expect that this flow is weak and should be directed towards the contact line where there is more evaporation. Could you please have a look at it?
Hello Jessica, very well explained. I am working on the pressure cooker, like water evaporation and building pressure inside the cooker. Can you help in this regard? I really appreciate any help you can provide.
Hi manibhushan, I would love to help you with this project, but I’m currently backlogged with work. Try booking me through Fiverr after the holidays if you still need help!
Great Job Madam, I did not three phase flow models like solid-liquid- solid in comsol with time dependent variables, please upload an video on this modeling madam.
Hello, I am in the field of food drying and I am interested in understanding how the reduction of moisture can influence changes in the geometry of food products. I would greatly appreciate any guidance or information on how to effectively determine and control these changes. Thank you in advance for your assistance. Best regards,
Hi, thanks for watching. I have modeled lyophilisation before (freeze drying), and I think it should retain the shape of the original item once in dehydrated cake. If just dehydrating, not freeze drying, the process would depend on the interstitial space between cell surfaces of the food or other material. There are way to import or create porous media profiles into your geometry, which are available on their website.
Very helpful video together with the file. Thank you. I am trying to model a similar system but now drop is partially immersed in oil (solid is replaced with oil fluid). Should I use three phase fluid interface?
Hi thanks for watching! If the oil phase doesn’t undergo any deformation, then I wouldn’t include it. If it’s something like a 3 phase system of water, oil, and air bubbles being entrained in the mixture, that might be an oversimplification. I would say start with as simple a model as possible and slowly make it more complex.
@@JessicaHoffmanTutorials Thank you for the reply. The oil phase also undergoes deformation as the partially submerged droplet become smaller. So the mesh at the water-oil interface also should displace.
Hello Jessica, I wanted to simulate droplet evaporation but with contact line pinned. Could you please tell me how can I simulate such evaporation process?
Hello Jessica, Sorry to bother you again. It would be great if you could tell me how I can simulate moving interface in an evaporating droplet where one end of the interface remain fixed. Thanks in advance.
Hello Jessica, This tutorial is very helpful for the evaporation model. my research area is water droplet impact on the solid surface. When the droplet impacts the solid surface, it will spread. so, I need to calculate the surface energy of the droplet with time using the formula integration of sigma*dA. My question is how to calculate the change in surface area (dA) of the droplet with time? Can you help me? please.
Hello Ajit, thank you for watching my video! As far as your question, if you have a working model, I believe the sigma*dA piece you want to plot/analyse can be done by adding a global probe for the domain/boundary/edge. Check out doc.comsol.com/5.5/doc/com.comsol.help.comsol/comsol_ref_definitions.12.100.html
Please find some documentation on inverted mesh elements here doc.comsol.com/6.0/doc/com.comsol.help.comsol/comsol_ref_mesh.20.27.html#:~:text=Alternatively%2C%20you%20can%20avoid%20problems,for%20the%20main%20Component%20node.
Hi, thank you for these explanation videos, very helpful. I designed a model to generate a microdroplets (oil & water) by T-junction, the first problem is when the droplets arrived to the reservoir, they mix in one big droplet. And the second problem, i try to find a reverse way (mechanical or chemical) to release the contain of these microdroplets, any ideas?! And thank you in advance.
Hi thank you! I’m not sure I fully understand the problem. I am familiar with microfluidic droplet generators, but I would need to see your model. Please email me to discuss paid work. Jessica.Hoffman87@gmail.com
Rg is the geometric coordinate that denotes the changing radius of droplet, and R0 is the starting radius. So at time 0, mesh_disp is multiplied by 1. At all other times it’s multiplied by a fraction
Hi Jessica, I am working on the project where I have to track the shape of water droplet while diffusing into porous surface. Could you please help me out?
Thanks for the tutorial and explanation! I have been looking at molecular dynamics simulations and wondered if they might be a better fit for my research as it is easier to model the dipole of water molecules aligning in an electric field using this kind of software compared to COMSOL and similar packages? Goes back to the Taylor Cone example, and I am trying to model evaporation of water using an electric field to enhance evaporation. Since most of the effect is a result of alignment of dipoles and reduced hydrogen bonding at the boundary layer, I´m not sure how to model this in COMSOL but perhaps it is possible? th-cam.com/video/Ej9qXaPmf-g/w-d-xo.html
Hi Jessica, thanks for walking through this. One thing to note when writing out the ODE for mesh displacement. The variable "spf.vn" is NOT the phi velocity component. After some digging in equation view, I found the variable under the "Fluid-Fluid Interface 1" boundary condition. The variable "spf.vn" is the Normal Mesh Velocity at Boundary 11 - the droplet edge arc. Not to be confused with "spf.nv" which is different. The full expression for it is below, which amounts to the dot product of the quantity (velocity field vector on the down/inner side of the boundary - (mass flux scalar/density scalar)*interface normal vector) with the mesh normal vector. (Apparently XD) that gives the total normal mesh velocity in Comsol language.
spf.vn = (down(u)-spf.Mf*spf.iNr/down(spf.rho))*spf.nrmesh+(down(v)-spf.Mf*spf.iNphi/down(spf.rho))*spf.nphimesh+(down(w)-spf.Mf*spf.iNz/down(spf.rho))*spf.nzmesh
So I believe the ODE is a way of telling Comsol to track the instantaneous change of the mesh displacement as the total velocity at the point where the droplet meets the glass. Effectively as the simulation solves, it tracks the total mesh displacement by integrating up all those small changes over time.
The two expressions used for Prescribed Mesh Displacements are written to link the geometry radius Rg to the initial placements of the droplet (at one multiple of R0) and the glass disc (at 5 multiples of R0). The initial width of the exposed glass disc is then 4 multiples of R0.
Hi thank you so much for the detailed response! I will pin this so others who watch will benefit.
You are amazing Dr. Hoffman keep going
Hi friend, I only have a MS, no doctorate, but I’ll take the promotion. 😉 thank you for the kind words. I will come back to COMSOL tutorials soon.
Wonderful tutorial! Ms. Hoffman, Thanks very much.
Thanks so much for your helpful tutorial！！
Thank you for this model. I have noticed that the laminar flow velocity inside the drop is very high: > 350 um/s! Also, this flow is circulating within the drop. I would expect that this flow is weak and should be directed towards the contact line where there is more evaporation. Could you please have a look at it?
Hello Jessica, very well explained. I am working on the pressure cooker, like water evaporation and building pressure inside the cooker. Can you help in this regard? I really appreciate any help you can provide.
Hi manibhushan, I would love to help you with this project, but I’m currently backlogged with work. Try booking me through Fiverr after the holidays if you still need help!
Hello Jessica, this model uses a constant contact angle. I wonder how to make the droplet pinned with a constant contact radius?
Great Job Madam, I did not three phase flow models like solid-liquid- solid in comsol with time dependent variables, please upload an video on this modeling madam.
I’m getting error as “Unknown function or operator : D”. But I have defined D in parameters1
Thank you for sharing, but it would be better if you could clarify from the beginning that following your steps will not yield the correct answer.
Hello,
I am in the field of food drying and I am interested in understanding how the reduction of moisture can influence changes in the geometry of food products. I would greatly appreciate any guidance or information on how to effectively determine and control these changes. Thank you in advance for your assistance.
Best regards,
Hi, thanks for watching. I have modeled lyophilisation before (freeze drying), and I think it should retain the shape of the original item once in dehydrated cake. If just dehydrating, not freeze drying, the process would depend on the interstitial space between cell surfaces of the food or other material. There are way to import or create porous media profiles into your geometry, which are available on their website.
Very helpful video together with the file. Thank you. I am trying to model a similar system but now drop is partially immersed in oil (solid is replaced with oil fluid). Should I use three phase fluid interface?
Hi thanks for watching! If the oil phase doesn’t undergo any deformation, then I wouldn’t include it. If it’s something like a 3 phase system of water, oil, and air bubbles being entrained in the mixture, that might be an oversimplification. I would say start with as simple a model as possible and slowly make it more complex.
@@JessicaHoffmanTutorials Thank you for the reply. The oil phase also undergoes deformation as the partially submerged droplet become smaller. So the mesh at the water-oil interface also should displace.
I see. I honestly don't know and would reach out to comsol official support on their forum for help.
Hi Jessica, thank you very much for this tutorial. Can we use kinetic evaporation model (Schrage's or Tanasawa's) in COMSOL?
Hi 👋 I’m not sure about these models! Best of luck
Hello Jessica,
I wanted to simulate droplet evaporation but with contact line pinned. Could you please tell me how can I simulate such evaporation process?
Hello Jessica,
Sorry to bother you again. It would be great if you could tell me how I can simulate moving interface in an evaporating droplet where one end of the interface remain fixed. Thanks in advance.
How do you mean exactly? What is the physical description of problem?
Hello Jessica, This tutorial is very helpful for the evaporation model. my research area is water droplet impact on the solid surface. When the droplet impacts the solid surface, it will spread. so, I need to calculate the surface energy of the droplet with time using the formula integration of sigma*dA. My question is how to calculate the change in surface area (dA) of the droplet with time? Can you help me? please.
Hello Ajit, thank you for watching my video! As far as your question, if you have a working model, I believe the sigma*dA piece you want to plot/analyse can be done by adding a global probe for the domain/boundary/edge. Check out doc.comsol.com/5.5/doc/com.comsol.help.comsol/comsol_ref_definitions.12.100.html
@@JessicaHoffmanTutorials Thank you Jessica
Its showing avoid inverted mesh elements please help me
Please find some documentation on inverted mesh elements here doc.comsol.com/6.0/doc/com.comsol.help.comsol/comsol_ref_mesh.20.27.html#:~:text=Alternatively%2C%20you%20can%20avoid%20problems,for%20the%20main%20Component%20node.
@@JessicaHoffmanTutorials Thank You so much mam it's working now.
Hi, thank you for these explanation videos, very helpful. I designed a model to generate a microdroplets (oil & water) by T-junction, the first problem is when the droplets arrived to the reservoir, they mix in one big droplet. And the second problem, i try to find a reverse way (mechanical or chemical) to release the contain of these microdroplets, any ideas?! And thank you in advance.
Hi thank you! I’m not sure I fully understand the problem. I am familiar with microfluidic droplet generators, but I would need to see your model. Please email me to discuss paid work. Jessica.Hoffman87@gmail.com
What was the reason for the particular expression for the prescribed mesh displacement? (mesh_disp*Rg/R0)
Rg is the geometric coordinate that denotes the changing radius of droplet, and R0 is the starting radius. So at time 0, mesh_disp is multiplied by 1. At all other times it’s multiplied by a fraction
Hi Jessica, I am working on the project where I have to track the shape of water droplet while diffusing into porous surface. Could you please help me out?
Hi abhijeet, I’m not taking new clients at this time.
Hello
if we increase the temperature the program is not working and error occur.
please tell us how to solve the problem
I can’t say without details.
Mam, Could you please share droplet parameter file mam.
Thanks for the tutorial and explanation! I have been looking at molecular dynamics simulations and wondered if they might be a better fit for my research as it is easier to model the dipole of water molecules aligning in an electric field using this kind of software compared to COMSOL and similar packages? Goes back to the Taylor Cone example, and I am trying to model evaporation of water using an electric field to enhance evaporation. Since most of the effect is a result of alignment of dipoles and reduced hydrogen bonding at the boundary layer, I´m not sure how to model this in COMSOL but perhaps it is possible? th-cam.com/video/Ej9qXaPmf-g/w-d-xo.html