Fluids

How to find Mixing/Blending time in a batch reactor using uds ot tracer?

• aishum96
Subscriber
Hello all!,nIm working on my final year project: Mixing of non-Newtonian fluidsnImpeller: Rushton Turbine 180 rpmnI need to calculate the mixing time using using racer. This is the method im doing:nSet up steady flow with fluidnDefine UDSnMake the flow transientnSwitch off flow, turbulence and switch on UDS scalarnMark the region nPatch the region with the UDSnReport definitions: Vertex average of UDS scalar at different pointsnRun the calculation for time step size 0.01 and number of time steps as 10000nHowever the results I get are weird. Im aware of getting the concentration Vs time curve at different points.nPlease help me out!n
• DrAmine
Ansys Employee
Starting from your result, you enble transient solver, then species model, you define a mixture with two additional tracers having same properties like your fluid. Then you define regions in your domain where you patch the tracer concentrations as initioal conditions. You solve only for these two equations and get a report plot over the time.nnWith UDS same can be done you need however to understand that the UDS itself has no dimensions but it is likely you consider it as a concentration so mass per volume.n
• aishum96
Subscriber
Hello sir,nThankyou so much for responding to my query.nCould you please explain thisnYou solve only for these two equations and get a report plot over the time.nwhich two equations you are referring to is it (Flow and Turbulence)?nAnd also im using Natrosol as working fluid, should i define one tracer or two ?.Im a beginner at ANSYS please be patient and help me.nThankyou.n
• DrAmine
Ansys Employee
You disable all equations like flow, turbulence or energy and you keep only the tracer equations as they need to be solved. We bascically solve on frozen flow field!nnBecause you are beginner: please go through the Fluent Standard Tutorial to get familiar with Menus and Panels!nnI guess only one tracer is required: so a mixture of your fluid + dummy-fluid having some properties is enough.n
• aishum96
Subscriber
sure sir I will do that.nAnd then for concentration vs time plot how do we put report definations?.Report definations----species---mass or molar concentration?nHow do we get these plots in cfd post at different points?nn
• aishum96
Subscriber
nnHow will I know that to what value I have to patch? in the figure 2?n
• DrAmine
Ansys Employee
Mass Fraction cannot be larger than 1. Patch it to 1.nAlso please think about updating to a supported Ansys Fluent version.n
• Rob
Ansys Employee
Additionally, we have a uniformity index option in the current releases which makes calculating mixing a lot easier than it used to be. n