Learning Forum

[cats1]

Hello everyone,nHow can I compute the mean residence time of particles inside a fluid? nMy simulations are steady state. At the moment I'm using the pathlines colored by particle time to get the maximum value of the residence time. My idea was to export these pathlines and then do the average of the residence times but when I do this the file that I'm exporting contains only the X,Y,Z coordinates of my points and the time step, not actually the residence time. As a result I get an avg value which is higher than the max (which I compute on Ansys - pathlines dialogue box).nI know this approach to compute the mean RT is wrong, is there any other way to do it?nI'm using the pathlines and not the DPM because I would use massless particles in a steady state configuraton, so I figured out that using pathlines in post-processing is quicker and allows me to choose a specific surface from which release the pathlines.nnThank you n

[ai0013]

Try going to Results/ParticleTracks.nCheck that the write option includes your variables of interest, time is always appended. You can also select among a list of variables, which are to be exported (The list contains x vel, y vel, z vel, Re number, diameter, mass, density, Residence time, and many more ...)n

[cats1]

Thank you for your answer! Unfortunately I don't think I could do this because I didn't use a particle modeln

[ai0013]

So, If you are not using DPM, then you can try what is suggested here: http://oss.jishulink.com/upload/201608/1470277792947_FLUENT_%E9%AB%98%E6%89%8B%E8%BF%9B%E9%98%B6%E2%80%94Modeling_of_Residence_Time_Distribution_in_FLUENT.pdfnnI'd go for the pulse method and monitor the concentration of a passive specie at my outlet or surface of interest.n

[Rob]

You can release particles from a surface too, you just need to set up the injection. If you do use particles the DPM out file on the outlet can be used to get particle residence time. The other approach is to look up mean age of air, it's a technique used in the HVAC industry that's been adapted for pretty much everything else. n

[cats1]

Thank you both! I will work on thatn