Learning Forum

[SB_22]

HellonnI am simulating a steady state laminar flow inside a reactor operating at low pressure and high temperature. If I use low value of momentum URF (0.2 in my case) my solution gets converged up to 10-14 and net fluxes are almost 0 and point monitors also gets steady. But if I increase the URF value from 0.2 to 0.3 and re run my solution without initializing it again gives me convergence only up to 10-1 and my fluxes are also not close to zero.nMy question is can I trust the solutions obtained from low value of URFs?nRegards.n

[Amine Ben Hadj Ali]

You can trust it if you ran for a lot of iterations and the results are not changing anymore. n

[SB_22]

Thanks a lot Sir. nSir I have one more doubt regarding buoyancy. As I increase operating pressure of reactor, more eddies starts forming inside reactor and it becomes very difficult for laminar model to converge even if Reynolds number<2300 but if I use K-epsilon model instead solution converges smoothly. Can I use turbulent flow models to deal with buoyancy even if Reynolds number falls in laminar region or there is any method of dealing with this problem using laminar model. (in my reactor gravity is acting opposite to the direction of gas flow i.e. gas flow is from bottom to top and temperature difference between reactor temperature and inlet temperature is large-900C)nRegardsn

[Rob]

Take a step back from the simulation. If you consider the physical reactor, what is going on? Is the flow steady, or do you see/expect the flow field to change with time once the system is at equilibrium? nSimulation is a tool we use to explain flow/structures/electrons/heat etc however before we start working on a model we need to have a rough idea of what's going on in the device. Understanding that is why we do a degree in engineering, and then continue to learn after University. nis right when he says we can trust results with low UR after ALOT of iterations. What he didn't add is that you also need to understand WHY using a low UR can be OK, and that at times it's not. Ie why does a low UR help in this case, what flow feature are you trying to avoid, and how is this linked to using a turbulence model (there is a correlation/link)? We both know the answer, you're on the path to understanding why. n

[SB_22]

Greetings,nIn the physical reactor flow is steady and I do not expect the flow field to change with time once system is in equilibrium.nSir what do you mean by why does a low UR help in this case, what flow feature are you trying to avoid, and how is this linked to using a turbulence model?.nBefore posting my problem here I tried to read a lot of articles online but I did not get any answer to my problem.nCould you please share an article or a link that can elaborate this. nLooking forward to your great assistance and invaluable support n guidance.Regardsnn

[Rob]

Inlet and outlet flow may be steady, but what about in the middle? In a trickle bed reactor the overall process is steady but bubbles move through the system and gas streams may move around based on where the liquid holds up. Not sure about articles as most are either very academic (so very rigorous) and we don't share our best practice documents on the forum (they're available to our registered users: your University may have access). Most of what I know is from experience, and general observation. n