Sand Grain Roughness in a Pipe - Please help

WanderleyGrespan · January 13, 2017, 09:07

Hello everyone.
I'm trying to understand how to find the equivalent roughness sand grain.

Here is the problem, i have a pipe of 2", commercial steel with absolute roughness of 0.046 mm.

But the CFX needs the Rougness sand Grain in the CFX-Pre and I'm really confuse about this.

I've already read some references but i still don't understand.

So please, help me to find out what is the equivalent rougness sand grain for this problem and how to caculate.

Thank you everyone.

urosgrivc · January 16, 2017, 02:38

Hi I would also appreciate it alot if someone could explain the conversions,
how to get from let say Ra to eq. sand grain roughnes
I have found some papers,
But vhen I tried to evaluate those results and conversion equations I do not get the same results, so I am confused as there is no concrete ansver to be found.

https://drive.google.com/open?id=0Bw...ExIQTJpejA3UXc Please look at the picture where I explained Why I dont think that even papers about conversions are corect. Am I wrong, What did I miss ?

There is quite a few papers on vhat sand grain roughnes represents and what it changes in the boundary layer, but not on how it can be usefull for us in the simulation, to include real life measurments as nobody seems to measure sand grain rouhnes.

I am interested in this becouse i would like to include roughnes in my CHT simulation, as my parts are made from cast iron (quite rough), are causing ventilation losses while rotating and heat trasfer is going on and as I understand it should shift velocity gradient near the wall an that will efect heat transfer, this would probably improve my results.

Thank You

January 13, 2017, 09:07	Sand Grain Roughness in a Pipe - Please help	#1
WanderleyGrespan New Member Wanderley Grespan Join Date: Dec 2016 Posts: 14 Rep Power: 9	Hello everyone. I'm trying to understand how to find the equivalent roughness sand grain. Here is the problem, i have a pipe of 2", commercial steel with absolute roughness of 0.046 mm. But the CFX needs the Rougness sand Grain in the CFX-Pre and I'm really confuse about this. I've already read some references but i still don't understand. So please, help me to find out what is the equivalent rougness sand grain for this problem and how to caculate. Thank you everyone.

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January 16, 2017, 02:38		#2
urosgrivc Senior Member urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11	Hi I would also appreciate it alot if someone could explain the conversions, how to get from let say Ra to eq. sand grain roughnes I have found some papers, But vhen I tried to evaluate those results and conversion equations I do not get the same results, so I am confused as there is no concrete ansver to be found. https://drive.google.com/open?id=0Bw...ExIQTJpejA3UXc Please look at the picture where I explained Why I dont think that even papers about conversions are corect. Am I wrong, What did I miss ? There is quite a few papers on vhat sand grain roughnes represents and what it changes in the boundary layer, but not on how it can be usefull for us in the simulation, to include real life measurments as nobody seems to measure sand grain rouhnes. I am interested in this becouse i would like to include roughnes in my CHT simulation, as my parts are made from cast iron (quite rough), are causing ventilation losses while rotating and heat trasfer is going on and as I understand it should shift velocity gradient near the wall an that will efect heat transfer, this would probably improve my results. Thank You