Relationship between Reynolds number and plug flow

[volothampus]

I have a situation where I have a 3" pipe and want to reach a certain residence time in the pipe. The fluid is nylon at approximately 300 poise. I've done an experiment and found that I get channeling. My pipe length is 36" and flow is about 16 lb/hr. I can get 40 minutes RT when filling an empty pipe, but doing a tracer study, I found that it is only 20 minutes, which suggests channeling. I am wondering if there is too small of a Reynolds number to achieve true plug flow. Is there some correlation there? What are the "rules of thumb" for PFR's?

The pipe is vertical and filling from the bottom. Should I try using a static mixer?

 

[moltenmetal]

Suggest you read a chemical reaction engineering text such as Levenspiel or Fogler to refresh your memory.

Plug flow doesn't happen until you have not just turbulent flow, but fully developed turbulent flow (Re > 10,000). Doubtful that you're going to get Reynolds numbers that high with a viscosity of 30,000 cP at anything approximating a reasonable pressure drop.

You NEED static mixers, and even single tube static mixers may not be enough.

 

[Oldliar]

As nylon is a non-newtonian fluid (viscoelastic), I guess you cannot use the reynolds as you would do for a newtonian fluid? -or can you assume that the 'flow conditions' are similar to those of a newtonian fluid and thus use the reynolds as we know it?

 

[volothampus]

Ah yes... Fogler... His book is an argument for another day.

Thanks for the insight. I doubt I can realistically get the Reynold's number over 1 with nylon and my equipment.