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[ayan_dg]

I have a peculiar problem of pumping a viscous liquid (54 cP) by a centrfugal pump. The pump will transfer the liquid to a distance of about 1 km. Due to a long discharge line as per pressure drop calculation a 3 inch line is suitable, but in this 3 inch line velocity profile is becoming laminar. With a 2 inch line ,pressure drop is very high about 19 bar whereas with a 3 inch line it is about 2 bar. Is laminar flow acceptable ?

[latexman]

Yes, laminar flow is acceptable. 54 cP is not really that viscous when you consider the whole spectum of fluids pumped all over the world. I've had experience with fluids from 10⁵ to 10⁶ cP and I've talked to folks that have handled higher than that. In those cases laminar flow is the only practical solution.

There is no reason to avoid the laminar flow regime. However, it is common practice to avoid the transition flow regime because it is inherently unstable and you can get huge swings in processes if it switches from laminar to turbulent to laminar to turbulent. I've heard operators tell stories of processes going unstable because someone dropped a pipe wrench on a line that was operating smoothly in the transition zone. So, design well into the laminar or turbulent region, and avoid the transistion zone, if possible.