2 replies to this topic

[cea]

I would like to know, how exactly line roughness factor of pipe contributes to line pressure drop calculation?
Further, Whether zeta factor for valve, is same as equivalant length? If not, how does it contributes to line pressure drop?

What difference in line pressure drop we can expect with & without considering pipe roughness factor for gravity flow lines?

Regards,

Aniket

[pleckner]

No offense but this question seems to be more what I would expect from a student than from a graduate chemical engineer and, if true, should be listed in the Student Forum.

Saying this, the roughness factor is a made up of two terms, the relative roughness of a pipe and the pipe diameter. The rougher the pipe, the more resistance to flow and thus a larger friction factor and a higher pressure drop. The friction factor term is used in the equation to calculate pipe pressure drop and is directly proportional to the line pressure drop. I invite you to read my ariticle on the use of equivalent lengths and K values in pressure drop calcuations, which can be found on this website.

For me to answer the second part will require a clarification by you because I've been doing this stuff for 30 years and I am not familiar with the "zeta" factor for valves. The equivalent length for a valve can be calculated a number of ways. If you have the Cv of the valve, this can be converted into a K value (using the Darcy equation) and from here, an equivalent length can be calculated. Also, CRANE Technical Paper No. 410 gives K values for valves and one can then convert to equivalent lenght if one wishes (but something I'm against doing; again read my article).

And for the last question, the same difference you would expect for any pipe. More roughness, the harder it is to flow. Gravity is just a way of inducing flow without the aid of a mechanical device (read pump). Both work the same way, providing a pressure differential to induce flow.

[Zauberberg]

I agree with Pleckner. If this all-possible-questions-trend is going to be continued in the future, very soon someone will come up with a question "What is the normal boing point of H2O", or "What is the name of river that passes below Danube bridge"?

It wouldn't be so bad to check your home literature or different internet resources before posting a question.