4 replies to this topic

[PMGreen]

Hi guys!
I would like to hear (read...) some clarification regarding flowmeter selection.
The fact is just simple: usually in flowmeter selection tables (for guidance), I can see applications for clean, non-viscous fluids and viscous fluids (among many others). However, which value of viscosity shall I consider of a "limit" between viscous and non-viscous fluids?

My application requires a flowmeter for a fluid in the range of 50 to 200 cP (kind of vacuum residue) and I would like to use an orifice plate (I think it works, maybe conic type), instead of a wedgemeter or similar.

Thanks a lot. I appreciate any advice.

[tore.alvestad]

Hi guys!
I would like to hear (read...) some clarification regarding flowmeter selection.
The fact is just simple: usually in flowmeter selection tables (for guidance), I can see applications for clean, non-viscous fluids and viscous fluids (among many others). However, which value of viscosity shall I consider of a "limit" between viscous and non-viscous fluids?

My application requires a flowmeter for a fluid in the range of 50 to 200 cP (kind of vacuum residue) and I would like to use an orifice plate (I think it works, maybe conic type), instead of a wedgemeter or similar.

Thanks a lot. I appreciate any advice.

Hi

Measurement of viscous liquids depends on Reynolds number. This is because below Re = 2000 the flow is laminar therefore the orifice plate in unable to measure. The recommended minimum RE is 3000 hence the flow is turbulent. As the viscosity increases the Reynolds number decreases, there are charts and graphs that represent this relationship.


Hope this answers your question

Tore Alvestad

[PMGreen]

Hi Tore
you are quite right.
However, i can increase Reynold changing the pipe diameter, but that's not the point.
I´m sure that in terms of "equations and calculations" I can use an orifice meter.

I'm just asking if there is some sort of "criteria" (based on experience, perhaps) to separete fluids in terms of viscosity, in order to choose the more suitable instrument for the application.

thanks anyway for your comments

[Doggert]

Hi Tore
you are quite right.
However, i can increase Reynold changing the pipe diameter, but that's not the point.
I´m sure that in terms of "equations and calculations" I can use an orifice meter.

I'm just asking if there is some sort of "criteria" (based on experience, perhaps) to separete fluids in terms of viscosity, in order to choose the more suitable instrument for the application.

thanks anyway for your comments

PM,

I think your question would be best answered by a representative of a company that sells a number of different types of flowmeters.

I've dealt with suppliers on a number of flowmeters in the past, and normally they have standard "rule of thumb" ranges that are set by the engineers in the manufacturer's companies - especially if you're dealing with a "big" name like Endress+Hauser.

This can save you a lot of time in not needing to "re-invent the wheel". These companies want to be able to give good confidence that their products will work, so use their engineering work to your advantage. Even if you don't want to trust their work completely, you can at least gain insight into how THEY approached the issue (i.e., what technology they used, what basis for selection of that technology, the governing principles) and go from there.

The bottome line is that regardless of when you get the information, you're still going to have to verify that the vendor's items meet your criteria. This is a way to "kill two birds with one stone".

Sorry for the long-windedness on something you probably already knew. Hope this helps.

[JoeWong]

However, i can increase Reynold changing the pipe diameter, but that's not the point.
I´m sure that in terms of "equations and calculations" I can use an orifice meter.

PMGreen,
There is criteria to determin line size...adjusting pipe diamter may not be a good idea..somehow you will be limited by line sizing criteria and line loss...there is beta ratio you need to comply to...

Squeezing line size to get high velocity (hence high RE) will lead to large line loss...i did not further investigate...you may encounter problem with turndown where low flow, line loss with drop accordingly. it is very difficult to match the conditions...

Orifice is a device to create pressure drop and flow is interpreted from the pressure drop...If you let inlet P change significantly according to upstream line loss, you will loss your accuracy immediately...

I have taken some effort to google and snap the viscosity limitation for orifice plate flowmeter before i response to this email...most manufacturer use RE (function of flowrate, diameter, density, viscosity) as criteria...

From design point of view, if you can maintain turbulent flow at turndown condition with RE greater than required RE, you may use orifice...

In addition, if your fluid is multiphase (residue, water, soild), low flow tends to create laminar flow and phase separation occur...this further affect the meter accuracy..

Other than checking with vendor as proposed by Doggert, you may tap experience from previous project and exisitng operator...



JoeWong