12 replies to this topic

[Mahesh@A&M]

I have a 1" vortex flow meter that is installed on a 1" water line with a range of 0 - 10 gpm. Flow is controlled at 7 gpm using a manual valve on upstream on flow meter.

Though the header pressure is constant, flow fluctuates between 2 to 8 gpm. Due to recent freezong weather in Houston, flow went to zero but upon spraying steam over the piping and flow meter, I was surprised to see steady flow rate at 6 gpm. Flow started fluctuating after removing steam hose.

Please help me with the problem.

Thank You

[ankur2061]

Mahesh,

Vortex flowmeters run on the principle of Vortice shedding based on the Reynolds number of the fluid. Reynolds number being a function of the pipe ID, velocity, density and viscosity of the fluid any major changes in either of these parameters will effect the performance of the meter. For a fixed pipe diameter and given flow there are no velocity changes. What plays a major role in vortex flowmeters is the density and viscosity. Any major fluctuations / changes in these parameters will reflect in the flowmeter readings.

Vortex flowmeters perform best at Reynolds number values above 10,000. In sub-zero temperatures, the viscosity of water increases rapidly thereby decreasing the Reynolds number. In all likelihood in your case due to the increase in viscosity at subzero temperatures and considering that your flow rate is very small (7 gpm), the Reynolds number dipped below 10,000 and the flowmeter started behaving erratically.

Vortex flowmeters should not be selected in applications where the flow regimes are laminar and a high measurement accuracy is required. This has been my practical experience with Vortex flowmeters

Some links that give more information on Vortex flowmeters are provided below:

http://www.efunda.co...owmeter_vtx.cfm

http://books.google.... meters&f=false

Hope this helps.

Regards,
Ankur.

[Mahesh@A&M]

Ankur,

Thanks for your response.

Reynolds number at 6 gpm through 1" sch 40 pipe at 80F is 20,953. At this temperatures, flow fluctuates.

Reynolds number at 6 gpm through 1" sch 40 pipe at 32 deg F is 10,085. Here as you mentioned flow goes erratic and reads zero.

What kind of flow meters do you recommend for this application.

I have same problem with mag meter in a 3/4" line with 0.6 gpm. Flow is laminar here (Reynolds number : 1553 at 32 degF)

** I just realized I mistyped "fluctuation" word wrong in the topic section. Apologies!!!

Thank You and appreciate your help.

Mahesh

Edited by Mahesh@A&M, 13 February 2011 - 03:15 PM.

[Art Montemayor]

Mahesh:

Have any Coriolis flow meters in service in your plant? If so, what has been your experience with that kind of flow device?

If not, have you looked into using them on critical or important, accurate flow service? I mention this because of the excellent results I've obtained from them in the past. I started using them in 1995 and the total, installed + maintenace cost was very competitive with other types of meters - even orifices. I would expect - with recent, experienced competition in the field - that the cost incentive for coriolis devices is now even better. I am curious.

[Mahesh@A&M]

Mr. Art,

Coriolis(mass) flow meters that we have in critical service especially on process side like solvents and 4500 centipoise polymer are working real fine. We get them from E&H.

Due to cost factor and moreover for water service, I was talking about mag and vortex meters.

Is it common to use coriolis meters (if high head loss is OK) for water service?
Thank You
Mahesh A&M

[Art Montemayor]

Mahesh:

Endress+Hauser has produced some fine instrumentation hardware that is not only reliable, but cost effective. I have used their radar level detectors since the early 90's and seen their instrumentation products increase in quality and low competitive pricing. Their coriolis meters are very competitive and I would ask your local rep to give you a visit and try to economically justify their application on your water service. I know they produce a line of cost-effective meters in the size range of 3/8" to 1". What is really interesting is that you already have experience with this product in your plant and have, I presume, a good, documented history of the TOTAL, all-in cost for these meters. I mean the total capital + the operating maintenance costs. In my experience, we found that the maintenace parts and labor cost were essentially zilch for several years on-going. This was a terrific economic advantage over other maintenance-prone meters and allowed us to make a change and save money.

I never found the coriolis meters to have a large pressure drop characteristic. I am interested in knowing if that is a characteristic of the Endress+Hauser models - and why.

I know from experience that you can work with Endress+Hauser in the Houston area with that kind of approach - that the cost effectiveness of the instrument helps and that the operating costs also assist in justifying a change in that direction. As you probably already have noticed, the feature of no moving parts except for a vibrating tube makes for a care-free, maintenance department holiday. And that is good for business as well.

If you go for finding out if there is an economic incentive, let us know the results.

[breizh]

On top of the suggestion given to you ,
Let you have a look at this resource :

http://www.efunda.co...eter_select.cfm

Breizh

[Chemical9]

Hope it helps.

Attached Files

•  Flowmeter selection.pdf   104.03KB   68 downloads
•  FlowSelectionWallChart.pdf   87.24KB   61 downloads

[JMW]

Well, how interesting.
The flow rates quoted are well within the range for which vortex meters are suitable and, come to that, mag meters also.
We ought to start by saying that it is just worth checking with the manufacturer's specifications that the meters you have were supplied for this duty just to be sure.

But you say the problem has been observed with both technologies.
Does that mean that originally there was a mag meter but this was changed out for the Vortex meter?
If so I wouldn't now go out and buy yet another meter technology just so you can see the same thing happen again.
In fact, if I observed this with a mag meter operating within its declared flow range, I would want to know why.
I'd be even more curious if I saw it with a second different technology and certainly at this point I would suspect it is not the flow meter.

You do not say what water quality this is.
This might help. Unless this is highly pure water, the mag meter should have managed nicely.

Neither meter should behave like this.
Before going to mass flow I think I'd really like to know what is happening.
The options might include this being an actual flow rate fluctuation.
It could be you have poor electrical earths.
Maybe you have air in the line.

Perhaps you have an installation problem that would affect both meters. For example, you don't have the necessary straight pipe before or after the meter or you have swirl generated by sharp elbows immediately upstream.

Normally when looking for suspected flow meter errors you might hire a clamp on ultrasonic to investigate the flow behaviour.
But with this problem a first pass with a bucket and a stop watch will tell you a great deal.
You might also allow the flow to escape through a nozzle so you can witness the flow spouting out and observe the behaviour during one of these flow fluctuation events. Being able to see what is happening can be very helpful.
.

[JMW]

PS I'd relocate that manual valve to downstream of the flow meter, especially if the pipe discharges to atmosphere after a short run....... it is rarely a good idea to install the valve upstream of a flowmeter.

[JMW]

PPS if flow stopped when iced up and you restored flow with steam, I suspect that you initially got a partial opening and that for once, your line was fully flooded at the flow meter.
It would be nice if you could sketch the installation for us.

[Mahesh@A&M]

JMW,

Thanks for your inputs. I will have the installation sketch tomorrow.

Thank You

[Mahesh@A&M]

I finally had a chance to meet ENDRESS+HAUSER to discuss about reliable flow meter for this application and cost comparison between Vortex and coriolis meters.

As Ankur mentioned, flow fluctuation in vortex flow meter is due to low velocities(Reynolds number around 20,000) and lower density (here Reynolds number is 11,000 at 34 F) at freezing weather.

We replace 1" meter to 1/2" vortex meter and it is working fine now.

Art,

We hardly had any maintenance on these type of meters. We occasionally had problem with vortex meters on other installations primarily due to fouling.

E+H said coriolis meters are typically costs 2 to 3 times more than vortex meters (depends on single tube vs dual tube)

Thank You
Mahesh A&M