CR4® - The Engineer's Place for News and Discussion®


Previous in Forum: Radar Type Level Transmitter   Next in Forum: Difference in Absolute and Relative Pressure Gauge
Close
Close
Close
13 comments
Active Contributor

Join Date: Jan 2017
Posts: 16

Wake Frequency

08/02/2017 3:29 AM

Calculating wake frequency we must need fluid velocity.But in case of a thermowell to be installed at the bottom of a vessel, where total amount of fluid will come, it will be agitated,and then transfer to some other place via gravity force or pump.Now in this case i dont have flow rate/Velocity of fluid into the vessel.So how can i calculate wake frequency for the thermowell? Should i consider in late/out late flow rate of the vessel or the RPM of the agitator ?Any suggestion guys.

Thanks

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26689
Good Answers: 700
#1

Re: Wake frequency

08/02/2017 3:34 AM

A <...wake frequency...> is relevant to a vortex-shedding flowmeter. Thermowells contain temperature instruments, which are part of first-order systems that don't have a frequency in themselves; any frequency response is likely to be measured in ones and tens of seconds, and not milliseconds as would be the case with a flowmeter.

Any vessel with an agitator will achieve thermal equilibrium throughout the fluid at a speed far higher than a practical temperature instrument can detect. Frequency calculation for such an arrangement is something not previously encountered here, on the basis of a distinct lack of need.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 18942
Good Answers: 335
#2

Re: Wake frequency

08/02/2017 7:30 AM

Maybe a little more information would be helpful on what your trying to accomplish here.

__________________
phoenix911
Register to Reply
Active Contributor

Join Date: Jan 2017
Posts: 16
#3
In reply to #2

Re: Wake frequency

08/02/2017 8:08 AM

Dear phoenix911

Thank you for your response.Please let me know the information you required.I can give you.Normally for a thermowell to be installed in a pipeline required information are :Process data: Velocity,temp,density,Thermowell dimensions etc.In this case i have all of them except velocity of the fluid into the vessel.

Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 18942
Good Answers: 335
#4
In reply to #3

Re: Wake frequency

08/02/2017 8:28 AM

Thank you,... I feel their is something missing here, and you would have more information on your process that what a stranger would have where Wake Frequency is used to determine the size of the Thermowell.

Since you need the flow rate to determine this,.. you need to take an educated guess based on with what information you have and an educated guess with what's missing..

And far as calculating your thermal size,... there are plenty of suppliers that have calculators online that can assist you, with the information you have.

__________________
phoenix911
Register to Reply
Guru
Hobbies - Musician - Engineering Fields - Chemical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jan 2007
Location: Moses Lake, WA, USA, Thulcandra - The Silent Planet (C.S. Lewis)
Posts: 3929
Good Answers: 174
#7
In reply to #3

Re: Wake frequency

08/02/2017 10:36 AM

To get the average velocity in a pipeline, divide the volumetric flow rate by the cross-sectional area of the pipe:

v = Q/A

Make sure you keep units consistent.

__________________
"Reason is not automatic. Those who deny it cannot be conquered by it. Do not count on them. Leave them alone." - Ayn Rand
Register to Reply
3
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26689
Good Answers: 700
#5

Re: Wake frequency

08/02/2017 9:14 AM

Thermowells fitted to pipes are often installed in one end of a tee such that the tip of the thermowell impinges the static streamline just before the fluid changes direction into the side port of the tee. Provided the fluid velocity and the pipe diameter are compatible (<3m/s for liquids and <10m/s for gases, for example) there is rarely any need to consider vibrational frequencies as a result of the fluid's passage.

Consideration of the resonant frequency of a thermowell installed in a vessel in most process industries is somewhere between [extremely rare] and [practically unheard of].

Most thermowells are machined in such a way that the overall shape doesn't have a dominant resonant frequency. In any case, the presence of a temperature measuring element inside it is likely to lower it owing to the presence of more mass than for an empty thermowell and an increase in stiffness as a result. Thermowell manufacturers do not tend to test and publish figures as a result.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 3)
Anonymous Poster #1
#6

Re: Wake Frequency

08/02/2017 9:30 AM

If it's your own wake, the frequency would usually be one/lifetime. if you're discussing attendance of the wakes of others, the frequency would be expected to increase with your age, up to about 75 yo.

Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13438
Good Answers: 152
#8
In reply to #6

Re: Wake Frequency

08/02/2017 1:31 PM

Hilarious!

You do know why they call them "wakes"? Same reason they used to attach a bell to a pull string fed into the coffin...

It is like when all those contribution solicitations arrive in the mail, and you get buried alive in a mountain of junk mail.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
2
Active Contributor
Engineering Fields - Nuclear Engineering - New Member

Join Date: Feb 2013
Location: Washington (the state), 2 blocks from the Columbia River
Posts: 16
Good Answers: 4
#9

Re: Wake Frequency

08/03/2017 12:24 PM

I had to dig into this thermowell stuff a while back. If the TW vibrates it can break and let the stuff in the pipe out. ASME PTC 19.3 TW-2016 is used for solid drilled bar stock thermowells in tapered, straight or stepped designs to address if the wake frequency will be a problem or not. Google “thermowell wake frequency” and you can find information, examples of damage and on line calculators.

And some situations may not lend themselves to use the side port of a tee as PWSlack suggested. For 1 or 2 inch pipe, fairly easy and when done right gives the best results vs. other configurations. Might not work for a 42 inch pipe as well, e.g. insertion of the TW into the fluid straight in thru the wall.

Example of general information: http://www.wikapolska.pl/upload/DS_IN0015_en_co_1353.pdf

Information on the standard: http://www2.emersonprocess.com/en-us/brands/rosemount/temperature/thermowells/calculations/pages/index.aspx

An online calculator: http://www2.emersonprocess.com/en-us/brands/rosemount/temperature/thermowells/calculations/pages/preliminary.aspx

Just the top 3 hits from my Google search.

And yes, you do need to know the fluid velocity to do a wake frequency calculation. But the usual situation is flow in a pipe, like water in a river; not agitated in a vessel as you describe. And if you agitate it long enough, like with a propeller that spins in only one direction, you will have a fluid velocity; just not an easily (for me) determined one.

__________________
The reward for a job well done is another job.
Register to Reply Good Answer (Score 2)
Active Contributor

Join Date: Jan 2017
Posts: 16
#10
In reply to #9

Re: Wake Frequency

08/05/2017 2:52 AM

Thank you JL dowell for your nice answer, So i have to consider agitator rpm and in this case, i have my agitator rpm.Now i need fluid velocity.Is there any way?or if i convert this rpm into simply mean velocity by basic physics formula would that be okay or are there a lot of fluid mechanics inside it ? Pardon me if something is silly here.

Thank you again

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26689
Good Answers: 700
#11
In reply to #10

Re: Wake Frequency

08/07/2017 3:06 AM

It would benefit the forum to know why this calculation is necessary in this particular case.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19977
Good Answers: 749
#12
In reply to #11

Re: Wake Frequency

08/07/2017 3:13 AM

Perhaps the whim of some local bureaucrat. Or regulatory org. Or some hotshot specifying engineer.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26689
Good Answers: 700
#13
In reply to #12

Re: Wake Frequency

08/07/2017 3:15 AM

Based on the information received so far, the forum might never discover this and put it to good use. So much for Monday mornings...

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Register to Reply 13 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Anonymous Poster (1); James Stewart (1); JL Dowell (1); Mahmud Reza (2); Mikerho (1); phoenix911 (2); PWSlack (4); Tornado (1)

Previous in Forum: Radar Type Level Transmitter   Next in Forum: Difference in Absolute and Relative Pressure Gauge

Advertisement