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Q 4
- Thread starter amrfd
- Start date
amrfd,
1. Stop yelling! (All CAPS equals "Yelling"). Just use caps for the first word that starts a sentence, for the proper noun "I",for peoples names and some other selected cases.
2. I don't think you meant to use the word "speed". I think you intended to use the term "rate of flow" or "flow rate". Is that correct?
3. A flow rate of 1 to 3 meters per second is not fast or unusual.
4. Why are you asking this question?
5. Can you give us more information about your situation?
1. Stop yelling! (All CAPS equals "Yelling"). Just use caps for the first word that starts a sentence, for the proper noun "I",for peoples names and some other selected cases.
2. I don't think you meant to use the word "speed". I think you intended to use the term "rate of flow" or "flow rate". Is that correct?
3. A flow rate of 1 to 3 meters per second is not fast or unusual.
4. Why are you asking this question?
5. Can you give us more information about your situation?
msquared48
Structural
Is the subject matter regarding a Star Trek character?
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
racookpe1978
Nuclear
A James Bond support and new design character? (But, then again, he did not to yell much either ...)
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- #5
When English isn't your first language, the words speed and velocity can be easily confused and incorrectly interchanged. As an engineer who deals with fluids daily, velocity is a common term easy to mix up with speed when I might be speaking another language.
Agreed on the ALL CAP's however.
That said, 1-3 M/S is a balance between pressure drop and erosion effects. You can certainly flow water at higher velocities than 3 M/S, but the pumping costs - initial equipment costs for higher Horsepower pumps and operating costs for higher horsepower - will be very expensive. And, depending on your piping materials, erosion wear can become a factor.
Google "flow accelerated corrosion".
One M/S is rather slow, even for pump suction piping, but 1.5 - 2 M/S is not. Three M/S is bordering on getting into high pressure drop.
I hope this answers the question.
rmw
Agreed on the ALL CAP's however.
That said, 1-3 M/S is a balance between pressure drop and erosion effects. You can certainly flow water at higher velocities than 3 M/S, but the pumping costs - initial equipment costs for higher Horsepower pumps and operating costs for higher horsepower - will be very expensive. And, depending on your piping materials, erosion wear can become a factor.
Google "flow accelerated corrosion".
One M/S is rather slow, even for pump suction piping, but 1.5 - 2 M/S is not. Three M/S is bordering on getting into high pressure drop.
I hope this answers the question.
rmw
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1
- #6
When selecting a size for a pipeline you are looking for the optimum long term economic balance between capital cost and running cost. This will set the size of the pipe and therefore the velocity of flow. It turns out to usually be in the range you have given, but generally the higher end of that range is used in larger pipes (or even more than 3 m/s in very large pipes) and lower velocities in that range for smaller pipes.
As rmw has pointed out there are many factors that come into this economic analysis - purchase and installation of the pipe and pumping equipment, cost of power, maintenance costs etc.
But apart from the economics there are other factors like erosion (which I suppose is also an economic issue to a degree, but I am thinking of safety here), self cleaning requirements, water hammer, noise and safety issues (like excessively high pressures), which all have an impact on the allowable velocity.
And then there is the whole subject of gravity flow where there is no pumping cost.
Just remember that the range you have given is a useful rule of thumb for initial estimates, and don't use it for your final design.
Katmar Software - Engineering & Risk Analysis Software
"An undefined problem has an infinite number of solutions"
As rmw has pointed out there are many factors that come into this economic analysis - purchase and installation of the pipe and pumping equipment, cost of power, maintenance costs etc.
But apart from the economics there are other factors like erosion (which I suppose is also an economic issue to a degree, but I am thinking of safety here), self cleaning requirements, water hammer, noise and safety issues (like excessively high pressures), which all have an impact on the allowable velocity.
And then there is the whole subject of gravity flow where there is no pumping cost.
Just remember that the range you have given is a useful rule of thumb for initial estimates, and don't use it for your final design.
Katmar Software - Engineering & Risk Analysis Software
"An undefined problem has an infinite number of solutions"
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1
- #7
Katmar,
You have hit the essence of the reason for specifying a target velocity, but the actual numbers that the OP mentioned come from a specific empirical API erosional velocity equation (it is early in the morning and I'm not up to looking up which API document it is in):
v=100 ft/s / (fluid density in lbm/ft^3)^0.5
Using all fps units and then converting the answer to mks I get 3.9 m/s for pure water. If I convert 100 ft/sec to 30.40 m/s and 62.4 lbm/ft^2 to 1,000 kg/m^3 then the equation gives me 0.964 m/s. Like many empirical equations, the units are coincidental (dividing a velocity by a density does not yield a velocity) and it doesn't translate well, but the 1 m/s comes from translating the input and the 3 m/s comes from translating the output.
Another example of an empirical equation that doesn't translate is the rule of thumb that hydrotest water in bbl/thousand ft is about equal to the ID of the pipe in inches squared. This equation happens to work even though the units look odd (in^2^ft does not equal bbl). For example, if I have 10,000 ft of 8 inch ID pipe, the actual internal volume is 622 bbl, the rule of thumb gives you 640 bbl. If I convert the output then I need 101,751 L, if I convert 8 inches to 203 mm; 10,000 ft to 3048 m; and 1000 ft to 30.48 m then I get 412,902 L. You really have to be careful with empirical equations.
Penpipe,
It is a really bad idea to chastise someone with the wrong information. The word he was looking for was "velocity" which is "speed" plus a direction vector. "Rate of flow" is generally taken to mean "flow rate" which is an ambiguous reference to either "mass flow rate" or "volume flow rate". His use of "speed" was far less ambiguous than your use of "rate of flow".
David
You have hit the essence of the reason for specifying a target velocity, but the actual numbers that the OP mentioned come from a specific empirical API erosional velocity equation (it is early in the morning and I'm not up to looking up which API document it is in):
v=100 ft/s / (fluid density in lbm/ft^3)^0.5
Using all fps units and then converting the answer to mks I get 3.9 m/s for pure water. If I convert 100 ft/sec to 30.40 m/s and 62.4 lbm/ft^2 to 1,000 kg/m^3 then the equation gives me 0.964 m/s. Like many empirical equations, the units are coincidental (dividing a velocity by a density does not yield a velocity) and it doesn't translate well, but the 1 m/s comes from translating the input and the 3 m/s comes from translating the output.
Another example of an empirical equation that doesn't translate is the rule of thumb that hydrotest water in bbl/thousand ft is about equal to the ID of the pipe in inches squared. This equation happens to work even though the units look odd (in^2^ft does not equal bbl). For example, if I have 10,000 ft of 8 inch ID pipe, the actual internal volume is 622 bbl, the rule of thumb gives you 640 bbl. If I convert the output then I need 101,751 L, if I convert 8 inches to 203 mm; 10,000 ft to 3048 m; and 1000 ft to 30.48 m then I get 412,902 L. You really have to be careful with empirical equations.
Penpipe,
It is a really bad idea to chastise someone with the wrong information. The word he was looking for was "velocity" which is "speed" plus a direction vector. "Rate of flow" is generally taken to mean "flow rate" which is an ambiguous reference to either "mass flow rate" or "volume flow rate". His use of "speed" was far less ambiguous than your use of "rate of flow".
David
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1
- #8
1 m/s sweeps most of the delaterous materials, along prohibiting excessive build ups. Over 3 m/s can be erosive and will tend to have high pressure drops, as well as getting into a range where transient pressures can become more significant.
Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus
![[smile]](/data/assets/smilies/smile.gif "[smile] [smile]")
ornerynorsk
Industrial
Good one, europipe. I don't think Sr would have been a barrel of laughs.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
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