What happening when low pressure and high flow rete?

[GOBLINTECHNIC]

For the piping with equal size along the single piping system.

1. Is the flow rate is equal along the piping system ?
(A1V1 = A2V2)
2. If the answer from first question is ture. Flow rate at the end of piping system is equal to the flow rate at the first point of piping system but have more pressure drop along this piping system. and then What happen in this even?

 

[zdas04]

1. NO. Area times volume is meaningless. Area times velocity is volume flow rate at actual conditions. If your product is gas then the volume flow rate at standard condirions is equal along the pipe, but the volume flow rate at actual condirions varies widely. Mass flow rate is also constant. For a liquid you can generally ignore the changes in density, but the key word there is "generally". I'm working on a project where it get impossible answers if I ignore density changes.

2. It is not true, so I guess I don't have to try to puzzle out what the heck you are talking about.

David

 

[BigInch]

What's the fluid? Is it non-Newtonian?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[stanier]

In slurry pipelining you need to consider that the fluid may move faster than the solids in heteregenous flow. The slurry density in the piplein is different to that entering or leaving the pipeline. Reference Wilson, Addie and Clift.

 

[BigInch]

Do you have wax deposition in the cooler sections of pipeline?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[stanford94]

restate the problem in English....

 

[nhliew]

Hi everybody,

I think Goblintechnic meant V=Velocity. Volumetric Flow = Cross Section Area x Velocity.

Other than that I can only speculate that goblintechnic wanted to know:
If volumetric flowrate at point 1 equals to that of point 2, and the fluid experiences pressure drop between the two points, the fluid expands. Where does the extra volume go?
Answer - if there is a pressure drop across a pipeline, then the volumetric flow entering and exiting cannot be the same without energy being added into the fluid or mass being taken out of it.

NH Liew

 

[BigInch]

The actual volumetric flow and the mass flow in the pipe during steady state flow are both the same. The density of the fluid changes to make sure that it stays so.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ione]

I am glad to read that at least someone (BigInch) knows the continuity equation.

 

[BigInch]

You can even change the pipe diameter and its true. Velocity changes to make it so, hence A1 V1 = A2 V2.

zdas said it first, but I thought it needed restating.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ione]

Goblintechnic,

Bernoulli’s equation states that for inviscid, non rotational and incompressible fluid the total head H along a streamline is constant

H = z + p/(rho*g) + V^2/(2g) = const

Where:
p is the pressure,
V = the average fluid velocity,
rho = the fluid density,
z = the pipe elevation
g= the gravity acceleration constant.

For a real viscous fluid streamline, part of the energy is turned into heat and lost, and pressure drop between two points of the streamline is the energy difference between the aforesaid points.
So pressure drops intervene in a balance energy equation, without affecting mass conservation (continuity equation).

 

[rmw]

If you don't have pressure drop, then you don't have fluid flow.

rmw

 

[nhliew]

Good day,

I must apologize for neglecting to mention that my comment was based on gas flow.
Having P1>P2, it follows that the gas at Point 2 expands, i.e. there is a reduction of density. Therefore Qa2(actual volumetric flowrate)>Qa1. This being said, mass flow (kg/s) and volumetric flow in standard conditions (std ft3/s) remain the same.
Going forward, Qa1=A1V1 and Qa2=A2V2. Since cross section area remain the same A1=A2, then V2>V1.
However, I am simplifying the equation to the extent of assuming constant temperature and compressibility factor (z).

 

[BigInch]

ione, I think rmw is complaining that you left out the -HL flow friction term. Should be there when there is flow.

nhliew, It applies to liquid flow also, just the effects are not so pronounced as in gases. The only basic difference between liquid and gas P-V relationship is the magnitude and the shape of the "z" curve. A very small change in a fluid's volume results in a very large change in pressure, or v/v.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ione]

For compressible fluids, it is important to define the flow regime: subsonic or supersonic.
For these fluids and from Hugoniot theorem:
dA/A = (M^2-1)* dV/V
where A = transverse area of the pipe
dA = transverse area variation
M = Mach number
V = fluid velocity
dV = fluid velocity variation

If the fluid expands (that is it accelerates) dV/V>0 in a subsonic regime (M<1) the section must contract (dA/A<0)
If the fluid expands (that is it accelerates) dV/V>0 in a supersonic regime (M>1) the section must increase (dA/A>0)
If the fluid contracts (that is it decelerates) dV/V<0 in a subsonic regime (M<1) the section must increase (dA/A>0)
If the fluid contracts (that is it decelerates) dV/V<0 in a supersonic regime (M>1) the section must decrease (dA/A<0)
If M = 1 the section must be constant (dA/A=0)

 

[BigInch]

too much.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ione]

BigInch,

I’d like to meet you as you’re not only very skilled, but you’ve also an innate sense of humour, whilst here in Italy engineers are usually quite humourless.

 

[BigInch]

I worked a lot with Snamprogetti and I'm afraid I'll have to agree with you.

But really I don't think lack of humor is necessarily a fault of engineer's themselves, but more of engineering work, which lacks latitude and freedom for the expression of humor, as most people know it. Engineers themselves do have a sense of humor; its just "different" when compared to "normal people's" sense of humor. We're just a very misunderstood lot.

I think this is a good example of what I mean. When I was little I asked my father what the difference was between AM and FM radio. My dad told me that FM stations were in New York. When I finally learned what the difference really was, at first I was mad at my father for having lied to me, but when I got over it, I thought that was one of the funniest things that he ever did having that joke on me and waiting another 15 years for me to get it. He was a metallurgist. Then I found out he did it again with that thing about F=MA that really should be E/c^2 * A So much for engineering humor. And yes ... I am also afraid that I am an exception to just about every (non-thermodynamic) rules. You've just seen the tip of the iceberg.

Globalintechnic, sorry for the attempted hijack.




**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/