Mass flow calc

T

Thread Starter

Tresco

Can someone please advise the calculation for mass flow for a gas stream, given process flow, pressure & temperature conditions, and assuming a fixed (known) gas composition.

regards,
Phil McKay
TRESCO INTERNATIONAL (AUST) PTY LTD
Silvan, Vic, Australia
[email protected]
 
I am sorry I do not have an answer but I would like to expand on this question. This sounds fairly elementary but it has been a while since I
studied this and I have some basic questions as I am in need of implementing some controls for density measurement.

1. Are there any good resources on the subject of mass flow ie density vs SPG vs temp vs viscoscity etc. on the web (I realize ISA etc probably has books and I am looking there) ?

2. I am confused over the relationship of these measurements, for instance I need to measure the % solids of a corn starch slurry in a paper mill and currently we use nuclear gauges which have been nothing but trouble (mostly because I think we don't know what we are doing and I will admit it).

We want to switch to Micro Motion mass flow but have some questions about accuracy and how we test that accuracy. Also I am not sure that I fully understand the relationship between SPG and % solids as related to temperature, I think there are multiple curves for each temp and therefor
cannot just use the SPG signal. I also do not understand the relationship of water and its ability to be (I have been told) a SPG less than 1 at certain mixtures and temperatures ??

Currently they use a float to test this and I argue that this float is only good at a particular temperature. We also use a refractometer but again I think it is only good at a particular temp. Is there some good way like
cooking out the water etc that is fairly quick and yet fairly accurate ??
Also can someone explain a refractometer and the floats principles to me (I think I know but again have been given 200 opinions).

We ask Micro Motion but only get sales people (no offense) and never really got our "deeper" questions answered. I have found that everyone is an expert on the subject until I say "what if ........" then I get all kinds of answers.

Any help on this subject would be greatly appreciated and I do not want to deviate from this original post but if I am this confused, maybe there are others..............

Thanks in advanced as always "Much appreciated".....

Dave Ferguson
Systems Group
Blandin Paper Company
UPM-Kymmene
DAVCO Automation
 
Dave:
I did my best to put our fried Phil in the gear.
Specific gravity is pain in the neck as some gas do not refer to standard T,P conditions, this is why working mass flow is technical.
I'm not sure if I understand correctly the word
'float' in your posting. I presume you mean the float type rotameter: that one is quite tricky.
When it comes to very specifics concerning a particular project, you may end up with some complicated equation. But at the end the matter simplifies to special graduation of the scale. Fisher Porter (Germany) did several for us on SF6.

[email protected] dr.qc.ca

Embark in the Phil gear.
 
B

Bruce Durdle

The volume of 1 kg-mol an ideal gas at O deg C, 101.3 kPa is 22.41 m3.

So if you know the volumetric flow rate at flowing pressure and temperature, convert this to base conditions as above. If you know the
composition, you know the MW, and can bend the equations to find mass flow from volumetric flow.

Cheers,

Bruce
 
L

Larry Kolbert

Sure would like to know more about the existing gauges. Many are used in the Paper Industry with success so it would be good to sort out your
difficulties.

Would need to know pipe size, density range, etc. to make the evaluation.

[email protected]
 
H
Dear Mr. Tresco,
Here I have a formula for flow calculation with press and temperature compensation & hope this can helping you.

Fo = ( ( (P+1.01325x100) / (Pb+1.01325x100) ) X ( (Tb+273.15) /
(T+273.15) ) ) X Fi

Fi = Measured flowrate
P = Measured Press ( kPa )
T = Measured Temperature ( º C )
Fo = Corrected flowrate
Pb = Reference pressure ( kPa )
Tb = Reference temperaure ( º C )

BR,
Herry
 
K

Keven Dunphy

If a coriolis mass flow meter is used, such as is manufactured by Micro Motion, then changing pressure, temp, or composition have no impact on mass flowrate. This assumes that the flow is indicated in mass flow units, ie lbs/hr.

If it is desired that the flow units are expressed in terms of standard volumn units, then simply divide the indicated mass flow by the standard density of the gas (this assumes a constant composition fluid).

For more information please consult www.micromotion.com or contact me directly.

Best Regards,

Keven Dunphy
Micro Motion
New Business Development
303 530 8048
 
B

Bruce Durdle

With a Coriolis meter, you should be able to select mass flow or volumetric flow - the sensor inherently is capable of finding density from the natural frequency of vibration. Certainly this is the case with Micromotion.

Bruce
 
K

Keven Dunphy

Bruce is right on the money... a Micro Motion coriolis meter is capable of determining an online measurement of actual density. However, this usually only applies to liquid flow applications... if you desire an output in gallons, for instance, then the actual density
can be used to adjust the indicated mass flow to gallons.

In the case of a gas flow however, the actual density is not of much use. Instead, the reference value of standard density would be used
to scale the mass flow output to "standard volumn units". For constant composition gases, standard density values are readily availble in rreference books. If a mixed gas stream needs to be
measured, then one has several options. Since this is not the case with this question, I won't go into that in any detail.

Best Regards

Keven Dunphy
 
W

Wayne Brinkman

Keven, A buddy of mine just pointed me to this site. There is not a lot of Coriolis activity. Wayne
 
If it is desired that the flow units are expressed in terms of standard volumn units, then simply divide the indicated mass flow by the standard density of the gas (this assumes a constant composition fluid).

For more information please consult http://www.micromotion.com or contact me directly.

Best Regards,

Keven Dunphy
Micro Motion
New Business Development
303 530 8048
 
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