Mass flow calculation

M

Thread Starter

Moller

Hello friends;

I want to calculate the mass flow of 11 stage axial compressor. I know the following parameters
1. Compressor discharge pressure
2. Compressor discharge temperature
3. Compressor inlet pressure
4. Possibly area/dia of the compressor
5. Air density i.e rho

I have no venturi meter or other measurement in the field. I need guidelines how i calculate the air mass flow in PPS.

Please help me in this regard
 
N

Namatimangan08

>PLease help me I am still waiting
>experts.
>Regards

I'm not sure whether it can be done based on the parameters you have given. I will try to figure it out later.

Normally a GT supplier will provide you with a index differential pressure correlation. With the parameters that you have provided & with index differential pressure provided by your supplier I'm sure you can find air mass flow rate.

That index differential pressure is a kind of empirical correlation between index reading and mass flow. It measures the mass flow deviation from the reference if one of the input parameters has changed from the expected value.
 
Hi,

Can you explain me this in detail? Its rare to get the mass flow rate measurement and need this for gas turbine performance calculations.

Thanks in advance.
 
N

Namatimangan08

If you don't have index pressure differential given to you by your supplier. I'm afraid I cannot explain any further.

There is another way (second best to do it. In this case you ought to know turbine inlet pressure and temperature. I give you some clues.

Q_flugas =m_f *CV

This shall be made equal to :

(m_air)*cp_air*( TIT-CDT)+m_f*cp_f(TIT-CDT)

You end up something like this.

m_f*CV_f = m_air*cp_air*(TIT-CDT)+m_f*cp_f (TIT-CPD)

Where:

m_air= air mass flow rate -This is what you want

m_f = fuel mass flow rate

cp = heat coefficient at constant pressure

TIT = turbine inlet temp

CDT = compressor discharge temp

The assumption is heat loss from combustion chamber to ambient air is negligible. If you can approximate heat loss you can include in the calculation.

All the variables other than m_air shall be known. Otherwise forget it. Those cps you can get them from standard table for the average temperatures.

Note: This method is not the substitution to using index DP method.
 
Hi,

Thanks for your prompt reply!!

The second method is based on the heat balance, but i'm afraid if we can get the turbine pressure and temperature.

I'm still not clear on the differential pressure you were mentioning.Can you explain me about the index pressure differential, so that i can check with the supplier? What data exactly should i ask for to the supplier?

Thanks in advance.
 
N

Namatimangan08

> I'm still not clear on the differential pressure you were mentioning.Can you
> explain me about the index pressure differential, so that i can check with
> the supplier? What data exactly should i ask for to the supplier?

It is based on empirical correlation between parameters that made up the index and air mass flow rate. I give you simple example..very simplified one and not be that close to index pressure method. Only the underlying principle that is similar.

During commissioning for CPD =15bars, ambient air pressure =1bar, intake DP 3mBar, ambient temperature =15Cel, GVO= Fully open, the measured mass flow rate is 505kg/s. Any change in the parameters that are used to calculate index pressure will be used to calculate mass flow deviation from the referenced condition.

Note that the parameters that made up the index pressure might not be similar with my example. Let see if I can find them up for you.
 
N

Namatimangan08

> I'm still not clear on the differential pressure you were mentioning.Can you
> explain me about the index pressure differential, so that i can check with
> the supplier? What data exactly should i ask for to the supplier?

You mean turbine inlet temp? That was expected but I think turbine inlet pressure more or less equals to compressor discharge pressure, if we ignore pressure drop between compressor outlet to turbine inlet.
 
Thanks for your reply..

Please let me know the parameters that made up the index pressure and their correlations. Is this correlation varies with different gas turbines? Can you give me some reference to this correlations? what data should i ask supplier regarding this index differential pressure? Also, does the referenced condition refers to ISO conditions?

[email protected]
 
N

Namatimangan08

I will e-mail you separately. For the interest of other posters let me try to explain how GT air mass flow rate can be determined using index pressure. I just explain what have been produced by others. Not my own methodology.<pre>
X axis : Index DP/Pic Dimensionless

Y axis : G*(SQRT(B))/S kg/s

G= Inlet air flow (kg/s)

B= (Ric/29.383)* (Tic+273.2)/300

S= Pic X(14.233/14.1)

Tic= Inlet air temp (Cel)

Ric = Gas constant of inlet air (m/K)

Pic= Inlet air pressure (kg/cm2 abs)

Index DP =Index diff pressure (kg/cm2) -- I think this one should be gauge pressure.

This is based on MHI 230++MW GT. The given correlation is as follows:

Index DP/Pic 0.15 0.2 0.25 0.3 0.35

G*SQRT(B)/S 480 530 575 625 665 kg/s</pre>
My opinion : Most likely index DP is turbine exhaust pressure

Thank you.
 
Cv is the (liquid) flow coefficient for a control valve. The flow equation is:

Q = Cv * SQRT(deltaP/G)

where:
Q = flow in gallons(US) per minute
deltaP = the differential pressure across the valve in PSI
G = specific gravity of the liquid at the flowing conditions
 
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