4 replies to this topic

[mrbabu]

for a preliminary design
I am simulating several different operating conditions
for a centrifugal compressor on a saturated
natural gas stream,
for these calc's I use the polytropic model
included in PRODE PROPERTIES which
allows both dry and wet gas
(rigorous polytropic stage with phase equilibria),
the different operating conditions which
I wish to evaluate include dry gas and wet gas,
according the results with wet gas
the evaporation of the liquid water phase within
compressor generates an inter-cooling effect and the
compressor exit gas temperature is reduced
with an increase of gaseous phase mass flow,
as final result the specific work of
the compression process is reduced,
this seems an important factor which
affect polytropic efficiency,
my question concerns the value to enter,
I have estimated values for dry gas but
not for wet gas.

[PaoloPemi]

I agree that the evaporation of the condensate within
compressor affects specific work of
the compression process,

however,

for the usually very low amounts of condensate

allowed by centrifugal compressors

I assume the values given for dry gas

(i.e. from the manufaturer's curves or usual preliminary values)

 

so, altough PRODE allows to define

any amount for liquid fraction,

in preliminary design of centrifugal stages,

when no accurate values are available,

I assume for polytropic efficiency

the values given for dry gas

Edited by PaoloPemi, 31 October 2013 - 06:00 AM.

[mrbabu]

thanks Paolo, at last I decided to estimate stage efficiency for an existing compressor (inverse process, given inlet and outlet conditions) with the software, the numbers are (more or less) in agreement with those provided by manufacturer, however the amount of condensate has been estimated by software (not measured) and that may introduce some errors.

[PaoloPemi]

mrbabu,

 

(of course) that is a possibility,

i.e. if you know the conditions at inlet and outlet of compressor

in Excel you can utilize the macro for estimating polytropic efficiency,

 

Paolo

[marchem]

mrbabu,

I did the same to simulate a screw compressor,

as first step the efficiency has been determined at some specific condition,

in the second step I modified the operating condition (keeping efficiency) to see if calculated values did agree with those provided by manufacturer,

results need some evaluation as for screws there are several parameters as oil flow to consider  

however it may be useful for estimates.