17 replies to this topic

[Kachisa]

Dears All,

Could you please explain me surge does not happen in pump but it exists to centrifugal compressor ?

 

Any explanation will be highly appreciated.

 

Thanks in advance.

[fallah]

 

Could you please explain me surge does not happen in pump but it exists to centrifugal compressor ?

 

 

Kashisa,

 

Mostly because a compressible fluid, contrary to an incompressible fluid, can store additional pressure energy in a blocked outlet condition (or something like this) which could go backward through the compressor.

[Kachisa]

Thank you Fallah for your explanation. 

But the phenomena does not happen in volumetric compressor as well, so I do not think the fluid capacity of energy storage decide this phenomena. 

Edited by Kachisa, 11 October 2017 - 05:43 AM.

[fallah]

 

What kind of energy stored in liquid ? It is converted to thermal ?

But why do gas can not storage this energy ?

 

Kachina,

 

Yes, the energy provided by pump to a trapped liquid will mostly converted to thermal energy...

 

In a gas the part of applied force converted to thermal and the rest will be stored as pressure energy...

Edited by fallah, 11 October 2017 - 05:48 AM.

[Kachisa]

Thank you Fallah for your explanation. 

But the phenomena does not happen in volumetric compressor as well, so I do not think the fluid capacity of energy storage decide this phenomena. 

[fallah]

 

But the phenomena does not happen in volumetric compressor as well, so I do not think the fluid capacity of energy storage decide this phenomena. 

 

 

Kachisa,

 

Yes, it won't happen in a positive displacement compressor...
 

[Kachisa]

So, what is the key element which decides this phenomena ?

It seems to me that it would not be fluid energy storage capacity ...

Edited by Kachisa, 11 October 2017 - 06:01 AM.

[fallah]

So, what is the key element which decides this phenomena ?

It seems to me that it would not be fluid energy storage capacity ...

 

Kachisa,

 

You might think about the surge in pump systems which can be occurred due to sudden closing a discharge valve or a pump shut off. You should note that such phenomena is due to incompressible liquid momentum cannot compressed while strikes to an obstacle and has to fluctuate in opposite directions till falling in zero kinetic energy conditions. 
 

Edited by fallah, 11 October 2017 - 07:36 AM.

[Bodhisatya]

Thank you Fallah for your explanation.
But the phenomena does not happen in volumetric compressor as well, so I do not think the fluid capacity of energy storage decide this phenomena. [/quote]

Positive Displacement Compressors are Constant volume,variable pressure machine ,whereas turbo Compressors are Constant pressure ,variable flow machine ,so surge phenomenon is prevalent in Centrifugal Compressors.

Bodhisatya

[Kachisa]

Mr. Bodhisatya,

Could you please detail your explanation please.

What do you refer to "turbo Compressors are Constant pressure ,variable flow machine" ?

 

Thanks in advance

[fallah]

 

Could you please detail your explanation please.

What do you refer to "turbo Compressors are Constant pressure ,variable flow machine" ?

 

 

Kachisa,

 

It's actually: "Centrifugal compressors are the machines with variable flow at relatively constant head".

[Kachisa]

I got it, this sujet is clearer for me.

Thank All.

[Bobby Strain]

But you didn't get enough information to understand the dynamics of a "dynamic" machine. There are lots of sources for you to learn if you search with your favorite search engine. And, centrifugal pumps can also experience surge phenomena and need similar anti-surge protection as a dynamic compressor.

 

Bobby

[Kachisa]

Mr. Bobby,

Thank you for your advice, and this is the way I do now to get a better understanding on this subject.

Honestly, from my experience, sometime my clients asked my to install an anti surge valve even on a reciprocating compressor. 

However, a lot of document/ discussion on line told me that there is no surge problem on volumetric compressor.

Do you have any idea.

 

Thank you.

[fallah]

 

Thank you for your advice, and this is the way I do now to get a better understanding on this subject.

Honestly, from my experience, sometime my clients asked my to install an anti surge valve even on a reciprocating compressor. 

However, a lot of document/ discussion on line told me that there is no surge problem on volumetric compressor.

Do you have any idea.

 

 

Kachisa,

 

In fact, what your client asked to install around a reciprocating compressor isn't an anti surge line/valve but it actually is a spill back line including a control valve for capacity control.

[Kachisa]

Mr. Fallah,

You are right. I got confused.

Thank you so much

[fallah]

Kachisa,

 

 

The water hammer or surge phenomena in a pump is happened mostly due to sudden fluid velocity change (pump trip or sudden discharge valve closing) from the value corresponding to normal flow rate toward zero....The case will be the same for compressors too, but with much lower intensity due to handling the gas rather than liquid...

 

But in a centrifugal compressor as the discharge valve is closed or demand is so reduced, the differential head across the compressor will increase which pushes the compressor goes back along the performance curve same as a pump.  When the differential pressure gets too large while forward flow is continued, contrary to a pump, the flow will reverse through the compressor, which reduces the pressure at the outlet to compensate the pressure reduction at the inlet.  At the moment, the differential pressure is low enough for forward flow to be rebuilt.  The process repeats again and again if no protection is provided as anti surge which might lead to catastrophic failure of the compressor.

[Princissa]

Hello!

could you explain to me the phenomenon of surge  in  axial compressor? thank you.