Liquid Refrigerant and Centrifugal Compressors

[mpeck1982]

I have a water cooled chiller that utilizes R-134a refrigerant. This chiller is equipped with a centrifugal 2-stage compressor, condenser, economizer, and an evaporator. The refrigeration cycle shows that in the economizer (intercooler) has a line going to both the evaporator and a line bypassing the evaporator and going into the 2nd stage of compression. The refrigerant is in liquid state going into the economiser. I always thought that liquid refrigerant can damage compressors. Is that true?

 

[MintJulep]

Yes. Liquid in a compressor is generally bad.

Likely your system has a choke to limit the amount to a very small percent of total flow, so that it nearly instantaneously flashes to vapor when mixed with the hot interstage gas.

 

[mpeck1982]

There is a modulating valve on the line going from the economizer to the compressor. I'm guessing if the compressor's gas refrigerant gets to hot the economizer valve will open sending small amount of liquid refrigerant from the economizer to the compressor. This can help get desirable setpoints leaving the compressor.

 

[Drazen]

Flash cooler is constructed in a way that line which leads to compressor inter-stage contains vapor liquid refrigerant is already expanded to inter-stage pressure; liquid and vapor phases are separated by port construction, and finally mass ratio of vapor leaving cooler to superheated vapor leaving 1st stage compression ensures that vapor mixture entering 2nd stage is in superheated region as well.

It has to be that way; if you would have any liquid in compressor you would hear it very well, and you would have to collect broken pieces of equipment as well.