Crankcase heaters for compressor

[hibik1]

Hi all,


From what I know, crankcase heaters are used to heat the oil used in scroll compressors so that there will be no mixing between the refrigerant and the oil.


What about 'oil free' centrifugal compressors (like the danfoss turbocor). Do they still need crankcase heating since they do not have any oil in the system?

Thanks!


Regards,

Hibik1

[Grizzly]

Welcome to the forum Hibik1.

Seeing as there is no oil or a sump then the answer is no.

A crankcase heater serves 2 purposes.

1 to warm the oil thereby reducing its viscosity, which reduces drag upon star-up and during running.

2. warming the oil causes any refrigerant mixed in with the oil to boil off.

Most compressors will handle a small amount of Liquid but trying to compress liquid is not good for obvious reasons which I am sure you are aware of.

A turbo is a centrif and therefore is not affected in the same way as other types.
Grizzly

[aramis]

No. The carkcase heaters are used to reduce the velocity of refrigerant migration into the oil.

There will still be mixing of oil + refrigerant but to a lesser degree, but even with the crankcase heater you can get lots of refrigerant in the carter if

- The compressor is off for very long periods of time (even with the crankcase heater on!).
- The compressor is at a lower temperature than the evaporator (with the crankcase heater on).

This is why you also need pump down!

As to your question: NO, Turbocor compressor do not need crankcase heaters, oil separators, ...

Read: http://www.turbocor.com/literature/pdfs/articles/frictionless.pdf

[mark957]

hi Hibik
The refrigerant tends to condense in the parts of the colder cooling circuit.
The purpose of the resistance of the heating oil in the crankcase and to maintain the highest temperature than in the rest of the circuit, thus causing the evaporation of the refrigerant by the oil.