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nevinjohn
21-05-2014, 01:37 PM
How is oil avioded in compressor?
Since oil stays in the refrugerant line, wont it cause any troble to the compressor, since its in liquid form, and is incompressible? Any thoughts?

Rob White
21-05-2014, 04:16 PM
.

Oil belongs inside the compressor, it lubricates the moving parts.
On a fridge system we don't want oil in the pipes, it belongs in the comp..

What do you imagine the oil does inside the fridge circuit?
Oil inside the pipes and heat exchangers just takes up space,
we want it inside the compressor so the moving parts are kept lubricated.

The compressor does pass a small amount of oil over and into the
pipework but the design of the system is to get the oil back to the
comp as soon as possible.

Rob

.

mbc
21-05-2014, 07:08 PM
if we had oil in inside pipe it bring down our efficiency because:
oil stop ideal cool transferring comes from refrigerant .
oil hold up good gas and liquid flow .
too much oil inside suction line might damage our compressors.
too much oil in condenser reduce capacity of that.
we have to stop running of oil to inside of pipe by choosing of good oils and putting oil separators and also
oil should comeback to our compressor easily and smooth by right piping .

nevinjohn
22-05-2014, 06:35 AM
Yes, unfortunatly this is not the case all the time. Although it is supposed to stay inside the compressor, it doesnt happen most of the time. Some oil is pumped from the compressor to the liquid line (and travells the entire refrigeration cycle, before comming back to the compressor), and this is one the reasons that manufacturers recommend to avoid much bends in refigerant pipes, as there is a chance of oil being trapped there. Remember, heavy duty refigerant compressors are provided with crank case heaters so that the mixing of refrigerant with oil can be avoided which could lead to potential compressor damage! Please google "Flooded compressors - Danfoss" Refer this link http://www.danfoss.com/North_America/NewsAndEvents/Archive/Company+News/2009/Why-Compressors-Fail---Flooded-Starts/4BD7A120-A99D-4D95-8DA2-D904D68CAAC5.html

Rob White
22-05-2014, 08:07 AM
Yes, unfortunatly this is not the case all the time. Although it is supposed to stay inside the compressor, it doesnt happen most of the time. Some oil is pumped from the compressor to the liquid line (and travells the entire refrigeration cycle, before comming back to the compressor), and this is one the reasons that manufacturers recommend to avoid much bends in refigerant pipes, as there is a chance of oil being trapped there. Remember, heavy duty refigerant compressors are provided with crank case heaters so that the mixing of refrigerant with oil can be avoided which could lead to potential compressor damage! Please google "Flooded compressors - Danfoss" Refer this link http://www.danfoss.com/North_America/NewsAndEvents/Archive/Company+News/2009/Why-Compressors-Fail---Flooded-Starts/4BD7A120-A99D-4D95-8DA2-D904D68CAAC5.html


Do not confuse oil with liquid refrigerant.

Oil inside the system is designed to be inside the compressor
and will flow around the system until it gets back to the compressor.

You are talking about flooding the compressor with liquid refrigerant.
The Danfoss link you give is explaining what would happen if liquid
was inside the compressor at start up.

Read the whole article.

http://www.ra.danfoss.com/TechnicalInfo/Approvals/Files/RAPIDFiles/17/Article/FloodedStarts/Why%20Compressors%20Fail%20Part%202-web.pdf

Why Compressors Fail
Part 2 - Flooded Starts
This compressor is fi tted with both a crankcase
heater and insulated jacket to help prevent
refrigerant migration to the compressor oil.
Insert: Here we see a belt type crankcase heater.
REFRIGERATION AND AIR CONDITIONING Field Service Note 007
Flooded starts are probably the major cause of compressor failures. Flooded starts occur when liquid refrigerant
has migrated from the system and condensed into the compressor oil. Migration can occur in all systems up to a
point, due to the vapour pressure of the refrigerant being greater than the vapour pressure of the oil. It is the
refrigerant vapour that migrates and then condenses into the colder compressor oil.

Rob

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nevinjohn
22-05-2014, 09:33 AM
Do not confuse oil with liquid refrigerant.

Oil inside the system is designed to be inside the compressor
and will flow around the system until it gets back to the compressor.

.

My question is the same. This small amount of oil that will flow in the system lines. . This will eventually enter the compressor (the motor and bearings) and the cylinder!! This is where the actual compression takes place. Since oil being liquid, how can this be handled? Is there some tolerance for this small amount of liquid oil which will enter the actual compression process.. (in the scroll wheel or the piston/cylinder)?

And as per what mbc said, this small amount of oil will cause some kind of fouling in the evaporator lines, leading to in efficient heat transfer, isnt that correct?

Rob White
22-05-2014, 11:46 AM
.

Everything you say is correct but
the amount of oil in every stroke of
the piston is so small it is not an issue.

If a large quantity of oil got into the piston
it would cause damage, but it normally is
in such small quantities as not to matter.

As you said if it is in the pipes and heat exchangers
it will lead to inefficient heat transfers and
logging in the wrong places.

The system will be designed to return the oil
back to the comp.


Rob

.

Brian_UK
22-05-2014, 11:11 PM
Consider this a new hermetic, tin can, compressor may have oil filing the bottom of the can to a depth of 40mm when it is stationary.

When the compressor runs some oil mist is pumped through the compressor and around the system, the OK level is now 38mm.

This condition will remain for the rest of it's operating life.

Oil coming back with the refrigerant flow combines with the oil in the compressor sump.

shibualex
23-05-2014, 05:34 AM
dear all

pls can i get a help for-

many of our skm chillers compressor failure due to chemical reaction.
what is the chemical reaction in chiller?
how it is happening ?

nevinjohn
26-05-2014, 07:38 AM
dear all

pls can i get a help for-

many of our skm chillers compressor failure due to chemical reaction.
what is the chemical reaction in chiller?
how it is happening ?

You could've started a new thread. For your question, yes chemical reaction can occur:-
1. if impurities are found in the system.
2. A different blend of compressor oil is used (which mixes with the refrigerant)

Impurities can happen if there was a compressor burn out, dust or air entrapped in the system. It should have been addressed during commisioning. Was the system charged with refrigerant, or was it done at site? It it was done at site, check the logs and you might find the cause!

Balance Piston
26-05-2014, 02:51 PM
dear all

pls can i get a help for-

many of our skm chillers compressor failure due to chemical reaction.
what is the chemical reaction in chiller?
how it is happening ?

You need to provide more information.

Chiller type?
Compressor type?
Refrigerant type?
What is the process....what are you chilling?
Operating pressures / temps?
Have you performed an oil analysis? Was it the Karl Fischer method? TAN number? H2O? Particle count?
Have you performed a refrigerant analysis?
Do you have water cooled oil coolers?
Do you cycle the chillers or are they in continuous operation?

Provide as much information as possible.