Oil Trapped In Heat Exchanger(evaporator)

Hi All,
Im brand new to this forum so this is my first tread.
Please be patient with me.
I have a unit here that is running down to temperatures of -70 DegC.
It is a Carlisle Compressor running on R507A. We are using Emkarate RL32H and a Temprite Model 506 oil seperator. The system runs through either a direct expansion valve or alternatively through a Motorised smart cool valve into a Heat Exchanger depending on the requirement of the unit at that point.

When the unit is running through the expansion valve there in no problems but when the heat exchanger is required we get large amount of oil building up in the heat exchanger which is inefficient and causing me problems. The Heat Exchanger is providing -50DegC oil through the heat axchange and when we use the direct expansion for another application we get -70Deg C.

Im wondering is this oil seperator good enough to remove the oil from the circuit or should i be using different compressor oil.

This issue has been going on now for some months and the manufacturers of the machine have not been very good with recomendations etc.

I look forward to your thoughts on this people and thanks in advance to all who may help.

Kind Regards

[quote=bcfrug;191806]Hi All,

When the unit is running through the expansion valve there in no problems but when the heat exchanger is required we get large amount of oil building up in the heat exchanger which is inefficient and causing me problems. The Heat Exchanger is providing -50DegC oil through the heat axchange and when we use the direct expansion for another application we get -70Deg C.



Please explain the operation further, I am a little confused about the change over from the expansion valve to the "heat exchanger" is the expansion valve not feeding a heat exchanger? also provide any other information you can on this unit, is it custom or standard ? who built it? what is it's typical operation? -70 indefinetly? any defrost? oil and seperator seem pretty standard for the application, perhaps a piping issue. You may need to add Pentane or similar, I have worked with various cascade units for years with out using it but it depends on your application and how th equipment is utelized.

Quote:

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Originally Posted by bcfrug

Hi All,
Im brand new to this forum so this is my first tread.
Please be patient with me.
I have a unit here that is running down to temperatures of -70 DegC.
It is a Carlisle Compressor running on R507A. We are using Emkarate RL32H and a Temprite Model 506 oil seperator. The system runs through either a direct expansion valve or alternatively through a Motorised smart cool valve into a Heat Exchanger depending on the requirement of the unit at that point.

When the unit is running through the expansion valve there in no problems but when the heat exchanger is required we get large amount of oil building up in the heat exchanger which is inefficient and causing me problems. The Heat Exchanger is providing -50DegC oil through the heat axchange and when we use the direct expansion for another application we get -70Deg C.

Im wondering is this oil seperator good enough to remove the oil from the circuit or should i be using different compressor oil.

This issue has been going on now for some months and the manufacturers of the machine have not been very good with recomendations etc.

I look forward to your thoughts on this people and thanks in advance to all who may help.

Kind Regards

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Welcome bcfrug.
Cascade systems are not something I deal with so please bare with me!

Basically the info I have (Attached below) states that your oil (RL32H) has a pour point of -46c.
Which it would appear does not allow the type of temps you are mentioning.
As an aside, if this used to work with this grade of oil. Have you considered that as these oils are highly Hygroscopic. There may be an excessive water content in the oil?
I hope the little I have listed is Helpful?
Cheers Grizzly

Hi bcfruc
for this type of system you will need to use a more efficient oil separator - it appears the oil is causing a blockage. The system will need to separate around +99% of the oil so check out a secondary lo temp separator/fractional distillation. At this temp oil becomes a problem so remove/isolate it and the problem is gone. As Grizzly mentioned above moisture is also a problem at this temp but be careful not to cook it under an evacuation. Look at a chemical desiccant. I have only worked on a few -70degC systems. Also check out the load match including refrigerant velocity.

Quote:

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Originally Posted by Tesla

Hi bcfruc
for this type of system you will need to use a more efficient oil separator - it appears the oil is causing a blockage. The system will need to separate around +99% of the oil so check out a secondary lo temp separator/fractional distillation. At this temp oil becomes a problem so remove/isolate it and the problem is gone. As Grizzly mentioned above moisture is also a problem at this temp but be careful not to cook it under an evacuation. Look at a chemical desiccant. I have only worked on a few -70degC systems. Also check out the load match including refrigerant velocity.

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Thanks Telsa. I have been onto the seperator supplier and it turns out the seperator installed in the machine was the wrong one. When machine is not under load too much oil is escaping out into the system.

Fair play and thanks for your help. Hopefully thats it.