Thermosyphon oil coolers design data

[Mike W]

Hi,
We have a new system that uses a thermosyphon oil cool and are experiencing issues with it and have identified the issue to be insufficient height difference between the drain outlet of the condenser to the inlet connection on the receiver, this appears to be preventing the condenser from draining properly. We are having trouble finding any technical design data on how to calculate the required the required height before we carry out any modification. We have the Frick Thermosyphon oil cooling document but its a bit vague it this area ( condenser to receiver). Can some one please point me towards decent design data?

Spiral Freezer application
Ammonia,
Screw compressor 220 kW @ -41/ 35
108kW oil cooling load
Condenser 880kW ( sized for pull down )


best regards Mike.

[RANGER1]

Mike,
Is this a new system, has it worked before?
Does it have one condenser or two.

Have you 100% eliminated air from system, as air in condenser can upset the boat.

Also if no air purger installed have to be careful with inward leaks, as well as when servicing.

Normally height from thermosyphon receiver to oil cooler is more critical as the driving force.

[Grizzly]

Hi Mike.
I help look after a ammonia spiral freezer plant that Historically had intermittent starving of the Oil thermo syphon
Circuit.

What we did was have a preferential Pot fabricated. (imagine a crucifix shape)
Basically its a large bore pipe cylinder with the Horizontal liquid line from the condenser (before the Receiver) connected to its Left hand port.
With the liquid feed to the receiver on the opposite side. In between on the large pipe is a bulls eye sight glass.
Below these connections is 2/3rds of the pipe with original Thermo syphon connection now connected.

Basically the Thermo syphon pipe takes preference over the liquid line to the receiver.
Since fitting this probably 10 / 12 yrs ago (could even be longer?) the oil cooling circuit rarely stalls as it is now independent of the fluctuating Receiver levels and pressures.
I tried to find some photos but as yet I have not found any.
Good luck.
Grizzly.

[tfr1235]

As grizzly explains "always full" auxiliary container is missing
it is a pressure vessel that goes between the liquid outlet of the condensers and the receiving vessel
the liquid enters above, the outlet to the receiver is halfway (overflow), and the outlet for the oil coolers below
its function is to guarantee the provision of liquid to the oil coolers
Does the discharge line have a venturi installed?
Is the balance line correctly installed?

[Mike W]

Mike,
Is this a new system, has it worked before?
Does it have one condenser or two.

Have you 100% eliminated air from system, as air in condenser can upset the boat.

Also if no air purger installed have to be careful with inward leaks, as well as when servicing.

Normally height from thermosyphon receiver to oil cooler is more critical as the driving force.

The system is new and was fully evacuated and has an air purger, the issue we have is that the discharge pressure increases and eventually the system stops. It is also observed that when the system stops the receiver fills up and we believe that the liquid is not draining correctly from the condenser. We are looking into the vent line piping now.

The height from the receiver to the thermosyphon is 3.5 meters.

[RANGER1]

The system is new and was fully evacuated and has an air purger, the issue we have is that the discharge pressure increases and eventually the system stops. It is also observed that when the system stops the receiver fills up and we believe that the liquid is not draining correctly from the condenser. We are looking into the vent line piping now.

The height from the receiver to the thermosyphon is 3.5 meters.


No worries Mike.
So what size is the vent line at the moment.
Normally off top of liquid receiver, piped to inlet of condenser & reasonably sized, 80nb
Do you have 1 or more condensers, any "P" traps.

If you had a valve to atmosphere, you could temporarily run a line or hose to economiser or compressor suction to vent off top to see if helps.

[Segei]

It would be good to see piping.

[Josip]

It would be good to see piping.

Agree with Segei ...

Sounds something wrong with equalising-vent pipe (receiver-condenser/s) ...

Is it possible to upload schematic diagram ... ?

Best regards, Josip

[Mike W]

Agree with Segei ...

Sounds something wrong with equalising-vent pipe (receiver-condenser/s) ...

Is it possible to upload schematic diagram ... ?

Best regards, Josip


Hi
We reviewed design data from the IIAR and found that we have insufficient height from the condenser outlet to the receiver inlet, we should 4-5 feet PLUS the the liquid head equivalent of the pressure drop in the vent line. In the short term we have connected up the liquid injection until we can sort out the height issue.

Thanks for the feedback

Mike W

[mbc]

hi
minimum high is 2.4 m( 8 ft)
between thermosyphon and oil cooler
and capacity of that should be 5 minutes of work in total usage

[Segei]

Typically condenser outlet has P trap. From condenser liquid flow to thermosyphon receiver and overflow go to high pressure receiver. Sometimes thermosyphon and high pressure receivers are combined. IIAR mentioned about height of drop leg or P trap. This isn’t height difference between condenser and receiver.

[RANGER1]

Typically condenser outlet has P trap. From condenser liquid flow to thermosyphon receiver and overflow go to high pressure receiver. Sometimes thermosyphon and high pressure receivers are combined. IIAR mentioned about height of drop leg or P trap. This isn’t height difference between condenser and receiver.

Segei,
This sounds like a combined thermosyphon/ liquid receiver, so it would require the height of a drop leg & “P” trap to overcome condenser pressure, would you agree.

Balance line could not be oversized as well.

[Segei]

Yes I agree that they need certain height of P trap to prevent condenser flooding. However OP mentioned about height difference between condenser and receiver. Receiver should be just below the condenser to provide free liquid draining. Condenser can be located on the roof and receiver in compressor room. Height difference is significant. However if height of P trap is undersized condenser will be flooded.

[Josip]

Hi all,

I do agree with all numbers and advices from IIAR, ASHRAE etc...
all advices and numbers are for the best installation practice what
is not always possible to follow ... then we try to do our best for
given situation ... been there many times like many of you ...

An engineer cannot discuss or give proper advice
without ref. scheme of final installation with height differences.

I believe that piping layout between condenser, receiver together with
oil cooler is not good ... a lot "if" ....

OP asked for help/advice whatever, we would like to help, but without
complete information all this is "Old Wifes Tales"

Sorry if I sound impolite, but it is really hard to be helpful and do not know
anything about problem we try to discuss ...

I remember start up of one ammonia refrigeration plant in SA with ammonia
oil cooler (around year 2002. ... all piping executed "by the book" and after start up ...
compressor shutdown by high oil temperature ...
:confused: how is that possible ... (owner and his guests there and plant is not running - madness
.... but no other way then to check all ...
soon we found closed valve on vent pipe between oil cooler intermediate receiver and condensers ...
all valves were "Danfoss" with cap ... not possible to see valve position with installed cap.

Very funny today, but not in that time on site, believe me.


Best regards, Josip