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Vytux123
24-07-2009, 10:47 AM
I have a new project were oil cooling by thermosyphone would be very acceptable.

HSN8591-160 x3 units

Compressor model HSN8591-160
Refrigerant R404A
Evaporating SST -40°C
Condensing SDT 45°C
Operating mode ECO
Discharge gas temp. 80°C
Suct. gas superheat 10K
Oil volume flow 2.89 m³/h
Oil cooler outlet 48.8 °C
Oil cooler load 46.3 kW

But here I got the problem, because I can‘t find the tubing for refrigerant.
Other question is: What is the refrigerant boiling temperature in the thermosyphone?
I read the Bitzer manuals, but didn’t find the information I’m looking for.

Thank you in anticipate!!!

RANGER1
25-07-2009, 02:25 AM
Boiling point is same as saturated condensing pressure .

Can you explain what you mean by " I can't find the tubing for refrigerant " ?

Magoo
26-07-2009, 01:44 AM
As per RANGER1, what pipe size?. I would be inclined to lower the SDT to +40'C to reduce oil temp with thermosyphone oil cooling, the bitzer screws are fine at full load , but unloaded and they tend to cook the screw rotors, even with economizers. Been there done that, had to add suction liquid injection to sub-cool suction vapour at low load. Thermostically controlled on suction entering compressor.

Vytux123
29-07-2009, 06:40 AM
Thank you for answer RANGER1 an Magoo,
Excuse me for my language.
I wanted to ask how to calculate tubes for refrigerant circuit. Meaning diameters of liquid tube and diameter of gas tube.

What do you think about intermediate vessel for refrigerant between condenser and thermosyphone? is it necessary?

sterl
29-07-2009, 03:16 PM
Vessel of some form necessary for 3-compressors with 3-thermosyphon coolers but reservoir is often combined into HP receiver in the form of a weired section, at sufficient height to drive the T-Syphons.

T-Syphon exchangers make great oil stills and with R-404 you may have to figure out a sampler at the T-syphon heat exchanger to get oil back to compressor.

Though its not the easiest way: for 3-machines on an arrangement that will not grow in future, is often simplest to set up the HEX as a single cooler and circulate the oil from the separators to the cooler...You can even eliminate some of the "count" of oil filter (shells) in this manner.

Magoo
30-07-2009, 03:38 AM
Due to close approach between oil leaving temp and receiver liquid temp, the heat transfer between oil and refrigerant is based on actual surface area and vertical separation between thermosyphon oil cooler and receiver vessel.
Cannot figure your suggestion of an intermedaite vessel.
Another consideration is that the condenser has to accomodate the added oil heat of rejection with thermosyphone, alot of people forget that point.

Vytux123
30-07-2009, 08:10 AM
Good morning J
My idea about intermediate vessel is to make bigger pressure to the (gravity force) t-syphone oil cooler, but now I see, that there is possible to lift up the HP receiver for that proposes.
About condenser: I evaluated the increased heat rejection from oil cooler to condenser, I even a little bit oversized the condenser for liquid subcooling, and reducing pressure drop. By calculations I made it is good idea to have 3-5K liquid subcooling.
I would be interesting to see your opinion about liquid subcooling. The main idea of mine about liquid subcooling is increscent velocity of R404a gas to carry out oil from t-syphone heat exchanger.

As Sterl noticed I must avoid of oil stills in heat exchanger, so I begin to think about automatical oil draining from heat exchanger to liquid separator, o other suction line’s position.

It would be very interesting and useful to hear your opinion about the t-syphone systems with R404a refrigerant.
I made quit a lot systems with air and liquid oil coolers, but never with t-syphone. One of our customer has very good experience with t-system and R404a from the past.

Waiting for your comments very much!