Bitzer ST-140-2 Mode D'emploi page 65

8 Variant: refrigerant cooled external oil coolers (thermosiphon oil cooling)
Thermosiphon oil cooling is based on the principle of gravity circulation of refrigerant on the high pressure side.
Features:
• independent of other heat transfer fluids (air / water), therefore universally applicable
• efficient and economical, especially at higher capacity
• in contrast to liquid injection without negative influence on performance and reliability
• however: special system design required, e.g. the condenser must be installed above the oil cooler
For oil cooling, refrigerant is branched off from the accumulator and fed directly into the lower oil cooler. In counter-
flow to the hot oil, part of the liquid refrigerant evaporates under heat absorption. As a two-phase mixture, it flows
back to the condenser inlet either directly or via the accumulator. (In the design with accumulator, the liquid part is
separated). The evaporated part is then liquefied again in the condenser when mixed with the discharge gas flow.
To ensure gravity circulation, the liquid line to the oil cooler must have a certain height difference: A defined excess
pressure can be achieved through the liquid column, which must be higher than the sum of the pressure losses in
the pipes, oil cooler and condenser. If necessary, a refrigerant pump or injector can be used to support circulation.
A modulating oil mixing valve controls the oil temperature. An alternative is the regulated refrigerant supply to the
oil cooler.
The following illustrations show examples of design variants of thermosiphon circuits. Each system must be calcu-
lated and designed individually. Data is available in the BITZER SOFTWARE and the Technical Information
ST-500 . Detailed calculation documents are available on request.
ST-140-2 // PDF Download 65