Originally Posted by
Nico
The design with the connection to the pump and with the expansion valve that you refer to makes sence to me Tycho.
Proper control under various conditions, easy to calculate and posibility to distribute to several compressors.
I would do it that way too.:)
However, I like to know about the "troublesome" design where the density of the oil and refrigerant are crusial for proper working of the oil rectifier.
This is what I understood design wise so far (see attached drawing).
I have understood the idea is this (please correct me if I am wrong):
We look at a running system, at least one compressor is running, motor valve V04.02 is open for >15%, solenoid V07.02 is open.
Refrigerant with oil will flow into heat exchanger H07.04 and temperature of the refrigerant/oil mix starts rising.
Refrigerant boils off and that gas returns to the compressor through the piping on top.
The concentration of the refrigerant with oil goes up, until it reaches the maximum miscibility for that refrigerant with that oil at that temperature and that pressure.
If more refrigerant is boiled off than the we will see separated oil and depending the density of the oil and refrigerant it will be on top or on the bottom.
We assume that the refigerant is heavier than the oil and thus oil starts floating on top of the refrigerant.
As this process continues, the liquid level in the heat exchanger rises because the density of the liquid is less in this leg of the communicating vessels.
If we assume that the density of the oil is 0.9kg/dm3 and that of the refrigerant is 1.3kg/dm3, than the difference in height will be like 45% of the height of the oil colomb on top of the refrigerant/oil mix.
So when there is 1m oil floating on top of the refrigerant/oil mix, than the level in H07.04 is 0.45m higher than in the separator.
So far so good, but now what?
Should the oil level reach the outlet of the heat exchanger at this point so that the oil flows to the compressor?
In that case the suction line should not be like on my drawing but at the same level as the liquid in the separator which I think is not a good idea.
How do I get that oil up say two meters up to the main suction line?
Should I install a check valve in the liquid supply, e.g. after V07.04 so that the pressure in the heat exchanger can rise to push the oil into the suction line (like with a coffee machine)?
That might work I think.
I could make a branch somewhere high in the heat exchanger and pipe that straight to the compressor suction with a solenoid valve to open when that compressor is running.
The level in the separator must always be the same for this system, e.g. HP float valve arrangements not allowed, am I correct?
It won't be easy to calculate the capacity of this recitifier.
It must be sensitive for variations in separator level
It must be sensitive for density:
>different refrigerants have digfferent densities (although syntetic refrigerants are mostly 1.3-1.4kg/dm3)
>some refrigerants like CO2 have very different densities at different emperatures
>different oil have different densities too, from AB oil (0.9kg/dm3) to PAG (1.05kg/dm3)
Hence, the design is good for one specific refrigerant oil combination at specific conditions?
Does anyone have a P&ID or mechanical drawing of a proven good working system?