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[mark beiser]

The vending machine and automotive systems that use CO2 are transcritical cycles, they don't actually condense the CO2 refrigerant.
Liquid in any part of the cycle would be very very bad for the equipment.

[icemeister]

The vending machine and automotive systems that use CO2 are transcritical cycles, they don't actually condense the CO2 refrigerant.
Liquid in any part of the cycle would be very very bad for the equipment.

This is partly true, since in a transcritical cycle when the heat rejection is done, there is no condensing going on as would be the case in a subcritical system. This is why a transcritical "condenser" is called a gas cooler.

There is a liquid phase present in the transcritical cycle but it occurs after the expansion device during expansion when the pressure drops below the critical point, creating a two phase flow to the evaporator where the liquid is boiled off. The CO2 refrigerant then enters the compressor slightly superheated.

Here's a very good explanation from Danfoss:

http://www.ra.danfoss.com/TechnicalI...0%28CO2%29.pdf

This a video produced by Danfoss which shows CO2 phase changes and also gives a little historical background of CO2 refrigeration, which was first introduced way back in 1850 and peaked in the 1920s.

http://video.google.com/videoplay?do...81612782948466

[mark beiser]

Here's a very good explanation from Danfoss:

http://www.ra.danfoss.com/TechnicalI...0%28CO2%29.pdf

Thanks, that is just a little bit more informative than the 8 year old ACHR News article I was looking at.
For a while I was sort of following how things were playing out in Europe with the vending and automotive CO2 stuff, but never really dug into the details of what is going on at each point in the cycle.

Then I lost interest in it.

[SolarMike]

Many of the fridgies in Europe complain about CO2 systems blowing up in supermarkets, pretty dangerous. Most of the mini-splits over there are CO2 as well as the govt is forcing the phaseout of anything with a high global warming potential.

Most new domestic fridges are Propane also.

[coolerik]

We got a few CO2 Supermarkets out this way, but from what I understand they are running a secondary refrigerant (glycol or whatever) would love to learn more about it.. Couple guys on here have some experience with these systems, there is even pictures.. i cant remember where.

[jpsmith1cm]

Many of the fridgies in Europe complain about CO2 systems blowing up in supermarkets, pretty dangerous. Most of the mini-splits over there are CO2 as well as the govt is forcing the phaseout of anything with a high global warming potential.

Most new domestic fridges are Propane also.

The reasons for those blowouts were bad joining procedures.

[SolarMike]

The reasons for those blowouts were bad joining procedures.

Very true....

[Control Man]

they are running a secondary refrigerant

http://www.coldsystemsllc.com/co2-refrigeration.html