cryogenic cooling

[akubatova]

Hi,
I can cool GC either with CO2 or nitrogen, depending which valve system and coolant I get. Nitrogen cools more effectively at the same time consumption is higher. But is anybody able to give more specific estimates about consumption. I know this is depended on the frequency of use, but in general? If it is week for nitrogen tank what it is for CO2 when cooling to 5 °C?
Thanks

[GasMan]

Frequency of use should appear high in your choice. The problem with liquid nitrogen is that it will boil off even if you are not using it, whereas a liquid CO2 cylinder can be turned off. If you are not going to use your GC that often at 5'C, then go for CO2, otherwise I would go for liquid nitrogen.

As many GC's use air to cool down the oven by 'sucking' air in an inlet and blowing the hot air out through a vent, it is possible to put a heat exchanger on the inlet and pump coolant through it from a chiller. For your application at 5'C this would be ideal. Your comsumption then would be electricity for the pump and cooler. You will then not have the problem of the cryogenic supply running out in the middle of a run.........

Gasman