The third way of putting cold inside an insulated box is to turn liquid carbon dioxide into snow inside it. Liquid CO2 under pressure is released through a nozzle, part of it turns to snow as the pressure drops, and the snow cools by sublimating like dry ice.
| Method | Where the cold comes from | What it requires |
|---|---|---|
| Eutectic plate | Phase change | Freezer, time, plate fleet |
| Dry ice | Sublimation | Supply chain, ventilation |
| CO2 snow | Snow formed by pressure drop | Liquid CO2 line, nozzle |
Filling takes seconds, but the site needs a liquid CO2 tank, a line and a filling point,. For a plant that already uses CO2 in food processing the cost table changes; if cold transport is the only reason, a comparison of plates and dry ice usually comes out better.
The snow turns to gas at -78.5 °C just as dry ice does and collects in a closed space. In a case reported by the CDC, a driver carrying dry ice in a closed cab lost consciousness within minutes. Ventilate the filling point, train staff and do not open the box in a closed room.
