Dry ice (frozen CO2) is used in many applications throughout the world - all utilizing its unique heat transfer abilities. Compared to "wet" ice (frozen water), dry ice has the advantage of going through a double phase change - sublimation - directly from solid to gas, resulting in high energy exchange.
The thermodynamic properties of dry ice vary depending on type and wrapping. Blocks and pellets are the two most commonly used types of dry ice. The heat transfer ability for these two differs, mainly because of the varying surface areas.
Dry ice characteristics
Blocks have few heat exchanging surfaces and dense structural properties. This enables a slow, even and long-lasting heat transfer. Small blocks are referred to as bricks or slices.
Pellets have a larger heat-exchanging area due to its many surfaces. This enables faster sublimation and quicker absorption of heat.
Wrapping
Commercially, dry ice is available as wrapped and unwrapped. Wrapping works as insulation, slowing down the sublimation process of the dry ice. As different materials have different insulating properties, the type of wrapping used will influence the performance of the dry ice. The thicker the wrapping, the slower the heat transfer will be.
Envirotainer recommendations
Dry ice type
For Envirotainer dry ice containers, dry ice in blocks weighing between 2 and 7 kg are recommended. This will enable a stable heat transfer and allow the blocks to be loaded evenly in the dry ice bunker. Pellets and small slices will give a more sensitive set-up and may cause overcooling. The structural properties of pellets will also allow a lower amount of dry ice to be loaded into the dry ice bunker.
Wrapping
Both wrapped and unwrapped dry ice may be used in Envirotainer dry ice containers, but depending on ambient temperatures, seasonal recommendations allow optimised performance. The wrapping used should be only thin plastic or paper. Always remove the ice from cardboard boxes prior to loading into the dry ice bunker. For products to be kept in the temperature range of 2°C-8°C, the following is recommended:
- In ambient temperatures from +10°C to 25°C, use wrapped dry ice (winter)
- In ambient temperatures from +25°C to 40°C, use unwrapped dry ice (summer)
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