Sublimation of solid CO2 dry ice for cooling at low temperatures below -50°C.

A research project of ILK Dresden will be presented. The natural substance carbon dioxide is used as working substance for special refrigeration applications in the temperature range below -50°C. For carbon dioxide the use of the sublimation (that means transition from solid to gaseous phase) is necessary, since the triple point is -56.6°C. The basic idea to reach low temperatures is to use the sublimation heat of dry ice in a similar manner like the evaporation in a usual compression refrigeration process. Two fundamental directions of development will be shown: 1. Sublimation of solid carbon dioxide in a surrounding gas phase: The cooling capacity is provided directly at the sublimator heat exchanger. Because of the relatively poor heat transfer in the gas phase for this sublimation, variant new technologies had to be developed in order to reach the best possible refrigeration performance. 2. Sublimation of solid carbon dioxide in a liquid: An advantageous heat transport is possible via the liquid phase. For this purpose a suitable fluid had to be found. This fluid must meet the requirements for optimal sublimation and refrigeration performance at low temperatures. Additionally this fluid must not be flammable.