Ice slush
Ice slurry ( English ice slurry ) is a heat transfer medium and consists of a mixture of small ice particles (0.01-0.5 mm), water and a freezing point lowering agent such. B. ethanol , salt or glycol . Heat carriers are usually referred to as cold carriers if they are intended for use below 0 ° C.
properties
Ice slush as a coolant has the following properties:
- high specific heat capacity or large specific enthalpy of fusion
- large heat transfer coefficient
- easy to pump
- non-toxic (especially systems with table salt or ethanol)
- Due to the high heat capacity, the flow speed in the system can be reduced by half
- this reduces the pump output by a quarter
- the heat exchangers require no or only minor modifications
- It is possible to simply increase the performance of existing systems by using ice slush
- No ice storage and heat exchanger required, the storage ice is pumped directly as a coolant
- Ice slush in direct contact cools faster and more gently than flake ice
Ice slush is an environmentally friendly coolant with a high energy density because the melting enthalpy of the ice ( latent heat ) is also used. In contrast to conventional coolants or brine systems, the formation of ice particles is therefore intentional.
In contrast to the mixture of water and antifreeze as a single-phase refrigerant, ice slush is a two-phase refrigerant. When the temperature drops, a partial separation takes place, and small spherical ice particles with a diameter of approx. 0.01 to 0.1 mm are formed, surrounded by an increasingly concentrated anti-freeze solution, so that ice slurry is present just above the solidification temperature.
In order to counteract solidification through the connection of the ice crystals, the ice slurry must always be kept in motion; for example, storage vessels are to be equipped with stirring devices. The lower the application temperature, the higher the required proportion of antifreeze (of course only up to the eutectic ).
literature
- Michael Kauffeld, Masahiro Kawaji, Peter W. Egolf (Eds.): Handbook on Ice Slurries. Fundamentals and Engineering. International Institute of Refrigeration, Paris 2005, ISBN 2-913-149-44-8 .
- Fluidized Bed for Ice Slurry Production . (Project at Delft University of Technologies).