298 94 307/02 Untersuchungen zum Stand der Umsetzung des ...

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rect evaporation systems that the enthalpy of the refrigerant is lower. It is precisely at this
point that the new binary ice system comes in:
Whereas water exhibits an enthalpy (differential) of 25 kJ/kg at a temperature difference
of 6 K, and glycol brine approx. 23 kJ/kg, binary ice with an ice concentration of 10% has
an enthalpy (differential) of 33 kJ/kg at 10% of 66 kJ/kg and at an ice concentration of
20% and 6 K temperature difference ("runback accentuation") of approx. 90 kJ/kg.[?]
The higher enthalpy can be utilised advantageously from the following viewpoints:
• Refrigerated transportation: In order to achieve a specific level of refrigeration dur-
ing transportation, in terms of binary ice, a considerably lower quantity of fluid needs to be
transported, since the melting enthalpy inherent in the ice is very high.
As a result, the energy expenditure required for transfer pumping the refrigerant is lower.
In addition, utilisable enthalpy is increased if there is an additional runback accentuation.
• Cold storage: Generally, ice is excellently suited as a storage medium. In this re-
gard, the utilisable enthalpy difference of binary ice manifests itself in modest storage vol-
umes.
The largely constant temperature of binary ice allows its utilisation temperature to be set
higher than in the case of brine. This contributes to energy savings.
• Utilisation temperature: A further significant advantage, for example in relation to
utilisation in supermarkets in terms of "plus range refrigeration" (refrigerated food cabinets
with temperatures of between +2 0 C and +6 0 C), lies in the fact that, in binary ice systems,
at the surface of the air coolers, temperatures need not be as low as in conventional sys-
tems with direct evaporation or indirect cooling through brine.
As a result, much less water is expelled from the re-circulated air of the refrigerated food
cabinet.
This water is extracted to a substantial degree from the stored products, which can ad-
versely affect their quality.
Through the lower water precipitation and higher surface temperature at the
heat exchanger, there is less or no build-up of ice in binary ice systems on the heat
transfer lamellas, on the basis of which energy and investment cost expenditure in terms
of defrosting fall away or are only required at large time intervals.