!
Filling
17
10. Filling with Bath Liquid
The selection of the proper bath liquid (heat transfer liquid)
influences the capacity of a temperature control unit deci-
sively. The technical data with special emphasis on the tem-
perature accuracy was established in accordance with
DIN 58 966 (water at 70
°
C).
The temperature accuracy will decrease the higher viscosity
of the heat transfer liquid and the lower its heating capacity
is.
It is difficult to arrive at valid statements which can be applied
as a general rule as the length of the hoses, the volume and
the material of the connected systems have a great influence
on this accuracy.
The heating up and the cooling down time of a system to be
temperature controlled can be influenced by the bath liquid
too. Oil, for instance, cuts this time in half when compared to
water.
10.1 Recommended bath liquids
5 to 95
°
C
Distilled Water
•
Normal tap water leads to calcareous deposits neces-
sitating frequent unit decalcification.
Calcium tends to deposit itself on the heating ele-
ment. The heating capacity is reduced and service
life shortened!
•
Water, of course, can be employed up to 95
°
C, howev-
er above 80
°
C water vaporization reaches a level
which necessitates the liquid to be constantly replenis-
hed.
–30 to 80
°
C
Water with Antifreeze
In applications below 5
°
C the water has to be mixed with an
antifreeze. In doing so, the amount of antifreeze added
should cover a temperature range 10
°
C lower than the oper-
ating temperature of the particular application. This will pre-
vent the water from gelling (freezing) in the area of the evap-
orating coil the surface area of which is much colder than the
working temperature. An excess of antifreeze deteriorates
the temperature accuracy due to its high viscosity.
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