CANNON Instrument Company | Appendix II: Choosing a Temperature Bath Liquid
Appendix II: Choosing a Temperature Bath
Liquid
The ideal bath liquid would possess low viscosity, high heat capacity, and low vapor pressure over a
wide range of temperatures. In addition, the liquid should have a very high flash point and be relatively
low in cost. If the fluid is for use in a kinematic viscosity bath where it is necessary to view the
instruments through the bath liquid, then it is important for the liquid to be clear and provide high
visibility. Unfortunately, no single fluid meets all these requirements. When selecting a fluid, keep the
following guidelines in mind as shown in Table 6.
Table 6: Ideal Bath Liquid
Viscosity
Should be low so moderate stirring can effectively eliminate temperature
gradients in the bath.
Heat Capacity
Temperature gradients in the bath are less rapid with a high heat capacity.
With the exception of water, most choices for bath fluids will have about the
Volatility
A liquid with a low vapor pressure will require more frequent replenishment.
Further, rapid evaporation at the bath surface produces a cooling effect,
making temperature control more difficult.
Because no single fluid can be used at all possible bath temperatures, the choice of a suitable fluid must
begin by establishing the temperature range over which the bath will be operated. Refer to Table 7 for a
list of operating temperature ranges and suitable bath liquids for use in these ranges.
Table 7: CT-2000 Bath Fluid Options (10 °C to 150 °C)
Isopropyl alcohol, low-viscosity silicones
Water, low-viscosity oils, silicones (Dow 200 fluid, 1 cSt)
60 °C to 135 °C
White oils with oxidation inhibitor, IBF oil, Silicones (DOW 200
fluid, 20 cSt)
Silicones (Dow 200 fluid, 20 cSt)
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