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8.1.10.1
Water
Water is often used because of its very low cost, availability, and excellent tem-
perature control characteristics. Water has very low viscosity and good thermal
conductivity and heat capacity which makes it among the best fluids for control
stability at low temperatures. Temperature stability is much poorer at higher
temperatures because water condenses on the lid, cools and drips into the bath.
Water is safe and relatively inert. The electrical conductivity of water may pre-
vent its use in some applications. Water has a limited temperature range, from a
few degrees above 0C to a few degrees below 100C. At higher temperatures
evaporation becomes significant. Water used in the bath should be distilled or
softened to prevent mineral deposits. Consider using an algicide chemical in the
water to prevent contamination.
8.1.10.2
Ethylene Glycol
The temperature range of water may be extended by using a solution of 1 part
water and 1 part ethylene glycol (antifreeze). The characteristics of the ethylene
glycol-water solution are similar to water. Use caution with ethylene glycol
since the fluid is very toxic. Ethylene glycol must be disposed of properly.
8.1.10.3
Methanol
Methanol or methyl alchohol is often used at low temperatures below 0C.
Methanol is relatively inexpensive, has good control characteristics, and has a
low freeze point. Methanol is very toxic so care must be taken when using and
disposing of this fluid.
8.1.10.4
Mineral Oil
Mineral oil or paraffin oil is often used at moderate temperatures above the
range of water. Mineral oil is relatively inexpensive. At lower temperatures
mineral oil is quite viscous and control may be poor. At higher temperatures
vapor emission becomes significant. The vapors may be dangerous and use of a
fume hood is highly recommended. As with most oils mineral oil will expand
as temperature increases so be careful not to fill the bath too full that it over-
flows when heated. The viscosity and thermal characteristics of mineral oil is
poorer than water so temperature stability will not be as good. Mineral oil has
very low electrical conductivity. Use caution with mineral oil since it is flam-
mable and may also cause serious injury if inhaled or ingested.
8.1.10.5
Silicone Oil
Silicone oils are available which offer a much wider operating temperature
range than mineral oil. These oils are more expensive as well. For information
on silicone oils contact Fluke Calibration.
General Operation
23
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