Cost; Commonly Used Fluids; Water (Distilled); Ethanol - Fluke 7380 User Manual

WARNING: Fluids at high temperatures may pose danger from BURNS,
FIRE, and TOXIC FUMES. Use appropriate caution and safety equip-
ment. Read the MSDS sheets.
Fluids may be flammable and require special fire safety equipment and proce-
dures. An important characteristic of the fluid to consider is the flash point. The
flash point is the temperature where there is sufficient vapor given off that
when sufficient oxygen is present and an ignition source is applied, the vapor
ignites. This does not necessarily mean that fire is sustained at the flash point.
The flash point may be either of the open cup or closed cup type. Either condi-
tion may occur in a bath situation. The closed cup temperature is always the
lower of the two. The closed cup represents the contained vapors inside the
tank and the open cup represents the vapors escaping the tank. Oxygen and an
ignition source are less available inside the tank.
The soft cutout should be set to meet the temperature limits of the selected
fluid.
Environmentally hazardous fluids require special disposal according to applica-
ble federal or local laws after use.
8.1.9

Cost

Cost of bath fluids may vary greatly, from cents per gallon for water to hun-
dreds of dollars per gallon for synthetic oils. Cost may be an important consid-
eration when choosing a fluid.
8.1.10

Commonly Used Fluids

Below is a description of some of the more commonly used fluids and their
characteristics.
8.1.10.1

Water (Distilled)

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 0°C to a few degrees below 100°C. At higher temperatures
evaporation becomes significant. Water used in the bath should be distilled or
softened to prevent mineral deposits. Consider using an algaecide chemical in
the water to prevent contamination.
8.1.10.2

Ethanol

Denatured ethanol (ethyl alcohol) is often used at lower temperatures between
–80°C and 10°C. It has good viscosity over its range and is inexpensive. Toxic-
8 General Operation
Heat Transfer Fluid
27