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7 General Operation
Example:
The final depth of Dow Corning 710 silicone oil in the bath tank is to be 9.2
inches when heated from 25 to 300°C. What should the starting depth be?
Expansion coefficient for 710 oil on Table 2, K= 0.00077 inch/inch/°C
Ending temperature, T
E
= 300°C
Starting temperature, T
S
= 25°C
Ending depth, D
E
= 9.2 inches
D
S
= 9.2/[0.00077 (300-25) + 1] = 7.59 inches
7.1.6 Electrical Resistivity
Electrical resistivity describes how well the fluid insulates against the flow of
electric current. In some applications, such as measuring the resistance of bare
temperature sensors, it may be important that little or no electrical leakage oc-
cur through the fluid.
In such conditions choose a fluid with very high electrical resistivity.
7.1.7 Fluid Lifetime
Many fluids degrade over time because of vaporization, water absorption, gel-
ling, or chemical break-down. Often the degradation becomes significant near
the upper temperature limit of the fluid, substantially reducing the fluid’s
lifetime.
7.1.8 Safety
When choosing a fluid always consider the safety issues associated. Obviously
where there are extreme temperatures there can be danger to personnel and
equipment. Fluids may also be hazardous for other reasons. Some fluids may
be considered toxic. Contact with eyes, skin, or inhalation of vapors may cause
injury. A proper fume hood must be used if hazardous or bothersome vapors
are produced.
Warning: Fluids at high temperatures may pose danger from BURNS,
FIRE, and TOXIC FUMES. Use appropriate caution and safety equip-
ment.
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 at which there is sufficient vapor given off so that
when there is adequate oxygen present and an ignition source is applied the va-