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
8.1.6
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 electri-
cal resistivity.
8.1.7
Fluid Lifetime
Many fluids degrade over time because of vaporization, water absorption, gel-
ling, or chemical breakdown. Often the degradation becomes significant near
the upper temperature limit of the fluid, substantially reducing the fluid’s
lifetime.
8.1.8
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 or adequate ventilation system. 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 where there is sufficient vapor given off that
when adequate oxygen is present and an ignition source is applied the vapor ig-
nites. 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 open cup flash point is measured under
the condition of vapors escaping the tank. The closed cup flash point is mea-
29
8 General Operation
Heat Transfer Fluid
