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8.1.4 Thermal Conductivity
Thermal conductivity measures how easily heat flows through the fluid. Ther
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mal conductivity of the fluid affects the control stability, temperature unifor
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mity, and probe temperature settling time. Fluids with higher conductivity
distribute heat more quickly and evenly improving bath performance.
8.1.5 Thermal Expansion
Thermal expansion describes how the volume of the fluid changes with temper
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ature. Thermal expansion of the fluid used must be considered since the in
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crease in fluid volume as the bath temperature changes may cause overflow.
Excessive thermal expansion may also be undesirable in applications where
constant liquid level is important. Many fluids including oils have significant
thermal expansion.
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
resistivity.
8.1.7 Fluid Lifetime
Many fluids degrade over time because of evaporation, 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 conditions of extreme hot or cold there can be danger to people
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 va
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pors are produced.
Warning: Fluids at high temperatures may pose danger from BURNS,
FIRE, and TOXIC FUMES. Use appropriate caution and safety equip
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ment.
Fluids may be flammable and require special fire safety equipment and proce
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dures. An important characteristic of the fluid to consider is the flash point. The
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8 General Operation