User manual

27
General Operation
Stirring
Freezing Point: The freezing point of a fluid is an obvious limitation to stir ring. As
the freezing point is approached high viscosity may also limit performance.
Pour Point: This represents a handling limit for the fluid.
Viscosity: Points shown are at 50 and 10 centistokes viscosity. When viscosity is
greater than 50 centistokes stirring is very poor and the fluid is unsatisfactory for bath
applications. Optimum stirring generally occurs at 10 centistokes and below.
Fume Point: A fume hood should be used. This point is very subjective in na ture and
is impacted by individual tolerance to different fumes and smells, how well the bath is
covered, the surface area of the fluid in the bath, the size and ventilation of the facility
where the bath is located and other conditions. We as sume the bath is well covered at
this point. This is also subject to company policy.
Flash Point: The point at which ignition may occur. The point shown may be either
the open or closed cup flash point. Refer to the flash point discussion in Section 8.2.8.
Boiling Point: At or near the boiling point of the fluid, the temperature stabil ity is
difficult to maintain. Fuming or evaporation is excessive. Large amounts of heater
power may be required because of the heat of vaporization.
Decomposition: The temperature may reach a point at which decomposition of the
fluid begins. Further increasing the temperature may accelerate decomposi tion to the
point of danger or impracticality.
Stirring 8.3
Stirring of the bath fluid is very important for stable temperature control. Prior to
taking measurements, always make sure that the bath is stirring the fluid. The fluid
must be mixed well for good temperature uniformity and fast controller response. The
stirrer is adjusted for optimum performance. Table 4 on page 28 shows nominal stirrer
motor settings for several fluids.
Note: If the bath is used with the probe basket removed, stir motor settings need
to be changed so that a small vortex can be seen in the liquid. If any water is
mixed with oil when exceeeding temperatures of 90°C the bath will boil over.
Warning: Do not mix water and oil when exceeding temperatures of 90°C