Fluke 7312, Руководство пользователя

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8.1.4 Thermal Conductivity
Thermal conductivity measures how easily heat flows through the fluid. Ther-
mal conductivity of the fluid affects the control stability, temperature unifor-
mity, and 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 much the volume of the fluid changes with
temperature. Thermal expansion of the fluid must be considered since the in-
crease in fluid volume as the bath temperature increases may cause overflow. It
may be dangerous to permit the fluid to overflow the tank. It may also cause
loss of valuable bath fluid. Excessive thermal expansion may also be undesir-
able in applications where constant liquid level is important.
Thermal expansion coefficients of several fluids are shown in Table 2, Table of
Bath Fluids. Fluid manufacturers can also provide this information. The ther-
mal expansion coefficients are shown in units of cm/cm/°C, however, the values
are the same for any units of length. Divide the value by 1.8 for °F coefficients.
The following equation may be used to find the desired depth:
De = Ds [K(Te-Ts)+1]
Or
Ds = De/[K(Te-Ts)+1] where De < or = The Maximum Fill Depth
Where:
K=Expansion coefficient
Te=Ending Temperature
Ts=Starting Temperature
De=Ending Depth
Ds=Starting Depth
The maximum fill depth is typically 0.5 to 0.8 inches below the level of the
gasket at the top of the bath tank (not the top of the bath lid). Judgment must be
made with different stirring arrangements to prevent splashing on the gasket or
lid of the bath.
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, Te=300°C
Starting temperature, Ts=25°C
Ending depth, De=9.2 inches
7312 TPW Maintenance Bath
User’s Guide
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