Furnace Core - Fluke 9116A User Manual

A brief description of the functions of the buttons follows:
SET - Used to display the next parameter in a menu and to store parameters to
the displayed value.
DOWN - Used to decrement the displayed value of parameters.
UP - Used to increment the displayed value.
EXIT - Used to exit from a menu. When "EXIT" is pressed any changes made
to the displayed value are ignored.
4.2

Furnace Core

The furnace core consists of the heater, insulating materials, heat pipe, heat
pipe support blocks, and the housing with water cooling. Refer to Figure 1 on
page 10.
The heater is embedded in a fiber ceramic insulating block. A hollow section
through the center contains the heat pipe.
The heat pipe is a double wall Inconel cylinder containing sodium. The mini-
mum working temperature of the Sodium heat pipe is about 500°C. The heat
pipe must be heated slowly (about 1-2 hours) to this temperature. The tempera-
ture may then be raised more quickly to the desired set-point. When the work-
ing temperature is achieved, the sodium circulates throughout the tube
providing a uniform temperature. The heat pipe has a lifetime of many years.
Do not use the heat pipe unnecessarily at high temperatures which reduces the
lifetime. Refer to the Section 5 for more information.
CAUTION: In the unlikely event that the heat pipe should leak, do not at-
tempt to put out the fire with water or chemical fire extinguishers. Smother the
fire with dry soda ash in accordance with the MSDS sheets at the end of this
manual.
The heat pipe is centered in the heating element and supported by means of fi-
ber ceramic blocks. One block fits into the bottom of the heat pipe and a second
fits over the top centering the heat pipe in the heater assembly. The top block
also supports the control HTPRT and cutout thermocouple. The heat pipe is
shipped separately since its weight would damage the heater and supports if it
were in place during shipment.
The entire heater and heat pipe assembly are contained and supported by a
sheet metal housing. Copper cooling coils are attached to the outside of this
housing. These cooling coils allow some of the heat lost to be removed from
the lab area reducing the lab heat load. They are accessible on the rear of the
furnace chassis (see Figure 5).
Air is circulated through the gap surrounding the furnace core. This keeps the
chassis cool. Do not shut off the furnace while at high temperatures or the fan
will turn off allowing the chassis to become hot. Alternatively, if used, the wa-
ter cooling could remain on until the furnace is cool.
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