- NOTES ON TEMPERATURE CONTROL

Superpressure

NOTES ON TEMPERATURE CONTROL
   

Temperature in reaction vessels may be controlled manually or automatically

by controlling the current in the electric heating jackets or the vessels.
The heating jackets in reaction vessels have two or more interlaced elements wound in parallel. Unless otherwise specified, two-element heaters controlled manually with a three-heat switch are furnished with the jacket.
With the Switch in "High" position, both heater elements are connected in parallel to give full wattage; with the switch in "Medium" position, one heater element only is turned on to give half wattage; in "Low" position, both heater elements are in series to give quarter wattage.
When the customer specifies that a variable-voltage transformer (auto-transformer) or automatic controller is to be used, we will provide tagged leads so that these instruments can be readily connected by the customer.
When a variable-voltage transformer is connected as shown above, one element of the heating jacket is turned on or off as required, the other element being controlled by the transformer.
Where automatic control is desired, an automatic indicating controller may be used, or where temperature record is required, an automatic recording controller may be used. Since the circuit operating the controller is independent of the heater circuit, one voltage may be used to operate the controller and another voltage may be used in the heater circuit.
When using an indicating or recording controller, and with the 3-heat switch in the "High" position, both heater elements are connected in parallel through the controller. With the switch in the "Medium" position, both heater elements are connected in series through the controller. By using this method, close control can be obtained at all temperatures.

 
It has been found that very close temperature control can be obtained by providing two thermocouples-one for control and one for indicating or recording. The control thermocouple is inserted in a slot in the inner shell of the heating jacket of a reaction vessel so that it lies between the heating elements and the outside wall of the reaction vessel. This control thermocouple is connected to an automatic temperature controller which is set for a temperature somewhat higher than the temperature inside the reaction vessel. To compensate for heat losses, a pencil-type or pipe-type thermocouple should be used for control.
A second thermocouple may be inserted in the reaction vessel thermowell to indicate or record the actual temperature of the reactants.

control as close as 1°C

may be obtained by this arrangement.