Chemglass CG-1972-65 - Manual (Page 15)

15
Heating Liquids. Each power level is associated with a volume range, which acts as a guide when
heating solutions with heating mantles. When solutions are heated with heating mantles set the power
switch to the range that includes the volume of solution being heated [Note: this switch is set to the
volume of solution, not the size of the flask]. For example to heat 250 ml of toluene to 80
o C in a 1 L
round bottomed flask choose the third power setting (50 - 500 ml) since the solution volume falls within
this range. There are situations when a power level other than that indicated by the front panel should be
used:
Example Power Setting Explanation
80 ml toluene
100 ml flask
100 ml heating mantle
SP = 80
o C
50 - 500 ml
(25% power)
Organic solvents heated to ≈ 50 - 110
o C are set to the volume
range on the front panel. When choosing between 2 power
settings (i.e. 80 ml also falls within both the 10 - 100 ml range
and the 50 - 500 ml range) choose the higher setting.
80 ml collidine
100 ml flask
100 ml heating mantle
SP = 170
o C
300 ml - 2 L
(50% power) Even though the solvent volume is less than the range of this
power setting, it should be used because high temperatures
require additional power.
80 ml water
100 ml flask
100 ml heating mantle
SP = 80
o C
300 ml - 2 L
(50% power) While the setting 50 - 500 ml would work, since the heat
capacity of water is twice that of a typical organic solvent
(1 cal/g/
o K), a higher power setting can be used to
compensate for the higher heat capacity.
125 ml toluene
1 L flask
1 L heating mantle
SP = 80
o C
10 - 100 ml
(10% power) When the heating mantle size is substantially larger (≥ 5X)
than the volume being heated (i.e. the heating mantle has
excess heating capacity for the volume being heated), a lower
power setting gives better control.
150 ml toluene
250 ml flask
250 ml heating mantle
SP = 35
o C
10 - 100 ml
(10% power) Even though the solvent volume isn’t included in this power
setting, it should be used because low temperatures are better
regulated with less power.
Avoid switching between the different power levels while the controller is heating. Specifically, do not
initially set the controller on a high power level to rapidly heat the solution, and decrease the power level
to the correct setting as the solution approaches the set point. Changing power levels doesn’t damage the
controller, but it will reduce its heating performance.
Heating Equipment. Two factors need to be considered when heating equipment (ovens, hot plates,
furnaces, HPLC columns, etc.); (1) placement of the temperature sensor (Section 2.4) and, (2) the
appropriate power setting. The best guide to the correct power setting for various pieces of equipment is
the researcher's experience. If your best guess is that the equipment needs 1/3 full power to heat to the set
point, set the power switch on the 300 ml - 2 L setting (i.e., 50% power, it’s usually better to have too
much power rather than too little). If the heater heats too slowly, increase the power (to the >2 L setting),
if it heats too fast or has excessive overshoot, decrease the power (to the 50 - 500 ml setting). If the
amount of power seems to be adequate, but the heater doesn’t heat with stability, the controller probably
needs to be tuned (see Section 2). Section 3.8 shows the type of performance you should expect from the
controller with different pieces of equipment.