68
Degassing an externally closed application
Danger!
If heating too fast, it is possible by having varying boiling point liquids in the thermal
fluid, that sudden boiling can occur in the lowest boiling point fluid. An exit of hot fluid
through the expansion vessel is the result. Also, the hot remnants of low boiling point
fluids will accumulate in the expansion vessel. Due to expansion and material flow of
the hot thermal fluid a temperature sensor notes the increasing temperature in the
expansion vessel. A passive cooling device prevents too high temperatures in the
expansion vessel and therefore protects the thermal fluid. Depending on the type and
quantity of the low boiling point fluids, it is possible that the expansion vessel reaches a
temperature >70°C. Under the menu point
Over-temperature Prot.
the tripping
temperature of the over temperature sensing can be extended to 100°C in Degassing
mode (in normal mode the maximum temperature is limited to 70°C). Be careful of the
hot surface of the expansion vessel under this condition. Suitable precautionary
measures should be made (contact protection, warning indications).
Water should never be used as thermal fluid, not even with anti-freeze solutions. Please
note that some thermal fluids can be hygroscopic (absorb moisture). The effects of this
can be seen as the working temperature of the fluid drops. Carrying out the degassing
procedure above can remove this water from the thermal fluid. Typical boiling points
are: water e.g. 100°C, and ethanol 68°C.
Hygroscopic problems can also be avoided by using an inert gas blanket in the
expansion vessel. An accessory sealing kit can be obtained from Huber (Sealing kit
#6523).
NOTE!
-
If the heat transfer fluid is changed from one with a lower boiling point to one
with a higher boiling point, then residues from the first fluid will boil off causing
vapours in the fluid circuit. The vapours can form bubbles in the fluid line
causing a drop in fluid pressure. This can cause a safety cut off of the machine.
When degassing the bubbles collect in the pump housing, pass into the
expansion vessel (18) and then escape through the expansion vessel cap / filling
port on the top of the vessel (22, 17) as vapour.
-
After cleaning, filling, and air-purging the unit and application as described in
chapters
Changing thermal fluid / Internal cleaning
and
Filling an externally
closed application
select the
Degassing
option by pressing the
Start&Stop
function from the main menu.
-
Start temperature control, and the degassing program.
-
Increase the set-point in steps (say 10K each step) up to the maximum operating
temperature. After each step, wait until the temperature in the expansion vessel
has approximately stabilised. This should avoid fluid over-flowing the expansion
vessel, due to large vapour bubbles escaping quickly from the system.
-
Once the expansion vessel has cooled back down to ambient temperature, the
degassing process is complete.
-
Deactivate the degassing program and stop temperature control.
-
Drain of the expansion vessel and fill in new, clean thermal fluid.
