@DNOVA THS_R410A-IOM-1304-E
10
4
THS - Evacuation and Charging Operations
This type of work must be carried out by qualified personnel only trained to do their job in
accordance with current laws and regulations.
4.1
Introductions
The simultaneous presence of liquid and vapour makes it necessary for both to be in a state of saturation ( Gibbs law ),
as shown in Fig. 3). In conditions of thermal equilibrium, the pressure in the tank corresponds to the T of the surrounding
environment; a withdrawal of refrigerant charge will cause pressure drops, which will be associated with:
•
.. withdrawal of refrigerant charge: .... pressure drop inside the tank;
•
.. pressure drop inside the tank: ........ T drop & change of status;
•
.. T drop & change of status: .. .......... evaporation of part of the liquid, causing a cooling down of the liquid;
•
cooling of liquid:
thermal exchange with ambient air, further evaporation of remaining liquid;
the original pressure in the tank will be restored after a certain period of time.
Fig. 3
Gibb’s law diagram
4.2
Full vacuum and charge of the unit
Vacuum cycle
In general it is better to apply a “long” rather than a “hard” vacuum: reaching a low pressure too abruptly may in fact
cause that any remaining humidity evaporates instantaneously, thus freezing part of it.
Fig. 4
Vacuum cycle diagram
The Fig. 4 represents a vacuum cycle and an optimal subsequent pressure rise for the refrigeration devices we
manufacture. Generally in bigger refrigeration systems or if there is a suspicion of an extensive quantity of humidity in the
refrigeration circuit, the vacuum needs to be “broken” by using anhydrous nitrogen. Then the steps of evacuation need to
be repeated as described before. This operation facilitates the removal of remaining and/or frozen humidity during the
evacuation process.
P
Enthalpy h
T tank/ambient
Saturated gas
Saturated
liquid
P [Pa]
Time
200 s
6
150
