Table of Contents
SiEN34-705
3.2.6 Vacuum Drying
What is vacuum
Vacuum drying is:
drying?
"The use of a vacuum pump to vaporize (gasify) the moisture (liquid) inside the pipes and expel
it leaving the pipes completely dry inside."
At 1 atm (760 mmHg) the boiling point (evaporating temperature) of water is 100°C but if a
vacuum is created inside the pipes using a vacuum pump then the boiling point is rapidly
reduced as the degree of the vacuum is increased. If the boiling point is reduced to a level
below that of the ambient temperature then the moisture in the pipes will evaporate.
When outside temperature is 7.2°C
As shown in the table on the right, the degree
of vacuum must be lowered below –752mmHg.
The evacuation of air conditioner piping provides the following effects.
1. Vacuum drying
2. Removes air and nitrogen (used in air-tightness test) from the inside of pipes.
Therefore, it is necessary to ensure that the both purposes have been achieved in the vacuum
drying operation.
General Information
Key points
Lower the degree of vacuum to below –755mmHg
Boiling point
of water (°C)
∗mmHg
40
–705
30
–724
26.7
–735
24.4
–738
22.2
–740
20.6
–742
17.8
–745
15.0
–747
11.7
–750
→
7.2
–752
0
–755
Above figures (mmHg) are gauge pressure readings.
Required degree
of vacuum
Outside
temperature
range
Evaporation
point
Temperature
(C°)
(V1216)
Installation
Pressure
Pa
Torr
7333
55
4800
36
3333
25
3066
22
2666
20
2400
18
2000
15
1733
13
1333
10
1066
8
667
5
39
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