2. Guideline for each installation process
29 _ Heat pump 50Hz/R410A
Part 3 Design and installation
2.7. Vacuum drying work
2.7.1 What is Vacuum drying?
Vacuum drying is : The use of a vacuum pump to vaporize(gasify) the moisture (liquid) inside the pipe and expel it leaving
the pipes completely dry inside.
At 1 atm(760mmHg) 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.
Example
When outside temperature is 11.7°C as shown in the table on the right
, the degree of vacuum must be lowered below -750mmHg
The evacuation of air conditioner piping provides the following effects.
- Vaccum drying
- Removes air and nitrogen(used in air-tightness test) from the inside
of pipes.
Therefore , it is necessary to ensure that both purposes have been
achieved in the vacuum drying operation.
Boilng point of
water(°C)
40 -705 7,333 55
30 -724 4,800 36
26.7 -735 3,333 25
24.4 -738 3,066 22
22.2 -740 2,666 20
20.6 -742 2,400 18
17.8 -745 2,000 15
15.0 -747 1,733 13
11.7 -750 1,333 10
7.2 -752 1,066 8
0-7556675
The degree
of a vacuum
Pressure
mmHg Pa Torr
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