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 What is relative humidity? 

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What is relative humidity?

何謂相對濕度

Relative humidity define the ratio of vapor density (pressure) and saturated vapor density (pressure) in the same temperature. 

For example:
The maximum capacity of vapor quatity is 100 units in a certain volume at 25 ℃ . There are only 50 units vapor in the volume. The relative humidity is equal to 50%.

(50/100)*100%=50%RH

If there are 95 units vapor in the volume. The relative humidity is equal to 95%. The air is so wet that some electrical products may be demage.

(95/100)*100%=95%RH 

Saturation Vapor Pressure

Temperature

Saturation Vapor Pressure

C

F

mmHg

Pa

g/m3

-20

-4

0.8

106

0.84

-10

14

1.9

252

2.00

0

32

4.6

611

4.85

10

50

9.2

1,227

9.40

20

68

17.5

2,338

17.3

30

86

31.8

4,245

30.4

40

104

55.4

7,381

51.1

50

122

92.6

12,345

82.8

60

140

149.5

19,934

129.7

70

458

233.8

31,179

196.9

80

176

355.3

47,377

290.8

90

194

525.9

70,121

418.4

100

212

780.0

101,325

588.6

Phase diagram of water

Vapor pressure of saturated salt in water

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