The room has a relative humidity of 68% at a temperature of 18 ° C.

The room has a relative humidity of 68% at a temperature of 18 ° C. After a while, the window glass fogged up. To what temperature was the glass cooled?

Data: t (temperature in the specified room) = 18 ºС; φ (relative humidity) = 68% = 0.68.

Constants: ρp (density of saturated vapors) = 15.4 g / m3.

1) Absolute air humidity: ρ = φ * ρp = 0.68 * 15.4 = 10.472 kg / m3.

2) Glass cooling temperature: the table “saturated water vapor pressure and its density” shows that the glass should have cooled slightly less than 12 ºС (ρ = 10.7 g / m3).

Answer: The glass in the indicated room has cooled slightly below 12 ºС.