humidity and dew point
DESCRIPTION
HUMIDITY AND DEW POINT. Humidity. amount of water vapor in the air. Specific Humidity. ACTUAL amount of water vapor in the air at a given time and place Units - g of water vapor / Kg of air. Saturated Air At a steady temperature the amount of water vapor is at it’s peak (maximum) - PowerPoint PPT PresentationTRANSCRIPT
HUMIDITY HUMIDITY AND AND
DEW POINTDEW POINT
Humidity amount
of water vapor in the air
Specific Humidity ACTUAL
amount of water vapor in the air at a given time and placeUnits - g of
water vapor / Kg of air
Saturated AirAt a steady temperature the
amount of water vapor is at it’s peak (maximum)
Rate of condensation = Rate of evaporation
• Dependent on air temperature• Higher the air temp. - greater
the amount of water vapor in the air
• Water vapor in air doubles every 10°C
Dew Point The temperature at
which air is cooled to become saturated and condensation begins
More water vapor in the air
Less the air has to cool
Higher the Dew Point
weather.stives-town.info
Relative Humidity Comparison of the specific humidity and
the maximum amount of water vapor that the air can hold at a given temperature and pressureUNIT - %
Relative humidity = specific humidity X 100% maximum capacity
100% Rel. Hum. – saturated air0% Rel. Hum. – dry air
Psychrometer Instrument to
measure humidity
Dry bulb – measures air temp.
Wet bulb – has a water soak wick around the bulb – water evaporates – cools the air
Evaporation is a cooling process
Psychrometer
Dry air - greater evaporation - greater cooling - greater the difference in the 2
temperatures High humidity – no evaporation (saturated
air)- temperatures of the 2
bulbs will be the same or very close
Evaporation question
Why do you feel so hot and sticky on hot, humid days in the summertime?
Answer
High humidity means air has a lot of water vapor in it. Your body sweats but the water has no where to go so it stays on your body and you feel sticky and aren’t cooled by the evaporation of the sweat.