Definitions
Dry-bulb temperature (DBT)
• The dry-bulb temperature (DBT) is
the temperature of air measured by a
thermometer freely exposed to the air, but
shielded from radiation and moisture. DBT is
the temperature that is usually thought of as
air temperature, and it is the true
thermodynamic temperature.
Wet-bulb temperature
Wet bulb temperature is the lowest temperature to
which air can be cooled by the evaporation of
water into the air at a constant pressure. It is
therefore measured by wrapping a wet wick
around the bulb of a thermometer and the
measured temperature corresponds to the wet
bulb temperature.
Humidity
• Humidity is the amount of water vapour in the
air. If there is a lot of water vapour in the air,
the humidity will be high. .
• Relative humidity is the amount of water vapour
actually in the air, expressed as a percentage of
the maximum amount of water vapour the air
can hold at the same temperature.
humidity ratio
• The specific humidity or humidity ratio of an
air sample is the ratio of the weight of water
vapor contained in the sample compared to
the weight of the dry air in the same sample.
• Or
• Humidity ratio is the ratio of weight of
moisture to the weight of dry air in the air–
vapor mixture
Dew point
• The dew point is the temperature to which air
must be cooled -at constant pressure- in order to
achieve a relative humidity (RH) of 100% (become
saturated with water vapor). At this point the air
cannot hold more water in the gas form, then
when cooled further , the water vapor will
condense to form liquid water (dew).. ...
The higher the dew point rises, the greater the
amount of moisture in the air
Specific Enthalpy
• Specific Enthalpy is the total energy in a
system due to pressure and temperature per
unit of mass in that system. Specific
enthalpy is used in thermodynamic equations
when one wants to know the energy for a
given single unit mass of a substance. The SI
units for specific enthalpy are kJ/kg (kilojoules
per kilogram).
Specific volume
• Specific volume is the ratio of a
material's volume to its mass, which is the
same as the reciprocal of its density. In other
words, specific volume is inversely
proportional to density.
Latent and Sensible Heat
• Latent and sensible heat are types of energy
released or absorbed in the
atmosphere. Latent heat is related to changes
in phase between liquids, gases, and
solids. Sensible heat is related to changes in
temperature of a gas or object with no change
in phase.
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