Definitions
In cooling, it is common to work with [mass flow rate/flow work] qm (in kg/s or kg/h) because the [volume flow rate] qv (in m3/s or m3/h) are variable according to the temperature (1 kg of air increases in volume with a rise in temperature).
DRY BULB TEMPERATURE in °C: the real
temperature of humid air observed through a thermometer or a temperature
sensor. It is the air temperature indicated by thermometer not affected by the
air’s humidity.
WET BULB TEMPERATURE in °C: it is the
temperature recorded by a thermometer whose bulb is covered by a wick soaked in
water. Humid temperatures are always inferior to dry temperatures and only when
the relative humidity is at 100% can both temperatures be identical.
ADIABATIC SATURATION
TEMPERATURE: it is the temperature where the humid air can attain
adiabatic saturation through the evaporation of water, that is to say the humid
temperature (no gain or loss of the heat [to the environment]).
DEW POINT TEMPERATURE
in °C: it is the temperature from which the water vapor contained in
humid air starts to condense when in contact with a cold surface. During
cooling, the humidity ratio and the partial pressure of the water vapor remain
constant.
HUMIDITY RATIO or moisture content,
mixing ratio, specific humidity: it is the mass of water (liquid, solid, vapor)
contained on a kg of dry air. This water weight remains constant when the
relative temperature varies without falling below the dew point temperature. If
the temperature falls below the dew point temperature, a part of this water
mass will condense into droplets on the coldest surfaces.
RELATIVE HUMIDITY in %: it is the [level]
of the water vapor mass contained in a certain quantity of humid air and the
mass of vapor that it could contain if it was saturated at the same
temperature. At 100%, the air is completely saturated. At 50%, the air contains
half of what it could if it was saturated at the same temperature. When the
humidity level reaches 100%, droplets of liquid form on objects.
SPECIFIC VOLUME in m3/kg of air: it is the volume occupied by the weight of a kilogram of dry air in a set of specific conditions.
[VOLUMIC MASS] in kg/m3 of humid air: it is the mass of a m3 of humid air. The pressure of the mixture (dry air + water vapor) is equal to the sum of the pressure that each constituent might have if it was alone occupying the entire volume. Therefore, in one m3 of humid air, we can find the sum of the constituent masses; it is the sum of [volumic] masses of dry air, water vapor, [to] partial pressure and designated temperatures.
ENTHALPY: total energy (heat)
contained in a specific weight of humid air (by convention, considered to be
nul to 0°C). Enthalpy includes perceptible and latent heat contained in the
air.
LATENT HEAT: perceptible heat is
the heat (energy) in the air due to the air’s temperature. Latent heat is the
heat (energy) in the air due to the air’s humidity. Afterwards, the air with
the same quantity of energy can be hot dry air (high perceptible heat) or
refreshed humid air (high latent heat).
Vapor pressure (Pv): It is the
partial vapor in the air. This pressure is the same as the saturating vapor
pressure at dew point temperature.
Saturating vapor
pressure (Pvs): it is the maximal vapor pressure that the air can tolerate at a
given temperature. The saturating vapor pressure increases with the
temperature.
Complementary Definitions
SHF (Sensible Heat
Factor) – ratio of perceptible heat and total heat.
By-pass factor: this factor is a
function of physical characteristics of the [battery] and the expected
functioning conditions. It is considered that it represents the percentage of
air that passes through the [battery] without being altered.
Adiabatic cooling: cooling takes place
almost in parallel to the adiabatic curves in the [psycrometric] diagram. This
cooling is called “adiabatic cooling”. This is the case when water is misted
into fine droplets in a space, without heat input at the same time; the energy
necessary for evaporation is taken from the surrounding air.
