Ashrae psychrometric chart sea level
It is typically the y-axis, the vertical axis, of the graph. Humidity ratio (also known as moisture content, mixing ratio, or specific humidity) is the proportion of mass of water vapor per unit mass of dry air at the given conditions (DBT, WBT, DPT, RH, etc.).Note: the notion that air "holds" moisture, or that moisture dissolves in dry air and saturates the solution at some proportion, is an erroneous (albeit widespread) concept (see relative humidity for further details). Lines of constant RH reflect the physics of air and water: they are determined via experimental measurement. RH is dimensionless, and is usually expressed as a percentage. Relative humidity ( RH) is the ratio of the mole fraction of water vapor to the mole fraction of saturated moist air at the same temperature and pressure.It duplicates information available via other humidity properties and the saturation curve. The dewpoint temperature is measured easily and provides useful information, but is normally not considered an independent property. At this saturation point, water vapor would begin to condense into liquid water fog or (if below freezing) solid hoarfrost, as heat is removed. Dew point temperature ( DPT) is that temperature at which a moist air sample at the same pressure would reach water vapor saturation.
The slope of the line of constant WBT reflects the heat of vaporization of the water required to saturate the air of a given relative humidity. The WBT is the same as the DBT when the air sample is saturated with water.
In practice, this is the reading of a thermometer whose sensing bulb is covered with a wet sock evaporating into a rapid stream of the sample air.
Mixtures of air and water vapor are the most common systems encountered in psychrometry. The psychrometric ratio is an important property in the area of psychrometrics as it relates the absolute humidity and saturation humidity to the difference between the dry bulb temperature and the adiabatic saturation temperature. Humid heat is the constant-pressure specific heat of moist air, per unit mass of dry air. k y = convective mass transfer coefficient, kg m -2 s -1.h c = convective heat transfer coefficient, W m -2 K -1.It may be evaluated with the following equation : where: The psychrometric ratio is the ratio of the heat transfer coefficient to the product of mass transfer coefficient and humid heat at a wetted surface. The most common system of interest, however, are mixtures of water vapor and air because of its application in heating, ventilating, and air-conditioning and meteorology. The principles of psychrometry apply to any physical system consisting of gas-vapor mixtures.