It is typically plotted as the abscissa (horizontal axis) of the graph.The term comes from the Greek psuchron () meaning cold 1 and metron () meaning means of measurement.
In human terms, our thermal comfort is in large part a consequence of not just the temperature of the surrounding air, but (because we cool ourselves via perspiration) the extent to which that air is saturated with water vapor. Such substances include cotton, paper, cellulose, other wood products, sugar, calcium oxide (burned lime) and many chemicals and fertilizers. Industries that use these materials are concerned with relative humidity control in production and storage of such materials. Ashrae Psychrometric Chart #1 Trial Applications ItIn many industrial applications it is important to avoid condensation that would ruin product or cause corrosion. Wood destroying fungi generally do not grow at relative humidities below 75. The term dry-bulb is customarily added to temperature to distinguish it from wet-bulb and dew point temperature. In meteorology and psychrometrics the word temperature by itself without a prefix usually means dry-bulb temperature. Technically, the temperature registered by the dry-bulb thermometer of a psychrometer. The name implies that the sensing bulb or element is in fact dry. WMO provides a 23-page chapter on the measurement of temperature. The value indicated by a wet-bulb thermometer often provides an adequate approximation of the thermodynamic wet-bulb temperature. Speeds up to 5,000 ftmin (60 mph) are best but it may be dangerous to move a thermometer at that speed. Errors up to 15 can occur if the air movement is too slow or if there is too much radiant heat present (from sunlight, for example). Ashrae Psychrometric Chart #1 Manual Operation ToA sling psychrometer requires manual operation to create the airflow over the bulbs, but a powered psychrometer includes a fan for this function. Knowing both the dry-bulb temperature (DBT) and wet-bulb temperature (WBT), one can determine the relative humidity (RH) from the psychrometric chart appropriate to the air pressure. Usually the level at which water vapor changes into liquid marks the base of the cloud in the atmosphere hence called condensation level. So the temperature value that allows this process (condensation) to take place is called the dew point temperature. A simplified definition is the temperature at which the water vapour turns into dew (Chamunoda Zambuko 2012). However, in psychrometrics, the term quantifies the total volume of both the dry air and water vapour per unit mass of dry air. This property of air-water vapor systems simplifies drying and cooling calculations often performed using psychrometric relationships. The ASHRAE -style psychrometric chart, shown here, was pioneered by Willis Carrier in 1904. It depicts these parameters and is thus a graphical equation of state.
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