# Surface treatment knowledge

Humidity: Humidity refers to the amount of moisture in the air. Physical definition: Air humidity is a physical quantity used to express the amount of water vapor in the air or the degree of air humidity.
Relative humidity: The ratio of the humidity of the actual air to the humidity when it reaches saturation at the same temperature.

unit:%

Relative humidity (RH) = Ma/Mg * 100% / t

Ma = the amount of water in the air

Mg = the maximum volume of the air that can contain water

t = temperature

The water saturation of the same volume of air changes with temperature. The higher the temperature, the higher the water saturation of the air.

Absolute humidity: The ratio of the mass of water vapor in the air to the total volume of humid air.

Dew point temperature: The temperature at which humid air with a mixing ratio of γ is saturated with water under a given pressure. The saturated vapor pressure of water at this temperature is equal to the vapor partial pressure of humid air with a mixing ratio of γ.

Dew point: refers to the temperature at which saturated water vapor in the air begins to condense. When the relative humidity is 100%, the temperature of the surrounding environment is the dew point temperature. The lower the dew point temperature is than the temperature of the surrounding environment, the lower the possibility of condensation, which means that the drier the air, the dew point is not affected by temperature, but affected by pressure.

Saturated water vapor pressure: The pressure generated under saturated air. The saturated water vapor pressure indirectly reflects the water vapor pressure in the atmosphere and is a coefficient of temperature. The higher the temperature, the more water molecules are contained in the air; on the contrary, the less.

Saturation difference: Under certain temperature conditions, the difference between saturated water vapor pressure and the actual water vapor pressure at that time, indirectly indicates the water vapor content in the air, in hPa. d=E-e, d=0, r=100%. When discussing the intensity of water surface evaporation, the saturation difference is often used, because the size of the saturation difference indicates the evaporation capacity of water. The higher the temperature, the greater the saturation difference, the stronger the evaporation; the lower the temperature, the smaller the saturation difference, and the slower the evaporation. .

Mixing ratio: The ratio of the mass of a certain gas contained in humid air to the mass of dry air that it coexists.

Specific humidity: The ratio of the sub-volume of water vapor in humid air to the sub-volume of dry air.

Volume ratio: The ratio of the number of moles of water vapor to the total number of moles.

Mole Fraction of Water Vapor: The ratio of the number of moles of water vapor to the total number of moles.

Water vapor partial pressure: the pressure when the water vapor in the moisture (volume V, temperature T) exists alone under the same V and T conditions.