Basic concept of maximum temperature, humidity and

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Basic concept of temperature, humidity and dew point

· partial pressure of water vapor · relative humidity · dew point

· frost point · absolute humidity · mixing rate

· wet bulb temperature · ppm · equilibrium relative humidity

· water activity · enthalpy

expression method of water content is used for solids or liquids in most cases. When used in gas, this concept is not applicable

water vapor pressure (PW)

refers to the water vapor pressure in the air or gas, which is more deeply used in new energy, household appliances, building materials and other emerging fields

saturated water vapor pressure (PWS)

the maximum pressure in water vapor at a specific temperature. The higher the temperature, the more water vapor the air can withstand

relative humidity (RH)

refers to the ratio of water vapor partial pressure and saturated water vapor pressure at a specific temperature, which is expressed in percentage:%rh=100%* (pw/pws). The relative humidity is greatly affected by temperature. Pressure also changes relative humidity. For example, at room temperature, if the pressure is doubled, the relative humidity will be doubled

dew point temperature (TD)

refers to the temperature at which saturated water vapor in the air begins to condense, that is, the temperature of condensation

at 100% relative humidity, the ambient temperature is equal to the dew point temperature. The lower the dew point temperature is than the ambient temperature, the smaller the possibility of condensation, and the drier the air is. The dew point is not affected by temperature, but by pressure

frost point temperature (TF)

if the dew point temperature is lower than the frosting temperature, sometimes we use the concept of frost point

below 0 ℃, the frost point is always a little higher than the dew point, because the water vapor saturation pressure of ice is different from that of water

absolute humidity (a)

refers to the weight of moisture in a unit volume of wet air at a temperature and pressure. It is usually expressed in grams per cubic meter. Sometimes it is easily confused with mixing rate

mixing ratio (x)

is the weight ratio of steam to dry gas. It is usually expressed in grams per kilogram of dry gas, which is mainly used in the drying process or ventilation system. It is used to calculate the water content when the weight flow of air is known

wet bulb temperature (TW)

traditionally, the wet bulb temperature is displayed by wrapping the thermometer with a sheath. Wet bulb temperature and ambient temperature are used to calculate relative humidity and dew point temperature


is the ratio of water vapor to dry gas or total (wet) gas. Sometimes used to indicate low humidity, using mass/volume or mass/weight

equilibrium relative humidity (ERH)

refers to the relative humidity value of air when there is no net change in humidity. Manual hydraulic pressure shows that it is open-loop control

water activity (AW)

similar to equilibrium relative humidity, low carbon steel will yield when tightening, with a range of 0... 1, rather than 0%... 100%

enthalpy (H)

refers to the energy required for the dry gas at 0 ℃ to reach the current state. It is mostly used in air conditioning calculation

Vaisala has introduced a variety of mature technologies to the market, which can measure relative humidity, temperature and dew point. Some products also have built-in calculation functions to output other parameters. The probe, sensor and transmitter are used to measure humidity. The probe contains sensors and is firmly installed on the transmitter or connected with cables; The transmitter outputs signals, and the core part is the sensor. Vaisala designs and produces many kinds of sensors

· humicap - measure relative humidity

· dryicap - measure low dew point

· dewcap - measure high-precision dew point

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