What Is the Frost Point?

Frost point is also called dew point, which refers to the temperature at which air is isobarically cooled to below 0 ° C, so that the water vapor [on the ice surface] in the air reaches saturation, and also the temperature at which water vapor condenses into frost.

The frost point is also called the dew point (above 0 ° C, the temperature when the air is saturated with water vapor due to cooling is called the "dew point temperature"), which means that the air is cooled at isostatic pressure to below 0 ° C, so that the water vapor (on the ice surface) in the air reaches The temperature at saturation also refers to the temperature at which water vapor condenses into frost. [1]
Frost point is the abbreviation of "Frost Point Temperature", and it is one of the methods for expressing air humidity. Under the condition that the water vapor pressure is not changed, the air temperature is reduced to a temperature when the ice surface is saturated, that is, at the sub-zero temperature, the current water vapor pressure is regarded as the corresponding temperature when the ice surface is saturated with water vapor pressure. It can be directly measured with a frost point meter, or it can be obtained based on the water vapor pressure check table or calculation at that time. The frost point temperature is generally lower than the dew point temperature and decreases with height. [2]
Frost
1. The frost point range generated by the Swsy-S low frost point humidity generator device can be extended to -80 ° C, and the accuracy is slightly better than that of the secondary precision dew point meter, that is, the uncertainty of the dew point is 0.15 ° C (between -70 and -50 ° C ), Suitable for the calibration of commonly used cold mirror or other types of dew point hygrometers (dew point range: -80 20 , dew point uncertainty 2 3 ). It can be compared with a first-class precision dew point meter when tracing the source, and it can basically cover the measurement verification requirements of the dew point hygrometer in the military industry when the value is transferred. [9]
2.The hybrid method humidity generator requires a dry gas source in terms of the principle of humidity generation. This device overcomes the disadvantages of most previous drying devices such as large volume, large mass, and high temperature of the frost point of the output gas. The method has the advantages of small volume, small mass, reusable and easy to carry, and the temperature of the output dry air frost point can reach below -70 ° C. [10]
3. In heat pump systems, frosting is a common phenomenon in system operation. When the surface temperature of the outdoor heat exchanger is lower than the air dew point temperature, water vapor in the air will condense; when the temperature is lower than 0e, the condensation on the surface of the evaporator will form frost. The increase in the thickness of the frost layer on the surface of the evaporator not only causes a large additional thermal resistance on the wall of the tube, but also narrows the air passage on the coil and increases the resistance to the flow of air. As a result, the heating capacity of the heat pump is greatly reduced, and the evaporator capacity Significantly decreased, fan power consumption increased, and working conditions deteriorated. At the same time, it may cause accidents. Therefore, research on frost point control will change this situation. [11]

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