In winter, we will see a common phenomenon. Due to the low outdoor temperature, the humid and hot indoor air will condense on the window glass, making the window glass blurred. If we observe and study carefully, if we turn on the dehumidifier indoors to gradually remove the humidity in the room, even though the outdoor temperature is still the same, we will find that the dew on the window glass will gradually disappear, and the window glass will be heavy again. Reveal the essence of transparency and cleanliness.
If the outdoor temperature drops at this time, when the temperature drops to a certain level, although the dehumidifier has made the indoor air very dry, there will still be a fuzzy dew layer on the window glass. This phenomenon shows that the condensation temperature on the glass is related to the moisture content of the atmosphere in which the glass is located. Further research has found that this relationship is a one-to-one correspondence, that is, each condensation temperature (we call it the dew point temperature) corresponds to the environment A value for the moisture content of the atmosphere.
The dew point can be simply understood as the temperature at which the water vapor content in the gas reaches the saturation state, and is one of the ways to express the humidity of the gas; it can be seen that the dew point temperature is a unit system for measuring the moisture content of the gas. The dew point analyzer is an instrument that measures the moisture content in a gas based on this unit system.
In summary, the object measured by the dew point meter is inseparable from gas, and the corresponding gas is nothing more than three uses: power gas, medium gas and ambient gas
As a power source, power gas is supplied to pneumatic instruments and pneumatic equipment, and is widely used in industrial fields and industrial sites with special explosion-proof requirements.
As a process medium, or participate in process reaction, or as a protective gas, or as a standard gas, the medium gas is widely used in the corresponding production process in modern industry. As a process environment, it is widely used in civil industry and In the relevant technological environment of the military industry.
A. Electrolysis method:
That is, the moisture absorbed by the desiccant is electrolyzed into hydrogen and oxygen through the electrolytic cell and discharged. The electrolysis current is proportional to the moisture content, and the humidity of the sample gas can be measured by detecting the current. This method makes up for the shortcomings of the gravimetric method. The measurement range can reach below -80℃, and the accuracy is good, and the price is low; the disadvantage is that the gas path of the electrolytic cell needs to be dried for a long time before use, and it is corrosive and clean to the gas The requirements are higher.
B. Vibration frequency method:
It is to replace the desiccant in the gravimetric method with a hygroscopic quartz crystal. According to the characteristics of different vibration frequencies when the crystal absorbs water and the quality of the crystal is different, let the sample gas and the standard dry air flow through the crystal, thus producing different vibration frequency differences. △f1 and △f2, the humidity of the sample gas can be obtained by calculating the difference between the two frequencies. This method has the same advantages as the electrolysis method, and it does not need to be dried before use.
Application of dew point meter
Application 1: Chilled mirror dew point meter participates in environmental control
In pharmaceutical factories, electronics factories, cigarette factories, textile factories, factories and many other controlled environments, a large number of relative humidity sensors are used to monitor environmental humidity parameters. Affected by environmental factors and the material properties of the sensor itself, capacitive relative humidity sensors are in danger of drifting, which makes the humidity of some key process links not 1**% controlled.
The principle of cold mirror is Z’s basic humidity measurement method, which directly measures the dew point. The advantages of the chilled mirror dew point meter are high accuracy, fast response, quick response, good repeatability, and can achieve “zero” drift; through the chilled mirror dew point meter to participate in environmental control, we can have full confidence in ensuring the humidity parameters of the key links All in control.
Application 2: Chilled mirror dew point meter establishes humidity standards
Due to the above mentioned humidity sensor drift problem, many companies (pharmaceutical factories, electronics factories, cigarette factories, textile factories) that use a large number of temperature and humidity sensors are faced with heavy and trivial calibration tasks; establishing a complete , Accurate and reliable internal humidity calibration system used to be the dream of many companies. Now this dream that seemed expensive in the past has become possible, enabling companies to calibrate humidity sensors anytime and anywhere while having a highly confident humidity standard.
Application 3: Control the working efficiency of the rotary dryer
The lithium-ion battery assembly workshop and the medicine drying process all use rotary dryers to dry the air below the dew point of -40-60°C. The rotary dryer regenerates by heating the dry air. The heating temperature determines the efficiency of the drying and is also an energy-consuming link. By closely monitoring the dew point value of the dry air, thereby adjusting the regeneration temperature of the rotary dryer, energy saving can be achieved under the premise of ensuring that the humidity requirements are met.
Application 4: Compressed air drying device
After compressed air is compressed, the dew point value will rise, causing moisture to be easily condensed out, causing damage to the compressed air system.
By drying the compressed air, the dew point of the compressed air can be reduced. The usual method is to dry by a double-column drying device. The double-column drying device consists of two drying columns filled with desiccant. When one of them is working, the other will regenerate the desiccant by heating or depressurizing. By monitoring the dew point of the output compressed air, the switch between the two drying columns can be adjusted reasonably, so that the operation can achieve the purpose of energy saving.
Application 5. Natural gas purification plant, gas filling station, transportation, drying, LNG receiving/revaporization device
Compressed air dew point sensor
Dew point sensor working principle
Dew point meter for compressed air
Dew point of air at atmospheric pressure