Humidity refers to the degree of dryness and wetness of the air, that is, the physical quantity of water vapor contained in the air.[9]Contained in a certain volume of air at a certain temperaturesteamThe less, the drier the air is;steamThe more, the more humid the air is.The degree of dryness and wetness of the air is called "humidity".In this sense, commonly usedAbsolute humidity, relative humidity, comparative humidityMixing ratio、Saturation differenceas well asthe dew pointAnd other physical quantities;If in wet steamsteamThe percentage of the weight of the steam in the total weight (volume) of the steam is called the humidity of the steam.The humidity that the human body feels comfortable is: the relative humidity is less than 70%.
Humidity, generally atmeteorologyThe middle refers toair humidity, it isatmosphereinsteamContent of.In airliquid stateorsolid stateIs not included in the humidity.Air without water vapor is calledDry air。Since the water vapor in the atmosphere can account for 0% to 4% of the air volume, the composition of various gases in the air generally refers to the composition of these components in dry air.
The degree of dryness and wetness of air, or the physical quantity indicating the amount of water vapor contained, is called humidity.The mass of water vapor contained in unit volume of air is called absolute humidity.Because it is difficult to directly measure the density of water vapor, it is usually expressed by the pressure of water vapor.The absolute humidity of the air does not determine the speed of water vapor on the ground and people's sense of humidity.The absolute humidity of the air at a certain temperature and the percentage of saturated pressure at the same temperature are called relative humidity.[1]
Water vapor pressure(formerly known asAbsolute humidity）It refers to the pressure of water vapor in the air, and the unit is hPa, taking one decimal place;
relative humidityUsing the ratio of the actual water vapor pressure in the air to the saturated water vapor pressure at the temperature at that timepercentageMeans, integer;
Dew point temperatureIt refers to the temperature when cooling reaches saturation under the condition of constant water vapor content and air pressure in the air, expressed in degrees Celsius (℃), taking one decimal place.WithHygrometerIt can also measure the continuous record of relative humidity and the minimum relative humidity.
Representation
HygrometerMultiple quantities are used to indicate the humidity of the air.The most commonly used ones are listed below:
Dew point is used forMeasuring humidityThis instrument is called a hygrometer.
Humidity unit
RH is relative humidity, which is defined by dew point temperature.Interpretation of the term "humidity": It is stipulated in the metrology method that humidity is defined as "the quantity of physical image state".The humidity in daily life refers to relative humidity,% rh.In general, that is, the amount of water vapor (vapor pressure) contained in the gas (usually air) is the same as the amount of saturated water vapor in the air（saturation vapor pressure ）Percentage of.
Absolute humidity
Absolute humidity refers to the content ofsteamThe unit is generally g/m3.The maximum absolute humidity is the maximum humidity under saturated condition.Absolute humidity is meaningful only with temperature, because the amount of humidity that can be contained in the air changes with temperature, and the absolute humidity is also different at different temperatures, because the volume of air changes with temperature.However, the closer the absolute humidity is to the maximum humidity, the smaller its change with temperature.
The following is the formula for calculating absolute humidity:
A hygrometer is recording the relative humidity. Relative humidity is the ratio between absolute humidity and maximum humidity. Its value shows how high the saturation of water vapor is.Air with a relative humidity of 100% is saturated.The relative humidity is 50%, and the air with the same temperature isSaturation pointHalf ofsteam。Water vapor in the air with relative humidity over 100% is generally condensed.As the temperature increases, the air can contain more water, that is to say, the relative humidity will decrease when the temperature rises with the same amount of water vapor.Therefore, it is necessary to provide temperature data while providing relative humidity.Dew point can also be calculated from relative humidity and temperature.
formula
The formula for calculating relative humidity is as follows:
Specific humidityIs the quality of water in the air andMoist airThe ratio between the masses of.If no condensation or evaporation occurs, the specific humidity of a closed air at different heights is the same.The symbol of the highest specific humidity under saturated condition is S.
The following is the calculation of specific humiditysFormula of:
Electrical characteristic method of chemical substances
Ionic crystal condensation hygrometer
The commonly used instruments for measuring humidity are wet and dry bulb thermometers,Hair hygrometer(meter) and resistance humidity gauge, etc.
a) DryWet bulb thermometer: Use a pair of thermometers with the same shape installed in parallel, one to measure the air temperature and weigh the dry bulb thermometer, and the other one to weigh the wet bulb thermometer with absorbent gauze soaked in distilled water.When the air is not saturated, the wet bulb will consume heat due to surface evaporation, which will reduce the wet bulb temperature.At the same time, the wet bulb continuously gets heat supply from the air flowing through the wet bulb.When the heat consumed by the wet bulb due to evaporation is in balance with the heat obtained from the surrounding air, the wet bulb temperature will no longer continue to decline, resulting in a dry wet bulb temperature difference.The difference between dry and wet bulb temperatures is mainly related to the air humidity at that time.The smaller the air humidity is, the faster the water on the wet bulb surface evaporates, the more the wet bulb temperature drops, and the greater the temperature difference between the wet and dry bulbs;On the contrary, the greater the air humidity, the slower the evaporation of water on the wet bulb surface, the less the wet bulb temperature drops, and the smaller the temperature difference between the wet and dry bulb.Of course, the temperature difference between wet and dry bulb is also related to some other factors, such as the ventilation speed near the wet bulb, air pressure, wet bulb size, wet bulb wetting mode, etc.The air humidity at that time can be calculated theoretically according to the dry and wet bulb temperature and taking into account some other factors.The wet and dry bulb thermometer is the main instrument for measuring humidity at present, but it is not suitable for use at low temperature (below - 10 ℃).
b) Hair hygrometer (hygrometer): hair hygrometer or humidity recording instrument is made of skimmed human hair (or cattle casings) with the characteristics of elongation when air is wet and shortening when air is dry. Its humidity measurement accuracy is poor. Hair hygrometer is usually used when the temperature is below - 10 ℃.
c) Resistive humidity sensor: based on the principle that the moisture absorption film changes its resistance with the change of humidity, there are two common types: carbon film humidity sensor and lithium chloride humidity sensor.The former usesPolymerResistance sheet composed of the a certain proportion of the colloidal liquid prepared with the conductive material carbon black and adhesive, and coated on substrate;The latter is to coat a layer of lithium chloride alcohol solution on the substrate. When the air humidity changes, the concentration of lithium chloride solution changes accordingly, which also changes the resistance of the humidity measuring membrane.This type of element has lower humidity measurement accuracy than the psychrometer, and is mainly used forRadiosondeAnd telemetry equipment.
d) Film humidity sensitive capacitor: it is a capacitor with polymer as the medium, which changes the capacitance value due to absorption (or release) of water vapor.It is exquisitely made and has excellent performance. It is often used in sounding instruments and telemetry.
e) Dew point instrument: an instrument that can directly measure the dew point temperature.Cool a mirror in the wet air of the sample until dew drops (or ice crystals) appear on the mirror. Measure the average temperature of the mirror, which is the dew (frost) point temperature.It has high humidity measurement accuracy, but needs a mirror with high smoothness, a temperature control system with high accuracy, and an optical detection system for dew drops (ice crystals) with high sensitivity.During use, the pipe that sucks sample air must be kept clean, otherwise the impurities in the pipe will absorb or release moisture, causing measurement error.[2]
Humidity in China
Announce
edit
Data inversion products
The degree of wetness is an indicator of the degree of climate wetness, which is expressed by the ratio of income and expenditure of ground water.According to the Agricultural Climate Zoning and Methods, the moisture coefficient of China can be classified into seven levels, namely, drought, semi-arid, dry and semi humid, wet and semi humid, wet, humid and over humid.Provide basis for national agricultural construction.The national humidity information products areGeographic condition monitoring cloud platformOne of the meteorological/climate environment series data products launched.
At present, the existing products include China's products from 2000 to 2011 year by year, month by month, ten day by day and day by day.[3]
Meaning and purpose
Announce
edit
Air humidity has important applications in many aspectsAtmospheric scienceIn meteorology and climatology, it is mainly an important value in theory, but plays a relatively small role in practical application.
Meteorology hydrology
When it rains, air humidity is very large. In meteorology and hydrology, humidity is an important data determining evaporation and transpiration.It has differentClimatic zoneThe production of plays a decisive role.Water vapor in the atmospherewater cycleIt is also indispensable in the process.Through water vapor, water can move quickly on the surface of the earth.Water forms precipitation, clouds and other phenomena in the atmosphere, which determine the earth's weather and climate.
And inweather forecastIs more commonly used for relative humidity.It reflects the possibility of rain and fog.In hot weather, high relative humidity makes people (and other animals) feel hotter because it prevents sweat from volatilizing.Humans can thus develop a heat index.
Medical Science
In medicine, the relationship between air humidity and breathing is very close.Under certain humidity, oxygen can easily enter the blood through the alveoli.The average person feels most comfortable at a relative humidity of 45-55%.The relative humidity in overheated and unventilated rooms is generally low, which may be harmful to the skin and irritating to mucous membranes.Too high humidity affects the sweating function of regulating body temperature, and people will feel stuffy.Generally speaking, people feel better in the condition of high temperature but low humidity (such as desert) than in the condition of low temperature but high humidity (such as rainforest).The humidity of anesthetic gas is very critical when anesthesia is carried out through breathing.Anesthetic gas used in medicine is generally stored without water. If humidity is not added when using, it will cause evaporation and water loss in human lungs.
Under any temperature condition, humid air is harmful to human body.
Research shows that when the humidity is too high, the pineal gland in the human body secretes a large amount of pineal hormone, which makes the concentration of thyroxine and adrenaline in the body relatively lower, and the cells will be "lazy", and people will be listless and depressed.Working and living in places with high humidity for a long time is also easy to suffer from wet arthralgia;If the humidity is too low, evaporation will speed up, and dry air will easily take away water from the human body, making the skin drynasal cavityMucosa is stimulated, so when dry and cold air invades in autumn and winter, respiratory diseases are easily induced.In addition, too much or too little air humidity is conducive to the propagation and spread of some bacteria and viruses.According to scientific measurement, when the air humidity is greater than 65% or less than 40%, the bacteria multiply and breed fastest. When the relative humidity is 45% - 55%, the bacteria die faster.
Relative humidity usually acts on the human body together with air temperature and air pressure.Modern medical meteorological research shows that the relative humidity suitable for human body is: when the room temperature is 25 ℃ in summer, it is comfortable to control the relative humidity at 40% - 50%;When the room temperature is 20 ℃ in winter, the relative humidity is controlled at 60% - 70%.In summer, due to the effects of high temperature, low pressure and high humidity, human sweat is not easy to be discharged and evaporated after sweating, which will make people irritable, tired and anorexic;In winter, the humidity is sometimes too low and the air is too dry, which can easily cause upper respiratory tract mucosal infection and colds.According to scientific experiments, the incidence of arthritis will increase significantly when the diurnal variation of temperature is greater than 3 ℃, the diurnal variation of air pressure is greater than 10 hPa, and the diurnal variation of relative humidity is greater than 10%.
The high temperature index of human death is also closely related to air humidity.When the temperature and humidity reach a certain limit, the heat of the human body cannot be dissipated, and the body temperature will rise, so that people will die if they exceed the heat tolerance limit of the human body.Therefore, the standard of disastrous weather in China is,Yangtze RiverThe highest temperature in the south is higher than 40 ℃, or the highest temperature is 35 ℃, and the relative humidity is greater than 60%;The highest temperature in the north of the Yangtze River reaches 35 ℃, or the highest temperature reaches 30 ℃, and the relative humidity is greater than 65%.
In summer, when the humidity increases and the water vapor tends to be saturated, the heat dissipation function of the human body will be inhibited, making people feel very hot and irritable.In winter, when the humidity increases, the heat conduction will speed up about 20 times, making people feel more cold and depressed.Due to the damage of the synovium and surrounding tissues of the affected area, the ability of arthritis patients to resist external stimuli is weakened, and they cannot adapt to the intense cooling, which aggravates the condition or soreness.If the humidity is too low, people will feel dry mouth and tongue, even throat swelling and pain, hoarseness andEpistaxis, and induce colds.The investigation also shows that when the relative humidity is above 90%, 25 ℃ will make people feel like 30 ℃.Dry air can absorb sweat at the same speed as human sweat glands produce sweat, making us feel cool.However, the air with high humidity is already full of water, so it is powerlessReabsorptionMoisture, so sweat has to accumulate on our skin, so that our body temperature keeps rising, and at the same time, our mental strength is overloaded.[4]
Air humidity meansMoisture contentAnd degree of wetnessMeteorological elements。Ground air humidity refers toSurface meteorological observationThe air humidity at the specified height (i.e. 1.25~2.00 m, 1.5 m in China).It is installed in the shutter box byWet and dry bulb thermometerThere are three basic forms measured by instruments such as the basic station and the hygrometer (4 regular observations per day for the basic station and 24 regular observations per day for the reference station), namelyWater vapor pressure, relative humidityDew point temperature。Water vapor pressure (once called absolute humidity) refers to the pressure of water vapor in the air, and the unit is hpadecimalOne;Dew point temperature refers to the temperature when cooling reaches saturation under the condition of constant water vapor content and air pressure in the air.
biology
In biology, especially in ecology, air humidity is a very critical quantity.It decides oneecosystemComposition of.The opening and closing of stomata on the leaf surface of plants and the respiration of plants.Some animals likesnailThey can absorb oxygen only when their skin has certain humidity.
Storage and production
The humidity in the warehouse where the fruit is stored determines the maturity of the fruit.High humidity in the warehouse where metal is stored may cause corrosion.Many other goods such as chemicals, cigarettes, wine, sausages, wood, artworks, integrated circuits, etc. must also be stored at a certain humidity or under the condition of zero humidity.Therefore, in many warehouses, museums, libraries, computer centers and certain factories (such as microelectronics industry), there are air conditioning devices to control indoor humidity.
Agriculture and forestry
The low humidity of foggy forest can lead to water loss and yield reduction of soil and plants in agriculture.
Humidity is also a very critical quantity in forestry and forest industry.In a sawmill, people tend to water the wood piled up there.Wood itself has its own humidity, and its humidity in the air is gradually close to the ambient humidity of the air.The change of humidity in the wood will lead to the change of wood volume, which is very critical for the forest industry.[5]
Generally, when wood is stored, the air can directly contact with all directions of it, so as to avoid wood deformation or mildew.When paving the floor, it is best to let the wood of the floor stay in the house for a day or two to make it the same as the humidity in the house, otherwise the wood of the floor may stretch or shrink after paving.[6]
Architecture
In architectural physicsthe dew pointIt is a very important quantity.If the temperature in a building is different, the water in the humid air flowing from the high temperature part to the low temperature part may condense.Mold may develop in these places, which must be taken into account in architectural design.In addition, relative humidity is an important indicator to measure the indoor thermal environment of buildings. Building physics considers that when the subjective thermal feeling of the human body is neutral, the wind speed is not more than 0.15 m/s, and the relative humidity is 50% as the most comfortable thermal environment, which is also a benchmark for the design of indoor thermal environment.
Static electricity and humidity
The drier the air is, the easier it will generate static electricity, and the relative humidity (RH) will affect the surfaceAccumulated chargeHas a direct impact on performance.The higher the relative humidity, the shorter the time that the object stores the charge,surface charge Reduction (because of the increase of relative humidity) can be achieved through recombination or conduction. When the relative humidity increasesconductivityIt also increases.
When the air gradually dries (the percentage of relative humidity decreases), the change in the ability to generate static electricity is determined and obvious.When the relative humidity is 10% (very dry air), 35kV charge can be generated when walking on the carpet, but it will be sharply reduced to 7.5kV when the relative humidity is 55%.The optimal range of the relative humidity of the working environment is 30% - 50%.Some clean places generally require a relative humidity of 50%. Due to the presence of devices that are sensitive to corrosion and humidity, other environments require lower relative humidity.
Centrifugal humidifierHigh speed motor is used to drive the composite impeller to rotate to generate vacuum, and the water in the water storage tankatmospheric pressureUnder the action of the water absorber, it is pressed to the composite atomization impeller, which is transformed into a fine fog with a diameter of 5um. The breeze passing through the lower air inlet is sent to the fog outlet, where it joins with the high-speed air flow of the upper air inlet to form a high-speed aerosol, which is sprayed into the air. The aerosol contacts with the residual heat in the air, and is fully vaporized to achieve the purpose of humidification.
When the tap water enters the humidifying bucket, the water level gradually rises.Power on the humidifier electrode. When the water level overflows the electrodeConductivityAnd constituteCurrent loopAnd heat the water to boiling point to output clean steam.With the steam output, the water level gradually decreases.At this time, the water inlet valve is energized and opened, and water is fed again until the proper water level is reached, and steam continues to be generated.
When the concentration of minerals in the humidifying bucket becomes higher and higher, the drain valve will automatically open to drain the waste water, and the humidifier will replenish new water and continue the humidifying process.
Using tap water with too high or too low conductivity may lead to too fast loss of humidification bucket or insufficient humidification amount
The ultrasonic humidifier uses the principle of ultrasonic high-frequency oscillation to atomize the water into particles of 1-5 microns, and then diffuses the water mist into the air through the pneumatic device, so as to achieve the purpose of uniformly humidifying the air.It is characterized by addingWet strengthLarge, uniform humidification, high humidification efficiency;Energy saving and power saving;Ultra long service life;Humidity automatic balance, water free automatic protection;It also has the functions of medical atomization, cold compress bath surface, jewelry cleaning, etc;The disadvantage is that there are certain requirements for water quality.
The humidifier mainly works by the atomizer. A simple humidifier can be made by connecting the power supply to the centrifugal humidifier atomizer. This is not true because it has avacuumOfAtmospheric pressureFunction, you can't do it, so there's no way to talk about voltage.[7]
dehumidification
Operating principle of dehumidifier:
Rotary dehumidifierThe core structure ofhoneycombIt is the most critical part of the dehumidifier to absorb water. It is composed of a special glass fiber carrier containing a little metal titanium and active silica gel. Its honeycomb structure design can not only attach the hygroscopic agent to the maximum extent, increase the surface area of the wet air in contact with the hygroscopic agent, improve the working efficiency of the dehumidifier, but also have high strength,It can be well applied to various complex working environments.
On both sides of the runner, the diaphragm made of silicone rubber with high sealing performance divides the entire surface into two sectors: 270 ° processing sector;90 degree regeneration restore sector.
When the wet air to be dehumidified (called treated air) enters the treatment area, the water vapor in the wet air is absorbed by the active silica gel in the runner to get dried, and the dried air is sent out through the blower.With the increase of water absorption, the treatment sector gradually tends to be saturated.In order to maintain its stable dehumidification performance, it is necessary to regenerate and restore the moisture absorbent in the runner. At this time, the saturated runner, driven by the motor, slowly turns into the regeneration area to start the regeneration process.
Regeneration air (usually taken from outdoor or machine room) reaches 100~140 ℃ after being heated, and then is blown into the regeneration area in reverse direction. Under high temperature, the absorbed water in the runner isDesorptionA large amount of regeneration air is lost during desorptionsensible heat, its own temperature decreases and becomes full of waterMoist air, which is led to the outdoor by the fan, thus completing the water transfer.After regeneration and dehydration, the runner regains its strong moisture absorption capacity and, driven by the motor, turns to the working area for dehumidification.
The above dehumidification and regeneration processes occur at the same time. The air is constantly dried, and the runner is constantly regenerated, so as to ensure the continuous and constant working state of the dehumidifier.The speed of the runner is 8~12 r/h, and the required power is very small. The air parameters at the outlet of the dehumidifier only depend on the parameters of the inlet air and the control of the regenerative energy.[8]
