Humidity detailed data collection
Basic Introduction Chinese Name: Humidity mbth: Humidity Pinyin: shī dù Specialty: Earth Science/Meteorology/Physics Attribute: Physical Quantity Category of Atmospheric Dryness: Absolute Humidity/Relative Humidity/Specific Humidity Concept, Content, Basic Form, Representation, Measurement Method, Humidity, Meaning and Use in China, Meteorology and Hydrology, Medicine, Biology, Storage and Production, Agriculture, Forestry, Architecture. Liquid or solid water in the air is not considered as humidity. Air without water vapor is called dry air. Because the water vapor in the atmosphere can account for 0% ~ 4% of the air volume, when listing the components of various gases in the air, it generally refers to the composition of these components in dry air. The degree of dryness and wetness of the air, or a physical quantity indicating how much water vapor is contained in the air, is called humidity. The mass of water vapor contained in air per unit volume is called absolute humidity. Because the density of water vapor is difficult to measure directly, it is usually expressed by the pressure of water vapor. The absolute humidity of air does not determine the speed of water vapor on the ground and people's feeling of humidity. People call the absolute humidity of air at a certain temperature and the percentage of saturated air pressure at the same temperature as relative humidity. There are three basic forms of humidity, namely water vapor pressure, relative humidity and dew point temperature. The hygrometer is recording the relative humidity. Water vapor pressure (once called absolute humidity) indicates the pressure of water vapor in the air. The unit is hectopascals (hPa), with one decimal place reserved. Relative humidity is expressed as the percentage of the ratio of actual water vapor pressure to saturated water vapor pressure in the air at the current temperature, taking an integer; Dew point temperature refers to the temperature when the water vapor content in the air and the air pressure reach saturation during cooling. Units are expressed in degrees Celsius (℃), with one decimal place reserved. When equipped with a hygrometer, it can also measure the continuous record of relative humidity and minimum relative humidity. Representation: Several quantities of hygrometer are used to represent the humidity of air. The most commonly used examples are as follows: water vapor pressure, absolute humidity, relative humidity and wet dew point. The instrument used to measure humidity is called a hygrometer. The unit of humidity RH is relative humidity, which is defined by dew point temperature. Noun explanation of humidity: In metrology, humidity is defined as "the quantity of image state". Humidity in daily life refers to relative humidity, expressed in %rh. In a word, it is the percentage of saturated water vapor (saturated water vapor pressure) of gas (usually air) under the same conditions as its air. Absolute humidity Absolute humidity refers to the mass of water vapor contained in a certain volume of air, and its unit is generally gram/cubic meter. Maximum absolute humidity is the highest humidity in saturated state. Absolute humidity is meaningful only when there is temperature, because the amount of humidity that can be accommodated in the air changes with temperature, and the absolute humidity is different at different temperatures, because the volume of air changes with temperature. However, the closer the absolute humidity is to the highest humidity, the smaller its change with temperature. The following formula is used to calculate the absolute humidity: the symbols are: e-steam pressure in Pascal (Pa)-gas constant of water = 461.52j/(kg k) t-temperature in Kelvin (k) m-mass v of water dissolved in air in kilogram (kg). The relative humidity (RH) hygrometer records the relative humidity. Relative humidity is the ratio of absolute humidity to maximum humidity, and its value shows how high the saturation of water vapor is. Air with a relative humidity of 100% is saturated air. The relative humidity is that 50% air contains half of water vapor, reaching the saturation point of air at the same temperature. Water vapor in the air with relative humidity exceeding 100% will generally condense out. With the increase of temperature, the more water can be contained in the air, that is to say, the relative humidity will decrease with the increase of temperature for the same amount of water vapor. Therefore, it is necessary to provide temperature data and relative humidity. Dew point can also be calculated by relative humidity and temperature. Calculate relative humidity with the following formula: symbols are: ρw- absolute humidity, unit ρ w/m3, max maximum humidity, unit ρm3 e- water vapor pressure, unit ρPascal e- saturated water vapor pressure, unit ρPascal s- specific humidity, unit ρkg s- maximum specific humidity, and unit ρ kg specific humidity is water melted in air. If there is no condensation or evaporation, the specific humidity of enclosed air at different heights is the same. The symbol of the highest specific humidity in saturated state is S. The following is the formula for calculating the specific humidity S. The symbol used is: similar maximum specific humidity is: the symbol used in the formula is: MX— mass, unit ρx— density, unit ρx— total volume of wet air, unit ρrw— gas constant of water, unit ρ/(kg Kelvin) rl— gas constant of dry air, and unit is joule. Kelvin mwater-molar mass of water =18.01528g/mol-molar mass of dry air = 28.9634g/mol e-steam pressure, in Pascal p-air pressure, Pascal e-saturated steam pressure, in Pascal measurement and dry-wet bulb measurement. Commonly used instruments for measuring humidity include dry-wet bulb thermometer, hair hygrometer and resistance hygrometer. A) Dry and wet bulb thermometer: Use a pair of thermometers with the same shape, one of which is called dry bulb thermometer and the other is called wet bulb thermometer, and wrap them with absorbent gauze to keep distilled water saturated. When the air is not saturated, the wet bulb needs to consume heat due to surface evaporation, thus reducing the temperature of the wet bulb. At the same time, the wet ball continuously gets heat supply from the air flowing through the wet ball. When the heat consumed by evaporation of the wet bulb is in balance with the heat obtained from the surrounding air, the temperature of the wet bulb will not continue to drop, resulting in the temperature difference between the dry bulb and the wet bulb. The temperature difference between dry bulb and wet bulb is mainly related to the air humidity at that time. The smaller the air humidity is, the faster the water on the surface of wet bulb evaporates, the more the temperature of wet bulb drops, and the greater the temperature difference between dry bulb and wet bulb. On the contrary, the greater the air humidity, the slower the evaporation of water on the surface of wet bulb, the smaller the temperature drop of wet bulb and the smaller the temperature difference between dry bulb and wet bulb. Of course, the temperature difference between wet and dry balls is also related to other factors, such as ventilation speed, air pressure, wet ball size, wet ball wetting mode and so on. According to the temperature values of dry and wet bulbs and considering other factors, the air humidity at that time can be calculated theoretically. Dry wet bulb thermometer is the main instrument for measuring humidity at present, but it is not suitable for low temperature (below-10℃). B) Humidity meter: The hair hygrometer or humidity recording instrument is made by using the characteristics of defatted human hair (or cattle casing) that it stretches when the air is wet and shortens when it is dry. Its humidity measurement accuracy is poor, and the hair hygrometer is usually used when the temperature is below-10℃.
C) Resistive humidity sheet: Based on the principle that the resistance value of moisture-absorbing diaphragm changes with humidity, there are two commonly used humidity sensitive resistors with carbon film and lithium chloride humidity sheet. The former is to mix polymer, carbon black, conductive material and adhesive into a certain proportion of colloidal liquid and coat it on the substrate to form resistance; The latter is to coat a layer of lithium chloride ethanol solution on the substrate. When the air humidity changes, the concentration of lithium chloride solution changes, which also changes the resistance of humidity measuring diaphragm. The humidity measurement accuracy of these components is lower than that of hygrometer, and they are mainly used in radiosondes and telemetry equipment.
D) Thin film humidity-sensitive capacitor: It is a capacitor with polymer as the medium, and its capacitance changes due to absorption (or release) of water vapor. It is exquisitely made and has excellent performance, and is often used in radiosondes and telemetry.
E) Dew point meter: an instrument that can directly measure dew point temperature. Let a mirror cool in the humid air of the sample until dew (or ice crystal) appears on the mirror, and measure the average temperature of the mirror, which is the dew (frost) point temperature. It has high humidity measurement accuracy, but it needs a mirror with high smoothness, a temperature control system with high accuracy and an optical detection system with high sensitivity to dew (ice crystals). When in use, the pipeline for inhaling sample gas must be kept clean, otherwise impurities in the pipeline will absorb or release water, resulting in measurement errors. The retrieved product humidity of China humidity data indicates the climate humidity index, which is expressed by the ratio of surface water budget. According to the agricultural climate zoning and methods, the humidity coefficient of China can be divided into seven grades, namely, drought, semi-drought, drought and semi-humidity, humid and semi-humid, humid, humid and over-humid. Provide a foundation for the country's agricultural construction. The national humidity information product is one of the meteorological/climatic and environmental data series products launched by the geographic national conditions monitoring cloud platform. Distribution map of China's wetting coefficient in 2005. At present, the existing products include China products from 2000 to 20 1 1 year by year, by month, by ten days and by day. Significance and uses Air humidity has important uses in many aspects, and it is mainly an important value in theory in meteorology, climatology and meteorology, but it has little effect in practical application. Meteorology and Hydrology When it rains, the air is very humid. In meteorology and hydrology, humidity is an important data to determine evaporation and transpiration. It plays a decisive role in the formation of different climatic zones. Water vapor in the atmosphere is also essential in the water cycle. Water can move quickly on the surface of the earth through steam. Water forms precipitation, clouds and other phenomena in the atmosphere, which determine the weather and climate of the earth. Relative humidity is commonly used in weather forecast. Reflects the possibility of rain and fog. In hot weather, high relative humidity will make people (and other animals) feel hotter because it hinders the evaporation of sweat. Humans can therefore calculate the heat index. Medicine In medicine, air humidity is closely related to breathing. Under certain humidity, oxygen can easily enter the blood through alveoli. The average person feels most comfortable at 45-55% relative humidity. The relative humidity of overheated and unventilated rooms is generally low, which may be harmful to the skin and irritating to the mucosa. Excessive humidity affects people's perspiration function of regulating body temperature, and people will feel stuffy. Generally speaking, people feel better in high temperature and low humidity (such as desert) than in low temperature and high humidity (such as rainforest). The humidity of anesthetic gas is very important when anesthesia is performed by breathing. Anesthetic gases used in medicine are generally stored without water. If humidity is not added during use, it will cause evaporation and water loss in human lungs. Humid air is harmful to human body at any temperature. Studies have shown that when the humidity is too high, the amount of pineal hormone secreted by the pineal gland in the human body is also large, which makes the concentration of thyroxine and adrenaline in the body relatively low, cells will be "lazy", and people will be listless and depressed. Working and living in a place with high humidity for a long time is also prone to dampness; If the humidity is too low, evaporation will be accelerated, and dry air will easily take away the moisture of the human body, making the skin dry and the nasal mucosa stimulated. Therefore, when dry cold air invades in autumn and winter, it is easy to induce respiratory diseases. In addition, too much or too little air humidity is conducive to the reproduction and spread of some bacteria and viruses. Scientifically speaking, when the air humidity is more than 65% or less than 40%, the germs multiply fastest, and when the relative humidity is 45%-55%, the germs die faster. Relative humidity usually acts on human body together with air temperature and air pressure. Modern medical meteorological research shows that the suitable relative humidity of human body is: when the room temperature is 25℃ in summer, it is more 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 the dog days of summer, due to the effect of high temperature, low pressure and high humidity, sweat is not easy to be discharged and evaporated after sweating, which will make people fidgety, tired and lose appetite. Sometimes the humidity is too low and the air is too dry in winter, which is easy to cause upper respiratory tract mucosal infection and cold. According to scientific experiments, when the daily variation of temperature is greater than 3℃, air pressure is greater than 10 hectopascal, and relative humidity is greater than 10%, the incidence of arthritis will increase significantly. The high temperature index of human death is also closely related to air humidity. When the temperature and humidity reach a certain limit, the human body's heat will not be emitted, and the body temperature will rise, so that people will die if they exceed the heat resistance limit of the human body. Therefore, the standard of disastrous weather in China is that the highest temperature in the south of the Yangtze River is higher than 40℃, or the highest temperature is 35℃ and the relative humidity is higher than 60%. The highest temperature in the area north of the Yangtze River is 35℃, or 30℃, and the relative humidity is above 65%. In summer, when the humidity increases and the water vapor tends to be saturated, it will inhibit the heat dissipation function of the human body and make people feel very stuffy and irritable. In winter, when the humidity increases, the heat conduction will be accelerated by about 20 times, which makes people feel colder and more depressed. Arthritis patients' ability to resist external stimuli is weakened due to the injury of synovium and surrounding tissues in the affected area, and they can't adapt to severe cooling, which makes their condition worse or sore. If the humidity is too low, people will feel thirsty because of a large amount of water loss in the upper respiratory mucosa, and even have a sore throat, hoarse voice and nosebleeds, which will induce a cold. The survey also shows that when the relative humidity is above 90%, 25℃ will make people feel like 30℃. Dry air absorbs sweat at the same speed as human sweat glands produce sweat, which makes us feel cool. However, the air with high humidity is full of water and can no longer absorb water, so sweat has to accumulate on our skin, which makes our body temperature rise continuously and our heart overwhelmed. Air humidity is a meteorological factor that indicates the water vapor content and humidity in the air. Ground air humidity refers to the air humidity at the height specified by ground meteorological observation (i.e.1.25 ~ 2.00m, and1.5m in China). There are three basic forms of measurement (4 times a day at the basic station and 24 times a day at the reference station), namely water vapor pressure, relative humidity and dew point temperature. Water vapor pressure (once called absolute humidity) indicates the pressure of water vapor in the air, and the unit is hectopascals (hpa), with one decimal place reserved; Dew point temperature refers to the temperature at which 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 determines the composition of an ecosystem. Opening and closing of stomata on plant leaves and respiration of plants. Some animals, such as snails, can only absorb oxygen when their skin has a certain humidity. Storage and production in the warehouse where fruits are stored, humidity determines the maturity of fruits. Excessive humidity may lead to corrosion in warehouses where metals are stored. Many other commodities, such as chemicals, cigarettes, wine, sausages, wood, artworks, integrated circuits, etc. It must also be stored at a certain humidity or zero humidity. Therefore, in many warehouses, museums, libraries, computer centers and some factories (such as microelectronics industry), there are air conditioning devices to control indoor humidity. The low humidity of fog forest in agriculture and forestry will lead to the loss of water and production of soil and plants in agriculture. Humidity is also a very critical quantity in forestry and forest industry. In the sawmill, people often water the wood piled there. Wood itself has its own humidity, and its humidity in the air gradually approaches the humidity around the air. The change of humidity in this kind of wood will lead to the change of wood volume, which is very important for forest industry. Generally speaking, wood should be stored in such a way that air can directly contact it from all directions to avoid wood deformation or mildew. When laying the floor, it is best to leave the wood of the floor 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 laying. Building dew point is a very important quantity in architectural physics. If the temperature in the building is different, the water in the humid air flowing from the high temperature part to the low temperature part may condense. These places may take shape, and architectural design must take this phenomenon into account. In addition, relative humidity is an important index to measure the indoor thermal environment of buildings. When the subjective thermal sensation of human body is neutral, the wind speed is not more than 0. 15m/s and the relative humidity is 50%, which is also a benchmark for indoor thermal environment design. Static electricity and humidity The drier the air, the easier it is to generate static electricity. Relative humidity (RH) has a direct influence on the performance of surface charge accumulation. The higher the relative humidity, the shorter the time for an object to store charge, and the way to reduce the surface charge (because the relative humidity increases) can be through recombination or conduction. When the relative humidity increases, the electrical conductivity of air also increases. When the air gradually dries (the percentage of relative humidity decreases), the change of electrostatic capacity is definite and obvious. When the relative humidity is 10% (very dry air), when walking on the carpet, it can generate 35kV charge, but when the relative humidity is 55%, it will drop sharply to 7.5kV. The optimum range of relative humidity in working environment is 30%-50%. Some clean places generally require 50% relative humidity, while other environments require lower relative humidity because the equipment is sensitive to corrosion and humidity. Working principle of centrifugal humidifier: centrifugal humidifier uses high-speed motor to drive compound impeller to rotate to generate vacuum. Under the action of atmospheric pressure, the water in the water storage tank is pressed to the compound atomizing impeller by the water absorber, and becomes fine mist with a diameter of 5um. After passing through the breeze in the lower inlet, it is sent to the mist outlet, where it merges with the high-speed airflow in the upper inlet, forming a high-speed mist to be sprayed into the air. The aerosol contacts with the residual heat in the air and completely vaporizes to achieve the purpose of humidification. Working principle of polar humidifying electrode steam humidifier: When tap water enters the humidifying barrel, the water level gradually rises. Energize the electrodes of the humidifier. When the water level overflows the electrodes, a current loop is formed between the electrodes through the conductivity of water, and the water is heated to boiling, and clean steam is output. With the steam output, the water level gradually decreases. At this time, the water inlet valve is electrified and opened, and water is fed again until it reaches a suitable water level and continues to generate steam. When the mineral concentration in the humidifying barrel is getting higher and higher, the drain valve automatically opens to discharge wastewater, and the humidifier supplements fresh water to continue the humidifying process. Using tap water with too high or too low conductivity may lead to too fast loss or insufficient humidification of the humidifying barrel. Principle of ultrasonic humidifier: Ultrasonic humidifier uses the principle of ultrasonic high-frequency oscillation to atomize water into 1-5 micron particles, and then diffuses the water mist into the air through pneumatic device, thus achieving the purpose of humidifying the air evenly. It is characterized by high humidification intensity, uniform humidification and high humidification efficiency; Save energy and electricity; Long service life; Automatic humidity balance, automatic protection without water; It has the functions of medical atomization, cold water bath and jewelry cleaning. The disadvantage is that there are certain requirements for water quality. Humidifier mainly works by atomizing sheet. A simple humidifier can be made by connecting the power supply to the centrifugal humidifying atomizer. This is not true, because it has a vacuum atmosphere, and you can't do it, so the voltage can't be discussed. Working principle of dehumidifier: The core structure of rotary dehumidifier is a continuous rotating honeycomb drying wheel, which is the most critical part of dehumidifier to absorb water. It consists of a special glass fiber carrier containing a small amount of metallic titanium and active silicone rubber. Its honeycomb structure design can not only attach moisture absorbent to the maximum extent, increase the contact surface area between wet air and moisture absorbent, and improve the working efficiency of dehumidifier, but also has high strength and can be well applied to various complex working environments. On both sides of the wheel, the whole surface is divided into two sectors by a highly sealed diaphragm made of silicone rubber: a 270-degree machining sector; 90-degree regenerative deceleration sector. When wet air (called process air) that needs dehumidification enters the treatment zone, the water vapor in the wet air is absorbed by the active silicone rubber in the runner, thus being dried, and the dried air is sent out by the blower. With the increase of moisture absorption, the treated sector is gradually saturated. In order to maintain its stable dehumidification performance, it is necessary to regenerate and reduce the hygroscopic agent in the runner. At this time, the saturated runner is driven by the motor and slowly turns into the regeneration zone to start the regeneration process. Regenerated air (usually taken from outdoor or machine room) is heated to 100~ 140 degrees, and then blown into the regeneration area in the opposite direction. At high temperature, the absorbed moisture in the runner is desorbed. Due to the loss of a lot of sensible heat in the desorption process, the temperature of the regenerated air is reduced, and it becomes wet air full of moisture, which is guided by the fan and discharged outside, thus completing the transfer of moisture. However, after regenerative dehydration, the runner recovered its strong moisture absorption ability and was transferred to the work area for dehumidification under the drive of the motor. The dehumidification and regeneration processes are carried out at the same time, and the air is continuously dried and the rotating wheel is continuously regenerated, thus ensuring the continuous and constant working state of the dehumidifier. The rotating speed of the runner is 8~ 12 rpm, and the required power is extremely small. The parameters of air at the outlet of dehumidifier only depend on the parameters of inlet air and the control of regeneration energy.