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The three states of water
Release time:
2022-09-21 18:38
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Water is a substance that is ubiquitous on Earth. It is colorless, odorless, and non-toxic, and can exist in three different states—solid, liquid, and gas—depending on temperature. Under ideal conditions, water freezes into ice at 0°C, at which point its density is relatively low. When we heat an ice cube, the temperature does not rise immediately but remains at 0°C until it has absorbed a latent heat of fusion amounting to 80 kcal/kg. Only then does the ice gradually melt into water at 0°C, during which time both solid and liquid phases coexist. Once the liquid water has reached saturation at 0°C, each additional kilocalorie (kcal) of heat added will raise the temperature of 1 kilogram (kg) of water by 1°C. As heating continues, the water's temperature steadily rises until it reaches 100°C. The temperature change from 0°C to 100°C is referred to as sensible heat—the heat that is obvious and measurable—and can be directly indicated by a thermometer. The specific heat capacity of water is 1 kcal/kg, meaning that it takes 1 kcal of heat to raise the temperature of 1 kg of water by 1°C. At 1 atmosphere of pressure, when the temperature of liquid water reaches 100°C, the water begins to boil; this temperature is known as the boiling point. If heat continues to be supplied beyond this point, the water's temperature will no longer rise. Instead, the water gradually transforms into steam through a phase change—from liquid to gas. This phenomenon is called the latent heat of vaporization: although heat is continuously absorbed, the temperature shown on the thermometer remains unchanged. The latent heat of vaporization is extraordinarily high, at 539 kcal/kg—about 5.4 times greater than the sensible heat (100 kcal/kg).
Sensible heat—the increase or decrease in enthalpy is clearly reflected in a change in temperature.
Latent heat—the increase or decrease in enthalpy does not result in a visible change in temperature;
Known as the latent heat of vaporization and the latent heat of liquefaction.
At 1 atmosphere:
The specific heat capacity of liquid water is 1 kcal/kg℃.
The latent heat of fusion of water is 80 kcal/kg℃.
The latent heat of vaporization of water is 539 kcal/kg·°C.
In the humidification industry, the goal is to use external energy to convert liquid water into vapor and then, with the aid of external forces, deliver the vapor to the space that requires humidification.
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Offshore platform, ship, marine engineering, nuclear power, satellite launch center
To ensure worker comfort, enhance work efficiency, or prevent static electricity from interfering with the normal operation of equipment, it is essential to maintain appropriate temperature and humidity levels in the working environment. Typically, temperature control involves either cooling or heating. When cooling is required, some moisture is removed from the air; conversely, when heating is needed, the outdoor air often has a very low moisture content. Therefore, these environments invariably require humidification.
Humidifying the air can prevent damage to collectibles caused by the drying and cracking of fibers due to excessively low relative humidity from air conditioning. Many priceless manuscripts, books, artworks, floppy disks, magnetic tapes, and other items housed in museums—without being stored in spaces with proper temperature and humidity control—can easily suffer severe damage. However, environments suitable for these items often have lower temperatures, which can be uncomfortable for visitors. Generally, the lower limit for relative humidity for paper-based collections in museums is 40%; for items such as floppy disks and magnetic tapes, which need to be protected from drying out and becoming brittle, the lower limit is 36%. Organic collections, on the other hand, require even lower-temperature environments. Moreover, museum collections typically alternate between display areas and storage rooms; it’s important to note that even in environments with controlled temperature and humidity, heat conduction from outside walls or radiation from switching lights can still cause fluctuations in surface temperature, leading to moisture evaporation and structural damage to the collections. Furthermore, when a collection is moved from a cooler storage room into a warmer display area, its surface temperature gradually rises, causing internal moisture to migrate toward the surface and condense there—a phenomenon known as "moisture transfer." This process can accelerate the deterioration of the collection. The following temperature and humidity levels are recommended for museum environments:
Modern agricultural edible mushroom preservation and refrigerated food processing
The normal growth of edible fungi and other plants requires appropriate temperature and humidity conditions. To store foods such as fruits and vegetables, it is necessary to control the temperature and humidity of the air in order to maintain the quality and freshness of agricultural products. Generally, the humidity should be kept between 70% and 95% RH. Low relative humidity can lead to increased moisture loss in fruits, resulting in a decline in their quality grade and ultimately affecting profitability. In food processing—such as baking bread, cakes, and confectionery—both the production process and storage must prevent food cracking caused by excessively low relative humidity.
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Increased static electricity can easily damage integrated circuit chips. In data centers, preventing service interruptions is critical, and humidification systems must ensure both reliability and redundancy.
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Air humidification can prevent fiber cracking and static electricity caused by excessively low relative humidity in the air, thereby avoiding disruptions in the production process and ensuring good product quality. The recommended temperature and humidity levels are as follows:
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