Morning dew on the leaves and fogging of the windshield of your car, the disappearance of gasoline from long-term storage tanks and the loss of long-awaited rain, all these processes are combined by a constant change in the state of matter of the substance by the substance. In a more detailed study of the conditions for the transition of vapor — liquid and even vapor — solid, it was noticed that not only temperature, but also pressure influence their flow.
So in the section of thermodynamics, among other physical concepts, the definition of saturated steam appeared, and the saturated vapor pressure of each individual substance became the subject of study and accurate measurements. All descriptions and definitions of saturated steam are reduced to the consideration of some closed system in which a substance resides simultaneously in two aggregate states, steam and liquid (sometimes a solid), and the balance between them is achieved by the presence of a certain temperature and pressure. Their change leads to boiling or condensation of liquids or to sublimation, desublimation of solids.
In other words, the concentration of the substance in the vapor state reaches the maximum possible value for the available temperature and pressure. The system occupies a position of a certain equilibrium in which the amount of steam and its properties get constant values.
The processes taking place inside a closed system are interesting in that the saturated vapor pressure is absolutely independent of the volume of the vessel. If you provoke an increase (decrease) in volume, for example, using a piston, then in the first case this leads to an increase in the amount of steam, and in the second to condensation, the transition of steam into a liquid. It is possible to influence the pressure of saturated steam only by changing the temperature.
A formula that can be found on the pages of even a school textbook is able to describe saturated vapor pressure. But a visual manifestation of the properties of saturated steam can be observed in the toy “drinking chicken”, which rightfully won the title of pseudo-engine. An uncomplicated design of two flasks welded together, fixed in the middle on an axis like a children's swing, demonstrates how the periodic evaporation and conditioning of the ether poured in brings the toy into constant motion. The pressure of saturated steam receives periodic impulses to change by lowering (cooling) the head of the toy in a container with water.
But the main practical application of knowledge of the properties of saturated steam goes far beyond creating idle amusements and toys. Widespread instruments for measuring air humidity and dew point. Knowledge of humidity control methods makes it possible to achieve the most favorable microclimatic conditions in rooms. This not only plays an important role in creating favorable conditions for human life, but also is necessary for the preservation of objects in warehouses, archives, libraries ...
These issues play a special role in the fuel and energy industry, where one has to deal with the storage and transportation of large volumes of combustible liquids and gases. The use of special valves that release the pressure of saturated gasoline vapor, although it leads to a partial loss of valuable substance, but protects against more unpleasant consequences arising from excessive pressure of the fuel in large containers for its storage. The gas liquefaction technology relies heavily on the laws and properties of saturated steam, its application not only facilitated the transportation of this type of fuel, but also made it available for use in the automotive industry. Cars with HBO not only save the financial resources of their owners, but also have a positive effect on the environment.