Surely many had to watch the picture, standing like an open container with water after a while is empty.If it cover to cover, the water is not going away.The reason is known to all - the water evaporates.Explanation of the phenomenon is simple: part of the water molecule has a fairly high speeds in order to leave the liquid.Here is the process of moving the liquid to the gaseous state is called evaporation.
Another process, namely the conversion of steam into the liquid, is called condensation.These two processes, evaporation and condensation, are constantly: some of the water evaporates, some - condensed.If the volume above the water surface is unlimited, then dominated by the process of evaporation.The evaporated water is removed, for example, occurs over the surface of open water, and the liquid is gradually transformed into gaseous - vapor.
But if the amount of free space above the liquid is limited, there is a somewhat different situation.The evaporated water can not leave the volume above the water surface and form a saturated vapor.So it called vapor in equilibrium when the amount of evaporated water and condensed steam are equal.The water does not decrease, and does not come, there comes a state of equilibrium between evaporation and condensation.
We now know that such a saturated vapor, and its properties, may prove to have quite curious.From the outset we have determined that the amount of free space above the liquid surface is limited.Above it formed saturated steam.And if now this free volume decrease?What will happen?In this case, a balance between condensation and evaporation violated.Begins to dominate the process of condensation, the amount of moisture will increase, and the pair - decrease.
steam pressure at which it is in equilibrium with the liquid, called vapor pressure.If we reduce the amount of free space above the water, the vapor pressure increases.The consequence of this will be a transition to water vapor.At higher pressures, the liquid takes up less space than the saturated steam.From this follows another finding, if the temperature is constant, the vapor pressure at any volume of the same.
There is another option of Conduct couple - the volume above the water surface is reduced, and the transition into the liquid vapor occurs.So, on the surface it is the unsaturated vapor.In the future, the volume decreases at a constant temperature, the steam begins to turn in the water - so formed saturated steam.But not for nothing has been agreed, provided that all takes place at a constant temperature.There is a certain its value at which steam can be transformed into liquid.
This value is called the critical temperature.Substance gas remains above the critical temperature, and if it is below the critical value, the gas is converted into liquid.Each substance has its critical temperature.It is worth mentioning two more particular couple: it can be both wet and dry saturated steam.When wet with droplets of water, and the dry vapor does not contain moisture.
There is the so-called superheated steam - is dry steam at a temperature above the critical.In this case, it is considered that in the closed volume is no longer fluid and only steam is present.Superheated steam is mainly used in engineering and energy.The high temperature of the superheated steam allows to transport it using steam and use the steam turbine.Due to the lack of water in the superheated steam turbine life increases.
The article considers what a saturated steam, its types and properties, as well as the process of its formation and transformation of a liquid.
