In the examination of the thermodynamical relations between the materials, we need to define special terms. We use these terms for the natural and physical properties or stuff. One of these natural or physical terms is saturated vapor and saturated liquid. So, we will try to explain what is saturated vapor and saturated liquid and the importance of this term for thermodynamics and others.
What is the Saturated Vapor and Liquid?
The saturated liquid is the state of a pure liquid where the liquid is about to vaporize. As you know, the vaporization of the water starts at 212°F or 100°C. It is true but it is only true for the atmospheric pressure. Because we try to boil the water at atmospheric pressure generally.
The atmospheric pressure is 14.696 psi or 101 Pa. Water boils at this pressure value at 212°F. With the changing temperature, the boiling or vaporizing temperature of water changes.
The logic of the saturated vapor is the same as the saturated liquid. If we think of the reverse phase change of the liquid from the vapor phase to the liquid phase, the vapor that is condensed is saturated vapor.
In thermodynamical calculations, we are using different liquids at different pressures. So, it is not easy to fully understand what is the saturated liquid.
Saturation Temperature and Saturation Pressure
Again, if we give the water example, the saturation temperature of water at 14.696 psi pressure is 212°F. and the saturation pressure of the water for 212°F temperature is 14.696 psi. So, you understand that these two saturation temperatures and the saturation pressure values are dependent on each other.
The saturation temperature of a pure liquid is the initial vaporization temperature of this liquid at the given pressure. Because, with the changing pressure, this value changes.
Also, the saturation pressure of a pure liquid for a temperature value is the pressure where vaporization starts.
We need to enhance our viewpoint for the water boils at 212°F to saturation temperature and pressures of pure materials.
Phase Change Heat
If a pure substance reaches the saturation temperature to be a saturated liquid, there is a need for latent heat to change this liquid to fully vapor. The temperature is the same but the phases are not. So, we need to understand that at the same temperature, the energy level of vapor is higher than that of liquid.
Latent Heat of Vaporization
This is a very important term for saturated liquids. For example, water reaches 212°F, and transformation to the vapor phase requires energy. We call this energy as the latent heat of vaporization. During the phase change, the temperature does not change but energy does.
Important Applications of Saturated Liquids
As we stated above, there are different kinds of applications of saturated liquids. These liquids and pressure levels can change.
With the proper adjustments between the saturation temperatures and pressures of liquids, we can produce various useful applications.
Refrigerant 134-a in Refrigerators
Refrigerators are very important thermodynamical applications. We are using thermodynamical cycles in refrigerators. Also, refrigerant 134-a is a very useful liquid for refrigerators.
The importance of refrigerant 134-a is that the saturation temperature is very low in atmospheric pressure. The saturation temperature of refrigerant 134-a is -14.8°F. So, if you put this liquid at atmospheric temperature, it will start to boil at room temperature. This property makes the refrigerant 134-a is very useful liquid for cooling applications.
Liquid Nitrogen Applications
Maybe you know liquid Nitrogen from the interesting videos on Instagram or Facebook. You may see this as a very cold liquid pouring from a can with lots of vapor. This is because, the saturation temperature of the liquid nitrogen in atmospheric pressure is -320.8°F. So, Nitrogen will start to evaporate rapidly at room temperature.
They use Nitrogen generally in the cooling applications of cryogenic applications. Also in scientific applications such as superconductivity, they use Nitrogen to cool the materials for superconductivity. Because superconductivity properties come out at very low temperatures.
Vacuum Freezing and Cooling
Vacuum freezing and cooling applications of the vegetables is a very common application. With this cooling application, vegetables are held much more fresh for a long time.
In vacuum freezing applications, the ambient pressures are dropped to a certain degree. Because of this temperature drop, the saturated vapor and saturated liquid temperatures drop for water. So, lots of water evaporates from the vegetables which will hold them dry. Dry vegetable leaves will stay fresh longer times.
So on a thermodynamical basis, we need to understand the real difference between the condensation and vaporization of liquids. The real science between them is like above.
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