About Critical point
First of all, the term of “critical point” is a physics term, however, it is often seen in other fields as well. A fluid exceeding the critical point is called supercritical fluid and it is called supercritical water in case of water.
So, what is a “critical point”?To put it simply, it suggests the point where liquid and gas are identical. When the temperature of liquid and steam rise by being heated, their volume increase but their weight remain unchanged. As it is heated, the volume increase while the weight is the same. This phenomenon can also be explained as that the pressure increase as the temperature rise. Not by heating liquid and fluid under constant pressure but by heating them with increasing pressure simultaneously, the points in which the temperature does not get higher anymore, which is called the critical temperature, and the pressure does not get higher anymore, which is called the critical pressure, being identical appears.
This point is called the critical point and substances at the critical point has both characteristics of liquid and gas. In other words, the critical point can be described as the point where liquid and gas are identical, as stated above.
The critical point can be also said as the point that there is no heat of vaporization.
Also, the gas having lower pressure than the critical pressure is stated as steam, and the substance being subjected to a pressure and temperature higher than its critical point is stated as supercritical fluid which suggests the fluids being in special state that cannot be said as liquid nor gas.
When a water exceeds the critical point, it is said to be “the supercritical water” and its characteristics are changed to completely different from solid, liquid and gas.
Since substances other than water also move to special states, these supercritical fluids are being utilized in various fields of industries. For example, it is used in coffee extraction, decomposition of environmental pollutant, reprocessing of spent nuclear fuel, etc.
About Critical point