State of aggregate


  • State of aggregate
  • Supercooled liquid
  • Boiling Temperature / Condensing Temperature
  • Saturated Vapor
  • Superheated Vapor

State of Aggregation:
The state of aggregation of a substance is the state in which a substance is. The states of aggregation that we deal with in automotive technology (on this website, for example, for air conditioning) are: a solid, liquid and gas.
Many pure substances occur in these 3 states of aggregation. At a low temperature they form a solid, at higher temperatures a liquid and at even higher temperatures a gas. The transition of the solid into a liquid is called melting, the evaporation of liquid into a gas. Conversely, the transition from gas to liquid is called condensing and from liquid to solidification. This all depends on temperature and pressure.
In the air conditioning of a car, 2 out of 3 of these aggregate states apply to the refrigerant. It is important to understand the transition from liquid to vapor to understand the principle of air conditioning. The solid does not occur, because that would mean that the refrigerant freezes in the system. It is very important that this does not happen, because of expansion in the parts (leading to breakage) and blockages in the system.

Supercooled liquid:
This is liquid with a lower temperature than the boiling temperature (condensation temperature).
Example: Water freezes at a temperature below 0 degrees Celsius, and therefore changes into a solid form. It boils at a temperature of 100 degrees Celsius and then turns into vapor. The state between these 2 temperatures (1 to 99 degrees) is called a supercooled liquid.

Boiling Temperature / Condensing Temperature:
The boiling temperature and the condensing temperature are equal to each other. At this temperature, the liquid begins to boil and the process of changing from liquid to vapor (condensation) begins, or vice versa. Then the vapor changes to liquid state.
Example: Water starts boiling at a temperature of 100 degrees Celsius. This temperature is the cooking temperature. The water will then begin to turn to vapor. (This is what we call cooking). Conversely, when the temperature is lowered from eg 100 degrees to 99 degrees Celsius, the vapor will slowly change back to liquid. We call this condensing.

Saturated Vapor:
At the boiling (or condensing) temperature, the liquid changes to vapor, or vice versa. At this point, there is both liquid and vapor present and we call this the saturated vapor.
Example: When we boil water in a pan, condensation comes off. The water level drops as the water changes from liquid state to vapor. When the temperature increases, the temperature of the water does not rise more than 100 degrees Celsius, but the process of transition to vapor is only accelerated. Only when all the water has disappeared (ie when everything has gone into a vaporous state) do we no longer talk about saturated vapour, but about superheated vapour.

Superheated Vapor:
Superheated vapor means that the vapor has a higher temperature than the boiling temperature of the substance. In the case of superheated vapor, all liquid has changed into vapor form, so that there is no more liquid present at all.
Example: Water starts to boil at a temperature of 100 degrees Celsius, thus reaching the boiling temperature. When all the water has been used up and the temperature of the vapor rises even further, (eg 120 degrees Celsius) we call this superheated vapor.

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