Changes In State

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying Evaporation And Condensation

Courtesy of VOLVO CARS OF NORTH AMERICA.

Evaporation

As the heat is transferred to the water, the temperature of the water increases successively. However water cannot receive and store infinite quantities of heat.

At approximately 100°C (212°F) and normal air pressure, the water cannot consume any more heat.

If the supply of heat to the water continues, the water will give off as much heat as it is supplied with.

The water disposes of the excess heat by converting to steam. As long as there is still water, the temperature remains at 100°C (212°F) in both the boiling water and in the steam.

Eventually all the water will evaporate.

If further heat is applied to the steam, its temperature will rise (= super heated steam).

NOTE: Do not confuse the amount of heat and the temperature. For example a burning match has a temperature of approximately 600°C (1112°F), but gives off little heat; possibly enough to heat the water in a thimble a couple of degrees.

Condensation

If the supply of heat is removed, the steam will condense into water after a while.

This is because the heat is transferred from the hot steam to the cooler surrounding.

During condensation, as much heat is released as was consumed during evaporation.

Quantity of heat

Different amounts of heat are required to raise the temperature of the water, to evaporate the water, to super heat the steam and to condense the steam into water.

If, for example, we have a certain amount of heat which we will call 1 unit it would be as follows:

1 unit to increase the temperature of the water from room temperature (20°C) (68°F) to boiling point.
7 units to convert the boiling water to steam.
0.45 units to super heat the steam.
7 units to condense the steam to water.

Most heat can also be transferred when the water changes from one state to another.

This applies to all liquids, including refrigerants.

This is one of the reasons that it is so important that the amount of refrigerant in the air conditioning correct.

Too much refrigerant in the evaporator the refrigerant heats up but evaporates only partially a smaller amount of heat is taken from the air leading to reduced capacity.
Too little refrigerant in the evaporator the refrigerant evaporates and the steam is super heated a smaller amount of heat is taken from the air reduced capacity.