On the left liquid, in the middle mixed,
on the right gaseous. |
The diagram shows the individual changes in the state in the circulation of the coolant. The enthalpy rises and falls with the temperature. This here is special, because it is based on the mass of 1 kg. That on the X-
axis is called the 'specific enthalpy'. If we leave out the base of 1 kg, the enthalpy with the unit kJ remains. In this case, the energy in the coolant is meant, e.g., the vibrational energy of the molecules, but without any
work done to change the volume.
Let's begin with the figure 1, where the compressor also starts it's work. What it finds, apart from the tiniest droplets and a bit of oil, is only coolant vapour. The compressor performs all the work, raises the pressure
considerably and the temperature as well, as you can see on the path from 1 to 2. In the condenser (liquifier) it is then first of all, cooled down to condenser- or boiling point (3) and then after further heat dissapation, is
past out into the open and the complete coolant is liquified (4 - 5).
So, in point 5 it is in liquid form. In the practice e.g., the condenser and /or the pressure difference are thus dimensioned, that the point 5 does not lie exactly on the boiling line (left), but a bit further to the left into the
field of the liquid coolant. this ensures that it contains no gaseous components, whose flow through the expansion valve would be too slow. This is followed by the decompression, whereby, the pressure reduction
from e.g., 16 to 3 bar causes a considerable drop in temperature.
From point 5 to point 6 it goes through the evaporator, which is the purpose of the whole procedure. Here the coolant takes on the warmth of the fresh-air flowing into the interior and then becomes gaseous. To
guarantee the protection of the compressor, from point 6 to point 1 it is after-heated. This can be achieved to a certain extent, e.g., by laying the tubing in the engine compartment. Indeed, there are also other
possibilities. Anyhow, the point 1 does not lie directly on the dew-line, but a bit more to the right into the gaseous area. 08/13
