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Thermodynamics 3



Here, once again, the steam-pressure curve of water can be seen. What interests us right now, are the areas outside of between 0C and 100C. As a basic explanation, below the curve water remains in a liquid state, however, only as far down as 0C. At temperatures to the left of the curve, water turns to ice.

Above this curve, water always takes on a gaseous form, i.e., it turns into steam. If one could manage to generate a vacuum of 0,01 bar (10 hPa) at -20C, one would have steam, which would abruptly turn to ice if the pressure were to be increased.

The other side of the curve rises up to more than 1 bar (1.000 hPa). Thus, if the pressure is increased to above normal, water could be kept in a liquid state. Particularly in the automobile field there is one good example, the positive-pressure cooling. In this case, the cooling system is kept under pressure, so that one can still cool with water which has a temperature of nearly 120C.

The background to this: Todays engines make higher temperatures possible through the choice of certain materials and show their appreciation e.g., by providing a somewhat higher efficiency, which amounts to a lower fuel consumption. The disadvantage is: If e.g., because of a defect, the positive pressure cannot be maintained, the water dissipates as steam with a temperature of 100C and the engine is not sufficiently cooled. 09/13


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