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Thermodynamics 2



Because water has it's highest density at 4C, it's liquid form is perfectly suited in winter, to seep into the road surface> and as ice, to carry out it's destructive work. A piece of ice, always increasing in size soon gathers enough force, to split even solid rock.

It is important to emphasize, that it is only water that expands at temperatures below 4C. All other substances contract. Together with all other substances however, the oscillations of the water molecules also become slower. At -273,15C they stop moving all together, this is also valid for all other substances.

If Celsius had known this in his own lifetime, he wouldn't have graded his scale according to the dew- and boiling point of water. Thus, we have at least one additional scale, named after Lord Kelvin, and which doesn't have the additional degree sign. The scale begins at the absolute zero-point, has however, taken over the grading of the Celsius-scale. This means that 0C is 273,15 K(elvin).

IdentifierUnit
tC(elsius)
TK(elvin)

Important for thermodynamics is, if possible, always to calculate with the absolute pressure and the absolute temperature. The environment at room temperature is designated at 1 bar pressure and 293 K. Once one has become accustomed to it, it's quite simple. Thus, one can e.g., if the pressure and the volume of a gas at a certain temperature are known, precisely calculate how the pressure of this amount of gas changes at a different temperature.

If then, a cylinder, shortly after the intake, contains a half a liter of air having 1 bar absolute-pressure at 373 K, according to the formula:

p1*V1/T1 = p2*V2/T2

at a compression of 1/10 now has 13 bar (13.000 hPa) absolute, and a temperature of 485 K. The temperature has thus risen from 100C to 212C. 09/13

Precondition
The drawn-in air is treated like an ideal gas.
There is neither an influx- nor an exhausting of air.
Friction during the movement is not considered.

The complete comprehensible calculation is in the picture at the top ...

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