| |
Temperature
Temperature
is an important property of a fluid that is a measure of the average
energy associated with its component molecules. If two systems in contact
are in thermal equilibrium, i.e. there is no net energy transfer between them,
they are said to have t he same temperature. Various temperature scales
are used to measure this quantity. The Kelvin temperature is based on thermodynamic
reasoning and introduces the concept of a lower limit to this quantity,
Absolute Zero or 0 K. This scale is related to the Celsius temperature
scale which has the same "degree" size by assigning the value -273.16
C to 0 K.
Many properties of materials are temperature dependent.
For an "ideal" gas the parameters (p, v, T) are related through an
"equation of state:" pv = RT where R is known as the Gas Constant and has the value
8.314 J/mole.K (for air R = 287.03 m2/s2.K). If the
pressure of the gas is 1 atmosphere and its temperature is 273.16 K this relationship
indicates that the molar specific volume is 0.0224 m3/mole = 22.4
liters/mole.
As the temperature is increased at constant pressure, the equation of state
indicates that the specific volume increases linearly with temperature.
To a good approximation, many gases can be treated as ideal gases provided
their temperature is above the critical temperature, i.e. they cannot undergo
a phase transformation to the liquid state. For nitrogen the critical
temperature is 126 K, for carbon dioxide 304 K and for water vapor 647 K.
Nitrogen is therefore a reasonable "ideal gas" at room temperature
(273 K) whereas CO2 and H20 can both be condensed into
liquids by the application of pressure at room temperature. For CO2
this requires about 45 atmospheres (4.48 x 106 Pa). |
|
