Direct Energy, 2018a

174 8.2 Thermodynamic Properties
Units for Pressure
1
m N 2 =1Pa
1 bar =10 5 Pa
1 mmHg= 133.322 Pa
1 atm = 101, 325 Pa
1 psi =6.894757 · 10 3 Pa
Table 8.1: Pressure unit conversion factors [68].
history, of the sample. These properties can be classied as intensive or
extensive [2, p. 10]. An intensive property is independent of the size or
extent of the material. An extensive property depends on the size or extent
[2, p. 10].
Volume V is an extensive property measured in m 3 or liters where 1 L =
0.001 m 3 . Pressure P is an intensive property measured in the SI units of
pascals where 1 Pa=1
m N 2 . Pressure is also measured in a wide variety
of other, non-SI, units such as bars, millimeters of mercury, or standard
atmospheres as listed in Table 8.1. Pressure measures are often specied in
comparison to the lowest possible pressure, of a complete vacuum, and such
pressure measurements are called absolute pressure measurements [102, p.
15-17]. In some cases, values are specied as the dierence above the local
atmospheric pressure, and these measurements are called gauge pressure
measurements [102, p. 15-17]. In other cases, values are specied as the
dierence below the local atmospheric pressure, and these measurements
are called vacuum pressure measurements [102, p. 15-17]. Unless otherwise
specied, the term pressure in this text refers to absolute pressure, not
gauge or vacuum pressure.
Symbol Quantity Unit Ext/int
V Volume m 3 Extensive
P Pressure Pa Intensive
T Temperature K Intensive
S
Entropy
J
K
Extensive
Table 8.2: Thermodynamic properties.