Environmental Engineering Reference

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and
R
is the gas constant. If Equation (5.6) is valid, then

PM

RT
,

′
=

ρ
V

(5.7)

that is, the volumetric capacity increases linearly with compression pressure

P
. However, the compressed hydrogen gas cannot be treated as an idea gas

due to strong intermolecular interactions, and the equation of state can be

approximated as

PV

tank
=

nZRT

,

(5.8)

where
Z
is called the compressibility factor, and is a function of both tem-

perature
T
and pressure
P
, as shown in Figure 5.2. The volumetric capacity

can be estimated as

PM

ZRT
.

′
=

ρ
V

(5.9)

′

ρ
V
may not be a monotonic

Depending on the compression temperature,

function of
P
. Table 5.1 shows the calculated

ρ
V
values at 20°C for a 150-L

′

FIGURE 5.2
Compressibility factor of hydrogen.
Source
: Reproduced with permission from Zhou and

Zhou [3].

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