Established Methods Based on Compression and Cryogenics - Hydrogen Generation, Storage, and Utilization - page 78

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].