Phase II Final Report - NASA's Institute for Advanced Concepts

Chapter 3.0 Vehicle Design
3.5 Fuel Storage and Production
factor (Z) for the hydrogen gas. [22] Where P and T are the gas pressure and temperature respectively
and R is the gas constant for hydrogen (4157 N m/kg °K)
ρ = P / ZRT Equation 3-36
Z = 0.99704 + 6.4149E-9 P Equation 3-37
The tradeoff with utilizing high density/high pressure storage is the increase in tank mass necessary
to withstand the higher pressures. The wall thickness of the tank will increase with the
increasing hoop stress due to the higher gas pressure. The calculation of the tank mass for hydrogen
gas stored under pressure is a fairly straightforward analysis. This analysis is outlined
below.
For this analysis it is assumed that hydrogen will follow the behavior of an ideal gas represented
by the equation of state,
P V H =nZRT Equation 3-38
where R is the gas constant for hydrogen and has a value of 4157.2 (N m/°K kg), P (Pa) is the
pressure of the gas, V H (m 3 ) is the volume, and T (°K) is its temperature.
Using the gas constant given above, Equation 3-42 can be restated as follows, where m H is the
mass of hydrogen:
V H = 4157.2 Zm H T / P Equation 3-39
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