Hydrogen tube vehicle for supersonic transport: 3. Atmospheric merit

To compare 24 common gases as potential operating atmospheres for tube vehicles, equations are derived for aerodynamic (tunneling) performance of the atmosphere and molar energy density of the tube vehicle. Aerodynamic performance is a function of the speed of sound and Reynolds number, and energy density is a function of the free energy of reduction or oxidation of the tube gas and the stoichiometric coefficients of the stored reactants. The product of these two parameters determines the rank of atmospheric merit. Hydrogen exhibits the highest aerodynamic performance, yields the fourth highest energy density, and has the highest overall merit. Acetylene, ammonia, and methane, in decreasing order, follow hydrogen in merit. Although superficially a promising tube gas, helium is below average in merit because of low energy density of the vehicle.

► The atmosphere of a vehicle operating within an enclosed tube can be varied at will.
► 24 common gases are compared as prospective tube gases.
► Equations are derived for the parameters aerodynamic performance and energy density.
► The rank of an atmosphere's figure of merit is the product of these two factors.
► Hydrogen has highest atmospheric merit, followed by acetylene, ammonia, and methane.