Volumetric density, compressed hydrogen

Figure 5.5 Volumetric density of compressed hydrogen gas as a function of gas pressure including the ideal gas and liquid hydrogen. The ratio of the wall thickness to the outer diameter of the pressure cylinder is shown on the right-hand side for steel with a tensile strength of 460 MPa. A schematic drawing of the pressure cylinder is shown as an inset.

A comparison of the volumetric energy densities of compressed hydrogen gas, liquid hydrogen and other fuels is presented in Figure 1.11 methane represents natural gas and octane represents petrol. The data show that highly compressed methane and liquid fuels are much superior to hydrogen. 

One of the biggest problems with hydrogen stored as a compressed gas is its very low volumetric density and the resulting need for large storage facilities. Liquefied hydrogen provides one solution to this problem. 

Fig. 6.2 The six basic hydrogen storage methods and phenomena. The gravimetric density prr, the volumetric density pv, the working temperature T and pressure p are listed. RT stands for room temperature (25°C). From top to bottom compressed gas (molecular H2) in a lightweight composite cylinder (tensile strength of the material is 2000 MPa) liquid hydrogen (molecular H2), continuous loss of a few percent per day of hydrogen at RT physisorption...

The hydrogen absorption-desorption capacity of alloy such as Tii iCrMn is 1.6-1.8mass% in the pressme range of 33 MPa and 0.1 MPa at 233-296 K. The calculated volumetric H2 density of the hybrid system composed of the alloy and the compressed hydrogen at 35 MPa is 1.6 times larger than that of the compressed hydrogen. 

As mentioned above, physical properties of aqueous solutions of inorganic citrates were systematically investigated only in few cases. These are aqueous solutions of neutral and acidic sodium and potassium citrates and diammonium hydrogen citrate. Mostly, the volumetric and compressibility properties are reported, and they are based on measured densities and speed velocities. In deahng with a particular physical property, all available citrates are considered together. 

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