Expansivity, liquid hydrogen

Expansivity. Liquid hydrogen has a rather large coefficient of thermal expansion, when compared to ordinary fluids. Also, the vapor pressure curve of hydrogen is rather steep. As a consequence, the mere fact of pressurizing a tank of liquid hydrogen from one atmosphere to approximately two atmospheres causes the liquid to warm to about 23 K and the level to rise by about 5%. Thus, the liquid level of a closed hydrogen tank will rise upon pressurization, while the mass contents actually remain the same. 

Liquid hydrogen fluoride has a large coefficient of thermal expansion, and temperature increases can result in contaiiuncnt failure if tliere is no room for tlicnnal expansion of the liquid. Thus liquid-full equipment presents a special liaztird. A liquid-full vessel is a vessel tliat is not vented and lias little or... 

We have seen that hydrogen becomes slightly warmed in this process, so that its liquefaction by free expansion would be impossible under ordinary conditions. Dewar in 1900 showed, however, that if the hydrogen was previously cooled, it suffered a further cooling on free expansion, and in this way he obtained liquid hydrogen. Olszewski (1902) found that the inversion point of hydrogen is situated at — 80 6° C. This effect of temperature is general, and implies that the ratio of the potential to the kinetic... 

Expansion of liquid hydrogen to gaseous hydrogen in confined spaces... 

The potential hazard associated with expansion of liquid to gas is substantial for hydrogen, as it is for other cryogenic fluids. Careful attention must be given to the location of relief devices in liquid hydrogen handling systems. 

Pipeline transportation of liquid hydrogen is realized on a small scale and short range. Stainless steel is usually taken for the inner line with low heat conduction spacers as a support in the vacuum jacket. The Kennedy Space Center in Florida uses an LH2 and LOX pipeline of 500 m length with an irmer pipe diameter of 0.15 m. Flow rates achieved are up to 250 LH2 per minute and 100 m LOX per minute, respectively [12]. Transfer is realized by applying pressure, no pumps. Major concerns besides heat leakage is the mechanical stress imposed on the irmer line due to contraction / expansion, pressure oscillations upon cooldown, or two-phase flow. 

Similarly, thermal stresses can be produced if a temperature differential exists across an element of a low-temperature system or if materials with unlike expansion coefficients are bonded together Sagata has presented an interesting summary of the problems associated with the thermal stresses created by liquid hydrogen in insulated tanks. 

From the temperature-entropy diagram, the parameters associated with isentropic expansion of saturated liquid hydrogen from several initial pressures were evaluated. These parameters include the isentropic spouting velocity, sonic velocity, Mach number, specific flow area, and the volume ratio of vapor to mixture Fr. The results are shown graphically in Figs. 1 through 4. 

The preceding analysis outlines a possible method of designing a liquid-hydrogen pump. However, an experimental program would be required to verify this conclusion and to determine the limits of useful expansion. 

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