Hydrogen-helium mixtures

At 17.4°, 20.4° and 21.8°K, there appear to be no critical points for the helium-hydrogen mixtures this is indicated by phase equilibrium data calculated at these temperatures at pressures up to 7000 psia. If a critical point were reached, thepylx curves for helium and hydrogen could converge to the same value at the critical point, but there appears to be no tendency toward convergence even at pressures of 7000 psia. Unfortunately, no experimental data exist to verify this calculation. Virial coefficients calculated from the correlation are in good accord with the experimental data of Varekamp and Beenakker [ ], as shown in Table V. 

The NPD sensor is a rubidium or cesium bead contained inside a small heater coil. The helium carrier gas is mixed with hydrogen and passes into the detector through a small jet. The bead, heated by a current passing through the coil, is situated above the jet, and the helium-hydrogen mixture passes over it. If the detector is to respond to both... 

F. Allario and N. Wainfan, Electric field distribution in pulsed high-frequency current density discharges in helium and helium-hydrogen mixtures, J. Appl. Phys. 40(2), 675-681 (1969). 

A carrier gas, such as nitrogen, helium, or a helium/ hydrogen mixture, sweeps the pyrolysis gases into any of four downstream systems of reactors, scrubbers, separators, and detectors for the determination of the carbon monoxide content, hence of the oxygen in the original fuel sample. The result is reported as mass % oxygen in the fuel. 

Figure 6. XPS wide scans of a commercial copper/aluminum extruded catalyst obtained using silicon Ka x-radiation A. untreated catalyst B. following 200 C for 12 hours in 10% hydrogen/90% helium gas mixture.

At many plants, fluxes are added to the metal to reduce hydrogen contamination, remove oxides, and eliminate undesirable trace elements. Solid fluxes such as hexachloroethane, aluminum chloride, and anhydrous magnesium chloride may be used, but it is more common to bubble gases such as chlorine, nitrogen, argon, helium, and mixtures of chlorine and inert gases through the molten metal. 

Natural Gas - A mixture of hydrocarbon compounds and small amounts of various nonhydrocarbons (such as carbon dioxide, helium, hydrogen sulfide, and nitrogen) existing in the gaseous phase or in solution with crude oil in natural underground reservoirs. 

Baum, E. H. Gas chromatographic analysis of hydrogen-helium gas mixtures. Anal. 

Procedure. After the catalyst has reached a steady state synthesis activity the synthesis gas stream is switched to a hydrogen/helium gas mixture (ratio 0.25) at a velocity of 0.75 cm-fys and 0.25 MPa. The temperature in the reactor is held at 550 K. When the production of hydrocarbons is very small, the H2/He stream is replaced by synthesis gas for 20 seconds, whereafter again l /He is fed to the catalyst. Pressure, temperature and feed are carefully held constant during this treatment. A second experiment is carried out that is almost identical to the one described above. The only difference is that instead of a mixture of hydrogen and helium pure helium is used in the periods between the introduction of synthesis gas. 

Because the diffusion coefficient of UF into hydrogen is about 20 percent higher than into helium, optimum pressures for UFg-hydrogen mixtures would be about 20 percent higher than the foregoing values. The inference then is that the data of Fig. 14.23 were obtained with a nozzle with a throat spacing around 0.4 mm. 

A hazardous potential was thought to exist in the AVR HTGR, Julich, with a hydrogen-carbon monoxide-helium-air mixture, which could evolve in a water ingress accident scenario with an estimated 8 % H2 + CO concentration resulting from the corrosive reaction between steam and hot fuel element graphite. Ignition experiments in a combustion chamber were conducted in 1971 to examine the lower combustibility limit in respective gas mixtures. The tests have shown that a mixture with 22 % H2 + CO was not flammable at temperatures up to 120 °C [54],... 

The only disadvantage to the use of hydrogen as a carrier gas is the real or perceived explosion hazard from leaks within the column oven. Experience has shown that the conditions required for a catastrophic explosion may never be achieved in practice with forced air convection ovens. However, commercially available gas sensors will automatically switch off the column oven and carrier gas flow at air-hydrogen mixtures well below the explosion threshold limit. A considerable difference in the relative cost of helium in the USA and Europe has resulted in different preferences on the two continents. For open tubular columns helium is widely used in the USA for safety rather than theoretical considerations while hydrogen is commonly used in Europe. 

Figure 4.5 shows hydrogen flux data of Eltron Research Inc., again for an ideal hydrogen-helium feed mixture, for a membrane of Group IVB-VB material... 

The parameters for the helium-hydrogen system were evaluated with the assumption of temperature dependence according to (8), (11), and (12). For the value of <322, the vapor pressure of hydrogen was fitted at 17.4°K and the value of an was determined from helium P-V-T data in the temperature range from 15 to 40 K at pressures from 10 to 27 atm. The mixture parameter was determined from the limiting value of pyjx for helium in hydrogen, from the data of Smith at 17.4°K. 

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