Helium partial pressure

Figure 2. Helium + water—mole fraction solubility at 1 atm helium partial pressure vs. temperature. At temperatures above 353 K (O) (6) ( , ) (1). The 590 K value of Wiebe and Gaddy was not included in the linear regression.

A gas mixture at a total pressure of 1.0 atm consisting of 80% helium and 20% neon will have a helium partial pressure of 0.80 atm and a neon partial pressure of 0.20 atm. 

The idea of the novel helium detection is a helium partial pressure sensor based on the known method of separating gases by a semipermeable membrane with gas-specific permeation. The component of the gas which is to be detected, in this case helium, is separated in the non-ionised state using the membrane. The amount of the separated helium is measured behind the membrane in a hermetically sealed volume, using a total pressure measurement in the evacuated volume. The change of total pressure in the enclosed volume corresponds to the helium partial pressure in front of the sensor membrane with a high selectivity for helium. 

Quartz is well permeable to helium. The selectivity of a pinhole-free, amorphous quartz membrane is very high for helium. Only hydrogen and neon show a significant permeation rate, but for this application this is negligible. In the enclosed volume behind the membrane the helium partial pressure rises to a pressure proportional to the partial pressure of the process side environment of the sensor. The total pressure of the external environment of the sensor system does not show any influence on the pressure inside the sensor volume. 

To achieve the very low initial fluorine concentration in the LaMar fluorination process initially a helium or nitrogen atmosphere is used in the reactor and fluorine is bled slowly into the system. If pure fluorine is used as the incoming gas, a concentration of fluorine may be approached asymptotically over any time period (Fig. 3). It is possible to approach asymptotically any fluorine partial pressure in this manner. The very low initial concentrations of fluorine in the system greatiy decreases the probabiUty of simultaneous fluorine coUisions on the same molecules or on adjacent reaction sites. 

Sf.ef-Test 4.14A A baby with a severe bronchial infection is in respiratory distress. The anesthetist administers heliox, a mixture of helium and oxygen with 92.3% by mass 02. What is the partial pressure of oxygen being administered to the baby if atmospheric pressure is 730 Torr ... 

FIGURE 8.21 The variation of the molar solubilities of oxygen, nitrogen, and helium gases with partial pressure. Note that the solubility of each gas doubles when its partial pressure is doubled. 

What is the partial pressure of helium when 8.0 grams of helium and 16 grams of oxygen are in a container with a total pressure of 5.00 atm ... 

Using alkane-helium mixtures with alkane partial pressures from 0.001 to 0.1 torr and total pressure of 1.0 torr to ensure thermal equilibrium between the surface and the ambient gas, Sault and Goodman " found that the sticking probabilities for alkanes on Ni(100) increased in the order methane... 

Partial pressure analysis using a mass spectrometer or the pressure rise method may be used to differentiate between these two causes. Since the pressure rise method will only prove the presence of a leak without Indicating Its location In the apparatus. It Is advisable to use a helium leak detector with which leaks can, in general, also be located much more quickly. 

In this case the gas quantity per unit of time Is the leak rate being sought the total pressure may not be used, but only the share for helium or the partial pressure for helium. This signal Is delivered by the mass spectrometer when It Is set for atomic number 4 (helium). The value for Is a constant for every series of leak detectors, making It possible to use a... 

The smallest detectable partial pressure for helium is Pmin He" pumping speed for helium would be... 

Following a dead period (or delay time ) up to a discernible signal level, the signal, which is proportional to the partial pressure for helium, will rise to its full value of p g = Q/S in accordance with equation 5.9 ... 

Systematic diffusion experiments were also conducted with self-supported zeolite wafers (7-14 mg cm ) which were activated at 10 Pa and 675 K for 1.5 h. Prior to contact with the sorbate, the IR cell was filled with dried helium as a carrier gas. Subsequently, one or two components (benzene or ethylbenzene), carried by helium bubbling through thermostatted saturators, could be admitted. A system of mass-flow controllers allowed for an independent change of the partial pressures while the total pressure could be kept constant [22]. The time required to pass the sorbate from the inlet valve to the place of the zeolite wafer was about 4 s. IR spectra were obtained in intervals as short as 0.37 s. 

Figure 4 demonstrates the counter-diffusion of ethylbenzene vs. benzene. In this experiment, benzene was first taken up at 415 K from a stream of benzene in helium, with a benzene partial pressure of 1.15 mbar, until a steady state was reached (spectrum No. 0). Subsequently, ethylbenzene was admixed (1.15 mbar) with the benzene partial pressure and the total rate of the gas ilow remaining constant. Counter-diffusion is indicated by the decrease of the typical benzene absorbance at 1478 cm and the development of the typical ethylbenzene bands at 1605,1496 and 1453 cm (spectra Nos. 1-5). 

Starting with a 10% nitrogen-in-helium mixture, the sample, held slightly above ambient pressure, is immersed in the coolant. When the adsorption signal is complete, the pressure is raised to 2 atm, which increases the partial pressure of nitrogen to 0.2 atm or the equivalent of a 20 % mixture at 1.0 atm. After the completion of each adsorption signal, the pressure is incrementally increased until, at ISOpsia saturation is reached. 

The catalytic measurements were performed in a continuous flow system (23.5 cm3/min total flow) in a fixed bed reactor. In this reactor a standard amount of (0.30 g) catalyst was used. The carrier gas used was helium. The partial pressure of nitrobenzene was 1.2xl03Pa (total pressure 1.01xl0sPa). The composition of the reaction mixture was determined by GC analysis. 

Our study of the kinetics of the reaction of carbon with steam (152) was conducted by the circulation flow method under atmospheric pressure in the temperature-range of 900-1000°C. Dilution with helium was employed to vary the sum of partial pressures of the reaction participants. The experiments were carried out with nonporous graphite of high purity (the content of admixtures did not exceed 10"5%). The roughness factor of graphite was found to be 2-2.5 (from electrochemical measurements). Equation (390) proved not to be obeyed quantitatively the results of the variation of PHl in a broad range by addition of H2 to the gas mixture at the inlet do not form a straight line in the plot 1/r11 vs. PH2 ... 

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