Low-density “gas

Low Density Gases. A fan may have to operate on low density gas because of temperature, altitude, gas composition (high water vapor content of the gas can be a cause of low density), reduced process pressure, or a combination of such causes. To develop a required pressure, the fan has to operate at a considerably higher speed than it would at atmospheric pressure, and hence it must operate much closer to top wheel speed. Bearing life is shorter, and the fan tends to vibrate more or can be overstressed more easily by a slight wheel unbalance. Abrasion of the blades from dust particles is more severe. Therefore, a sturdier fan is needed for low density gas service. 

The great impact of density in this example and in Table 1 should be noted. Probably the most common specification error is to use the large AP values characteristic offiquids in low density gas systems. 

Acoustic Coupling When the shell-side fluid is a low-density gas, acoustic resonance or coupling develops when the standing waves in the shell are in phase with vortex shedding from the tubes. The standing waves are perpendicular to the axis of the tubes and to the direction of cross-flow. Damage to the tubes is rare. However, the noise can be extremely painful. 

I lydrogen is a low-density gas at ambient conditions. It liquefies at -253°C. For storage hydrogen must be compressed nr liquefied. 

When the well is circulated through the choke line, a rapid loss in hydrostatic pressure is seen when the kick fluid begins to enter the choke line. Hydrostatic pressure is lost because low density gas is displacing the drilling mud from the small volume of choke line. Small kick volumes can result in long columns of gas in the choke line. Surface choke response must be rapid enough to prevent new kick fluid from entering the well due to the reduction in bottomhole... 

When k < 1/4 the roots (1.79) are real, and Kj(t) decays monotonically with time. For low-density gas... 

It is often obtained from Eq. (1.71) when the kernel is assumed to relax much quicker than the solution to be found. Then it is nothing more than a low-density gas approximation to Eq. (1.71), valid when conditions (1.83) or (1.88) are met. For these conditions the differential theory is expected to be binary in collisions, and... 

Low-density gas hydrate-suppressive drilling fluids have been developed for deep-water applications. These fluids are glycol based [764,766]. 

A. Khaund. Sintered low density gas and oil well proppants from a low cost unblended clay material of selected composition. Patent US 4668645,1987. 

The second generalization is the reinterpretation of the excluded volume per particle V(). Realizing that only binary collisions are likely in a low-density gas, van der Waals suggested the value Ina /I for hard spheres of diameter a and for particles which were modeled as hard spheres with attractive tails. Thus, for the Lennard-Jones fluid where the pair potential actually is... 

The selection of the column type is mainly determined by the composition of the sample. In general open-tubular (capillary) columns are preferred for low-density (gas-like) SFC, whereas packed columns are most useful for high-density (liquid-like) SFC. Open-tubular columns can provide a much larger number of theoretical plates than packed columns for the same pressure drop. Volumetric flow-rates are much higher in packed column SFC (pSFC) than in open-tubular column SFC (cSFC), which makes injection and flow control less problematic. 

An ideal gas is a relatively low-density gas. The pressure p, temperature T, and specific volume v of an ideal gas are related by an equation of state, pv = RT, where i is a constant for a particular gas and is called the gas constant. Air, helium, and carbon dioxide are ideal gases. The properties of an ideal gas can be found in tables such as air tables. 

As mentioned in Section 3.4, clusters of metal atoms of varying sizes can be prepared. The presence of alkali atom clusters in the vapour phase is well documented. Such clusters have a much lower ionization energy than that of an isolated atom and also have a high electron affinity. The probability of electron transfer is therefore considerably greater in a metal cluster. It is indeed known in the case of caesium that as the density of caesium increases (from isolated atoms in a low-density gas to a liquid), larger clusters form and charge-transfer becomes increasingly favoured as the density... 

The translational spectra of pure liquid hydrogen have been recorded with para-H2 to ortho-H2 concentration ratios of roughly 25 75, 46 54 and 100 0, Fig. 3.9 [201, 202]. For the cases of non-vanishing ortho-H2 concentrations, the spectra have at least a superficial similarity with the binary translational spectra compare with the data shown for low frequencies (< 250 cm-1) of Fig. 3.10 below. A comparison of the spectral moments of the low-density gas and the liquid shows even quantitative agreement within the experimental uncertainties which are, however, substantial. 

Supercritical water represents a potentially important component of sonochemistry, in addition to the free-radical reactions and thermal/pyrolytic effects. Because the reaction occurs at or close to the bubble/water interface, compounds more hydrophobic than p-NPA are expected to exhibit even higher hydrolysis rate enhancements. Finally, the existence of the supercritical phase in an ultrasonically irradiated solution suggests a modification of the conventional view of the reactive area at the cavitation site. This region is normally considered to consist of two discrete phases a high-temperature, low-density gas phase and a more condensed, lower temperature liquid shell. 

It is based on a trap in which positrons from a low energy beam are confined in a region of low density gas. As will be shown in subsection 6.3.2 below, this approach has been particularly valuable in elucidating positron annihilation on large molecules, where some form of temporary attachment of a positron to the molecule may play an important role. 

A number of practical situations involve heat transfer between a solid surface and a low-density gas. In employing the term low density, we shall mean those circumstances where the mean free path of the gas molecules is no longer small in comparison with a characteristic dimension of the heat-transfer surface. The mean free path is the distance a molecule travels, on the average, between collisions. The larger this distance becomes, the greater the distance required to communicate the temperature of a hot surface to a gas in contact with it. This means that we shall not necessarily be able to assume that a gas in the immediate neighborhood of the surface will have the same temperature as the heated surface, as was done in the boundary-layer analyses of Chap. 5. Because the mean free path is also related to momentum transport between molecules, we shall also be forced to abandon our assumption of zero fluid velocity near a stationary surface for those cases where the mean free path is not negligible in comparison with the surface dimensions. 

The development of pulsed Fourier-transform NMR spectrometers has greatly increased the sensitivity of NMR measurements, allowing spectra to be obtained for and other nuclei at natural abundances and low sample concentrations. In this experiment this enhanced capability is utilized in a low-density gas-phase measurement of the equilibrium constant Kp for H-D exchange in the reaction... 

We derive a numerical model for the effect of a spatial temperature gradient on the local equilibrium of a chemical reaction in a low--density gas (Knudsen regime). The gas consists of two constituents and the chemical reaction is assumed to take place at the walls of the container. The numerical results are compared with experimental results on the equilibrium 2Na - Na2. From the comparison it follows that the chemical accommodation coefficient for a Na2 wall collision is essentially equal to 1. 

The first studies of CO2 dispersions at pressures around 10 MPa (1,500 psi) were reported in 1978 (48,49). Before that time virtually all experiments were performed on true foams (i.e., near atmospheric pressure on dispersions of a low-density gas in a continuous liquid phase). For this historical reason, the literature on FOR often refers to high-pressure dispersions as "foams, even though the phase, physical, and flow properties of a dispersion in which both phases have a liquid-like density and compressibility cannot always be assumed similar to those of a true foam (66). For many (but not all) mechanistic studies it may be appropriate to employ a foam, and atmospheric pressure emulsions are appropriate stand-ins for high-pressure emulsions of the same chemical composition. However, atmospheric pressure foams cannot be used when the correct answer depends on replicating all of the physical properties of a dispersion that exists only at high pressure. 

---