Gas expansion experiments

Figure 4.2 Joule s gas expansion experiment. On allowing gas to flow into the right-hand container, no temperature change was observed.

The gas expansion experiment of Joule, shown in Fig. 4.2, took place completely irreversibly no work was done, because no resistance was offered from outside. The overall change is ... 

However, it does have certain disadvantages which may lead to serious experimental errors in gas adsorption measurements [1.46-1.49]. This will be demonstrated by a set of helium gas expansion experiments performed at the Institute of Fluid- and Thermodynamics (IF l) at the University of Siegen, Siegen during 1994 - 2002 as follows. 

Figure 1.5. Determination of the (known) volume (51.10 cm ) of a calibration cylinder by gas expansion experiments using gases He (5.0), (5.0) and CH4 (5.5) at...

It should be emphasized that the auxiliary quantity (f2v) only includes measurable quantities. Hence its numerical value is known from the gas expansion experiment. According to Eq. (2.4), can be called reduced mass of the adsorbed phase as it is the difference between the mass of the adsorbed phase (m ) and the mass of the sorptive gas that would be included in the void volume of both the sorbent and the sorbate phase (V ) [2.3, 2.7]. As this quantity also is unknown, some model assumptions for it have to be introduced to calculate the adsorbed mass (m ) fromEq. (2.4). 

The volumes Vac, Vsv should be determined experimentally by using a sample, preferably a cylinder of cahbrated volume (Vo) made of dense material (Ti, Au) and performing gas expansion experiments as described above. The amount of gas adsorbed on the surface of the sample normally can be neglected. ... 

For binary coadsorption equilibria with non-isomeric gas components (Ml 7 M2) gravimetric-chromatographic measurements are not needed. Instead densimetric-volumetric measurements are recommended [6]. The measurement procedure can be grasped from the experimental scheme sketched in Figure 5 below. Basically, a gas expansion experiment is combined with a density measurement of the equilibrium sorptive gas mixture by the buoyancy of a sinker coupled to a magnetic suspension balance. 

Today there are several experimental methods available to measure pure gas and gas mixture adsorption equilibria on porous rigid or swelling sorbent materials. All these methods have their specific advantages and disadvantages [1]. Choice of any of them depends mainly on the purpose of measurement and/or accuracy and reliability of data needed. For quick measurements of restricted accuracy gas expansion experiments or volumetric measurements are recommended. If high accuracy data are needed, weighing procedures, i. e. gravimetry should be used... 

Gas-phase experiments at 155 °C. were carried out in a 250-ml. cylindrical Vycor reactor in a hot-air furnace. Later experiments were done in a 500-ml. borosilicate glass flask heated in an oil bath. With either system, di-terf-butyl peroxide, oxygen, and isobutane were metered into the reaction vessel in that order by expansion from the vacuum line the pressure of each component was measured using a mercury or oil manometer. Mercury vapor was excluded from the reaction vessel. 

Operation experience with the natural gas expansion plant of EWV Stolberg... 

As we have already seen, for the application of most manometric techniques for the determination of the amount adsorbed it is necessary to have an accurate knowledge of the volumes of two parts of the overall dead space. The first is the connecting volume located between the stopcock above the adsorbent bulb and the lowest valve of the dosing volume (see Figure 3.2). The second, and more important, volume is that of the dead space within the adsorbent bulb. Although the connecting volume does not need to be determined for each experiment, its value can be checked in the first stage of the gas expansion calibration procedure. 

Fig. 6. Dynamic expansion experiment Relaxation of the gas pressure, after a step like change of the pressure in the sample cell, due to molecular diffusion of the gas into the open porous monolithic material.

The basic idea of the dynamic pressurization (DP) experiment is similar to the dynamic gas expansion (DGE) method. Both use a sudden pressure change around a gel specimen to initiate gas flow into or out of the sample, thus avoiding the delicate leakage problems typically encountered in static gas flow setups. While DGE monitors the gas pressure outside the gel as a function of time and deduces the permeability from its equilibration behavior (in principle a dynamic pycnometry experiment). DP utilizes the dynamics of the elastic deformation of the gel to deduce both elastic modulus and permeability. The deformation, or strain, is a consequence of the pressure difference between the interior and the exterior of the specimen. For example, after a sudden increase in pressure, the gas in the gel pores is initially only slightly compressed along with the elastic compression of the gel. After a characteristic time, the pressure equilibrates and the gel ideally springs back to its original dimensions. 

The growing technology provided experience in coping with the more conventional cryogenic hazards associated with material s brittleness, with cold flesh "burns," and with liquid to gas expansion in confined spaces. 

Later workers accepted Porter s assignment without reservation [88], The gas phase spectrum was reproduced by Berry using phenyl azide as the precursor [25]. Laser-induced fluorescence attributed to triplet phenyl nitrene was observed upon pumping the 368 nm transition in ordinary gas phase experiments and in supersonic jet expansions where very highly resolved spectra could be generated [89a]. 

The following points in the design of a FI hydride generation AAS system, based mainly on our own experiences using gas expansion separators, is worth mentioning... 

To complete the derivation of the functional form of the time-domain line shapes seen in the pulsed nozzle experiment, we consider the characteristics of the pulsed nozzle gas expansion. We assume that all expanding particles travel at constant speed Vq on radial paths originating at the nozzle. Using the geometry of Figure 10, the velocity field v(r) may be written as... 

The physics of volumetric gas adsorption experiments is simple a given amount of sorptive gas is expanded into a vessel which includes a sorbent sample and which initially has been evacuated. Upon expansion the sorptive gas is partly adsorbed on the (external and internal) surface of the sorbent material, partly remaining as gas phase around the sorbent. By a mass balance, the amount of gas being adsorbed can be calculated if the void volume of the sorbent, i. e. the volume which can not be penetrated by the sorptive gas molecules is known - at least approximately. 

Upon expansion from the storage vessel the sorptive gas may not only be adsorbed on the surface of the sorbent material but also on the walls of the adsorption vessel and the tube connecting both vessels. This may cause additional uncertainties in measurement. These often but not always can be reduced by performing complementary experiments with gas expansion to the empty adsorption chamber including no sorbent material at all. To reduce wall adsorption electropolishing of all inner surfaces is recommended. An experiment allowing to determine wall adsorption is described in Chapter 4, Sect. 3.6. 

In step-up pressure experiments, i. e. gas expansion and adsorption processes with remnant gas in the adsorption chamber, cp. Figs. 2.1, 2.6, the uncertainties of the adsorbed mass accumulate due to the algebraic structure of the sorptive gas mass balance equation... 

Enhanced safety following ATWS. Gas expansion modules. Experiment for the response time required. 

In order to consolidate the bases of theoretical treatments and understand clearly the effective limits of approximate models, molecular beam gas-phase experiments are an ideal choice to study molecular systems under well-controlled conditions [1]. They allow making a clear picture of isolated system properties and then introducing the perturbation due to the environment in a controlled way. Given the characteristics of the supersonic expansion, it is possible to obtain cold isolated molecules distributed in very few quantum states as well as complexes that are held together by weak interactions including clusters that are not stable under the usual static gas-cell... 

It suffices to carry out one such experiment, such as the expansion or compression of a gas, to establish that there are states inaccessible by adiabatic reversible paths, indeed even by any adiabatic irreversible path. For example, if one takes one mole of N2 gas in a volume of 24 litres at a pressure of 1.00 atm (i.e. at 25 °C), there is no combination of adiabatic reversible paths that can bring the system to a final state with the same volume and a different temperature. A higher temperature (on the ideal-gas scale Oj ) can be reached by an adiabatic irreversible path, e.g. by doing electrical work on the system, but a state with the same volume and a lower temperature Oj is inaccessible by any adiabatic path. 

Rare-gas clusters can be produced easily using supersonic expansion. They are attractive to study theoretically because the interaction potentials are relatively simple and dominated by the van der Waals interactions. The Lennard-Jones pair potential describes the stmctures of the rare-gas clusters well and predicts magic clusters with icosahedral stmctures [139, 140]. The first five icosahedral clusters occur at 13, 55, 147, 309 and 561 atoms and are observed in experiments of Ar, Kr and Xe clusters [1411. Small helium clusters are difficult to produce because of the extremely weak interactions between helium atoms. Due to the large zero-point energy, bulk helium is a quantum fluid and does not solidify under standard pressure. Large helium clusters, which are liquid-like, have been produced and studied by Toennies and coworkers [142]. Recent experiments have provided evidence of... 

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