Density, gases from compressibility

Formation water density is a function of its salinity (which ranges from 0 to 300,000 ppm), amount of dissolved gas, and the reservoir temperature and pressure. As pressure increases, so does water density, though the compressibility is small... 

When a gas is compressed, it heats up. When it expands, it cools. Anyone who uses a bicycle pump knows this. However, it is no longer true for electron or neutron gases at very high densities. This deviation from the ideal gas laws has a catastrophic effect on stars. Moreover, the behaviour of a photon gas with regard to volume changes differs from that of a typical gas made up of atoms,... 

Some foam products are subjected to up to 10 major impacts in their lives, therefore a foam may need to be selected so that the performance is still adequate. Products, subjected to hundreds of thousands of impacts as in running shoe midsoles, were dealt with under fatigue. It appears that the higher density HDPE (419) and PP foams loose a significant amount of their protection after several impacts, but nevertheless it may be possible to use sufficient foam thickness to provide the required protection. If low density EVA foams are used, the impact energy densities are much lower, as the majority of the resistance is from compressing the cell gas. Ankrah and co-workers (33) performed multiple impacts on LDPE/ESI blend foams, and found... 

Modem developments are centered around the calculations of the radial distribution function g (r), which is the ratio of the densiiy of molecules al a distance r from a given molecule, to the average density in the gas. The compressibility can be expressed straightforwardly in terms of g (r) as follows. 

Moreover, the density of the compressible gas phase can be calculated from the modified Gas law ... 

The unique properties of underwater explosions are due to the high velocity of sound in water meaning that the pressure-wave travels approximately four times faster in water than it does in air. Furthermore, due to the high density and low compressibility of water, the destructive energy (from the explosion) can be efficiently transferred over relatively large distances. The most important effects caused by an underwater explosion are the corresponding shock-wave and the gas bubble pulsations. 

It is immediately apparent that (248) will give the correct zero-frequency xc potential value for Harmonic Potential Theorem motion. For this motion, the gas moves rigidly implying X is independent of r so that the compressive part, Hia, of the density perturbation from (245) is zero. Equally, for perturbations to a uniform electron gas, Vn and hence nn, is zero, so that (248) gives the uniform-gas xc kernel fxc([Pg.126]

Reduced temperatures below 1.0 are subcritical and the gas becomes liquefied with increasing pressure. The density changes from the low value of the gas phase to the high value of the liquid phase. Then it remains almost constant with rising pressure because the liquid is almost incompressible. As reduced temperatures approach unity the isothermal compressibility of the gas rises rapidly. At values above unity in the supercritical area there is no further liquefaction and the gas density can be adjusted continuously with increasing pressure, which offers the option to adjust the dissolving power. 

Solids are obviously very different from gases. A gas has low density and high compressibility and completely fills its container. Solids have much greater densities, are compressible only to a very slight extent, and are rigid—a solid maintains its shape irrespective of its container. These properties indicate that the components of a solid are close together and exert large attractive forces on each other. 

A simple example may be given. Carbon dioxide is often used in separations around 40°C. At 315 K (42.8°C), its density doubles, from 0.3 kg dm to 0.6 kg dm , when pressure is brought from 8.36 to 10.15 MPa, that is, a 21% increase. Notice that a similar increase of density in a low-pressure gas, commonly regarded as a highly compressible state, can only be achieved with a 100% increase in pressure. 

Let us assume for purposes of this paper that we can know the composition of a gas from some suitable measurement. It is then possible, in principle, to calculate pertinent properties such as heating value, relative density, compressibility factor. Unfortunately, as often happens in practice, these supposedly unambiguous calculations become clouded by accepted procedirres, misconceptions, misguided regulations. The discussion in this paper attempts to dispel the misconceptions and to clarify the accepted procedures. As for the regulations, it is only possible to wish that they would not always choose the path of maximum irrationality and to try to perform the calculations in the least offensive (technically) marmer possible. The calculations described in this paper reflect those suggested in GPA Standard 2172-85. However, this paper contains considerable amplification and discussion of the techniques. 

From this we can see that gas density depends on pressure (in other words, the gas is compressible) and on absolute temperature. At very high pressures or very low temperatures, the density of a gas can approach or even exceed that of a liquid, and it is then difficult to distinguish the two states... 

Faraday discovered benzene and isobutylene (C4H8) in the liquid separating from compressed oil-gas. He determined the composition of benzene as bicarburet of hydrogen CgH (C=6), i.e. He found its vapour density... 

A fluid in the supercritical region can have a density comparable to that of tbe liquid, and can be more compressible than the liquid. Under supercritical conditions, a substance is often an excellent solvent for solids and liquids. By varying the pressure or temperature, the solvating power can be changed by reducing the pressure isothermally, the substance can be easily removed as a gas from dissolved solutes. These properties make supercritical fluids useful for chromatography and solvent extraction. 

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