Changing density gases

For the flow of gases, expansion factor Y, which allows for the change in gas density as it expands adiabaticaUy from pi to po, is given by... 

In the surrounding atmosphere, a blast wave is experienced as a transient change in gas-dynamic-state parameters pressure, density, and particle velocity. Generally, these parameters increase rapidly, then decrease less rapidly to sub-ambient values (i.e., develop a negative phase). Subsequently, parameters slowly return to atmospheric values (Figure 3.7). The shape of a blast wave is highly dependent on the nature of the explosion process. 

Strekalov M. L., Burshtein A. I. Quantum theory of isotropic Raman spectra changes with gas density, Chem. Phys. 60, 133-48 (1981). 

A reactive gas is slowly bubbled into a column of liquid. The bubbles are small, approximately spherical, and are well separated from each other. Assume Stokes law and ignore the change in gas density due to elevation. The gas is pure and reacts in the liquid phase with first-order kinetics. Derive an expression for the size of the bubbles as a function of height in the column. Carefully specify any additional assumptions you need to make. 

Most fluidized-bed processes operate within the temperature and pressure ranges of ambient to 1100°C and ambient to 70 bar, respectively. Over this temperature range, gas viscosity increases by a factor of about 3 to 4, depending upon the type of gas. If the pressure of the system remains constant while temperature is changed, the gas density decreases over this temperature range by a factor of 1373/293 = 4.7. If system pressure is increased without changing temperature, the gas density is increased by the same factor as the pressure ratio—which would be approximately 70 1 for a change in pressure from ambient to 70 bar. 

This expression indicates that cyclone efficiency should not change with gas density because (pp - pg) is insensitive to changes in pressure. However, cyclone efficiency should decrease with gas viscosity because it is harder for a particle to travel to the cyclone wall in a more viscous fluid. 

Blast - Is the transient change in gas density, pressure, and velocity of the air surrounding an explosion point. 

Gas-liquid chromatography. A process for determining the components of a gaseous stream. The gas is passed through a series of fine mesh screens. The finest are coated with a liquid. The setup causes the components to move through at different rates. At the tail end, they are detected, one after another, by thermal conductivity changes, density differences, or ionization detectors. 

The above simple example shows that in the special case of constant fluid density the space-time is equivalent to the holding time hence, these terms can be used interchangeably. This special case includes practically all liquid phase reactions. However, for fluids of changing density, e.g., nonisothermal gas reactions or gas reactions with changing number of moles, a distinction should be made between r and t and the correct measure should be used in each situation. 

For cases without the phase change between gas and solid phases, I, Frk, and grk vanish. Thus, assuming constant material densities and using Eq. (5.129), the volume-averaged continuity equation, Eq. (5.120), becomes... 

The influence of pressure on eg is caused by the change of gas density only. Probably the most widely applicable relationships are from Wilkinson and Van Dierendonck [44] ... 

The simulated and experimental variations of the end-of-run (i.e., 8 hr.) isomerization rates with density are compared in Figure 1. Details of the experiments are provided elsewhere [2, 3]. At subcritical densities, the extraction of coke precursors is insignificant. Hence, an increase in the concentration of the hexene and coke precursors (i.e., oligomers) leads to lower isomerization rates. At near-critical densities, the extraction of coke precursors becomes significant. Hence, the isomerization rate increases. Both the experimental and simulated rates show a decreasing trend when the density is increased from near-critical to supercritical values. This is attributed to pore-diffusion limitations as the fluid changes from gas-like to liquid-like. Above 2.0 pc, the isomerization rate increases with density as the ability of the reaction mixture to extract the coke precursors increases. 

Due to the limited response time of suitable sensors fast sorption or gas transport processes on a time scale below a second are hard to monitor. To significantly improve the resolution in time an interferometric pressure sensor can be applied. The central part of the interferometric pressure sensor presented is a Michelson-interferometer this set-up is sensitive to changes in gas pressure as the index of refraction, and thus the optical path length for a laser beam within the interferometer, is a function of the gas density. 

In 1822, Cagniard de la Tour showed the existence of a critical temperature for each individual substance above which such a substance can only occur as a fluid and not as either a liquid or a gas. This critical point is reached as one moves upward along the gas-liquid coexistence curve, where both temperature and pressure increase. The original liquid becomes less dense through thermal expansion and the gas becomes more dense as the pressure rises. At the critical point, the densities of the two phases are equal, the distinction between the gas and liquid vanishes and the coexistence curve comes to an end at the critical point, where the substance is described as a fluid. Supercritical fluids exhibit key features such as compressibility, homogeneity and a continuous change from gas-like to liquid-like properties. 

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