Gas movement

I. Gas movement. In most cases, over 90 percent of the gas volume produced from the decomposition of sohd wastes consists of methane and carbon dioxide. Although most of the methane escapes to the atmosphere, both methane and carbon dioxide have been found in concentrations of up to 40 percent at lateral distances of up to 120 m (400 ft) from the edges of landfills. Methane can accumulate below buildings or in other enclosed spaces on or close to a sanitaiy landfill. With proper venting, methane should not pose a problem. 

If the design of Figure 4-41 is used for liquid-vapor separation at moderately high liquid loads, the liquid sliding down Lhe walls in sheets and ripples has somewhat of a tendency to be torn off from the rotating liquid and become re-entrained in the upward gas movement. 

The ideal gas equation and the molecular view of gases lead to several useful applications. We have already described how to cany out calculations involving P-V-n-T relationships. In this section, we examine the use of the gas equation to determine molar masses, gas density, and rates of gas movement. 

Passive gas control systems control gas movement by altering the paths of flow without the use of mechanical components. There are generally two types, high-permeability and low-permeability. 

Active perimeter gas control systems control off-site gas migration with the use of an active control system to alter pressure gradients and paths of gas movement by mechanical means. Three or four major components are required in active perimeter gas control systems ... 

Further, landfill characteristics, such as production of landfill gases, may limit the use of ET covers. The cover system may not adequately control gas emissions since typical ET cover designs do not have impermeable layers to restrict gas movement. If gas collection is required at the site, it may be necessary to modify the design of the cover to capture and vent the gas generated in the landfill. In addition, landfill gas may limit the effectiveness of an ET cover, because the gases may be toxic to the vegetation.13 45... 

Any material that provides adequate protection against water should at least limit convective soil gas movement. Properly applied waterproofing materials should help block pressure-driven entry of soil gas. 

DSMA Atcon, Ltd., A Computer Study of Soil Gas Movement into Buildings, Report 1389/1333, Department of Health and Welfare, Ottawa, Canada (1985). 

The change in Gibbs function during gas movement gas molecules move from high pressure to low... 

It should be clear from Equation (4.39) that gas movement in the opposite direction, from low pressure (/>(finai)) to high (/Amman) would cause AG to be positive, thereby explaining why the process of gas going from low pressure to high never occurs naturally. Stated another way, compression can only occur if energy is put into the system so, compression involves work, which explains why pumping up a car tyre is difficult, yet the tyre will deflate of its own accord if punctured. 

Finally in the diffusa- section 5 the pressure is recovered from the kinetic motion of the gas through some kind of shock wave - the fact which is well known in gas dynamics. Certainly the pressure recovers not up to the initial inlet value. The pressure losses (typically 20 - 30% at present) depend on the desired temperature in the working section 3 (as desired temperature is lower the gas movement is faster and pressure recovering is more difficult). This section acts like a compressor in TET. 

Using valve trays. Their sideways gas movement alleviates liquid channeling (Sec. 7.3.2, item 9). On the basis of eliminating the stagnant regions, Biddulph (168) expects valve tray efficiencies in... 

The electrodes were arranged as a stack of bipolar electrodes as shown in Figure 23. Aluminum formed at the lower electrodes in each individual cell flows concurrently together with the chlorine gas to the central vertical shaft, where the metal sinks to the bottom and the gas rises to the top. The gas movement promotes the necessary circulation of the electrolyte. Due to the compact bipolar arrangement and the short interpolar distance (10-20 mm) the electrical energy consumption was as low as 9.5 kWh/kg Al. 

Control of gas movement by recovery. The movement of gases in landfills can also be controlled by installing gas-recovery wells in completed landfills (see Fig. 22-63h). This is considered an active venting system. Clay and other lines are used when landfill gas is to be... 

In p-enclosures with fast moving parts (motors, generators, internal cooling fans), the pressure differential (referring to the environmental atmosphere) is strongly influenced by the protective gas movement caused by the rotor or internal fans, which may result in a negative pressure differential at some points of the p-enclosure, e.g. at the suction side of the internal fan. Generally, a positive pressure differential shall be maintained at all points inside the p-enclosure. 

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