Compressibility of the gas

Fuller s equation, applied for the estimation of the coefficient of diffusion of a binary gas mixture, at a pressure greater than 10 bar, predicts values that are too high. As a first approximation, the value of the coefficient of diffusion can be corrected by multiplying it by the compressibility of the gas /... 

Once the bubble point is reached (at point B), the first bubble of ethane vapour is released. From point B to C liquid and gas co-exist in the cell, and the pressure is maintained constant as more of the liquid changes to the gaseous state. The system exhibits infinite compressibility until the last drop of liquid is left In the cell (point C), which is the dew point. Below the dew point pressure only gas remains in the cell, and as pressure is reduced below the dew point, the volume increase is determined by the compressibility of the gas. The gas compressibility is much greater than the liquid compressibility, and hence the change of volume for a given reduction in pressure (the... 

Gas reservoirs are produced by expansion of the gas contained in the reservoir. The high compressibility of the gas relative to the water in the reservoir (either connate water or underlying aquifer) make the gas expansion the dominant drive mechanism. Relative to oil reservoirs, the material balance calculation for gas reservoirs is rather simple. A major challenge in gas field development is to ensure a long sustainable plateau (typically 10 years) to attain a good sales price for the gas the customer usually requires a reliable supply of gas at an agreed rate over many years. The recovery factor for gas reservoirs depends upon how low the abandonment pressure can be reduced, which is why compression facilities are often provided on surface. Typical recovery factors are In the range 50 to 80 percent. 

Similar to volumetric efficiency, isentropic (adiabatic) efficiency T is the ratio of the work required for isentropic compression of the gas to work input to the compressor shaft. The adiabatic efficiency is less than one mainly due to pressure drop through the valve ports and other restricted passages and the heating of the gas during compression. 

Low-speed units are typically integral in design as shown in Figure 10-4. Integral means that the power cylinders that turn the crank shaft are in the same case (same housing) as the cylinders that do the compressing of the gas. There is one crank shaft. Typically, integrals are con-... 

The solution of the work compression part of the compressor selection problem is quite accurate and easy when a pressure-enthalpy or Mollier diagram of the gas is available (see Figures 12-24A-H). These charts present the actual relationship of the gas properties under all conditions of the diagram and recognize the deviation from the ideal gas laws. In the range in which compressibility of the gas becomes significant, the use of the charts is most helpful and convenient. Because this information is not available for many gas mixtures, it is limited to those rather common or perhaps extremely important gases (or mixtures) where this information has been prepared in chart form. The procedure is as follows ... 

This problem involves the compressibility of the gas and its moisture content. These will be taken into account in the following design. 

Adiabatic Head. The height in ft of gas supported at the compressor discharge as the gas discharges into a system at the desired pressure level is the adiabatic head. The compression of the gas column is adiabatic. The temperature and pressure of the compression column will be related by the adiabatic expression. 

The power requirement is then that for compression of the gas from pressure Pi to P3 and for imparting the necessary kinetic energy to it. Under normal conditions, however, the kinetic energy term is negligible. Thus for an isothermal efficiency of compression 17. the power required is ... 

Figure 5.143. For CONFL02, at t = 3.5 min. the pressure Pi was increased from 150 to 300 N/m, at t = 8.5 it was decreased to 200 and at t = 19 further to 150. This resulted in an increase in Z and a compression of the gas phase volume Vq and opposite changes later in the simulation.

A further rising of the reservoir causes a compression of the gas in the capillary C (closed). Capillary D is open and connected to the vacuum system. The difference Ah between the two mercury heights corresponds to a pressure difference Ap = pg-Ah (Ah in mm gives numerically Ap in torr) p is the density of mercury. If the compression of the gas in B and C is isothermal, we can write ... 

The reader interested in the liquefaction technologies can see, for example, ref. [14,15], We will only remind that in most cases, the gas cooling is obtained by the Joule-Thomson process an isothermal compression of the gas is followed by an expansion. This procedure leads to a cooling only if the starting temperatures are lower than the inversion temperature 7] = 6.75 TCI (for a Van der Waals gas), where TCI is the critical temperature. 

If the cell where the Pomeranchuck process takes place is used to cool something else besides 3 He, the presence of the solid, which is a very bad conductor, may be a serious drawback. The shape of the 3 He melting curve prevents the compression of the gas through a capillary connected to a compressor at room temperature. In fact, a solid block would be formed where the capillary is at T = 315mK. For this reason, a cell with flexible walls, as that shown in Fig. 7.5, is necessary. 

At the lower temperatures, a greater attraction exists between the molecules, so the compressibility of the gas is significant. This causes the product of P V to be smaller than predicted. Because P V is found in the denominator in the foregoing equation, the calculated molecular weight would tend to be higher than the molecular weight actually is. 

In some cases the change of quality will be negligible so the second term in the numerator of equation 7.65 can be neglected. The other feature leading to acceleration, namely the compressibility of the gas phase, is responsible for the form of the denominator. Sometimes gas compressibility will be negligible, particularly if the overall pressure is high this is the case in gas-oil pipelines. 

Because the attraction between molecules becomes more significant at lower temperatures due to a decrease In kinetic energy of the molecules, the compressibility of the gas Is Increased. This causes the product P 1/ to be smaller than predicted. P V s found in the denominator in the equation listed above, so the molecular weight tends to be higher than its ideal value. 

Ref 22, pp 161-62. Under the title "Thermal Effect of Impact is discussed initiation of liquid expls, such as NG, NGc, etc. It differs from initiation of solid expls (discussed on p 153 of Ref 22) in that there is no friction between crystals as in solids, but everything depends on rise of temperature created by adiabatic compression of gas or vapor in minute bubbles.. For example, with NG contg a bubble as small as 0.1 mm in diam 100% explns can be obtd with impact energy of 400 gram-cm, while 10 to 10 g-cm are required when no gas bubble is present. The temp T2 reached in a bubble due to adiabaric compression of the gas depends, in the case of ideal gas, on the... 

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