Compression and expansion of gases

The work term in an energy balance is unlikely to be significant unless a gas is expanded or compressed as part of the process. To compute the pressure work term  

If the compression or expansion is isothermal (at constant temperature) then for unit mass of an ideal gas  

In industrial compressors or expanders the compression or expansion path will be polytropic , approximated by the expression  

The work produced (or required) is given by the general expression (see Volume 1, Chapter 8)  

The value of n will depend on the design and operation of the machine. 

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The compression and expansion of gases is covered more fully in Section 3.13. 

Use the kinetic-molecular theory to explain the compression and expansion of gases. (13.1)... 

The discussion of the chain statistics permits one, thus, to have a more quantitative description of a flexible, linear macromolecule. The random coil of a sufficiently long molecule can be compared in mass-density and randomness to an ideal gas at atmospheric pressure. The elastic compression and expansion of gases are caused by changes in entropy. It will be shown below that corresponding behavior exists for the extension and contraction of random-coil macromolecules (entropy or rubber elasticity, see Sect. 5.6.5). Combining many random coils into a... 

Thus, theoretically, the clearance volume does not affect the work done per unit mass of gas, since Vi — V4 is the volume admitted per cycle. It does, however, influence the quantity of gas admitted and therefore the work done per cycle. In practice, however, compression and expansion are not reversible, and losses arise from the compression and expansion of the clearance gases. This effect is particularly serious at high compression ratios. 

The economic operation of processes which involve the compression and expansion of large quantities of gases, such as ammonia synthesis, nitric acid production and air... 

Robert Boyle (1627-1691). Boyle was an Irish chemist and physicist who studied the compression and expansion of air and other gases and discovered that the volume of gas at a constant temperature varies inversely with its pressure (Boyle s law). 

Compression and expansion through a small hole lowers temperature further.) Exceptions are He and H2, for which repulsion dominates. -> The effect is used in some refrigerators and to effect the condensation of gases such as oxygen, nitrogen, and argon. 

Figure 3.2 I The destructive force of an explosion is due in part to the expansion of gases produced in the reaction. This molecular scale diagram illustrates the effect. In a soUd explosive, relatively large molecules are packed very closely together. When the reaction occurs, the products are usually smaller gas molecules. These gases are initially formed in a volume similar to that of the solid. Because densities are typically hundreds of times smaller in gases than in solids, the products are very highly compressed. The gas must expand to lower its density, and this produces a shock wave.

Although we have used gases as an example, Equations 7.1 and 7.3 also apply to the compression or expansion of liquids and solids by an external pressure. 

The PXS is designed to operate without the use of active equipment such as pumps and AC power sources. The PXS depends on reliable passive components and processes such as gravity injection and expansion of compressed gases. The PXS requires a one-time alignment of valves upon actuation of the specific components. 

Chermin, in a series of articles, discusses the thermodynamics of some classes of hydrocarbon and hydrocarbon derivatives. Edmister, in Applied Hydrocarbon Thermodynamics , includes information on equations of state, Mollier charts for pure hydrocarbons, compression and expansion charts for gases, and details of petroleum distillation calculations. Green has reviewed the thermodynamic properties of organic oxygen compounds and the thermodynamic properties of the normal alcohols Cl to Ci2. Justice has treated the thermodynamic properties and electronic energy levels of some rare-earth sesquioxides. 

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