Gas Compression The Basic Idea

This chapter estabhshes the basis for the Second Law of Thermodynamics. It is not critical that you read this chapter to be able to understand the more practical chapters on compression that follow. But for those readers who have technical training, wouldn t it be lovely to actually understand the basis for the Second Law of Thermodynamics. Wouldn t it be grand to really see the beauty and simplicity of the basis for the adiabatic compression work equation  

I have also written this chapter so that the nontechnical reader can easily comprehend the basis for this Second Law. 

Robert Juhus Mayer was a physician practicing near Bavaria in the 1840s. As part of his research into human metabolism, he decided to determine the equivalence between heat and work. 

Heat means British thermal units, or the amount of fuel we have to burn to increase the temperature of a pound of water by one degree Fahrenheit. Work means foot-pounds, or the amount of effort needed to raise a one pound brick by one foot. 

The experiments that people like Dr. Mayer performed established the technical basis for the industrial revolution. Dr. Mayer himself laid the foimdation for the main pillar supporting this technical basis. 

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The basic idea of the dynamic pressurization (DP) experiment is similar to the dynamic gas expansion (DGE) method. Both use a sudden pressure change around a gel specimen to initiate gas flow into or out of the sample, thus avoiding the delicate leakage problems typically encountered in static gas flow setups. While DGE monitors the gas pressure outside the gel as a function of time and deduces the permeability from its equilibration behavior (in principle a dynamic pycnometry experiment). DP utilizes the dynamics of the elastic deformation of the gel to deduce both elastic modulus and permeability. The deformation, or strain, is a consequence of the pressure difference between the interior and the exterior of the specimen. For example, after a sudden increase in pressure, the gas in the gel pores is initially only slightly compressed along with the elastic compression of the gel. After a characteristic time, the pressure equilibrates and the gel ideally springs back to its original dimensions. 

Equation (7.24) is of fundamental importance in surface sdence. It rdates interfadal forces with the adsorption of a vapor to a solid surface. The concept goes back to Michael Polanyi and it is known as the potential theory of adsorption [802]. The basic idea is that vapor molecules close to a surface feel a potential-similar to the gravitation field of the earth. The potential isothermally compresses the gas dose to the surface. Once the pressure becomes higher than the equilibrium vapor pressure, it condenses and forms a liquid film. 

But the idea of gas turbine itself can be traced back to a 1791 patent by Barber, who wrote of the basic concept of a heat engine for power generation. Air and gas were to be compressed and burned to produce combustion products these were to be used to drive a turbine producing a work output. The compressor could be driven independently (along the lines of Whittle s early thoughts) or by the turbine itself if it was producing enough work. 

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