Nonabsorbing gas

The design engineer often encounters the situation in which a nonblack body is surrounded completely by a large enclosure containing a nonabsorbing gas. An example would be a steam line exposed to the atmosphere. Under these conditions, little error is introduced by assuming that none of the heat radiated from the source is reflected to it, and Eq. (6) or (7) can be simplified to... 

Equilibrium is another extremely important factor to be considered in controlling the operation of absorption systems. The rate at which the pollutant will diffuse into an absorbent liquid will depend on the departure from equilibrium that is maintained. The rate at which equilibrium is established is then essentially dependent on the rate of diffusion of the pollutant through the nonabsorbed gas and through the absorbing liquid. Equilibrium concepts and relationships are considered in a later problem. 

When the forces between a particle and another condensed species are treated, thermodynamics and statistical mechanics of the aerosol (particles plus gas) enter through temperature dependence of the interaction forces. However, actual aerosol particle interaction forces may be altered in a fundamental way if one or both of the particles or surfaces absorb molecules from the suspending gas. ASH et al. [5.4] considered nonionic systems in which the relative velocity of the particle and surface or other particle is "sufficiently small, in relation to the rates of absorption and desorption, that absorption equilibrium is maintained as the particles move together, collide and then either adhere or separate." They, therefore, assume constant temperature for the entire aerosol system implying at least several nonabsorbing gas molecular collisions with the sorbent species between each sorbate interaction that is to say, the sorbate must be a minority (< 10 percent) species in the gas. By use of conventional equilibrium thermodynamics they derive the expression for the excess force (beyond van der Waals and electrostatic) between two bodies due to sorption as... 

As shown in Figure 16-15, filter correlation analyzers use a rotating gas filter through which the IR beam passes. The filter has two compartments, one for the gas of interest and the other for a nonabsorbing gas such as nitrogen. When the gas of interest is in the beam, it selectively attenuates the IR source to produce a reference beam. The sample beam is produced by the transparent gas. Typically, the IR source is chopped at a fairly high frequency (360 Hz) whereas the filter rotates at a fairly low frequency (30 Hz). A modulated signal is produced that is related to the concentration of the analyte gas. 

For a detailed discussion of radiation, the reader is referred to the textbook literature [81-83]. We note here that a simple expression holds for describing the radiant flux received by a small pellet, located in a large cavity, the surface of which is isothermal, in the presence of nonabsorbing gas ... 

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