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This article discusses the propagation of compressional waves in fluid-saturated elastic porous media. Both harmonic and transient pulses are considered. In general, two modes of wave propagation exist. In the case of a transient pulse, these modes lead to a two-wave structure. It is not possible to obtain closed-form solutions for the general case of transient loading, but considerable insight may be obtained from certain limiting cases (e.g., no viscous coupling, large viscous coupling) for which analytical solutions are derived by means of Laplace transform techniques. Strong viscous coupling leads to the coalescence of the two wave fronts into a single front; in this case the material behaves like a single continuum with internal dissipation. Solutions for the general case are obtained both by numerical inversion of the Laplace transforms and by direct finite-difference methods.

In large-diameter bubble cap towers, or even moderate-size towers carrying high liquid loads, the hydraulic gradient set up between upstream and downstream ends of a plate becomes an important factor in determining the maximum liquid load the plate can handle and still maintain uniform distribution of vapor over the plate.This gradient has been measured under varying conditions on an experimental plate, and data for one type of bubble cap are given as a function of liquid rate, vapor rate, liquid depth above slots, and certain structural characteristics. Charts can be constructed to enable quick checking of allowable liquid rates.

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