The factors affecting the efficacy of a closely packed bed of mixed cotton and a supporting fiber (Teflon, glass, Dynel) were evaluated for oil-in-water dispersions. Several other waterorganic systems were also tested. Superficial velocities ranged from 0.2 to 3.5 ft./min. Succeiful coalescence was attained a t interfacial tensions as low as 3.5 dynes/cm. Dispersed phase viscosity was varied from 1.4 to 137 centipoise. For a mixed-fiber bed with a specific ratio of fiber species, there is an optimum bed depth for best performance; High-speed cinephotomicrographic observations a t 1 0 0~ and up to 4,000 frames/sec. indicated that fiber wettability is not the most important factor for successful operation.Organic chemicals must be purified during their manufacture by contacting them with immiscible solutions in a washin or extraction operation. The immiscible solution the field of petroleum products such as gasoline and kerosene. Fuel for modem jet-powered airplanes is a articularly important product in which the presence of water is a very critical problem (7). The reverse situation, in which very fine droplets of an oil phase are dispersed in a large amount of water, is of considerable interest in the prevention of contamination of rivers, harbors, and beaches.If a water phase is dispersed in an organic liquid by any of the efficient turbulence creating mixers presently in use, an emulsion will be f o n e d . If both liquids are pure (no surfactants present), the emulsion will be of a temporary nature and both phases may be recovered by a simple settling operation. If a strong surfactant is present, the emulsion may be a permanent one requiring special methods to break it. Two types of temporary emulsions are recognized (1 2 ) . The first (primary) is characterized by a drop size of the order of 100 p and will separate readily in a few seconds or minutes by simple settling. If one or both of the two liquids involved contains polar compounds, one or both of the two layers which result from the settling operation will be clouded with a fine mist or fog of extremely fine droplets of the opposite phase (1). Such fogged layers are called secondary emulsions and consist of untold billions of droplets of submicron size suspended in a fieId of the opposite phase. These secondary emulsions cannot be settled clear for many minutes or hours. Coalescence of these tiny droplets into large ones is necessary if the emulsion is to be broken and separation attained.Passage of an emulsion through a fibrous bed will often cause coalescence and facilitate separation (1 2) ; sometimes such beds are dependable and sometimes not. The mechanism of their operation is shrouded in vagueness and conjecture. No accepted theory exists on how they accomplish the coalescence of the submicron droplets into large ones of manageable size. Were one available, it would facilitate design and aid selection of materials of construction of such devices. The present work is con-

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Institute of Gas Technolagy, Chicoso, Illinois 60616To study heat and mass transfer in fuel cells, we must have a good description of fluid motion in the geometrically complex gas compartments ( 2 ) . We have already shown that a good description of such a motion can be obtained by the use of Darcy's law (1,3) because the flow is slow. To describe two-dimensional motion we need two permeabilities. These can be either measured or obtained by the solution of the creeping flow equations. Unfortunately the solution of the three-dimensional Navier-Stokes equations, even for the typical geometric element involved in, for example, Allis-Chalmers plates, is excessively timeconsuming with present generation computers (3). Therefore we decided to take the empirical approach. We measured the two penneabilities. PRESSURE DROP M€ASUREMENTSThe apparatus and procedure for making pressure drop measurements have already been described (1) for the case of an actual oxygen plate. In this study the inlet and outlet ports of an Allis-Chalmers hydrogen plate were cut and distributor systems (called slotted ribs in Figure 1) introduced before and after the fuel cell plate (Section 11 in Figure 1). The purpose of the distributors was to obtain one-dimensional flow in the test section. The permeability was calculated using Equation Page 1010July, 1971Equation (1) by replacing the length B with the width of the plate A. By this method the values of the permeabilities were calculated to be k, = 2.2 x 2 1.7 x 10-9 sq. ft. and k, = 1.78 xHaving obtained the values of the permeabilities, it is now possible to verify the applicability of Laplace's equation to describe the flow inside the cavities. The Laplace's equation (1)

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