The Flow of Fluids Through Activated Carbon Rods: Iii. The Flow of Adsorbed Fluids

Abstract

Total flow rates of gases through activated charcoal rods are regarded as consisting of the sums of comparatively independent flows through macropores and micropores. The flow rate through the macropore system is related to the relevant adsorptio~i isotherm by means of all empirical equation having three arbitrary constants. The empirical eqr~ations can be fitted to all of our observed results within the experitneatal error. Assunling that the adsorbate behaves as a one, cornpoltent fluid such as a gas in a gravitational field, it is shown that compresslve s~~r f a c e forces give rise to large fluid pressures within micropores. A very simple flow equation is derived which is qualitatively in agreement with observed results and which indicates a mean micropore diameter of the order of lo-' cm. The derived equation illustrates the nature of the physical factors involved and shows that surface forces may increase flow rates of adsorbable gases by \.cry large factors. The increased flow rates are due mainly to the greatly increased densities and to the increased pressure gradients resulting from the actiou of surface forces. A n~odel porous adsorbent is presented which exhibits many properties of real adsorbent systems and illustrates especially the relations between adsorbate densities and the various tensions and pressures existing within micropore systems. GENERAL CONSIDERATIONSThe flow rate in mass units, Q,,,, of a Maxwellian fluid through a pipe of circular cross section may be described by the equation, where d p / d z is the pressure gradient a t any point along the axis of the pipe; r ,

Rates of flow through microporous solids

“…Flood and Tomlinson (11,12,22) have observed appreciable surface rates for pure adsorbed-gas flow through solid-carbon rods.…”

Influence of sorption on sound propagation in granular activated carbon

“…Moreover, rarefaction and sorption processes are not the only physical processes likely to be influencing sound propagation in materials with very small pores. For example, activated diffusion, surface diffusion, film condensate flow, capillary condensate flow, molecular diffusion, and Knudsen diffusion have been reported to significantly influence the isothermal mass transport in activated carbon 2,14,15,16,17,36,46,47,48 . Some of these processes have been considered in the model but a detailed investigation of their influence on sound interaction with multiscale porous materials is an interesting topic for future research that might lead to their more effective exploitation in acoustics.…”

THE MICROPORE FLOW OF H2O AND D2O THROUGH ACTIVATED CARBON RODS

“…Such increased flow rates have been attributed to flows through the micropore systems by ( a ) surface diffusion (2, 3, 4) and (b) laminar or viscous flow of liquid adsorbate. Previous work in this laboratory (8,9) indicates that in the case of our carbon the second of these alternative mechailisms is the dominating one when the quantity adsorbed is a t all large. 'Manuscript received M a y 17, 1956.…”

“…I11 runs with unfilled plugs the same type of holder was used as described previously (9,12), the carbon rod being held between two funnel-shaped glass tubes and the sides surrounded with mercury, thus preventing gas flow around the carbon. When we used metal-filled plugs this holder was not satisfactory as the mercury amalgamates immediately with the low melting alloy in the plug.…”

“…I t has been well established (1,3,9) that in the absence of appreciable absorption, the flow of gases through active carbons is a viscous flow with slip through the macropore system. The flow rate may be described by the well-known equation From flow data for a gas such as helium the constants A and B can be evaluated and Equation [I] used to calculate flow rates of other gases of known viscosities a t various temperatures, provided that the gases are not strongly adsorbed.…”