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Unformatted text preview: Abstract: The objective of this experiment is to study the diffusion of a gas in a porous solid and to determine experimentally the effective diffusion coefficient by a single pellet apparatus. In this experiment, there were five runs and every run had different flowrate. From the graph that shows the relation between ( 1 ) and F, the value of the limiting value of the first absolute moment was obtained ( 1 = 3.75 s) then it was corrected until it equals to . From the previous value of ( 1 ) corr , the effective diffusion coefficient was calculated and it was equal to . The percentage difference of the effective diffusion coefficient, when it was compared with the theoritical value ( s cm D e / 04477 . 2 = ) was equal to . Introduction: Diffusion of gases through porous solid are of practical importance in a variety of chemical processing industries such as catalysts, adsorbents etc. In porous media, the solute diffuses through the fluid when the pores were filled with a liquid. The diffusion effectively takes place over a longer distance than it would in a homogenous material. That is because of the pores are not straight. In addition, diffusion can occur over a smaller cross sectional area than that available in a homogenous material. In this experiment, N 2 and He are used since the larger the difference in thermal conductivities, the larger the response peaks are. Equipment: The apparatus basically consists of (1) a single pellet holder, (2) carrier and sample gas flow lines and (3) a detector and a recorder. The single pellet holder, which is made of aluminum, has two parts. The base part has a cylindrical cavity of diameter 1.94 cm. The upper part, which is inserted into the base cavity has an outside diameter slightly smaller than the diameter of the opening of the base. The mold containing the solid pellet is placed into the base cavity. This arrangement produces a single cylindrical pellet of 1.35 cm in the diameter and 0.841 cm in length. The data analysis requires that the concentration in the lower chamber small and having sufficiently large flow. The cylindrical single pellet was made from CaO powder by use of a press and the pellet does not adsorb the gases used. The carrier gas (He) flows through upper and lower chambers. The gases are passed directly to the upper and lower faces of the catalyst. The pressure on both sides of the pellet must be kept the same (to prevent forced convection) and this is achieved by adjusting the Flowrate of a gas to the upper chamber using the needle valve3....
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This note was uploaded on 09/27/2011 for the course CHEMICAL E CHE 309 taught by Professor M.elgaily during the Fall '09 term at King Fahd University of Petroleum & Minerals.
- Fall '09