M. Sami Selim

A rate-based model for the design of gas absorbers for the removal of CO2 and H2S using aqueous solutions of MEA and DEA

A rate-based model was developed for the design of acid gas absorbers using aqueous alkanolamine solutions. The model adopts the film theory and assumes that thermodynamic equilibrium among the reacting species exists in the bulk liquid. The diffusion-reaction equations for the reacting species in the liquid film are solved using collocation techniques. Heat effects accompanying diffusion and reaction are accounted for using appropriate heat balances on each tray. The algorithm adopts a plate-by-plate calculation starting at the bottom of the tower. Tray hydraulics was added to the algorithm to ensure proper operation of the tower. The program was developed to handle either monoethanolamine (MEA) or diethanolamine (DEA) as chemical solvents.

Predictions of the solubility of acid gases in monoethanolamine (MEA) and methyldiethanolamine (MDEA) solutions using the electrolyte-UNIQUAC model

Abstract A thermodynamic model was developed for representing vapor–liquid equilibria (VLE) of the CO 2 –H 2 S–MEA–MDEA–water system. The model accounts for chemical equilibria in the liquid phase and physical equilibria between the liquid and vapor phases. Activity coefficients are represented by the electrolyte-UNIQUAC equation. The present extension uses an ion-pair interaction approach and satisfies both the principles of like-ion repulsion and local electroneutrality. Contributions from long-range ion–ion interactions are represented by a Debye–Huckel formula suitable for mixed solvents, water and alkanolamines. Adjustable parameters of the electrolyte-UNIQUAC equation, representing short-range binary interactions, were determined by data regression using binary, ternary, and quaternary system VLE data. Predicted H 2 S and CO 2 vapor pressures are in good agreement with the reported experimental data for aqueous solutions of a single acid gas as well as mixtures of H 2 S and CO 2 in MEA and MDEA and their mixtures in the temperature range 25–120°C.

Hydrate Dissociation in Pipelines by Two‐Sided Depressurization: Experiment and Model

Abstract: Experimental data were obtained on the dissociation of short methane hydrate plugs in a simulated pipeline. The hydrate plugs were dissociated by the method of two‐sided depressurization. Results indicated that plug dissociation occurred radially and not axially. This results in extreme safety concerns, listed herein. When the system was depressurized to atmospheric pressure, ice was formed from the dissociating hydrate plug, which aided in the dissociation process. A model describing hydrate dissociation assumes that heat is conducted radially into the plug from the surroundings. The model is in quantitative agreement with the data using no fitted parameters. A rapid pressure reduction to atmospheric pressure on both ends of the hydrate plug leads to the optimal dissociation rate.

Sedimentation and brownian diffusion coefficients of interacting hard spheres

Abstract Einstein (1905) derived an expression for the diffusion coefficient of an isolated spherical colloid. Since that work, there have been two general methods for analyzing Brownian diffusion in colloidal suspensions at finite concentrations. One follows Einsteins thermodynamic argument postulating a gradient in chemical potential as being the driving force behind diffusion together with a thermodynamic analysis of sedimentation-diffusion equilibrium (Batchelor, 1976). The other approaches diffusion in a statistical fashion, deriving the macroscopic diffusion coefficient from a microscopic analysis of Brownian motion (Felderhof, 1978). In principle, both methods are correct and should give identical results, but the distinctly different approaches have produced some controversy. To test the various theories, of Brownian diffusion, experiments were conducted measuring the sedimentation and Brownian diffusion coefficients of uncharged rigid spheres. Sterically stabilized silica spheres dispersed in cyclohexane were used as a model colloid. The osmotic compressibility of this system was found to be well described by the Carnahan- Starling equation for hard spheres. The sedimentation coefficient of the silica spheres was measured over a wide range of concentration in a closed bottom container. A light extinction method was used to monitor the fall speed of the interface that develops during gravity sedimentation. The diffusion measurements were made using Taylors hydrodynamic stability method. A laser optical-fiber system capable of direct monitoring of the penetration depth and concentration profile of the diffusing species along the diffusion column was developed. The measurements were found to be in fair agreement with Batchelors theoretical results for sedimentation and Brownian diffusion of hard spheres.

FRICTION LOSSES FOR FLOW OF SLURRIES IN PIPELINE BENDS, FITTINGS, AND VALVES

ABSTRACT Resistance coefficients for flow of suspensions of well defined glass beads of narrow size fractions in 1-inch and 2-inch straight pipes, in standard 45°, 90° and 180° bends, in 90° smooth bends of various curvature radii, and also in gate and globe valves were measured. The measurements were made for two sizes of fine glass beads, -325 mesh and -200-325 mesh, covering wide ranges of turbulent Reynolds number and solids concentrations from 0 to 50 weight percent. These friction loss data were analyzed with regard to the effects of Reynolds number and suspended solids concentration, and the calculated resistance coefficients were compared with those estimated from available design procedures recommended for turbulent single-phase Newtonian flow. Within the range of particle sizes examined in this work no particle size effects could be discerned. The effects of Reynolds number and suspended solids concentration on the friction loss measurement were calculated.

Momentum and heat transfer in the entrance region of a parallel plate channel: developing laminar flow with constant wall temperature

A new integral method of solution is presented for developing laminar flow and heat transfer in the entrance region of a parallel plate channel with uniform surface temperature. Unlike earlier Karman-Pohlhausen analyses, the new analysis provides solutions which are free from jump discontinuities in the gradients of the velocity and temperature distributions throughout and at the end of the entrance region. The hydrodynamic and thermal results from the present analysis therefore join smoothly and asymptotically to their fully-developed values. The heat transfer results obtained are further found to agree well with previously published numerical solutions.

SIMULTANEOUS DEVELOPMENT OF VELOCITY AND TEMPERATURE PROFILES IN THE ENTRANCE REGION OF A PARALLEL PLATE CHANNEL: LAMINAR FLOW WITH UNIFORM WALL HEAT FLUX

Available boundary layer type solutions to the combined hydrodynamic and thermal entrance region problem are known to exhibit a discontinuity in the gradients of the velocity and temperature distributions in the entrance region. A new solution is presented which alleviates this shortcoming. The new solution is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Das (1982) to hydrodynamically developing flow in a channel. This concept is extended to the combined entry length problem by dividing the thermal entrance length into two lengthwise regions, a thermal inlet region and a thermally filled region. In the former, the effect of heat transfer between fluid and wall is confined within the thermal boundary layer developing along the wall. At the end of the thermal inlet region, the thermal boundary layers meet at the duct axis but the temperature profile is not yet developed. In the thermally filled region, the heat effects propagat...

Water seepage through soils with a sloping surface

An analytical solution is derived for a two-dimensional soil with a sloping surface under steady and water-saturated flow conditions. The soil was assumed to consist of several layers where each layer was horizontally stratified. Moreover, the lower layer was assumed to be bounded by an impermeable barrier, whereas the soil surface was assumed to be of constant slope (terraced type) or of an arbitrary configuration. Each layer was considered anisotropic in nature where the hydraulic conductivity in the vertical and horizontal directions are dissimilar. Potential and stream functions were obtained and several flow nets are presented for two-layered soils with varying degrees of anisotropy. The results shown illustrate the significance of the degree of anisotropy of each soil layer on the water flow pattern, the relative flow rate as well as the volume of water passing through individual soil layers.

SIMULTANEOUSLY DEVELOPING LAMINAR FLOW AND HEAT TRANSFER IN THE ENTRANCE REGION OF A CIRCULAR TUBE WITH CONSTANT WALL TEMPERATURE

The developing flow and heat transfer in the entry region of a heated circular tube is analyzed for the case of constant wall temperature. An integral or boundary-layer solution is presented which has a number of advantages over earlier Karman-Pohlhausen integral analyses. Thus, in the present analysis, the velocity and temperature distributions, the local and mean drag coefficients, and the local and mean Nusselt numbers approach their fully-developed values asymptotically. The new analysis is based on the hydrodynamic inlet-filled region concept originally proposed by Ishizawa (1966) and later adopted by Mohanty and Asthana (1978) to flow through a circular tube. This concept is extended to the combined entry-length problem by introducing a thermal transition region, herein called the thermally-filled region, between the thermal inlet boundary-layer region and the thermally fully-developed region. A thermal shape factor is also introduced which ensures smooth transition of all pertinent thermal quantiti...