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The effective mass transfer area (a [subscript e]), liquid film mass transfer coefficient (k [subscript L]), and gas film mass transfer coefficient (k [subscript G]) of eleven structured packings and three random packings were measured consistently in a 0.428 m packed column. Absorption of CO₂ with 0.1 gmol/L NaOH with 3.05 m packing was used to measure a [subscript e], while air stripping of toluene from water with 1.83 m packing was used to measure k [subscript L], and absorption of SO₂ with 0.1 gmol/L NaOH with 0.51 m packing was used to measure k [subscript G]. The experiments were conducted with liquid load changing from 2.5 to 75 m³/(m²*h) and gas flow rate from 0.6 to 2.3 m/s. Packings with surface area from 125 to 500 m²/m³ and corrugation angle from 45 to 70 degree were tested to explore the effect of packing geometries on mass transfer. The effective area increases with packing surface area and liquid flow rate, and is independent of gas velocity. The packing corrugation angle has an insignificant effect on mass transfer area. The ratio of effective area to surface area decreases as surface area increases due to the limit of packing wettability. A correlation has been developed to predict the mass transfer area with an average deviation of 11%. [Mathematical equation]. The liquid film mass transfer coefficient is only a function of liquid velocity with a power of 0.74, while the gas film mass transfer coefficient is only a function of gas velocity with a power of 0.58. Both k [subscript L] and k [subscript G] increase with packing surface area, and decrease with corrugation angle. A new concept, Mixing Point Density, was introduced to account for effect of the packing geometry on k[subscript L] and k [subscript G]. Mixing Point Density represents the frequency at which liquid film is refreshed and gas is mixed. The mixing point density can be calculated by either packing characteristic length or by surface area and corrugation angle: [mathematical equation]. The dimensionless k [subscript L] and k [subscript G] models can then be developed based on the effects of liquid/gas velocity, mixing point density, packing surface area: [mathematical equation] [mathematical equation]. Mi is the dimensionless form of Mixing Point Density (M), which is M divided by a [subscript P]³. Because Mi is only a function of corrugation angle (θ), it is a convenient transformation to represent the effect of θ on mass transfer parameters. An economic analysis of the absorber was conducted for a 250 MW coal-fired power plant. The optimum operating condition is between 50 to 80 % of flooding, and the optimum design is to use packing with 200 to 250 m²/m³ surface area and high corrugation angle (60 to 70 degree). The minimum total cost ranges from $4.04 to $5.83 per tonne CO₂ removed with 8 m PZ.

To screen amine solvents for application in CO2 capture from coal-fired power plants, the equilibrium CO2 partial pressure and liquid film mass transfer coefficient were characterized for CO2-loaded and highly concentrated aqueous amines at 40 – 100 °C over a range of CO2 loading with a Wetted Wall Column (WWC). The acyclic amines tested were ethylenediamine, 1,2-diaminopropane, diglycolamine®, methyldiethanolamine (MDEA)/Piperazine (PZ), 3-(methylamino)propylamine, 2-amino-2-methyl-1-propanol and 2-amino-2-methyl-1-propanol/PZ. The cyclic amines tested were piperazine derivatives including proline, 2-piperidineethanol, N-(2-hydroxyethyl)piperazine, 1-(2-aminoethyl)piperazine, N-methylpiperazine (NMPZ), 2-methylpiperazine (2MPZ), 2,5-trans-dimethylpiperazine, 2MPZ/PZ, and PZ/NMPZ/1,4-dimethylpiperazine (1,4-DMPZ). The cyclic CO2 capacity and heat of CO2 absorption were estimated with a semi-empirical vapor-liquid-equilibrium model. 5 m MDEA/5 m PZ, 8 m 2MPZ, 4 m 2MPZ/4 m PZ and 3.75 m PZ/3.75 m NMPZ/0.5 m 1,4-DMPZ were identified as promising solvent candidates for their large CO2 capacity, fast mass transfer rate and moderately high heat of absorption. The speciation in 8 m 2MPZ and 4 m 2MPZ / 4 m PZ at 40 °C at varied CO2 loading was investigated using quantitative 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. In 8 m 2MPZ at 40 °C over the CO2 loading range of 0 – 0.37 mol CO2/mol alkalinity, more than 75% of the dissolved CO2 exists in the form of unhindered 2MPZ monocarbamate, and the rest is in the form of bicarbonate and dicarbamate; 19% - 56% of 2MPZ is converted to 2MPZ carbamate at 0.1 - 0.37 mol CO2/mol alkalinity. A rigorous thermodynamic model was developed for 8 m 2MPZ in the framework of the Electrolyte Nonrandom Two-Liquid (ENRTL) model. At 40 °C, the reaction stoichiometry for 2MPZ and CO2 is around 2 at lean loading but diminishes to 0 at rich loading. Bicarbonate becomes the major product at CO2 loading greater than 0.35 mol/mol alkalinity. The predicted heat of CO2 absorption is 75 kJ/mol at 140 °C and decreases with temperature when CO2 loading is above 0.25. The mass transfer rate data for 8 m 2MPZ was represented with a rate-based WWC model created in Aspen Plus®. The reaction rate was described with termolecular mechanism on an activity basis. With minor CO2 loading adjustment and regression of pre-exponential kinetic constants and diffusion activation energy, a majority of the measured CO2 fluxes in the WWC experiments were fitted by the model within ±20% over 40 – 100 °C and 0.1 – 0.37 mol CO2/mol alkalinity. The diffusion activation energy for 8 m 2MPZ at the rich loading is about 28 kJ/mol. The activity-based reaction rate constant at 40 °C for 2MPZ carbamate formation catalyzed by 2MPZ is 1.94×1010 kmol/m3•s. The calculated liquid film mass transfer coefficients are in close agreement with the experimental values. The liquid film mass transfer rate is dependent on the diffusion coefficients of amine and CO2 to the same extent at lean loading and 40 °C. The sum of the powers for the two diffusivities is approximately equal to 0.5 over the loading range of 0 – 0.4 mol CO2/mol alkalinity. The sum of the powers for the dependence of the liquid film mass transfer coefficient on the carbamate formation rate constants (k2MPZ-2MPZ and k2MPZCOO--2MPZ) approaches 0.5 at very lean loading at low temperature, but it decreases as CO2 loading and temperature is increased. At 100 °C, the physical liquid film mass transfer coefficient is the most important factor that determines the liquid mass transfer rate. The pseudo-first order region shifts to higher range of physical liquid film transfer coefficient as temperature increases. / text

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Les polymères sont de plus en plus répandus dans différents secteurs industriels comme une alternative aux métaux. En effet, les composants en polymère permettent une réduction accrue du poids et une meilleure inertie chimique dans les structures où ils sont utilisés. Ils permettent également une réduction du frottement sans recourir à des systèmes de lubrification externe. Parmi ces polymères, le PTFE - connu sous le nom du Teflon et découvert en 1938 - se caractérise par une morphologie semi-cristalline particulière où les molécules de PTFE forment des superstructures dites « à bandes ». Il possède d’excellentes propriétés thermiques, un très faible coefficient de frottement et une très bonne inertie chimique justifiant sa vaste utilisation dans différentes applications : comme renfort de type lubrifiant solide, revêtement antiadhésif, isolant électrique des câbles dans le domaine de l’aéronautique, récipients pour des produits chimiques réactifs. Ce travail de thèse s’inscrit dans ce contexte et adopte une démarche tribologique globale. Il étudie les réponses tribologiques d’un contact PTFE/Ti-6Al-4V sollicité en fretting-usure alternatif - notamment en mode glissement total et reciprocating - dans une configuration cylindre/plan. Les paramètres étudiés sont : nombre de cycles, vitesse de glissement, force normale et propriétés thermomécaniques et surfaciques des matériaux. Cette étude propose de nouvelles formalisations analytiques basées sur l’approche d’Archard et établit des lois de frottement et d’usure qui intègrent les effets de ces paramètres. Le rôle joué par le film de transfert dans la détermination des réponses tribologiques est également mis en évidence. / The tribology of thermoplastic polymers is nowadays one of the major issues in several engineering fields. These non-metallic materials increasingly provide a useful alternative to metals that are in contact with a harder counterface. Areas of application are various and include offshore oil-drilling, aeronautics and the automotive industry and biomedical applications such as prosthesis designs. The aim of polymer-metal, and especially PTFE/Ti-6Al-4V, designs is to reduce wear and friction. Polytetrafluoroethylene (PTFE) is one such interesting thermoplastic polymer that has been closely studied since it was discovered in 1938. It is a high-performance engineering polymer characterized especially by a high melting point, chemical inertness and low coefficient of friction due to its banded structure. PTFE is a tribologically attractive material, widely used especially as a solid lubricant in a variety of dry sliding tribosystems. The purpose of this study is to evaluate friction and wear rate evolution for gross slip fretting-reciprocating sliding conditions of PTFE/Ti-6Al-4V interface in a cylinder/plane configuration. Various investigations have been made to study the influence of wear test conditions: number of cycles, sliding speed, normal force, materials thermomechanical and surface properties. Analysis aimed to determine tribological processes as well as formulation of experimental evolution of friction and wear rates regarding selected parameters. Finally, characterization of the transfer film formed on the counterpart under repeated cyclic sliding is undertaken to determine its role and its interference with wear and friction response.

Fakt ist, ein Erklärfilm ist nicht die alleinige Lösung für die aktive Lehre und auch nicht für Blended-Learning-Szenarien. Es bedarf immer einen Wechsel unterschiedlicher Methoden und unterschiedlicher Medien, die sich im Lernprozess abwechseln, um die verschiedenen Lerntypen anzusprechen. Fakt ist aber auch, der Erklärfilm spielt beim Lernen eine Schlüsselrolle. [... aus der Einleitung]

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