Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 11 (1974), S. 379-390 
    ISSN: 1572-9613
    Keywords: Probability density ; density matrix ; tunneling phenomena
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Methods based on the density matrix for calculating the time-dependent probability density of a quantum system approaching equilibrium are presented. Explicit expressions are derived for the time-dependent probability density for a double-well potential. The effects of tunneling and transitions between energy levels on the probability density are discussed. For the case of closely spaced energy levels, a partial differential form of the density matrix equation is derived and used to calculate time-dependent probability densities.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 21 (1979), S. 301-311 
    ISSN: 1572-9613
    Keywords: Quantum mechanical friction ; tunneling ; Brownian motion ; transport ; energy dissipation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Kanai model of a quantum mechanical Brownian particle is used to examine the effect of interactions between particles and their environment. Random forces cause the thermalization of the particle. Reflection of a particle from a step barrier is analyzed. The problem of tunneling of the Brownian particle through a rectangular barrier is solved. Finally, a solution for a Brownian particle in a box is presented.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 272-283 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rates of hydrogenation of α-methyl styrene were measured at 40.6°C and 1 atm in a recycle, trickle-bed reactor using a palladium/aluminum oxide catalyst. Data for different hydrogen concentrations in the gas and liquid feed streams suggested that except, at high liquid flow rates, on part of the outer surface of the catalyst the mass transfer limitation was very small, indicating a gas covered type of surface. A procedure was developed for evaluating effectiveness factors for the nonuniform boundary conditions existing when part of the particle surface is covered by gas.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 591-602 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The thermal response of a packed bed subject to step changes in fluid temperature was measured in the Peclet number range from 10 to 103. Fluid temperature and particle temperatures were measured independently at six different axial locations in the bed as a function of time. From the temperature breakthrough curves we were able to calculate the spatial separation between the fluid and solid temperature fronts. The measured values were higher by a factor of 2 to 3 than those predicted by traditional heat transfer models. Longitudinal effective thermal conductivities were also computed and compared to theoretical predictions. The new heat transfer model developed in a previous paper is able to account for these differences between experimental results and the predictions of the dispersionconcentric and continuous solid phase models used by previous investigators. Steady-state experiments were used to measure lateral effective thermal conductivities. A temperature gradient was imposed at the top of the bed perpendicular to the flow direction and its spread was measured at different axial locations in the Peclet number range from 10 to 103. The predicted lateral effective thermal conductivities calculated using mass transfer data to estimate the hydrodynamic dispersion effect were significantly lower than the measured values. This is possibly due to the influence of viscosity and density gradients in the flow field in the packed bed.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 277-288 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Longitudinal and lateral dispersion coefficients were measured at various axial positions in a packed bed in the Peclet number range from 102 to 104. Three different types of packings were used: uniform size particles, a narrow size distribution, and a wide size distribution. For the case of uniform particles the longitudinal dispersivities were found to be strong functions of position in the bed unless the dispersion length satisfies a constraint dependent on the value of the Peclet number. Generally, the larger the Peclet number, the larger the required length for constant axial dispersivities to be achieved. For the case of the wide size distribution, longitudinal dispersivities were larger than in the uniform particle case, and they required a longer dispersion length to achieve a constant value. This suggests a characteristic length for dispersion larger than the mean hydraulic radius. The lateral dispersivities were found to be insensitive to the distribution of particle sizes or location in the bed.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 1027-1030 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 1015-1024 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is proposed for mass transfer of gases across surface-active films and into an aqueous phase. The interfacial region (1) obeys local equilibrium conditions, (2) has a capacity for the dissolved gases greater than the solubility in water, and (3) has a diffusion coefficient three orders of magnitude less than for that in water. The model is solved for and compared with three different experiments: the transient diffusion through monomolecular films into quiescent liquids studied by Plevan and Quinn (1966), the gas absorption through surfactant films into falling liquid films investigated by Emmert and Pigford (1954), and the frequency response of concentration pulses in surfactant films reported by Whitaker and Pigford (1966). The model consistently describes these experiments previously explained by three different models that either ignored the capacitance of the film or assumed local non-equilibrium.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 581-590 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new model is developed for the transient thermal response of a packed bed, using the method of spatial averaging. Equations for the average temperature of the fluid and the solid phase are derived from the point equations for thermal energy in each phase. The new model exhibits some unusual convective and dispersive coupling between the equations for the average fluid and solid temperatures. The response of the model equations to a pulse disturbance is analyzed. It is found that after a sufficiently long time has elapsed, the temperature pulses for the fluid and solid phases will be separated by a constant distance and will spread or disperse about their centroids at an equal rate. The pulse separation predicted by the new model equations is larger than that predicted using more conventional analyses of heat transfer in packed beds. Effective thermal conductivities measured under steady state conditions can differ significantly from those observed in transient experiments due to the spread in temperature pulses caused by heat exchange between phases. Estimates are made of the magnitude of the more important terms affecting longitudinal and lateral effective thermal conductivities under flow conditions, in order to make possible a direct comparison between theory and experiment in a companion paper.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 369-380 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The liquid holdup and the pressure drop for two-phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas-liquid-solid contact lines. The reduced wetting conditions are also the cause of the increase in liquid holdup observed when the surface tension of the liquid is decreased. In this case, the amount of liquid retained in the bed is controlled by the extension of the wetted regions due to the more favorable contact angles as the surface tension decreases. The transition from the trickling to the pulsing flow regime was also dependent on the history of the process.A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode. This correlation is based on the experimental determination of the liquid phase relative permeability as a function of the the liquid phase reduced saturation and the determination of the gas phase relative permeability as a function of the gas phase saturation and the gas phase Reynolds number. The new data are analyzed in the light of the theory developed in the first part of this paper.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 353-368 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The hydrodynamics of trickling flow in packed beds is modeled by representing the porous medium as an array of parallel conduits of circular cross section.First, a straight tube model is developed and analytical solutions are obtained for the relative permeabilities of the gas and liquid phases. Then a periodically constricted tube model is proposed and the equations of motion are solved numerically to determine the effect that surface tension forces have on the relative permeabilities. The constricted tube model predicts that the relative permeabilities of the phases are appreciably sensitive to surface tension forces, a prediction that seems at odds with experimental observations. This discrepancy may be caused by the assumption of fully wetted surface area of particles employed in the model.The straight tube model confirms experimental results indicating that the liquid phase relative permeability is, for practical purposes, insensitive to the gas flow rate and to the gas-to-liquid density and viscosity ratios. Both conduit models show that the gas phase relative permeability curves are strong functions of the gas phase Reynolds number when this parameter is small. For large gas Reynolds numbers, a single curve for the relative permeability as a function of saturation is obtained. These trends are observed in previous experimental studies.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...