Significant Radial Gradients Research Articles

Behavior of a pilot plant fixed-bed reactor during catalyst deactivation

The behavior of an non-adiabatic, non-isothermal fixed-bed reactor used for the hydrogenation of toluene has been studied under the influence of catalyst deactivation caused by continuous addition of thiophene to the reactant feed. Axial and radial temperature and concentration profiles were measured during deactivation. In spite of significant radial temperature gradients (Biot number = 5.25), it was possible to describe the reactor behavior with a one-dimensional pseudohomogeneous model. Mean cross-sectional temperatures can be used since the measured radial profiles are parabolic. The activation energy for thiophene adsorption derived from the measured profiles (4.7 kJ/mole) agrees with previous direct determinations in the literature.

Simple method for the modelling of the behaviour of a non-isothermal, non-adiabatic fixed-bed catalytic reactor

The behaviour of a non-isothermal, non-adiabatic fixed-bed reactor used for the hydrogenation of toluene has been investigated. Although large radial temperature gradients existed in the reactor, a simple pseudo-homogeneous one-dimensional model was found to be suitable to describe the reactor behaviour. The model is based on the application of a mean cross section temperature which is derived from radial temperature profiles measured at two axial positions in the catalyst bed. Measured radial temperature profiles exhibited a parabolic shape. The mean cross section temperature applied corresponds to the temperature at the radial position (r/R) 2 = 0.5. The model equations were solved by means of the orthogonal collocation method and Gear's variable step integration algorithm. Measured radial toluene concentrations indicated that no significant radial toluene concentration gradients existed in the catalyst bed. Axial temperature and toluene concentration profiles measured during steady-state operation are compared with the corresponding profiles calculated with the reactor model.

Autothermal reactors with internal heat exchang—I Numerical and experimental studies in the multiple steady-state region

Detailed numerical and experimental studies in the multiple steady-state region of an autothermal reactor with internal countercurrent heat exchange were conducted. The mildly exothermic water-gas shift reaction was used in the studies. In this distributed-parameter system multiple steady states were found experimentally. Although significant radial and longitudinal temperature gradients exist, one-dimensional (radially-lumped) simulations predict mean behavior quite well. For two-dimensional simulations, Legendre polynomial trial functions give faster convergence than Jacobi polynomials when using orthogonal collocation methods. Inflections in the radial temperature gradients were measured near the hot spot although not predicted by the simulations. Significant temperature jumps at the inner wall upstream of the hot spot were also measured. Production of hydrogen could be conducted at surprisingly mild conditions if the reactor could be controlled in a stable mode essentially identical to the middle unstable steady state.

The V - /2.2 micron/ colors of elliptical galaxies

Infrared photometric measurements of 19 normal and giant elliptical galaxies are reported which were made with apertures having diameters 0.1 to 1.3 times the visual galactic diameters. The derived V (2.2 micron) colors, ranging from 3.15 to 3.60 magnitudes, are compared with the results of Grasdalen (1975) for 28 spiral and elliptical galaxies. All but one of the present magnitudes are found to be systematically brighter than Grasdalen's by 0.07 to 0.46 magnitude, and no significant radial color gradient is observed.

The Pioneer 9 electric field experiment

We present a detailed analysis of the Pioneer 9 VLF electric field observations for 20 selected storm periods covering a heliocentric range extending from 0.754 AU to 0.99 AU. Although data from only two low frequency channels are available, the results of the present study tend to confirm the preliminary speculation by Scarf and Siscoe (1971) that the turbulentE-field spectrum in the disturbed solar wind has a significant radial gradient.

Spectroscopic studies of the decay of hydrogen plasmas in aT-tube

This paper reports on spectroscopic studies of the decay of hydrogen plasmas generated in a relatively low energyT-tube of conventional design equipped with a reflector. These measurements indicate that the plasma behind the reflected front is not quiescent, but suffers a severe expansion with flow velocities ∼105 cm s−1 (velocities of the incident and the reflected front are 7×106 and 3.4×106 cm s−1). The net energy loss during the first two microseconds of the decay is almost entirely due to radiative losses (principally Ly-α radiation) and no significant radial temperature gradients are observed.