Measurements have been made of concentration fluctuations and turbulent fluxes for two passive plumes from an elevated and a ground-level source in a turbulent boundary layer. For the concentration fluctuations, results are presented for the variance, the intermittency, peak values of concentration, probability-density functions and spectra. The balance of terms in the variance transport equation is examined, as is the overall level of fluctuations along the plume. It is shown that most of the production of fluctuations occurs very near the source. Then, the level of fluctuation decays, roughly in accordance with a balance between advection and dissipation. For the turbulent fluxes of concentration, results are presented for the vertical and lateral fluxes, with the associated behaviour of the vertical and lateral eddy diffusivities. The balance of terms in the transport equations for the fluxes is examined. The essential differences between vertical diffusion from ground-level and elevated sources and between near-field and far-field behaviour are shown to be due to the relative importance of the advection and diffusion terms in these equations.

Concentration fluctuations and fluxes in plumes from point sources in a turbulent boundary layer

The light-scatter technique has been used to study the nozzle-fluid concentration field in an isothermal, turbulent, axisymmetric air/air free jet with the nozzle air marked by an oil smoke. The data on the mean concentration field appear to be the most accurate yet obtained, due to the peculiar advantages of the technique. The turbulent concentration fluctuations have been characterized as to intensity, spectral distribution, and two-point correlation. The intermittency factor has been measured and the properties of the turbulent fluid computed. Comparison with the results of other investigators who used heat to mark the nozzle fluid indicates a close similarity between the concentration and temperature fields.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112067001430

The nozzle-fluid concentration field of the round, turbulent, free jet

The dynamic behaviour of fluidized bed reactors for solid catalyzed gas phase olefin polymerization

A fluidized bed membrane reactor for the steam reforming of methane

Scale-up of bubbling fluidized bed reactors — A review

A comprehensive investigation has been made of the boundaries of the regime of bubbling aggregative fluidization. Experiments were done with sand, glass beads, clover seed, and iron shot fluidized with helium, air, and freon-12 in columns 2.5, 5, 10, and 21 cm in diameter. Bed heights ranged from 1 to 60 column diameters, particle diameters from 0.07 to 1.1 mm, particle densities from 1300 to 7600 kg/m3, and gas densities from 0.17 to 5.2 kg/m3. Correlations are presented for the void fraction at the minimum bubbling point and for the superficial fluid velocity at the points of minimum fluidization, minimum bubbling, and minimum slugging.

Onset of fluidization and slugging in beds of uniform particles

Mixing in the interaction zone of two round free jets with nozzle axes intersecting at half-angles of 15, 30, and 45 deg. has been studied by the smoke scattered light technique. The fields of mean concentration and concentration fluctuation intensity were mapped with one jet marked with smoke, the other jet marked, and both jets marked. The correlation function between the concentration fluctuations associated with fluid of the two nozzle streams has been calculated from the results and is an important characteristic of the mixing field and a significant measure of molecular mixedness. A transport equation for the associated covariance function is derived, and the special features of the mathematical modeling problem for this class of mixing process are discussed. The implications of the results for processes involving chemical reactions are examined.

Mixing in the interaction zone of two free jets

The nearly homogeneous, isotropic turbulence field in the core of a fully developed pipe flow was chosen as the medium for turbulent dispersion of a smoke tracer injected from a point on the centerline. By using the optical probe technique the fields of the mean and fluctuating point concentration were mapped at several Reynolds numbers, and spectral analyses made of concentration fluctuations on the plume axis. With the use of sheet illumination, the mean and fluctuating components of the integral material concentration in a plume cross section were measured and the fluctuating component was spectrally analyzed. The maximum Reynolds number was 684,000, the maximum ratio of root-mean-square concentration fluctuation to mean concentration exceeded 100% for points and 40% for sheets, and the turbulent Peclet number was found to equal 850. The existence of standard flow conditions was confirmed by measurement of the frictional drag coefficient and the mean concentration field.

H. A. Becker

Papers

Onset of fluidization and slugging in beds of uniform particles

Mixing in the interaction zone of two free jets

Turbulent dispersion in a pipe flow