George E. Klinzing

HEAT TRANSFER IN MULTIPHASE CONTACTORS

A procedure for the prediction of wall-bed heat transfer coefficient for bubble columns and gas-solid fluidized beds is developed on the basis of hydrodynamic behavior of these contactors. A comparison between the predicted and experimental values of heat transfer coefficient over a wide range of design and operating variables is presented. An attempt is made to analyze the occurrence of maxima in heat transfer coefficient with respect to gas velocity in the case of fluidized beds. A procedure for the calculation of the optimum superficial gas velocity is outlined.

Pickup and saltation mechanisms of solid particles in horizontal pneumatic transport

Abstract Both pickup and saltation mechanisms of solid particles have been examined from an experimental viewpoint, in relation to the prediction of the minimum conveying velocity required in horizontal pneumatic transport systems that operate in dilute-phase. Several experiments were carried out to determine pickup, saltation, and particle velocity of a wide variety of materials using different techniques. The use of dimensional analysis and the experimental findings led to a simple correlation useful to predict pickup velocity of coarse particles (above 100 μm). Noteworthy is the existence of a pipe diameter effect on the pickup mechanism, an important result to consider in scale-up procedures. For the first time in pneumatic transport, pickup and saltation mechanisms of solid particles in horizontal pipelines have been related, with the aid of branching and stability analysis. These ideas open new avenues to full understanding of the complex behavior of particles conveyed pneumatically through pipelines.

Pressure fluctuations in pneumatic conveying systems

There exist a direct relationship between the flow patterns and the power spectral density function of the static wall pressure fluctuations and the differential pressure fluctuations. The probability density function was found to be helpful in distinguishing between oscillatory and non-oscillatory flow. In general, the frequency domain analysis was more useful in the classification of the flow patterns than the amplitude domain analysis. The choice of the sampling frequency and the record length is critical for accurate analysis of the signals. For homogeneous flow conditions, the shape of the power spectrum of the pressure fluctuations from the various taps is the same; however, small frequency shifts are observed. For degenerate dune flow, the shapes of the spectrums can be quite different but the total power in the lower frequency ranges is identical. For regular dune flow, the same spectrum is obtained regardless of the tap location. Both static and differential pressure fluctuations could be uniquely identified with the flow patterns, however, their relative performance is not the same over the entire range of the operating conditions. Static pressure transducers were found to detect homogeneous and stratified flows much better.

Pneumatic transport — a review (generalized phase diagram approach to pneumatic transport)

Abstract Pneumatic transport of solids is reviewed in respect of the phenomena, the problem areas, current acceptable practice and theories. Measurement techniques and devices are discussed as to their importance in providing necessary and fundamental measurements to understand and use pneumatic transport. A generalized phase diagram has been proposed to describe pneumatic transport. This generalized theory has been taken a step further in trying to incorporate the pressure loss term into the diagram that can describe the dilute- and dense-phase regimes more clearly.

Vertical gas-solid transition flow with electrostatics

Abstract Choking in vertical pneumatic transport in the presence of electrostatics was examined using a 0.0254 m dia. plexiglas tube and 150 μm dia. glass particles. Electrostatics was found to make the choking transition more violent and occur at a higher air velocity.

Dense-phase transport: Vertical plug flow

Abstract The transport of coal particles at low velocities by forming plugs was studied in a 0.0254-m vertical pipe. The pressure drop and the plug velocity were measured at different air flow rates and for different plug lengths. The conditions to produce stable plugs were studied. The pressure drop was found to be independent of the air flow rate and to vary linearly with the plug length. The plug velocity was independent of the plug length in the conditions studied. A model that predicts the pressure drop was tested and found to be in good agreement with the experimental data. It suggests that in the case of vertical plug flow at low velocities, gravitational forces are the most important ones.

Individual electrostatic particle interaction in pneumatic transport

Abstract Electrostatic charging and discharging of particles in pneumatic transport has been experimentally investigated under a variety of conditions. The basic system consisted of flowing glass beads 75 μm and 150 μm in diameter at dilute loadings up to 1.0 with varying relative humidities from 25 to 65%. A series of five nickel electrodes 228 μm in diameter measured particle interactions with the wall along the flow path. The charge and currents transferred were measured by an electrometer-based recording system. Different types of particle—wall interaction were noted and contact frequencies were measured. Analogy of the particle hit was made with the penetration theory. At constant loadings, greater electrostatic effects were seen for small particles over large particles due to the high particle number density and thus increased interactions for the smaller particles. Higher loadings at low relative humidities also produced increased electrostatic effects.

High-pressure vertical pneumatic transport investigation☆

Abstract Vertical pneumatic transport was investigated in a 0.026 m i.d. Lucite tube at various pressures. Nitrogen was the conveying gas at pressures of 101, 790, 2170 and 4238 kPa. Pressure drop, particle velocity, pressure fluctuations and flow patterns were measured or visually observed and recorded. Choking velocity, velocity at minimum pressure drop and the particle friction factor were also investigated at these elevated pressures. Glass beads (97 and 545 μm) and coal (89 and 505 μm) were used as the conveyed solids. The use of Lucite tubing was made possible by encapsulating the entire transport system in a high-pressure containment vessel and pressurizing the outside and the inside of the transport tube simultaneously. A Zenz-type diagram of pressure drop per unit length versus superficial gas velocity was plotted at all pressures investigated. As pressure increased, the curve shifted toward a higher pressure drop at a given gas velocity. Gas velocity at minimum pressure drop thereby decreases as the pressure increases. The same trend is observed for the choking velocity. Average particle velocity of the gas—solid flow mixture approaches the superficial gas velocity at higher pressures more readily than it does at lower pressures. Investigation of the friction factors for the small particles (89 and 97 μm) at elevated pressures revealed that the friction factors due to the gas and solid were dependent on the loading of the system. Expressions were developed for predicting the frictional pressure drop for the gas and solid at low loadings for small particles. Correlations for particle velocity, choking velocity, particle friction factor and velocity at minimum pressure drop are recommended for designing dilute-phase (i.e. ϵ>0.9) high-pressure transport systems.

Inter-relation of electrostatic charging and pressure drops in pneumatic transport

Les resultats experimentaux obtenus avec du cuivre, du verre et du Plexiglas, montrent que la perte de charge due aux contributions electrostatiques sont fonction a la fois de la densite du nombre des particules et de la capacite de charge maximale des particules

Flow measurement in pneumatic transport of pulverized coal

Etude experimentale des facteurs influant sur les performances de 2 debitmetres massiques de suspensions de charbon pulverise dans un gaz