Shrikant Dhodapkar

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.

A simplified correlation for solids friction factor in horizontal conveying systems based on Yang's unified theory

Abstract A new correlation for friction factor in horizontal pneumatic conveying is proposed, based on the unified theory of Yang. Two drawbacks to the original correlation presented by Yang are the implicit nature of the equations and the inability of the correlation to predict saltation. The new correlation is based on an analysis of experimental data for particle velocity recently obtained. Knowing the particle velocity allows an explicit calculation of the friction factor and thus a prediction of the pressure drop. An added benefit to this method is the prediction of the saltation point.

Survey of characterization techniques of dry ultrafine coals and their relationships to transport, handling and storage

Abstract Handling of fine materials is always problematic because of the great variability in system configurations and in interacting properties that control the behavior of the solids in these systems. Three dry ultrafine coals having mass-mean diameter from 7 to 25 microns have been subjected to a variety of tests to explore their characteristics and suitability for transport, handling and storage. Flow and storage tests were conducted to evaluate the relationships between the coal characteristics and their performance under these conditions. The characterization was carried out experimentally by measuring the following coal properties: a1. flooding — related to bin/feeder performance; a2. absorption of pressure pulses — related to bin performance; b1. Hausner ratio — cohesive factor — related to fluidization, bin/feeder performance, conveyability; b2. de-aeration — related to bin/feeder performance, conveyability; b3. fluidization — related to bin/feeder performance, conveyability; c1. pickup velocity — related to conveyability; d1. shear stress — related to bin performance; e1. size and size distribution —general classification; e2. shape — general classification. The measured values of the various parameters are reported and related to the flow observations. Of particular interest is the relation between flooding and degree of aeration and between pressure wave absorption and aeration, which leads to the suggestion that several flow problems can be modified by controlling the degree of aeration in the bin or hopper.

Plug flow movement of solids

Abstract The development and application of plug flow of solids in pipelines first occurred in the mid 70s. This flow is also termed dense phase flow or pulse-piston flow since the plugs are somewhat like moving packed beds and the operation is usually carried out with a plug of solids and a plug of air all conveyed at low velocities. This study addresses the entire system operating with distinct pulse-piston behaviors which determine the appropriate pipe diameters for a given solids capacity and fixed amount of energy. A development is presented for the minimum plug length utilizing the basic characteristics of the powder. A case study of an existing pipeline and desired capacity is presented with determination of the energy requirements for a particular transport line. Both impermeable and permeable plugs are considered.

Phase equilibria in horizontal pneumatic transport

Abstract In an analogy to thermodynamics, the phase behavior of horizontal pneumatic systems is discussed. Two separate phases are described which can be termed dilute and dense. These two phases can and do exist in equilibrium states dependent on the chosen state variables of gas flux, solids flux, and solids volume fraction. Experimenal data from 0.0266-m and 0.0504-m diameter pipes is described using a van der Waals analog equation which is capable of predicting the coexistence of the dilute and dense phases.

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

ABSTRACT A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266xa0m and 0.0504xa0m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.

Application of thermodynamic approach to pneumatic transport at various pipe orientations

Abstract Application of thermodynamic analogy to pneumatic transport in 0.0266-m and 0.0504-m systems held at various angles of inclination was investigated. An equation of state similar to the van der Waals has been suggested for these systems. Measurements in these experimental set-ups included pressure drops, particle velocities, and solids mass flow rates in both the upper and lower halves of the pipe. These measurements were used to describe the phase behavior of the systems studied. It was found that the van der Waals analog is capable of describing the phase behavior of these systems. A method has been proposed to estimate the parameters of the van der Waals analog equation.

ELASTICITY ANALYSIS FOR CYCLONE OPTIMISATION

ABSTRACT High performance cyclone can be designed using optimisation techniques. Elasticity analysis has been used to demonstrate its utility for optimum design of cyclone. In this paper effectiveness factor, q(qxa0=xa0-In Pn/(▵P.Surf)) is used for elasticity analysis. Various standard equations have been studied and compared on the basis of this effectiveness factor. Optimum gas outlet diameter and effect of particle size on it, is presented for various design models available in literature. It is concluded that it is possible to increase the efficiency of an existing cyclone by charging the gas outlet diameter to an optimum value calculated from elasticity analysis. This will avoid any major modification in the existing cyclone to increase the collection efficiency of the cyclone.