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RESEARCH PAPERS

J. Eng. Ind. 1969;91(2):293-294. doi:10.1115/1.3591560.
Abstract
Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):295-302. doi:10.1115/1.3591561.

Helical Screws are commonly used to extract bulk solids from the outlet slots of hoppers. The manner in which material flows into the screw affects the flow characteristics of the hopper, residence periods of the contents in various locations, segregation, attrition and torque requirements of the screw. Regimes of motion of the solids in various sections of the equipment are outlined and a simple qualitative analysis enables predictions to be made based on material factors and screw dimensions. Consequential factors are discussed relevant to design and applications.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):303-314. doi:10.1115/1.3591562.

Examination is made of similar conditions concerning transport phenomena in the conveyance of particulate suspensions by gases. The paper, in large part, concerns conveyance in straight ducts. Pressure loss and heat transfer are considered together with the influence of electrostatic charging in fully developed flow. The case of suspensions of fine particles is considered from the point of view of a continuum. The different natures of flow both near and away from the duct wall are elucidated. The influence of agglomerative tendencies and particle/particle contact is also considered. The importance of the flow regime concept is illustrated for more involved situations where several factors contribute to overall transport phenomena.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):315-322. doi:10.1115/1.3591563.

Investigations show that production efficiency of foundries is influenced strongly by the nature and the use of means of transport. An important aspect of foundry transport is that of moulding sand. Impressive gains in space, as well as a decrease in capital investment may be had by applying pneumatic transport of moulding sand. The paper presents a basic approach to the nature of pneumatic transport of sand in a horizontal and circular tube, and indicates an approach to the calculation of the pressure gradient to be overcome. Although the analysis of the transport in a stationary laminar flow is interesting, it appears that sand is carried through a narrow sector of the tube, symmetrical to the vertical plane, and below the horizontal plane [1]. In the actual case of sand transport in a turbulent air current through a tube with a rough inner wall, sand is carried through the boundary layer at the complete circumference of the tube. It is easily seen how to generalize the approach for sand transport in a turbulent air current through a tube at an inclination to the horizontal, up to the vertical, and how to increase sand transport by injecting air which increases the turbulence of the boundary layer carrying the sand. After the various parameters for the stationary transport have been deduced, it appears to be possible to analyze the introduction of the sand grains into the air current as well as their acceleration to stationary motion [1].

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):323-328. doi:10.1115/1.3591564.

Is it possible to tell in advance if a material has a tendency to flood, or not? Powder materials often behave like liquids when aerated. There are engineers who still have not heard about these, even though they are used in solving material handling problems. Bad experiences are often their first meeting with the problem, a meeting characterized by surprise and trouble. At Fiskaa Verk, Elektrokemisk A/S, a particular problem with flooding of ground calcined anthracite was successfully solved by Dr. Jenike, and the method is described in [1]. Problems of this type are common, and in order to prevent such incidents in the future, some tests were made to find out if it is possible in advance to decide whether a material has a tendency to flood or not. A simple method was arrived at. Some characteristic qualities helping to clarify the problems of powder materials are also described.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):329-333. doi:10.1115/1.3591565.

A study of the literature on screw conveyers and feeders has been made. Most of the work is concerned with conveying material and in these cases the degree of fill in the trough is kept low to protect intermediate bearings and minimize power requirements. An equally important application for the screw, but one which has received less attention, is its use as a constant rate feeder and in this case the screw is run full. The object of the present work has been to find the effect of various parameters on screw performance at all degrees of fill. Experiments are described in which the effects of screw geometry, speed, filling, and the use of materials with different properties have been investigated.

Topics: Screws , Bearings , Geometry
Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):335-338. doi:10.1115/1.3591569.

Injected air facilitates flow of a noncohesive powder through an orifice. The effect of injected air on the flow rate of raw-mix powder (used in cement production) through an orifice has been measured. It is shown that the flow rate of noncohesive solids may be determined by an energy balance that includes the expansion energy of the air.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):339-344. doi:10.1115/1.3591570.

It is proposed that three loading conditions should be considered in the analysis of loads acting on a bin: Initial loading which occurs when bulk solid is charged without any of it being withdrawn, flow loading which occurs after flow has been established, and switch loading which occurs during the switch from initial to flow loading. The last is transient but, while it acts, it exerts large concentrated forces. The importance of the flow pattern is outlined and an expression is given for the high local force which frequently acts at the transition from the vertical part to the converging part of a bin.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):345-352. doi:10.1115/1.3591571.

Cohesionless wedges formed by free discharge at the apex exist completely in the active critical state. With active failure movement, sections only of the wedge may be in the active state. Base settlement induces intermediate stress states between the active and passive.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):353-356. doi:10.1115/1.3591572.

The paper studies the conditions of conveying material on an oscillating trough. Two criteria for estimating the efficiency of different designs of such conveyers are proposed. The analysis of the problem put in evidence the conditions required to obtain displacement of the conveyed material up or down on an inclined oscillating plane conveyer and those to be avoided as design points.

Topics: Design , Displacement
Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):357-364. doi:10.1115/1.3591573.

Depending on the stress state, a bulk solid, regarded as the elastic-plastic material, can exhibit workhardening, worksoftening or perfectly plastic properties. During continuing motion, the solid flow can be assumed as incompressible, and the stress field satisfies a condition of critical state which can be identified with the Coulomb yield condition. The model of Coulomb material is introduced; such material satisfies the Coulomb yield condition and the flow law associated with this condition by the plastic potential rule. In general, the Coulomb material is stronger than the considered bulk solid in the critical state. The kinematic approach and the familiar upper bound theorem are applied in order to determine lower bounds on pressure exerted by the flowing material on bin walls and to determine flowability criterion. In the latter section, the flow induced by a horizontally moving rough plate is analyzed and two flow patterns are considered.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):365-372. doi:10.1115/1.3591574.

The test results described are a portion of a current comprehensive series of investigations. No attempt is made to produce the values for wall frictional and bottom loads, which were measured simultaneously with horizontal pressure. Data obtained from the measurements prove that, although standard specifications on the calculation of silo loads are incorrect in some details, adherence to these loading data will not damage silos.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):373-381. doi:10.1115/1.3591575.

The flow of granular materials through curved or straight discharge chutes is classified as either “fast” or “slow.” Fast flow is the more efficient and occurs when the material flows in contact with the chute bottom and side walls, but does not make contact with the top. On the other hand, slow flow occurs when the material is in contact with all four faces of the chute. Under fast flow conditions, the grain stream thickness varies along the chute with the minimum thickness occurring near the point where the mean stream velocity is a maximum. The paper investigates the conditions governing fast flow and presents an approximate analysis to account for the grain stream thickness variation. The analysis, based on the assumption of steady flow, involves the solution of nonlinear differential equations. An equivalent friction coefficient is introduced to account for the frictional drag on the chute bottom and side walls; this friction coefficient is not constant but is found to vary with the changing stream thickness. Results of experimental investigations performed on chutes of known geometric shape are correlated with the analytical solutions. High-speed cine photography is used to determine the actual velocities and paths of individual grains in the moving stream, thus enabling the velocity profiles to be determined at different points along the stream. The paper presents data and recommendations for optimum chute design. These data include suggestions relating to the best chute shape to meet a given set of conditions and information concerning the optimum chute cutoff angles to avoid flow obstructions.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):382-384. doi:10.1115/1.3591576.

Air pressure different from that in the surrounding atmosphere develops in the bulk of granular material flowing out of an open bin through the bottom orifice. When measured on the axis of a small laboratory apparatus the differences have been found to oscillate about a mean changing along the bin and reaching its maximum/negative/well above the orifice. Pressure difference at a given point inside the bed depends upon the orifice size, and upon the size of solid particles. Equalization of the air pressure just above the orifice with that of the air outside the bin influences flow rate of the material. It is suggested that the overlooking of these effects is to some extent responsible for the great variety of flow rate equations so far proposed.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):385-389. doi:10.1115/1.3591577.

Large volumes of radioactive granular solids are being safely and efficiently handled, pneumatically, on a production scale in the Waste Calcining Facility at the Idaho Chemical Processing Plant. The low-pressure system uses no mechanically operated equipment, and hence has required minimal maintenance. Several unique devices in nonaccessible areas control and direct the flow of the solids from a cyclone and a fluidized bed to underground storage bins. A flow control valve is used to divert solids from a common supply header to any selected terminal by using an airstream to disturb the solids angle of repose. A pneumatic ejector is used for the dual purpose of removing solid fines from a low pressure cyclone and of preventing a backflow of air into the cyclone which would reduce its air-solids separation efficiency. An air purging system is used in the solids removal line from the fluidized bed to control solids flow, and thereby regulate the bed level in the vessel. The absence of moving parts in these devices makes them particularly attractive for use where reliable operation and minimum maintenance is of utmost importance.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):390-394. doi:10.1115/1.3591578.

For several years gas-cooled high temperature reactors have been developed in Germany, the main feature of which are their pebble-type fuel elements. The pebble bed is in the state of a continuous circulation process which is the reason for a series of nuclear and technical advantages. To make use of these advantages, comprehensive experimental studies on the flow behavior of a pebble bed were carried out. First, experimental equipment and the most successful method of measurement are described. Then typical results of parameter studies are reported as well as a theoretical model to calculate the pebble bed flow behavior. At last typical functions describing the flow behavior in the core of the THTR 300 MWe Prototype Reactor are reported.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):395-399. doi:10.1115/1.3591579.

The flow of bulk solids such as ore, coal, sugar and salt from storage bins depends on the pressures exerted by the bin walls on the solids. In the past the flow properties of bins have been determined on the basis of steady flow pressures. Recent experimental and theoretical work has shown that much larger pressures may be exerted on the solids during the initial filling of the bin. In this paper the effect of these initial pressures on the flow properties of bins is described and examples given for using the initial pressures to predict flow stoppages.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):400-404. doi:10.1115/1.3591580.

The author has designed over one hundred major tanks that store plastic powders and pellets. This article gives some practical examples of how to analyze and design plastic storage tanks. Examples were taken from files of completed projects. All tanks are classified as either shallow or deep; an example of each is given. A series of four articles was written to report on a study about vessels made of aluminum or steel, and joined by bolting or welding. The first three articles are “Bolted Aluminum—Alloy Connections,” “Welded Tanks for Dry Bulk Plastic Storage,” and “Bolted Tanks for Storage of Plastics.” The state-of-the-art is presented. Although computer programs have been developed, some equations still used are empirical, and the assumptions are conservative. Not all authorities agree on the proper method of analysis. A research study of the whole tank, rather than its parts, should be made.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):406-413. doi:10.1115/1.3591585.

Bins with flat bottoms and multiple openings are commonly used in industry to store granular solids because of their lower cost and because they occupy smaller vertical space than bins with a singular hopper outlet. However, in many flat-bottom bins the live capacity is much smaller than the bin volume because the spacing of openings does not permit the flow patterns above the openings to intersect. A theory has been developed to predict the boundary of the flow patterns that occur in these bins when circular openings are used, and experimental results in a small-scale bin have been found to agree closely with the theory. Boundaries of flow patterns are a function of the effective angle of friction of the material, the diameter of the opening, and the head of material in the bin. In general, the flow patterns expand outward from the edge of the opening, and become almost vertical near the top of the bin. Results of this study make it possible to determine which materials can be satisfactorily stored and which opening designs must be used to achieve adequate live-storage capacity in flat-bottom bins.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):414-421. doi:10.1115/1.3591588.

Experimental evidence shows that plasticity theory is a suitable framework for analyzing the flow of bulk materials in bins and hoppers. It thus serves as a rational guide for the collection of requisite design data including the distribution of stress and velocity throughout the moving mass of material.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):423-433. doi:10.1115/1.3591591.

The flowing of the granular materials in bins is governed, particularly in the case of small ratios of aperture diameter to particle size, by the constant formation and breaking down of arches, known as dynamical arches. In unfavorable circumstances the arches may become stable and the aperture clogged. By building up a mechanical model of the arch the fields have been found in which a stable and a dynamical arch, respectively, may be formed, enabling a bin to be judged with respect to the danger of stable arch formation. A stable field allows of studying the interaction of arch stresses and deformation of materials starting from the stress curve of the arch as a function of the curvature, and from the curve of deformation of the material as a function of the stress. It is, therefore, possible that the elasticity of the material diminishes the stable field or even reduces it to zero. In the case of nonelastic materials, the collapse of the arch may be introduced by making the lower part of the aperture wall elastic. Stable arches can now be prevented from forming by choosing the elasticity of the resilient aperture wall in such a way that if the stress increases the wall expands sufficiently to cause the required collapse. The theory underlying this solution enables the elasticity constant and the required expansion to be calculated.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):435-448. doi:10.1115/1.3591594.

During storage, flow and handling of solids, particles in the micron range tend to adhere to walls or to each other. Such processes can cause severe disturbances and sometimes require the shut down of whole plants or costly reconditioning of caked products. Different binding mechanisms which can be classified into five groups and several undergroups can be responsible for adhesion and agglomeration. In Part 1 of the paper the occurrence and importance of the different possible binding mechanisms in respect to storage, flow and handling of solids is discussed and some equations for estimating binding forces are presented. Part 2 discusses the buildup of deposits in pneumatic conveying systems, the caking tendencies of fertilizers and methods for preventing severe adhesion or agglomeration in these special cases.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):450-457. doi:10.1115/1.3591596.

Overpressures up to four times the static pressure have been measured during discharge of sand from a model silo. The overpressures can be associated with the fundamental flow patterns. Design and calibration of the pressure cells ensured that underegistration and arching did not occur. The work suggests that previous pressure measurements may be unreliable due to inadequate pressure measuring devices. The measured overpressures were generally greater than those recommended for use in design by the recently revised German and Russian codes. A more conservative design approach is suggested herein.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):460-476. doi:10.1115/1.3591600.

In recent years many reinforced concrete grain silos have suffered serious damage either from inadequate foundations, or from incorrect reinforcement of bin walls, or from faulty structural work. The author discusses several instances of damaged grain silos and reasons for the failures, and gives methods of assuming correct bin loads and of designing reinforced concrete grain silos to prevent such failures.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):478-487. doi:10.1115/1.3591603.

The behavior of samples of free flowing sand under applied shear stress have been investigated in an annular shear cell of novel design. Measurements of critical porosity, dilation and shear stress are reported and discussed. A random chord size distribution is proposed to characterize a bed of particles and a relationship between this parameter and the critical porosity is derived. Experimental and theoretical values are compared.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):489-492. doi:10.1115/1.3591606.

The assumption that a smooth wall finish, such as stainless-steel mill finish as opposed to carbon steel, will give mass flow in a less steep cone is not always valid. This paper presents case studies of how the kinematic angle of friction (φ′ ) between dry bulk solids and bin walls affects the design of mass flow hoppers and how it varies for different materials.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):497-500. doi:10.1115/1.3591608.

This paper reports upon an experimental investigation of gas dynamic rarefaction waves in rarefaction wave tubes to determine effects of large length to diameter ratios. A fitted equation is presented from which reasonable predictions can be made on the pressure deviation between a real and an ideal rarefaction wave. Transient boundary-layer effects cause an attenuation of the pressure which becomes more pronounced as the length to diameter ratio is increased. At a length to diameter ratio of 895, the pressure damping was essentially complete in one cycle for initial pressure ratios in excess of 1.6.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):501-506. doi:10.1115/1.3591609.

Pool-boiling experiments were performed in helium from high purity copper which had been exposed to various amounts of fast neutron radiation. The residual effects of the radiation influenced the pool boiling in two ways: First by decreasing the thermal conductivity of the copper substrate; and second by inducing residual radioactivity in the copper. The changes in the conductivity influenced the unsteady heat conduction process associated with nucleate boiling. The residual radiation from the copper augmented the bubble nucleation in the superheated helium in a manner similar to a bubble chamber. The relative magnitudes of the two effects were influenced by surface smoothness.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):508-512. doi:10.1115/1.3591612.

The large deformation of an elastic mount consisting of an infinite elastic strip of rectangular section bonded between two rigid plates under the combined loading of shear and normal forces is considered. The material is assumed to be homogeneous, isotropic and elastic, and has strain energy function of Mooney type. Explicit solutions are obtained for the case when strain in the normal direction is small. For this case, simple formulas relating the applied loads and deflection are given.

Commentary by Dr. Valentin Fuster
J. Eng. Ind. 1969;91(2):513-519. doi:10.1115/1.3591613.

Experimental data are presented for natural convection heat transfer and for the point of inception of vapor formation for liquid hydrogen and liquid nitrogen. Nucleate boiling results with liquid hydrogen are also presented, indicating the so-called hysteresis effect with increasing and decreasing heat flux. The variables covered include heater surface material, roughness, and orientation.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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