Clive E Davies

Accumulation of Gold Nanoparticles in Brassic Juncea

Enzymatic digestion is proposed as a method for concentrating gold nanoparticles produced in plants. The mild conditions of digestion are used in order to avoid an increase in the gold particle size, which would occur with a high-temperature process, so that material suitable for catalysis may be produced. Gold nanoparticles of a 5–50-nm diameter, as revealed by transmission electron microscopy (TEM), at concentrations 760 and 1120 ppm Au, were produced within Brassica juncea grown on soil with 22–48 mg Au kg−1. X-ray absorption near edge spectroscopy (XANES) reveals that the plant contained approximately equal quantities of Au in the metallic (Au0) and oxidized (Au+1) states. Enzymatic digestion dissolved 55–60 wt% of the plant matter. Due to the loss of the soluble gold fraction, no significant increase in the total concentration of gold in the samples was observed. However, it is likely that the concentration of the gold nanoparticles increased by a factor of two. To obtain a gold concentration suitable for catalytic reactions, around 95 wt% of the starting dry biomass would need to be solubilized or removed, which has not yet been achieved.

The effect of pipeline location on acoustic measurement of gas–solid pipeline flow

Abstract The flow velocity and solids concentration in a pneumatic conveying line can be measured in-line and non-invasively from measurements of the axial propagation of active acoustic signals. This paper investigates the performance of a prototype meter in regions of developing flow, in particular after a horizontal 90° pipe bend where strong particle roping behaviour has been observed. The effect of the location of the instrumentation on the accuracy and reproducibility of the measurement is discussed.

The use of Helmholtz resonance for measuring the volume of liquids and solids.

An experimental investigation was undertaken to ascertain the potential of using Helmholtz resonance for volume determination and the factors that may influence accuracy. The uses for a rapid non-interference volume measurement system range from agricultural produce and mineral sampling through to liquid fill measurements. By weighing the sample the density can also measured indirectly.

Slip velocity and axial dispersion measurements in a gas-solid pipeline using particle tracer analysis

Abstract Pulses of radioactive tracer particles were injected into a dilute phase pneumatic conveying system, and their passage along the pipeline was recorded at a number of points. The pipeline incorporated both horizontal and vertical orientations, and horizontal and vertical bends. Solids slip velocities were calculated from these measurements and showed that the effect of bends on the solids flow can extend for a long distance downstream of the bend exit. The dispersion of the injected pulses along the pipeline is discussed, and dispersion values calculated assuming a simple axial dispersed plug flow model. The results yielded dispersion coefficients higher than those characteristic of turbulent fluid mixing. They also indicated an area about 4 m (50 pipe diameters) downstream from the exit of two consecutive 90° horizontal bends where the solids experienced high localised dispersion. This has been attributed to the resuspension of material which continues to flow in strands or ropes for some distance after the bend exit.

The slot flow meter: a new device for continuous solids flow measurement

The slot flow meter (SFM) is a device for measuring continuously a flow of granular material. The meter is a hopper, open at the top and closed at the bottom, with vertical sides containing vertical slots. The hopper is fed continuously from above with granular material which flows out through the slots; because the flow through a slot depends upon the depth of powder upstream of the slot, the inventory of granular material in the hopper is uniquely determined by the flow rate. Hence by mounting the hopper on a load cell to measure the inventory, the flow can be inferred: the cell reading gives a continuous measure of flow rate. Experimental and theoretical work on the flow of granular material through vertical slots is described. Calibration was by an in situ technique based on the dynamic response to change of input flow. This technique was tested against direct calibration (bucket-and-stopwatch) for a pilot-scale unit installed in the particle circulation loop of a fast fluidised bed.

Velocity measurements in dense down flow of bulk solids using a non-restrictive acoustic method

Abstract The velocity of a dense down flow of particles in a conduit can be measured in-line and non-invasively using acoustic waves to detect the passage of characteristic patterns in the local voidage. These patterns are, however, distorted as they flow through the conduit due to the relative motion between the particles, and shear zones at the wall. This work investigates the effect that the particle velocity and acoustic sampling parameters have on the correlation and velocity measurement of these patterns.

The behaviour of a dense stream of non-cohesive particles impacting on an inclined plate

Abstract When a coherent circular stream of small non-cohesive particles impacts onto a smooth inclined surface, it is dispersed as a thin sheet. The particles appear to move down the plate parallel to the plate surface on paths which straighten to run parallel to the longitudinal axis of the plate at points remote from the impact point. Interest in the post-impact behaviour of a falling particle stream was prompted by its potential use in mixing devices and in removing oversize material from bulk flows. Experimental measurements carried over a range of conditions have provided information on the shape, structure and mass distribution in an impact fan. A mathematical model has been formulated and a comparison has been made with one experimental condition. The agreement between measured fan shapes and mass distributions and model predictions is good.

The Effect of Heaped and Sloped Powder Layers on Ejection Times and the Residence-Time Distribution of a Conical Mass-Flow Hopper

The flow of a hypothetical Coulomb material flowing under gravity from a conical mass-flow hopper is modelled using stress field theory. The assumptions inherent for a Coulomb material can be combined with the assumption of radial flow within the hopper to determine the velocity profile within the hopper. From the velocity profile, ejection times and residence time distributions may be calculated. Since, in a real granular system, the powder layer interface is generally not flat, but sloped at some angle, (nominally the angle of repose), the residence time distribution and ejection times will be dependent on the initial geometry of the powder layers. Residence time distributions and ejection times are calculated for a given granular material in a conical mass-flow hopper firstly for the case of flat layers, secondly for the case where the powder forms a conical heap at the angle of repose, and thirdly for the case when the powder is sloping against a wall. It is found that the shape of the powder layers greatly changes the residence time distribution and ejection times in the system, and needs to be considered when performing residence time measurements in the industrial setting.

A brief investigation into ejection times from a conical mass flow Hopper - Coulomb and conical model difference

A conical mass flow hopper system is modelled using stress field theory as found in [1]. The authors present the governing equations for the stress and velocity fields under the radial flow assumption for the Coulomb and conical yield functions. The ejection times for the two models are compared and are shown to be vastly different between the two models. The residence time distributions for the models are presented. We conclude that the choice of model has a large effect on the predicted mixing as a powder travels through the hopper system.

Tracking the Transitions in Gas-Fluidized Beds with Measurements of Pressure Fluctuations

When a packed bed of powder is fully fluidized to the bubbling state it undergoes two principal transitions. The first is at the point of incipient fluidization and the second is at the onset of bubbling. The superficial gas velocity at the point of incipient fluidization is the minimum fluidizing velocity, U mf , and minimum bubbling velocity, U mb , is the superficial velocity at the onset of bubbling. By convention, U mf is experimentally determined with a plot of bed pressure drop versus superficial gas velocity, and U mb is found by visual observation; both velocities can be crucial to the design and operation of fluidized beds. In this paper, we present experimental results for sand and lactose powders in an 80-mm fluidized bed. We have analyzed fluctuations in bed pressure drop signals, obtained at ambient conditions for increasing and decreasing gas flows, using signal standard deviation, σ, and von Neumann ratio, T, and plotted values of these parameters against superficial velocity, bed pressure drop, and bed height. Our findings show that T is more sensitive to changes in the internal state of a fluidized bed than σ, with distinct and abrupt changes in T occurring at superficial velocities consistent with the values of U mf and U mb determined by conventional methods. This work has provided further support for the use of T as an indicator of the transitions occurring in powder fluidization.