Flow of slurries of coarse particles at high solids concentrations

Using a lock hopper feeding system, gravel and coal shale slurries containing particles of median diameter approximately 4 mm were transported at high concentrations through a pipe of I.D. 7.87 cm at velocities below 3.5 m/s^?1. In addition to the usual measurements of velocity, delivered concentration and hydraulic gradient, in-situ concentrations and particle velocities were determined. With these measurements, a two-layer model of stratified flow of the type proposed by Wilson was examined and found to give satisfactory predictions. Coefficients of wall friction were found to vary with velocity. Minimum values of these coefficients agreed with the results of direct shear tests. This variation could be attributed to stick-slip processes at low velocities and a change in the nature of the interparticle stress at higher velocities.     

Startup of a pipeline containing settled solid particles

Experimental studies have shown that, provided a threshold velocity is exceeded, bed of solid particles can be displaced from pipelines at low pressure gradients using fluid velocities near the limit-deposit velocity. The time scale of the process depends upon three factors: fluid acceleration, bed erosion and displacement. Results are reported for water slurries of a silica send of d₅₀ = 0.43 mm. A simple model for the transient response is proposed.     

Dermal Drivers of Injury-Induced Inflammation: Contribution of Adipocytes and Fibroblasts

Irregular inflammatory responses are a major contributor to tissue dysfunction and inefficient repair. Skin has proven to be a powerful model to study mechanisms that regulate inflammation. In particular, skin wound healing is dependent on a rapid, robust immune response and subsequent dampening of inflammatory signaling. While injury-induced inflammation has historically been attributed to keratinocytes and immune cells, a vast body of evidence supports the ability of non-immune cells to coordinate inflammation in numerous tissues and diseases. In this review, we concentrate on the active participation of tissue-resident adipocytes and fibroblasts in pro-inflammatory signaling after injury, and how altered cellular communication from these cells can contribute to irregular inflammation associated with aberrant wound healing. Furthering our understanding of how tissue-resident mesenchymal cells contribute to inflammation will likely reveal new targets that can be manipulated to regulate inflammation and repair.     

A blind approach to closed-loop identification of Hammerstein systems

This paper is a continuing study of the blind approach for the Hammerstein identification in Sun et al. (1999) and Bai and Fu (2002). In the framework of a closed-loop sampled-data system, the output is sampled faster than the updating period of the input. The parameters of the linear dynamics are consistently estimated from the information of the output only, after which the unmeasurable inner signal is uniquely reconstructed. The noise effect is explicitly considered in both the parameter and inner signal estimation. The estimation of the system orders and time delay are studied on the basis of two groups of basic equations obtained by polyphase decomposition. The proposed blind approach is validated and illustrated by a simulated numerical example.     

Soft Surface Nanostructure with Semi-Free Polyionic Components for Sustainable Antimicrobial Plastic

Surface antimicrobial materials are of interest as they can combat the critical threat of microbial contamination without contributing to issues of environmental contamination and the development drug resistance. Most nanostructured surfaces are prepared by post fabrication modifications and actively release antimicrobial agents. These properties limit the potential applications of nanostructured materials on flexible surfaces. Here, we report on an easily synthesized plastic material with inherent antimicrobial activity, demonstrating excellent microbicidal properties against common bacteria and fungus. The plastic material did not release antimicrobial components as they were anchored to the polymer chains via strong covalent bonds. Time-kill kinetics studies have shown that bactericidal effects take place when bacteria come into contact with a material for a prolonged period, resulting in the deformation and rupture of bacteria cells. A scanning probe microscopy analysis revealed soft nanostructures on the submicron scale, for which the formation is thought to occur via surface phase separation. These soft nanostructures allow for polyionic antimicrobial components to be present on the surface, where they freely interact with and kill microbes. Overall, the new green and sustainable plastic is easily synthesized and demonstrates inherent and long-lasting activity without toxic chemical leaching.     

A one-dimensional model of plug flow pneumatic conveying

A one-dimensional model of pulse or plug flow is proposed. This type of flow is observed at high mass ratios of solids to gas and requires gas velocities orders of magnitude less than dilute phase systems. Plug stability criteria are examined by considering the axial interparticle stresses within single plugs and the effect of the radial transmission of these stresses on wall friction. Establishment of the fluid pressure gradient within the plug and the existence of a settled layer of solids in the interplug space are shown to be important requirements. These concepts are used in the formulation of an empirical pressure drop equation which is used in the correlation of experimental data. Comparison of predicted and experimental values is reasonable for the air-sand system considered. The model should be of value in the planning and interpretation of future experimental studies.     

Turbulent flow in helically ribbed pipes

Velocity profiles, turbulence intensities and Reynolds stresses were determined in pipes containing three helical ribs equally spaced on the pipe wall. Pitch to diameter ratios of 8 and 11 were used. The fluid considered was air and measurements were made with X wire probes calibrated for pitch and yaw effects. The ribs appeared to affect the axial flow via the tangential component which reached a maximum below the ribs in most cases. Evidence of increases in mixing length near the wall and decreases in the central core was obtained. These are in agreement with recent theoretical predictions of other workers. Turbulence intensities were not significantly altered when normalized with the usual friction velocity.     

Automatic detection and quantification of stiction in control valves

Stiction is a common problem in spring-diaphragm type valves, which are widely used in the process industry. Although there have been many attempts to understand and detect stiction in control valves, none of the current methods can simultaneously detect and quantify stiction. Conventional invasive methods such as the valve travel test can easily detect stiction, but are expensive and tedious to apply to hundreds of valves to detect stiction. Thus there is a clear need in the process industry for a non-invasive method that can not only detect but also quantify stiction so that the valves that need repair or maintenance can be identified, isolated and repaired. This work describes a model free method that can detect and quantify stiction that may be present in control valves using routine operating data obtained from the process. No additional excitation or experimentation of the plant is required. Over a dozen industrial case studies have demonstrated the wide applicability and practicality of this method as an useful diagnostic aid in control loop performance monitoring.     

Predicting thermal breakthrough in heterogeneous media from tracer tests

Analysis of the conservation equations demonstrates that the ratio of fluid-to-temperature velocities is a constant, even in heterogeneous media. Because tracers move at the bulk fluid velocity, tracer test analysis can be used to predict temperature declines at production wells that result from injection. Tracer histories are transformed into predicted temperature histories through a simple variable transformation. Examples demonstrate that the method works well for single-phase flow in heterogeneous (but porous) media. In the presence of strong permeability correlation (layering), the method's accuracy degrades somewhat; the onset of cooling, however, is still predicted reasonably accurately.