Advances in the Theory and Practice of Hydrocyclone Technique
With numerical simulation of hydrocyclone separation based on the Navier-Stokes and mass transfer equations, it is possible to perform hydrocyclone experiments on a computer. With the help of computational engineering, the cost of conducting hydrocyclone experiments in the planning phase of new hydrocyclone units can be cut drastically. The simulation models also enable a deeper insight into the static and dynamic process behaviour in hydrocyclones. It is shown that the solids stored in the hydrocyclone represents a sensitive process variable for separation in the hydrocyclone. On this basis, a new control concept for a hydrocyclone battery has been developed. As the solids concentration in the feed increases, the combined overflow of all the hydrocyclones in the battery is throttled. At the same time, the feed pump speed is increased. In this way, while the total throughput remains constant, the volume split changes to effect that more solid material is discharged in the hydrocyclone underflow. This computer-based process control system is ideally suited for hydrocyclones in separation plants for tunnel driving projects as well as for those integrated closed-circuit grinding
True Grit. A Grit Removal Efficiency Investigation at Five Wastewater Treatment Plants
The Hampton Roads Sanitation District (HRSD) owns and operates thirteen wastewater treatment plants (WWTP) in Southeastern Virginia. Several HRSD WWTPs experience abrasive wear to equipment, reduced operating volume in aeration tanks and digesters, premature equipment repairs and increased maintenance cost due to poor grit removal. In 2007 and 2008 HRSD embarked upon a grit removal study at five of the WWTPs. The objective of the study was to evaluate the grit removal efficiencies of these plants. The study compared three medium energy forced vortex grit units, a gravity settling detritor, and an aerated grit system. All five plants use hydro cyclones and classifiers. The study concluded the detritor had the highest grit removal efficiency and the angle of the hydro-cyclone is a contributing factor in grit removal efficiency. The study also recommended several equipment and operational strategies to improve grit removal at the other facilities.
Efficacy for Dealing With Terrorism Precautionary Behavior: Laying the Groundwork for Communication Effectiveness
In order to formulate effective communication and intervention strategies to respond to the widespread lack of preparedness for public health crises resulting from natural and human-made disasters, researchers have developed models describing the interrelationships between factors associated with emergency preparedness decisions. Empirical research has generally assumed that two key elements of most health behavior theories—self-efficacy and response efficacy—additively influence the decision to prepare, despite compelling theoretical rationale for an interactive relationship. The few studies that have investigated interactions in preparedness outcomes have not tested the Social Cognitive Theory prediction that non-zero levels of both efficacy types are required before individuals will engage in any preparedness behavior. Based on the responses of 3,101 participants in the National Survey of Disaster Experiences and Preparedness, this study tested additive, interactive, and conditional main effect hypotheses about the influence of self-efficacy and response efficacy for dealing with terrorism on preparedness due to terrorism six years after the September 11, 2001, terrorist attacks. A significant self-efficacy × response efficacy interaction effect on preparedness was found, in addition to a significant response efficacy effect when perceived self-efficacy was zero, contrary to the expectation from Social Cognitive Theory. These results offer insights into the cognitive processes underlying individuals’ decisions to prepare for disasters such as terrorist attacks, and highlight the importance of considering more complex theory-based cognitive interaction models in designing effective communication strategies to facilitate individual emergency preparedness.