On the motion of vertical and oblique sand jets in stagnant immiscible liquids

Sand jets and particle clouds in water and viscous fluids have been a frequent subject of intense research and are pertinent to many environmental, industrial, and engineering processes. Mixing and dispersion of sand jets and particle clouds in water have been studied to design and optimize wastewater dredging disposal and marine bed capping. Motion of dispersed particles in viscous fluids is of great interest in design and operation of oil-sand tailing ponds and modeling magma flows. The motion of vertical and oblique sand jets passing through an immiscible layer is controlled by the properties of background fluids, the physical characteristics of sand particles, and the initial release conditions. Predicting the fate of the instantaneously released sediments in stratified oil-water system requires knowledge of how various physical factors contribute to the formation process of sediment clouds. Laboratory experiments were conducted to study the behaviour of particle clouds passing through two immiscible fluids (i.e., oil and water), formed by instantaneous release of dry sand particles from different angles and various heights above the oil layer, and to understand the effects of controlling parameters on the formation of particle clusters. Different air release heights h, release angle θ, nozzle diameters do, and sand masses m were tested. Nozzle size and mass of sand particles were grouped to form a non-dimensional parameter as L/do where L is the length of pipe filled up with sand particles. Wide ranges of aspect ratios (1≤L/do≤19.6 for vertical and 1.5≤L/do≤24.5 for oblique sand jets) were considered. Air release height was normalized to form non-dimensional air release height as η. Effects of the characteristics of sand jets in air such as mass flow rate, sand impact velocity, and jet diameter on the evolution of oily sand jets were investigated. It was found that the diameter of sand jet in air linearly correlated with the nozzle diameter. Evolution of oily sand jets with time was investigated using image processing and boundary visualization techniques. Different shapes of the frontal head and various evolution patterns were observed based on the initial parameters. The frontal width and velocity of oily sand were measured for different evolution times. Dimensional analysis was performed, and empirical correlations were introduced to predict the frontal width and velocity of particle clouds passing through immiscible layer. The average shear stress in the immiscible layer and in the early stages of evolution was calculated from the measurements: the normalised shear stress between sand particles and the immiscible layer was found to linearly increase with the impact momentum. The average drag coefficient of sand jet front was calculated and results were compared with the classical drag models. The average drag coefficient of oily sand jets was found to be smaller than the drag coefficient of individual sand particles in a steady-state condition

Heat transfer in forced convective flow boiling.

Imperial Users onl

Advances in Hydraulics and Hydroinformatics Volume 2

This Special Issue reports on recent research trends in hydraulics, hydrodynamics, and hydroinformatics, and their novel applications in practical engineering. The Issue covers a wide range of topics, including open channel flows, sediment transport dynamics, two-phase flows, flow-induced vibration and water quality. The collected papers provide insight into new developments in physical, mathematical, and numerical modelling of important problems in hydraulics and hydroinformatics, and include demonstrations of the application of such models in water resources engineering

Laser-Driven Particle Acceleration - Improving Performance Through Smart Target Design

Laser-driven particle acceleration makes use of sub-picosecond, pulsed, high-power laser systems, capable of producing intensities ~10^{19} W/cm^2 at the laser focus to form plasmas, and use ultra-relativistic and nonlinear dynamics to produce quasistatic acceleration fields. This allows electrons to be accelerated to ~100 MeV over sub-centimetre distances, while protons may be accelerated to the ~10 MeV regime. In addition, novel sources of x-ray radiation become available with these schemes. The topics covered in this thesis focus mainly on target normal sheath acceleration of protons in the overdense plasma regime and laser wakefield acceleration of electrons in the underdense regime. An experimental approach leads to novel acceleration concepts and investigations on properties of new target designs. In the overdense plasma regime, hollow microspheres were found to have the potential to enhance the conversion of laser energy into proton energy. The microscopic structure of the material used as target has impact on electron beam filamentation during electron transport through the target bulk. Long-range order was found to result in smoother beams of TNSA-produced protons as compared to amorphous structures. In addition it was demonstrated that short pulse (fs) laser-solid interactions produce magnetic fields, the strength of which can reach 10 kT, mimicking astrophysical conditions. In the underdense regime, it was found that when tailored appropriately, density ramps can provide means of dividing the laser wakefield acceleration process into four steps: nonlinear laser evolution, trapping, bunch transfer into the second bucket, and acceleration, resulting in beams with reduced relative energy spread and divergence compared to self-injection by a nonlinear plasma wave. It was further shown that capillaries can be used to improve efficiency by guiding and refocusing the laser light onto the central axis. Short bursts of soft x-rays were produced inside capillaries. Finally, the use of an asymmetric laser field at the focus facilitated off-axis electron injection into the accelerating phase of a plasma wake oscillation and enhanced x-ray emission

Problems experienced and envisioned for dynamical physical systems

The use of high performance systems, which is the trend of future space systems, naturally leads to lower margins and a higher sensitivity to parameter variations and, therefore, more problems of dynamical physical systems. To circumvent dynamic problems of these systems, appropriate design, verification analysis, and tests must be planned and conducted. The basic design goal is to define the problem before it occurs. The primary approach for meeting this goal is a good understanding and reviewing of the problems experienced in the past in terms of the system under design. This paper reviews many of the dynamic problems experienced in space systems design and operation, categorizes them as to causes, and envisions future program implications, developing recommendations for analysis and test approaches

Aeronautical engineering: A continuing bibliography with indexes (supplement 223)

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system in January, 1988

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences