Magnitude Of Pressure Fluctuations Research Articles

Numerical modelling of non-Newtonian slurry in a mechanical flotation cell

Certain mineral slurries used in the minerals processing industry have been shown to exhibit non-Newtonian rheologies, particularly with finer particle sizes and at higher solid concentrations. Research has also shown that a cavern containing yielded fluid surrounded by stagnant fluid form around the impeller during the agitation of non-Newtonian fluids exhibiting yield stresses, and this is therefore hypothesised to occur inside mechanical flotation cells which may adversely affect fluid hydrodynamics. A single phase non-Newtonian fluids was modelled using CFD, using the Herschel–Bulkley non-Newtonian model with constants derived from experimentally determined Bindura nickel ore slurry, known to be rheologically complex due to the presence of fibrous mineral types, such as serpentine. The modelling methodology was first validated against published experimental results in a stirred tank, and results were experimentally validated using piezoelectric pressure transducers to measure the magnitude of pressure fluctuations due to the fluid velocity in order to define the cavern boundary. Both experimental and numerical findings show that a cavern forms around the stator, with its size depending on slurry yield stress. It was also found that the shear–stress transport (SST) k – ω turbulence model predicted the cavern boundary most accurately.

A Closed Counter-Current Two-Phase Thermosyphon Loop of a Cold Neutron Source in HANARO Research Reactor

An experimental study was carried out to delineate the flow characteristics in a closed countescurrent two-phase thermo syphon with concentric tubes. This is to be installed in the HANARO research reactor as a part of a Cold Neutron Source(CNS). In the present investigation, experiments ata room temperature with Freon-II3 as a moderator were performed. Results show that, based on the magnitude of pressure fluctuation, the flow regimes could be divided into 4 distinct ones in the () plane, where represents the volume of the charged liquid and the heat load: a stable flow regime, an oscillatory flow regime, a restablized flow regime and a dryout flow regime. For >2.5l, the flow is stable at low . However, as increases, the flow becomes oscillatory and finally restablizes As increases, the oscillation amplitude decreases, reaching to the restablized flow region at low , and the liquid level in the moderator cell remains high. In the oscillatory flow regimes, for a fixed VI; the oscillating period of time varies with , having a minimum value at a certain value of . The heat load, where the oscillating period of time is minimum, decreases as increases.

テーパー付き流動層の流動特性に及ぼす分散板構造の影響

The effect of a change in pressure drop in a distributor on the fluidizing characteristics in a tapered bed was investigated by measuring the pressure drop in the bed and the volume mean diameter of the bubbles. These measurements indicated that the volume mean diameter of the bubbles could be estimated with the magnitude of pressure fluctuation in the bed. In addition, a larger pressure drop in gas distributors was found to result in a smaller pressure fluctuation in the beds. Finally, the magnitude of the pressure fluctuation and the averaged pressure drop were found to be the important indices to characterize the fluidizing state of the powder beds.

Speed control of a hydraulic motor using an on/off solenoid valve.

As microcomputers have become widespread and the response speed of on/off solenoid valves has been improved, digitally controlled hydraulic systems are used in many applications. This paper deals with speed control of a hydraulic motor using an on/off solenoid valve which is driven according to PWM control. Intermittent flow through the on/off solenoid valve causes large pressure fluctuations accompanied by speed fluctuations. In order to reduce these, the on/off solenoid valve and a hydraulic motor are connected by a high-pressure flexible hose. A compromise is made between the magnitude of pressure fluctuations and system response speed. The present work shows the usefulness of the speed control method in applications where simplicity of the hardware is desired and high response speed is not needed.

A diagnosis of pressure fluctuations in a draft tube.

Since the operating range of a Francis turbine is limited by the draft tube surge, the magnitude of pressure fluctuation at the draft tube wall should be examined at the test using a model turbine. However, there is the serious problem that the nature of pressure fluctuation depends on the measuring point which differs point by point even in one cross section of the inlet cone. The present authors attempted to explain it as a result of the difference in phase between two fluctuating components, rotating type and synchronous type, both of which were generated by the orbital motion of a spiral vortex core. Thus, based on this concept, we developed a method to evaluate the two components separately using pressure data measured at two taps which were installed at an angle of 90 deg in the cross section. The experimental results indicate that the proposed method is usable as a diagnosis of pressure fluctuations which are generated by a spiral vortex core in a draft tube.

Comments on Crocco's Solution and the Independence Principle for Compressible Turbulent Boundary Layers

The purpose of the present note is to show that on a flat plate where both the wall temperature and mean wall pressure are constant, neither of the limitations of parallel flow or of unity for the turbulent Prandtl number are required in order for the Crocco solution to apply to the turbulent boundary-layer flow. It is shown herein that this result is subject to restrictions on the magnitude of pressure fluctuations. The same analysis is generalized to show that the compressible turbulent boundary layer on an isothermal swept flat plate is independent of the spanwise flow if the molecular Prandtl number is unity.