• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 35
  • 11
  • 7
  • Tagged with
  • 771
  • 54
  • 26
  • 22
  • 20
  • 19
  • 19
  • 18
  • 18
  • 17
  • 14
  • 13
  • 13
  • 12
  • 11
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Three dimensional flow in an axial flow impeller

Gupta, Krishna Swaroop January 1970 (has links)
No description available.
2

Pulsations from rotary positive displacement gas meters

Jeannon, Josue Marc January 1975 (has links)
An acoustic model is developed to predict the acoustic pressure waves generated by rotary positive displacement gas meters. The meter is approximated, in the long wavelength limit, to a small, rigid and circular piston, pulsating with harmonic time dependence inside an infinite baffle. The acoustic source volume velocity is first derived from the geometry of the measuring part of the meter. Rayleigh's formulation is then applied to derive the acoustic pressure fields of the meter for both the unducted and the ducted situations. The effects of the self-induced pressure waves on the registration of the meter are then considered. The performance of the meter is dependent on the configuration of the pipe network to which the meter is attached. The meter calibration curve can be seriously distorted by the self-induced acoustic pressure waves. The effectiveness of concentric Helmholtz type resonators to suppress undesired sound pressure waves in meter systems is discussed. Experimental verification shows that the acoustic model developed is adequate to predict the "a.c" response of rotary positive displacement gas meters for most of the common pipe elements. Linear plane wave theory is used throughout and the effects of flow and friction are assumed to be negligible.
3

The whirl instability of a rigid rotor in a flexibly supported gas lubricated journal bearing

Boffey, David Alan January 1972 (has links)
No description available.
4

Fluid flow and mass transfer in an annulus with the inner cylinder rotating

Shahbenderian, A. P. January 1961 (has links)
No description available.
5

Particle image velocimetry and its application in the study of gas velocities in the freeboard above bubbling fluidised beds

Rix, Steven J. L. January 1998 (has links)
Velocity measurements have been made of the complex flow in the freeboard region about bubbling fluidised beds. Most research was carried out using a 5 m-tall bed, which had a 0.3m x 0.3m square-sided cross-section. Velocity profiles have been measured at various heights above the bed surface. These velocity profiles should allow elutriation calculations to be made, determining the carry-over of fine particles from bubbling fluidised beds. The technique used, Particle Image Velocimetry (PIV), is relatively new and is reviewed here. PIV enables simultaneous velocity measurements to be made at thousands of different points in a fluid flow, allowing transient flow structures to be seen (<I>e.g.</I> short-lived vortices and jets of rapid gas flow). In contrast, most previous research on the topic has used single-point measurement techniques such as Laser Doppler Anemometry, which yield a time series of velocity measurements at a given point but no information about the velocities at nearby points during this time (making it difficult to detect unsteady features of the flow). In this work , velocities have been calculated from PIV flow recordings using a digital analysis method, based on the calculation of an autocorrelation plane for small square-sided area elements from the flow record. This technique is assessed in detail, by means of Monte Carlo simulations. An optimum diameter has been obtained for digital particle images. Recommendations are also given for the minimum and maximum separations of these images, if a good yield of highly accurate vectors is to be obtained after analysis. For digital analysis using square-sided interrogation areas, it is felt that these new recommendations are more appropriate than the older values given by Keane & Adrian (1990, 1991) using circular interrogation spots. It was found that unexpectedly large errors can arise in these PIV measurements due to auto-correlation wrap-around, if the image separations and analysis parameters have certain values. The conditions under which these errors arise have been investigated. New research allowed a model to be developed, which appears to describe these wrap-around errors satisfactorily.
6

Flow patterns in flat-bottomed silos

Watson, Graham Redpath January 1993 (has links)
The work in this thesis is directed towards the measurement and prediction of the shape of the flow channel in granular solids as they discharge from flat-bottomed silos. It is widely believed that the flow pattern affects the pressure distribution against the walls and so also the stresses in the silo structure. Thus, a reliable means of predicting the shape of the flow channel has important design implications. Kinematic analysis is used as the basis for the theoretical work. The governing partial differential equation contains one unknown empirical parameter: the kinematic parameter. Finite element formulations are developed and implemented to solve for the steady-state vertical velocity field in flowing granular solids for a range of conjectured kinematic parameters. The formulations are applied to the analysis of flow from flat-bottomed silos with planar or axisymmetric geometries. Criteria are proposed to define the boundary between flowing and near-stationary solid. The flexibility of the finite element method allows many original kinematic analyses to be carried out <i>e.g</i> the analysis of silos with more than one outlet; the analysis of planar silos with eccentrically-positioned orifices; the analysis of the effect of a spatially-varying kinematic parameter and the modelling of the top surface displacement are all claimed to be original. Experiments are carried out in a half-cylindrical flat-bottomed silo. A rigid transparent sheet is used to form the front wall. The bisection of the flow in this way allows direct observation of flow mechanics to be made and the shape of the flow channel boundary can also be traced. Two solids are tested: a rough, frictional solid (sand) and a smooth, free-flowing solid (polypropylene pellets).
7

A Lattice-Boltzmann and particle image velocimetry study of bounded oscillatory flow

Tonge, Steven James January 2005 (has links)
Bounded oscillatory flows occur in many situations. The Lattice-Boltzmann model (LBM) is used to simulate oscillatory flows into the intermittently turbulent regime, in both two- and three-dimensions. The result of one of the three-dimensional simulations is also compared to Particle Image Velocimetry (PIV) measurements of an equivalent flow. After a review of some theory of oscillatory flow and also the methods used in the LBM simulations and PIV measurements, a two-dimensional LBM is used to simulate oscillatory flow in an infinite two-dimensional channel. The development of turbulence over the oscillatory cycle is observed and presented. A three-dimensional LBM simulation of oscillatory flow in an infinite three-dimensional channel is performed and the result presented and compared to results from the infinite two-dimensional channel. A further simulation is performed with the three-dimensional LBM applied to an infinite square duct. The development of turbulence is again observed and compared to the LBM simulation in an infinite three-dimensional channel. The results of PIV measurements of a flow equivalent to that in the LBM simulation in an infinite square duct are then presented and compared to the results of the three-dimensional infinite square duct simulation. The results of this work clearly show that the LBM is a useful tool for simulating bounded oscillatory flows and also provides a clear insight into the transition to turbulence in this type of flow.
8

A study of the near wake of a model wind turbine using particle image velocimetry

Whale, Jonathan January 1996 (has links)
Whole-field velocity and vorticity measurements have been obtained in the near wake of a model wind turbine using the technique of Particle Image Velocimetry (PIV). The experiments were conducted in a water channel with the turbine operating over a range of tip speed ratios, λ = 1.6 - 8. These were tip speed ratios pertinent to full-scale turbine operation and assured that the ratio of velocities at a full-scale machine were reproduced at the model. The corresponding range of Reynolds numbers, based on blade chord, was 2,600 - 16,000. Results have been presented for both a 2-blade flat-plate rotor and a 3-blade model replica of a full-scale wind turbine. An analysis of the velocity structure of the wakes produced mean and turbulent velocity profiles and made comparisons with results from both full-scale measurements and wind tunnel tests. Scale effect was isolated as a limiting factor in extrapolating velocity deficits from the PIV results to full-scale. An analysis of the vorticity structure identified behaviour in the wake which influenced the geometry and stability of the vortex system. The PIV images confirmed that the simple models currently being used by the wind turbine industry for design purposes are fundamentally flawed. Comparisons were made with simulations from a sophisticated vortex wake code being developed at the University of Stuttgart. Significant discrepancies were identified in wake development. The study is viewed as a first step in determining the detailed physical processes governing wind turbine wake behaviour in order that advanced rotor performance methods may be developed.
9

The physical and mass transfer properties of bubbles in a fluidised bed

Pereira, J. A. F. da R. January 1977 (has links)
No description available.
10

The jamming of dense suspensions under imposed stress

Holmes, Colin January 2004 (has links)
Suspensions of solid particles within a solvent display a variety of interesting rheological behaviour. The viscosity can vary with applied stress, resulting in materials which become thinner or thicker as they are driven more strongly.  Thickening can become so severe that the flow becomes erratic on a macroscopic level, suggesting that the material acquires a solid-like character, at least transiently. This idea is supported by recent experiments in which initially fluid suspensions are transformed into a persisting solid upon shearing. Behaviour reminiscent of this can be observed in granular materials. For example, the flow of grain from a hopper under gravity is often halted as ‘arches’ of force bearing particles form. In such a situation, the solidity of the material arises only as a result of applied forces and transient flow. There has been much speculation regarding the nature of these jamming phenomena, in particular whether or not there is a link between jamming and the glass transition. In this thesis, we present a model in which jamming is treated as a stress induced glass transition. This leads to predictions of the rheological behaviour and the structural dynamics in such a scenario. We also discuss the link between rheology and the glass transition more generally, arguing that common explanations for thickening in dense colloids are unlikely to be complete, as they essentially ignore the presence of the glass transition. Finally, we discuss the relevance of jamming phenomena to the industrial process of granulation.

Page generated in 0.0237 seconds