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  • 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.
71

A study of column separation accompanying pressure transients in an aviation kerosene pipeline

Swaffield, J. A. January 1970 (has links)
Column separation on both the upstream and downstream sides of a valve in an aviation kerosene pipeline was the subject of an investigation involving the method of characteristics to solve the partial differential equations governing pressure transient propagation. Particular attention was given to obtaining accurate velocity results at the instant the predicted pressure at a section reached vapour pressure. A test rig utilizing L.56 aluminium alloy fuel piping and other aircraft standard components and pumping Aviation Kerosene Specification 2494, was employed to investigate the phenomenon and test the computing procedures. For separation upstream of a valve following closure, a comparison of the computed and observed results indicated an accuracy within 3% for the first peak following valve closure and 5% for the cavity duration. Computed results within 10% of the observed were obtained for the later peaks following cavity collapse. Observation and filming of the sequence of events downstream of the valve during and following closure indicated that the air released during initial separation remained out of solution. The effect of this air was significant but could be included, in terms of its partial pressure, in the cavity boundary equations. The predicted cavity collapse pressures were consistently above those observed. Predicted values of maximum and minimum pressures, and their event times, following valve closure were, at worst, within 10% of the observed results. Analysis of the released gas indicated that it had normal air composition. Measurement of column velocity from the films and the use of a hot film probe and anemometer supported the assumptions made with reference to column motion. The hot film probe results demonstrated that this flow measurement technique was practical in this application.
72

Effects of condensation on steam-water, counter-current flooding in a vertical tube

Ahmed Husham Mahmood, H. M. January 1988 (has links)
During a loss of coolant accident in a pressurised water reactor, emergency core cooling water is introduced via the downcomer annulus. The water may have to penetrate or overcome steam formed in the vessel due to the depressurisation. A typical counter-current flow situation can be created and dependent on the relative flow rates water may be prevented from reaching the reactor core with serious consequences. This,thesis considers the events leading up to this occurrence in a vertical, 54.75 mm diameter, 1 m long, stainless steel tube, to represent and provide a basic understanding of the situation occurring during a loss of coolant accident. Results are presented for air-water and steam-water flows with emphasis on the experimental and theoretical studies of the steam-water flow situation where direct contact heat transfer occurs. The air-water flooding data are shown to be well represented by a Wallis type flooding correlation. The steam-water flooding data are found to lie above the corresponding air-water data with their characteristic dependent on the water inlet subcooling. The percentage of the air/steam flow extracted with the water flow at the bottom porous sinter was found to exert a negative effect on the flooding phenomena. A theoretical model was developed to predict the liquid film thickness along the tube, and agreement with the experimental results demonstrated. A second theoretical model was developed to evaluate the temperature across the liquid film and along the test tube and from this model, the effective turbulent diffusivity was evaluated, leading to an estimate of the turbulent viscosity of the film under conditions in which substantial condensation took place. A semi-empirical model based on a linear stability analysis of a uniform liquid film and a counter-current flow of steam, was developed and modified for accelerating film flows. This model is shown to be capable of dealing with the steam-water flooding situation since reasonable agreement with the air-water flooding data is obtained. A modified Wallis type flooding correlation based on the experimental data, and accounting for non-equilibrium effect on flooding, is presented and discussed. A visualisation technique was developed and used to determine the flooding location in the section.
73

The behaviour of air pockets in hydraulic structures with particular reference to dropshaft/tunnel bends

Himmo, S. K. M. January 1986 (has links)
No description available.
74

Inelastic collapse of pipes under external pressure and bending

Tay, C. J. January 1978 (has links)
No description available.
75

Pipe design for improved particle distribution and improved wear

Raylor, Benjamin January 1998 (has links)
This thesis describes the use of swirl-inducing pipes in water and water/mixture flows, with a particular emphasis on production of swirl before a bend. The author takes ideas for imparting swirling action to particle laden liquids which have occurred in one form or another throughout the 20th Century. The aim of the project was to reduce wear and produce better particle distribution throughout a bend. In the present investigation two methods were used in the examination of swirl-inducing pipes, namely experimental and numerical. The experimental method made use of a Swirly-flo pipe, which is normally found in marine boilers and is used to improve heat exchanger efficiency. The Swirly-flo was then placed onto an experimental test rig, which was specifically designed to provide insight into the use of swirl-inducing pipes. The numerical method came from a commercial Computational Fluid Dynamics (C.F.D.) package which allowed the author to examine various shapes for pipes and provided information on the flow fields in a swirl-inducing pipe. From the experimental results it was shown that swirling the flow before a bend produced less pressure drop across the bend than non-swirling flow. However, the Swirly-flo pipe produced a greater pressure loss across its length than the standard pipe. By swirling the particles before the bend the particles were more evenly distributed throughout the bend, which has the potential to remove the characteristic wear zones. Computational Fluid Dynamics was used to investigate various Swirly-flo designs. These studies indicated that the optimum pitch to diameter ratio was shown to be 8 for a constant pitch Swirly-flo pipe, which was consistent with previous work.
76

The mechanics of pipe whip

Prinja, N. K. January 1987 (has links)
No description available.
77

A study of compressibility and scale and their influence in dead-end pressure filtration

Willmer, S. A. January 1996 (has links)
A systematic study has been made of the factors which influence compressibility in cake filtration. A fully automated dead-end pressure filtration rig was designed, constructed and assembled at Loughborough and used to provide accurate data for an experimental matrix. The parameters investigated included pressure, feed concentration, time, surface charge, size and shape of the particulate material and scale of filtration. A proven electrical resistance measuring technique was used to determine transient solids concentrations through a filtering cake/suspension and subsequently interpret filtration performance. The particulate materials calcite and zinc sulphide dispersed in water were used to span a range of filter cake compressibility. The initial results from experiments using calcite were found to be reproducible and generally followed the expected trends. More compressible materials, such as zinc sulphide, were subsequently filtered at different pHs to investigate the influence of surface charge. Filter cells of different filter sizes were used to examine the influence of scale on filtration. Several curious observations were made such as sudden increases in filtrate rate at apparently stable process conditions and lower concentration measurements near the base of the cake. The importance of considering all scale-up parameters and their relation to each other is highlighted in the work. Further points such as the definition of compressibility over a narrow range of pressure and the structure of the filter cake have been discussed. The results were analysed with the use of conventional and new filtration theories. The conventional and modem theories generally gave good predictions of cake height for all the materials tested but for unstable/compressible suspensions the prediction of the concentration profile was less accurate. The use of the maximum solids concentration value at the base of the cake has been suggested to reduce this error and so help prevent filter under sizing. Results indicating retarded packing compressibility have been discussed along with volume-time data which suggest an influence of scale on filtration. Scale-up constants were found to vary considerably in some cases. Large changes in cake resistance were seen for small changes in cake concentration suggesting a need to use other structural characterising parameters as well as macroscopic cake concentration values. The Koenders and Wakeman model gave good predictions of the first linear part of the volume-time relationships for stable suspensions. Conclusions are drawn on the influence of each of the studied parameters on the filtration of compressible materials.
78

Position controlled disc valve

Lau, K. S. January 1987 (has links)
Recent developments of electro-hydraulic disc valves at Surrey University have shown that with a careful balance between the hydraulic and magnetic forces, this type of valve can be used as a digital or proportional device. As the valve is simpler in construction and involves very few critical dimension compared with a servo-valve, the sensitivity to contamination is considerably reduced. The dynamic response of the valve is fast due to utilising high electro-magnetic and fluid forces for actuation. The research described in this thesis is an extension of earlier work by Yuksel and Usman to improve electro-hydraulic disc valves by applying closed-loop position or pressure control to the disc. From an investigation of an unbalanced single disc valve, it was found that using position feedback can help to stabilise the disc under varying load conditions. A special differential capacitive transducer to measure the disc position was designed and constructed and was found to perform satisfactorily. As the pressure-flow characteristic of the valve can be varied by controlling the disc position, the function of the valve is similar to an electrically controlled variable orifice. Various modular configurations are proposed to perform more complicated control functions. In the final part of the research, a double disc valve is described for used in an application study to control the damping characteristic of a modified vehicle shock absorber. Initially, the valve was designed for closed-loop position control due to the non-linear hydraulic and magnetic forces. Results show that the valve can be controlled to generate the required range of damping force and has adequate dynamic performance with a response time in the range of 10 to 30 msec. However, tests using direct pressure control were also carried out. Preliminary results indicate that pressure feedback is preferable to position feedback and that by using lead compensation together with a proportional plus integral controller, stable operation is possible.
79

Interactive gas flow analysis

Aylmer, Steven F. January 1980 (has links)
No description available.
80

On the mechanics of flexible pipes, umbilicals and marine cables

Tan, Zhimin January 1992 (has links)
No description available.

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