Academic literature on the topic 'Internal channel pressurisation'

The use of channel pressurisation in drawing microstructured optical fibres (MOFs) potentially allows for fine control of the internal structure of the fibre. By applying extra pressure inside the channels it is possible to counteract the effect of surface tension which would otherwise act to close the channels in the fibre as it is drawn. This paper extends the modelling approach of Stokes et al. (J. Fluid Mech., vol. 755, 2014, pp. 176–203) to include channel pressurisation. This approach treats the problem as two submodels for the flow, one in the axial direction along the fibre and another in the plane perpendicular to that direction. In the absence of channel pressurisation these models decoupled and were solved independently; we show that they become fully coupled when the internal channels are pressurised. The fundamental case of a fibre with an annular cross-section (containing one central channel) will be examined in detail. In doing this we consider both a forward problem to determine the shape of fibre from a known preform and an inverse problem to design a preform such that when drawn it will give a desired fibre geometry. Criteria on the pressure corresponding to fibre explosion and closure of the channel will be given that represent an improvement over similar criteria in the literature. A comparison between our model and a recent experiment is presented to demonstrate the effectiveness of the modelling approach. We make use of some recent work by Buchak et al. (J. Fluid Mech., vol. 778, 2015, pp. 5–38) to examine more complicated fibre geometries, where the cross-sectional shape of the internal channels is assumed to be elliptical and multiple channels are present. The examples presented here demonstrate the versatility of our modelling approach, where the subtleties of the interaction between surface tension and pressurisation can be revealed even for complex patterns of cross-sectional channels.

Mathematical modelling is used to examine the unsteady problem of heating and pulling an axisymmetric cylindrical glass tube with an over-pressure applied within the tube to form tapers with a near uniform bore and small wall thickness at the tip. To allow for the dependence of viscosity on temperature, a prescribed axially varying viscosity is assumed. Our motivation is the manufacture of emitter tips for mass spectrometry which provide a continuous fluid flow and do not become blocked. We demonstrate, for the first time, the feasibility of producing such emitters by this process and examine the influence of the process parameters, in particular the pulling force and over-pressure, on the geometry. There is not a unique force and over-pressure combination to achieve the desired geometry at the tip but smaller over-pressure (hence force) yields a more uniform bore over the entire length of the emitter than does a larger over-pressure (and force). However, the sensitivity of the geometry to small fluctuations in the parameters increases as the over-pressure decreases. The best parameters depend on the accuracy of the puller used to manufacture the tapers and the permissible tolerances on the geometry. The model has wider application to the manufacture of other devices.

The opening of magmatic hydraulic fractures is an integral part of magma ascent, the triggering of volcano seismicity, and defusing the explosivity of ongoing eruptions via outgassing magmatic volatiles. If filled with pyroclastic particles, these fractures can be recorded as tuffisites. Tuffisites are therefore thought to play a key role in both initiating eruptions and controlling their dynamics, and yet their genesis remains poorly understood. Here we characterise the processes, pressures and timescales involved in tuffisite evolution within the country rock through analysis of the sedimentary facies and structures of a large sub-horizontal tuffisite vein, 0.9 m thick and minimum 40 m in length, at the dissected Húsafell volcano, western Iceland. The vein occurs where a propagating rhyolitic sheet intrusion stalled at a depth of ∼500 m beneath a relatively strong layer of welded ignimbrite. Laminations, cross-stratification, channels, and internal injections indicate erosion and deposition in multiple fluid pulses, controlled by fluctuations in local fluid pressure and changes in fluid-particle concentration. The field evidence suggests that this tuffisite was emplaced by as many as twenty pulses, depositing sedimentary units with varying characteristics. Assuming that each sedimentary unit (∼0.1 m thick and minimum 40 m in length) is emplaced by a single fluid pulse, we estimate fluid overpressures of ∼1.9–3.3 MPa would be required to emplace each unit. The Húsafell tuffisite records the repeated injection of an ash-laden fluid within an extensive subhorizontal fracture, and may therefore represent the fossil record of a low-frequency seismic swarm associated with fracture propagation and reactivation. The particles within the tuffisite cool and compact through time, causing the rheology of the tuffisite fill to evolve and influencing the nature of the structures being formed as new material is injected during subsequent fluid pulses. As this new material is emplaced, the deformation style of the surrounding tuffisite is strongly dependent on its evolving rheology, which will also control the evolution of pressure and the system permeability. Interpreting tuffisites as the fossil record of fluid-driven hydrofracture opening and evolution can place new constraints on the cycles of pressurisation and outgassing that accompany the opening of magmatic pathways, key to improving interpretations of volcanic unrest and hazard forecasting.

Nanoelectrospray ionisation (nESI) is a useful technology for assessing the chemical composition of various liquid samples using mass spectrometry (MS). Signi cant e orts have been made in the design of nESI emitters, as their shape and geometry are critical to the electrospray performance and subsequent MS detection. In the actual manufacturing of these emitters through the heat and draw process, the desired geometry cannot, at present, be achieved. In particular, the inner channel reduces in size, which is not desirable. To improve the sensitivity of biological and chemical mass spectrometry and avoid clogging of the tip, a small near-uniform bore of 10 - 20 m is desirable with the external wall tapering over a length of around 5mm from 75 - 150 m in radius to a sharp end with a radius around 8 - 15 m. Through mathematical modelling, we demonstrate, for the rst time, the feasibility of producing such emitters using the heat and draw process with the addition of pressure in the channel to prevent any reduction in size. In this thesis, we consider the unsteady problem of heating and pulling of an axisymmetric cylindrical glass tube, using asymptotic methods to exploit the slenderness of the tube and over-pressure applied within the inner channel, to form tapers with a near uniform bore and small wall thickness at the tip. This is an unsteady extensional ow problem. As the glass temperature increases, the viscosity reduces until the central heated region extends and thins rapidly to yield an hour-glass shape. During stretching, the cross-sectional geometry will also deform under the e ects of surface tension and applied pressure, with the pressure counteracting the closure of the channel by surface tension and, perhaps, further expanding it. When cooled and cut transversely at the centre, two identical tapered capillaries are obtained. In this thesis, we assume molten glass is a Newtonian uid, and develop coupled ow and energy models to examine in detail the in uence of the process parameters on the geometry, namely the pulling force, pressure, temperature, and surface tension. The use of an over-pressure in the channel, to counteract the reduction in its size as the crosssectional area decreases due to pulling and the channel closes due to surface tension, is of particular interest. The model and solution method described in this thesis enable determination of a pulling force, channel over-pressure, and draw time to achieve tapers with the desired internal diameter and wall thickness at the very tip from a given tubular bre for a temperature dependent viscosity.
Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 2022

The influence of soil sedimentation on the pipe walking phenomenon is investigated analytically via a set of coupled nonlinear partial differential equations where the effects of operating variables such as internal fluid temperature variation, prestress and internal pressurization, Coriolis and axial accelerations of the internal fluid and cross sectional area change are fully captured. For this problem, a segment of an offshore pipeline resting on the ocean floor is idealized as elastic beam on an elastic foundation using recently refined Euler-Bernoulli beam theory. By invoking integral transforms, closed form analytical expressions for displacement of the fluid-pipe-soil interaction system associated with pipe walking is computed. Simulated results showed that pipe walking phenomenon is strongly dependent on sedimentation level, friction at the interface of pipe-ocean sub soil layer, temperature variation, fluctuations in internal fluid pressurisation and oscillatory strain of the pipe in both transverse and longitudinal modes.