Imperial College London

We specialise in the termination of optical fibres, connectors and devices across diverse sectors, medical, aerospace, sensor, telecommunications, defence and more.

Imperial College London

Consultancy, Design and manufacture of a working prototype to be used within the Research department of Fluid Mechanics: fibre optic sensor assembly to be used to monitor and measure the flow of bubbles within an oil pipeline.

Multiphase transportation in pipelines is very common in the hydrocarbon industry. The flows can be highly complex; therefore it is important to investigate the behaviour of multiphase flow within pipelines to ensure a safe design of the transportation process.

Slug flow is one of the most common flow regimes observed in hydrocarbon transportation, in which the pipe cross-section is filled alternately with liquid and gas. In liquid slug, there are small bubbles entrained and form a bubbly zone. It’s important to investigate the characteristics of the entrained bubbles since they have a direct influence on the flow turbulence characteristics.

Optical probes are used to locally detect the presence of the gas bubbles in two liquid-gas phase systems. The measurements are based on different refractive indexes between the gas and liquid phase.  A light source is transmitted through an optical fibre to the tip. When the tip is dipped into a gas phase, the light is mainly reflected, travelling back to the light receiver, when the tip is immersed in a liquid environment, the light is scattered and almost no light is reflected back to the receiver device which leads to a weak electric signal. The time-dependent signal consists of a succession of crenel shaped transitions. The duration of each individual crenel represents the residence time of a gas bubble penetrate through the probe tip.

The optical probes we have been commissioned need to be inserted into a 3-inch horizontal pipe in order to take the measurement. A complete design of the optical probe system was developed and produced by Alker.

Each probe consists of a pair of two fibres. A small part of the plastic silica coating at one end of the fibre was removed then two pieces of the naked fibres were inserted into a short stainless-steel tube, the tip was carefully welded, then slightly pulled back into the needle tube and mounted in place using epoxy resin.

In order to examine the flow structure at different vertical levels of the flow, 3 optical probes were positioned side by side. To protect the naked optical fibres, each probe was housed by a 2 mm stainless steel tube bent into an elbow. These tubes were tightly clamped by a supporting tube which provides a firm support and prevents excessive vibration in experiments. The probes were housed within a stainless-steel tube, the fibres coming out from the tube were assembled into a micro-armoured stainless-steel encasement terminated with SMA 905 connectors.

The probe system must be calibrated offline first. Each end of the fibre is connected to an emitter and a receiver; meanwhile an oscilloscope is connected to the receiver in order to give the electrical signal. The first test is to examine the response from the probe when it passes through a gas-liquid interface. This test can be done merely moving the probe tip in and out of the water surface in a glass beaker. Then more complicated tests are performed on bubble penetrations, a digital high-speed video camera is used to enables a comparison to the signal profile from the oscilloscope.

Alker has extensive experience in working with Universities and Higher Education facilities worldwide. Our other customers within this sector include among others: Oxford, Cambridge, Bristol, Edinburgh, Nottingham, Essex, Glasgow, Wisconsin, Helsinki and Poznan Universities, RISE Research Institute of Sweden, Institute of Technology Tallaght, Hilase Institute of Physics etc. We are proud to work with hundreds of research centres around the world.

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