Flow visualisation studies

Studies, of velocity profiles across horizontal planes in vapour columns, using Laser Doppler Velocimetry, have shown that fliis recirculation mass flow R(vapour) increases with height fi om a finite value at flie liquid surface to a maximum which can greatly exceed the boil-off, and flien decreases to zero at the roof of the vessel. Flow visualisation studies have revealed that elements of the core flow are sucked into the wall boundary layer flow at all levels down to the liquid/vapour interface hence, the variation of R with height and the linear variation of boundary layer thickness with height. 

Figures 27 and 28 show how the combined application of MR imaging and flow visualisation allows us to study the deposition of fines within fixed beds. This is a common problem in reaction engineering. For example, during process...

The choice of MPE tubes for the test section allowed easier measurements and results closer to industrial reality. Further studies should put the stress on the accurate influence of channel geometry and confinement on heat transfer with diabatic flow visualisation and a large variety of channels configurations. 

So, when the LNG rollover event happened at La Spezia in 1971, we were quickly involved in trying to understand what had happened. Subsequent research programmes, using the more sophisticated flow visualisation and measurement techniques we developed in the later 1970s, enabled us to reproduce and study rollover events between stratified layers of cryogenic liquid mixtures. In particular, we were able to visualise what happens in a rollover event using laser Doppler and photographic and video systems. 

It is planned to apply this type of fast flow visualisation to different test sections of the TOPFLOW facility. In the first experiments, the flow pattern in a vertical pipeline of 200 mm diameter will be studied. A special developed sensor will allow to achieve a spatial resolution of 3 mm at a measuring rate of 2 500 frames per second. For this purpose, the sensor must consist of 64 transmitter and 64 receiver wires (64 x 64 measuring matrix). 

Studies with many types of porous media have shown that for the transport of a pure gas the Knudsen diffusion and viscous flow are additive (Present and DeBethune [52] and references therein). When more than one type of molecules is present at intermediate pressures there will also be momentum transfer from the light (fast) molecules to the heavy (slow) ones, which gives rise to non-selective mass transport. For the description of these combined mechanisms, sophisticated models have to be used for a proper description of mass transport, such as the model presented by Present and DeBethune or the Dusty Gas Model (DGM) [53], In the DGM the membrane is visualised as a collection of huge dust particles, held motionless in space. 

Flow cytometry [141, 142] is a technique that allows the measurement of multiple parameters on individual cells. Cells are introduced in a fluid stream to the measuring point in the apparatus. Here, the cell stream intersects a beam of light (usually from a laser). Light scattered from the beam and/or cell-associated fluorescence are collected for each cell that is analysed. Unlike the majority of spectroscopic or bulk biochemical methods it thus allows quantification of the heterogeneity of the cell sample being studied. This approach offers tremendous advantages for the study of cells in industrial processes, since it not only enables the visualisation of the distribution of a property within the population, but also can be used to determine the relationship between properties. As an example, flow cytometry has been used to determine the size, DNA content, and number of bud scars of individual cells in batch and continuous cultures of yeast [143,144]. This approach can thus provide information on the effect of the cell cycle on observed differences between cells that cannot be readily obtained by any other technique. 

In the planning of a field polymer flood, it would therefore not be necessary to carry out 2-D floods in order to reproduce the recovery mechanism if improved vertical sweep were the objective of the polymer flood. Numerical simulation would simply be used to investigate these mechanisms. However, it is interesting to study experimental results from scaled layered systems since certain issues can be illustrated in particularly instructive ways. For example, the fluid dynamics of viscous slug breakdown or the flow patterns in the placement of viscous polymer slugs can be visualised very directly using such experiments (Sorbie etal, 1990). 

Such columns have proved to be especially useful for studies of bubble properties and as a means of qualitatively viewing the fluidization characteristics of given powders [3-5]. Arena et al. [6] employed a thin, two-dimensional riser to visualise flow structures with a video system capable of 2000 frames per second. 

Sensors of this kind were applied at FZR to an air-water flow test loop in a vertical pipeline (inner diameter D = 51.2mm) as well as to a cavitating flow behind a fast acting valve. The high resolution of the sensor allowed to obtain bubble size distributions and to study the evolution of the flow structure along the pipe [7]. The maximum time resolution available to perform these experiments was 1200 measurements per second. Recently, the measuring rate was increased to 10 000 frames per second with sensors of 16 x 16 measuring points. In the result it is possible to visualise and quantify individual bubbles or droplets at a much higher flow velocity, than before. 

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