Flow visualization

Video images from this technique have been used to show fluctuations in the discharge angle of impellers, the degree of flow compartmentalization and impeller interaction in multiple impeller systems, and to show the cavern size when mixing yield stress or highly shear thinning liquids. 

For examination of mixing behavior, light sheet visualization is important, particularly in multiple-impeller systems, to help the experimentahst think about suitable points of addition to study a mixing system, possible choice of feed location, and an initial estimate of suitable probe locations for mixing time experiments. Further tests should be performed to provide more detailed information on suitable choices of probe location. 

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The design and operation of a flow visualization system for highly viscous fluids, such as silicon rubber, has been reported by Ghafouri and Freakley (1994). This system consists mainly of a rotating roll and fixed-blade assembly, as is shown in Figure 5.7, and can be used to generate and maintain, essentially. 

Figure 5.7 Schematic diagram of the modelled flow visualization rig...

Above Re = 10 the vortex shedding is difficult to see in flow visualization experiments, but velocity measurements still show a strong spectral component at St = 0.2 (Panton, p. 392). Experimental data suggest that the vortex street disappears over the range 5 X 10 < Re < 3.5 X 10 , but is reestablished at above 3.5 X 10 (Schhchting). 

Boyce, M.P., A Practical Three-Dimensional Flow Visualization Approach to the Complex Flow Characteristics in a Centrifugal Impeller, ASME Paper No. 66-GT-83, June 1983. 

Using this assumption, one ean apply this flow visualization method to any working medium. 

This chapter covers a description of conventional measurement techniques used in ventilation as well as othei related topics such as flow visualization, laser- based measurement techniques, and scale model experiments. 

When a dye is injected into a fluid, the resulting streak lines provide flow visualization of fluid particles that have passed the same density of the fluid. 

More information on flow visualization can be found in Chapter 12. 

In order to control the movements of contaminants it is useful to be able to see how both the contaminant and the induced airflows move. A number of flow visualization methods have been developed some are more suitable for laboratory research applications whereas others are quite widely used in industrial situations. We are primarily interested in this latter category. The methods involve releasing a tracer (for example gas, aerosol, or heat) and making visible its path. While in most cases the methods are subjective, their use is invaluable. Ideally the tracer should be nontoxic, nonirritating, inexpensive, and highly visible at low concentrations. The system should be easily portable, self-contained, easy to use, and be controllable. 

A review of flow visualization techniques suitable for use in hospital laboratories was carried out several years ago. 

Chapter 12 contains more on flow visualization and measurement techniques. 

The main purpose with flow visualization is to make the airflow field or the emission and transport of air contaminants visible and thereby possible to study. In technical terms, flow visualization gives possibilities to study airflow field and contaminant dispersion and changes in it depending on general changes in geometry, boundary conditions, inlet and exhaust airflow, etc. It is... 

There are of course a number of methods that can be classific d a- methods for the visualization of airflow and contaminant dispersion. This i.hapter describes some of these that are useful for designers of industrial vcntilatiou. Methods that not are presented in more detail here are, for example, to fill small soap bubbles or ordinary balloons with helium in order to stuiiy the airflow field in large rooms. A large number of textbooks focus on flow- visualization. The research in this area can also be followed in The lournal of Floif Visualization and Image Processing. -... 

Fig. 27. Abrupt contraction cell for flow visualization, birefringence and degradation measurements A inlet (from a peristaltic pump of a pressurized reservoir B outlet (atmospheric pressure or partial vacuum) C interchangeable metallic nozzle with a sapphire tip D capillary flow meter E glass window for flow visualization AP pressure drop (from pressure transducers)...

The behavior of the flow in micro-channels, at least down to 50 pm in diameter, shows no difference with macro-scale flow. For smooth and rough micro-channels with relative roughness 0.32% turbulent flow occurs between 1,800 < Recr < 2,200, in full agreement with flow visualization and flow resistance data. In the articles used for the present study there was no evidence of transition below these results. 

Photograph of a counterflow burner system and the nonreacting flow visualization using a laser sheet. 

E. F. Matthys 1988, (Measurement of velocity for polymeric fluids by a photo-chromic flow visualization technique the tubeless siphon), J. Rheol. 32 (8), 773-788. 

Early studies of the transition to turbulence relied on flow visualization techniques for liquid flow through arrays of spheres. Jolls and Hanratty (1966) found a transition from steady to unsteady flow in the range 110<7 e< 150 for flow in a dumped bed of spheres at N — 12, and they observed a vigorous eddying motion that they took to indicate turbulence at Re — 300. In regular beds of spheres, Wegner et al. (1971) found completely steady flow with nine regions of reverse flow on the surface of the sphere for Re — 82, and similar flow elements but with different sizes in an unsteady flow at Re — 200. Dybbs and Edwards (1984) used laser anemometry and flow visualization to study flow... 

Instrumental resolution, 23 132 Instrumentation. See also Instruments calibration of, 21 161 capillary electrophoresis, 4 633 composition measurement, 11 785 for fermentation, 11 36—40 flow rate, 11 781-783 flow visualization, 11 785-786 fluid mechanics, 11 781-786 food processing, 12 87-88 gas chromatography, 4 611 6 413-414 infrared spectroscopy, 14 225-228 23 137-138... 

Consider a flow visualization study in which a small patch of dye is injected instantaneously into the flowing fluid. This will tag an element of the fluid and, by following the course of the dye, the path of the tagged element of fluid is observed. If, however, the dye is introduced continuously, a streakline will be observed. A streakline is the locus of all particles that have passed through a specified fixed point, namely the point at which the dye is injected. 

Although in general, particle paths, streaklines and streamlines are different, they are all the same for steady flow. As flow visualization experiments provide either the particle path or the streakline through the point of dye injection, interpretation is easy for steady flow but requires caution with unsteady flow. 

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