Experimental particle image velocimetry

There are many nonintrusive experimental tools available that can help scientists to develop a good picture of fluid dynamics and transport in chemical reactors. Laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and sonar Doppler for velocity measurement, planar laser induced fluorescence (PLIF) for mixing studies, and high-speed cameras and tomography are very useful for multiphase studies. These experimental methods combined with computational fluid dynamics (CFDs) provide very good tools to understand what is happening in chemical reactors. 

Recently Lin et al. (1996) applied the VOF method to study the time-dependent behavior of bubbly flows and compared their computational results with experimental data obtained with a particle image velocimetry (PIV) technique. In their study the VOF technique was applied to track several bubbles emanating from a small number of orifices. Lin et al. reported satisfactory agreement between theory and experiment. 

Experimental and computational aeroacoustics and emissions of modern swirl combustor flows are underway. Preliminary measurements of turbulent non-premixed flame sound highlight the influence of combustion as a sound source. Particle Image Velocimetry measurements in swirl combustors reveal the influence of heat release and its effect on the complex spatial structures that are present. Acoustic measurements in confined turbulent jets are used to better understand sound sources in such flows. Computational aeroacoustics studies of unconfined and confined flows and flames have allowed acoustic source identification. Preliminary LES of diffuser and swirl combustor flowfields serve as benchmarks for future combustion simulations. 

Intrusive measurement techniques such as a Pitot static tube and hot-wire anemometer [24-26], and nonintrusive techniques such as laser Doppler velocimeter and particle image velocimetry (PIV) have been used to study the flow field. Goh, Kusadomi, and Gollahalli [13-15] mapped the velocity field in the flame using a Pitot static tube with a pressure transducer (Barocel). Details of the techniques and selection guidelines are presented in books on experimental aspects of fluid mechanics. Interested readers are referred to Holman [27], Goldstein [28], and Miller [29], to name a few. 

Fig. 20.3 Water currents generated by the courtship stationary paddling of male blue crab. View from above, the male performing courtship stationary paddling. Particle imaging velocimetry was used to visualize water currents generated by this behavior. Arrows indicate the direction of the currents, with the length of the arrows being proportional to the velocity. Results show that the water current was directed away from the male at a mean velocity of 3.1 cm/s. From Kamio et al. (2008), reproduced with permission of The Journal of Experimental Biology...

Recently the radial flow was measured experimentally using particle image velocimetry (PIV) analysis [54]. Interestingly, the velocity of a radial flow increased from zero at the center to its maximum at around 70 % of the radius of the droplet, which remained pinned during evaporation (Fig. 3.6) [54]. Interestingly, the intermediate radial position of maximum velocity within the droplet is not... 

Such a velocity distribution given by Eq. 31 was verified experimentally by Yan et al. [8] in which a method is proposed to simultaneously determine the zeta potentials of the channel surface and the tracer particles in aqueous solutions. This is achieved by carrying out microscale particle image velocimetry (micro-PIV) measurements of the electrokinetic velocity distributions of tracer particles in both open- and closed-end microchannels under the same water chemistry condition. 

Detailed three-dimensional measurements of ICEO flows are now possible in microfluidic devices. Using particle-image velocimetry applied to thin optical slices, the ICEO flow field around a platinum cylinder has recently been reconstructed experimentally (Fig. 5b) and found to agree well with the theory, up to a scaling factor which could perhaps be attributable to compact-layer effects [6]. There has also been extensive experimental work on AC electro-osmotic flows in microfluidic devices, as discussed in a separate article. 

Various flow visualisation techniques have been utilised to obtain experimental results from local gas hold-ups and bubble size distributions (BSD) in a gas-liquid mixed tank. Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA), Capillary suction probe (CSP), High-speed video imaging (HSVI) and Electrical Resistance Tomography (ERT) techniques have been applied. The applicability of various techniques is dependent on the location of the measurement, the physical properties of the gas-liquid flow, the gas hold-up and the size of the tank. 

A number of experimental measurement techniques are discussed, with a focus on noninvasive optical techniques such as particle image velocimetry and digital image analysis, as well as a number of academic numerical modeling tools such as discrete particle model and two-fluid model. Not only hydrodynamic aspects, such as the emergence of defluidized zones and solids circulation profile inversion, but also the effect on the bubble size distributions are discussed for wall-mounted membranes and horizontally immersed membranes. 

Gas velocity (e.g., particle image velocimetry (PIV)) Defined as boundary ctmdition at the inlet Experimental data difficult to get... 

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