Particle-image velocimetry

Particle image velocimetry (PIV) is used to trace particle motion in a fluid flow or for direct observation of flow phenomena. The particles are illuminated with a plane sheet of light and images are taken with a known time separation [84]. The distance of particle in a controlled time difference can be calculated to provide a 2D velocity map. 

A PIV application was used to observe particle movements/distributions in a crossflow module during filtration of yeast cells (without spacer) [85]. A particle velocity map was also defined to describe flow distribution along the rectangular crossflow module (without membrane) with spacers [86]. In another experiment, the flow velocity distribution within the fiber bundle (nine fibers in a 3 x 3 array) was observed to identify the presence of dead zones (indicated by particle movements) during bubble injections [84]. It was found that if small bubbles were introduced from the center of the bundle, a dead zone was formed and caused fiber blockage. 

Fouling deposition in crossflow membrane filtration can be indicated by the deceleration of particles on the membrane surface. PIV was used to identify early fouling phenomena (particle decelerations) and the dead zone during membrane filtration [84]. PIV has the same limitation as other optical methods, like DOTM, as it requires optically transparent solutions. However, how this technique can be extended to real module with a large number of fibers is a challenge and it may be limited to laboratory validation of bubbling and computational fluid dynamic models of MBR systems. 

In MBR application, biofouling and biofilm originate from the complex nature of the feed. Biomass mixed liquor contains solids, inert, colloids, macromolecules and microorganisms in the soluble fractions. As in any biological process, the microorganisms involved in MBR tend to colonize any fixed support material or membrane surface. Moreover, once filtered, the biomass and its components are 

PT Measurement of fouling thickness dining the filtration of synthetic wastewater on tubular membrane Unable to detect the individual bacterial cell interactions [63] 

The idea of PIV is to find the most likely location of a small area from an image at time t in a later image at time t + At. This location will be an approximation of the displacement Ax for the center of the small area. In the LSQ framework, the ideal particle becomes a small patch from the frame at t and the image becomes the frame at f + At. A simple adaptation of (2.22) gives 

At) is the average squared difference between the image at time t + At and a small rectangular patch of size /xfe centered at xq at time t, shifted by Axq. Then, for each position xq of interest the displacement Ax or velocity Ax/At can be determined by finding the minimum of x over Axq 

The parameters I and h should be chosen such that they are small enough that the velocity is approximately constant over the region, but large enough that there are distinct features in the region. 

To assist in achieving a linear relationship between phase and diameter. Table 4-4 lists some typical scenarios and optical configurations that work best. 

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For most existing measuring methods, the actual motion of individual nano-particles in two-phase flow cannot be observed easily. Conventional particle image velocimetry (PIV) apparatus can measure the particles in micro scale... 

Kim, M. J., Beskok, A., and Kihm, K. D., "Electro-Osmosis-Driven Micro Channel Flows A Comparative Study of Microscopic Particle Image Velocimetry Measurements and Numerical Simulations, Exp. Fluids, Vol. 33, No. 1, 2002, pp. 170-180. 

On comparing the two flames, it is evident that the flow structure of the lean limit methane flame fundamentally differs from that of the limit propane one. In the flame coordinate system, the velocity field shows a stagnation zone in the central region of the methane flame bubble, just behind the flame front. In this region, the combustion products move upward with the flame and are not replaced by the new ones produced in the reaction zone. For methane, at the lean limit an accumulation of particle image velocimetry (PIV) seeding particles can be seen within the stagnation core, in... 

Hirasawa, T., Sung, C.J., Yang, Z., Joshi, A., Wang, H., and Law, C.K., Determination of laminar flame speeds of fuel blends using digital particle image velocimetry Ethylene, M-butane, and toluene flames, Proc. Combust. Inst., 29,1427, 2002. 

Figure 7.2.5 provides a visualization of a localized extinction event in a turbulent jet flame, using a temporal sequence of OH planar LIF measurements. The OH-LIF measurements, combined with particle image velocimetry (PIV) reveal that a distinct vortex within the turbulent flow distorts and consequently breaks the OH front. These localized extinction events occur intermittently as the strength of the coupling between the turbulent flow and the flame chemistry fluctuates. The characteristics of the turbulent flame can be significantly altered as the frequency of these events increases. 

Fajardo, C.M. and V. Sick, Flow field assessment in a fired spray-guided spark-ignition direct-injection engine based on UV particle image velocimetry with sub crank angle resolution. Proceedings of the Combustion Institute, 31(2) 3023-3031, 2007. 

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. 

Virdung, T. and Rasmuson, A. (2008) Solid-liquid flow at dilute concentrations in an axially stirred vessel investigated using particle image velocimetry. Chem. Eng. Commun., 195 (1), 18-34. 

Note that when solving the CFD transport equations, the mean velocity and turbulence state variables can be found independently from the mixture-fraction state variables. Likewise, when validating the CFD model predictions, the velocity and turbulence predictions can be measured in separate experiments (e.g., using particle-image velocimetry [PIV]) from the scalar field (e.g., using planar laser-induced fluorescence [PLIF]). 

Post, M. E., and L. P. Goss. 1993. Two-color particle-imaging velocimetry in vortex structures. 31st Aerospace Sciences Meeting Proceedings. AIAA Paper No. 93-0412. 

Other measurements of Hanratty s p have been made or inferred from various techniques, including a hot film probe just under the water surface (Brumley and Jirka, 1987), particle image velocimetry in a vertical laser sheet leading up to the water surface with a florescent dye to indicate water surface location accurately (Law and Khoo, 2002) and PIV on the water surface (McKenna and McGillis, 2004 Orlins and Gulliver, 2002). The measurements of Law and Khoo (2002) are especially interesting because the following relationship was developed from experiments on both a jet-stirred tank and a wind-wave channel ... 

M. Raffel, C.E. Wilier, J. Kompenhans, Particle Image Velocimetry A Practical... 

Feng-Chen Li and Koichi Hishida, Particle Image Velocimetry Techniques and Its Applications in Multiphase Systems... 

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