Particle Image Velocimetry PIV Technique

The PIV method is a fairly new technique, capable of simultaneous velocity measurements at many points in a plane. This gives information on large scale structures, vorticity, etc. which is very difficult or impossible to obtain from one-point measuring techniques. 

The traditional non-intrusive laser based measurement techniques like LDV and flow visualization, did provide either a point measurement or a qualitative indication [38]. The conventional techniques could not provide quantitative and instantaneous flow information for a whole flow plane. The ability to quantify transient multiphase flow phenomena is crucial to the understanding of the flow mechanism and development of fundamental theories. These limitations of the conventional measuring techniques were overcome by the PIV technique which combines the accuracy of LDV with the qualitative information from the flow visualization and is a quantitative technique for measuring the instantaneous flow field for a plane. 

---

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. 

In order to determine the critical velocity difference for the initiation of KHI, it is necessary to measure the velocities of salt water flow and silicone oil flow near the silicone oil/salt water interface. A particle imaging velocimetry (PIV) technique is described as it is considered the most adequate for this purpose. 

The improvement in accuracy achieved by the complex closures compared to the simpler ones can also be questionable. Osenbroch ]67] and Mortensen ]60] successfully applied the combined particle image velocimetry (PIV)/planar laser induced fluorescence (PLIF) technique to measure the instantaneous velocity and reacting species concentration in mixing devices like a mixing channel, pipe, and multi-functional channel reactor. The measured... 

The conventional approaches to anemometry are laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) [6,37,38]. The former is employed to obtain point-like measurements of one velocity component, whereas a combination of two or three LDV systems allows for the measurement of the vectorial structure of the velocities. The PIV is, instead, conceived for two-dimensional acquisition of velocity fields. One important industrial application of these techniques is in laser diagnostic of gas turbines and engines [9]. For instance, atomization of liquid fuels into droplets is typical of modern IC engines and one can study the fuel-air mixing that is an essential factor in efficient combustion. In... 

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. 

Optical techniques, i.e., laser Doppler velocimetry O DV), particle image velocimetry (PIV), and holographic PIV, have matured as successful nonintrusive velocity measurement techniques for large-scale applications. Panigrahi et al. [2] obtained the shear stress from PIV measurements by assuming the validity of law of the wall for turbulent flow. In recent years, the p-PIV has matured as a successful velocity measurement technique for MEMS applications [3]. 

To determine the displacement distributions on the surface of the limestone specimens, digital pictures of the specimen were taken to perform an image analysis technique, called Particle Image Velocimetry (PIV). 

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. 

Laser Doppler Velocimetry (LDV) (Joshi et al. 2001) and PDA (Schafer et al. 2000) are optical techniques that have been used to determine BSDs, gas hold-up and flow patterns. Detectors observe the Doppler shift and phase difference when bubbles pass through the volume of the intersection of two laser beams. Doppler effect is related to the velocities of bubbles and the phase difference is related to the sizes of bubbles. Particle Image Velocimetry (PIV)... 

By confining the fluidized bed in one direction and using a translucent waU, visual access is restored so that the bed behavior can be studied fuUy and non-intrusively using optical techniques, such as particle image velocimetry (PIV) or digital image analysis (DIA), which are discussed in detail below. With these techniques, it is possible to obtain information on the instantaneous flow fields, but it remains difficult to translate the 2D results quantitatively to 3D. As a learning tool that allows to see and verify different aspects of the bed behavior (e.g., bubble size distribution, instantaneous particle fluxes) however, such techniques are unrivaled. The main focus of this chapter therefore lies on these optical techniques. 

---