An introduction to heat transfer

The development of the method of particle image velocimetry (PIV) is traced by describing some of the milestones that have enabled new and/or better measurements to be made. The current status of PIV is summarized, and some goals for future advances are addressed.

Twenty years of particle image velocimetry

The size specifications for suitable tracer particles for particle image velocimetry (PIV), particularly with respect to their flow tracking capability, are discussed and quantified for several examples. A review of a wide variety of tracer materials used in recent PIV experiments in liquids and gases indicates that appropriately sized particles have normally been used. With emphasis on gas flows, methods of generating seeding particles and for introducing the particles into the flow are described and their advantages are discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/8/12/005/pdf

Tracer particles and seeding for particle image velocimetry

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Very large-scale motions in the form of long regions of streamwise velocity fluctuation are observed in the outer layer of fully developed turbulent pipe flow over a range of Reynolds numbers. The premultiplied, one-dimensional spectrum of the streamwise velocity measured by hot-film anemometry has a bimodal distribution whose components are associated with large-scale motion and a range of smaller scales corresponding to the main turbulent motion. The characteristic wavelength of the large-scale mode increases through the logarithmic layer, and reaches a maximum value that is approximately 12–14 times the pipe radius, one order of magnitude longer than the largest reported integral length scale, and more than four to five times longer than the length of a turbulent bulge. The wavelength decreases to approximately two pipe radii at the pipe centerline. It is conjectured that the very large-scale motions result from the coherent alignment of large-scale motions in the form of turbulent bulges or packets of...

Very large-scale motion in the outer layer

To the special issue on the 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14)

Particle image velocimetry (PIV) is a nonintrusive measurement technique that can be used to study the structure of various fluid flows. PIV is used to measure the time-varying, full-field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. The quantitative spatial velocity information can be further processed into information of flow parameters such as vorticity and turbulence over extended areas. The objective of this study was to apply recent advances and improvements in the PIV flow measurement technique to the full-field, nonintrusive analysis of a three-dimensional, two-phase fluid flow system in such a manner that both components of the two-phase system could be experimentally quantified.

Three-dimensional investigation of the two-phase flow structure in a bubbly pipe flow

Rod bundles are widely used in industry today with applications ranging from nuclear reactors, heat exchangers, and steam generators. Accurately modeling the inherently unsteady and turbulent flow within these rods is essential in order to design for optimal efficiency while controlling vibration, noise and heat transfer. The problem complicates further when spacer-grids are used within the rods to maintain separation and structural rigidity. Computational modeling can be a useful alternative to the costly process of manufacturing and testing prototypes, but its accuracy needs to be checked with detailed experimental data. This paper describes an experimental database obtained using two-dimensional Time Resolved Particle Image Velocimetry (TR-PIV) measurements within a 5 × 5 rod bundle with spacer-grids. One of the unique characteristic of this set-up is the use of the Matched Index of Refraction technique employed in this investigation which consists of immersing plastic rods with a similar index of refraction as the one for water to achieve optical transparency across the spacer grid. This unique feature allows flow visualization and measurement within the bundle without rod obstruction. This approach also allows the use of high temporal and spatial non-intrusive dynamic measurement techniques namely TR-PIV to investigate the flow evolution below and immediately above the spacer. The data base presented includes explanation of the various cases tested such as boundary conditions, rig dimensions, measurement zones, and the test equipment in order to provide a good base for Computational Fluid Dynamics (CFD) simulations. Turbulence analysis of the obtained data is provided in order to gain insight of the physical phenomena and to compare the possible results obtained from computational simulations.Copyright © 2010 by ASME

Yassin A. Hassan

Papers

To the special issue on the 14th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-14)

Three-dimensional investigation of the two-phase flow structure in a bubbly pipe flow

Experimental Turbulence Analysis of Fuel Bundle With Spacer Grids

Measurement of two-phase interfacial drag in stratified flow with pulsed laser velocimetry

Experimental Study of Flowfield and Pressure Fluctuation of a Supersonic Impinging Jet