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

The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in the whole volume (global) of interest. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various three-dimensional, bubbly two-phase flow situations. This information is useful for developing or improving existing computer constitutive models that simulate this type of flow field. It is also useful for understanding the detailed structure of two-phase flows.

Three-dimensional Bubbly Flow Measurement Using PIV

Technical session summaries

Permeability and compression of fibrous porous media generated from dilute suspensions of fiberglass debris during a loss of coolant accident

Applying tet-to-hex meshing method to complex nuclear reactor geometries for spectral element code

Bubble dynamics of pool boiling of nanofluids has been experimentally investigated. The boiling surface was prepared with an average surface roughness of 120 nm. Alumina Oxidewater based nanofluids at a constant concentration of 0.05 wt. % have been used in this investigation. The bubble growth rate, bubble departure diameter and departure frequency have been observed using high speed imaging during pool boiling of pure water and nanofluids at a wall superheat of 104.4 oC. Number of nucleation sites was activated in the case of nanofluid against one site for pure water. The bubble diameter observed in the case of nanofluids was about 60 % smaller than that observed for pure water. Nanofluid’s bubble departure frequency reached 500 Hz while the bubble frequency observed in the case of pure water was about 23 Hz. In addition, the bubble growth rate showed dependence on the type of working fluid used.

Yassin A. Hassan

Papers

Three-dimensional Bubbly Flow Measurement Using PIV

Technical session summaries

Permeability and compression of fibrous porous media generated from dilute suspensions of fiberglass debris during a loss of coolant accident

Applying tet-to-hex meshing method to complex nuclear reactor geometries for spectral element code

Bubble dynamics of pool boiling with nanofluids