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 development and modification of any computer code necessitate assessment and validation of the code. A similar task prevails with the release of the thermal-hydraulic analysis code RELAP5/MOD3. RELAP5/MOD3 has been developed by EG and G Idaho, from its predecessor code RELAP5/MOD2, after identifying certain deficiencies in the latter. The work presented here assesses the RELAP5/MOD3 computer code. The objective of this study is to evaluate the predictions of the RELAP5/MOD2 and RELAP5/MOD3 computer codes, using a model of a full-length, 30-tube once-through steam generator (OTSG). The RELAP5/MOD3 results for the test facility generally show a reasonable agreement with the data for the primary-side temperature profiles. However, the secondary temperature profile predicted by RELAP5/MOD3, at 65% load, compares fairly well with data and is better than the RELAP5/MOD2 results.

Simulation of a 30-tube once-through steam generator with RELAP5/MOD3 and RELAP5/MOD2 computer codes

Because of the complex nature of coolant flow in nuclear reactors, current subchannel methods for light water reactor analysis are insufficient. The large eddy simulation method has been proposed a...

A Perspective on Large eddy Simulation of Problems in the Nuclear Industry

The complex behavior of thermal fluids in nuclear reactors require the usage of computational fluid dynamics (CFD) codes for design and analysis. In order to use CFD codes, they require regular benchmark problems to ensure the predictions are reasonable representations of reality. The twin jet water facility (TJWF) designed and built at the University of Tennessee, Knoxville was created for this purpose. The facility features twin planar-like turbulent free shear jets injecting fluid into a transparent tank to study a variety of flow behavior. The experimental work using this facility by Texas A&M University was used for the benchmarking activities. This work was conducted using a steady Reynolds-averaged Navier–Stokes formulation to simulate the flow behavior. It was determined that the standard k–ε and elliptic blending Reynolds stress model (EBRSM) turbulence models can be used to simulate the twin jet behavior with reasonable success for design and analysis activities.

/pdf/simulations-of-twin-turbulent-planar-like-jets-injected-into-18gb9cqtsg.pdf

Simulations of Twin Turbulent Planar-Like Jets Injected into a Large Volume using RANS

Complex geometries and randomly connected void spaces within packed beds have hindered efforts to characterize the underlying transport phenomena occurring within. In this communication, we present our experimental studies on a facility of randomly packed spheres that can be a representative of sections within a reactor core in a nuclear power plant. The results of high-fidelity velocity measurements can be seen using Time-Resolved Particle Image Velocimetry (TR-PIV) at the pore scales and near the wall boundary in the Matched Index of Refraction (MIR) facility. The MIR approach allows for a non-invasive analysis of the flow within packed spheres at the microscopic scales with high temporal and spatial resolution. Flow characteristics obtained from the TR-PIV measurements at various Reynolds numbers are presented. The results include the first- and second-order flow statistics, such as mean velocity, root-mean-square fluctuating velocity and Reynolds stresses. Effects of the wall boundary and Reynolds numbers on flow patterns are currently being investigated. Comparisons of the mean velocities, root-mean-square fluctuating velocities, and Reynolds stress components show the increase of flow mixing and turbulent intensities within the gaps between spheres in the packed bed. Sizes of recirculation regions, however, seem to be independent of the increase of Reynolds numbers.Copyright © 2018 by ASME

Yassin A. Hassan

Papers

Simulation of a 30-tube once-through steam generator with RELAP5/MOD3 and RELAP5/MOD2 computer codes

A Perspective on Large eddy Simulation of Problems in the Nuclear Industry

Simulations of Twin Turbulent Planar-Like Jets Injected into a Large Volume using RANS

Time-Resolved Velocity Measurements in a Matched Refractive Index Facility of Randomly Packed Spheres

COMMIX predictions of a thermal mixing test