Laser-based Particle Image Velocimetry Research Articles

CFD and PIV Investigation of a Liquid Flow Maldistribution across a Tube Bundle in the Shell-and-Tube Heat Exchanger with Segmental Baffles

The paper presents the results of research on liquid flow maldistribution in the shell side of a shell-and-tube heat exchanger (STHE). This phenomenon constitutes the reason for the formation of the velocity reduction area and adversely affects heat transfer and pressure drop. In order to provide details of the liquid distribution in STHE, two visualization methods were utilized. First, computational fluid dynamics (CFD) code coupled with the k-ε model and the laser-based particle image velocimetry (PIV) technique was applied. The tests were carried out for a bundle comprising 37 tubes in an in-line layout with a pitch dz/t = 1.5, placed in a shell with Din = 0.1 m. The STHE liquid feed rates corresponded to Reynolds numbers Rein equal to 16,662, 24,993, and 33,324. The analysis demonstrated that the flow maldistribution in the investigated geometry originates the result of three main streams in the cross-section of the shell side: central stream, oblique stream, and bypass stream. For central and oblique streams, the largest velocity reduction areas were formed in the wake of the tubes. On the basis of the flow visualization, it was also shown that the in-line layout of the tube bundle helps to boost the wake region between successive tubes in a row. Additionally, unfavorable vortex phenomena between the last row of tubes and the lower part of the exchanger shell were identified in the investigations. The conducted studies confirmed the feasibility of both methods in the identification and assessment of fluid flow irregularities in STHE. The maximum error of the CFD method in comparison to the experimental methods did not exceed 7% in terms of the pressure drops and 11% in the range of the maximum velocities.

Simultaneous measurement of velocity and temperature fields during natural convection in a water-filled cubical cavity

Many advanced schlieren systems have been reported in the literatures and a great number of it are associated in gas flow study, commonly air. Present research proposes an efficient use of Z-type schlieren technique for simultaneous measurement of ray-averaged velocity as well as temperature fields beside qualitative flow visualization. Experiments are conducted to study natural convective flow in de-ionized water in a differentially heated cubical enclosure. The same set of transient schlieren images has been used for simultaneous measurement of velocity and temperature field. The velocity field is also determined by using laser based particle image velocimetry (PIV) to compare with schlieren based technique. The developed schlieren system has been used to obtain ray-averaged quantities, such as, thermal and hydrodynamic boundary layer thicknesses, temperature gradient and temperature fields, distribution of local Nusselt number along the thermally active walls, average Nusselt number and velocity field. In this work, the above quantities have been simultaneously determined for the first time using halogen projector lamp based Z-type calibration schlieren system. The results inspire the use of calibration schlieren system for the study of natural convective flow in water-filled cubical enclosures. The above results also provide experimental data as new benchmark for researchers to compare results for high Rayleigh number free convective flow with water as the working medium.

Hemodynamic forces in the left and right ventricles of the human heart using 4D flow magnetic resonance imaging: Phantom validation, reproducibility, sensitivity to respiratory gating and free analysis software.

PurposeTo investigate the accuracy, reproducibility and sensitivity to respiratory gating, field strength and ventricle segmentation of hemodynamic force quantification in the left and right ventricles of the heart (LV and RV) using 4D-flow magnetic resonance imaging (MRI), and to provide free hemodynamic force analysis software.Materials and methodsA pulsatile flow phantom was imaged using 4D flow MRI and laser-based particle image velocimetry (PIV). Cardiac 4D flow MRI was performed in healthy volunteers at 1.5T (n = 23). Reproducibility was investigated using MR scanners from two different vendors on the same day (n = 8). Subsets of volunteers were also imaged without respiratory gating (n = 17), at 3T on the same day (n = 6), and 1–12 days later on the same scanner (n = 9, median 6 days). Agreement was measured using the intraclass correlation coefficient (ICC).ResultsPhantom validation showed good accuracy for both scanners (Scanner 1: bias -14±9%, y = 0.82x+0.08, R2 = 0.96, Scanner 2: bias -12±8%, y = 0.99x-0.08, R2 = 1.00). Force reproducibility was strong in the LV (0.09±0.07 vs 0.09±0.07 N, bias 0.00±0.04 N, ICC = 0.87) and RV (0.09±0.06 vs 0.09±0.05 N, bias 0.00±0.03, ICC = 0.83). Strong to very strong agreement was found for scans with and without respiratory gating (LV/RV: ICC = 0.94/0.95), scans on different days (ICC = 0.92/0.87), and 1.5T and 3T scans (ICC = 0.93/0.94).ConclusionSoftware for quantification of hemodynamic forces in 4D-flow MRI was developed, and results show high accuracy and strong to very strong reproducibility for both the LV and RV, supporting its use for research and clinical investigations. The software including source code is released freely for research.

Characterization of interactions between hot air plumes and water sprays for sprinkler protection

One important aspect of the complex sprinkler protection process is the interaction between the water spray and the fire plume. In order to provide suitable data for the development and validation of a LES-based fire protection models, such as FireFOAM, a series of small-scale experiments were conducted to examine the interaction of hot air plumes and water sprays through combined gas–liquid velocity and droplet size measurements. Laser-based particle image velocimetry (PIV) was used to acquire the spatially-resolved velocity data; and a shadow imaging system (SIS) was used to measure the water droplet size and volume flux. Hot air plumes with three convective heat release rates (1.6, 2.1 and 2.6kW) were selected to interact with a water spray at a discharge rate of 0.084Lpm. The velocity field of the hot air plume and ceiling flow with/without water spray, the droplet size and volume flux of water spray with/without hot air plume were measured. The interaction between the hot air plume and water spray was characterized by the location of the interaction boundary with the momentum ratio of the hot air to that of the spray. The results showed that that the momentum ratio and the evaporation effect due to hot air on the water droplets played a significant role to change the interaction structure and the ceiling layer pattern.

Non-unique convection in a three-dimensional slot-vented cavity with opposed jets

This study aims to investigate multiple flow structures in a three-dimensional chamber with opposed jets. Numerical computations focus on the effect of inlet velocity on the air flow pattern, especially on multiple steady flow characteristics for Reynolds maintaining 10 5 . Three distinct branches of steady-state flows are found for this configuration. A complete study of stability of each branch is performed for varying velocity of the left inlet continuously between 0 and 3. The results are presented by stability diagrams showing the critical parameters corresponding to transition from one steady-state branch to the other state within multiple flow range. In parallel with numerical development, an experimental system was set up where adjustable flow rate was prescribed to produce variation of supplying jets. The corresponding vector flow fields, on a scale model, were measured by a laser-based particle image velocimetry (PIV) system. The multiple flow structures were validated both by numerical simulation and experimental investigation.

On the characteristics of a twin-jet STOVL fountain

AbstractThe interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry and laser Doppler velocimetry. Measurements were made with nozzle pressure ratios of between 1·05 and 4, nozzle height-to-diameter ratios of between 2·4 and 8·4, nozzle splay angles of between ±15 degrees and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate and momentum flux ratio are discussed. Mean fountain upwash velocity profiles were found to be self-similar for all test conditions. A distinct frequency of fountain oscillation was identified but only at a nozzle height of 4·4 diameters.

Flow Measurements in a Short Takeoff, Vertical Landing Fountain: Parallel Jets

DOI: 10.2514/1.38296 The interaction of multiple jets with the ground is of great importance for the design and operation of short takeoff, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry. Measurements were made with nozzle pressure ratios of between 1.05 and 4, nozzle height-to-diameter ratios of between 2.4 and 8.4, nozzle splay angles of between 15 deg, and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate, and momentum flux ratio are discussed. In general, it was found that the inclusion of nozzle splay did not significantly alter the distribution of fountain momentum flux ratio relative to the equivalent parallel configuration.

Behaviour of flow at the junction of cylinder and base plate in deep water

The present study aims at looking into the nature of the horseshoe vortex system and its interaction with the wake-flow region in the base of circular cylinder mounted on a base plate in deep water. These kinds of flows have been attracting considerable attention due to its importance in engineering applications. Flow fields in plan and side-view planes were visualized using a laser based particle image velocimetry to examine the flow structure quantitatively for the range of Reynolds number 1500⩽Red⩽9600. The analysis of the cinema of instantaneous flow data, time-averaged velocity vectors map, streamlines, vorticity patterns, Reynolds stress correlations and fluctuations of the velocity components clearly demonstrate that the flow structure occurred in the base of the cylinder is three dimensional. The area of flow field occupied and affected by the horseshoe vortex system around the cylinder varies as a function of Reynolds number. This horseshoe vortex system emanating from the upstream of the cylinder swirls while travelling in the main flow direction. Counter-clockwise rotating vortices take place downstream of the cylinder in vertical plan-view plane. These swirling and rotating vortices in the junction region of the plate and cylinder cause scour mechanisms. Horseshoe vortices magnify the entrainment process and circulatory motions between the main and wake-flow regions downstream of the cylinder which stimulate the scour mechanisms.

Experimental investigation on inner two-phase flow in counter-flow spray saturator for HAT cycle

An experiment investigation of inner two-phase flow in the counter-flow spray saturator (CFSS) for humid air turbine (HAT) cycle and the simulation of the moving distance of water droplets in counter-flow air are presented here aimed at the understand of two-phase flow in the CFSS in detailed. Dual phase Doppler anemometry (DualPDA) system is applied to obtain the spatial change of the droplet size spectrum in the flow-field to correlate droplet size–velocity correlation. The local measurement profiles of 3D mean velocities and diameters of water droplets are obtained by averaging droplet size classes. Moreover, DualPDA signal processing allows for accurate determination of the volume flux of spherical water droplets. The transient velocity fields are measured by a laser-based particle image velocimetry (PIV) system. The commercial CFD software, FLUENT, is used to simulate the maximum moving distance of water droplets with different diameters and inlet velocities in the counter-flow air with different inlet velocities, then the quantity of water droplet entrainment in the saturator can be estimated.

Factorial Modeling for Transient Solid Particle Velocity in a Fluidized Bed Combustor Cold Model

ABSTRACT Transient hydrodynamics phenomena in the fluidized bed combustor (FBC) freeboard have been critical in the past two decades. Within a 152 mm ID FBC cold model, solid particle transient velocities were measured and analyzed with the assistance of advanced laser-based particle image velocimetry (PIV) instrumentation. Two layers of swirling secondary air were injected into the cold model. The PIV system was applied to the FBC cold model to visualize transient solid particle velocity. A series of transient solid particle velocity profiles were generated for the factorial analysis. In each profile, the solid particle velocity vectors (Vx and Vy) for 10 × 10 grids were generated. Analysis of variance (ANOVA) was used to determine the significant factors that affect transient solid particle velocities, time, and position coordinates. Then, the 1010 factorial design method was used to develop a specific empirical model of transient solid particle velocity in the FBC freeboard, which was in the shape of Vx = f1(t, x, y) and Vy = f2(t, x, y). This unique factorial analysis method proved to be a very effective and practical method to evaluate experimental conditions and analyze experimental results in the FBC systems.

Convection in modulated thermal gradients and gravity: experimental measurements and numerical simulations

This paper presents an investigation on natural convection in a cavity with imposed modulated thermal gradients or modulated gravity forces. Numerical computations are presented, which are based on the finite element solution of the transient Navier–Stokes and energy balance equations, along with appropriate thermal boundary conditions or time-varying gravity forces. In parallel with numerical development, an experimental system is setup where oscillating wall temperatures are prescribed to produce modulated temperature gradients and the velocity fields are measured by a laser-based particle image velocimetry (PIV) system. Computed results compare well with experimental measurements for various conditions. With the mathematical model, so verified by experimental measurements, numerical simulations are carried out to study the effects of modulation frequency and Prandtl number on the fluid flow. Results show strong non-linear interaction in a fluid with a relative high Prandtl number within the intermediate range of modulated frequency. It is also found that for a fluid with a small Prandtl number typical of molten metals and semiconductor melts, modulated gravity and thermal gradients produce almost the same flow field both in structure and in magnitude.

Regression Analysis on Vertical Components of the Transient Solid Particle Velocity in a Fluidized Bed Combustor (FBC)

The transient solid particle velocity analysis in a fluidized bed combustor (FBC) freeboard is critical for its efficient and reliable operation. An experimental cold model (152 mm ID 2 610 mm height) of an FBC was designed and fabricated. Transient solid particle velocities in the FBC freeboard model were measured and analyzed with the assistance of an advanced laser-based particle image velocimetry (PIV) instrumentation. The PIV was applied to the FBC cold model to visualize the transient solid particle movement in the area of interest (AOI). Sixteen particle velocity profiles were generated in a 1.6 s time period. In each profile, a 3 (columns) 2 1 (row) grid was set. The regression analysis with the independent variables of X (x coordinate) and t (time) were applied to develop a specific empirical model for a transient solid particle vertical velocity component (V y ) within the AOI. The model shows that the V y within the AOI could be expressed as V y =f{sin C 1 X, cos C 2 t, e m C3t }, where C 1 , C 2 , and C 3 are constants.This unique regression analysis method was proven to be very effective and practical for evaluating the experimental conditions and analyzing experimental results in FBC systems.