Hydro-dynamically modified seeding for micro-PIV

Fluid flow distribution among parallel channels usually plays an important role on the global performance improvement of tubular process equipment, but remains difficult to be properly measured by experimental methods. This paper presents a systematic study on the measurement of flow distribution in a multi‐channel fluidic network using Particle Image Velocimetry (PIV) technique. For the precise measurement of flow‐rate in each individual channel, standard 2 dimensions, 2 components PIV technique is used to obtain velocity vectors on multiple sampling planes parallel to the flow direction, so as to reconstruct accurate velocity profiles on the cross‐sectional surface. Such procedure is repeated for every micro‐ (mini‐) channel to obtain the actual flow distribution properties in the fluidic network.Pre‐test results on a double‐channel device indicate that the maximum possible deviation of PIV measurements is 13.1% with respect to those of a flange flowmeter, implying that the PIV technique is relatively accurate and reliable. PIV results on the flow distribution in a 15‐channel fluidic network are then compared with Computational Fluid Dynamics simulation results under the same working conditions. A quite good agreement could be observed. Moreover, the locations and sizes of vortices in the distributor have a significant influence on the flow distribution. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Throughout their useful life structures demand monitoring to verify their conditions of use. Thus, the need arises to seek methodologies capable to evaluate displacements and deformations in structural components of buildings. The objective of this research was to evaluate the use of the particle image velocimetry (PIV) technique to analyze test specimen behavior during a static bending test, additionally a displacement map is presented. The PIV technique measures variations of position of a region in an object from consecutive images from a loading session. The tests were performed on wood of Pinus oocarpa and Eucalyptus grandis, plywood panels, laminated veneer lumber (LVL) and oriented strand board (OSB). The results obtained by the PIV technique were compared to values obtained from dial indicators. It was verified that in all the materials tested, the PIV technique presented results similar to those found in the dial indicators. By means of the Student t test, with a significance level of 1%, some regions of analysis the values found by the PIV technique and the dial indicators were statistically similar. For the analyzed regions that did not achieve statistical equality, a correction equation was calculated (R² higher than 0.99). It was concluded that the PIV technique, with properly adjusted setup, presented results similar to those obtained in the conventional tests, proving its accuracy and reliability in displacement measurements, with the advantage of being a non-destructive and contactless structure monitoring technique.

Experimental study on multiphase flow in fracture-vug medium using 3D printing technology and visualization techniques

The effect of drag reducing additive on the structure of turbulence in concentric annular pipe flow was investigated using Particle Image Velocimetry (PIV) technique. Experiments were conducted using a 9m long horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The drag reducing additive was a commercially available partially hydrolyzed polyacrylamide (PHPA). The experiments were conducted using 0.1% V/V polymer concentration, giving a drag reduction of 26% at a solvent Reynolds number equal to 56400. Near wall local fluctuating velocity values were determined by analysing the PIV data. The root mean square (RMS) values of radial velocity fluctuations showed a significant decrease with the use of drag reducing additive. The RMS values of axial velocity fluctuations near the wall (Y+<10) were similar for both water and polymer fluid flow; though, higher peaks were obtained during the polymer fluid flow. As compared to water flow, a strong reduction in vorticity was observed during polymer fluid flow. The degree of vorticity reduction on the inner wall was higher than that of the outer wall. Results of the viscous dissipation and the shear production terms in the kinetic energy budget showed that less energy was produced and dissipated by the route of turbulence when using polymer fluid.

The fluid flow field within an enclosed cylindrical chamber with a rotating flat disc was calculated using a finite volume computational fluid dynamics (CFD) model and compared with particle image velocimetry (PIV) measurements. Two particular laminar cases near the Transitional flow regime were investigated : Reynolds number Re = 2.5 x 10 4 , chamber aspect ratio G (h/R d ) = 0.2 and Re = 4.2 x 10 4 , G (h/R d ) = 0.217. This enabled direct comparison with the numerical and experimental results reported by other researchers. The computational details and some major factors that affect the computed accuracy and convergence speed are also discussed in detail. PIV results containing some 4300 velocity vector points in each of seven planes for each case were obtained from the flow field parallel to the rotating disc. It was found that PIV results could be obtained in planes within the boundary layers as well as the core flow by careful use of a thin laser illumination sheet and correct choice of laser pulse separation. There was close agreement between numerical results, the present PIV measurements and other reported experimental and numerical results.

For this study, a scaled model test is conducted to investigate the deflection of a laterally loaded pile and soil deformation in loose sand. An optical experimental setup is developed to capture images of soil movement and the readings of strain gauges along the pile. The deflection of the pile, derived from readings of the strain gauges, increases with the increasing lateral loads. Additionally, the displacement fields of ground surface and profile from a series of images are calculated using the particle image velocimetry (PIV) technique. This technique provides a more accurate estimate of the pile deflection compared with the double integration (DI) method. The images illustrate that the sand rotated in a position approximately 160 mm deep, which is identical to the results of the DI method. Finite-element analysis is used to simulate the model test, which verifies the accuracy of the PIV technique. The results demonstrate that the PIV technique and this optical setup are suitable for solving ...

Ensemble correlation PIV applied to bubble plumes rising in a bubble column

Thermocapillarity is a physical phenomenon used in many industrial processes, mainly in the field of miniaturization. Thermocapillary forces are the base of thermocapillary pumping (TCP), in which a drop of liquid moves through a microchannel or flat surface after temperature gradient occurs. The objective of this work was to study the thermocapillary convection during pumping without inserting external particles, monitored by the Particle Image Velocimetry (PIV) technique. The experiment consisted of a Pasteur tube containing a yellow fluorescein solution (0.02, 0.04, 0.06, 0.08, and 0.1 Molar), illuminated by a laser beam of 545 nm, 40 mW. After 2 minutes of illumination, the thermocapillary movement occurred at a distance of 0.05 mm below the meniscus when using a laser beam of 545 nm, 3 mW. The images were captured by a charge-coupled device (CCD) camera and processed using the PIV technique. The results showed an internal conversion capacity between the intersystem crossing, vibrational, and relaxation phenomena, also demonstrating the potential for applying the proposed approach. The images presented velocity distribution caused by thermocapillarity. The PIV was a useful tool for convective flow analysis if connected to appropriate image processing and enhancement techniques. In conclusion, the research showed the images with velocity distribution caused by thermocapillarity.

Vacuum preloading combined with prefabricated vertical drains is a widely used system for improving soft clay-dredged slurry deposits. However, the influence of the initial water content on clogging is not yet fully understood. In this study, laboratory model tests were conducted on slurry with initial water contents of 106%, 133%, and 159% during vacuum preloading. The process of vacuum preloading was monitored from the perspectives of discharged water volume, pore water pressure, as well as the displacement and strain profile of soil patches by using the novel particle image velocimetry (PIV) technique. The results showed that the clogging formation process could be divided into three stages based on the water discharge rate: rapid formation, transition, and slow formation. An increase in initial water content resulted in a larger horizontal displacement, leading to a thinner and denser clogging zone with lower permeability coefficients and a reduced rate of pore pressure dissipation. Empirical equations for the thickness of the clogging zone versus time were proposed using the PIV technique, providing a reference for theoretical consolidation calculations and making the calculations more practical by considering the variation of the clogging zone during vacuum preloading.

Effect of corrugated channel phase shifts on flow structures and heat transfer rate

Existing literature of previous particle image velocimetry (PIV) studies of fish swimming has been reviewed. Historically, most of the studies focused on the performance evaluation of freely swimming fish. Technological advances over the last decade, especially the development of digital particle image velocimetry (DPIV) technique, make possible more accurate, quantitative descriptions of the flow patterns adjacent to the fish and in the wake behind the fins and tail, which are imperative to decode the mechanisms of drag reduction and propulsive efficiency. For flows generated by different organisms, the related scales and flow regimes vary significantly. For small Reynolds numbers, viscosity dominates; for very high Reynolds numbers, inertia dominates, and three-dimensional complexity occurs. The majority of previous investigations dealt with the lower end of Reynolds number range. The fish of our interest, such as rainbow trout and spring and fall chinook salmon, fall into the middle range, in which neither viscosity nor inertia is negligible, and three-dimensionality has yet to dominate. Feasibility tests have proven the applicability of PIV to flows around fish. These tests have shown unsteady vortex shedding in the wake, high vorticity region and high stress region, with the highest in the pectoral area. This evident supports the observations by Nietzel et al. (2000) and Deng et al. (2004) that the operculum are most vulnerable to damage from the turbulent shear flow, because they are easily pried open, and the large vorticity and shear stress can lift and tear off scales, rupture or dislodge eyes, and damage gills. In addition, the unsteady behavior of the vortex shedding in the wake implies that injury to fish by the instantaneous flow structures would likely be much higher than the injury level estimated using the average values of the dynamics parameters. Based on existing literature, our technological capability, and relevance and practicability to Department of Energy's Hydropower Program, we identified three major research areas of interest: free swimming, the boundary layer over fish, and kinematic response of fish. We propose that the highest priority is to characterize the kinematic response of fish to different turbulent environments such as high shear/turbulence and hydrodynamic disturbances created by solid structures such as deflector and turbine runner blade; the next priority is to map the boundary layer over swimming fish; the last is to document the behavior of freely swimming fish, focusing on fish of our interest. Grid turbulence and Karman vortex street will be employed to map the boundary layers over fish and investigate the effects of environmental disturbances on the swimming performance of fish, because they are well established and documented in engineering literature and are representative of fish's swimming environments. Extreme conditions characteristic of turbine environments, such as strong shear environment and collision, will be investigated. Through controlled laboratory studies, the fish injury mechanism from different sources will be evaluated in isolation. The major goals are to: gain first-hand knowledge of the biological effects under such extreme hydraulic environments in which fish could lack the capability to overcome the perturbations and be vulnerable to injury; Better understand field results by integrating the laboratory studies with the responses of sensor fish device; More importantly, provide well-defined validation cases and boundary conditions for geometry-based computational fluid-structure interaction modeling in order to simulate the complex hydraulic environments in advanced hydropower systems and their effects on fish, greatly enhancing the potential to use CFD as a bio-hydraulic design alternative.

The Application of Microfluidics in Preparing Nano Drug Delivery Systems

We have measured the flow field inside microdroplets formed by two immiscible fluids in a microchannel using micro particle image velocimetry (micro-PIV) technique. An aqueous liquid with fluorescent particles was injected in an immiscible carrier flow. Both velocity fields during the droplet formation process and during the passage in straight, rectangular microchannels were measured and evaluated. We observed that at a certain layer the direction of the outer circulation flow in the droplet is the same as that of the droplet motion. The results indicate that the immiscible carrier fluid flows through the gaps between the aqueous droplet and the rigid channel wall at a velocity faster than the droplet itself.

A novel technique is presented for non-intrusive microflow control with laser-induced local temperature gradient. In microscale, fluid behavior is quite different from that in macroscale, especially an effect of fluid or interfacial properties on microflow becomes significant. The technique described in this paper utilizes the property change of fluids caused by a light-induced temperature change, i.e., photothermal effect. Absorption of a focused laser beam causes the local spot in temperature. Since the viscosity of general fluids has strong temperature dependence, a generation of local temperature gradient in microfluids results in the corresponding viscosity distribution, which is directly related to the flow behavior in microflow. In order to demonstrate the validity of this concept, we have developed an experimental system to irradiate focused laser beam on a flow in a microfluidic device and to measure velocity profile of the microflow simultaneously. As a heating source, a compact laser diode (LD) with the visible wavelength of 635nm is employed. Velocity measurement is performed by a micro particle image velocimetry (micro-PIV) technique. Optical separation between LD absorption and excitation/emission of fluorescent particle for micro-PIV measurement is confirmed. Change in the microflow behavior in a rectangular microchannel (500 μm × 50 μm) during the LD irradiation due to the photothermal effect is observed.

The fluid particle velocities in the overturning jet of a breaking wave have been measured by the Particle Image Velocimetry (PIV) technique. Monochromatic waves with wave height of 14.5 cm and wavelength of 121 cm were generated in the water depth of 20 cm. The measured fluid particle velocity at the tip of the overturning jet reached 1.68 times of the phase velocity calculated from the linear wave theory. Fluid particle accelerations were estimated from the velocity data with the following results: The overturning jet enters the horizontal water surface with an acceleration of 1.1 g at an angle of 88° downward. The PIV technique was also used to measure the instantaneous vertical vorticities generated by breaking waves. The number and locations of the vortices on the horizontal plane appear to be random. The maximum instantaneous vorticity was in the order of magnitude of 20–30 s−1, whereas the ensemble-averaged vorticity was quite small.