Role of surface-tension additive in coating framing effect topography

A variety of techniques have been proposed in the literature for sprinkler drop characterization. An optical particle tracking velocimetry (PTV) technique is proposed in this paper to determine drop velocity, diameter and angle. The technique has been applied to the drops emitted by an isolated impact sprinkler equipped with two nozzles (diameters 3.20 and 4.37 mm) operating at a pressure of 175 kPa. PTV has been previously used to determine the velocity vector of different types of particles. In this research, PTV was used to photograph sprinkler drops over a region illuminated with laser light. Photographs were taken at four horizontal distances from the sprinkler, which was located at an elevation of 1.65 m over the soil surface. Drop angle and velocity were derived from the displacement of the drop centroid in two images separated by a short time step. Centrality and dispersion parameters were obtained for each drop variable and observation point. Results derive from the analysis of 2,360 images. Only 37.5 % of them (884 images) contained drops which could be processed by the PTV algorithm, resulting in a total of 3,782 drops. A filtering algorithm just validated 1,893 valid drops, which were successfully analyzed. The proposed technique uses expensive equipment requiring continued protection against irrigation water. This methodology has proven valuable to characterize irrigation water drops. Despite its robust measurement procedure, further comparison with other techniques seems necessary before this optical technique can be recommended for practical use in sprinkler drop characterization.

A stereoscopic particle tracking velocimetry (SPTV) technique based on the 2-frame hybrid particle tracking velocimetry (PTV) method was developed. The expansion of 2D PTV to SPTV is facilitated by the fact that the PTV method tracks individual particle centroids. To evaluate the performance and measurement accuracy of the present SPTV technique, it was applied to flow images of rigid body translation and synthetic standard images of jet shear flow and impinging jet flow. The data processing routine and measurement uncertainty of the SPTV technique are compared with those of conventional stereoscopic particle image velocimetry (SPIV). In addition, the centroid translation effect of 2D particle image velocimetry (PIV) is defined and its effect on SPIV measurements is discussed. Compared to the SPIV method, the SPTV technique has inherited merits of concise and precise velocity evaluation procedures and provides better spatial resolution and measurement accuracy.

To validate the particle motion in flighted rotating drum (FRD), a laboratory FRD was built and operated at 15% filling degree and 10 rpm rotation speed using plastic balls as bed material. The particle tracking velocimetry (PTV) and magnetic particle tracking (MPT) techniques were applied to investigate the particle flow behavior. The 3D particle flow was modeled by Discrete Element Method (DEM) with LIGGGHTS. The height of the barycenter of all overall particles and particle instantaneous velocity were calculated from PTV and DEM data. The 3D time-averaged particle velocity distributions obtained from MPT experiment and DEM simulation were compared.Keywords: flighted rotating drum; particle motion; particle tracking velocimetry; magnetic particle tracking; DEM simulation.

Marangoni flow is the motion induced by a surface tension gradient along a fluid–fluid interface. In this study, we report a Marangoni flow generated when a bath of surfactant contacts a pre-wetted film of deionized water on a vertical substrate. The thickness profile of the pre-wetted film is set by gravitational drainage and so varies with the drainage time. The surface tension is lower in the bath due to the surfactant, and thus a liquid film climbs upwards along the vertical substrate due to the surface tension difference. Particle tracking velocimetry is performed to measure the dynamics in the film, where the mean fluid velocity reverses direction as the draining film encounters the front of the climbing film. The effect of the surfactant concentration and the pre-wetted film thickness on the film climbing is then studied. High-speed interferometry is used to measure the front position of the climbing film and the film thickness profile. As a result, higher surfactant concentration induces a faster and thicker climbing film. Also, for high surfactant concentrations, where Marangoni driving dominates, increasing the film thickness increases the rise speed of the climbing front, since viscous resistance is less important. In contrast, for low surfactant concentrations, where Marangoni driving balances gravitational drainage, increasing the film thickness decreases the rise speed of the climbing front while enhancing gravitational drainage. We rationalize these observations by utilizing a dimensionless parameter that compares the magnitudes of the Marangoni stress and gravitational drainage. A model is established to analyse the climbing front, either in the Marangoni-driving-dominated region or in the Marangoni-balanced drainage region. Our work highlights the effects of the gravitational drainage on the Marangoni flow, both by setting the thickness of a pre-wetted film and by resisting the film climbing.

Studying local liquid velocity in liquid–solid packed bed using the newly developed X-ray DIR technique

Sub-millimeter-bubble injection is one of the most promising techniques for enhancing heat transfer for the natural convection of liquids. So far, we have investigated experimentally the heat transfer enhancement by sub-millimeter bubbles. However, the effects of the bubble diameter on the heat transfer have not yet been understood. The purpose of this study is to clarify the effects of bubble diameter on the heat transfer enhancement by sub-millimeter bubbles for the laminar natural convection of water along a vertical heated plate. We conduct temperature measurements using thermocouples and velocity measurements using a Particle Tracking Velocimetry (PTV) technique. We also carry out two-dimensional numerical simulations to comprehensively understand the effects of bubble injection on the flow near the heated wall. Temperature measurements show that the heat transfer coefficient increases with a decrease in the bubble diameter. This is due to a significant increase in the bubble advection effect.

In this paper we present a set of wave flume experiments for a solitary wave reflecting off a vertical wall. A particle tracking velocimetry (PTV) technique is used to measure free-surface velocity and the velocity field in the vicinity of the moving contact line. We observe that the free surface undergoes the so-called rolling motion as the contact line moves up and down the vertical wall, and fluid particles on the free surface almost always flow toward the wall except at the end of the reflection process. As the contact line descends along the wall, wall boundary layer flows move in a downward direction and therefore the boundary layer acts like a conduit through which the surface-rolling-induced flow escapes from the meniscus. However, during the last phase of the reflection process flow reversal occurs inside the wall boundary layer. An approximate analytical solution is developed to explain the flow reversal feature. Very good agreement between the approximate theory and measured data is obtained. Because of the flow reversal, boundary layer flows collide with the surface-rolling-induced flows. The collision gives rise to a jet ejecting from the meniscus into the water body, which later evolves into a small eddy. It is noticed that the fluid particles in different regions such as the free stream, the free-surface boundary layer and the wall boundary layer, can be transported to other regions by passing through the meniscus.

Small-scale physical model tests were conducted to investigate the morphodynamics of a sandy beach of uniform grain size in the lee of single impermeable submerged breakwater under oblique incident waves. The primary objective of the tests was to assess the performance of a submerged breakwater on a littoral drift environment. Different patterns and mechanism of the currents behind this structure were identified on fixed and movable beds using a particle tracking velocimetry (PTV) technique. The physical model tests showed consistent results for the beach morphology and the subsequent shoreline response with the geometry and the position of the submerged breakwater under the same wave condition. Submerged breakwaters were found to perform well under oblique waves if the volume enclosed behind these structures is filled artificially. Attempts were also made to establish a relationship between shoreline evolution and relevant parameters associated with waves and structures. These preliminary results are sufficient to develop practical design guidelines for submerged breakwaters under obliquely incident waves.

A micro-bubble injection is one of the most promising techniques of enhancing the heat transfer for laminar natural convections of liquid. However, flow and heat transfer structures for laminar natural convections of water with micro-bubbles have not yet been fully understood. The purpose of this study is to clarify the effects of the micro-bubble injection on the laminar natural convection of water along a vertical heated plate using thermocouples and a Particle Tracking Velocimetry (PTV) technique. The experimental results show that the heat transfer coefficients with micro-bubble injection are higher compared with those without micro-bubble injection as the bubble flow rate increases or the wall heat flux decreases. It is concluded from the velocity measurements that the heat transfer enhancement for the laminar natural convection results from the significant increases in the liquid mean rise velocities and the liquid RMS velocities due to micro-bubble injection.

Quantitative image analysis and measurement of flow fields in convective heat transfer has great importance for the optimum energy consumption problems. In natural and forced convection phenomena of fluids, the complexity of flow field prevents us from detailed three dimensional (3D) experimental analyses of steady/unsteady dynamics in fluids. These flow fields have locally different density and temperature values and yet to be observed quantitatively. Recent development of the Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques lead us to the quantitative investigation of flow fields in experimental researches. On the other hand, in image measurements density and temperature distributions have been grasped only in two-dimensions (2D). These qualitative image analyses of flow fields were obtained by using classical flow visualizing techniques, such as shadowgraph and color schlieren method. This paper describes the quantitative measurement of convective flow field using our originally proposed color striped background oriented schlieren (CSBOS) method. The obtained measured image data is used for CT reconstruction and 3D temperature gradient distributions.

Mixing vessels are widely used for blending and chemical reactions. Although much has been done on mixing processes, the complex, three-dimensional flow phenomena are still not well understood. The purpose of our first step in this research is the simulation and validation of time-resolved, three-dimensional velocity vector data. Such results are an essential part of the design of mixing systems, but are generally not available to the engineers. The computational work involves direct numerical simulation (DNS) and large eddy simulation (LES) of the Navier-Stokes equations. Later, modeling of the Reynolds averaged Navier-Stokes (RANS) equations will be undertaken as a simplified approach. Simulations and modeling are being validated by experiments. Two flow mixing systems are under investigation. First and most important for validation is an opposed jet flow system that offers some unique characteristics that can be used for validation of DNS/LES simulations. It also has applications in the injection molding of plastics. Second, simulations of impeller driven mixing vessels that are more commonly used in processing are under development. Here the moving mesh system adds complexity. In addition, visualization of both numerical and experimental results, 3-D particle tracking velocimetry (PTV) techniques have been developed. The proposed paper will address the problems in the modeling of chemical mixing and discuss the results of simulation and validation.

This paper describes velocity measurements of the micro-scale three-phase flow containing micro-bubbles and micro-particles in a vertical channel. A Particle Tracking Velocimetry (PTV) technique is used to estimate the velocities of micro-bubbles and micro-particles. The measurement shows that the probability distribution of the bubble location in the vicinity of the wall for the three-phase flow is lower than that for the two-phase flow. The measurement also shows that the RMS value of the bubble fluctuation velocity in the streamwise direction for the three-phase flow is high compared with that for the two-phase flow. This is related to the suppression of bubble motion in the wall-normal direction resulting from the existence of particles.

Influence of tank geometry and flow pattern in fish distribution

<p><span>We experimentally investigated the internal dynamics of stationary mono- and bidisperse granular avalanches in an inclined conveyor belt flume. We used the refractive index matching technique to visualize and obtain information from within the granular bulk. In combination with particle tracking velocimetry and coarse-graining techniques, we were able to calculate continuum particle distributions and velocity fields. The experimental avalanches had distinct flow regions: (i) a convective-bulged front, (ii) a compact-layered tail, and (iii) a breaking size segregation wave structure, serving as a transition between the former two. To describe the dynamics of these regions, we computed local strain rates in the form of its tensor invariants. The invariants varied notably between regions; while the largest values and non-linear distributions were found at the front, linear distributions were observed in the tail. In general, and although that slip was considerable at the base of the flow, time-averaged velocity profiles were found to be well captured by a Bagnold model. Based on recent developments in particle-size segregation theory, we calculated the segregation flux within the bidisperse avalanches. In those experiments, we found that segregation flux was higher at the front than at the back, a fact that was confirmed by the observed recirculation of large particles at the front. All our experimental data show a strong link between rheology and segregation, a result that will provide grounding for new developments in segregation theory.</span></p>

Morphology and flow behavior of buoyant bubble plumes