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a Flowchart of the image dilation method for streak segmentation; b an example of converged single streak after 12 loops; c segmentation of two close streaks. The red line marks the boundary of each streak during dilation
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A new phosphor particle streak velocimetry (phosphor-PSV) diagnostic with high spatial resolution was recently demon-
strated (Fan et al. in Opt Lett 46:641, 2021), where individual phosphor particles, excited by a short pulse laser, form streaks
as a results of their displacement by the flow during their relatively long luminescence decay. The loc...
Citations
... An overview of current approaches can be found in Zhang et al. (2024). In Fan et al. (2022), the authors describe pulse-shaped excited phosphor particles as a linearly moving light source with mono-exponential intensity decay. Due to the temporal gradient of the emission, the problem of directional ambiguity can be solved here. ...
Extended particle streak velocimetry (E-PSV) is a novel approach for comprehensive 2D flow measurement. It extends the measuring range of particle streak velocimetry (PSV) via particle tracking velocimetry (PTV). By using long camera exposure when recording moving tracer particles, streaks are created in areas of high flow velocities (PSV). In areas of low velocity, in contrast, particles are imaged point-shaped (PTV). E-PSV hereby offers the advantage of continuous measurement with PSV-typical setups, particularly when areas close to the wall and vortices require to be recorded simultaneously with areas of high velocity. For precise extraction of the flow information, a new model for the description of particle images is presented. It is based on the assumption that the intensity of a tracer can be modeled by a 2D Gaussian function. The temporal integral of the moving Gaussian is approximated by combining analytical calculation with values from a lookup table. We show that by this method even curved streaks can be reconstructed with subpixel accuracy under noise and quantization effects. The technique is demonstrated using a film flow in vicinity of a microstructure.
... Besides the use of voltage to control illumination, fluorescence and phosphorescence can also be used for brightness changes throughout the trajectory, referred to as brightnesscoding Fan et al. (2021Fan et al. ( , 2022. A pictorial overview of these techniques is shown in Fig. 10 and a brief summary of the most common approaches follows. ...
Particle streak velocimetry (PSV) is a Lagrangian velocity measurement method based on streak imaging of moving particles and is regarded as the origin of particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Recently, the PSV technique has undergone further developments, realizing measurements of three velocity components in three dimensions (3D3C), by combining with stereoscopic observation, defocused imaging, light field photography and /or holography. Moreover, image processing algorithms based on deep learning have been successfully applied to PSV. Compared with PIV and PTV, the PSV technique can exhibit several advantages, including extending the upper limit of the velocity measurement range under the same equipment conditions, measuring with lower illumination intensity, often an overall lower equipment complexity and cost for the same measuring requirement, as well as avoiding the particle matching problems of PTV. However, the PSV method also has obstacles to overcome, such as directional ambiguity and the difficulty in identifying streak crossings. For the directional ambiguity problem, there are currently time-coding, color-coding, brightness-coding and determination methods using additional image frames that can be employed. The main application areas of PSV currently include microfluidics, high-velocity flows and large-scale flow field measurements. This review presents the state of the art of PSV and summarizes advantages, disadvantages, accuracy, complexity and application of various configurations. The configurations discussed are focused on those measuring three velocity components and several examples are described in which PSV can be advantageously applied. The review concludes with some future developments that can be anticipated.
... The previous studies most similar to the work presented in this paper use longexposure streak imaging to determine velocity and direction [22,[35][36][37]. The most similar method is by Voss et al. [35], where a two-color intensity modulation LED PTV system was demonstrated. ...
... Another similar measurement technique is that outlined by Fan et al. in Refs. [36,37], where phosphor decay particle streaks were used to determine velocity magnitude and direction of phosphor particles. The limitation of this work is that the decay times of the phosphor particles are fixed by the particle composition, and so particles are specifically tailored for certain flow velocity regimes. ...
... The system outlined in this paper can be thought of as quasi-combination of the techniques in Refs. [35][36][37]. The primary benefit of this proposed system is that the intensity modulation is passive, a natural byproduct of the capacitance discharge in the LED circuit itself. ...
A particle tracking velocimetry (PTV) system is demonstrated that eliminates the
need for expensive lasers and cameras, and encodes the particle tracks with a known intensity variation which allows for high-resolution particle velocity and directionality determination. Using a light-emitting diode (LED) as the light source significantly reduces cost and allows for eye-safe operation, in comparison to traditional laser systems. The intensity variation control is passive, being dictated by the capacitance discharge rate in the LED pulsing circuit. The decay rate can be adjusted with the LED circuit capacitors/resistors, while the duration of the decay can be adjusted with the LED trigger pulse width. Because the intensity decay illumination is controlled by the LED, a single long exposure camera image is used to
acquire images of the particle streaks, and there is no need for a more complicated
and costly double-pulsing camera. With the intensity coding of the light, a single-camera/single-LED system can identify particles entering of leaving the illumination
plane, but cannot discern the direction toward or away from the camera. By using
a two-color system, three-dimensionality of the particle tracks can be determined.
... However, the long lifetime (∼ 26 μs) of this phosphor when seeded in a very fast fluid would result in an image with streaks. Interestingly, these streaks were utilized in a recent velocimetry concept [43,44]. Although it would be possible to derive two color ratio too by fitting streaked images, for simultaneous thermometry and velocimetry, this is not the focus of this study, thus we restrain the use of SMP:Sn 2+ to the slow flow in the liquid dispersion and bulky seeded gaseous flow cases. ...
... A second objective is to reach a higher measurement density by fitting multiple particles simultaneously inside a single fitting window. Finally, it is clear that the technique should be extended to simultaneous thermometry and velocimetry, for example in combination with Particle Tracking Velocimetry (PTV) or with the recently developed phosphor Particle Streak Velocimetry (phosphor PSV) technique [43,44], to access the coupled turbulent fluctuations terms. ...
... Interestingly, these streaks were utilized in a recent velocimetry concept [35,36]. Although it would be possible to derive two colour ratio too by fitting streaked images, for simultaneous thermometry and velocimetry, this is not the focus of this study, thus we restrain the use of SMP:Sn 2+ to the slow flow in the liquid dispersion and bulky seeded gaseous flow cases. ...
... A second objective is to reach higher measurement density by fitting multiple particles simultaneously inside a single fitting window. Finally, it is clear that the technique should be extended to simultaneous thermometry and velocimetry, for example in combination with Particle Tracking Velocimetry (PTV) or with the recently developped phosphor Particle Streak Velocimetry (phosphor PSV) technique [35,36], to access the coupled turbulent fluctuations terms. ...
We introduce a measurement concept using seeded thermographic phosphor particles, which achieves high spatial resolution and rejection of surface induced signals, and is thereby applicable to resolve two-dimensional temperature distribution in sub-millimiter thermal boundary layers. Unlike previous implementations of ratiometric phosphor thermometry in fluid flows, which is based on the division of two spectrally or temporally separated images of the luminescence from clusters of seeded particles, here we treat the individual phosphor particles as independent temperature detectors positioned at the discrete particle locations. 2D rotated Gaussian functions are fitted to each particle image as to integrate particle signals in the two frames for ratio-based thermometry and to position the particles with sub-pixel resolution (< 10μm). In addition, the fitting method allows to separate the luminescence signal of the imaged particles from interfering signals with a low spatial frequency, for example from surface reflection or re-scattering of luminescence light. After assessing the spatial resolution, and the robustness of the temperature measurements against high levels of re-scattered signals, near-wall measurements are demonstrated. The ability to finely resolve the temperature distribution within a 500 µm thin thermal boundary layer is validated against the laminar Prandtl-Blasius equation. As the thermometry counterpart and complement to Particle Tracking Velocimetry, this technique allows to probe the fine details of heat transfer in boundary layers.
In a typical coding method for particle streak velocimetry, the streak shape is divided into two dots and one line by controlling the illumination timing. In this study, several parameters were formulated to optimize the streak shape in a uniform flow using a theoretical approach. In contrast, for non-uniform flows, the formulation of optimal conditions does not provide a common criterion for all flow fields. Therefore, we developed a streak simulation technique based on a two-dimensional flow field and investigated a numerical approach to identify the optimization conditions for non-uniform flows. The test flow fields considered were the Couette flow, von Karman vortex, and Rankine vortex, with the streak number considered one of the parameters affecting the failure of the streak shape, increasing from 100 to 1300. In addition, another parameter, the magnification factor acting on the mean velocity of the flow field, was increased from 0.2 to 1.2. Furthermore, five types of streak failure factors were identified and analyzed based on their frequency of occurrence. The results of the two-dimensional streak simulation showed that the condition for maximizing the number of non-failure streaks for each flow field was successfully identified, and an estimation of the optimal illumination time was obtained. Additionally, vector densities of 0.001 vectors per pixel were achieved for the von Karman and Rankine vortices. The streak simulation can be an effective tool for evaluating the availability of PSV.Graphical abstract
The present work aims to investigate thermal performance of a solar flat plate collector using water and Cu-MWCNTs nanoparticle-based hybrid nanofluid both experimentally and numerically. X-ray diffraction and FESEM with EDAX mapping were performed to characterize nanoparticles. The experimental setup was developed for thermal performance of FPC varying flow rates (0.5, 1.0, 1.5 LPM), inclination angle (25°, 30°, 35°, 40°, 45°), volume concentration (0%, 0.1%, 0.2%, 0.3%, 0.4%), and intensity (400 W/m²). The 3D numerical model having similar geometry as of actual flat plate collector was modeled using Fluents 15.0. The SST turbulence model was used to capture the chaotic changes in the velocity, temperature, and pressure fields. The experimental findings revealed 79.74% improvement in instantaneous efficiency at 0.4% vol., 1.5 LPM, 45° inclination angle, and 400 W/m² intensity. The maximum deviation between the experimental and numerically calculated outlet and inlet temperature difference (ΔT) was 3.5% using a hybrid nanofluid. When numerical data are compared, instantaneous efficiency and heat gain both deviate by 2.8% and 2.9% from experimental values. Because of the numerical simulation analysis, it is possible to observe the temperature and flow pattern in flat plate collectors using nanofluids under a set of operating conditions, which would not be possible without the simulation.
The present work aims to investigate thermal performance of a solar flat plate collector using water and Cu-MWCNTs nanoparticle-based hybrid nanofluid both experimentally and numerically. X-Ray diffraction, FESEM with EDAX mapping were performed to characterize nanoparticles. The experimental setup was developed for thermal performance of FPC varying flow rates (0.5, 1.0, 1.5 lpm), inclination angle (25°, 30°, 35°, 40°, 45°), volume concentration (0%, 0.1%, 0.2%, 0.3%, 0.4%) and intensity (400 W/m ² ). The 3D numerical model having similar geometry as of actual flat plate collector was modeled using Fluents 15.0. The SST turbulence model was used to capture the chaotic changes in the velocity, temperature, and pressure fields. The experimental findings revealed 79.74% improvement in instantaneous efficiency at 0.4% vol., 1.5 lpm, 45° inclination angle, and 400 W/m ² intensity. The maximum deviation between the experimental and numerically calculated outlet and inlet temperature difference (ΔT) was 3.5% using a hybrid nanofluid. When numerical data are compared, instantaneous efficiency and heat gain both deviate by 2.8% and 2.9% from experimental values. Because of the numerical simulation analysis, it is possible to observe the temperature and flow pattern in flat plate collectors using nanofluids under a set of operating conditions, which would not be possible without the simulation.
