FIGURE 3 - uploaded by Rafael Castrejon-Pita
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(Colour online) Sectional view of the millimeter-scale printhead. Relative sizes are in correct proportion. The nozzle shape consists of a 45 degree (half-angle) conical inlet, followed by a parallel cylindrical section 2.2 mm in diameter and 2.2 mm long.
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The shadowgraph technique is discussed in terms of some modern application to fluid visualization and the characterization of freesurface flows. A brief description of shadowgraph photography is presented which emphasizes the parameters which need to be controlled to obtain useful images for digital processing and analysis. Several examples of sha...
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... model printhead used to generate and harmonically disturb the jets is a modified version of a design described elsewhere [10]. Briefly, it consists of a sealed, pressur- ized liquid-filled chamber with the outlet nozzle in its lower surface and a rubber membrane forming the upper face, as shown schematically in Fig. 3. The membrane is in contact with the liquid on one surface and with an electromagnetic vibrator on the other, and is used to transmit the oscillatory motion from the actuator to the fluid. The vibrator (LDS Test and Measurement Ltd, model V201) is driven by an amplifier (Nikkai 250, total harmonic distortion <0.025%) connected to a ...
Citations
... The contact angle, which occurs when solids are wetted by liquids, has an important place in many application areas such as lubrication, coating, printing, waterproofing and detergent [1,2]. A wide range of applications has emerged, from materials such as self-cleaning glass by controlling wettability to high-tech areas such as microfluidic control, corrosion resistance, water-oil separation, medical material production, implant dental technology [3][4][5][6][7]. Researchers are working on increasing the wettability in order to ensure that the denture material can be better adhered to in the mouth. ...
... Contact angle measurements were made with the computer program prepared using Eqs. (2)(3)(4)(5)(6). The realized contact angle measure- ...
The solid material's wettability behavior is determined by the contact angle value. The wettability of materials is critical in the coating, lubricating, and insulating industries. In high-tech industries including corrosion resistance, water-oil separation, medical material production, implant technology, and friction reduction, the contact angle is very important. A new method called the full angle method was used to measure the contact angle and compared with current methods. The wettability behavior of plexiglass, which is employed in a variety of applications ranging from lighting to decorating, and industrial designs to accessory production, was explored in this study. The measurement of the contact angle was done by dropping 1.8 M (molar) of saltwater over the plexiglass materials. In order to examine the effect of evaporation on the contact angle, changes in contact angle, height and baseline were investigated depending on the waiting time.
... The main limitations of traditional high-speed imaging are a lack of shockwave visibility and a fixed single imaging plane. However, shadowgraph imaging provided a qualitative approach with more depth of information, and shockwave dynamics of different mediums, based on the significant differences in refractive index [69]. The trade-off was that the imaging plane collapsed into a two-dimensional image. ...
Blunt and blast impacts occur in civilian and military personnel, resulting in traumatic brain injuries necessitating a complete understanding of damage mechanisms and protective equipment design. However, the inability to monitor in vivo brain deformation and potential harmful cavitation events during collisions limits the investigation of injury mechanisms. To study the cavitation potential, we developed a full-scale human head phantom with features that allow a direct optical and acoustic observation at high frame rates during blunt impacts. The phantom consists of a transparent polyacrylamide material sealed with fluid in a 3D-printed skull where windows are integrated for data acquisition. The model has similar mechanical properties to brain tissue and includes simplified yet key anatomical features. Optical imaging indicated reproducible cavitation events above a threshold impact energy and localized cavitation to the fluid of the central sulcus, which appeared as high-intensity regions in acoustic images. An acoustic spectral analysis detected cavitation as harmonic and broadband signals that were mapped onto a reconstructed acoustic frame. Small bubbles trapped during phantom fabrication resulted in cavitation artifacts, which remain the largest challenge of the study. Ultimately, acoustic imaging demonstrated the potential to be a stand-alone tool, allowing observations at depth, where optical techniques are limited.
... En particular, se identificó la correlación de las variaciones de alta y baja intensidad de la luz con el índice de refracción del aire a diferentes temperaturas. Como resultado, se determinó la dependencia entre las propiedades térmicas y ópticas del aire.En 2009, Álvarez Herrera C. en su trabajo de posgrado en el Centro de Investigaciones en Óptica A.C., titulado "Medición de temperatura y análisis en flujos de fluidos transparentes utilizando la técnica Schlieren"[9], desarrolló la técnica Schlieren a partir del método de la curva de calibración, el cual permitió medir la temperatura promedio que provoca la desviación de los haces de luz causados por las variaciones de los índices de refracción.En 2011, Castrejon Garcia R. y sus colaboradores trabajaron en el Centro de Investigaciones en Energía de la Universidad Nacional Autónoma Metropolitana (UNAM), en el proyecto "The shadowgraph imaging technique and its modern application to fluid jets and drops"[10]. En este trabajo se desarrollaron tres arreglos experimentales, los cuales operaron con diferentes configuraciones de la técnica Shadowgraph. ...
En el estudio experimental de la dinámica de termofluidos es de gran relevancia establecer técnicas de visualización basadas en métodos ópticos no invasivos. Entre estas técnicas se tiene a la de Shadowgraph, la cual consiste en introducir un haz de luz a través de un objeto opaco con nula refracción, o de un fluido, para extraer información de campo sin intervenir directamente con él. En particular, a partir de la técnica Shadowgraph es posible analizar los cambios en la fase de la luz, los cuales llevan información sobre el estado del flujo a un plano de registro. Como resultado, en el fluido estudiado se puede evaluar cualitativamente en tiempo real las variaciones de la densidad, las distribuciones espaciales de temperatura y la distribución del índice de refracción.
En el presente proyecto de investigación, se diseñó y construyo un arreglo de difracción experimental basado en la técnica Shadowgraph directa con luz divergente. En este arreglo se utilizó una cámara de alta velocidad V1 ArduCam CMOS, un proyector portátil Vivitek Qumi Q5 Im y un sistema de desarrollo embebido Raspberry Pi 4B, así mismo se desarrolló el procesamiento de las imágenes adquiridas en el sistema de cómputo numérico Matlab (by Math Works, Inc). En particular, bajo esta configuración se estableció una dependencia entre el cambio de índice de refracción y la temperatura en el efecto de escape y combustión de gas butano. Como resultado de este análisis, se hace mención de que la configuración experimental propuesta bajo la técnica Shadowgraph se caracteriza por ser un arreglo con una rápida respuesta a los cambios de índice de refracción del fluido analizado. Adicionalmente, dicha configuración se adapta para analizar muestras de fluidos en un espacio reducido, así mismo se puede construir a un bajo costo y tener una interfaz sencilla.
... The droplet size spectrum can be measured with intrusive or non-intrusive methods [27]. Examples of non-intrusive systems are phase Doppler particle analysis (PDPA) [28], laser diffraction (LD) [29] and imaging principles, such as high-speed imaging (HSI), better known as shadowgraphy methods [30][31][32][33]. PDPA and HSI methods also allow the measurement of drop velocity at the same time [34]. ...
... The illumination source spreads uniform light on the spray, and, consequently, part of the light is refracted by the spray, leaving a shadow on the bright background [33,56,57,64]. This methodology, usually performed in a back-lighted arrangement for image acquisition, is often known as the shadowgraph technique [31]. In detail, the system consists of a camera equipped with high-magnification optics used to acquire images of the drops and synchronized with a light-emitting diode (LED) light source for irradiating the spray. ...
... They are normally placed at specific points for a given crop to check the spray coverage of a certain treatment. In addition, it is also recommended to place a large number of these targets to obtain a representative sample [31,69,70]. ...
Plant protection control based on the spray application of plant protection products is a very complex task depending on a series of factors, among which droplet size is the most influential for deposition and pesticide effectiveness. In fact, the adoption of the correct droplet size can ensure that the required dose reaches the target area and is not wasted, minimizes the off-target losses due to evaporation, drift and run-off and, at the same time, enhances the operator’s safety in terms of inhalation, ingestion and dermal exposure. In this paper, after defining some mean characteristic diameters helpful for a description of a drop population and focusing on the main drop size distribution functions for the statistical characterization of sprays, a critical analysis of known methods, both intrusive and non-intrusive, for drop size measurement is carried out by reviewing the literature. Among intrusive methods, the liquid immersion method and the use of water-sensitive papers are discussed, whereas, among non-intrusive methods, laser-based systems (laser diffraction, phase Doppler particle analysis) and high-speed imaging (shadowgrapy) are presented. Both types of method, intrusive and non-intrusive, can be used in machine-learning-based approaches exploiting regression techniques and neural network analysis.
... The imaging method is more advantageous, and it is important to visualize primary spray formation; a region where the transformation of the bulk liquid into droplets occurs. Shadowgraph imaging stands out as a usually inexpensive but powerful technique [12]. Asgarian et al., [13] make use of shadowgraph to acquire the droplet size distribution of an atomizer discharging a flat liquid sheet. ...
A swirl atomizer is a widely applied spray-generating device. The swirling motion of a swirl atomizer is induced either by a tangential inlet or a swirl-generating vane. The swirling effect produces a spray with a wide angle which is important in various applications such as gas cooling, diesel engine combustion, and automatic hand sanitizer. An intense swirling mechanism was reported to significantly affect the spray angle. An attempt was made by combining tangential inlet and swirl-generating vane in a single embodiment to create a more intense swirling effect. The experiment was conducted with pipe flow in transition and turbulence regimes. The shadowgraph technique was applied to acquire the spray images. The images were processed using image processing software. It was found that the combined swirling mechanism produces a wider spray angle compared to the individual tangential inlet swirl atomizer. It was also found that the swirling intensity has a bigger effect on the spray angle than the Reynolds number.
... The dark regions (shadow) in a shadowgram mark the boundaries of the object. Light transmittance is affected by scattering and absorption too. Figure 13 shows a shadowgraph image [21] of quenching oil jet spray from a 1.2 mm atomizer nozzle at 15 m/s and 38°C. Shadowgraphy has been used to visualize liquid jet breakup [23,24] at different length scales in-order to determine ligamentdroplet sizes, and speeds. ...
... In such cases, a dark shadow image with a bright background may result and therefore any kind of density variations analysis would be irrelevant. Shadowgraphs provide phase information (refractive index gradients) [21,25] or simply a monochromatic projected shadow image of the object [22,[26][27][28]. It can help in visualizing convective flows [29]. ...
... Shadowgrams of (a) quenching oil jet spray [21] and (b) water jet spray [22]. Shadowgraphy is easy and inexpensive to carry out, has a high spatial resolution for most practical purposes, is independent of the shape and material of the phase media and its relatively large field of view is well suited for size, shape, position, and velocity determination. ...
A concise review of the recent developments in some of the standard optical diagnostics applied for primary jet breakup studies has been presented here. Primary breakup is the core breakup of liquid jets and sheets into droplets upon its interaction with the ambient gaseous atmosphere. This phenomenon is encountered in various aerodynamic, fluid dynamic, and combustion situations. The imaging diagnostics reviewed here include photography, high-speed imaging, shadowgraphy, digital holography, ballistic imaging, jet core illumination, thermal imaging, Mie imaging, x-ray phase contrast imaging, and laser-induced fluorescence. The advantages and limitations of each technique, their success, and future developmental trend are discussed.
... [44] Particularly the shadowgraphy technique has been recognized in this field as being relatively easy, inexpensive yet powerful. [45] Shadowgraphy is an optical method used to visualize phenomena based on disturbance of refractive index in transparent media. The shadowgraph image consists of a bright background and a shadow of the interfaces between regions with different refractive index. ...
... The shadowgraph image consists of a bright background and a shadow of the interfaces between regions with different refractive index. The bright background is produced due to a lack of interactions between the surrounding medium and the light, while the light refracted at the object interface is dispersed, hence appearing dark in the images [44,45]. ...
Eine nachhaltigere chemische Industrie erfordert eine Minimierung der Lösungsmittel und Chemikalien. Daher werden Optimierung und Entwicklung chemischer Prozesse vor einer Produktion in großem Maßstab in kleinen Chargen durchgeführt. Der entscheidende Schritt bei diesem Ansatz ist die Skalierbarkeit von kleinen Reaktionssystemen auf große, kosteneffiziente Reaktoren. Die Vergrößerung des Volumens des Reaktionsmediums geht immer mit der Vergrößerung der Oberfläche einher, die mit dem begrenzenden Gefäß in Kontakt steht. Da das Volumen kubisch, während die Oberfläche quadratisch mit zunehmendem Radius skaliert, nimmt ihr Verhältnis nicht linear zu. Viele an der Grenzfläche zwischen Oberfläche und Flüssigkeit auftretende Phänomene können die Reaktionsgeschwindigkeiten und Ausbeuten beeinflussen, was zu falschen Prognosen aufgrund der kleinskaligen Optimierung führt. Die Anwendung von schwebenden Tropfen als behälterlose Reaktionsgefäße bietet eine vielversprechende Möglichkeit, die oben genannten Probleme zu vermeiden. In der vorgestellten Arbeit wurde eine effiziente Kopplung von akustisch schwebenden Tropfen und IM Spektrometer für die Echtzeitüberwachung chemischer Reaktionen entwickelt, bei denen akustisch schwebende Tropfen als Reaktionsgefäße fungieren. Das Design des Systems umfasst die berührungslose Probenahme und Ionisierung, die durch Laserdesorption und -ionisation bei 2,94 µm realisiert wird. Der Umfang der Arbeit umfasst grundlegende Studien zum Verständnis der Laserbestrahlung von Tropfen im akustischen Feld. Das Verständnis dieses Phänomens ist entscheidend, um den Effekt der zeitlichen und räumlichen Auflösung der erzeugten Ionenwolke zu verstehen, die die Auflösung des Systems beeinflusst. Der Aufbau umfasst eine akustische Falle, Laserbestrahlung und elektrostatische Linsen, die bei hoher Spannung unter Umgebungsdruck arbeiten. Ein effektiver Ionentransfer im Grenzflächenbereich zwischen dem schwebenden Tropfen und dem IMS muss daher elektrostatische und akustische Felder vollständig berücksichtigen. Für die Probenahme und Ionisation wurden zwei unterschiedliche Laserpulslängen untersucht, nämlich im ns- und µs-Bereich. Die Bestrahlung über µs-Laserpulse bietet gegenüber ns-Pulse mehrere Vorteile: i) das Tropfenvolumen wird nicht stark beeinflusst, was es ermöglichet, nur ein kleines Volumen des Tropfens abzutasten; ii) die geringere Fluenz führt zu weniger ausgeprägten Schwingungen des im akustischen Feld eingeschlossenen Tropfens und der Tropfen wird nicht aus dem akustischen Feld rückgeschlagen, was zum Verlust der Probe führen würde; iii) die milde Laserbestrahlung führt zu einer besseren räumlichen und zeitlichen Begrenzung der Ionenwolken, was zu einer besseren Auflösung der detektierten Ionenpakete führt. Schließlich ermöglicht dieses Wissen die Anwendung der Ionenoptik, die erforderlich ist, um den Ionenfluss zwischen dem im akustischen Feld suspendierten Tropfen und dem IM Spektrometer zu induzieren. Die Ionenoptik aus 2 elektrostatischen Linsen in der Nähe des Tropfens ermöglicht es, die Ionenwolke effektiv zu fokussieren und direkt zum IM Spektrometer-Eingang zu führen. Diese neuartige Kopplung hat sich beim Nachweis einiger basischer Moleküle als erfolgreich erwiesen. Um die Anwendbarkeit des Systems zu belegen, wurde die Reaktion zwischen N-Boc Cysteine Methylester und Allylalkohol in einem Chargenreaktor durchgeführt und online überwacht. Für eine Kalibrierung wurde der Reaktionsfortschritt parallel mittels 1H-NMR verfolgt. Der beobachtete Reaktionsumsatz von mehr als 50% innerhalb der ersten 20 Minuten demonstrierte die Eignung der Reaktion, um die Einsatzpotentiale des entwickelten Systems zu bewerten.
... For the sake of simplicity, the calculations of velocities and spray momentum flux are only detailed for nozzle P1 (Section 4.1), but the d 50 correlation is based on the data of both nozzles (Section 4.2). The geometry of the nozzle orifices corresponds to the intersection of a semi-ellipsoid at the end of the nozzle internal passage and a transverse curved slit, which results in an elliptical orifice as illustrated in Shadow imaging [33] was used to visualize the spray; a back light illuminated a region of the spray and a high speed camera was located on the opposite side to record the shadow of droplets in that region, see Figure 6(b). Two optical setups that we refer to as OS1 and OS2 were used to capture images of the spray. ...
In water atomization, a molten metal stream is fragmented by high-pressure water sprays by means of momentum transfer. In this work, a flat fan water spray is considered as a two-phase flow: water and a surrounding gas. An existing mathematical model for predicting the velocities of water droplets and entrained gas in a flat fan spray is improved. The total momentum flux of a spray is calculated for different spray travel distances, spray pressures and spray spreading angles, addressing the dependence of spray momentum flux on these parameters. A new quantity, the ‘effective momentum flux’, is introduced which also accounts for the effect of apex angle.
Finally, based on the results of lab-scale water atomization experiments, a correlation is proposed for the powder mass median size versus the effective momentum flux of the water spray, consolidating the influence of spray parameters including pressure, travel distance, spreading angle and apex angle.
... The shadowgraphy technique usually uses flash lamps, spark generation, LED lights, and lasers as the light source. 34 In this experiment, a green light LED 1000 watt (pulsed light source with a frequency of 50 nanoseconds) and two lenses: one to parallel the light and the other to focus the light on the camera lens were used. NIKON D3300 camera with a resolution of 6000 Â 4000 pixels was used. ...
In this study, the atomization of heavy fuel oil (Mazut) and diesel fuel at different pressures is compared experimentally. Also, the effects of temperature on the Mazut fuel atomization are investigated experimentally. Mass flow rate, discharge coefficient, wavelength, liquid film thickness, ligament diameter, spray angle, breakup length, and sature mean diameter are obtained for the Mazut and diesel fuel. Fuels spray images at different pressures and temperatures are recorded using the shadowgraphy method and analyzed by the image processing technique. Error analysis is performed for the experiments, and the percentage of uncertainty for each parameter is reported. The experimental results are compared with the theoretical results. Also, Curves are proposed and plotted to predict changes in the behavior of atomization parameters. Diesel fuel has less viscosity than Mazut fuel. Diesel fuel has shorter breakup length, wavelength, liquid film thickness, and sature mean diameter than Mazut fuel at the same pressure. Diesel fuel has a larger spray angle and a larger discharge coefficient than Mazut fuel at the same pressure. As the pressure and temperature increase, fuel atomization improves. The viscosity of Mazut fuel is decreased by temperature increase. As the fuel injection pressure and temperature increase, breakup length, wavelength, liquid film thickness, and sature mean diameter decrease; also, spray angle increases.
... A Photron Fastcam SA1.1 (675K-M1) high-speed camera and a Kern-Paillard YVAR 1:2.8 camera lens with focal length of 75mm are used to record the impact process for 2s with a frame rate of 20,000 frames per second, a field of view of 896 x 196 pixels and an effective optical resolution of 80µm/pixel, which corresponds to a magnification factor of 1:4. Shadowgraphy is an appropriate technique for the visualisation of drop impact dynamics [4] because the large difference in refractive indices between air and liquids causes a good contrast on the shadowgrams [14], as can be seen in Figure 22c. ...
An analytical solution is proposed to predict the crown propagation, generated by a single droplet impact on wetted walls. This approach enables a smooth transition from the inertia-driven to the viscous-controlled regime of crown propagation. The modelling strategy is based on the stagnation-point flow, because it resembles closely the hydrodynamic flow in the lamella and offers two main advantages. First, it allows a simple estimation of the wall-film thinning rate, caused by the impulse transfer from the impacting droplet to the wall film. Second, thanks to the self-similarity of the solution, it enables a straightforward estimation of momentum losses during film spreading along the wall. By incorporating this estimation into existing inviscid models, an excellent agreement with experiments is found during the entire crown elevation phase. In general, the analysis shows that momentum losses due to viscous effects cannot be neglected during a significant portion of crown propagation, particularly for thin wall films. The proposed methodology paves the way for predicting the inception of crown bottom breakup (CBB). In this case, the crown lamella disintegrates directly at its base due to the spontaneous creation of holes that create a web-like structure in the lamella prior to its break-up. Our theoretical analysis shows that this premature break-up of the crown lamella is associated to local instability effects, caused by the unbalance between inertial forces and surface tension.
