Morteza Ghorbani

Visualization and image processing of spray structure under the effect of cavitation phenomenon

This paper presents visualization and image processing of spray structure affected by cavitation bubbles and cavitating flow patterns. Experiments were conducted for a better understanding of cavitation and resulting flow regimes. Cavitation is generated with sudden pressure drop across a 4.5 mm long short micro-channel with an inner diameter of 152 μm connected to the setup using proper fittings. Generated cavitation bubbles and fluid flow patterns were observed by using a high speed camera. The spray structure was observed in four different segments and mainly the droplet evaluation in the lower segments for low upstream pressures was analyzed using several image processing techniques including contrast adjustments and morphological operators. Moreover, fluid flow regimes for different upstream pressures were investigated, and the flow patterns were analyzed in the separated regions of the spray.

Review on Lithotripsy and Cavitation in Urinary Stone Therapy

Cavitation is the sudden formation of vapor bubbles or voids in liquid media and occurs after rapid changes in pressure as a consequence of mechanical forces. It is mostly an undesirable phenomenon. Although the elimination of cavitation is a major topic in the study of fluid dynamics, its destructive nature could be exploited for therapeutic applications. Ultrasonic and hydrodynamic sources are two main origins for generating cavitation. The purpose of this review is to give the reader a general idea about the formation of cavitation phenomenon and existing biomedical applications of ultrasonic and hydrodynamic cavitation. Because of the high number of the studies on ultrasound cavitation in the literature, the main focus of this review is placed on the lithotripsy techniques, which have been widely used for the treatment of urinary stones. Accordingly, cavitation phenomenon and its basic concepts are presented in Section II. The significance of the ultrasound cavitation in the urinary stone treatment is discussed in Section III in detail and hydrodynamic cavitation as an important alternative for the ultrasound cavitation is included in Section IV. Finally, side effects of using both ultrasound and hydrodynamic cavitation in biomedical applications are presented in Section V.

Increasing the stability of nanofluids with cavitating flows in micro orifices

One of the most critical challenges for nanofluids in practical applications is related to their stability and reusability since a gradual agglomeration of nanoparticles in nanofluids occurs with time and is accelerated by heating. In this study, we propose a technique to maintain the performance and stability of nanofluids with the use of cavitating flows through micro orifices to prevent agglomeration and sedimentation of nanoparticles, which will increase the durability of the nanofluids. γ-Al2O3 (gamma-alumina) nanoparticles with a mean diameter of 20 nm suspended in water were utilized. In the current approach, a flow restrictive element induces sudden pressure, which leads to cavitation bubbles downstream from the orifice. The emerging bubbles interact with the agglomerated structure of nanoparticles and decrease its size through hitting or shock waves generated by their collapse, thereby increasing the stability and reusability of nanofluids. The method does not involve any use of expensive surfact...

Energy Harvesting in Microscale with Cavitating Flows

Energy harvesting from thermal energy has been widely exploited to achieve energy savings and clean technologies. In this research, a new cost-effective and environment-friendly solution is proposed for the growing individual energy needs thanks to the energy application of cavitating flows. With the aid of cavitating jet flows from microchannel configurations of different sizes, it is shown that significant temperature rise (as high as 5.7 °C) can be obtained on the surface of the thin plate. The obtained heat energy could be integrated to a thermoelectric power generator, which can be used as a power resource for consumer devices, such as cell phones and laptops. To explore the difference in the temperature rise with different microtube diameters, namely, 152, 256, 504, and 762 μm, and also with different upstream pressures of 10, 20, 40, and 60 bar, the cavitation flow patterns are captured and analyzed using an advanced high-speed visualization system. The analysis of the captured data showed that different flow patterns exist for different diameters of the microtubes, including a pattern shift from micro- to macroscale, which accompanied the pattern of temporal results very well.

Single Droplet Tracking in Jet Flow

Fluid systems such as the multiphase flow and the jet flow usually involve droplets and/or bubbles whose morphological properties can provide important clues about the underlying phenomena. In this paper, we develop a new visual tracking method to track the evolution of single droplets in the jet flow. Shape and motion features of the detected droplets are fused and Bhattacharyya distance is employed to find the closest droplet among possible candidates in consecutive frames. Shapes of the droplets are not assumed to be circles or ellipses during segmentation process, which utilizes morphological operations and thresholding. The evolution of single droplets in the jet flow were monitored via Particle Shadow Sizing (PSS) technique where they were tracked with 86 % average accuracy and 15 fps real-time performance.

Vision based cone angle estimation of bubbly cavitating flow and analysis of scattered bubbles using micro imaging techniques

Hydrodynamic cavitation is an effective and alternative treatment method in various biomedical applications such as kidney stone erosion, ablation of benign prostatic hyperplasia tissues and annihilation of detrimental cells. In order to effectively position the orifice of bubbly cavitating flow generator towards the target and control the destructive cavitation effect, cone angle of multi-phase bubbly flow and distributions of scattered bubble swarms around main flow must be determined. This paper presents two vision based solutions to determine these quantities. 3D Gaussian modeling of multi-phase flow and edge slopes of cross-section are used to estimate the cone angle in a Kalman filter framework. Scattered bubble swarm distributions around main flow were assumed as a normal distribution and analyzed with the help of covariance matrix of the bubble position data. Hydrodynamical cavitating bubbles were generated from 0.45 cm long micro probe with 152μm inner diameter under 10 to 120 bars pressures and monitored via Particle Shadow Sizing technique. Proposed methods enabled to quantize the increasing inlet pressure effect on bubbly cavitating multi-phase flow.

Visualization of Spray Structure at the Outlet of the Micro Orifices

Spray formation occurring at the outlet of short microchannels/micro orifices due to the cavitation phenomenon is of great importance in biomedical and engineering applications. The spray characteristics are affected dramatically by the flow regime in the micro orifice. If properties of the flow are identified in the outlet of the nozzle, the treatment of the spray can be predicted. These properties can be used as boundary conditions. The experimental investigations show that the cavitation phenomenon occurs in the orifice and strongly affects the spray characteristics. However, visualization of the spray at the outlet of the micro orifice is a challenging task, since the phenomena related to the spray are occurred in very small scale and also the region near to the micro orifice is not clear. Therefore there is an urgent need to new and advanced visualization techniques and measurement equipments. In this study, spray formation and atomization, bubble evolution at the outlet of a short microchannel of an inner diameter of 152 μm were experimentally studied at different injection pressures with the use of a high speed visualization system. High speed visualization was performed at four different segments to cover ∼15 mm distance beginning from the microchannel outlet to understand the spray formation mechanism. It was observed that cavitating bubbly flow is strongly affected by injection pressure. Up to an injection pressure of 50 bars bigger size droplets form at the outlet, while beyond 50 bar injection pressure, cavitation erosion of intensified cavitation becomes dominant leading to smaller droplet sizes and a more conical spray. The results showed a good agreement with previous studies. This energy could be exploited in several applications, where destructive effects of bubbly cavitating flows are needed.© 2015 ASME

Biomedical device prototype based on small scale hydrodynamic cavitation

This study presents a biomedical device prototype based on small scale hydrodynamic cavitation. The application of small scale hydrodynamic cavitation and its integration to a biomedical device prototype is offered as an important alternative to other techniques, such as ultrasound therapy, and thus constitutes a local, cheap, and energy-efficient solution, for urinary stone therapy and abnormal tissue ablation (e.g., benign prostate hyperplasia (BPH)). The destructive nature of bubbly, cavitating, flows was exploited, and the potential of the prototype was assessed and characterized. Bubbles generated in a small flow restrictive element (micro-orifice) based on hydrodynamic cavitation were utilized for this purpose. The small bubbly, cavitating, flow generator (micro-orifice) was fitted to a small flexible probe, which was actuated with a micromanipulator using fine control. This probe also houses an imaging device for visualization so that the emerging cavitating flow could be locally targeted to the de...

Design, prototyping and control of a flexible cystoscope for biomedical applications

Kidney stone and prostate hyperplasia are very common urogenital diseases all over the world. To treat these diseases, one of the ESWL (Extracorporeal Shock Wave Lithotripsy), PCNL (Percutaneous Nephrolithotomy), cystoscopes or open surgery techniques can be used. Cystoscopes named devices are used for in-vivo intervention. A flexible or rigid cystoscope device is inserted into human body and operates on interested area. In this study, a flexible cystoscope prototype has been developed. The prototype is able to bend up to ±40°in X and Y axes, has a hydrodynamic cavitation probe for rounding sharp edges of kidney stone or resection of the filled prostate with hydrodynamic cavitation method and contains a waterproof medical camera to give visual feedback to the operator. The operator steers the flexible end-effector via joystick toward target region. This paper presents design, manufacturing, control and experimental setup of the tendon driven flexible cystoscope prototype. The prototype is 10 mm in outer diameter, 70 mm in flexible part only and 120 mm in total length with flexible part and rigid tube. The experimental results show that the prototype bending mechanism, control system, manufactured prototype parts and experimental setup function properly. A small piece of real kidney stone was broken in targeted area.