A review of diaphragmless shock tubes for interdisciplinary applications

Shock tubes have emerged as an effective tool for applications in various fields of research and technology. The conventional mode of shock tube operation employs a frangible diaphragm to generate shockwaves. The last half-century has witnessed significant efforts to replace this diaphragm-bursting method with fast-acting valves. These diaphragmless methods have good repeatability, quick turnaround time between experiments, and produce a clean flow, free of diaphragm fragments in contrast to the conventional diaphragm-type operation. The constantly evolving valve designs are targeting shorter opening times for improved performance and efficiency. The present review is a compilation of the different diaphragmless shock tubes that have been conceptualized, developed, and implemented for various research endeavors. The discussions focus on essential factors, including the type of actuation mechanism, driver-driven configurations, valve opening time, shock formation distance, and operating pressure range, that ultimately influence the shockwave parameters obtained in the shock tube. A generalized mathematical model to study the behavior of these valves is developed. The advantages, limitations, and challenges in improving the performance of the valves are described. Finally, the present-day applications of diaphragmless shock tubes have been discussed, and their potential scope in expanding the frontiers of shockwave research and technology are presented.Comment: Review paper, 31 pages, 18 figures, manuscript draf

Development of a novel miniature detonation-driven shock tube assembly that uses in situ generated oxyhydrogen mixture

A novel concept to generate miniature shockwaves in a safe, repeatable, and controllable manner in laboratory confinements using an in situ oxyhydrogen generator has been proposed and demonstrated. This method proves to be more advantageous than existing methods because there is flexibility to vary strength of the shockwave, there is no need for storage of high pressure gases, and there is minimal waste disposal. The required amount of oxyhydrogen mixture is generated using alkaline electrolysis that produces hydrogen and oxygen gases in stoichiometric quantity. The rate of oxyhydrogen mixture production for the newly designed oxyhydrogen generator is found to be around 8 ml/s experimentally. The oxyhydrogen generator is connected to the driver section of a specially designed 10 mm square miniature shock tube assembly. A numerical code that uses CANTERA software package is used to predict the properties of the driver gas in the miniature shock tube. This prediction along with the 1-D shock tube theory is used to calculate the properties of the generated shockwave and matches reasonably well with the experimentally obtained values for oxyhydrogen mixture fill pressures less than 2.5 bars. The miniature shock tube employs a modified tri-clover clamp assembly to facilitate quick changing of diaphragm and replaces the more cumbersome nut and bolt system of fastening components. The versatile nature of oxyhydrogen detonation-driven miniature shock tube opens up new horizons for shockwave-assisted interdisciplinary applications. Published by AIP Publishing

Diaphragmless shock wave generators for industrial applications of shock waves

The prime focus of this study is to design a 50 mm internal diameter diaphragmless shock tube that can be used in an industrial facility for repeated loading of shock waves. The instantaneous rise in pressure and temperature of a medium can be used in a variety of industrial applications. We designed, fabricated and tested three different shock wave generators of which one system employs a highly elastic rubber membrane and the other systems use a fast acting pneumatic valve instead of conventional metal diaphragms. The valve opening speed is obtained with the help of a high speed camera. For shock generation systems with a pneumatic cylinder, it ranges from 0.325 to 1.15 m/s while it is around 8.3 m/s for the rubber membrane. Experiments are conducted using the three diaphragmless systems and the results obtained are analyzed carefully to obtain a relation between the opening speed of the valve and the amount of gas that is actually utilized in the generation of the shock wave for each system. The rubber membrane is not suitable for industrial applications because it needs to be replaced regularly and cannot withstand high driver pressures. The maximum shock Mach number obtained using the new diaphragmless system that uses the pneumatic valve is 2.125 +/- 0.2%. This system shows much promise for automation in an industrial environment

Computational and Microstructural Stability Analysis of Shock Wave Interaction with NbB2-B4C-Based Nanostructured Ceramics

Despite extensive research on developing different transition metal boride composites for aero-thermostructural applications, the understanding of the shockwave interaction using high pressure shock testing facilities and computational simulation of such interactions are much less explored. This aspect is even more important for much less explored ceramics, like NbB2-based materials. While addressing this aspect, the present investigation reports the thermostructural stability of spark plasma sintered NbB2-(0-40) mol % B4C composites under the hypersonic aero-thermodynamic conditions using a miniature detonation-driven shock tube facility. All the ceramic discs underwent mild surface oxidation, as a consequence to impulsive load together with the thermomechanical shock. Using the in situ recorded pressure pulse data together with conjugate heat transfer analysis, spatiotemporal evolution of ceramic surface temperature was computationally analyzed for the given test conditions. Importantly, the NbB2-(0 and 20) mol % B4C composite retained structural integrity even after exposure to 10 shock pulses with maximum reflected shock temperature and pressure of 5000 K and 37.5 MPa, respectively. In contrast, NbB2-40 mol % B4C underwent structural failure by shattering to pieces. An attempt has been made to rationalize such results on the basis of thermal shock resistance parameters, estimated using the Kingery and Hasselman model. It is observed that NbB2-(0 and 20) mol % B4C shows higher crack propagation resistance, that is, 20 and 30%, respectively, under thermal shock (R `') than NbB2-40 mol % B4C. Interestingly, all the shock exposed NbB2-B4C ceramics show a measurable increase in hardness, which is attributed to transient melting and solidification of constituent phases due to interaction with shock heated gas, for a short duration of similar to 5 ms. Taken together, the present study establishes the potential of NbB2-B4C composites for aero-thermostructural applications

Successful treatment of biofilm infections using shock waves combined with antibiotic therapy (vol 5, 17440, 2015)

This corrects the article DOI: 10.1038/srep17440

Successful treatment of biofilm infections using shock waves combined with antibiotic therapy

Many bacteria secrete a highly hydrated framework of extracellular polymer matrix on suitable substrates and embed within the matrix to form a biofilm. Bacterial biofilms are observed on many medical devices, endocarditis, periodontitis and lung infections in cystic fibrosis patients. Bacteria in biofilm are protected from antibiotics and >1,000 times of the minimum inhibitory concentration may be required to treat biofilm infections. Here, we demonstrated that shock waves could be used to remove Salmonella, Pseudomonas and Staphylococcus biofilms in urinary catheters. The studies were extended to a Pseudomonas chronic pneumonia lung infection and Staphylococcus skin suture infection model in mice. The biofilm infections in mice, treated with shock waves became susceptible to antibiotics, unlike untreated biofilms. Mice exposed to shock waves responded to ciprofloxacin treatment, while ciprofloxacin alone was ineffective in treating the infection. These results demonstrate for the first time that, shock waves, combined with antibiotic treatment can be used to treat biofilm infection on medical devices as well as in situ infections

Is cavitation a truly sensible choice for intensifying photocatalytic oxidation processes? – Implications on phenol degradation using ZnO photocatalysts

Phenols are recalcitrant compounds that constitute the majority of organic contaminants in industrial wastewaters. Their removal at large scales require a combination of various processes to reach the desired discharge quality. An extensive body of work has already been published in the area of phenol removal from wastewater, however none of them have focussed on a truly ‘sensible’ approach for coupling advanced oxidation processes (AOPs). Rather, a higher removal efficiency was targeted by unduly complicating the process by combining multiple AOPs. The most influential AOP as the primary method typically driven by the nature of the pollutant should form the basis for a hybrid AOP followed by a complementary AOP to intensify the oxidation process. This strategy is lacking in current literature. We address this knowledge gap directly by systematically identifying the best hybrid process for ZnO mediated photocatalysis of phenol. Either a cavitation mediated pre-treatment of ZnO or cavitation-photocatalysis-peroxide based hybrid AOP was investigated. While the pre-treatment approach led to >25% increase in phenol oxidation compared to bare ZnO photocatalysis, the hydrodynamic cavitation-photocatalysis-peroxide based system was found to have a cavitational yield 5 times higher than its acoustic cavitation counterpart. A new phenomenon known as the ‘pseudo staggered effect’ was also observed and established in hydrodynamic cavitation mediated photocatalysis-peroxide hybrid process for the first time. While we demonstrated that cavitation is a truly ‘sensible’ choice to enhance photocatalysis, the nature of the pollutant under investigation must always be the key driver when designing such hybrid AOPs