| dc.description.abstract | The emerging paradigms of shockwave research have opened up new horizons for interdisciplinary applications. This has inevitably driven research towards studying the propagation of shockwaves in miniature shock tubes (tube diameters typically in the range of 1−10 𝑚𝑚). Studies have revealed that while operating at this diameter range and low initial pressures (typically 𝑃1 < 100 𝑚𝑏𝑎𝑟) leading to low values of characteristic Reynolds numbers (typically 𝑅𝑒′ < 23,000 𝑚−1), results in the boundary layer playing a major role in shockwave attenuation. But there are very few studies addressing shockwave attenuation when shock tubes are operated at higher Reynolds number. Pressure measurements and visualization studies in shock tubes of these length scales are also seldom attempted due to practical difficulties. Given that premise, in the present work the shockwave attenuation due to wall effects and non-ideal diaphragm rupture in shock tubes of hydraulic diameters 2𝑚𝑚, 6𝑚𝑚 and 10𝑚𝑚 has been investigated at ambient initial driven section conditions (𝑇1 = 300 𝐾 and 𝑃1 = 1 𝑏𝑎𝑟 resulting in Reynolds number in the range 70,212 𝑚−1 – 888,627 𝑚−1). In this study pressure measurements and high-speed visualization have been carried out to find the effect of the pressure ratio, temperature ratio and molecular weights of driver gas on the shock attenuation processes. In order to study the effects of the driver/driven gas temperature ratios on the shock attenuation process, a new in-situ oxyhydrogen (hydrogen and oxygen gases in the ratio 2:1) generator has been developed. Using this innovative device, the miniature shock tubes are also run in the detonation mode (forward facing detonation wave). The results obtained using helium and nitrogen driver gases for these shock tubes reveal that as the hydraulic diameter of the shock tube is reduced, a larger diaphragm pressure ratio is required to obtain a particular strength of shockwave. The attenuation in the shockwave is found to be a function of the driver gas properties namely specific heat ratio (𝛾4), molecular weight (𝑀𝑤4), temperature (𝑇4) as well as the diaphragm opening time of the shock tube in addition to the parameters 𝐷,𝑃21,𝐿/𝐷,𝑅𝑒 and 𝑃1 as already suggested in previous reports. The visualization studies reveal that the effect of diaphragm opening time leading to longer shock formation distances appears to influence the shockwave attenuation process at these shock tube diameters. Further, it is also found that the strength of the shockwave reduces when the ratio 𝑇4/𝑇1 is higher. It is also seen that the length of the driven sections must be less than twice the length of the driver sections to reduce attenuation.
Based on the understanding of the nature of supersonic flow in a miniature shock tubes, a novel shock/blast wave device has been developed for certain innovative biotechnology applications such as needleless vaccine delivery and cell transformations. The new device has an internal diameter of 6 𝑚𝑚 and by varying the length of the driver/driven sections either shock or blast waves of requisite strength and impulse can be generated at the open end of the tube. In the shock tube mode of operation, shockwaves with steady time duration of up to 30 𝜇𝑠 have been generated. In the blast tube mode of operation, where the entire tube is filled with oxyhydrogen mixture, shockwaves with peak pressures of up to 550 𝑏𝑎𝑟 have been obtained with good repeatability. An attempt to power this device using solar energy has also given successful results. Visualization of the open end of the detonation driven shock tube reveals features typical of flow from the open end of shock tubes and has helped in quantifying the density field. The subsequent instants of the flow resemble a precursor flow in gun muzzle blast and flash. Typical energy levels of the shock/blast waves coming out this device is found to be about 34 𝐽 for an oxyhydrogen fill pressure of 5.1 𝑏𝑎𝑟 in the shock tube operation mode. Transformation of E.coli, Salmonella Typhimurium and Pseudomonas aeruginosa bacterial strains using the device by introducing plasmid DNA through their cell walls has been successfully carried out. There is more than twofold increase in the transformation efficiency using the device as compared to conventional methods. Using the same device, needleless vaccine delivery in mice using Salmonella has also been demonstrated successfully.
Overall, in the present thesis, a novel method for generating shockwaves in a repeatable and controllable manner in miniature scales for interdisciplinary applications has been proposed. Also, it is the first time that experiments with the different diameter miniature shock tubes have been carried out to demonstrate the attenuation of shockwaves as the hydraulic diameter of the shock tube decreases. Future research endeavors will focus on quantitative measurement of the particle velocity behind the shock waves, and also on the nature of the boundary layers to further resolve the complex flow physics associated with supersonic flows in these miniature shock tubes. | en_US |
