Vortex tube (VT) is a mechanical device with no moving parts. The fundamental principle of Vortex Tube is that it can split an incoming fluid flow of a constant pressure and constant temperature gas stream into two separate low pressure streams, one having higher enthalpy and the other having lower enthalpy than the inlet flow. So this device essentially works as a temperature separator. On separation from the device, a warmer flow exits through a terminal which is called the “hot end” and a low temperature stream comes out from another terminal known as the “cold end”. Just with a few bar pressure of compressed air at room temperature can produce a hot stream temperature of about 150°C and a cold stream temperature of about - 40°C. This temperature separation scheme allows us to get cooling and heating effect simultaneously using the same device which makes the Vortex tube one of the popular mechanical equipment and is used in many fields of engineering. The cooling or heating effect produced by this device is largely dependent on geometric parameters of the device itself. Since no exact theoretical correlation is there between the geometric parameters and the cooling (or heating) effect produced, VT design is solely based on empirical relations. There are quite a few geometric parameters which affect the cooling effect of this device and all the empirical correlation are needed to design the optimum VT for maximum cooling/heating effect. These relations can be derived in two ways, either by numerical methods or by experimental investigations. The first part of the thesis important geometric parameter of the VT namely the ratio of the “cold end” diameter (to the “tube diameter” , which has been numerically optimized in this work to achieve maximum temperature separation. In our efforts to design a VT based refrigeration system, optimization of the VT itself is not enough. A suitable heat exchanger (HX) which can extract the cold enthalpy from the VT also needs to be designed and cascaded with the VT to get the complete refrigeration system. The second part of the thesis is solely dedicated to the design of a suitable HX that can be used alongside a VT to produce refrigeration. The HXs design can be approached from two directions, dimensional aspect and material aspect. Rather than focusing on the dimensional aspect in this work we have concentrated of the material aspect of HX design. It is fairly obvious that the thermal conductivity (TC) of the HX material will play a crucial role on the cooling effect of the refrigeration system. Conventional metals with high TC can be used to design HXs but the downsides of using pure metals such as Copper, Iron are that they are heavy, quite expensive and highly reactive to corrosive fluids. Because of this, high TC ceramic material such as Aluminium Nitride (AlN) is quite often used to fabricate HXs and they are used for spot cooling in electronic systems. AlN has TC of 160 W/m-K which is high but not as high as of Copper or Iron. TC of AlN can be increased by mixing the right volume fraction of metal powder (such as pure Aluminium) with it to a great extent. So in a nutshell, instead of using pure AlN, if we use the particle reinforced binary composite [AlN + Al (powder)] to design a HX, we would achieve the benefits of having high TC as well as properties such as anti-corrosiveness, cost effectiveness and weight reduction. In the above context, prediction of TC of particle reinforced composite materials containing a base material of low TC and a filler material of high TC is of utmost importance. Till now a very few analytical heat transfer models are available in the literature that can accurately predict the TC value of such composites especially when high volume fraction of filler particles is added to the base material or if more than one type of filler particles are added. So in this thesis, three analytical heat transfer models have been developed that can predict the TC of binary as well as tertiary particle reinforced composites. The third and the final segment of the thesis deals with the performance study of a refrigeration system comprised of the optimized VT cascaded with a suitable HX made out of a particle reinforced composite material. The numerical results show how the HX effectiveness improves as the volume fraction of the filler particles in the composite increases. The key results of the works described in the thesis are as follows: • Through extensive numerical simulations it is shown that for = 0.5, the temperature separation in a VT is maximum. • The heat transfer models developed to predict the thermal conductivity of binary composites, shows the trend of how thermal conductivity varies with increasing volume fraction of filler. It has been shown that initially the thermal conductivity increases linearly with a small slope, then after a critical volume fraction an abrupt increment of slope is observed due to the formation of continuous heat conduction paths within the composite. Further increase in volume fraction shows linear increment of thermal conductivity with lesser slope as before. • The heat transfer model developed to predict the thermal conductivity of tertiary composites is suitable for low volume fraction (< 20 %). The model shows the addition of one component into the base matrix affects the distribution of the other component which is observed through the covariance. • The last part of the thesis shows that compared to a pure AlN heat exchanger, a heat exchanger made of AlN + 30 % volume fraction of pure Aluminium powder, has increased heat exchanger effectiveness by more than 50 %. Thesis outline is as follows: • Chapter 1 is a brief introduction to Vortex Tube. • Chapter 2 deals with the necessary literature review related to Vortex Tube as well as presently available heat transfer models that are equipped to handle composite materials to predict their TC. • Chapter 3 elaborates numerical modeling and optimization of a critical parameter ( to achieve maximum temperature separation in a VT. • Chapter 4 presents a stochastic heat transfer model to estimate the TC of Binary particle reinforced composites containing low volume fraction of filler particles. • Chapter 5 describes the development of a computational heat transfer model to predict the TC of Particle Reinforced Binary Composite materials containing high volume fraction of filler element. • Chapter 6 deals with a stochastic heat transfer model to calculate TC of Particle Reinforced Tertiary Composite materials containing low volume fractions of filler elements. • Chapter 7 consolidates all the necessary concepts and data from previous chapters to design the final cascaded VT based refrigeration system and presents a performance study. • The last chapter summarizes the entire work along with scope for future work.

L’exploration des quatre planètes géantes gazeuses, Jupiter, Saturne, Neptune et Uranus, est importante pour comprendre l’évolution de notre système solaire et plus généralement de l’univers. Les sondes entrant dans l’atmosphère des géantes gazeuses ont des vitesses de 20 à 50 km/s, largement supérieures aux vitesses d’entrée atmosphérique sur les autres planètes du système solaire. Il s’agit d’un problème complexe car les conditions d’entrées sont brutales et les vitesses associées dépassent largement les capacités des installations d’essai au sol actuelles. Cette thèse examine la possibilité de simuler expérimentalement les conditions d’entrées proposées pour Uranus et Saturne à 22.3 et 26.9 km/s avec un tube d’expansion à piston libre. D’abord, la possibilité de simuler les conditions directement en recréant la vitesse d’entrée réelle a été étudiée. Il a été trouvé qu’il était possible de simuler l’entrée d’Uranus mais seulement avec de grandes incertitudes. Pour cette raison, il a été proposé d’utiliser une substitution du gaz d’essai établie, dans lequel soit le pourcentage d’hélium dans l’atmosphère H2/He est augmenté, soit l’hélium est remplacé par du néon, un gaz noble plus lourd. Cela permet de simuler uniquement les conditions postchoc des entrées. Théoriquement, il a été constaté que ces substitutions permettaient de simuler l’entrée Uranus ou Saturne, ce qui a été confirmé expérimentalement à l’aide d’hélium. Notant l’intérêt actuel d’envoyer des sondes d’entrée atmosphérique vers ces deux planètes, cette étude a démontré que les capacités expérimentales requises sont disponibles pour la réalisation d’expériences simulées avec les modèles d’essais. / Exploration of the four gas giant planets, Jupiter, Saturn, Uranus, and Neptune, is important for understanding the evolution of both our solar system and the greater universe. Due to their size, flight into the gas giants involves atmospheric entry velocities between 20 and 50 km/s. This is a complex issue because the entry conditions are harsh but the related velocities are mostly beyond the capabilities of current ground testing facilities. As such, this thesis examines the possibility of experimentally simulating proposed Uranus and Saturn entries at 22.3 and 26.9 km/s in a free piston driven expansion tube, the most powerful type of impulse wind tunnel. Initially, the possibility of simulating the conditions directly by re-creating the true flight velocity was investigated. It was found to be possible to simulate the 22.3 km/s Uranus entry, but not without large uncertainties in the test condition. For this reason, it was proposed to use an established test gas substitition where the percentage of helium in the H2/He atmosphere is increased, or the helium is substituted for the heavier noble gas neon. This allows just the post-shock conditions of the entries to be simulated. Theoretically it was found that these substitutions allowed both Uranus or Saturn entry to be simulated, which was confirmed experimentally using helium. Noting the current interest in sending atmospheric entry probes to both of these planets, this study has demonstrated that the required experimental capabilities are available for performing simulated experiments using test models.

All of the members of the microsporidia possess a unique, highly specialized invasion mechanism that involves the polar tube and spore wall. This chapter reviews the data on the organization, structure, and function of this invasion organelle. The application of immunological and molecular techniques and recent genome sequencing data has resulted in the identification of multiple polar tube and spore wall proteins (SWPs). The interactions of these identified proteins in the formation and function of the polar tube and spore wall remain to be determined. Inside the spore, the polar tube is filled with material and is often termed the polar filament; however, this chapter uses the term polar tube to refer to this structure when it is within the spore as well as when it forms a hollow tube after germination and is found outside the spore. The chapter presents details on the spore activation and discharge.

published_or_final_version / Mechanical Engineering / Master / Master of Science in Engineering

The automotive industry is required to meet improved fuel efficiency standards and stricter emission controls. Aluminum tube hydroforming is particularly well suited in meeting the goals of lighter, more fuel-efficient and less polluting cars. Its wider use in industry is hindered however by the reduced ductility and more complex constitutive behavior of aluminum in comparison to the steels that it is meant to replace. This study aims to address these issues by improving the understanding of the limitations of the process as applied to aluminum alloys. A series of hydroforming experiments were conducted in a custom testing facility, designed and constructed for the purposes of this project. At the same time, several levels of modeling of the process, of increasing complexity, were developed. A comparison of these models to the experiments revealed a serious deficiency in predicting burst, which was found experimentally to be one of the main limiting factors of the process. This discrepancy between theory and experiment was linked to the adoption of the von Mises yield function for the material at hand. This prompted a separate study, combining experiments and analysis, to calibrate alternative, non-quadratic anisotropic yield functions and assess their performance in predicting burst. The experiments involved testing tubes under combined internal pressure and axial load to failure using various proportional and non-proportional loading paths (free inflation). A number of state of the art yield functions were then implemented in numerical models of these experiments and calibrated to reproduce the induced strain paths and failure strains. The constitutive models were subsequently employed in the finite element models of the hydroforming experiments. The results demonstrate that localized wall thinning in the presence of contact, as it occurs in hydroforming as well as other sheet metal forming problems, is a fully 3D process requiring appropriate modeling with solid elements. This success also required the use of non-quadratic yield functions in the constitutive modeling, although the anisotropy present did not play as profound a role as it did in the simulation of the free inflation experiments. In addition, corresponding shell element calculations were deficient in capturing this type of localization that precipitates failure, irrespective of the sophistication of the constitutive model adopted. This finding contradicts current practice in modeling of sheet metal forming, where the thin-walled assumption is customarily adopted. / text

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