Now showing 1 - 10 of 36
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    Design and development of a piezoelectrically actuated micropump for drug delivery application
    (01-01-2014)
    Eladi, Paul Braineard
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    Micropumps form the heart of several microfluidic systems like micro total analysis system (µTAS) and drug delivery devices, which have resulted from the advancement of silicon micromachining technology. Among the different available types of micropumps, valveless micropumps are better suited for biological applications as they do not have flow-rectifying valves and are less prone to clogging and wear. However, their main drawback is low thermodynamic efficiency. This can be improved if we have a better understanding of the effects of geometry on the performance. This forms one of the objectives of this work. This chapter describes the activity on the design and development of valveless micropumps. A numerical parametric study of the performance of valveless micropumps has been carried out and is presented to bring out the effects of different geometrical parameters. Based on these design approaches, silicon-based micropumps are fabricated and characterized. The performance of one of these micropumps is compared with designed value in this work.
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    Slurry erosion wear resistance of polyurethane coatings with B4C Nano powders for hydroturbine applications
    (01-01-2013)
    Syamsundar, C.
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    Maiti, A. K.
    Hydropower generation from the Himalayan rivers in India face challenge in the form of silt-laden water. These sediments contain abrasive particles which can erode the turbine blades and reduce turbine life. This calls for the development of newer materials for turbine blade. To address this issue in the present investigation, 16Cr- 5Ni martensitic stainless steel has been selected and coated with polyurethane (PU) reinforced with boron carbide (B4C) nano particles to improve the wear resistance. With the increase of B4C content (0-2 wt %) in PU the mechanical properties and erosion wear resistance were investigated. The Shore hardness and pull off adhesion were found to increase with the increased content ofB4C nano particles and from contact angle measurement the coated surfaces are shown to be hydrophilic in nature. This condition reflects better wetting and may be good for cavitation wear resistance. Slurry erosive wear tests were done at various test conditions determined by Taguchi design of experiments of impact velocity, impingement angle, erodent size and slurry concentration. The erosion area of the PU coated samples were analyzed with scanning electron microscope (SEM) and the erosion wear mechanism is discussed Analysis of variance studies of erosion rate indicated that B4C content in PU material is the single most important parameter and interaction of impact velocity and impingement angle are proved to be significant Artificial Neural Network and Genetic Algorithm were employed to arrive at the worst possible scenario.
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    Axial-flow hydrokinetic turbine array: Optimization and performance prediction
    (01-01-2019)
    Sharma, L.
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    Hydrokinetic Turbine (HKT) systems extract energy from marine currents and offer renewable technology for supplementing the energy requirements with no significant adverse effect on the environment or the habitat. However, the power output of an axial flow HKT is lower than the conventional hydraulic turbines. Hence, instead of deploying a single turbine, identical turbines may be coupled together in an array. This demands a further development in extracting maximum power available under practical conditions. In the present work three different array configurations, rectangular, equilateral triangle and isosceles triangle configurations, are discussed and the optimized configurations are taken up for further analysis. Flow velocity profiles are used to demonstrate the effect of each configuration on velocity distribution and its relation with the resultant performance of the turbine arrays. The performance of single and array of turbines are analyzed in the proximity of free surface and equilateral triangular pattern (Array 2) is found to be the best.
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    Design methodology of hybrid turbine towards better extraction of wind energy
    (01-02-2019)
    Jacob, Joe
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    Hybrid vertical axis turbines that combine Savonius and Darrieus turbines on a single shaft have been proposed as a way of combining the excellent starting torque of Savonius turbine with the high operational efficiency of the Darrieus turbine. Although hybrid turbines with improved starting characteristics have been demonstrated in literature, the performance of these turbines at higher tip speed ratios have been poor. In this work systematic study of stand-alone Savonius and Darrieus turbines have been carried out using experimental and numerical techniques as a precursor to studying their roles in hybrid configuration. The radius ratio of the two turbines, when combined in the form of a hybrid turbine, is identified as an important parameter that dictates the performance of hybrid turbines. An expression for an optimal radius ratio is derived and a methodology for designing hybrid turbines is proposed. The efficiency in energy conversion by hybrid turbine can be expressed in terms of a parameter called effectiveness given by the ratio of power produced by the hybrid turbine to the sum of the power produced by individual Darrieus and Savonius turbines. This idea has been verified through experiments and numerical simulations.
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    Experimental investigation of cavitating structures in the near wake of a cylinder
    (01-03-2017)
    Kumar, Pankaj
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    An experimental investigation of cavitating structures in the near-wake region of a cylinder is presented. From high-speed imaging of this subcritical flow (Reynolds number of 64,000), it is found that inception of cavities occurs in the shear layer. At the developed cavitation condition, the cavities in the separated zone and the free shear layer merge. A distinct spanwise variation in cavitation activity is observed. The non-dimensionalized correlation length at inception varies from close to a non-cavitating value of about 3.5 to about 1 at developed cavitation. The non-dimensionalized length of formation, characterized by crossover of the free shear layer and the wake axis, increases from 1 to 1.8 as the cavitation number is reduced from 85% to 50% of the inception value. A frequency analysis of the cavity dynamics indicates that although the vortex shedding frequency is dominant in the shear layer, there are peaks corresponding to other frequencies in other flow regions. The presence of a sharp peak at 125 Hz, corresponding to a Strouhal number of 0.2, along with a range of frequencies, is also verified independently through measurement of fluctuating pressure at the cylinder surface.
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    Influence of duct geometry on the performance of Darrieus hydroturbine
    (01-07-2012)
    Malipeddi, A. R.
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    Computational study is carried out to develop a new duct with the purpose of improving the performance of a straight-bladed Darrieus hydroturbine. Though Darrieus turbine is very simple to construct, it has some disadvantages when compared to axial turbines. These are a lower power coefficient and a variation in the torque produced within the cycle leading to periodic loading on the components of the turbine. The main objective of the present study is to retain the simple design and fabrication procedure of Darrieus turbine while reducing the disadvantages. In this study, a new duct is developed, for a given turbine design, that reduces the variation in torque over a cycle by appropriately directing the flow upstream and downstream the turbine while increasing power conversion. At the operating point, which is at a tip-speed ratio of 2, use of a duct reduces the torque ripple by a factor of 4.15 and the power coefficient(C p)is increased to 0.63 from 0.40. By choosing the position of the turbine in the duct appropriately, it is shown that the torque ripple may be reduced by a factor of 6.37, at the expense of the power coefficient. And, a maximum C p=0.644 is observed when the turbine center coincided with the throat of the duct. Similarly, the effect of varying other parameters such as the convergence angle of the duct and its external shape on the performance of the turbine are studied through numerical simulation. It is seen that there exists an optimum value in each case. While varying the convergence angle of the duct it is observed that the maximum power coefficient and lowest torque ripple are obtained at the same value of duct half angle, equal to 27°. The dependence of the power coefficient and torque ripple on duct convergence angle is weak. The duct with straight external shape is observed to have best performance with a peak power coefficient of 0.72, while the convex external shape has a peak of only 0.51. The external shape is observed to have a negligible effect of the torque ripple factor. Significance of the emerging trends of parameters are discussed. © 2011 Elsevier Ltd.
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    Experimental investigation on two-phase flow maldistribution in parallel minichannels with U-type configuration
    (01-08-2018)
    Madanan, Umesh
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    Nayak, Rajlakshmi
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    Two-phase flow in parallel minichannels finds a number of applications. Maldistribution between parallel channels reduces both the thermal and fluid-dynamic performances. To reduce the maldistribution effect, it is important to have information about the phase split in individual channels. The present study brings out the effects of various parameters like the channel diameter, number of channels, two-phase flow regimes, and void fraction on the flow split in two-phase flow inside a system of parallel channels for a U-type configuration. Experiments are carried out with the plug and slug regimes typical to minichannel flows. High speed photography is used for flow visualization and the pressure drop values in individual channels are measured with a differential pressure transmitter to quantify maldistribution. The time averaged void fraction is found using an image processing technique. A counterintuitive non-monotonous distribution of the void fraction in the channels brings out the fact that in two-phase flow splitting, the relative distribution of the two phases does not depend on pressure drop alone. Flow configuration and the two-phase flow regime in the header play a key role. An analysis with the existing separated flow model modified for minichannels reveals that although it is possible to estimate the orders of magnitude with respect to splitting, better splitting models still need to be developed. An empirical correlation for variation of the normalized pressure drop in the parallel minichannels, as a function of dimensionless distance along the header, is developed for each of the investigated flow regimes.
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    Cavitation characteristics of S-blade used in fully reversible pump-turbine
    (01-05-2014)
    Premkumar, T. M.
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    Kumar, Pankaj
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    S-shaped blade profiles with double camber find use in fully reversible turbomachines that can extract power from tides. Though noncavitating characteristics of S-blades were determined in the past, yet characterizing cavitating flow was not carried out. This work, which is the first step in this direction, uses a two-pronged approach of experimental and numerical characterization of cavitating flow past these hydrofoils. Experimental results indicate that as the angle of attack increases in either positive or negative directions, cavitation inception number increases. Minimum cavitation effect is observed at 2 deg, which is zero lift angle of attack. For higher angles of attack (±6deg, ±4deg) and moderate or low cavitation number (σ/σi≤0.3), unsteady cloud cavitation was characterized through visual observation and from pressure fluctuation data. It was observed that for unsteady cavity shedding to take place is the length and thickness of the cavity should be more than 50% and 10% of the chord length, respectively. Predicting flow past this geometry is difficult and the problem may be compounded in many applications because of laminar-to-turbulence transition as well as due to the presence of cavitation. Present simulations indicate that the k-kL-ω transition model may be useful in predicting hydrodynamic performance of this type of geometry and for the range of Reynolds number considered in this paper. Hydrodynamic performance under cavitation indicates that pumping mode is more adversely affected by cavitation and, hence, a fully reversible turbomachine may not perform equally well in turbine and pump modes as expected from noncavitating results. Copyright © 2014 by ASME.
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    Numerical prediction of periodic cavitation shedding in cylindrical orifice
    (01-01-2015)
    Mouvanal, Sandeep
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    Burkhardt, Axel
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    Cavitation structures inside orifice of high pressure fuel injector nozzles have a major influence on internal flow and quality of spray. The present work provides a detailed understanding of the effect of injection pressure on cavitation and its shedding in the form of cloud cavities inside a cylindrical orifice. Commercial computational fluid dynamics (CFD) software, ANSYS Fluent with Reboud’s correction on the eddy viscosity term of k-ω SST turbulence model is used for the numerical investigations. Comparison of the results with literature on experimental studies shows that the employed modification of turbulent viscosity term by a user defined function helps in prediction of reentrant jet induced cavity shedding. Compressible, multi-phase simulations revealed non-cavitating, periodic cloud shedding, super cavitating and hydraulic flip regimes. Fourier transformation is performed on the time series data of fluctuating vapor fraction to predict the frequency of shedding of cavities for various cavitation numbers. It is shown that with a reduction in cavitation number, length of cavity increases and shedding frequency decreases.
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    Material characterization of the encapsulation of an ultrasound contrast microbubble and its subharmonic response: Strain-softening interfacial elasticity model
    (01-06-2010)
    Paul, Shirshendu
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    Katiyar, Amit
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    Sarkar, Kausik
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    Shi, William T.
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    Forsberg, Flemming
    Two nonlinear interfacial elasticity models-interfacial elasticity decreasing linearly and exponentially with area fraction-are developed for the encapsulation of contrast microbubbles. The strain softening (decreasing elasticity) results from the decreasing association between the constitutive molecules of the encapsulation. The models are used to find the characteristic properties (surface tension, interfacial elasticity, interfacial viscosity and nonlinear elasticity parameters) for a commercial contrast agent. Properties are found using the ultrasound attenuation measured through a suspension of contrast agent. Dynamics of the resulting models are simulated, compared with other existing models and discussed. Imposing non-negativity on the effective surface tension (the encapsulation experiences no net compressive stress) shows "compression-only" behavior. The exponential and the quadratic (linearly varying elasticity) models result in similar behaviors. The validity of the models is investigated by comparing their predictions of the scattered nonlinear response for the contrast agent at higher excitations against experimental measurement. All models predict well the scattered fundamental response. The nonlinear strain softening included in the proposed elastic models of the encapsulation improves their ability to predict subharmonic response. They predict the threshold excitation for the initiation of subharmonic response and its subsequent saturation. © 2010 Acoustical Society of America.