Dhiman Chatterjee

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.

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.

Transdermal drug delivery (TDD), which enables targeted delivery with microdosing possibilities, has seen much progress in the past few years. This allows medical professionals to create bespoke treatment regimens and improve drug adherence through real-time monitoring. TDD also increases the effectiveness of the drugs in much smaller quantities. The use of polymers in the drug delivery field is on the rise owing to their low cost, scalability and ease of manufacture along with drug and bio-compatibility. In this work, we present the design, development and characterization of a polymer-based TDD platform fabricated using additive manufacturing technologies. The system consists of a polymer based micropump integrated with a drug reservoir fabricated by 3D printing and a polymer hollow microneedle array fabricated using photolithography. To the best of our knowledge, we present the fabrication and characterization of a 3D-printed piezoelectrically actuated non-planar valveless micropump and reservoir integrated with a polymer hollow microneedle array for the first time. The integrated system is capable of delivering water at a maximum flow rate of 1.03 mL/min and shows a maximum backpressure of 1.37 kPa while consuming only 400 mW. The system has the least number of moving parts. It can be easily fabricated using additive manufacturing technologies, and it is found to be suitable for drug delivery applications.

Zero-thickness interface models are developed to describe the encapsulation of microbubble contrast agents. Two different Rheological models of the interface, Newtonian (viscous) and viscoelastic, with rheological parameters such as surface tension, surface dilatational viscosity, and surface dilatational elasticity are presented to characterize the encapsulation. The models are applied to characterize a widely used microbubble based ultrasound contrast agent. Attenuation of ultrasound passing through a solution of contrast agent is measured. The model parameters for the contrast agent are determined by matching the linearized model dynamics with measured attenuation data. The models are investigated for its ability to match with other experiments. Specifically, model predictions are compared with scattered fundamental and subharmonic responses. Experiments and model prediction results are discussed along with those obtained using an existing model [Church, J. Acoust. Soc. Am. 97, 1510 (1995) and Hoff et al., J. Acoust. Soc. Am. 107, 2272 (2000)] of contrast agents. © 2005 Acoustical Society of America.

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.

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.

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.

Numerical studies on rocket pumps are computationally expensive and hence the secondary passages such as sidewall clearance gaps, wear ring gaps, axial balancing mechanism, coolant/lubricant paths, etc. in the pump are usually not considered. In this study, a liquid propellant pump with and without secondary passages are modelled and flow simulation results are compared to analyse the differences in cavitation, vortices and radial force predictions arising due to the presence/absence of the secondary flow passages. Single-phase and multiphase simulations are conducted for the design and two off-design points. It is predicted that the presence of secondary passages has a significant effect on the type of cavitation instability predicted and on the volume of cavity generated in the inducer due to which the radial forces generated also differ significantly. The presence of secondary passages predicted large fluctuations from the average radial forces generated by the inducer. These are not obtained if the leakages are not considered. This type of underprediction during the design phase might cause severe wear and tear in the bearings during actual operation. Thus, this study stresses the need for incorporating the secondary passages even at the design stages. This study also highlights the possibility of cavitation instability type manipulation using some means in the inducer which would be significant for cavitation control research in rocket pumps.

In gasoline direct injection engines, fuel injector nozzle is one of the vital components that determine the efficiency of fuel atomization which controls combustion and emission. There is an increased focus on developing better nozzles by studying the internal flow behavior especially during the needle transient phase and at the end of injection phase. Multiphase flow characteristics involving cavitation and hydraulic flip are observed inside the nozzle during its operation. At the end of injection, fuel inside the nozzle sac and nozzle holes is purged with the gas from the engine cylinder. The efficiency of this purging process is critical to prevent the carbon deposit formation on the wall of nozzle holes and on the surface of the nozzle tip. In this article, a numerical method is presented to predict the internal nozzle flow during the needle movement and during the end of injection to predict the purging capacity of a gasoline direct injection nozzle. Needle motion is accomplished using a moving mesh method via a user-defined function. The numerical model is compared with the X-ray measurements from the literature. Based on the validated model, the study is extended to analyze various parameters like injection pressure, nozzle hole location, number of nozzle holes and the inlet rounding of the nozzle hole which affects the effectiveness of nozzle purging. Fuel wetting at the nozzle tip after the end of injection is also numerically modeled to evaluate the thickness profile of the thin liquid film.

Micron-size bubbles encapsulated by a stabilizing layer of surface-active materials are used in medical ultrasound imaging and drug delivery. Their destruction stimulated by ultrasound plays a critical role in both applications. We investigate the destruction process of microbubbles in a commercially available contrast agent by measuring the attenuation of ultrasound through it. The measurement is performed with single-cycle bursts from an unfocused transducer (with a center frequency of 5 MHz) for varying pressure amplitudes at 50-, 100-, and 200-Hz pulse repetition frequencies (PRF) with duty cycles 0.001%, 0.002%, and 0.004%, respectively. At low excitation, the attenuation is found to increase with time. With increased excitation level, the attenuation level decreases with time, indicating destruction of microbubbles. There is a critical pressure amplitude (∼1.2 MPa) for all three PRFs, below which there is no significant bubble destruction. Above the critical pressure amplitudes the rate of destruction depends on excitation levels. But at high-pressure amplitudes the destruction becomes independent of excitation pressure amplitude. The results are interpreted to identify two different mechanisms of bubble destruction by its signature in attenuation, namely, slow dissolution by diffusion and catastrophic shell rupture. The different modes are discussed in detail with their implications in medical applications. © 2005 American Institute of Physics.