Rajnish Sharma

Fluid Dynamics-Based Analytical Model for Synthetic Jet Actuation

An analytical model for synthetic jet actuation based on the laws of fluid dynamics is presented. A synthetic jet actuator consists of a cavity with a driven wall and an orifice. Under actuation, the wall is oscillated, resulting in an oscillatory flow through the orifice. In the model, the driven wall is modeled as a single-degree-of-freedom mechanical system, which is pneumatically coupled to the cavity-orifice arrangement acting as a Helmholtz resonator. The latter was modeled using the unsteady form of the continuity and Bernoulli equations with a loss term. The model was validated against experimental data available in the published literature, and very good agreement is obtained between the predicted and measured frequency responses as well as for the phase relationships between velocities and pressures. The model and analysis based on it provide valuable insights into the behavior of synthetic jet actuators and reveal that air in the actuator cavity exhibits compressibility at all frequencies beyond the Helmholtz resonance frequency.

The influence of Helmholtz resonance on internal pressures in a low-rise building

Abstract This paper deals with an investigation of the phenomenon of Helmholtz resonance under oblique wind flow, and an examination of the applicability of the quasi-steady approach to internal pressures in buildings with a dominant opening. Studies on a 1:50 scale model of the Texas Tech University (TTU) test building in a boundary layer simulation show that ‘Helmholtz resonance under oblique wind flow’ produces an extremely strong response in internal pressure fluctuations, in comparison with that obtained under normal onset flow. It is verified that ‘eddy dynamics over the opening’ rather than ‘freestream turbulence’ is responsible for the intense excitation at oblique flow angles, implying that even if the Helmholtz resonance frequency were to be in the tail of the freestream turbulence spectrum, severe excitation would still be possible.Experimental measurements of internal pressures for a range of opening situations also reveal that the quasi-steady approach is inapplicable in the prediction of peak internal pressures. Furthermore, it is demonstrated that while the provisions of the Australian/New Zealand wind loading code—AS/NZS1170.2:2002, which is based upon the quasi-steady method, is adequate as far as mean internal pressures are concerned, it however underpredicts peak internal pressures in some situations. In particular, for the range of situations studied, measurements indicated that peak pressures were up to 25% higher than the AS/NZS1170.2:2002 provisions, in the case of openings in the positive pressure and sidewall regions. It is also shown that for openings located in the sidewall region, peak internal pressures could be just as extremely positive as it can be negative. It is suggested that in the calculation of internal pressures, the AS/NZS1170.2:2002 provide for the use of local pressure factors K l , that are at present applied only to external pressure calculations. Secondly, the code should provide for internal pressure coefficients to be both negative and positive, when openings are located in sidewall regions. Finally, in order to account for the effects of additional fluctuations arising from Helmholtz resonance oscillations, the possibility of the use of an internal pressure factor K i should be explored.

A wind generator system with an integrated boost converter

This paper presents a wind generator system with an integrated boost converter. With the proposed concept, the phase inductances of the generator can effectively be used as the boost inductor, eliminating the need for a separate inductor that is used in conventional wind turbine systems. Two topologies that allow for the use of phase inductances as the boost inductor are presented. The performance of the proposed generator system is evaluated using a novel SmartBlade wind turbine, which consists of extendible blades and a custom made PM generator. Simulations and experimental evidence of a 1.5 kW prototype system are presented to demonstrate the viability of the proposed concept, which would be attractive for small scale wind turbine systems.

Comprehensive Investigation of Diffuser/Nozzle Element at Low Reynolds Number Aimed at Valveless Pump Design

The performance of diffuser/nozzle element in valveless pumps depends upon a number of geometrical and operational parameters. In this study, the characteristics of low Reynolds number (Re < 100) flow through conical and planar diffuser/nozzle elements with varying half-angle and area ratio (AR) were investigated with simulations and experiments. The optimal half-angle, at which maximum diffuser efficiency occurs, was found to decrease with Reynolds number for both conical and planar elements. Therefore, the results provide a selection criterion for a diffuser/nozzle pair in a valveless micropump design, where no such criterion is available so far.

Jet Impingement Heat Transfer from a Circular Cylinder Located Between Confining Walls

*The heat transfer characteristics of a circular cylinder (diameter d) located between confining walls (at varying separation distance H apart) exposed to slot jet of air (of width w) from a contoured nozzle, and at a range of spacing z from the jet exit, has been studied experimentally and computationally. The study focussed on Reynolds number Re in the range 1000 – 12000. The results reveal that while the slot jet impinging on a cylinder in confined space generally yields higher average heat transfer rates relative to the uniform cross flow case; these are however almost always found to yield lower heat transfer rates in comparison with corresponding slot jet impingement without confining walls. Furthermore, in the Reynolds number range studied, it was found that a dimensionless confinement spacing H/d = 10 exists which consistently exhibits a minimum in cylinder heat transfer rate over all the non-dimensional jet exit to cylinder spacing z/w and ratio of cylinder diameter to slot width d/w that were investigated. It was established that reduction in heat transfer for confinements H/d between 10 and 16 is due to the jet becoming unstable and thereby periodically flapping across the cylinder, switching between the confining walls, in tandem with vortex shedding from the cylinder. This reduces the effectiveness of impingement and hence reduces the heat transfer rates. It is therefore concluded that jet impingement does not always enhance heat transfer rate, but may in fact reduce it under conditions in which the impingement target is located in the midst of confining walls. It was observed that the average of all the Nusselt numbers in a confined space reduces by about 17% when compared with a non confined cylinder. In summary therefore, the influence of confining walls around the cylinder has an unfavourable impact on the flow and therefore the heat transfer rates with jet impingement. The reduction in heat transfer rates with confining walls implies that a jet impingement heat transfer system designed using data obtained for jet impingement on a non-confined cylinder could compromise the effectiveness of the system, and may have a large bearing on the quality, efficiency and productivity as well as on the health and safety aspects of products and processes.

Low velocity digital air flow sensor from 3D printed PEDOT:PSS micro-hair structures

This paper reports a novel method for digital sensing of low-velocity air flow using high aspect-ratio 3D printed conducting polymer (PEDOT:PSS) micro-hair structures (1000 μm long, 5.5±0.5 μm diameter). By implementing multiple micro-hair structures as micro-switches that respond to air flows of particular velocities, a low-velocity digital flow sensor capable of detecting air flow in the range of 61 mm/s to 99 mm/s is demonstrated.

A PCB inductive sensor for compact ionic polymer metal composite (IPMC) displacement sensing used in biomedical pumps

This paper proposed the implementation of an inductive sensor which is able to accurately control the diaphragms deflection of portable biomedical pumps. Ionic polymer metal composite (IPMC), whose low actuating voltage (< 5V), high power efficiency and biocompatibility makes it a proven candidate for biomedical applications. However, due to its inherent nonlinear and time-variant attributes, relevant control methods with reliable and space-saving deflection sensors are required for IPMC driving applications. A practical, low cost and importantly, compact inductive sensor fabricated on a printed circuit board (PCB) is proposed and experimentally evaluated here. System identification and proportional-integral-derivative (PID) control results showed comparable performances as that of laser sensors and thus prove it to be a feasible alternative.

Chapter 15:Miniature Pump with Ionic Polymer Metal Composite Actuator for Drug Delivery

Miniature pumps are the key components in microfluidic systems. They are widely used in many applications such as lab-on-chip, micro-total analysis systems and micro-dosage systems. The most important component in a miniature pump is the actuating mechanism because it is directly related to factors such as flow rate, driving source and cost. Currently, the most common driving mechanisms are piezoelectric, electromagnetic, thermo-pneumatic and electrostatic. They all have their own advantages and disadvantages. The main advantages of using ionic polymer metal composites (IPMCs) as the actuating mechanisms are that they have large displacements at low voltages, which will correspond to large flow rates, making them good for long lifespans in portable and embedded applications. Here, we demonstrate a miniature pump actuated by an IPMC controlled using a proportional-integral-derivative controller with iterative feedback tuning. This chapter also shows the design, modelling and simulation of a valveless pump using a diffuser/nozzle structure.

a research platform for a smart-blade wind generation system

A research platform, which is designed for a novel smart-blade wind turbine system, is presented. The proposed platform, which allows for the integration of different renewable sources, consists of a smart-blade wind turbine, a permanent magnet (PM) generator, a rectifier, a hybrid super-capacitor/battery energy buffer, and a boost and bi-directional converter. The PM generator, designed for the power profile of the smart-blade turbine, is driven by an induction motor drive to emulate the wind conditions. The research platform is implemented in a Simulink/MATLAB environment with a dSPACE interface for real time control. It has a controller for peak power point tracking (PPPT) and a user interface for real time metering, and is expected to facilitate rapid prototyping and energy related research.

A modular distributed generation system with peak power point tracking

A modular based research platform that is suitable for combined operation of distributed generation sources is presented. The modular concept is adopted with a view to allow for easy integration of various renewable sources such as PV cells, bio-gas etc. A hybrid supercapacitor-battery storage and a converter, which facilitates bi-directional energy flow, are used to improve the versatility of the system. The proposed concept is demonstrated with peak power point tracking of a novel smart-blade wind turbine system. A prototype system is implemented with Simulink and dSPACE, and results are presented in relation to a peak power point tracking algorithm. A user interface, which is implemented in Controldesk and allows for real time metering and performance analysis, is also presented.