Faculty Publications

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    Development of micromixer for efficient mixing of blood and insulin in human arteries
    (Elsevier Ltd, 2023) Bagde, P.; Nayak, N.; Arumuga Perumal, D.
    In the present work, the computational analysis of passive micromixer with embedded obstacles is studied in detail. It also focuses on Y shaped microchannel with internal embedded obstacles. Different types of Y shaped microchannels are designed by altering the cross section, mixing length and number of obstacles. For simplicity, same velocities at both blood and insulin inlets are assumed. Microchannels are designed in CATIA V5 software and simulations were performed using ANSYS CFX 19.0 solver for steady state condition. Identification of geometric variables correlation with flow field variables is considered for better mixing design. Simulation results are compared with the help of calculating volume fraction at each section and average volume fraction at outlet with each other. It is found that, microchannel having rectangular cross section with circular and rectangular obstacles with reduced length for insulin inlet is giving highest average volume fraction at outlet. Also, one with elliptical cross section is able to give uniform average volume fraction at outlet. By observing mixing profile, it is seen that there is significant increase in mixing behaviour by introducing embedded obstacles as compared to without using it. © 2022
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    Three-dimensional multihelical microfluidic mixers for rapid mixing of liquids
    (2008) Verma, M.K.S.; Ganneboyina, S.R.; Vinayak Rakshith, R.; Ghatak, A.
    Rapid mixing of liquids is important for most microfluidic applications. However, mixing is slow in conventional micromixers, because, in the absence of turbulence, mixing here occurs by molecular diffusion. Recent experiments show that mixing can be enhanced by generating transient flow resulting in chaotic advection. While these are planar microchannels, here we show that three-dimensional orientations of fluidic vessels and channels can enhance significantly mixing of liquids. In particular, we present a novel, multihelical microchannel system built in soft gels, for which die helix angle, helix radius, axial length, and even the asymmetry of the channel cross section are easily tailored to achieve the desired mixing. Mixing efficiency increases with helix angle and asymmetry of channel cross section, which leads to orders of magnitude reduction in mixing length over conventional mixers. This new scheme of generating 3D microchannels will help in miniaturization of devices, process intensification, and generation of multifunctional process units for microfluidic applications. © 2008 American Chemical Society.
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    Comparative study of pool boiling heat transfer from various microchannel geometries
    (Elsevier Ltd, 2018) Walunj, A.; Sathyabhama, A.
    This paper presents the experimental investigation of pool boiling heat transfer enhancemrent using open microchannels. Rectangular, parabolic and stepped microchannels are fabricated on the 10 mm diameter circular copper test piece and their boiling characteristics are compared with that of the plain surface at saturated condition of distilled water. The effect of channel shape and geometrical parameter on the boiling heat transfer is studied. The channel top width and channel base width are varied from 250 ?m to 500 ?m and 500 ?m to 800 ?m, respectively. The fin tip thickness is varied from 200 ?m to 500 ?m. The channel height is fixed at 500 ?m. The morphology of bubble is observed by using high-speed camera. Compound study of bubble departure diameter and bubble frequency has proved the significant performance of parabolic and stepped microchannel. All the microchannel geometries enhanced the heat transfer rate. The modification of rectangular channel into parabolic and stepped microchannel resulted in the maximum of 88% and 169% enhancement, respectively at 11.7 °C wall superheat. At heat flux of 100 kW/m2, the heat transfer coefficient increased by 21.49–35.37% for different microchannels. The incipient temperature reduced by 13.72–23.18%. A semi-analytical model is developed to estimate the bubble departure diameter of the microchannel which predicts the present experimental data with mean absolute error of 5.58%. © 2017 Elsevier Ltd
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    Tunable adhesion and slip on a bio-mimetic sticky soft surface
    (Royal Society of Chemistry, 2019) Bandyopadhyay, S.; Sriram, S.M.; Parihar, V.; das Gupta, S.; Mukherjee, R.; Chakraborty, S.
    Simultaneous tuning of wettability and adhesion of a surface requires intricate procedures for altering the interfacial structures. Here, we present a simple method for preparing a stable slippery surface, with an intrinsic capability of varying its adhesion characteristics. Cross-linked PDMS, an inherent hydrophobic material commonly used for microfluidic applications, is used to replicate the structures on the surface of a rose petal which acts as a high adhesion solid base and is subsequently oleoplaned with silicone oil. Our results demonstrate that the complex hierarchical rose petal structures can arrest dewetting of the silicone oil on the cross linked PDMS base by anchoring the oil film strongly even under flow. Further, by tuning the extent of submergence of the rose petal structures with silicone oil, we could alter the adhesion characteristics of the surface on demand, while retaining its slippery characteristics for a wide range of the pertinent parameters. We have also demonstrated the possible fabrication of gradient adhesion surfaces. This, in turn, may find a wide variety of applications in water harvesting, droplet maneuverability and no-loss transportation in resource-limited settings. © 2019 The Royal Society of Chemistry.
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    Processing and investigation of mechanical characteristics on the polydimethylsiloxane/carbon black composites
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Hiremath, S.; Sangamesh, R.; Kulkarni, S.M.
    The mechanical adaptability of elastomers has enormous potential in fields such as energy harvesting, micro electro mechanical system (MEMS), sensor, and actuator. A significant issue is to improve the mechanical features of the elastomeric base material by incorporating an appropriate filler. The elastomer Polydimethylsiloxane (PDMS) is reinforced with carbon black (CB) particles that affect mechanical characteristics (Tensile strength, compressive strength, tear strength, etc) and that have a critical impact on the efficiency of the device. The current research examines the mechanical characteristics of plain PDMS with a concentration of CB filler between 5% and 25%. A solution casting method is used to prepare the composite substrate and investigate the impacts of CB loading performance on tensile, compression, tear, and hardness testing. The outcome shows an improvement in mechanical characteristics due to CB material for Young's module as 1.64-3.84 MPa, ultimate tensile strength as 1.86-4.8 MPa, 3.67-4.81 MPa compressive module with the same compressive strength up to 40 percent strain. The tear strength of the PDMS/CB composites is improved by ?111 percent at 25 percent volume fraction of the CB. The composite hardness of PDMS/CB increases by about 30 percent of the plain PDMS material. Continuing with this, Additional mechanical characteristics of PDMS/CB composites on shear and bulk modules are reported. © 2019 IOP Publishing Ltd.
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    Numerical simulation of flow in a wavy wall microchannel using immersed boundary method
    (Bentham Science Publishers, 2020) Kanchan, M.; Maniyeri, R.
    Background: Fluid flow in microchannels is restricted to low Reynolds number regimes and hence inducing chaotic mixing in such devices is a major challenge. Over the years, the Immersed Boundary Method (IBM) has proved its ability in handling complex fluid-structure interaction prob-lems. Objectives: Inspired by recent patents in microchannel mixing devices, we study passive mixing effects by performing two-dimensional numerical simulations of wavy wall in channel flow using IBM. Methods: The continuity and Navier-Stokes equations governing the flow are solved by fractional step based finite volume method on a staggered Cartesian grid system. Fluid variables are described by Eulerian coordinates and solid boundary by Lagrangian coordinates. A four-point Dirac delta function is used to couple both the coordinate variables. A momentum forcing term is added to the governing equation in order to impose the no-slip boundary condition between the wavy wall and fluid interface. Results: Parametric study is carried out to analyze the fluid flow characteristics by varying amplitude and wavelength of wavy wall configurations for different Reynolds number. Conclusion: Configurations of wavy wall microchannels having a higher amplitude and lower wavelengths show optimum results for mixing applications. © 2020 Bentham Science Publishers.
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    Thermodynamic irreversibility and conjugate effects of integrated microchannel cooling device using TiO2 nanofluid
    (Springer, 2020) Narendran, G.; Gnanasekaran, N.; Arumuga Perumal, A.P.
    Thermal management is highly essential for the latest electronic devices to effectively dissipate heat in a densely packed environment. Usually, these high power devices are cooled by integrating micro scale cooling systems. Most of the works reported in the literature majorly concentrate on microchannel heat sink in which the characteristics of friction factor and enhancement of heat transfer are analyzed in detail. However, due to the advent of compact electronic devices a crucial investigation is required to facilitate an amicable environment for the neighboring components so as to improve the reliability of the electronic devices. Henceforth, in the present study a combined experimental and numerical analysis is performed to provide an insight to determine the performance of a copper microchannel integrated with aluminium block using TiO2 nanofluid for different particle configurations. Needless to say, the present study, which also focuses on entropy generation usually attributed to the thermodynamic irreversibility, is very much significant to design an optimum operating condition for better reliability and performance of the cooling devices. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
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    Numerical simulation of buckling and asymmetric behavior of flexible filament using temporal second-order immersed boundary method
    (Emerald Publishing, 2020) Kanchan, M.; Maniyeri, R.
    Purpose: The purpose of this paper is to perform two-dimensional numerical simulation involving fluid-structure interaction of flexible filament. The filament is tethered to the bottom of a rectangular channel with oscillating fluid flow inlet conditions at low Reynolds number. The simulations are performed using a temporal second-order finite volume-based immersed boundary method (IBM). Further, to understand the relation between different aspect ratios i.e. ratio of filament length to channel height (Len/H) and fixed channel geometry ratio, i.e. ratio of channel height to channel length (H/Lc) on mixing and pumping capabilities. Design/methodology/approach: The discretization of governing continuity and Navier–Stokes equation is done by finite-volume method on a staggered Cartesian grid. SIMPLE algorithm is used to solve fluid velocity and pressure terms. Two cases of oscillatory flow conditions are used with the flexible filament tethered at the center of bottom channel wall. The first case is sinusoidal oscillatory flow with phase shift (SOFPS) and second case is sinusoidal oscillatory flow without phase shift (SOF). The simulation results are validated with filament dynamics studies of previous researchers. Further, parametric analysis is carried to study the effect of filament length (aspect ratio), filament bending rigidity and Reynolds number on the complex deformation and behavior of flexible filament interacting with nearby oscillating fluid motion. Findings: It is found that selection of right filament length and bending rigidity is crucial for fluid mixing scenarios. The phase shift in fluid motion is also found to critically effect filament displacement dynamics, especially for rigid filaments. Aspect ratio, suitable for mixing applications is dependent on channel geometry ratio. Symmetric deformation is observed for filaments subjected to SOFPS condition irrespective of bending rigidity, whereas medium and low rigidity filaments placed in SOF condition show severe asymmetric behavior. Two key findings of this study are: symmetric filament conformity without appreciable bending produces sweeping motion in fluid flow, which is highly suited for mixing application; and asymmetric behavior shown by the filament depicts antiplectic metachronism commonly found in beating cilia. As a result, it is possible to pin point the type of fluid motion governing fluid mixing and fluid pumping. The developed computational model can, thus, successfully demonstrate filament-fluid interaction for a wide variety of similar problems. Originality/value: The present study uses a temporal second-order finite volume-based IBM to examine flexible filament dynamics for various applications such as fluid mixing. Also, it highlights the relationship between channel geometry ratio and filament aspect ratio and its effect on filament sweep patterns. The study further reports the effect of filament displacement dynamics with or without phase shift for inlet oscillating fluid flow condition. © 2019, Emerald Publishing Limited.
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    Photomechanical actuation of polydimethylsiloxane/carbon black nanocomposite
    (Institution of Engineering and Technology jbristow@theiet.org, 2020) Hiremath, S.; Kulkarni, S.M.
    Materials such as carbon black (CB), carbon nanotube, graphene, etc. have been found to deform on exposure to the light source. Introducing these materials into polymers could convert them to photo-responsive composites. This is demonstrated by the experiment in which polydimethylsiloxane (PDMS) polymer containing CB nanofiller composites is prepared, and its photomechanical actuation from exposure to IR light source is recorded using a laser displacement sensor. The particle size analysis reveals the size of the CB, which is verified by the dynamic light scattering method. The UV-vis-IR spectrophotometer study shows that an increase in the light absorbance capacity of nanocomposites compared to the plain polymer. The PDMS/CB nanocomposite beam exhibited a significant deformation compared to plain PDMS. Deformation of the order of 10-11 mm is observed for a given IR source. The deformation found to have good repeatability but with some thermal hysteresis in cyclic actuation and de-actuation. © 2020 Institution of Engineering and Technology. All rights reserved.
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    Numerical investigation of engulfment flow at low Reynolds numbers in a T-shaped microchannel
    (American Institute of Physics Inc. claims@aip.org, 2020) Madana, V.S.T.; Ali, B.
    Microreactors play a major role in the intensification of industrial processes. The performance of microfluidic devices depends on the flow behavior and flow regimes present in such systems. In this work, single-phase flow behavior and associated flow regimes in a T-shaped microchannel are numerically analyzed using computational fluid dynamics (CFD). To predict the single-phase flow regimes, three dimensional transient CFD simulations are performed. The critical Reynolds number (Re) at which flow regime transition and onset of engulfment occur is identified (Recritical = 300). To achieve engulfment flow at lower Re, the inlet geometry of the microchannel is modified as a convergent (C)-divergent (D) section and its effect on engulfment flow is analyzed. When the C/D ratio is 9:1, the predicted pressure drop (?p) is found to be minimum (Recritical = 75, ?p = 5.4 kPa). The understanding of the engulfment flow regime is exploited through residence time distribution (RTD). The predicted RTD profiles indicate strong recirculation among vortices. The mixing index is calculated to quantify RTD, and it is found to be minimum when the C/D ratio is 9:1. The mixing performance is further verified by introducing buoyant particles in Lagrangian manner using discrete phase modeling. The predicted dynamics are qualitatively and quantitatively analyzed through Poincaré maps and Shannon's entropy for various convergent-divergent inlets to characterize mixing. Once again, the C/D ratio of 9:1 supports in enhancing mixing in the microchannel. Hence, the proposed micromixer based on geometric modifications at the inlet helps achieve the engulfment flow regime at low Re. © 2020 Author(s).