In the present endeavor, we discuss the enhancement strategy of important fluidic functionality, ... more In the present endeavor, we discuss the enhancement strategy of important fluidic functionality, i.e., mixing in an on-chip device embedded in a rotating disk both qualitatively as well as quantitatively. Our analysis, on accounting for the effect of rotation in the framework, uses a set of mechanically consistent classical fluid dynamic equations in describing the mixing of the constituent fluids comprehensively. Motivated by the need of benchmarking our modeling framework, we perform experiments in the limiting case of pure diffusion and show that suggestions from the experimental part of this endeavor verify the numerical results quite effectively. The results indicate that the effect of molecular diffusion and rotation-induced forcing non-trivially modulates the underlying mixing in the portable fluidic device. Of particular interest, we show that, even for weak molecular diffusion between the chosen fluid pair, strong advective transport of species as rendered by a higher rotational effect results in an enhanced mixing, that too achievable at short distances from the channel entry. Finally, a phase diagram mapping the mixing efficiency in the flow-fluid properties plane is provided, expected to be a design guideline for the portable fluidic systems/devices, typically used for mixing and diagnosis of bio-fluids.
International Journal of Heat and Mass Transfer, Jun 1, 2019
Convective flow of single-phase ferrofluids under the influence of constant and alternating magne... more Convective flow of single-phase ferrofluids under the influence of constant and alternating magnetic field has attracted attention as an effective strategy for enhanced heat transfer in mini/micro thermal systems. In the present study, an attempt has been made to gain deep insight of the heat transfer characteristics of single-phase ferrofluid flow in a heated stainless steel tube under the influence of constant and timevarying magnetic field. The governing parameters are mainly the magnetic flux density (B) and perturbation frequency (f) of the applied magnetic field. Three magnetic flux density value of B = 0 G, 700 G and 1080 G have been used for constant magnetic field. Constant value of B = 1080 G was used for alternating magnetic field while, frequencies of applied magnetic field has been varied from 0.1 Hz to 5 Hz. Flow Reynolds number was kept constant to Re = 66. Some 2-D numerical simulations have also been performed to qualitatively support the experimental data. The study is focused to delineate the mechanism of augmentation of heat transfer through the interaction of available force fields, i.e., interplay of magnetic force and inertia of the flow, and also the effect of various time scales on the flow and thermal behavior. Major inferences of the study are (a) on the application of external magnetic (constant and alternating), heat transfer augments (b) existence of a threshold frequency of external magnetic field for maximum augmentation as outcome of advective timescale and magnetic perturbation timescale. InfraRed Thermography (IRT) has been used to measure the wall temperature, while, some bright field visualizations have also been done to qualitatively support the explanations of experimental data.
We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spheric... more We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late-stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of increasing contact angle results in the time required for the complete wetting of drop becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature due to the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.
The images are captured at a resolution of. The captured images are processed 2 744×480 pixels fu... more The images are captured at a resolution of. The captured images are processed 2 744×480 pixels further to extract information from it, such as change in contact angle (CA), diameter, height, etc. a. Determination of CA: The captured side view images are processed in advance ACAM-NSC software to obtain the contact angle. The contact angle(CA) is measured by contour recognition based on the greyscale analysis of the images. The baseline is determined, and the droplet shape was fitted, choosing the more appropriate method. The droplet shape of our sample is determined by three main approaches, namely the tangential(polynomial approximation), young-Laplace,
Journal of Thermal Science and Engineering Applications, Jul 19, 2019
In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) syste... more In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) systems, where ferrofluid flow can be easily altered by the application of an external magnetic field leading to enhanced heat transfer from the hot surface of PV systems. The effect of both constant and alternating magnetic field on ferrofluid flow through a minichannel is explored numerically in the present work. A detailed parametric study is performed to investigate the effect of actuation frequencies of alternating magnetic field (0.5–20 Hz) and Reynolds numbers (Re = 24, 60, and 100) on heat transfer characteristics of ferrofluid. An overall enhancement of 17.41% is observed for heat transfer of ferrofluid in the presence of magnetic field compared to the base case of no magnetic field. For the case of alternating magnetic field, a critical actuation frequency is observed for each Reynolds number above which heat transfer is observed to decrease. The enhancement or decrease in heat transfer of ferrofluid is found to depend on several factors such as actuation frequency of alternating magnetic field, Reynolds numbers of ferrofluid flow, and formation/dispersion of stagnant layers of ferrofluid at the magnet location. Preliminary visualization of ferrofluid flow is also carried out to provide a qualitative insight to the nature of transportation of ferrofluid in the presence of an alternating magnetic field.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Feb 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
We report the experimental investigations on the mixing of a ferrofluid droplet with a nonmagneti... more We report the experimental investigations on the mixing of a ferrofluid droplet with a nonmagnetic fluid in the presence of a time-dependent magnetic field on an open surface microfluidic platform. The bright field visualization technique, in combination with the µPIV analysis, is carried out to explore the internal hydrodynamics of the ferrofluid droplet. Also, using the Laserinduced fluorescence (µLIF) technique, we quantify the mass transfer occurring between the two droplets, which in effect, determines the underlying mixing performance under the modulation of the frequency of the applied magnetic field. We show that the magnetic nanoparticles exhibit complex spatio-temporal movement inside the ferrofluid droplet domain under the influence of a time-dependent magnetic field, which, in turn, promotes the mixing efficiency in the convective mixing regime. Our analysis establishes that the movement of magnetic nanoparticles in presence of the time-periodic field strengthens the interfacial instability, which acts like a sparking agent to initiate an augmented mixing in the present scenario. By performing numerical simulations, we also review the onset of interfacial instability, mainly stemming from the susceptibility mismatch between the magnetic and non-magnetic fluids. Inferences of the present analysis, which focuses on the simple, wireless, robust, and low-cost open surface micromixing mechanism, will provide a potential solution for rapid droplets mixing without requiring pH level or ion concentration dependency of the fluids.
We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spheric... more We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late-stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of increasing contact angle results in the time required for the complete wetting of drop becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature due to the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.
In the present endeavor, we discuss the enhancement strategy of important fluidic functionality, ... more In the present endeavor, we discuss the enhancement strategy of important fluidic functionality, i.e., mixing in an on-chip device embedded in a rotating disk both qualitatively as well as quantitatively. Our analysis, on accounting for the effect of rotation in the framework, uses a set of mechanically consistent classical fluid dynamic equations in describing the mixing of the constituent fluids comprehensively. Motivated by the need of benchmarking our modeling framework, we perform experiments in the limiting case of pure diffusion and show that suggestions from the experimental part of this endeavor verify the numerical results quite effectively. The results indicate that the effect of molecular diffusion and rotation-induced forcing non-trivially modulates the underlying mixing in the portable fluidic device. Of particular interest, we show that, even for weak molecular diffusion between the chosen fluid pair, strong advective transport of species as rendered by a higher rotational effect results in an enhanced mixing, that too achievable at short distances from the channel entry. Finally, a phase diagram mapping the mixing efficiency in the flow-fluid properties plane is provided, expected to be a design guideline for the portable fluidic systems/devices, typically used for mixing and diagnosis of bio-fluids.
International Journal of Heat and Mass Transfer, Jun 1, 2019
Convective flow of single-phase ferrofluids under the influence of constant and alternating magne... more Convective flow of single-phase ferrofluids under the influence of constant and alternating magnetic field has attracted attention as an effective strategy for enhanced heat transfer in mini/micro thermal systems. In the present study, an attempt has been made to gain deep insight of the heat transfer characteristics of single-phase ferrofluid flow in a heated stainless steel tube under the influence of constant and timevarying magnetic field. The governing parameters are mainly the magnetic flux density (B) and perturbation frequency (f) of the applied magnetic field. Three magnetic flux density value of B = 0 G, 700 G and 1080 G have been used for constant magnetic field. Constant value of B = 1080 G was used for alternating magnetic field while, frequencies of applied magnetic field has been varied from 0.1 Hz to 5 Hz. Flow Reynolds number was kept constant to Re = 66. Some 2-D numerical simulations have also been performed to qualitatively support the experimental data. The study is focused to delineate the mechanism of augmentation of heat transfer through the interaction of available force fields, i.e., interplay of magnetic force and inertia of the flow, and also the effect of various time scales on the flow and thermal behavior. Major inferences of the study are (a) on the application of external magnetic (constant and alternating), heat transfer augments (b) existence of a threshold frequency of external magnetic field for maximum augmentation as outcome of advective timescale and magnetic perturbation timescale. InfraRed Thermography (IRT) has been used to measure the wall temperature, while, some bright field visualizations have also been done to qualitatively support the explanations of experimental data.
We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spheric... more We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late-stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of increasing contact angle results in the time required for the complete wetting of drop becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature due to the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.
The images are captured at a resolution of. The captured images are processed 2 744×480 pixels fu... more The images are captured at a resolution of. The captured images are processed 2 744×480 pixels further to extract information from it, such as change in contact angle (CA), diameter, height, etc. a. Determination of CA: The captured side view images are processed in advance ACAM-NSC software to obtain the contact angle. The contact angle(CA) is measured by contour recognition based on the greyscale analysis of the images. The baseline is determined, and the droplet shape was fitted, choosing the more appropriate method. The droplet shape of our sample is determined by three main approaches, namely the tangential(polynomial approximation), young-Laplace,
Journal of Thermal Science and Engineering Applications, Jul 19, 2019
In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) syste... more In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) systems, where ferrofluid flow can be easily altered by the application of an external magnetic field leading to enhanced heat transfer from the hot surface of PV systems. The effect of both constant and alternating magnetic field on ferrofluid flow through a minichannel is explored numerically in the present work. A detailed parametric study is performed to investigate the effect of actuation frequencies of alternating magnetic field (0.5–20 Hz) and Reynolds numbers (Re = 24, 60, and 100) on heat transfer characteristics of ferrofluid. An overall enhancement of 17.41% is observed for heat transfer of ferrofluid in the presence of magnetic field compared to the base case of no magnetic field. For the case of alternating magnetic field, a critical actuation frequency is observed for each Reynolds number above which heat transfer is observed to decrease. The enhancement or decrease in heat transfer of ferrofluid is found to depend on several factors such as actuation frequency of alternating magnetic field, Reynolds numbers of ferrofluid flow, and formation/dispersion of stagnant layers of ferrofluid at the magnet location. Preliminary visualization of ferrofluid flow is also carried out to provide a qualitative insight to the nature of transportation of ferrofluid in the presence of an alternating magnetic field.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Feb 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
We report the experimental investigations on the mixing of a ferrofluid droplet with a nonmagneti... more We report the experimental investigations on the mixing of a ferrofluid droplet with a nonmagnetic fluid in the presence of a time-dependent magnetic field on an open surface microfluidic platform. The bright field visualization technique, in combination with the µPIV analysis, is carried out to explore the internal hydrodynamics of the ferrofluid droplet. Also, using the Laserinduced fluorescence (µLIF) technique, we quantify the mass transfer occurring between the two droplets, which in effect, determines the underlying mixing performance under the modulation of the frequency of the applied magnetic field. We show that the magnetic nanoparticles exhibit complex spatio-temporal movement inside the ferrofluid droplet domain under the influence of a time-dependent magnetic field, which, in turn, promotes the mixing efficiency in the convective mixing regime. Our analysis establishes that the movement of magnetic nanoparticles in presence of the time-periodic field strengthens the interfacial instability, which acts like a sparking agent to initiate an augmented mixing in the present scenario. By performing numerical simulations, we also review the onset of interfacial instability, mainly stemming from the susceptibility mismatch between the magnetic and non-magnetic fluids. Inferences of the present analysis, which focuses on the simple, wireless, robust, and low-cost open surface micromixing mechanism, will provide a potential solution for rapid droplets mixing without requiring pH level or ion concentration dependency of the fluids.
We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spheric... more We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late-stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of increasing contact angle results in the time required for the complete wetting of drop becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature due to the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.
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