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Moo Hwan Kim - One of the best experts on this subject based on the ideXlab platform.
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surface wettability effect on flow pattern and pressure drop in adiabatic two phase flows in Rectangular Microchannels with t junction mixer
Experimental Thermal and Fluid Science, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract Wettability is an important parameter in micro-scale flow patterns. Previous research has usually been conducted in conventional microtubes due to limitations of visualizing flow patterns and fabricating Microchannels. However, most Microchannels in practical applications have Rectangular shape. Furthermore, pressure drop is closely related with flow pattern. Hence, we studied water liquid and nitrogen gas flows in Rectangular Microchannels with different wettabilities. The Rectangular glass Microchannels were fabricated from photosensitive glass, whose surface is hydrophilic. The surface of one was silanized using octadecyl-trichloro-silane (OTS) to prepare a hydrophobic microchannel. The two-phase flow pattern was visualized with a high-speed camera and a long distance microscope. The frictional pressure drop in the microchannel was measured directly with embedded pressure ports. The flow pattern and pressure drop in the hydrophobic microchannel were totally different from those in the hydrophilic microchannel. Finally, the two-phase frictional pressure drop was analyzed based on the flow patterns of different wettabilities.
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adiabatic two phase flow in Rectangular Microchannels with different aspect ratios part i flow pattern pressure drop and void fraction
International Journal of Heat and Mass Transfer, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract An aspect ratio is an important parameter for two-phase flow in a Rectangular microchannel. To study the aspect ratio effect on the flow pattern, pressure drop and void fraction, experiments of adiabatic liquid water and nitrogen gas two-phase flow in Rectangular Microchannels were conducted. The widths and heights of Rectangular Microchannels are 510 μm × 470 μm, 608 μm × 410 μm, 501 μm × 237 μm and 503 μm × 85 μm. Therefore, the aspect ratios of the Rectangular Microchannels are 0.92, 0.67, 0.47 and 0.16; and the hydraulic diameters of the Rectangular Microchannels were 490, 490, 322 and 143 μm, respectively. Experimental ranges were liquid superficial velocities of 0.06–1.0 m/s and gas superficial velocities of 0.06–71 m/s. Visible Rectangular Microchannels were fabricated using a photosensitive glass. And pressure drop in Microchannels was directly measured through embedded ports. The visualization of the flow pattern was carried out with a high-speed camera and a long distance microscope. Typical flow patterns in the Rectangular Microchannels observed in this study were bubble flow, transitional flow (multiple flow) and liquid ring flow. As the aspect ratio decreased, the bubble flow regime became dominant due to the confinement effect and the thickness of liquid film in corner was decreased. A void fraction in the Rectangular Microchannels has a linear relation with the volumetric quality. And the two-phase flow becomes homogeneous with decreasing aspect ratio owing to the reduction of the liquid film thickness. Like Zhang et al.’s [19] correlation, as the confinement number increased, the C -value in Lockhart and Martinelli correlation decreased. And a frictional pressure drop in the Rectangular Microchannels was highly related with the flow pattern.
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Flow pattern based correlations of two-phase pressure drop in Rectangular Microchannels
International Journal of Heat and Fluid Flow, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract Numerous pressure drop correlations for Microchannels have been proposed; most of them can be classified as either a homogeneous flow model (HFM) or a separated flow model (SFM). However, the predictions of these correlations have not been compared directly because they were developed in experiments conducted under a range of conditions, including channel shape, the number of channels, channel material and the working fluid. In this study, single Rectangular Microchannels with different aspect ratios and hydraulic diameters were fabricated in a photosensitive glass. Adiabatic water-liquid and Nitrogen-gas two-phase flow experiments were conducted using liquid superficial velocities of 0.06–1.0 m/s, gas superficial velocities of 0.06–72 m/s and hydraulic diameters of 141, 143, 304, 322 and 490 μm. A pressure drop in Microchannels was directly measured through embedded ports. The flow pattern was visualized using a high-speed camera and a long-distance microscope. A two-phase pressure drop in the microchannel was highly related to the flow pattern. Data were used to assess seven different HFM viscosity models and ten SFM correlations, and new correlations based on flow patterns were proposed for both HFMs and SFMs.
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adiabatic two phase flow in Rectangular Microchannels with different aspect ratios part ii bubble behaviors and pressure drop in single bubble
International Journal of Heat and Mass Transfer, 2010Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract One of the major flow patterns in a microchannel is an elongated bubble flow, which is similar to a long slug bubble. Behaviors and pressure drop for a single bubble in a Rectangular microchannel were studied. Based on the experiments in Part I of this paper, data for liquid superficial velocities of 0.06–0.8 m/s, gas superficial velocities of 0.06–0.66 m/s and AR of 0.92, 0.67, 0.47 and 0.16 were analyzed. The velocity, length, number, and frequency of the single bubble in the Rectangular microchannel were obtained from image processing based on a unit cell model. The bubble velocities were proportional to total superficial velocity. As the aspect ratio decreased, the portion of the bubble area increased due to the corner effect. New correlation of the bubble velocity for different aspect ratio was proposed. Also, bubble and liquid slug length, the number of the unit cell and bubble frequency were analyzed with different aspect ratios. The pressure drop for the single bubble in the Rectangular Microchannels was evaluated using the information of the bubble behavior. The pressure drop in the single elongated bubble was proportional to the bubble velocity. The pressure drop in the single elongated bubble in the Rectangular microchannel increased as the aspect ratio decreased.
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Adiabatic two-phase flow in Rectangular Microchannels with different aspect ratios: Part I – Flow pattern, pressure drop and void fraction
International Journal of Heat and Mass Transfer, 2010Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract An aspect ratio is an important parameter for two-phase flow in a Rectangular microchannel. To study the aspect ratio effect on the flow pattern, pressure drop and void fraction, experiments of adiabatic liquid water and nitrogen gas two-phase flow in Rectangular Microchannels were conducted. The widths and heights of Rectangular Microchannels are 510 μm × 470 μm, 608 μm × 410 μm, 501 μm × 237 μm and 503 μm × 85 μm. Therefore, the aspect ratios of the Rectangular Microchannels are 0.92, 0.67, 0.47 and 0.16; and the hydraulic diameters of the Rectangular Microchannels were 490, 490, 322 and 143 μm, respectively. Experimental ranges were liquid superficial velocities of 0.06–1.0 m/s and gas superficial velocities of 0.06–71 m/s. Visible Rectangular Microchannels were fabricated using a photosensitive glass. And pressure drop in Microchannels was directly measured through embedded ports. The visualization of the flow pattern was carried out with a high-speed camera and a long distance microscope. Typical flow patterns in the Rectangular Microchannels observed in this study were bubble flow, transitional flow (multiple flow) and liquid ring flow. As the aspect ratio decreased, the bubble flow regime became dominant due to the confinement effect and the thickness of liquid film in corner was decreased. A void fraction in the Rectangular Microchannels has a linear relation with the volumetric quality. And the two-phase flow becomes homogeneous with decreasing aspect ratio owing to the reduction of the liquid film thickness. Like Zhang et al.’s [19] correlation, as the confinement number increased, the C -value in Lockhart and Martinelli correlation decreased. And a frictional pressure drop in the Rectangular Microchannels was highly related with the flow pattern.
Chun Yang - One of the best experts on this subject based on the ideXlab platform.
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Numerical analysis of dynamic electro-osmotic flows of non-Newtonian fluids in Rectangular Microchannels
arXiv: Fluid Dynamics, 2010Co-Authors: Cunlu Zhao, Chun YangAbstract:Numerical analyses of transient electro-osmosis of a typical non-Newtonian liquid induced by DC and AC electric fields in a Rectangular microchannel are conducted in the framework of continuum fluid mechanics. The famous power-law constitutive model is used to express the fluid dynamic viscosity in terms of the velocity gradient. Transient start-up characteristics of electro-osmotic power-law liquid flow in Rectangular Microchannels are simulated by using finite element method. Under a DC electric field, it is found out and the fluid is more inert to the external electric field and the steady-state velocity profile becomes more plug-like with decrease of the flow behavior index of the power-law liquids. The numerical calculations also confirm the validity of the generalized Smoluchowski slip velocity which can serve as the counterpart for the classic Smoluchowski slip velocity when dealing with electrokinetic flow of non-Newtonian power-law fluids. Under AC electric fields, the fluid is more obviously accelerated during oscillations and the amplitude of the oscillating velocity is closer to the magnitude of the generalized Smoluchowski velocity as the fluid behavior index increases. These dynamic predictions are of practical significance for the design of microfluidic devices that manipulate non-Newtonian fluids such as biofluids, polymer solutions and colloidal suspensions.
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Joule heating and its effects on electrokinetic transport of solutes in Rectangular Microchannels
Sensors and Actuators A-physical, 2007Co-Authors: Gongyue Tang, H Q Gong, Chun Yang, Cheekiong ChaiAbstract:Abstract In this paper, the studies of the Joule heating and its effects on electrokinetic transport (i.e., electroosmotic flow and electrophoretic transport) of solutes in Rectangular Microchannels are reported. 3D mathematical models describing the Joule heating induced temperature field and its effects on the EOF and electrophoretic transport of solutes in Microchannels are developed, and the coupled governing equations are solved numerically using the finite volume based CFD technique. In addition, experiments are carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A Rhodamine B based thermometry technique was employed to measure the solution temperature distributions in PDMS microfluidic channels. The micro particle image velocimetry (micro-PIV) technique was used to measure the velocity profiles of the EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. Both the numerical simulations and the experimental results show that the presence of the Joule heating causes the EOF velocity to deviate from its normal “plug-like” profile; moreover, the numerical simulations show that Joule heating not only accelerates the sample transport but also distorts the shape of the sample band. The simulation results also reveal that the Joule heating and its effects in a PDMS/PDMS channel is more significant than those in a glass/PDMS channel.
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Characterization of electroosmotic flow in Rectangular Microchannels
International Journal of Heat and Mass Transfer, 2007Co-Authors: Cheng Wang, Chun Yang, Teck Neng Wong, Kim Tiow OoiAbstract:Abstract In this paper, the electroosmotic displacing process between two solutions (namely the same electrolyte of different concentrations) in a Rectangular microchannel is studied theoretically and experimentally. Firstly, the electric potential and velocity field in a Rectangular microchannel are obtained by solving the governing equations. Fourier transform method is used to solve the electrolyte concentration profile equation. The electric current versus time curve through the microchannel is predicted based on the concentration profile obtained. The current monitoring technique is then used to study the electroosmotic displacing process. The results from the measured current–time relations agree well with those from the prediction, suggesting a reliable theoretical model developed in this study.
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Dynamic aspects of electroosmotic flow in Rectangular Microchannels
International Journal of Engineering Science, 2004Co-Authors: Marcos, Chun Yang, Teck Neng Wong, Kim Tiow OoiAbstract:Abstract The study presents an analysis of the dynamic aspects of the electroosmotic flow in Rectangular Microchannels. An analytical solution for electrical potential distribution in the channel is obtained by solving the linearized Poisson–Boltzmann equation under the Debye–Huckel approximation. Dynamic electroosmotic flow field driven by an alternating electric field is solved analytically by using the Green's function method. Parametric studies are carried out to examine the time evolution of the electroosmotic flow under the effects of the channel size, ionic concentration, and zeta potential. Specifically, the effect of frequency-dependent AC electric field on the oscillating electroosmotic flow is discussed. In addition, the solution of the slip velocity approximation based on the Stokes second problem is presented for comparison with the results obtained from the analytical scheme developed in this study.
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Modeling forced liquid convection in Rectangular Microchannels with electrokinetic effects
International Journal of Heat and Mass Transfer, 1998Co-Authors: Chun Yang, Jacob H. MasliyahAbstract:Abstract The effects of the electric double layer near the solid–liquid interface and the flow induced electrokinetic field on the pressure-driven flow and heat transfer through a Rectangular microchannel are analyzed in this work. The electric double layer field in the cross-section of Rectangular Microchannels is determined by solving a non-linear, two-dimensional Poisson–Boltzmann equation. A body force caused by the electric double field and the flow-induced electrokinetic field is considered in the equation of motion. For steady-state, fully-developed laminar flows, both the velocity and the temperature fields in a Rectangular microchannel are determined for various conditions. The flow and heat transfer characteristics with⧹without consideration of the electrokinetic effects are evaluated. The results clearly show that, for aqueous solutions of low ionic concentrations and a solid surface of high zeta potential, the liquid flow and heat transfer in Rectangular Microchannels are significantly influenced by the presence of the electric double layer field and the induced electrokinetic flow.
Chiwoong Choi - One of the best experts on this subject based on the ideXlab platform.
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surface wettability effect on flow pattern and pressure drop in adiabatic two phase flows in Rectangular Microchannels with t junction mixer
Experimental Thermal and Fluid Science, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract Wettability is an important parameter in micro-scale flow patterns. Previous research has usually been conducted in conventional microtubes due to limitations of visualizing flow patterns and fabricating Microchannels. However, most Microchannels in practical applications have Rectangular shape. Furthermore, pressure drop is closely related with flow pattern. Hence, we studied water liquid and nitrogen gas flows in Rectangular Microchannels with different wettabilities. The Rectangular glass Microchannels were fabricated from photosensitive glass, whose surface is hydrophilic. The surface of one was silanized using octadecyl-trichloro-silane (OTS) to prepare a hydrophobic microchannel. The two-phase flow pattern was visualized with a high-speed camera and a long distance microscope. The frictional pressure drop in the microchannel was measured directly with embedded pressure ports. The flow pattern and pressure drop in the hydrophobic microchannel were totally different from those in the hydrophilic microchannel. Finally, the two-phase frictional pressure drop was analyzed based on the flow patterns of different wettabilities.
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adiabatic two phase flow in Rectangular Microchannels with different aspect ratios part i flow pattern pressure drop and void fraction
International Journal of Heat and Mass Transfer, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract An aspect ratio is an important parameter for two-phase flow in a Rectangular microchannel. To study the aspect ratio effect on the flow pattern, pressure drop and void fraction, experiments of adiabatic liquid water and nitrogen gas two-phase flow in Rectangular Microchannels were conducted. The widths and heights of Rectangular Microchannels are 510 μm × 470 μm, 608 μm × 410 μm, 501 μm × 237 μm and 503 μm × 85 μm. Therefore, the aspect ratios of the Rectangular Microchannels are 0.92, 0.67, 0.47 and 0.16; and the hydraulic diameters of the Rectangular Microchannels were 490, 490, 322 and 143 μm, respectively. Experimental ranges were liquid superficial velocities of 0.06–1.0 m/s and gas superficial velocities of 0.06–71 m/s. Visible Rectangular Microchannels were fabricated using a photosensitive glass. And pressure drop in Microchannels was directly measured through embedded ports. The visualization of the flow pattern was carried out with a high-speed camera and a long distance microscope. Typical flow patterns in the Rectangular Microchannels observed in this study were bubble flow, transitional flow (multiple flow) and liquid ring flow. As the aspect ratio decreased, the bubble flow regime became dominant due to the confinement effect and the thickness of liquid film in corner was decreased. A void fraction in the Rectangular Microchannels has a linear relation with the volumetric quality. And the two-phase flow becomes homogeneous with decreasing aspect ratio owing to the reduction of the liquid film thickness. Like Zhang et al.’s [19] correlation, as the confinement number increased, the C -value in Lockhart and Martinelli correlation decreased. And a frictional pressure drop in the Rectangular Microchannels was highly related with the flow pattern.
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Flow pattern based correlations of two-phase pressure drop in Rectangular Microchannels
International Journal of Heat and Fluid Flow, 2011Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract Numerous pressure drop correlations for Microchannels have been proposed; most of them can be classified as either a homogeneous flow model (HFM) or a separated flow model (SFM). However, the predictions of these correlations have not been compared directly because they were developed in experiments conducted under a range of conditions, including channel shape, the number of channels, channel material and the working fluid. In this study, single Rectangular Microchannels with different aspect ratios and hydraulic diameters were fabricated in a photosensitive glass. Adiabatic water-liquid and Nitrogen-gas two-phase flow experiments were conducted using liquid superficial velocities of 0.06–1.0 m/s, gas superficial velocities of 0.06–72 m/s and hydraulic diameters of 141, 143, 304, 322 and 490 μm. A pressure drop in Microchannels was directly measured through embedded ports. The flow pattern was visualized using a high-speed camera and a long-distance microscope. A two-phase pressure drop in the microchannel was highly related to the flow pattern. Data were used to assess seven different HFM viscosity models and ten SFM correlations, and new correlations based on flow patterns were proposed for both HFMs and SFMs.
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adiabatic two phase flow in Rectangular Microchannels with different aspect ratios part ii bubble behaviors and pressure drop in single bubble
International Journal of Heat and Mass Transfer, 2010Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract One of the major flow patterns in a microchannel is an elongated bubble flow, which is similar to a long slug bubble. Behaviors and pressure drop for a single bubble in a Rectangular microchannel were studied. Based on the experiments in Part I of this paper, data for liquid superficial velocities of 0.06–0.8 m/s, gas superficial velocities of 0.06–0.66 m/s and AR of 0.92, 0.67, 0.47 and 0.16 were analyzed. The velocity, length, number, and frequency of the single bubble in the Rectangular microchannel were obtained from image processing based on a unit cell model. The bubble velocities were proportional to total superficial velocity. As the aspect ratio decreased, the portion of the bubble area increased due to the corner effect. New correlation of the bubble velocity for different aspect ratio was proposed. Also, bubble and liquid slug length, the number of the unit cell and bubble frequency were analyzed with different aspect ratios. The pressure drop for the single bubble in the Rectangular Microchannels was evaluated using the information of the bubble behavior. The pressure drop in the single elongated bubble was proportional to the bubble velocity. The pressure drop in the single elongated bubble in the Rectangular microchannel increased as the aspect ratio decreased.
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Adiabatic two-phase flow in Rectangular Microchannels with different aspect ratios: Part I – Flow pattern, pressure drop and void fraction
International Journal of Heat and Mass Transfer, 2010Co-Authors: Chiwoong Choi, Moo Hwan KimAbstract:Abstract An aspect ratio is an important parameter for two-phase flow in a Rectangular microchannel. To study the aspect ratio effect on the flow pattern, pressure drop and void fraction, experiments of adiabatic liquid water and nitrogen gas two-phase flow in Rectangular Microchannels were conducted. The widths and heights of Rectangular Microchannels are 510 μm × 470 μm, 608 μm × 410 μm, 501 μm × 237 μm and 503 μm × 85 μm. Therefore, the aspect ratios of the Rectangular Microchannels are 0.92, 0.67, 0.47 and 0.16; and the hydraulic diameters of the Rectangular Microchannels were 490, 490, 322 and 143 μm, respectively. Experimental ranges were liquid superficial velocities of 0.06–1.0 m/s and gas superficial velocities of 0.06–71 m/s. Visible Rectangular Microchannels were fabricated using a photosensitive glass. And pressure drop in Microchannels was directly measured through embedded ports. The visualization of the flow pattern was carried out with a high-speed camera and a long distance microscope. Typical flow patterns in the Rectangular Microchannels observed in this study were bubble flow, transitional flow (multiple flow) and liquid ring flow. As the aspect ratio decreased, the bubble flow regime became dominant due to the confinement effect and the thickness of liquid film in corner was decreased. A void fraction in the Rectangular Microchannels has a linear relation with the volumetric quality. And the two-phase flow becomes homogeneous with decreasing aspect ratio owing to the reduction of the liquid film thickness. Like Zhang et al.’s [19] correlation, as the confinement number increased, the C -value in Lockhart and Martinelli correlation decreased. And a frictional pressure drop in the Rectangular Microchannels was highly related with the flow pattern.
Arman Sadeghi - One of the best experts on this subject based on the ideXlab platform.
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Pressure effects on electroosmotic flow of power-law fluids in Rectangular Microchannels
Theoretical and Computational Fluid Dynamics, 2014Co-Authors: Mohammad Ali Vakili, Arman Sadeghi, Mohammad Hassan SaidiAbstract:In this paper, the fully developed electroosmotic flow of power-law fluids in Rectangular Microchannels in the presence of pressure gradient is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A complete parametric study reveals that the pressure effects are more pronounced at higher values of the channel aspect ratio and smaller values of the flow behavior index. The Poiseuille number is found to be an increasing function of the channel aspect ratio for pressure assisted flow and a decreasing function of this parameter for pressure opposed flow. It is also observed that the Poiseuille number is increased by increasing the zeta potential. Furthermore, the results show that an increase in the flow behavior index results in a lower flow rate ratio, defined to be the ratio of the flow rate to that of a Newtonian fluid at the same conditions. Moreover, whereas the flow rate ratio in the presence of an opposed pressure gradient is smaller than that of a favorable pressure force for shear thinnings, the opposite is true for shear-thickening fluids.
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thermal transport characteristics pertinent to electrokinetic flow of power law fluids in Rectangular Microchannels
International Journal of Thermal Sciences, 2014Co-Authors: Mohammad Ali Vakili, Mohammad Hassan Saidi, Arman SadeghiAbstract:Abstract In the present study, the thermal characteristics of electroosmotic flow of power-law fluids in Rectangular Microchannels in the presence of pressure gradient are investigated. The governing equations for fully developed flow under H1 thermal boundary conditions are first made dimensionless and subsequently solved through a finite difference procedure for a non-uniform grid. The influence of the major parameters on thermal features of the flow such as the temperature distribution and Nusselt number is discussed by a complete parametric study. The results reveal that the channel aspect ratio and the non-Newtonian characteristic of the fluid can affect the thermal behavior of the flow. It is observed that decreasing the channel aspect ratio causes the energy generated due to the viscous heating to become more significant. Furthermore, the viscous dissipation is higher for shear-thickening fluids. The Nusselt number is ascertained to be an increasing function of the channel aspect ratio regardless of the flow behavior index and pressure gradient. Moreover, the results suggest that increasing the flow behavior index can either increase or decrease the Nusselt number, depending on the thermal conditions of the flow.
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Temperature Rise in Electroosmotic Flow of Typical Non-Newtonian Biofluids Through Rectangular Microchannels
Journal of Heat Transfer, 2013Co-Authors: Hadi Yavari, Mohammad Hassan Saidi, Arman Sadeghi, Suman ChakrabortyAbstract:Electroosmosis is the main mechanism for flow generation in lab-on-a-chip (LOC) devices. The temperature rise due to the Joule heating phenomenon, associated with the electroosmosis, may be detrimental for samples being considered in LOCs. Hence, a complete understanding of the heat transfer physics associated with the electroosmotic flow is of high importance in design and active control of LOCs. The objective of the present study is to estimate the temperature rise and the thermal entry length in electroosmotic flow through Rectangular Microchannels, having potential applications in LOC devices. Along this line, the power-law rheological model is used to account for non-Newtonian behavior of the common biofluids encountered in these devices. A mixed type of thermal boundary condition is employed at the channel surface, instead of routinely presumed constant wall heat flux or constant wall temperature conditions. A finite difference-based numerical method is employed for solving the governing equations in dimensionless form. An approximate solution, based on the premise of a uniform temperature field throughout the channel cross section, is also obtained for the bulk mean temperature, which is found to be of high accuracy. This, accompanied by the assessments of the temperature profile, reveals that the temperature variations in the channel cross section are negligible, and as a result, the bulk mean temperature can be used as a very precise estimate of the maximum temperature in an LOC device. Moreover, the evaluation of the entry length shows that a thermally fully developed flow is hardly achieved in practical applications because of small length scales involved. Accordingly, the maximum temperature rise may significantly be smaller than what is calculated based on a thermally fully developed flow assumption.
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electrokinetically driven fluidic transport of power law fluids in Rectangular Microchannels
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012Co-Authors: Mohammad Ali Vakili, Arman Sadeghi, Mohammad Hassan Saidi, A A MozafariAbstract:Abstract Electroosmosis is the predominant mechanism for flow generation in lab-on-chip devices. Since most biofluids encountered in these devices are considered to be non-Newtonian, it is vital to study the flow characteristics of common non-Newtonian models under electroosmotic body force. In this paper, the hydrodynamically fully developed electroosmotic flow of power-law fluids in Rectangular Microchannels is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A thoroughgoing parametric study reveals that the Poiseuille number is an increasing function of the channel aspect ratio, the zeta potential, the flow behavior index, and the dimensionless Debye–Huckel parameter. It is also found that the validity range of the Debye–Huckel approximation for shear-thickening fluids is much wider than that of shear-thinnings. Furthermore, while the dimensionless mean velocity is an increasing function of the channel aspect ratio and the dimensionless Debye–Huckel parameter, it is a decreasing function of the flow behavior index. Moreover, to increase the zeta potential is to increase the dimensionless mean velocity for shear-thinnings, nevertheless, its effect is not significant for shear-thickenings.
Lutfullah Kuddusi - One of the best experts on this subject based on the ideXlab platform.
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Entropy generation in Rectangular Microchannels
International Journal of Exergy, 2016Co-Authors: Lutfullah KuddusiAbstract:Entropy generation in a Rectangular microchannel with fully developed steady gaseous flow at slip flow regime is studied. Two different thermal versions, uniform temperature (H1) and uniform heat flux (H2) on the walls, are considered. Analytically obtained expressions for temperature and velocity fields are used for entropy generation calculations. The effects of rarefaction, geometry, Peclet number Pe and group parameter Br/ on entropy generation (irreversibility) and local variation of entropy generation are explored. The main findings are; irreversibility decreases with rarefaction regardless of the thermal versions, irreversibility increases with aspect ratio for H1 thermal version and exhibits very little change with aspect ratio for H2 thermal version. For H1 thermal version the points of maximal entropy generation are at the middle of walls. For H2 thermal version entropy generation is generally high at immediate vicinity of walls and decreases by departing the walls toward the centre of the microchannel.
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prediction of temperature distribution and nusselt number in Rectangular Microchannels at wall slip condition for all versions of constant wall temperature
International Journal of Thermal Sciences, 2007Co-Authors: Lutfullah KuddusiAbstract:Slip flow in Rectangular Microchannels heated at constant and uniform wall temperature (H1 boundary condition) is studied. The study is extended to the eight possible thermal versions that are formed of different combinations of heated and adiabatic walls. Integral transform method is applied to derive the velocity and temperature distributions and thus, the average Nusselt number for all the eight thermal versions. It is found that, for Microchannels with perfect accommodation for velocity and temperature, the rarefaction has a decreasing effect on heat transfer for all the eight thermal versions. The results of the paper for the special case of non-slip flow agree exactly with the results found for macrochannels in literature.
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prediction of temperature distribution and nusselt number in Rectangular Microchannels at wall slip condition for all versions of constant heat flux
International Journal of Heat and Fluid Flow, 2007Co-Authors: Lutfullah Kuddusi, Edvin CetegenAbstract:Slip-flow in Rectangular Microchannels heated at constant and uniform heat flux (H2 boundary condition) is studied. The study is extended to the eight possible thermal versions that are formed of different combinations of heated and adiabatic walls. The paper aims to show the effect of different thermal versions on heat transfer in microchannel. The velocity distribution that is required in determining of temperature distribution is obtained from the literature. Mathematical similarity between the heat conduction and convection problems is used to determine the temperature distribution in the microchannel. The solution of a heat conduction problem, available in the literature, is adapted to the heat convection problem in the microchannel. The velocity and temperature distributions thus found are used to determine the average Nusselt number for all the eight thermal versions. For the case studied, it is found that rarefaction has a decreasing effect on heat transfer in the Microchannels exposed to any of the eight thermal versions. The results of the paper for the special case of no-slip-flow agree exactly with the results found for macrochannels in the literature.