Fluid In Microchannel Research Articles

High-performance near-substrate heat sink with Tesla-like rotor-wing microchannel for chiplet cooling application

Microchannel heat sink provides a viable solution for enhancing thermal management in high-power chiplets. However, in consideration of cooling efficiency, low pressure drop, cost-effectiveness and reliability, it’s challenging to create an effective heat sink for a million-watt chip. Inspired by Tesla structure, this study introduces a Tesla-like rotor-wing microchannel (TRWM) to boost cooling performance. Due to the features of main channels, branch channels, and micro-islands in TRWM design, fluid in microchannel is effectively mixed and stirred with varied flow patterns, high temperature gradients and significant velocity gradients, which enhances the cooling capacity through precise fluid dynamics adjustment. Three different TRWMs are designed and compared by simulations. And the simulated results show that TRWM of 135° model achieves a maximum heat flux of 1514 W cm−2 @0.1 cm2 under a 60 K temperature rise, improving cooling efficiency by 19.4 % over the traditional channel design with 1221 W cm−2 @0.1 cm2. And then, the TRWM is fabricated using Ultraviolet Lithgraphie Galvanoformung Abformung (UV-LIGA) and bonding processes. Ultimately, the fabricated 135° TRWM sample demonstrated a heat dissipation capacity of up to 1446 W cm-2 @0.1 cm2 with a temperature increase of 60 K, which corresponds well with the simulated results. Moreover, the discrepancy between the actual and simulated values is less than 6.3 % under the same conditions. This performance provides a practical design solution for chiplet cooling and highlights the potential of bioinspired microfluidics.

Electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid through parallel plate microchannels with surface charge-dependent asymmetric slip

The investigation of electromagnetohydrodynamic (EMHD) flow of non-Newtonian fluids in microchannels represents a compelling intersection of fluid dynamics, electromagnetism and materials science, particularly demonstrating significant potential and importance in contemporary microfluidic applications. This work delves into the intricate mechanisms governing the EMHD flow of non-Newtonian Jeffrey fluids within parallel plate microchannels, with a specific focus on the influence of asymmetric slip boundary conditions that depend on surface charge. The EMHD flow is propelled by the amalgamation of the Lorentz force and a consistent pressure gradient. Analytical solutions for the velocity and volumetric flow rate of this problem are derived employing both the method of separation of variables and Cramer's rule. Initially, this study undertook comparisons with prior research, leveraging pertinent assumptions to validate the precision of our findings. Subsequently, the discussion shifts to the examination of how velocities are affected by surface charge effects under various slip boundary conditions at different Reynolds numbers. The results suggest that velocities are significantly influenced by surface charge effects under asymmetric slip boundary conditions compared to scenarios involving symmetric and single-wall type, irrespective of the Reynolds number, thereby highlighting the importance of this study. Finally, the relationships among key parameters such as surface charge density, Hartmann number, relaxation time and retardation time affecting volumetric flow rate are analyzed, while approaches and specific percentages for increasing or decreasing volumetric flow rate are provided. One of the more interesting findings is that the volumetric flow rate is expected to experience a 3.9% reduction, considering the influence of the surface charge effect. These findings are not only vital for advancing microfluidics but also have the potential to drive new innovations in related medical technologies, given the notable similarities in the physical properties of Jeffrey fluid and blood.

Numerical investigation on the enhanced heat transfer characteristics of non-Newtonian viscoelastic fluids in microchannel with chip arrays

Elastic turbulence is an efficient heat transfer method at microscale. In this work, we conduct a systematic investigation on the flow and heat transfer performances of viscoelastic polymer solutions in microchannels with chip arrays by means of high-fidelity numerical simulations. Focusing on the effects of fluid elasticity [i.e. polymer relaxation time (λ)] and flow Reynolds number (Re), we find that the synergistic interplay between inertial and elastic forces is strategically exploited to amplify convection, thereby facilitating an enhanced heat transfer performance. For highly elastic fluid, the Nusselt number (Nu) can be improved by 76.13 % compared to that of less elastic fluid, while the pressure drop is reduced appropriately. In addition, as the fluid elasticity increases, the pressure drop decreases and eventually converges to a constant. In the zone of elastic turbulence, the fluid reinforces the convective heat transfer, which can be ascribe to the deformation of long-chain polymer molecules. Particularly, we consider the effect of temperature-dependent λ on the heat transfer performance. Our results demonstrate that the increased temperature-dependent λ decreases the value of Nu, and the variation between values of variable and constant λ is reduced with increasing Re or λ. Hence, in some cases of large fluid elasticity or high Re, it is possible to safely ignore the impact of temperature-dependent λ with an acceptable accuracy. The present work provides important insights into the enhanced heat transfer via elastic turbulence, which could guide the applications in the field of chip cooling.

Thermally developing streaming potential-mediated pressure-driven flow of Phan–Thien–Tanner fluid in a microchannel

In this study, we have conducted a semi-analytical investigation into the streaming potential-mediated pressure-driven flow of hydrodynamically fully developed and thermally developing viscoelastic fluid in a parallel plate microchannel. We have utilized a simplified Phan–Thien–Tanner model to describe the rheology of the viscoelastic fluid. Our approach delved into the full Poisson–Boltzmann equation, deriving exact analytical solutions for the electrostatic potential distribution and velocity profile. Furthermore, we concurrently derived semi-analytical solutions for the temperature distribution and Nusselt number, accounting for the effects of heat generation from viscous dissipation and Joule heating in thermally developing flows. We have demonstrated that an increase in the degree of surface charge triggers the streaming potential field, while the volumetric flow rate escalates with the viscoelastic parameter εWik¯2. Moreover, we have observed that the magnitude of the dimensionless temperature decreases with increasing values of the effective Joule heating parameter Speff. Our analysis reveals that the streaming potential effect hampers fluid flow, resulting in an increase in the bulk fluid temperature and consequently reducing the heat transfer rate. We observe that the magnitude of the Nusselt number decreases with increasing Speff. The entropy generation analysis reveals that increasing the Peclet number amplifies flow and temperature gradients, leading to higher fluid irreversibility in microchannels. The Bejan number experiences a significant decrease across the channel, reaching its minimum at a specific axial location before stabilizing further downstream. We find that heat transfer irreversibility predominantly influences system irreversibility, except for the Brinkmann number Br = 0.01, where convective heat transfer dominates at the entrance region, transitioning to friction losses beyond the thermal entry zone.

Interplay of roughness and wettability in microchannel fluid flows—Elucidating hydrodynamic details assisted by deep learning

Under microconfinement, the complex interaction between surface roughness and fluid slippage yields unexpected variations in friction factor and drag reduction. These variations arise from the combined effects of roughness and hydrophobic interactions of the surface with the hydrodynamic field. Our study investigates alterations in frictional characteristics within long microchannels, considering fluid slippage, hydraulic diameter, and roughness. This exploration holds promise for precise drag reduction control applications for lab-on-a-chip and small-scale devices. To address computational limitations in analyzing diverse hydrodynamic conditions, we employ an artificial neural network prediction model, validated with experimental and numerical results. Contrary to the macroscopic conclusions obtained from the Moody chart, our findings indicate that fluid slippage, apart from surface roughness, significantly influences the friction factor. The interdependencies of friction factor on the flow and fluid parameters are thoroughly studied toward the proposition of a new slip-modified constricted flow friction factor formula, predicting friction in microchannels with combined roughness and hydrophobicity effects. This combined numerical and machine-learning approach presents a noteworthy counterpart to the moody chart at microscales offering the potential for a unified continuum-based description to include interfacial effects.

Dynamic interactions in MHD Jeffrey fluid: Exploring peristalsis, electro osmosis and homogeneous/heterogeneous chemical reactions

This paper investigates the behavior of magnetohydrodynamic (MHD) peristaltic flow with electroosmosis. The Jeffrey fluid in microchannel under the influence of homogeneous-heterogeneous chemical reaction has been taken. The heat absorption and nonlinear radiation are also scrutinized here. This study contributes to the fundamental understanding of complex fluid dynamics in microscale systems and offer valuable insights for designing and optimizing microfluidic devices. In the framework of mathematical simulation, the relevant dimensional nonlinear equations are reduced into dimensionless equations by using linear transformations. Thus Debye-Hückel linearization has been employed. The streamline approach with mathematical modelling has been performed within the limits of δ≪1 and Re→0. The appropriate equations for temperature and concentration with boundary conditions are solved by using perturbation approach whereas, the exact solution is found for velocity equation. A graphical depiction of crucial physical characteristics on velocity, temperature, concentration and streamlines are reported in the last section. It is observed that the velocity distribution decreases for the higher value of M (0.5≤M≤2) however, it increases for the escalating values of Uhs (−0.5≤Uhs≤1.5). When Rn(0.1≤Rn≤0.6) gets stronger then temperature profile decreases. It is noticed that the concentration profile decays owing to enhancement in Sc(−0.5≤Sc≤1.5). As the M (0.5≤M≤2) increases, the size of trapped bolus decreases. Escalating values of temperature ratio parameterθw(1.0≤θw≤1.6)enhances the Nusselt number. The novelty of this study lies in the comprehensive analysis of multiple complex phenomena in a single framework. The interplay between MHD electroosmotic flow, homogeneous heterogeneous chemical reactions, peristalsis, nonlinear thermal radiation, heat absorption and no-slip condition has not been explored in previous research.

The hydrothermal performance of non-Newtonian fluids in superhydrophobic microchannels

The hydrothermal performance of non-Newtonian fluids in superhydrophobic microchannels

Unsteady MHD Free Convection Flow of Fluid in Micro Channel in the Presence of Viscous Dissipation Between Vertical Parallel Two Walls

Convection is a process by which heat is transferred by movement of a heated water. The phenomenon where heat transfer process is driven by natural fluid motion due to temperature and density gradients is called free convection. The effect of slip velocity on thermal behaviours of MHD free convection flow over a vertical parallel two walls is the focus of this research. The mathematical equations which described the phenomenom includes momentum, magnetic field and energy equations. Condition for the existence and uniqueness of solution of the model equations were established using the approach of Lipschitz continuity. The model equations in dimensionless form were solved using Olayiwola’s generalized polynomial approximation method (OGPAM). The results obtained which contains the dimensionless parameters were presented graphically and discussed. It was observed that increase in Reynolds number and Knudsen number both enhanced the velocity distribution at the two walls. Also, magnetic field and temperature field were enhanced by magnetic prandtl number and Eckert number respectively.

Studies of interfacial wave properties during displacement with pure viscoelastic fluids in microchannels

In this study, new experimental data for the displacement of a Newtonian liquid by three pure viscoelastic (Boger) fluids with different relaxation times were obtained with imaging in a 500 μm microchannel. Results were compared against those from displacement using a Newtonian liquid. Small irregular waves were observed at the interface for the Newtonian displacement, while periodic instabilities were seen for all Boger fluid cases. The elastic Mach number (Ma), describing the ratio of the flow velocity with the elastic wave propagation velocity, was found to be the key parameter for correlating the wave properties in the case of Boger fluids. The amplitude of the wavy interface initially increased up to Ma = 0.5, before decreasing again. The frequency and the wave velocity increased monotonically with increasing Ma. For all configurations, a phase shift of π was found between the top and the bottom interfaces. Correlations from experimental data were developed for all wave properties. Based on these correlations, an empirical wave model was developed to describe the observed planar images and to reconstruct the three-dimensional waves, which resemble a helical structure.

Numerical model development for critical region flow and thermodynamic transitions of CO2 fluids in microchannel

Dramatic changes of thermophysical properties in the vicinity of critical point brings significant accelerating effect on the thermodynamic transitions of fluid. This study performs a confined geometric design with CO2 fluids passing through the critical zone in microchannel. Such a problem formulation combines the compressible Navier-Stokes equations with different property formulations to obtain critical anomaly effects at complex critical transport coefficients. Three equations of state (van der Waals (vdW), Redlich-Kwong (R-K) and Peng-Robinson (P-R) state equations) and their corresponding thermodynamic relations are derived in solving the governing equations of flow and heat transfer equations. Basic results are found to be consistent with theoretical asymptotic analysis, with linearly curves of pressure and a sudden shift of density (425 kg/m3–502 kg/m3) and velocity (0.82 m/s to 0.97 m/s) profiles when the microchannel flow across the critical region. The cascade effect between weakened radial thermal conductivity (λ ∼ (ρ – 1)-1/2, cp ∼ (ρ - 1)−2) and enhanced fluid expansion (βp ∼ (ρ - 1)−2) in the critical region is also shown to cause a sharp negative transition in temperature. In addition, the simulations demonstrate a qualitative comparison for three state equations, and the distinctions in quantitative terms (negative temperature value are −0.1 (vdW), −0.17 (R-K), and − 0.23(P-R)) are found to originate from stronger divergence characteristics (the specific heat cp and thermal expansion coefficients βp) in P-R gases than vdW and R-K gases.

Micromixing within microfluidic devices: Fundamentals, design, and fabrication

As one of the hot spots in the field of microfluidic chip research, micromixers have been widely used in chemistry, biology, and medicine due to their small size, fast response time, and low reagent consumption. However, at low Reynolds numbers, the fluid motion relies mainly on the diffusive motion of molecules under laminar flow conditions. The detrimental effect of laminar flow leads to difficulties in achieving rapid and efficient mixing of fluids in microchannels. Therefore, it is necessary to enhance fluid mixing by employing some external means. In this paper, the classification and mixing principles of passive (T-type, Y-type, obstructed, serpentine, three-dimensional) and active (acoustic, electric, pressure, thermal, magnetic field) micromixers are reviewed based on the presence or absence of external forces in the micromixers, and some experiments and applications of each type of micromixer are briefly discussed. Finally, the future development trends of micromixers are summarized.

Characterizing Quadratic Convection and Electromagnetically Induced Flow of Couple Stress Fluids in Microchannels

Characterizing Quadratic Convection and Electromagnetically Induced Flow of Couple Stress Fluids in Microchannels

Natural convection flow of third-grade fluid along an oblique permeable micro-channel with Hall effects: an irreversibility analysis

The third-grade fluid model is one of the unique models in all the non-Newtonian fluids, which is evolved for its particular implementation in petrochemical engineering, confectionaries, earth science and lubricating systems. Hence, the current work scrutinises the entropy generation and thermal analysis of non-Newtonian fluid in a permeable oblique microchannel. The effects of heat generation, thermal radiation and Hall effects on fluids in a microchannel have been explored. The rheological expressions of third-grade fluid are considered. By considering the desirable similarity variables the equation of motion was reduced to nonlinear ordinary differential equations. The Runge–Kutta-Fehlberg’s fourth-fifth-order technique along with the shooting method was adopted to solve these dimensionless expressions. The repercussion of this investigation upholds that the enhancement of distance parameters augments the thermal field. The amplification of the porosity parameter occurs with a decrement in the thermal profile. The secondary velocity profile declines with an enhanced value of the Hall parameter and seen improvement in the primary velocity profile.

Induced charge electro-osmotic mixing performance of viscoelastic fluids in microchannels with an electrically conductive plate

Micromixers have important applications in lab-on-a-chip, biomanufacturing, and chemical engineering. In this study, a micromixer with a conductive barrier plate based on the induced charge electro-osmosis is proposed. The Oldroyd-B constitutive model was chosen to characterize the flow characteristics of viscoelastic fluids, and the Poisson–Boltzmann model was used to characterize the electrokinetic properties. The effects of the installation of the conductive plate, the concentration of the polymer, and the shape of the conductive plate on the mixing were studied based on the finite volume method. The mixing efficiency of the viscoelastic fluids is 78.3% when a non-conductive plate is placed in the micromixer. However, placing a conductive plate increases the mixing efficiency to 89.8%. As the polymer concentration increases, the mixing efficiency increases, which is attributed to the elastic instability. As the curvature of the conductive plate increases from 0° to 360°, the mixing efficiency of the Newtonian fluid increases by 2.82%, while that of the polyacrylamide solutions at concentrations of 100 and 250 ppm increases by 5.31% and 1.97%, respectively.

Flow of magnetized Powell-Eyring fluid in microchannel exposed to non-linear radiation and constricted to slip regime by varying viscosity

ABSTRACT The present article exemplifies flow of Powell-Eyring fluid flowing in the microchannel which is placed horizontally. For this microfluidic flow, fluid is sucked and injected through the walls of the microchannel. The microchannel is also influenced by magnetic field and exposed to the non-linear radiation due to its extensive application to process the polymers, as the ultimate product quality relies on the heat controlling factors. Interest is laid on studying flow manner by differing viscosity. Flow is facilitated by slip and convective conditions. Non-linear equations are solved using finite difference code improved by using the Lobatto IIIA formula with the help of MATLAB software and findings are discussed using graphs. Results attained from the analysis claim that Powell-Eyring fluid parameters decline the velocity of the flow and enhance the skin-friction. The main concern of the present work is to maximize the heat transfer which could be attained by keeping Prandtl number low, thus for higher momentum diffusivity exhaustion in the heat transfer rate is recorded. Reynolds number also turns out to be critical factor as it accelerates the fluid flow at the suction wall and decelerates the velocity at the injection wall.

Enhancing stiffness-based cell sorting using power-law fluids in ridged microchannels

Sorting biological cells in heterogeneous cell populations is a critical task required in a variety of biomedical applications and therapeutics. Microfluidic methods are a promising pathway toward establishing label-free sorting based on cell intrinsic biophysical properties, such as cell size and compliance. Experiments and numerical studies show that microchannels decorated with diagonal ridges can be used to separate cell by stiffness in a Newtonian fluid. Here, we use computational modeling to probe stiffness-based cell sorting in ridged microchannels with a power-law shear thinning fluid. We consider compliant cells with a range of elasticities and examine the effects of ridge geometry on cell trajectories in microchannel with shear thinning fluid. The results reveal that shear thinning fluids can significantly enhance the resolution of stiffness-based cell sorting compared to Newtonian fluids. We explain the mechanism leading to the enhanced sorting in terms of hydrodynamic forces acting on cells during their interactions with the microchannel ridges.

Study of peristaltic activity in non-linear blood analysis of Williamson fluid in a microchannel

The present investigation is modeled to study the effect of homogeneous and heterogeneous reactions on the peristaltic blood transportation of electrically conducting Williamson fluid in an asymmetric microchannel under velocity slip conditions. The mechanism of heat transfer is also examined in conjunction with viscous dissipation and thermal radiation. Implementation of small Reynolds number and large wavelength concepts leads to a reduction in the complexity of the system. Series solutions for velocity, temperature, stream function, and concentration fields are found using the regular perturbation technique. Using Mathematica software, Simpson’s rule was used to evaluate the pumping features such as pressure rise and frictional force. The effects of embedded parameters are portrayed and discussed by using a graphical approach. The skin friction and Nusselt number at the channel walls are established for a choice of assessments of significant parameters and which are exhibited in a tabular manner. It is observed that an enhancement in the values of Weissenberg number fluid velocity reduces at the lower channel wall whereas it increases at the channel upper wall.

Electro-osmotic flow of generalized Maxwell fluids in triangular microchannels based on distributed order time fractional constitutive model

Based on the linearized Poisson–Boltzmann equation, the electro-osmotic flow of a generalized Maxwell fluid under an alternating field in an isosceles right triangle microchannel is studied. The finite volume method and L2 interpolation method are used to obtain the numerical solution. An analytical solution is constructed to verify the accuracy of the numerical solution. Under the alternating current, the velocity will oscillate periodically. The velocity amplitude of the Maxwell fluid with the distributed order time fractional derivative is larger than that of Newtonian fluids and fractional Maxwell fluids, which indicates that its elastic characteristics further promote fluid flow. However, oscillation of the velocity does not achieve synchronization with the oscillation of the electric fields. Furthermore, due to the existence of the angle effect, the velocity will develop at acute angles and form a larger value of velocity first. The numerical results show that the relaxation time, electrokinetic width, zeta potential, and angular Reynolds number play important roles in determining the velocity and amplitude of electro-osmosis.

Numerical simulation to model the effect of injection velocity on the thermo-hydraulic behavior of the microchannel fluid flow via Navier–Stokes equations joined with the slip velocity boundary condition

Numerical simulation to model the effect of injection velocity on the thermo-hydraulic behavior of the microchannel fluid flow via Navier–Stokes equations joined with the slip velocity boundary condition

Mixing inside droplet co-flowing with Newtonian and shear-thinning fluids in microchannel

The effect of external fluid on the mixing efficiency of miscible Newtonian liquids inside a two-dimensional microdroplet upon co-flow in a rectilinear microchannel is investigated numerically. With this aim, two different types of continuous media, Newtonian and Carreau–Yasuda shear-thinning fluids, are considered. The mixing time within a microdroplet is estimated from standard deviation of concentration from the average value. The dependencies of the mixing time on Péclet number, viscosity ratio of the fluid components and confinement parameter (ratio of the droplet initial diameter to microchannel cross-section size) are explored. It is shown that for both Newtonian and Carreau–Yasuda continuous phases, the corresponding mixing times in a microdroplet are the power-law functions of Péclet number. It was found that values of the corresponding exponents are determined by rheological properties of the fluids. Three distinct liquid mixing mechanisms inside microdroplet at different values of the confinement parameter are revealed.