Wavy Microchannel Research Articles

Conjugate effect on flow boiling instability in wavy microchannel

Three-dimensional numerical study on two-phase flow boiling in rectangular microchannel with wavy vertical wall configuration is considered that can be utilized for heat dissipation in high flux electronics devices. Straight and wavy microchannels are considered for comparison and analysis. Under conjugate heat transfer situation, effect of flow boiling instability in straight and wavy microchannel is numerically studied using water as the working fluid. Behaviour of bubble growth rate and two-phase flow pattern in straight and wavy microchannel are investigated for a wide range of parameters such as waviness (γ ~ 0 - 0.267), substrate thickness to channel height ratio (δsf ~ 1 and 5), wall to fluid conductivity ratio (ksf ~ 22 - 646), and mass flux (G ~ 118 - 590 kg/m2s). It is found that smaller bubbles are formed in wavy microchannel while confined and elongated bubbles are formed in straight microchannel which often causes flow clogging and premature dryout. The work also presents a comparative analysis between single-phase and two-phase flow boiling cooling technique in straight and wavy microchannel under same geometrical parameters and applied heat flux.

Thermohydraulic characteristics and entropy analysis of a novel clockwise and anti-clockwise twisted sinusoidal wavy micro-channel under pulsating inlet condition

Heat transfer performance of microchannel are becoming an important area of research with the current fast growing scenario of high speed computing and miniaturized electronic devices. These devices pile up large amount of heat accompanied by smaller surface area to release it. The current work examines unsteady, laminar flow heat transfer inside a novel twisted sinusoidal wavy microchannel. The channel with square cross section is wavy in nature as well as twisted. The first half portion of the channel is twisted clockwise, whereas the twist in the remaining part is having counterclockwise twist. The novel geometry promotes mixing of fluid layers leading to transport augmentation. The inlet pulsation follows sinusoidal pattern in time. The thermal performance parameter of the proposed novel geometry was assessed within a Reynolds number range of 1–100. Both the pulsation amplitude and Strouhal number are varied during the course of this study. To solve the governing equations, a finite volume based method was utilized. The Nusselt number data shows significant enhancement for the sinusoidal inlet velocity as compared to that of the steady case, i.e. without inlet flow pulsation. The performance enhancement criterion combining heat transfer and pressure drop shows significant improvement over steady flow case as well as for one-way twisted tube. Entropy generation, which is the measure of dissipated energy, is also reported in the present work.

Augmentation of heat transfer in a microtube and a wavy microchannel using hybrid nanofluid: A numerical investigation

The paper discusses the numerical investigation involving forced convective heat transfer (HT) in the laminar flow regime is carried out for nanofluid (NF) and hybrid NF (HNF) in a microtube and wavy microchannel. Water‐based Al2O3 NF and water‐based Al2O3‐Ag HNF is studied for this purpose. Reynolds number (Re), temperature, volume fraction, and nanoparticle (NP) size are varied for the analysis at a constant HT rate. Numerical results characterizing the performances of NF and HNF are presented in terms of the local HT coefficient. It is found that with the increase in Reynolds number, volume fraction, and temperature, local HT coefficient is increased. For Reynolds number of 50 and 𝜑 = 3%, a maximum of 11.03% increase in HT coefficient is obtained for microtube, while for the same case, a maximum of 10.16% is found for wavy microchannel. Comparison of NF and HNF reveals superior HT property of the later. However, microtube exhibits better HT coefficient than the wavy channel at constant heat flux, length, and area.

Simulation of the hydrodynamics and mass transfer in a falling film wavy microchannel

The flow in a liquid falling film is predominantly laminar, and the liquid-side mass transfer is limited by molecular diffusion. The effective way to enhance the mass transfer is to improve the liquid film flow behavior. The falling film behaviors of water, ethanol and ethylene glycol in nine different wavy microchannels were simulated by Computational Fluid Dynamics. The simulation results show that the falling film thickness exhibits a waveform distribution resulting in a resonance phenomenon along the wavy microchannel. The fluctuation of liquid film surface increases the gas–liquid interface area, and the internal eddy flow inside the liquid film also improves the turbulence of liquid film, the gas–liquid mass transfer in falling film microchannels is intensified. Compared with flat microchannel, the CO2 absorption efficiency in water in the wavy microchannel is improved over 41%. Prediction models of liquid film amplitude and average liquid film thickness were established respectively.

Thermal and hydraulic characteristics of a hybrid nanofluid containing graphene sheets decorated with platinum through a new wavy cylindrical microchannel

One approach to improve cooling efficiency of cylindrical microchannel heat sinks (CMCHS) is increasing the total wetted surface through cylindrical geometries instead of using flat configurations. In addition, the wavy structures using advanced working fluids is a novel technique to enhance the heat transfer in CMCHS. In this study, by using a graphene-platinum/water hybrid nanofluid as the working fluid, the effect of wavy-shaped fins on hydro-thermal performance of a cylindrical CMCHS is investigated numerically. Three-dimensional, steady, laminar flow is simulated using the finite volume method. The sinusoidal fins form the secondary flows in the channel, which disturb the boundary layer leading to intensification in heat transfer. Increasing the amplitude, concentration, and Reynolds number decrease the thermal resistance and facilitate heat transfer. The maximum value of the average heat transfer coefficient is calculated as 13387 W/m2K, while the highest pumping power and lowest thermal resistance are calculated to be 0.6 W and 0.031 K/W, respectively. A comparison between the wavy and straight CMCHSs shows that wavy fins can improve the heat transfer coefficient by up to 75%. The maximum performance evaluation criterion (PEC) is obtained at a concentration of 0.02% and Reynolds number of 600 for all amplitudes. Finally, multi-objective optimization is performed to find the optimal states that yield the highest heat transfer coefficient, lowest thermal resistance, and lowest pumping power regarding the designers’ demands. Optimization is conducted using genetic algorithm and the compromise programming method. The results obtained from the optimization indicate that nanoparticle concentration profoundly affects pumping power, while amplitude has severer influence on the thermal attributes. The main novelties of this work are to employ wavy fins in a CMCHS, as well as to use multi-objective optimization with regard to the relative importance of heat transfer and pumping power in this configuration.

Heat transfer and Helmholtz-Smoluchowski velocity in Bingham fluid flow

A mathematical study is developed for the electro-osmotic flow of a non-Newtonian fluid in a wavy microchannel in which a Bingham viscoplastic fluid model is considered. For electric potential distributions, a Poisson-Boltzmann equation is employed in the presence of an electrical double layer (EDL). The analytical solutions of dimensionless boundary value problems are obtained with the Debye-Huckel theory, the lubrication theory, and the long wavelength approximations. The effects of the Debyelength parameter, the plug flow width, the Helmholtz-Smoluchowski velocity, and the Joule heating on the normalized temperature, the velocity, the pressure gradient, the volumetric flow rate, and the Nusselt number for heat transfer are evaluated in detail using graphs. The analysis provides important findings regarding heat transfer in electroosmotic flows through a wavy microchannel.

Electro-osmotic flow of hydromagnetic dusty viscoelastic fluids in a microchannel propagated by peristalsis

A theoretical study is carried out to determine the electric and magnetohydrodynamics of a dusty Jeffrey fluid containing small particles propagating through a wavy asymmetric microchannel. A static transverse magnetic field is applied in the presence of an electric field. Slip effects are considered to examine the flow behavior. The dusty Jeffrey model is taken into account to review its response. The governing flow problem is modelled with the help of ionic Nernst Planck equation, Poisson–Boltzmann equation, and Debye length approximation. It is then transformed into a steady wave frame with the help of coordinate transformation. Using the lubrication approach (“long wavelength and zero's Reynolds number”) the normalized governing equations of fluid and particle-phase that corresponds to the second order coupled partial differential equations represents the contribution of Jeffrey fluid model. The linearized boundary value problem is solved analytically, and exact solutions are presented for axial velocity distribution, wall shear stress and pressure gradient. It is reported from the obtained results that the magnitude of the particle-phase is more as compared to fluid-phase for velocity field and shear stress however it is less for pressure gradient. The findings of the present model are applicable in designing the microfluidics devices for the use of various transport phenomena in micro level where particles as well as fluids are transported together. The present study can be further extended and applicable for three-dimensional profile with appropriate assumptions and modifications.

Thermal performance of a mini-channel heat exchanger (MCHE) working with CNT/GNP-based non-Newtonian nanofluids

In this work, the heat transfer of the non-Newtonian nanofluids inside a wavy microchannels heat exchanger (WMCHE) in cross-flow configuration has been experimentally and numerically studied. The Reynolds number (Re) does not have unique definition for non-Newtonian fluids. The non-Newtonian carboxyl methyl cellulose (CMC) aqueous solution containing 0.2 mass% CMC is used as base fluid (BF). The single-walled carbon nanotubes (CNT) and graphene nanoparticles (GNP) were added to the BF in 0.1 mass% as two other test fluids. Here, an equation based on the assumption of laminar flow is used in order to evaluate Re as a function of experimentally measured pressure drop. However, this assumption needs a similar form of friction factor relation to that of Newtonian fluids that is verified based on numerical simulation. In the presented work, finite element method (FEM) was utilized to perform the numerical modeling through Comsol Multiphysics software. Results show that as flowrate and relative waviness(2A/2L) increase, the convective heat transfer coefficient could be intensified. In terms of pressure drop, it was seen that with increasing the flowrate and relative waviness(2A/2L) of nanofluids, pressure drop was intensified. The results are compared to the experimental data and showed good agreement. The proposed performance index implies that GNP/BF nanofluid is the best one and both of two kinds of wavy configurations enhance the heat transfer efficiency, although the wavy two configurations are better.

Numerical Simulation of Flow in a Wavy Wall Microchannel Using Immersed Boundary Method

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 problems. 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.

Experimental study on two-phase boiling in wavy copper microchannels fabricated with ultrafast laser micromachining

In this study, the sinusoidal wavy (SW) copper microchannels with triangular cross section were fabricated with the ultrafast laser micromachining approach. The flow boiling of de-ionized water in SW microchannels were experimentally studied under mass fluxes of 43.43–217.15 kg (m2s)−1 and heat fluxes of 0–590 kW m−2. The flow patterns in the SW microchannels were visually observed and the boiling heat transfer characteristics were analyzed based on the obtained data. It shows the SW microchannel has a maximum enhancement of 127.7% in the local heat transfer coefficient with an acceptable increase of pressure loss compared to the straight one in the present work. In SW microchannels, a low degree of superheat can trigger the onset of nucleate boiling. A slow decreasing tendency of local heat transfer coefficient under a high effective heat flux or a high vapor quality was observed. The heat transfer mechanism of flow boiling in SW microchannels was analyzed based on the experimental visualization. Nucleate boiling and thin film evaporation are the dominant modes under different thermal boundary conditions. The flow boiling instability phenomenon in microchannels can be diminished using the wavy structures.

Microvascular blood flow with heat transfer in a wavy channel having electroosmotic effects.

The present paper addresses microvascular blood flow with heat and mass transfer in complex wavy microchannel modulated by electroosmosis. Investigation is carried out with joule heating and chemical reaction effects. Further, viscous dissipation is also considered. Using Debye-Huckel, lubrication theory, and long wavelength approximations, analytical solutions of dimensionless boundary value problems are obtained. The impacts of different parameters are examined for temperature and concentration profile. Furthermore, nature of pressure rise is also investigated to analyze the pumping characteristics. Important results of flow phenomena are explored by means of graphs.

Effect of Relative Waviness on Low Re Wavy Microchannel Flow

A 3-D, steady, conjugate numerical model is used to study the effect of waviness on laminar fluid flow and heat transfer characteristics associated with microsized wavy channels. The numerical model has been validated against available experimental data. It is observed that transition Re and average Nu are functions of waviness of the channel; however, friction factor remained constant at higher waviness. The augmentation of Nu with waviness is found to be resulting from increased levels of recirculation and secondary flows. Peak vorticity levels showed an increase of six times when relative waviness increased from 0.03 to 0.3 and is about 2.5 times when Re increased from 100 to 200. The effect of chaotic advection is not observed even for higher waviness channels at Re = 100.

Experimental and numerical investigation of heat and mass transfer in non-uniform wavy microchannels

To improve the thermal performance of microchannel heat sinks, non-uniform wavy microchannels were designed and their heat and mass transfer performance were studied by a numerical method. The effects of the Reynolds number, Re, and the peak deviation position on the thermal-hydraulic performances of the microchannels were analyzed based on the performance evaluation criteria (PEC) and the principle of entropy generation. The numerical analysis indicated that the heat transfer performance of the divergent wavy microchannel (denoted as MCH-41, with the peak position far from the fluid entrance) exhibited better heat transfer performance than that of the uniform (denoted as MCH-05) and the convergent wavy (denoted as MCH-14) microchannels. The thermal resistance and entropy generation of MCH-41 were lower than those of MCH-05 and MCH-14. Moreover, a flow visualization platform was established to observe the periodic pulsation characteristics of the fluid at Re = 693. The enhanced heat and mass transfer mechanism of the divergent wavy microchannel was further analyzed. The experimental results were in agreement with the numerical simulation results.

A new design of double-layered microchannel heat sinks with wavy microchannels and porous-ribs

A new design of double-layered microchannel heat sinks, which combines wavy microchannels with porous vertical ribs, is proposed in this work. The flow and heat transfer behaviors of the new design are investigated via a three-dimensional solid–fluid conjugate heat sink model. The superiority of the new design is highlighted by comparing the new design with three existing double-layered designs under constant pumping power constraints. The three existing designs include a design with straight microchannels and solid-ribs, a design with straight microchannels and porous-ribs, and a design with wavy microchannels and solid-ribs. The results show that porous-ribs reduce the pressure drop across heat sinks, whereas wavy microchannels induce Dean vortices and enhance coolant mixing. In a low pumping power region of 0.005 to 0.01 W, the coolant inlet velocity is found to be the most dominant factor to determine the cooling capacity of heat sinks, whereas in a high pumping power region of 0.1 to 0.2 W, the coolant mixing becomes the dominant one. The new design has both wavy microchannels and porous-ribs, thus providing the best cooling capacity among the four double-layered heat sinks in the whole pumping power range of 0.005 to 0.2 W. The new design is further optimized by single-parameter analyses. It is found that with a fixed pumping power of 0.05 W as constraint, there is an optimal wavelength or an optimal amplitude of wavy units to achieve the lowest thermal resistance; however, the thermal resistance monotonously reduces with the increase in porous permeability or the decrease in quadratic drag factor.

Numerical Investigation of Heat Transfer and Fluid Flow Characteristics in Circular Wavy Microchannels with Sidewall Rib

AbstractPurpose: Numerical investigation was carried out to study the hydro-thermal characteristics in circular wavy microchannels (CWMCs) with sidewall rib. Thermal resistance and pressure drop penalty were compared with sinusoidal wavy microchannels (SWMCs) design. Parametric study on sidewall rib was also carried to minimize the pressure drop penalty and to achieve lower thermal resistance. Introducing sidewall rib in the CWMCs leads to the formation of more Deans vortices. This leads to an effective fluid mixing and augments the convective heat transfer. Design methodology/approach: A computational solid domain was created in SOLIDWORKS and the fluid domain was produced by circular arc profile for the entire length of heat sink. 3-D numerical investigation was carried out using ANSYS FLUENT software. Created computational domain was imported into ANSYS WORKBENCH. Meshing was executed in ANSYS mesh module. The computational domains were meshed using hexahedral elements adopting match control on both sides of microchannel (MC). The numerical investigation was carried out in the Re range from 100 to 300 with constant heat flux (50 W/cm2) applied at the bottom of the channel. Heat transfer and fluid flow characteristics were explained with velocity vectors, velocity contours and temperature contours. Findings: From numerical studies, it is concluded that CWMC with sidewall rib width (0.15 mm) leads to 33.6 % lower thermal resistance than SWMC with pressure drop penalty. Originality/Value: Present study is useful to identify the optimum deign to augment the heat dissipation performance of microchannel heat sink.

Thermal and hydrodynamic analysis of non-Newtonian nanofluid in wavy microchannel

In this study, hydrodynamic and heat transfer of non-Newtonian nanofluid behavior is investigated in a wavy microchannel with rectangular obstacles. Aluminum oxide as nanoparticles (Al2O3) with 0.5% and 1.5% volume fractions and three different diameters (25, 45 and 100 nm) are added to pure water as a base phase to form a nanofluid structure. In order to form the non-Newtonian nanofluid, 0.5% carboxy methyl cellulose (CMC) is added to the nanofluid structure. Up and down walls of microchannels at the middle section where obstacles are located have constant 50,000 W⁄m2 heat flux. Inlet temperature is constant and equal to 298 K with different Reynolds numbers varying as 5, 50, 150 and 300. Rib heights varying between 3 and 7 μm for five cases with different nanoparticle volume fractions, nanoparticle diameters and Reynolds numbers are investigated. Nusselt number, friction factor and pressure drop are studied. Results indicated that the average Nusselt number is increased by increasing the volume fraction of Al2O3 nanoparticles. Also, the results show the largest friction factor value is obtained in the case with the highest obstacle height. It is observed that MC-3 case has maximum outlet temperature, and therefore is the best case among investigated cases.

Numerical Prediction of Heat Transfer and Fluid Flow Characteristics in a Circular Microchannel with Bifurcation Plate

Hydrothermal characteristics in circular wavy microchannels (CWMCs) with bifurcation plate have been numerically studied and compared with hydrothermal performance of sinusoidal wavy microchannels (SWMCs). Numerical study were carried out considering the Reynolds number (Re) ranging from 100 to 300. It was observed that, as the fluid flows through CWMC, it continuously absorbs heat from the channel leading to decrease in the temperature difference between the channel and the fluid. Hence, heat dissipation along the channel length decreases. To augment the heat dissipation along the fluid flow direction in CWMC, bifurcation plate (BFP) is introduced in the middle of the channel. CWMC with bifurcation plate has shown higher Nusselt number (Nu) with pressure drop penalty. The parametric study on bifurcation plate length was also carried out to minimize the pressure drop penalty and to achieve higher Nu. It is identified that CWMC with bifurcation plate length of 12.5 mm gives higher Nu with pressure drop penalty. Nu is further enhanced by providing slots on bifurcation plate. It is concluded that CWMC with BFP(10 mm) having slots gives the highest Nu than any other designs with pressure drop penalty.

Comparative study of conjugate heat transfer in a single-phase flow in wavy and raccoon microchannels

Purpose This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion factor (α), wall to fluid thermal conductivity ratio (ksf), substrate thickness to channel height ratio (dsf) and Reynolds number (Re) for obtaining optimum parameter(s) that leads to higher heat dissipation rate. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is designed to capture flow characteristics and heat transfer in single-phase laminar flow microchannels. The governing equations are solved using finite volume method. Findings The results are presented in terms of average base temperature, average Nusselt number, pressure drop, dimensionless local heat flux, dimensionless wall and bulk fluid temperature, local Nusselt number and performance factor including axial conduction number. Heat dissipation rate with raccoon microchannel configuration is found to be higher compared to straight and wavy microchannel. With waviness of γ = 0.167, and 0.267 in wavy and raccoon microchannel, respectively, performance factor attains maximum value compared to other waviness for all values of Reynolds number. It is also found that the effect of axial wall conduction in wavy and raccoon microchannel is negligible. Additionally, thermal performance of wavy and raccoon microchannel is compared with straight microchannel. Practical implications In recent past years, much complex design of microchannel has been proposed for heat transfer enhancement, but the feasibility of available manufacturing techniques to fabricate complex geometries is still questionable. However, fabrication of wavy and raccoon microchannel is easy, and their heat dissipation capability is higher. Originality/value This makes the difference in wall and bulk fluid temperature smaller. Thus, present work highlighted the dominance of axial wall conduction on thermal and hydrodynamic performance of wavy and raccoon microchannel under conjugate heat transfer situation.

Analytical Solution for Heat Transfer in Electroosmotic Flow of a Carreau Fluid in a Wavy Microchannel

This article explores the heat and transport characteristics of electroosmotic flow augmented with peristaltic transport of incompressible Carreau fluid in a wavy microchannel. In order to determine the energy distribution, viscous dissipation is reckoned. Debye Hückel linearization and long wavelength assumptions are adopted. Resulting non-linear problem is analytically solved to examine the distribution and variation in velocity, temperature and volumetric flow rate within the Carreau fluid flow pattern through perturbation technique. This model is also suitable for a wide range of biological microfluidic applications and variation in velocity, temperature and volumetric flow rate within the Carreau fluid flow pattern.

Cooling heat transfer and pressure drop of supercritical CO2 in wavy microchannels with consistent and opposite crests and troughs

A numerical study on cooling heat transfer and pressure drop of supercritical CO2 in horizontal wavy microchannels with consistent crests and troughs (WMCCT) and wavy microchannels with opposite crests and troughs (WMOCT) was conducted. The aim is to provide reference for optimal design in trans-critical CO2 gas cooler equipment. The influence of the channel structure on heat transfer coefficient, pressure drop, buoyancy effect, flow fields and overall thermal performance was analyzed. WMOCT and WMCCT show great advantages in heat transfer performance, while get slightly larger pressure loss punishment when compared with straight microchannel (SM). It is worthy to note that both heat transfer coefficient and pressure drop increase with increased amplitude or decreased wavelength in both WMOCT and WMCCT, which is particularly evident in WMOCT. Furthermore, the analyses carried out identified an optimal channel structure that could improve the overall thermal performance of microchannel gas coolers.