Straight Microchannel Research Articles

High-quality fabrication of diamond straight microchannels heat sink with large aspect ratio microchannels using UV nanosecond laser based on multi-feed method

The high heat flux density of modern chips presents a major challenge to their development. Single-phase or two-phase flow heat dissipation techniques using high thermal conductivity materials are seen as a potential solution. However, creating microfluidic channels from ultra-high thermal conductivity diamond materials is a significant challenge. In this paper, we present an experimental study on the fabrication of diamond heat sinks with high aspect ratio microchannels using a UV-nanosecond laser processing system, along with two multi-feed processing techniques for the collecting grooves and microchannels. We used a 1 μm spacing grid path combined with a polished multi-feed process to fabricate a 1600 μm deep collecting groove with a smooth bottom morphology. We also proposed a multi-area multi-feed fabrication technique for microchannels with an aspect ratio of 8:1 and a depth of 1600 μm. Finally, we have successfully fabricated a diamond straight microchannels heat sink, featuring a high aspect ratio and low phase change damage.

Performance of high-concentration photovoltaic cells cooled by a hybrid microchannel heat sink

The electrical performance and equipment lifetime of high-concentration photovoltaic cells depends heavily on efficient cooling. In this paper, we applied a hybrid configuration to the cooling of a high-concentration photovoltaic cell, an innovative pattern derived from a comprehensive study on the combination of oblique microchannel and micro pin fin. Results from this study found that an elliptical pin fin pattern conforming with streamlines most effectively removed heat flux with a Nusselt number of 65.44 at a Reynolds number 1250. Then, the performance evaluation of a photovoltaic cell with a concentration ratio of 1000 was carried out on the hottest day of each season in Shiraz under actual boundary conditions. With an average flow rate of 30 ml/min in the spring, the implementation of this hybrid design resulted in the photovoltaic cell achieving an electrical efficiency of 40.16 while still maintaining a constant surface temperature of 301 K. Unlike a straight microchannel, which failed to maintain a constant cell temperature throughout summer’s hottest hours, this hybrid configuration succeeded in sustaining cooling with an average flow rate of 90 ml/min. In the winter and autumn, the pump’s average power consumption required for cooling was about 25 and 38 mW, respectively. Moreover, the maximum output electrical power in the summer was 2.8 W, with pumping power contributing to 1500 mW.

Oblique microchannel merged with circle micro pin-fin as a novel hybrid heat sink for cooling of electronic devices

Recently, the advantages of microchannel and micro pin-fin heat sinks for cooling have become clear. This study delves into the effects of hybrid designs on electronic chip cooling by combining microchannel and pin-fin patterns. The research contrasts the performance of a straight microchannel heat sink (Case Ⅰ), circular pin-fin (Case Ⅱ), straight-circular pin-fin-straight (Case Ⅲ), and oblique grooved straight-circular pin-fin-oblique grooved straight (Case Ⅳ). Results show that Case Ⅳ's Nu number reaches 61 at Re = 1250, surpassing Case Ⅰ, Case Ⅱ, and Case Ⅲ by 517 %, 32 %, and 235 %, respectively. Case Ⅳ also has the highest pressure drop. The study calculates each Case's performance evaluation index (ƞ), highlighting the balance between enhanced Nu numbers and pressure drops. Case Ⅳ's ƞ is notably higher than Case Ⅱ and Case Ⅲ. To achieve a more uniform thermal distribution across the entire heat sink, the orientation of the oblique grooves is modified in Case Ⅳ, resulting in a new design labeled Case Ⅴ. While Cases Ⅳ and Ⅴ have similar Nusselt numbers, Case Ⅴ's design ensures consistent temperature distribution, reducing hotspot risks on the chip.

Thermal management of an asymmetrical wavy microchannel heat sink via Ag/water nanofluid

The ever-increasing demand for electronic systems to enhance their performance and processing speed has exponentially increased their heat generation, especially those containing microstructures with reduced surface area. Tackling these complex thermal management challenges creates an urgent need to design and model compact efficient cooling systems. In this investigation, a unique design of a microchannel heat sink with sinusoidal and absolute sinusoidal wavy walls with/without nanofluid is proposed. Heat transfer enhancement and fluid flow characteristics are numerically investigated by developing a two-dimensional finite element model for Reynolds numbers 5, 100, and 500. The periodicity of the wavy section and the different volume fractions of silver nanoparticles ranging from 0 to 4% in water are further considered. The entropy generation is analyzed using the Bejan number. The findings revealed that while the entropy generation rises in the absolute sinusoidal channel, it has a better heat transfer performance by 10.3%, 15.8%, and 16.6% than a straight microchannel for the ascending Reynolds numbers. Interestingly, the channel's heat transfer and thermal efficiency decrease when an unnecessary number of sinusoidal periods are used. The thermal efficiency improves by 3.35% compared to the straight microchannel by employing only one absolute sinusoidal wavelength along the channel.

Numerical analysis on thermal-hydraulic performance of optimized microchannel heat sink with slant ribs and quatrefoil rib-elliptical groove complex structures

A novel microchannel heat sink (MCHS-SREGQR) arranged with the spoiler element structure of the slant rib-elliptical groove-quatrefoil rib is proposed to meet the heat dissipation demands of electronic devices with high heat flux. The strategies for heat transfer enhancement are as follows: Firstly, the elliptical grooves are periodically arranged in the sidewalls of the microchannel and the quatrefoil ribs are set one-to-one at the centre of the grooves. The two structures complement each other's strengths and weaknesses. Secondly, the slant ribs are symmetrically arranged along the centreline of the channel. The slant ribs tend to expand along the flow direction, and produce diversion, guiding and gathering effects on the fluid, thus enhancing flow efficiency of the fluid domain in all aspects. Lastly, a novel quatrefoil rib is put forward, with a special structural design that both effectively inhibits the flow dead regions around the corners of the rib and significantly increases fluid turbulence. Three-dimensional numerical simulations are used to evaluate the effects of slant rib relative position, slant rib relative transverse spacing, and overall rib relative height on pressure drop, heat transfer capacity, and temperature field uniformity of the microchannel. Furthermore, the hydrothermal performance of MCHS-SREGQR is analyzed in comparison with a traditional straight rectangular microchannel and six other microchannels arranged with similar spoiler elements. The results indicate that when the Reynolds number is 696, the temperature at the heat source surface of MCHS-SREGQR decreases by 52.3% and the thermal resistance decreases by 66.6%, while the Nusselt number increases by 131% and the temperature uniformity increases by 76.8%. In addition, the field coordination number Fc increases by 131% and the performance evaluation criterion PEC can be achieved as 1.179.

Flexible liquid metal-based microfluidic strain sensors with fractal-designed microchannels for monitoring human motion and physiological signals

With the rapid advancement of wearable electronics, there is an increasing demand for high-performance flexible strain sensors. In this work, a flexible strain sensor based on liquid metal (LM)-integrated into a microfluidic device is developed with Peano-type fractal structure design. Compared with the microfluidic sensors with straight and wavy microchannels, the sensor with Peano-shaped channels shows lower hysteresis and improved stretchability. Furthermore, the increase of the fractal order can further improve the sensing performances. The third-order Peano sensor exhibits excellent mechanical and electrical properties, including high tensile capability (490.3%), minimal hysteresis (DH = 0.86%), ultra-low detection limit (0.1%), low overshoot, rapid response time (117 ms), as well as good stability and durability. By adding two independent and perpendicular straight channels to the Peano sensing unit, the feasibility of multi-directional strain recognition is demonstrated. To further improve the sensitivity of the Peano-shaped sensor, a multi-layer Peano sensor is developed, exhibiting remarkably enhanced sensitivity while maintaining low hysteresis. Overall, the developed LM-based microfluidic strain sensors enrolling Peano fractal geometry hold high potential for various wearable electronics applications.

Numerical study on flow and heat transfer in a novel symmetric sinusoidal wavy microchannel heat sink with rectangular rib prisms

To enhance thermal and overall performances, a novel microchannel heat sink (SSW-RP) was devised by integrating symmetric sinusoidal wavy sidewalls with rectangular rib prisms within the channels. A numerical comparative study was conducted to explore heat transfer mechanism in channels by investigating the flow and heat transfer characteristics of SSW-RP in comparison with those of smooth straight microchannel (MC), smooth straight microchannel with rectangular rib prisms (MC-RP), and symmetric sinusoidal wavy microchannel (SSW). The results show that the addition of rib prisms makes the fluid flow into wave peaks, reducing and even eliminating vortices from wave peaks of the symmetric sinusoidal wavy microchannel, thus significantly improving heat transfer performance. The new design SSW-RP had the highest relative Nusselt number, which reaches 4.16 at Re = 800. Further, the hydrothermal performance sensitivity of SSW-RP to the relative width (α) and length (β) of rib prisms is studied, and the best overall performance factor of SSW-RP finally can be achieved up to 1.88 at α = 0.35, β = 0.4 and Re = 800.

Simulation based investigation of Nusselt number and Poiseuille number in helical microchannels

Simulation based work carried out in order to understand the thermohydraulic characteristics of fluid flow in helical microchannel, with circular cross-section, that is subjected to constant heat flux is detailed in this work. Water is used as the fluid in this study and the study is carried out for Reynolds number ranging from 50 to 500. The helical path of the fluid increases the heat transfer coefficient and pressure drop for a specific Reynolds number in comparison with that in a straight microchannel. The increase in heat transfer coefficient and pressure drop associated with the helical microchannel manifests as increased Nusselt number and Poiseuille number. At Reynolds number of 50, the Nusselt number of the helical microchannel is 1.36 times higher than that of the straight microchannel while at Reynolds number of 500, this enhancement increases to 2.33. Regarding Poiseuille number of helical microchannel, it is higher than that of the Poiseuille number of straight microchannel by 1.02 and 1.72 at Reynolds number of 50 and 500, respectively. It is identified from this study that by shifting from straight microchannel to helical microchannel, the enhancement in Nusselt number is higher than the associated penalty, i.e. increase in Poiseuille number.

Optimal Design of Microchannel Heat Sink with Staggered Fan-Shaped Cavities and Ribs

In the present study, a three-dimensional numerical simulation is conducted to study the characteristics of fluid flow and heat transfer in a newly designed microchannel heat sink with fan-shaped cavities and ribs (MC-FCFR). The Reynolds number ranges from 147 to 736. A straight rectangular microchannel (MC-RC) is used as the baseline. The geometric parameters include the relative spacing θ, relative width α, and relative height β of the fan-shaped cavities and ribs. The overall performance index (OPI) of the MC-FCFR is evaluated in terms of the friction factor and Nusselt number. The OPI for the MC-FCFR with θ=3.56, α=1.63, and β=0.5 reaches 1.70.

A fluid-structure interaction method for soft particle transport in curved microchannels

A numerical framework is presented to predict the transport of soft elastic capsules immersed in an incompressible fluid with the aim of simulating inertial microfluidics applications. The flow evolution is modeled by a fully incompressible lattice Boltzmann method whereas a finite element model is considered for describing the dynamics of deformable structures. An immersed boundary technique is adopted to reconstruct the solution in the vicinity of the immersed surface and the time integration of the fluid-structure interaction problem is obtained by following an explicit procedure. The effectiveness of the framework is validated by means of several test cases involving: flows between two parallel plates for Reynolds numbers in the range 1÷100; capsules immersed in a fluid at Stokes regime exhibiting small and large deformations under shear; capsules migrating in a long straight microchannel with square cross-section at low-to-moderate Reynolds number. A very good agreement between the present results and literature data obtained using different numerical methods is found for all test cases. Finally, the method allowed to accurately simulate incompressible flows subjected to large pressure difference between the inlet and the outlet, characteristic of long curved microchannels, obtaining very smooth particle dynamics.

Fluid flow and heat transfer behavior of a liquid based MEMS heat sink having wavy microchannels integrating circular pin-fins

MEMS heat sink having wavy microchannels integrating circular pin-fins for cooling of microelectronic chips is proposed and analyzed in this work; the pin-fins are placed at the valleys and peaks of the wavy structure. The pumping power and thermal resistance of the proposed MEMS heat sink is higher and lower than that of MEMS heat sink having straight microchannels. At Reynolds number of 250, the maximum temperature of the microelectronic chip, generating 106 W/m2, when using the proposed MEMS heat sink is only 0.77 of that when using MEMS heat sink having straight microchannels; this ratio lowers to 0.6 at Reynolds number of 1250. The thermal resistance of the proposed MEMS heat sink is only 0.72 and 0.43 of that of the MEMS heat sink having straight microchannels at Reynolds numbers of 250 and 1250, respectively. Regarding the pumping power of the proposed MEMS heat sink, it is higher than that of the MEMS heat sink having straight microchannels by 2 and 3.7 at the lowest and highest Reynolds numbers, respectively. This work also analyzes the contribution of geometric features on the behavior of the proposed MEMS heat sink in terms of maximum temperature of the microelectronic chip, thermal resistance, and pumping power as well as that of microchannel employed in the proposed MEMS heat sink in terms of Poiseuille and Nusselt numbers. Maximum temperature of the microelectronic chip and thermal resistance decrease along with increase in pumping power with increase in amplitude, diameter of pin-fins, and hydraulic diameter of microchannel as well as with decrease in wavelength. Poiseuille and Nusselt numbers increased with rise in amplitude, diameter of pin-fins, and hydraulic diameter as well as decrease in wavelength. In addition, experiments have been conducted on two designs of the proposed MEMS heat sink to generate data for purposes of validating the model. The experimental data are compared with data from simulations and the difference between the two are within the uncertainty of experimental data thereby validating the model.

Three-dimensional numerical investigation of flow and heat transfer performances of novel straight microchannel heat sinks

Four-type novel single crystal diamond (SCD) straight microchannel heat sinks with different shapes (symmetrically inclined, turned symmetrically inclined, V-shaped, and X-shaped) are designed and investigated by the three-dimensional computational fluid dynamics method. These four-type microchannel heat sinks are evaluated in terms of fluid flow and heat transfer capabilities compared to the conventional rectangular straight microchannel (RSMC) heat sink. Our research indicates that the newly designed novel SCD microchannel heat sinks can enhance the heat dissipation effect in comparison to the conventional RSMC heat sink, thereby substantiating its potential for enhancing thermal management in electronic devices. Each V-shaped and X-shaped straight microchannel heat sink has a higher heat transfer capacity than the RSMC heat sink. Among the heat sinks involved in this work, the V-shaped SCD heat sink has the best surface temperature uniformity. The symmetrically inclined heat sink shows the lowest pumping power, with 14.1 % lower than that of the RSMC heat sink. The X-shaped SCD heat sink exhibits a significantly lower thermal resistance, with an 8.5 % reduction compared to the RSMC heat sink. Additionally, it demonstrates a substantially higher Nusselt number, with a 27.6 % increase relative to the RSMC heat sink. The X-shaped SCD heat sink has the highest heat transfer coefficient of up to 1.08 × 105 W/(m2·K), which is 20.4 % higher than that of RSMC heat sink. Owing to the highest performance evaluation criterion of 1.22, the X-shaped straight microchannel heat sink is the most optimal of the designed heat sinks.

Deciphering viscoelastic cell manipulation in rectangular microchannels.

Viscoelastic focusing has emerged as a promising method for label-free and passive manipulation of micro and nanoscale bioparticles. However, the design of microfluidic devices for viscoelastic particle focusing requires a thorough comprehensive understanding of the flow condition and operational parameters that lead to the desired behavior of microparticles. While recent advancements have been made, viscoelastic focusing is not fully understood, particularly in straight microchannels with rectangular cross sections. In this work, we delve into inertial, elastic, and viscoelastic focusing of biological cells in rectangular cross-section microchannels. By systematically varying degrees of fluid elasticity and inertia, we investigate the underlying mechanisms behind cell focusing. Our approach involves injecting cells into devices with a fixed, non-unity aspect ratio and capturing their images from two orientations, enabling the extrapolation of cross-sectional equilibrium positions from two dimensional (2D) projections. We characterized the changes in hydrodynamic focusing behaviors of cells based on factors, such as cell size, flow rate, and fluid characteristics. These findings provide insights into the flow characteristics driving changes in equilibrium positions. Furthermore, they indicate that viscoelastic focusing can enhance the detection accuracy in flow cytometry and the sorting resolution for size-based particle sorting applications. By contributing to the advancement of understanding viscoelastic focusing in rectangular microchannels, this work provides valuable insight and design guidelines for the development of devices that harness viscoelastic focusing. The knowledge gained from this study can aid in the advancement of viscoelastic particle manipulation technique and their application in various fields.

Particle Separation in a Microchannel with a T-Shaped Cross-Section Using Co-Flow of Newtonian and Viscoelastic Fluids.

In this study, we investigated the particle separation phenomenon in a microchannel with a T-shaped cross-section, a unique design detailed in our previous study. Utilizing a co-flow system within this T-shaped microchannel, we examined two types of flow configuration: one where a Newtonian fluid served as the inner fluid and a viscoelastic fluid as the outer fluid (Newtonian/viscoelastic), and another where both the inner and outer fluids were Newtonian fluids (Newtonian/Newtonian). We introduced a mixture of three differently sized particles into the microchannel through the outer fluid and observed that the co-flow of Newtonian/viscoelastic fluids effectively separated particles based on their size compared with Newtonian/Newtonian fluids. In this context, we evaluated and compared the particle separation efficiency, recovery rate, and enrichment factor across both co-flow configurations. The Newtonian/viscoelastic co-flow system demonstrated a superior efficiency and recovery ratio when compared with the Newtonian/Newtonian system. Additionally, we assessed the influence of the flow rate ratio between the inner and outer fluids on particle separation within each co-flow system. Our results indicated that increasing the flow rate ratio enhanced the separation efficiency, particularly in the Newtonian/viscoelastic co-flow configuration. Consequently, this study substantiates the potential of utilizing a Newtonian/viscoelastic co-flow system in a T-shaped straight microchannel for the simultaneous separation of three differently sized particles.

Characterization of MEMS heat sinks having straight microchannels integrating square pin-fins for liquid cooling of microelectronic chips

This work presents a liquid based MEMS (microelectromechanical systems) heat sink having straight microchannel integrating square pin-fins for cooling of microelectronic chips. Simulation based studies are carried out for evaluating the operation of this MEMS heat sink and the contribution of geometric features on its behavior. The behavior of the MEMS heat sink is calculated using pumping power and thermal resistance while the behavior of the flow passage is calculated based on of Poiseuille and Nusselt numbers. Investigations are done for Reynolds number ranging from 250 to 1500 when the MEMS heat sink is subjected to 1,000,000 W/m2. This study concludes that square pin-fins in the microchannel reduces the thermal resistance while raising the pumping power in comparison with microchannel without pin-fins. The decrease in the pitch of the square pin-fins results in increase in the pumping power and decrease in the thermal resistance. Moreover, it is identified that increase in the dimensions of the square pin-fins raise and reduce the pumping power and thermal resistance, respectively. The increase in the hydraulic diameter of the microchannel integrating square pin-fins results in lowering of both pumping power and thermal resistance. The Poiseuille and Nusselt numbers for different cases of straight microchannel integrating square pin-fins are quantified for the benefit of heat sink designers. Experiments are carried out in-house for generating data for purposes of validating the model.

Design and experimental study on wave-type microchannel cooling plates for marine large-capacity battery thermal management

In this paper, the wave-type microchannel cooling plates for marine large capacity battery thermal management are designed and tested. The cooling performances of the straight microchannel cooling plate (SMCP), the single-periodic wave microchannel cooling plate (SWMCP) and the double-periodic wave microchannel cooling plate (DWMCP) are experimentally investigated. The maximum temperature (Tmax) and temperature standard deviation (SD) of battery module during charge and discharge process are compared with the variation of the coolant inlet temperature (Tin), volume flow rate (qV) and the environmental relative humidity (RH). The experimental results demonstrate that decreasing Tin, increasing qV and decreasing RH would contribute to lower Tmax but higher SD. The cooling effectiveness of the wave-type microchannel cooling plates are validated by the reduced Tmax and the robustness in SD control. In particular, the newly designed DWMCP with the non-linear wave-type microchannel could relief the contradiction between cooling capacity and the temperature uniformity. For all the working conditions, the DWMCP could manage the Tmax and the SD below 41.5 °C and 0.96 °C, respectively.

A numerical study of sample preconcentration using ion concentration polarization in single microfluidic channels with dual ion-selective membranes

In this work, we investigated three single straight microchannel designs for the microfluidic biomolecule concentration device, including one traditional single channel and two innovative channels. These microchannels utilized the ion concentration polarization (ICP) phenomenon to preconcentrate very dilute sample biomolecules. By numerically solving coupled equations, Nernst–Planck, Poisson, and Navier–Stokes with appropriate boundary conditions, we provide insight into the ICP phenomenon and the preconcentration mechanism. From the detailed modeling results, we clarify the influence of important working parameters, including electric potentials, the ion-selective membrane dimensions, the channel dimensions, and the ionic strength of buffer solution on the formation of ICP and the enrichment rate of the charged biomolecules. These modeling results for various working conditions of the preconcentration systems highlight the advantage of generating a stronger electric field to preconcentrate biomolecules of two innovative channel designs over the conventional one. The findings are useful tips for the design and optimization of preconcentration microfluidic devices.

Mixing enhancement in a straight microchannel with ultrasonically activated attached bubbles

Liquids and reagents mixing at the microscales are of great significance to various lab-on-chip applications such as drug delivery and microreactor. This work demonstrated mixing enhancement based on microstreaming induced by ultrasonically activated attached bubbles in a straight microchannel. The bubbles were experimentally trapped in a microchannel fabricated with hydrophobic surfaces, and they demonstrated good stability to flow rate due to the lower surface energy of the system. The effect of the applied voltage and flow rate on the mixing performance was numerically and experimentally studied. Both results show that reducing the flow rate or increasing the voltage would improve the mixing efficiency. Furthermore, the proof-of-concept was successfully tested by utilizing it as a microreactor for sodium hydroxide and phenolphthalein at a throughput of 4 μL/min. The proposed chip can achieve diverse mixing processes based on the trapped bubble state than other microfluidic mixers. We believe the proposed design will be valuable for developing bubble-based biochemical and biological applications.

Proposing a Hybrid BTMS Using a Novel Structure of a Microchannel Cold Plate and PCM

The battery thermal management system (BTMS) for lithium-ion batteries can provide proper operation conditions by implementing metal cold plates containing channels on both sides of the battery cell, making it a more effective cooling system. The efficient design of channels can improve thermal performance without any excessive energy consumption. In addition, utilizing phase change material (PCM) as a passive cooling system enhances BTMS performance, which led to a hybrid cooling system. In this study, a novel design of a microchannel distribution path where each microchannel branched into two channels 40 mm before the outlet port to increase thermal contact between the battery cell and microchannels is proposed. In addition, a hybrid cooling system integrated with PCM in the critical zone of the battery cell is designed. Numerical investigation was performed under a 5C discharge rate, three environmental conditions, and a specific range of inlet velocity (0.1 m/s to 1 m/s). Results revealed that a branched microchannel can effectively improve thermal contact between the battery cell and microchannel in a hot area of the battery cell around the outlet port of channels. The designed cooling system reduces the maximum temperature of the battery cell by 2.43 °C, while temperature difference reduces by 5.22 °C compared to the straight microchannel. Furthermore, adding PCM led to more uniform temperature distribution inside battery cell without extra energy consumption.

Analysis and optimization of thermo-hydraulic characteristics of phase change slurry in wavy MCHS with porous fins based on RSM and desirability methods

In this study, the hydromechanical and diathermanous characteristics of microencapsulated phase change material (MPCM) slurry in wavy microchannel heat sink (MCHS) with porous fins are investigated by using two–phase mixture and Dacry–Brinkman–Forchheimer models. Based on the finite volume method (FVM) and response surface methodology (RSM), 54 cases considering 6 structural parameters are carried out. The correlations of Nusselt number (Nu) and friction factor (f) in straight and wavy microchannels with phase change slurry and porous fin designs are creatively proposed and unified. The maximum deviations between the actual and predicted values of Nu and f are 13.24% and 14.21%, respectively. In addition, the effects of radiator's parameters on Nu and f are emphatically discussed and analyzed by using three-dimensional surface diagram. It reveals that within the range of parameters tested, wavy amplitude (A) has the most obvious effect on responses, while channel aspect ratio (α) has the least impact on them. Moreover, the interactive effects between the five structural parameters are significant and complex, as one factor influences the impact of another on responses. Finally, the optimal parameters are obtained by desirability method with the goal of maximum Nu and minimum f. The results indicate that the overall performance of optimized configuration improved by 48.6% over the initial design. Our results may provide helpful guidance for the optimization design of MCHS, as significant improvement in heat transfer coefficient is expected to save substantial operating costs.