Fluid Mixing Research Articles

Multidirectionally Patterned Interdigital Transducers for Enhancing Acoustofluidic Streaming with Flexible Printed Circuit Board

AbstractAcoustic streaming generated by surface acoustic waves (SAWs) enables diverse acoustofluidic functions, such as fluid mixing, particle manipulation, and enhanced fluid transport, making SAWs valuable lab‐on‐a‐chip systems. However, conventional SAW devices are often limited to a specific acoustofluidic function once fabricated. Each function typically requires different devices or designs to produce other wave modes, making exploration costly and time‐consuming. A Multidirectional Interdigital Transducer (M‐IDT) on a Flexible Printed Circuit Board (FPCB) is presented, allowing easy reconfigurability and multidirectional SAW propagation. This versatile device enables rapid, multifunctional experimentation on a single replaceable substrate, facilitating efficient exploration of acoustofluidic effects. This device, alongside finite element simulations, investigates substrate in‐plane rotation angles (0°, 30°, 60°, and 90° relative to the X‐axis) and wave modes. Favorable acoustic velocities are observed using Rayleigh SAW (R‐SAW) at 0° and 30°, and using combined wave modes at 60°, and 90°. The pseudo shear‐horizontal SAW (P‐SH‐SAW) at 90° exhibits higher velocities than R‐ SAW at 0°. P‐SH‐SAW also improved acoustic streaming at lower power, with high‐viscosity fluids, substantial fluid volumes (1 mL), and within a 96‐well plate. The M‐IDTs reconfigurable nature allows rapid, cost‐effective testing, making it ideal for prototyping a wide range of acoustofluidic applications.

Numerical investigating the impact of fluid properties and oscillation frequency on micro mixer efficiency.

In this research, the impact of differing densities and viscosities of two dissolving fluids on their mixing efficiency, as well as the effects of various excitation frequencies on the performance of the mixer, have been examined. For this purpose, a two-dimensional microchannel equipped with an oscillating circular cylinder was used, operating within a Strouhal number range of 0.1-0.55, with an oscillation amplitude of 0.4 cylinder diameters in a direction perpendicular to the flow direction, at a blockage ratio of and Reynolds and Schmidt numbers of 50 and 10, respectively, utilizing a finite volume method based on elements. The results obtained indicate that mixing two identical fluids represents an ideal condition, wherein the highest level of mixing occurs compared to mixing two fluids with differing densities and viscosities. As the difference in viscosity and density between the two fluids increases, the level of mixing decreases, such that an increase in the logarithmic viscosity ratio up to R=2 results in a 257.66% reduction in mixing, and an increase in the density ratio up to S=3 leads to a 170.08% reduction in mixing efficiency. However, at points where the density and viscosity increase factors are equal (s=eR), the increase in density has a greater impact on reducing the mixing efficiency compared to the increase in viscosity. Specifically, at an increase factor of 3 for both density and viscosity, density has a 50% greater effect on reducing mixing efficiency than viscosity. Furthermore, it is observed that when two fluids have different densities and viscosities, changes in the Strouhal number have a lesser impact on the mixing index compared to when the two fluids are identical. By creating a difference in viscosity and density between the two mixing fluids, the mixer exhibits unique and distinct performance, such that for each viscosity and density ratio, it is observed different optimal Strouhal numbers independently. This research provides a fundamental understanding of the effects of differing density and viscosity, as well as the impact of excitation frequency on the mixing efficiency of the two fluids.

Enhanced Fluid Mixing in Microchannels Using Levitated Magnetic Microrobots: A Numerical Study

The efficient mixing of fluids at microscale dimensions presents challenges due to the dominant laminar flow regime which restricts convective mixing. This study introduces a numerical analysis of a novel microrobotic mixing system with a levitated propeller robot, driven by magnetic fields, within a Y-shaped microchannel with a square cross-section (500 × 500 μm). Our research investigates the fluid mixing effectiveness facilitated by the microrobot through various levitation heights and orientations to enhance the mixing index (MI). This index is tested under different conditions by leveraging the dynamics of the propeller robot, characterized by adjustable roll and pitch angles and varying levitation heights. The numerical simulations, conducted using COMSOL® (Finite Element Method, FEM) software, integrate Maxwell’s equations for magnetic field interaction with momentum and transport-diffusion equations to analyze fluid dynamics within the microchannel. Results indicate that the propeller robot can achieve an MI of up to 98.94% at a 150 μm levitation height and 1500 rpm propeller speed within 3 s. Additionally, the study examines the impact of propeller speed, Reynolds number, and robot length on mixing performance, providing comprehensive guidance for optimizing microscale fluid mixing in lab-on-a-chip applications.

Enhancing heat transfer in heat exchanger tube using four-shape cutting cone (FSCC) inserts: A numerical analysis

ABSTRACT The study introduces a new design modification for regular smooth tubes, incorporating the four-shape cutting cone (FSCC) to enhance heat transfer without increasing friction charge. Numerical simulations are used for processes heat and flow characteristics in the turbulent flow regime using certain parameters, ranging from 4000 ≤ Re ≤32,000. FSCC inserts can improve heat transmission, which lowers energy consumption in heat exchanger tube and helps achieve sustainability goals. A FSCC vortex was placed inside a smooth tube that measured 1500 mm in length, 30 mm in inner diameter (Din), and 35 mm in outer diameter (Do) for testing purposes. The FSCC measured (Dtop) = 20 mm at the top and Dbase = 28 mm at the base, with a thin 0.8 mm thickness (t). In this study, the Nusselt number (Nu), friction factor (fr), and thermal performance evaluation criteria (TPEC) are examined in relation to FSCC perforations (N = 0, 2, and 3) and pitch-to-hydraulic ratios (PR = P/Din = 2.5, 3.5, 4.5, and 5.5). The effects of perforations, i.e. hole number N = 0, 2, 3 and P/Din = 2.5, 3.5, 4.5, and 5.5, are considered for the analysis. The integrated tube has higher TPEC and average Nusselt numbers as compared to the smooth tube. Additionally, it uses perforations and to look at fluctuations in the average entropy generation rate (Savg). The study found that FSCC-inserted tubes have a 9.3 and 17.9 times higher Savgf than smooth tube at Re = 32,000 and 4000, respectively, for N = 0 FSCC heat exchanger tube, but at Re = 32,000, the Savgh of FSCC is 0.4 times lower. Smooth tube improves average entropy generation (Savg), while friction flow creates irreversibility defects. Smooth tube performance in Savg is inferior, with Savgh declining with Re and N. According to the study, vortex/swirl flow, boundary layer disturbance, and fluid mixing are the main factors influencing fluid flow, which is improved by the FSCC integrated tube and improves heat exchanger performance. Nusselt number and the friction factor both decrease as perforations increase while TPEC also increases. The results suggest that the FSCC is a useful tool for improving the efficiency of tube heat exchangers. The maximum TPEC is observed around 2.44 for N = 0 at Re = 4000 and P/Din = 3.5.

ENHANCING HEAT TRANSFER IN CHANNEL FLOW USING SYNTHETIC JETS

Synthetic jet's effectiveness in flow control, fluid mixing enhancement, and cooling has been established. The current study aims to examine the improvement of fluid blending and heat dissipation rate of two water inlets with varying temperatures in a channel that is disturbed by a synthetic jet at different excitation frequencies. The simulation analysis predicts the temperature distributions and the fully develop the velocity profile along symmetrical plane of the channel with interference of synthetic jet using establish CFD software. The RNG k- ε turbulence model was employed to compute the turbulent flow produced by the synthetic jet. A moving mesh approach was employed to replicate the movement of a synthetic jet diaphragm. The results indicate that the fluid flow behavior in the channel disrupted by the synthetic jet flow. Hence, indicating to an enhance in both the fluid flow velocity and the heat transfer rate. A higher frequency of the actuator enhances fluid mixing and reduces the channel distance required to achieve temperature equilibrium within the channel in comparison to a lower frequency of the actuator.

Injection Of air control of propeller performance

With the rise of bubble lubrication technology in transport ships, the interaction between propellers and bubble flow has become increasingly important. On the basis of solving the Reynolds averaged equation and the volume fraction equation, a numerical model of the propeller in a water air mixed fluid was established using the sliding mesh technique. Based on verifying the numerical calculation model of the semi-immersed propeller, uncertainty analysis was conducted on the KP505 propeller flow numerical model, and the open water performance of the propeller was calculated to be affected by the injection position and injection volume. A linear model was established to describe the relationship between the open water performance of the propeller at the axis and the injection rate. The performance surface model was used to describe the effect of the air injection position moving towards the blade tip on open water performance at different air injection rates. The strength and dissipation of the tip vortex and hub vortex of propeller are affected by the radial air injection position. Air injection at the axis causes the hub vortex to expand and connects the tip vortex to form a vortex ring in the far field. The air injection position moves towards the blade tip, and the vortex system at the blade tip accelerates and rapidly dissipates.

Onset of cabbeling instabilities in superconfined two-fluid systems

Convective-driven mixing in permeable subsurface environments is relevant in engineering and natural systems. This process occurs in groundwater remediation, oil recovery, CO2 sequestration, and hydrothermal environments. When two fluids come into contact in superconfined geometries like open fractures in rocks, complex molecular dynamics can develop at the fluid–fluid interface, creating a denser mixture and leading to cabbeling instabilities that propel solutal convection. Previous studies in superconfined systems have used models based on unstable density distributions—generating Rayleigh–Taylor instabilities—and analog fluid mixtures characterized by nonlinear equations of state—resulting in cabbeling dynamics—yet often neglecting interfacial tension effects, which is also relevant in miscible systems. This study incorporates the Korteweg tensor into the Hele–Shaw model to better understand the combined influence of geometry confinement and interfacial tension on the onset of cabbeling instabilities in two-fluid superconfined systems. Through direct numerical simulations, we investigate the system's stability, revealing that the onset, characterized by the critical time tc, exhibits a nonlinear relationship with the system's nondimensional parameters—the Rayleigh number Ra, the anisotropy ratio ϵ, and the Korteweg number Ko. This relationship is crystallized into a single scaling law tc=F(Ra,ϵ,Ko). Our findings indicate that geometry and effective interfacial tension exert a stabilizing effect during the initial stages of convection, stressing the necessity for further exploration of its influence on fluid mixing in superconfined systems.

Machining Performance of Ti6Al4V Nano Composites Processed at Al2O3 Nano Particles Mixed Minimum Quantity Lubrication Condition

Introduction: In this research work, an attempt was made to machine Ti6Al4V nano composites utilizing Al2O3 mixed nano fluid at minimum quantity lubrication condition, in which experiments were designed using the L16 orthogonal array, whereas Material Removal Rate, Surface Roughness, machining force and power were recorded as responses. Methods: The nano composites were fabricated using the stir casting technique and the nano particles were synthesized using the sol-gel technique. the microstructure revealed that the homogeneous dispersion of particles with dendric arms. Increased cutting speed and feed lead to more tool wear, which in turn causes a decrease in surface quality and an increase in surface roughness. Results: Larger areas of cut are often the consequence of higher feed rates, which increases the amount of friction between the work piece and the cutting edge. The machining force increases when the feed rate is increased. A higher feed rate produces a large volume of the cut material in a given length of time in addition to having a dynamic impact on the cutting forces. Conclusion: It also results in a corresponding increase in the typical contact stress at the tool chip interface and in the tool chip contact zone.

Enhanced flow boiling by manipulating two-phase flow in Tesla channel heat sink using HFE-7100

Flow boiling of dielectric fluids in copper microchannel heat sinks is highly desirable for cooling large-sized insulated gate bipolar transistor (IGBT) power electronic modules. However, dielectric fluids present challenges in flow boiling because of their unfavorable thermophysical properties. These factors make it difficult to enhance critical heat flux (CHF) without precooling. To address this, we developed a large copper heat sink (10 cm × 5 cm) with Tesla microchannels designed to suppress vapor backflow and promote intense fluid mixing. The microchannels have a high length to hydrodynamic diameter ratio of approximately 220, significantly higher than those in previous studies. Flow boiling experiments using HFE-7100 were conducted for both Tesla and plain-wall microchannels. Tesla channels demonstrated a 26.2 % increase in CHF and a 120 % improvement in heat transfer coefficient (HTC). These enhancements are attributed to the vapor backflow suppression and improved fluid mixing. Moreover, the standard deviation of wall temperature in plain-wall microchannels was 10 times higher than in Tesla channels, highlighting the effectiveness of the periodic Tesla valves in reducing two-phase flow instabilities. Flow pattern visualization was conducted to further understand the mechanism behind vapor regulation, clarifying the role of Tesla valves in controlling vapor backflow. This study demonstrates the potential of dielectric fluids in Tesla microchannels for flow boiling applications, offering a promising solution for cooling large electronics.

Optimizing thermal management with micropolar hybrid nanofluids in spatially dependent magnetic fields

Vortices play a pivotal role in fluid dynamics by enhancing fluid mixing and mass transport, making them crucial for numerous applications. Hybrid nanofluids, combining two types of nanoparticles, offer superior thermal conductivity and heat transfer compared to conventional nanofluids. This study examines the influence of localized magnetic fields on vortex dynamics in a micropolar hybrid nanofluid flow within a vertically oriented cavity, driven by moving horizontal lids along the +ve axis. Magnetic field strips are applied horizontally and vertically to control flow behavior. Using MATLAB-based algorithms and the finite difference method, we solve the governing equations of flow and heat transfer. Key parameters, including magnetic field strength, nanoparticle volume fraction, and Reynolds number, are analyzed for their effects on flow structures and temperature profiles. Results indicate that the magnetic field reduces microrotation and enhances laminar flow, influencing stress distribution and temperature gradients. These insights are valuable for optimizing microfluidic devices, heat exchangers, and drug delivery systems, where control over flow dynamics and temperature is essential.

Simulation analysis on ejector performance with inclusion of chevrons in primary nozzle

As an unconventional refrigeration system, the ejector refrigeration system (ERS) must achieve high performance. The performance of the ERS largely depends on the ejector’s entrainment ratio. In this numerical analysis, the effect of the inclusion of chevrons in the primary nozzle of the ejector has been studied. The three-dimensional, steady-state analysis has been carried out by solving turbulence and compressible equations, using periodic boundary conditions to study the mixing of the primary and secondary fluids. In this work, the chevrons have been incorporated in the primary nozzle to enhance the ejector’s entrainment ratio (ω) by improving the mixing of fluids. The reduction in the slip line between the two fluids has been found to be better in the chevron-incorporated nozzle than in the conical and bell-shaped nozzles. The number of chevrons (N) has been varied with a fixed tip angle (β=60∘). Analyzing 2, 4, 6 and 8 chevrons showed that the entrainment ratio of four chevrons increased by 12.98% of the conical nozzle.

Physics-Based and Data Driven Modeling of Electrophoretic Coatings: Hybrid and Multiphysics Strategy

Electrophoretic coatings are used in several applications where surface treatment is intended to provide corrosion protection. These coatings are widely used in the automotive, aerospace, or many other sectors. These kind of coatings are electrochemically applied and have good levelling, penetration, adhesion, and corrosion resistance properties. A wide variety of materials can be deposited by this technique and among these coatings, this presentation will focus on ceramic deposits. In this case, electrophoretic deposition is carried out using a suspension containing ceramic particles and the deposition takes place on a conductive substrate through the application of an electric field. The control of process parameters and post-processing parameters (heat treatment or sintering) necessary to consolidate the raw coatings obtained can be difficult to define.In order to improve process management and understanding of electrophoretic deposition, we will explore several strategies and modelling theories implemented in the field of electrophoretic coating through a comprehensive analysis in order to optimize the coating process, improve quality and increase efficiency on complex geometry parts. Several theoretical approaches and models have been used to better understand electrochemical interactions and forces involved in electrophoresis to identify parameters related to electrophoretic mobility. The multiple parameters involved in electrophoretic coatings make the modelling of this process complex and the models developed are neither universal nor applicable to all chemistries which requires a specific development for each electrolyte and suspension.In a second part, we discuss limits of theoretical models and describes a strategy to develop a new modelling approach. This approach combines a physics-based model of current distribution and a data-driven optimization applied to electrophoretic coating. This methodology allows to model the thickness distribution on a part with complex geometry on an industrial scale, with the ability to adapt to a variation in the chemistry of the suspension used. This hybrid methodology allow to reduce experimental and fundamental characterizations, and can be easily applied to a new chemistry to estimate and well describe the throwing power at a macroscale.Furthermore, in some cases, physics-based modeling with secondary distribution can exhibit accuracy defects when the local concentration of particles drops, due to their consumption and low mass transport phenomena.In order to better describe the process behavior in this specific case, we develop a multiphysics model of tertiary current distribution than can account for the local distribution of particles, particularly near the part. This modeling approach allows to better anticipate thickness distribution in areas with low fluid mixing and agitation. The local efficiency is linked to the local current and particle concentration, as describe by a two phase flow model.The models developed are intended to help accurately predict and control the distribution of coating thickness and also local particle concentration to predict critical depletion zones.In conclusion, this conference explore different modeling strategies of electrophoretic coatings, by focusing on the optimization of process parameters and the consideration of the different mechanisms governing deposition with the objective of improving coating distribution on complex part.

Fused Deposition Modeling of Chemically Resistant Microfluidic Chips in Polyvinylidene Fluoride.

Fused deposition modeling (FDM) is well suited for microfluidic prototyping due to its low investment cost and a wide range of accessible materials. Nevertheless, most commercial FDM materials exhibit low chemical and thermal stability. This reduces the scope of applications and limits their use in research and development, especially for on-chip chemical synthesis. In this paper, we present FDM fabrication of microfluidic chips with polyvinylidene fluoride (PVDF) for applications that require high thermal or chemical resistance. Embedded microchannels with a minimum channel width and heights of ~200 µm × 200 µm were fabricated, and the resistance against common solvents was analyzed. A procedure was developed to increase the optical transmission to result in translucent components by printing on glass. Chips for fluid mixing were printed, as well as microreactors that were packed with a catalytically active phase and used for acetal deprotection with a conversion of more than 99%. By expanding the use of fluorinated polymers to FDM printing, previously challenging microfluidic applications will be conducted with ease at the lab scale.

Fluid inclusion and multiple isotope geochemical constraints on the hydrothermal evolution and metal sources of the Qiaomaishan Cu–W skarn deposit, eastern China

The Xuancheng ore district of eastern China is a newly discovered district within the Middle and Lower Yangtze River Metallogenic Belt (MLYB) that hosts several magmato-hydrothermal related mineral deposits. The Qiaomaishan deposit is a representative example of the skarn deposits within this district and is also the only deposit within the district that hosts tungsten mineralization. However, the source of metals and the hydrothermal evolution of the mineralizing system that formed this deposit remain controversial. This study addresses these issues using new fluid inclusion microthermometric and isotopic data, including fluid inclusion H, quartz O, sulfide S, and pyrite Pb data, which constrain the evolution of the hydrothermal fluids within the system and the source of metal within the Qiaomaishan deposit. This study identified three main stages of hydrothermal evolution and paragenesis within the deposit, namely pre-ore (stage 1), syn-ore (stages 2 and 3), and post-ore formation stages. Stage 1 garnet (andradite)-hosted fluid inclusions homogenize between 390 °C and 590 °C and have salinities of 9–20 wt% NaCl equivalent whereas stage 2 quartz-hosted fluid inclusions homogenize between 200 °C and 460 °C and have salinities of 5–18 wt% NaCl equivalent. Finally, stage 3 quartz- and calcite-hosted fluid inclusions homogenize at temperatures of 120 °C–240 °C and 3–15 wt% NaCl equivalent salinities. The stage 2 quartz has oxygen and hydrogen isotopic compositions (δDfluid from −99 ‰ to −57 ‰; δ18Ofluid from 4.0 ‰ to 6.1 ‰) that are close to those expected for magmatic fluids, whereas stage 3 quartz (δDfluid from −105 ‰ to −86 ‰; δ18Ofluid from −1.7 to −0.6 ‰) records the mixing of meteoric and hydrothermal magmatic fluids. These fluid inclusion data suggest that cooling was the main mineralizing process involved in stages 1 and 2, and this process may favor the enrichment of tungsten and copper in the residual hydrothermal fluids. In contrast, fluid mixing became increasingly important between stages 2 and 3, leading to a reduction in salinity and temperature as well as changes in fluid isotopic compositions. Water–rock (W/R) interaction is also likely to have been an important process during deposit formation. The δ34S (2.7 ‰–5.7 ‰ with a mean of 4.3 ‰) of sulfides from the Qiaomaishan deposit also provide evidence that the sulfur within the deposit has a magmatic origin. The homogeneous pyrite Pb isotopic data (206/204Pb = 18.158–18.518, 207/204Pb = 15.592–15.650, and 208/204Pb = 36.179–38.634) for samples from the Qiaomaishan deposit further indicates that the metals within the deposit were derived from both mantle and crustal sources. In summary, the Qiaomaishan deposit formed from hydrothermal fluids derived from a magmatic source that subsequently cooled, mixed with meteoric water, and underwent W/R interaction, causing sulfide precipitation. The large-scale folding present in this area may also have been a key focus for mineralizing fluids and this a potential vector for use in mineral exploration as these structures focused both magmatism and fluid flow, promoting the formation of the skarn mineralization in this region.

Influences of submerged V-broken rib geometry on the hydrothermal performance of vortex and engulfment flow regimes within a T-channel

The current research presents a three-dimensional numerical study of detailed hydrothermal performance in a T-channel fitted with staggered V-broken ribs under laminar vortex and engulfment flow regimes (Re = 50 to 250) using CFD software tool FLUENT. Comprehensive parametrical investigations are executed to probe the influences arising from the geometrical parameters alterations of the V-broken ribs on the flow field and convective heat transfer characteristics in T-channel. A set of geometrical parameters involving, the orientation rib angles (θ = 30°, 45°, 60°), the pitch-to-outlet-channel width ratio (p/Wo = 1, 1.5, 2), the length-to-outlet-channel width ratio (l/Wo = 0.5, 0.75, 1), the height-to-outlet-channel height ratio (h/Ho = 0.2, 0.3, 0.4), and the staggered inclined rib arrangements (forward, backward, and mixed), are considered. With regard to all examined geometrical parameters, the presence of staggered V-broken ribs consistently enhances fluid mixing and convective heat transfer performance as compared with that without ribs. In addition, the findings illustrate that the V-broken ribs mounted on the bottom wall of the T-channel have approximately the same PEC at 45° and 60° orientation angles with a PEC of 2.23 at Re = 250. At Re = 250, the PEC improves by 40 % and 53 % in comparison to the standard T-channel for the 2 cm and the 4 cm of longitudinal pitch, respectively. Regarding, V-broken rib lengths of 1.5 cm and 1 cm, PEC shows similar trend and eventually reaches double, while the PEC for a 2 cm rib length is smaller than that of 1 and 1.5 cm. The results also exhibit that the smaller rib height of 2 mm gives higher PEC, approximately 2.15, in comparison to 3 mm and 4 mm. Finally, the backward V-broken rib arrangement provides the best PEC of the T-channel, around 2.42.

Discovery and genesis of high-temperature geothermal energy adjacent to the South Tibetan Detachment System, central Himalaya

The 193 °C geothermal fluids have been newly discovered in Lolo at the depth of 350 m through drilling in May 2024, identifying the occurrence of high-temperature geothermal energy adjacent to the South Tibetan Detachment System. Studies on such geothermal field will provide new insights into the distribution of high-temperature geothermal systems in Xizang. Here, we present element geochemistry (major and trace elements) and multi-isotope (H, O, and Sr) compositions of thermal spring, geothermal well, river, and snow waters to reveal the formation of the Lolo high-temperature geothermal system. The major elemental results of water samples show that the Lolo geothermal waters belong to Na-HCO3 type, mainly affected by carbonate dissolution, silicate weathering, and cation exchange through water-rock interaction. The positive correlations of trace alkali metals (Li, Rb, and Cs) and metalloid (B) with Cl indicate that these elements were derived from the same source, mainly released from Himalayan leucogranites with minor slate and limestone via water-rock reaction. The interpretation is further supported by varied Sr isotopic values recorded in geothermal waters. Combination of major and trace elements, and H-O isotopic results reveals that the geothermal waters were sourced from meteoric precipitation from the eastern parts of the region at an elevation of ∼4733 m, which were conducted along the WE-trending fault (F5). The temperature of deep geothermal reservoir was calculated to be 204–205 °C by using quartz geothermometers, and the temperature of shallow reservoir has been calculated to be 100–130 °C based on chalcedony geothermometers and computed mineral saturation index by PHREEQC. The shallow thermal fluids were suggested to be formed by mixing of deep thermal fluids with cold groundwater near to the surface, evidenced by positive linear correlations between B and Cl. The deep-circulated meteoric waters have been heated by partial melting and the circulation depth is up to ∼5 km. These new findings help us understand the formation of Lolo geothermal field and also provide guides in high-temperature geothermal resources exploration adjacent to the South Tibetan Detachment System.

Thermal and hydrodynamic characteristics of microencapsulated phase change materials slurry flow in wavy microchannels

Microencapsulated phase change material slurry (MPCS) is a novel cooling fluid with promising performance. This study numerically investigates heat transfer and flow characteristics of MPCS within wavy microchannels. MPCS is modeled as a homogeneous, Newtonian fluid. Five wavy geometries were examined across a Reynolds number range of 50 to 250 (laminar flow regime), varying in amplitude and wavelength. The model results show that with increase in Reynolds number and decrease in the amplitude and radius of curvature of wavy microchannels, the pressure drop and Nusselt number also increase. Furthermore, the results reveal that Dean vortices intensify with increasing wave amplitude and Reynolds number. Conversely, these vortices weaken as channel wavelength and radius of curvature increase. The formation of Dean vortices enhances fluid mixing and consequently improves the thermal performance of the slurry. The study concludes that in wavy microchannels employing MPCS, increasing the Reynolds number, increasing the channel amplitude with respect to wavelength, and decreasing the radius of curvature improves the overall performance. Also, the results reveal that in higher Reynolds numbers, the radius of curvature is the most effective parameter on the overall performance of wavy microchannels.

Numerical Investigation of Increasing-Decreasing Stepped Micro Pin Fin Heat Sink Having Various Arrangements

The ongoing trend of miniaturization of electronic devices, including computer processors, high-speed servers and micro-electro-mechanical system devices, should go hand in hand with their improved performance. However, managing heat remains a major challenge for these devices. In the present study, a numerical investigation was done on a micro-channel heat sink with an open-stepped micro-pin fin heat sink with various arrangements through ANSYS software. Pin fin was varied in a fashion of increasing and decreasing. The working fluid opted for was water in a single phase. The analysis takes into account varying thermo-physical properties of water. The operating parameters, i.e. the Reynolds number was taken as 100–350 and heat flux as 500 kW/m2. Arrangements selected were staggered and inline. Observations revealed that the staggered 2 arrangement has shown better thermal performance than other arrangements within the entire investigated range of Reynolds numbers because of the effective mixing of fluids. Furthermore, the inline configuration of micro pin fin heat sink has the worst performance. It is interesting to note that a very small difference was observed in the heat transfer capability of both staggered configurations, while the pressure drop in the staggered 2 arrangement has shown an elevated value at a higher Reynold number value compared to the staggered 1 arrangement.

Photocatalytic Magnetic Microgyroscopes with Activity-Tunable Precessional Dynamics.

Magnetic nano/microrotors are passive elements spinning around an axis due to an external rotating field while remaining confined to a plane. They have been used to date in different applications related to fluid mixing, drug delivery, or biomedicine. Here we realize an active version of a magnetic microgyroscope which is simultaneously driven by a photoactivated catalytic reaction and a rotating magnetic field. We investigate the uplift dynamics of this colloidal spinner when it precesses around its long axis while self-propelling due to the light induced decomposition of hydrogen peroxide in water. By combining experiments with theory, we show that activity emerging from the cooperative action of phoretic and osmotic forces effectively increases the gravitational torque, which counteracts the magnetic and viscous ones, and carefully measure its contribution. Finally, we demonstrate that by modulating the field amplitude, one can induce hysteresis loops in the uplift dynamics of the spinners.

Optimization Investigation of Bionic Fin Structure by Experimental and Numerical Modelling

Drawing inspiration from the fast-swimming shark’s structure and skin, we developed the bionic shark fin, featuring two distinct types: bionic curved fins and bionic curved slotted fins. The present study assessed the impact of mainstream Reynolds number, fin curvature, and fin slot thickness on thermal fluid performance. The findings demonstrated that the curved fin structure can enhance the fluid mixing, benefiting local thermal-hydraulic performance. Simultaneously, the slotted curved fins expanded the heat transfer surface area, and the local injection in slots significantly reduced hydraulic resistance, offering a novel solution for heat sink optimization. Optimal flow and heat transfer performance for bionic curved fins were achieved with the fin thickness of 2.4 mm, while for bionic curved slotted fins, the overall optimal thermal performance was attained with a fin thickness of 2.6 mm with the slot thickness of 1 mm. Overall, the bionic fins exhibited thermal performance improvements of 8.7% and 29% over straight fins, respectively. More importantly, the heat transfer and flow friction correlations with criterion of fin parameters were developed, and the robust predictive accuracy was verified.