Serpentine Channel Research Articles

Microfluidic capillary platform with hydrophilic PDMS for point-of-care immunoassays

Point-of-care (PoC) devices offer the possibility of fast and easy to use testing platforms. Self-driven capillary devices are particularly interesting because they can function without external pumps. Microfluidic devices often rely on polydimethylsiloxane (PDMS) prototyping; however, for self-driven microfluidics, its hydrophobic nature makes its use challenging. Bulk modification of PDMS through copolymers with hydrophilic moieties could be a practical solution because the copolymer is added prior to PDMS baking in a single-step process. In this work, a PDMS bulk modification with dimethylsiloxane-(60–70 % ethylene oxide) block copolymer was used to render PDMS hydrophilic. The addition of 1 % (w/w) copolymer resulted in a hydrophilic PDMS which was then used to fabricate the capillary devices. The microfluidic design included a serpentine channel with reagent entry points connected to a capillary pump and was closed by a membrane layer with conical shaped reservoirs. The reservoirs were designed to allow the sequential entry of the solutions and the device sealing and robustness were improved through PMMA frames with integrated magnets. A proof-of-concept was performed with food colouring demonstrating the capability of the device to flow the solutions sequentially. Finally, an immunoassay to detect the presence of Infliximab, a therapeutic antibody for chronic inflammatory diseases, was used to demonstrate the functionality of the capillary device. The versatility of the device was also shown by performing a fluorescent indirect immunoassay and a colorimetric indirect-ELISA for the detection of Infliximab with both approaches detecting Infliximab in the clinical range of interest (between 3 and 7 μg/mL).

Fabrication and Fluorescence Analysis of Rhodamine Dyes in Polycarbonate Serpentine Microfluidic System.

The synthesis of rhodamine dyes (R6G and R1010) and their fluorescence characterization within polymer-based microfluidics, offers an exciting and novel approach in materials science and chemical analysis. This work investigates the emission of polycarbonate substrates (PC) by UV-visible. The ablation threshold (16mj.sec-1) of PC at 193nm wavelength after that ablation process continued to produce microfluidic serpentine channels on PC by using G-Code. The fluorescence characteristics of Rhodamine 6G and Rhodamine 101 are investigated. Absorption and emission at peak wavelength were analyzed against R6G and R101 concentrations. Furthermore, the refractive indices of both R6G and R101 vis concentrations are examined. As a result at low concentrations, there was the highest overlapping, and at high concentrations, there was the smallest overlapping. R101 showed better photostability and a more consistent diffusion, whereas R6G had a faster diffusion and stronger fluorescence intensity. These differences were caused by the different molecular structures of the dyes and their interactions with the PCmicrochannel. Incorporating R6G and R101 dyes into a polycarbonate PC microfluidic chip would enhances both the resolution and sensitivity of fluorescence detection. The limited microfluidic setup facilitates ultra-high-resolution investigation and minimizing sample volumes, making it suitable for applications requiring precise measurements. The innovation relies on the utilization of the unique fluorescence characteristics of R6G (Rhodamine 6G) and R101 (Rhodamine 101) dyes to enhance the performance of polycarbonate microfluidic devices. R6G has high fluorescence quantum yield and stability, rendering it suitable for sensitive detection, while R101 offers superior brightness and improved resistance to photobleaching. Incorporation of these dyes into polymeric microfluidics improves sensitivity and facilitates real-time, dynamic sample analysis. This method offers a portable, economical solution with high-throughput capabilities, greatly enhancing both analytical and process accuracy across a variety of applications.

A novel bionic lotus leaf channel liquid cooling plate for enhanced thermal management of lithium-ion batteries

Battery Thermal Management Systems (BTMS) are pivotal in safeguarding the safety, efficiency, and lifespan of electric vehicles. In this study, we propose a bionic lotus leaf (BLL) channel liquid-cooled plate to mitigate temperature accumulation issues observed during lithium-ion battery (LIB) discharge. The primary objective is to enhance heat dissipation and achieve uniform temperature distribution within LIBs. We investigated the impact of different interior configurations and mass flow rates on individual lithium-ion battery (LIB) temperatures using single-variable analysis. Our findings indicate that higher inlet mass flow rates effectively lower the temperature increase in individual LIBs, albeit at the cost of inducing a significant pressure drop.The optimal parameter combination is determined through orthogonal analysis. Specifically, the channel angle (α) and inlet mass flow rate (M) are found to significantly influence the maximum temperature (Tmax) of LIBs. The number of channels (N) is optimized to enhance temperature distribution and reduce maximum temperature variation (ΔTmax) within LIBs. Furthermore, adjusting the channel width (D) substantially mitigated pressure drop (ΔP) in the BLL channel liquid cooling plate, thereby improving hydraulic pump efficiency. The identified optimal combination (M = 1.0 g s-1, N = 4, D = 2.5 mm, α = 90°) ensures that Tmax remains below 29.732 °C even during a 5C discharge, a critical requirement. Compared to a traditional serpentine channel with equivalent heat transfer area and inlet mass flow, the optimized BLL channel showed a decrease in Tmax by 0.776 °C, ΔTmax reduction by 2.445 °C, and ΔP reduced to only 43.44 % of that in the serpentine channel. The BLL channel proposed in this research can serve as a valuable reference for BTMS.

Experimental evaluation of green nanofluids in heat exchanger made oF PDMS

Conventional methods for synthesizing metallic nanoparticles face challenges such as instability and environmental concerns. Therefore, new, simpler, and more eco-friendly methods are being explored. In this context, the study reports a green synthesis process to produce magnetic iron oxide nanoparticles using an aqueous extract of the alga Chlorella vulgaris. This process leverages natural resources to create a sustainable nanofluid known as green nanofluid. To evaluate the characteristics of this nanofluid, experimental measurements of wettability, viscosity, thermal conductivity, and qualitative stability analysis were conducted. An experimental setup consisting of a heat exchanger made of polydimethylsiloxane (PDMS) was used to assess the thermal performance and the results were compared to theoretical equations and numerical simulation. Additionally, thermographic imaging of temperature gradients as the fluids passed over the heated surface of the serpentine channel were made. The main findings confirmed that the nanofluid was more stable than that obtained by traditional methods and had a more uniform temperature distribution over the heat exchanger. The higher concentration exhibited superior thermal performance compared to DI-Water. Moreover, the green nanofluid was used at a weight concentration of 0.1 wt%, provided thermal performance results of nearly 4.5% superior to those estimated by the numerical model and 6.4% higher than those experimentally obtained with the base fluid, respectively. Finally, the results obtained for the nanofluid also showed an average increase of around 5% in the viscosity of the base fluid, with a more significant sedimentation at a concentration of 0.1 wt%.

Numerical investigation of centrifugal passive mixing in Omega shaped microchannel and comparison with fixed platform

The extraction of DNA from isolated cells is crucial for diagnosing and treating various diseases, including cancer, which has become a leading cause of death in recent years. Circulating tumor cells (CTCs) in the blood can be separated from other blood cells, allowing for DNA extraction and analysis for further research. Microfluidic methods are more cost-effective than conventional DNA extraction techniques and have significant potential for high-throughput mixing in lab-on-a-chip (LOC) and lab-on-a-disk (LOD) devices without damaging DNA. Chemical methods for cell lysis, where the mixing of reagents is essential, are particularly efficient on these platforms due to the generation of secondary flows. This is especially true in microchannels with a serpentine design, which enhances mixing quality—a critical parameter for cell lysis efficiency. This study presents and compares the mixing capabilities of the two microchannel platforms (LOC and LOD). Additionally, we introduce a new Omega-shaped serpentine microchannel that combines features of both straight and curved serpentine channels. The mixing quality across all geometries and both platforms has been investigated. Our findings indicate that the centrifugal platform is the most effective for mixing at low inlet velocities. Furthermore, we examine the number of stages in the Omega channel and conclude that 7 Ω stages are sufficient for achieving high mixing quality (∼100 %).

Segmented catalyst layer with varied catalyst loading to improve the cost performance of proton exchange membrane electrolysis cell, a numerical investigation

In this work, a steady-state, three-dimensional and non-isothermal numerical model for a proton exchange membrane electrolysis cell (PEMEC) is established. Based on this model, the distribution of catalyst loading is specifically designed according to the flow characteristics of both parallel and serpentine channels. In general, the catalyst loading is progressively reduced from inlet to outlet along the flow direction to match the local water content, leading to an innovative segmented catalyst layer which has not been studied yet for PEMEC applications. The electrochemical behavior of different segmentation schemes is investigated by comparing their polarization curves normalized by either electrode area or catalyst loading, while other physical fields such as velocity, pressure, water mole fraction and temperature distributions are also characterized. The numerical results reveal that a reasonable distribution of catalyst can reduce its amount of usage while still maintaining most of the PEMEC performance. In other words, the cost performance is significantly improved. This is mainly attributed to the full use of uneven water distribution in the flow channel, which improves the catalyst utilization efficiency significantly. This strategy is proved to be effective for both serpentine and parallel channels, ensuring a broad application prospect.

Numerical analysis of bubble behavior in proton exchange membrane water electrolyzer flow field with serpentine channel

Green hydrogen, produced using renewable energy sources, represents a critical component in the transition to sustainable energy systems due to its clean and versatile nature. This research investigates the dynamic behavior of bubbles within the serpentine flow field of a Proton Exchange Membrane Water Electrolysis (PEMWE) cell, aiming to enhance the understanding of two-phase flow dynamics and improve the efficiency of green hydrogen production. Utilizing the Volume of Fluid (VOF) method, a three-dimensional unsteady model was developed to simulate the flow dynamics at the anode of a PEMWE system. The study explores the transition of bubbles from bubbly flow to slug and annular flow, highlighting the significant impact of bubble formation on mass transport and overall cell performance. The results demonstrate that larger bubbles impede liquid water delivery to reaction sites and cause unstable pressure drops. The investigation also examines the influence of wall contact angles on bubble behavior, revealing that hydrophobic surfaces lead to increased gas coverage and more oxygen accumulation inside the channel, which hinders mass transport. These findings underscore the necessity for optimized flow channel designs and enhanced surface treatments to mitigate bubble coalescence and improve PEMWE performance.

Experimental investigation for the influence mechanism of air intake method and humidity level on performance of proton exchange membrane fuel cells

As pivotal component of hydrogen fuel cell vehicles (HFCVs), proton exchange membrane fuel cells (PEMFCs) play a crucial role in determining performance and energy efficiency of HFCVs. In this study, comprehensive bench tests of fuel cell stack and electrochemical impedance spectroscopy (EIS) tests of single cells were conducted, and influence mechanisms of air intake methods and humidity levels on performance of stack and single cells at different locations were analyzed in depth. The results indicate that counter-flow inlet method exhibits superior voltage output performance and stability across various relative humidity (RH) and current densities (CDs). A moderate increase in RH can mitigate performance degradation, but excessive humidity can lead to flooding. When RH is increased to 60%, the voltage difference between co-flow and counter-flow of fuel cell stack does not exceed 0.05 V at 1.6 A/cm2. Meanwhile, the performance of cells near inlet end plate is consistently worse than those farther away under different inlet conditions. In addition, the performance trend of single cells in serpentine channels aligns with that of fuel cell stack, underscoring strong adaptability of mechanisms influencing performance under different conditions. These findings provide theoretical guidance and data support for optimizing performance and preventing failures in PEMFCs.

Thermal performance analysis of sinusoidal corrugated channels: A comparative study of thermo-hydraulic and entropy generation

The physical properties of working fluids—in terms of the Prandtl number—play a crucial role in determining their thermal performance in the internal flow, especially their viscosity. This study first considers the thermo-hydraulic and entropy generation of a sinusoidal corrugated channel in two configurations: symmetrical (raccoon) and asymmetrical (serpentine). Results are presented for different ranges of operating parameters, such as 100≤Re≤700 and 0.72≤Pr≤90, and for geometrical parameters such as the wave amplitude-to-wavelength ratio 0.2≤α≤0.6. In addition, the results of the two channels were compared with each other's and with the straight channel. Control transport equations are solved using finite element methods. It was found that the flow inside the wavy channels generated re-circulatory reigns, and their size was affected by the wave parameters as well as the Reynolds number. Also, employing high values of Pr extremely enhanced the heat transfer rate (HTR) of the wavy channels over the straight for all values of α and for both raccoon and serpentine channels. In addition, the results indicated that raccoon channels have higher HTR and performance factor compared to the serpentine channel. Finally, the thermal entropy generation dominated over the viscous entropy generation and its decrease with both Reynolds number and Prandtl number for raccoon and serpentine channels. This study focused on the heat transfer enhancement of the corrugated channels due to their importance in many industrial applications where the heat dissipation is critical to their work, including heat exchangers and heat sinks. Thus, the current numerical simulation primarily suggests utilizing the raccoon channel over the serpentine one, due to its higher thermal performance and nearly the same total entropy generation.

Deciphering the Evolution of Inertial Migration in Serpentine Channels.

Serpentine channels coupling inertial and secondary flows enable effective particle focusing and separation, showing great potential in clinical diagnostics and drug screening. However, the nonsteady secondary flows in the serpentine channel make the evolution of inertial migration unclear, hindering the development and application of the serpentine channel. Herein, to refine the inertial migration mechanism, we established a model with varying curvature ratios to study the effect of secondary flow on particle migration in the serpentine channel. This method used direct numerical simulation (DNS) to calculate inertial lift, mapped the inertial lift to cross sections of the serpentine channel, and deciphered the inertial migration by using the Lagrangian particle tracking (LPT) method. The inertial migration of microparticles is experimentally investigated to validate the established numerical model. The results indicate that particle migration in serpentine channels follows a two-stage migration. An increase in secondary flow accelerates the second stage of the migration process while slowing the first stage process. Subsequently, we investigated the effects of different parameters, including Reynolds number, aspect ratio, and blockage ratio, on the equilibrium positions of particles, providing guidelines for the high-resolution separation of particles. Taking flow resistance into account, the dimensionless study makes the separation of arbitrary-sized particles possible. This work reveals the migration mechanism in serpentine channels, paving the way for the inertial separation of the particles.

A numerical study of Elasto-inertial particle-focusing in straight and serpentine microchannels

Microfluidic devices have gained popularity in recent years due to their low cost and simplicity. Cell focusing linked with cell counting and cell separation used in clinical tests and point-of-care devices stands towards the top of every list of microfluidic applications. To focus and manipulate particles in a Newtonian medium, inertial microfluidics has been widely used. There is a requirement to replace a significantly more efficient approach given various particle-focusing positions near the channel walls recorded by inertial microfluidics. Here, the synergetic effect of elastic and inertial forces in relatively low-concentration viscoelastic fluids was investigated numerically. Utilizing particle-focusing behavior in straight and serpentine channels with different corner angles, by applying the numerical results obtained using the developed direct numerical simulation method (DNS) for elastic and inertial forces, we created a microchannel with a remarkable performance. As the flow regime transitions to elasto-inertial, where inertial forces are comparable to elastic forces in a straight microchannel, particles tend to concentrate at the channel centerline. As the flow rate increases, however, particle defocusing develops, and shear gradient lift forces ultimately overcome elastic forces in the channel's central region. Given that fluid flows at a higher velocity in the serpentine channel with a corner angle of 75° than in other channels, the Dean drag force induced by secondary flow serves to reduce particle defocusing rate at a given flow rate, making this channel a desirable platform for Elasto-inertial microfluidics. Particle focusing in a vertical direction was noticed as a benefit of elasto-inertial microfluidics, regardless of the geometry or flow rate of the particles passing through the channel. Finally, the impact of particle diameter on focusing behavior was studied. As particle diameter decreases, focusing width decreases and the focusing band shifts to the left side of the cross-section. We expect that the numerical evaluation of using viscoelastic medium in complex geometries can contribute to accelerate the three dimensional particle-focusing mechanism and enhance the efficiency of microdevices for cell and particle manipulation.

Effect of applying serpentine channels and hybrid nanofluid for thermal management of photovoltaic cell: Numerical simulation, ANN and sensitivity analysis

Regarding the importance of thermal management of solar PV cells to achieve higher efficiency and electricity output, a novel configuration by use of serpentine channels for cooling is proposed and numerically investigated in the present article. Moreover, a hybrid nanofluid, (MWCNT)-Fe3O4/water, is employed as the coolant to investigate its potential in further improvement of thermal management. Computational Fluid Dynamics (CFD) is applied to numerically simulate the systems and investigate the impacts of different factors. Performance of the proposed configuration is compared with cooling channels with simple structure without nanofluids. Simulations results revealed that the employment of serpentine channels leads to modification in the thermal management of the cell compared with the simple channel. The maximum improvement rate in this condition compared with simple channels is around 9.63 % that is obtained in case of maximum mass flow rate of coolant and solar radiation intensity. Despite increment in pressure loss by using the serpentine channel compared with the simple channel, 2.6 ×10−3 W and 9.3 ×10−4 W, respectively, in mass flow rate of 0.003 kg/s for water, increase in the generated electricity is much more in this case. Furthermore, numerical results show that applying the hybrid nanofluid with 0.1 % concentration can cause slight reduction in the temperature compared with using water. Moreover, Group Method of Data Handling (GMDH) and Multilayer Perceptron (MLP) neural network as intelligent methods used for estimation of the cell temperature and the maximum error for the developed model is approximately 1.1 % and 0.098 % for the GMDH- and MLP-based models, respectively. Finally, sensitivity analysis is implemented and it is shown that solar radiation intensity is the most influential factor on the cell temperature in condition of using serpentine channels while mass flow rate of the coolant has the minimum relevancy factor and consequently effect on the temperature of the solar cell.

Computational Fluid Dynamic Investigation of Local Flow-Field Conditions in Lab Polymer Electrolyte Membrane Fuel Cells to Identify Degradation Stressors and Performance Enhancers

The use of polymer electrolyte membrane (PEM) fuel cells as an alternative to internal combustion engines can significantly contribute to the decarbonization of the transport sector, especially for heavy-duty applications. However, degradation is still an issue for this type of component, affecting their durability and performance. In this scenario, a detailed analysis of the anodic and cathodic distributors’ flow-field geometry may help to identify some local stressors that trigger the degradation mechanism, such as local hot spots and reactants not having a uniform distribution. A computational fluid dynamic (CFD) methodology is able to provide a volumetric description of a PEM fuel cell so it can be a useful tool to better understand the physical phenomena that govern the component operations. In this work, the open-source simulation library openFuelCell2 is adopted for a detailed analysis of two different PEM fuel cells characterized by standard distributor geometries, namely a parallel channel geometry and a serpentine configuration. The library, based on the OpenFOAM code, has been extended with a novel implementation accounting for the catalytic activity reduction due to the platinum oxide (PtOx) formation occurring under certain particular conditions. The adopted methodology is firstly validated resorting to experimental data acquired for the two different fuel cell configurations. The analysis highlights that the PtOx formation leads to a reduction in the fuel cell performance reaching up to 60–80% when operating at high voltages. Then, the effect of the distributor geometries on the component performance is investigated by resorting to in-plane and through-plane physical quantity distribution, such as reactant concentration, pressure or velocity fields. While the parallel flow channel configuration shows some diffusion losses under the rib, the serpentine channel geometry configuration can achieve some local performance peaks thanks to the convective flow in the gas diffusion layer (GDL) driven by local pressure gradients. Furthermore, the local enhancement in terms of higher current density under the rib is associated with an effective heat removal due to the high thermal capacity of the bipolar plate, avoiding the generation of local hot spots.

Advanced microfluidic techniques for in situ PLGA microparticle formation: A dynamic solvent extraction approach

Microencapsulation processes often use the "solvent extraction/evaporation" technique, which involves (i) dissolving a polymer in an organic solvent (optionally with a bioactive component), (ii) forming microdroplets, (iii) removing the solvent, and finally (iv) harvesting and drying the particles ex situ. These last two steps lack control over the solidification processes, which adversely affects the morphology and size distribution of the final microparticles. In this study, we present a continuous production process for solid PLGA microparticles within a microfluidic chip, covering droplet formation, solvent extraction, and solidification. This method offers the advantage of enhanced control over the solidification process within a closed system, leading to morphologically uniform particles. The setup includes a co-axial junction integrated into a chip with an 80 cm long serpentine channel. We generated droplets with various PLGA/ethyl acetate concentrations and tracked their shrinkage until solidification. Results showed that all droplets underwent identical shrinkage processes with consistent rates, velocity profiles, and sizes. The shrinkage rate was linear and unaffected by PLGA concentration, which only influenced final particle size.To demonstrate our setup's advantages, we compared it with the conventional off-chip method, where droplets shrink in a beaker. Off-chip shrinkage was non-linear and inconsistent, influenced by factors such as the number of surrounding droplets and production time. Droplets produced within a 10-s difference had solidification delays up to 250 s. In contrast, on-chip production was uniform, predictable, and 4–10 times faster. SEM imaging confirmed that on-chip particles were consistently spherical with a rough, wrinkled surface, unlike the irregular, bumpy off-chip particles.In summary, on-chip production and shrinkage of PLGA particles is faster and produces more uniformly shaped particles compared to off-chip methods. This study suggests that on-chip production could significantly enhance the efficiency and quality of drug-loaded microparticles, particularly for drug delivery applications.

Additively manufactured, long, serpentine submillimeter channels by combining binder jet printing and liquid-phase sintering

Metallic microfluidic devices made from powder-bed additive manufacturing systems have received increasing attention, but their feasible channel geometry and complexity are often limited by lack of an effective approach to removing trapped powder particles within the channels or conduits of the sintered parts. Here, we present an innovative approach to fabricating long serpentine, high-aspect-ratio submillimeter channels made of stainless steel 316L (SS) by binder jet printing (BJP) and liquid-phase sintering. We leverage the unique nature of the BJP process, that is printing and consolidation steps are decoupled, enabling us to join two or more parts during the sintering step. Instead of constructing the channel device as a single part, we print multiple parts for easy powder removal and later join them to form enclosed channels. The key innovation lies in adding sintering additives like boron nitrides (BN) to the SS stock powder—at the SS/BN interfaces, liquid phase is locally generated at temperature much lower than the SS melting temperature, facilitating the bonding of the multiple parts as well as the consolidation of parts for near-full density. We systematically vary the sintering temperature to show how it affects the joining quality and the channel shape distortion. The joining quality such as the fracture strengths of the joined samples is measured by a pull test while the shape distortion is characterized by various imaging techniques. The feasibility of the proposed approach is demonstrated by fabricating a 400-mm-long, fully enclosed serpentine channel with a rectangular cross-section of 0.5 mm in width and 1.8 mm in height. The pressure drop across this 3D-printed SS serpentine channels is measured for air flow and compared to a standard gas flow model, showing that the device is free of leakage or clogs.

A new human metabolic rate sensing model optimization and wearable sensor realization

Accurate assessment of metabolic rate is crucial for predicting human thermal comfort. However, many existing instruments are bulky, invasive, and inconvenient. Additionally, wearable metabolic rate measurements have faced long-standing challenges due to a lack of a comprehensive theoretical model with easy-to-measure parameters. This paper optimizes our previously proposed theoretical approach for wearable metabolic rate measurement that incorporates heart rate, whole-body unit heat loss, skin resistance, and body muscle percentage. We have improved the evaluation approach for whole-body unit heat loss by introducing a newly designed convective heat loss coefficient from various body segments. Regarding the wearable sensor design, a heat loss measuring system with serpentine channel was verified as the most suitable design following calibration experiments. We also integrated a modified square-wave-based skin resistance design, resulting in an upgraded integrated metabolic sensor. To validate our sensor and model performance, we conducted experiments with ten subjects of both genders at three temperature conditions (22, 25 and 28 °C) and four levels of activities (rest, tiptoe heel, slight walk, and moderate walk). First, our results demonstrate a strong positive relationship between the metabolic rate obtained by our optimized sensor and Quark CPET instrument, with high coefficients of determination (highest:0.97 from the male group, 0.98 from the female group). Our approach achieved at least 96 % accuracy and less than 2.5 % uncertainty for both groups. Second and increasingly, we found that only one metabolic rate model was required across combined temperature conditions when the person was fixed. Third, the positive relationship was further improved by incorporating whole-body unit heat loss. Finally, we obtained information from different segments on skin temperatures. In summary, our study provides a powerful methodology for predicting and evaluating human metabolic rate through an innovative wearable approach. Our approach and sensor have the potential to substantially contribute to energy-saving efforts in smart buildings.

Research on the effect of connected cable-type channel structure and flow field arrangement on the performance of SOFC

In order to address Solid oxide fuel cells(SOFC) the issues of uneven gas distribution and low fuel utilization rate in conventional straight-channel. In this research, a connected cable-type channel with enhanced connectivity and broader radiation coverage was developed. The research revealed that in a singular flow channel scenario, the distribution of oxygen on the electrode within the connected cable-type channel exhibited greater uniformity compared to the conventional straight-channel design. The gas utilization rate is increased by 2.38% compared with the conventional straight-channel, and the output power density is increased by 8.55%. In the flow field, it is observed that the gas distribution on the cathode side of connected cable-type channel is significantly superior to that of the conventional straight-channel. In the case of a parallel flow field, the output power of the connected cable channel increases by 8.39% compared to the conventional straight channel, while the serpentine channel shows an increase of 11.65% in output power. Then, the impact of the flow field combination on the flow field was investigated. It was discovered that the output power of the cell could reach up to 5158.17 W/m2 when the serpentine-parallel staggered flow field distribution structure was utilized. This output was 11.33% higher than that of the parallel flow field.

Experimental and numerical study of improving flow and heat transfer in a serpentine cooling channel with topology-optimized TPMS porous structures

Serpentine cooling channels have been employed in various industrial applications to control the heat loads in the system by increasing heat transfer while lowering the total pressure loss. As additive manufacturing (AM) enables the fabrication of complex structures, more sophisticated cooling models have been proposed to improve the thermal performance of the serpentine channel. This work designs a high-performance serpentine cooling channel based on topology optimization and triply periodic minimal surface (TPMS). The transient liquid crystal thermography (TLC) is used to reveal the endwall heat transfer characteristics of the optimized serpentine channel infilled with the Diamond TPMS topology within the Reynolds number of 10,000–40,000. The overall and local flow structures are revealed by numerical simulation, and the results are compared with the baseline serpentine channel. The experimental results show that at the Reynolds number of 10,000, the topology-optimized model with the Diamond structure shows a higher wetted-area averaged Nusselt number in the second pass by 70.7 % while reducing the total pressure loss by 19.2 %, compared to the smooth channel. Within the studied Reynolds numbers, the heat transfer enhancement in the second pass is 2.30–2.39 times relative to a smooth channel. The numerical results show that the topology-optimized model significantly improves the thermal performance by up to 82.7 % compared to the baseline because the flow recirculation and the regions of low heat transfer are eliminated. The optimized channel also mitigates the negative effect of the Dean's vortices while keeping high turbulence and improving flow and heat transfer uniformity.

The clock in growing hyphae and their synchronization in Neurospora crassa

Utilizing a microfluidic chip with serpentine channels, we inoculated the chip with an agar plug with Neurospora crassa mycelium and successfully captured individual hyphae in channels. For the first time, we report the presence of an autonomous clock in hyphae. Fluorescence of a mCherry reporter gene driven by a clock-controlled gene-2 promoter (ccg-2p) was measured simultaneously along hyphae every half an hour for at least 6 days. We entrained single hyphae to light over a wide range of day lengths, including 6,12, 24, and 36 h days. Hyphae tracked in individual serpentine channels were highly synchronized (K = 0.60-0.78). Furthermore, hyphae also displayed temperature compensation properties, where the oscillation period was stable over a physiological range of temperatures from 24 °C to 30 °C (Q10 = 1.00-1.10). A Clock Tube Model developed could mimic hyphal growth observed in the serpentine chip and provides a mechanism for the stable banding patterns seen in race tubes at the macroscopic scale and synchronization through molecules riding the growth wave in the device.

Enhanced heat transfer in a two-dimensional serpentine micro-channel using elastic polymers

Elastic turbulence has emerged as a promising method to enhance heat transfer performance at the microscale. However, previous studies have mainly focused on the overall convective heat transfer performance in curved channels, overlooking the fact that the chaotic flow intensity varies along the streamline, leading to diverse local heat transfer characteristics. In this study, we systematically investigate the hydraulic and thermal properties of a dilute polymer solution under elastic turbulence conditions, where the inflow conditions exhibit a vanishing Reynolds number (Re) and high Weissenberg number (Wi), enabling a comprehensive understanding of the influence of polymers on the system. Through extensive direct numerical simulations using Rheotool, a two-dimensional curvilinear channel flow of an Oldroyd-B viscoelastic fluid is analyzed. By examining the variations of the friction factor and Nusselt number along the serpentine channel, we unveil both global and local characteristics of elastic turbulence. Based on the Wi value, we identify three distinct regimes. In the first regime (0<Wi≤3), we observe approximately 10% heat transfer enhancement accompanied by a roughly 5% reduction in the friction factor compared to laminar flow, known as polymer-induced thermal conductivity enhancement. In the second regime (3<Wi≤5), we observe a steep linear increase in heat transfer (around 30%) at the expense of up to 15% enhanced friction factor. Finally, in the fully developed elastic turbulence regime (Wi>5), we observe a remarkable heat transfer enhancement of up to 60% along with a reduced friction factor. The significant enhancement of heat transfer with increasing Wi can be attributed to the intensifying elastic instability resulting from the balance between normal stresses and streamlined curvatures.