Serpentine Design Research Articles

Decoupling pressure and distribution effects of flow fields on polymer electrolyte fuel cell system performance

The performance of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) is highly dependent on the flow distribution and pressure of reactant gases, which are controlled by flow field design. The relative importance of differing supply pressure requirements of flow field designs in PEMFCs is considered here. A First-Law analysis of the auxiliary system is developed in order to demonstrate how the pressure drop affects all auxiliary system components and fuel cell unit performance. A method of comparison is then proposed to eliminate the effects of pressure in the comparison of fuel cells with different flow field designs. This method is applied to the single serpentine and parallel designs by Computational Fluid Dynamics (CFD) simulation. It is shown that, of the serpentine design’s 17.1% better performance, mass transport effects provide 12.2% improvement, and pressure effects account for the remaining 4.9%. Finally, a metric is proposed by which the relative effect of pressure between different flow field designs may be estimated for past results not using the recommended method, and is demonstrated by application to results found in existing literature.

Effect of Electrode Structure and Electrolyte Flow on Performance of Redox Flow Battery

As a storage battery suitable for leveling output of renewable energy, a redox flow battery with features such as long life and high safety has attracted attention. Since a redox flow battery uses a pump for the electrolyte circulation, it is necessary to supply the electrolyte with keeping the pressure drop as small as possible. Mench et al. reported that the interdigitated design (IDD) of electrolyte flow fields can maintain lower pressure drop than the conventionally-used flow through design (FTD) (1). Some studies have reported that carbon paper electrodes show better cell performance with the serpentine design of electrolyte flow fields than carbon felt electrodes that have been widely used until now (2). In this study, by using the carbon felt electrode, I-V performance and pressure loss with two kinds of flow designs, the IDD and the FTD, were compared, and the influence of the flow designs on the cell performance was examined. In addition, the performance for the IDD was also compared with that using carbon paper electrode, and the influence of type of porous carbon electrode was investigated in the IDD. Furthermore, we tried to improve the cell performance by applying the combination of carbon felt and carbon paper electrodes with the IDD. Figure 1 shows schematic views of the FTD and the IDD. In the FTD, the electrolyte flows uniformly through the porous electrode, as shown in Figure 1(a), and reacts on the surface of carbon electrode. In the IDD, the electrolyte flows from the inlet flow path of the channel, dives into the porous electrode, and exits to the outlet flow path, as in Figures 1(b) and (c). In this study, two kinds of electrodes, carbon felt and carbon paper, were used, and the reaction area was 21.6cm2 (4.6cm × 4.7cm). The carbon felt with a thickness of 3.1mm was compressed to 2.0 mm, and four carbon papers with the thickness of 1.1mm (0.28mm × 4) were compressed to 0.85mm. Figure 2 shows the I-V characteristics with the FTD and the IDD. The SOCs are 40 and 80%, and the flow rate is 30mL/min. It was confirmed that the performance with the FTD is higher than that with the IDD with the same flow rate. Figure 3 shows the relationship between the pressure drop and the flow rate of the electrolyte using various flow fields. In the case of the FTD, the pressure loss for the carbon paper electrode with lower porosity becomes larger than that of the carbon felt electrode. In the case of the IDD, small pressure loss can be maintained regardless of the type of electrode. The IDD is suitable for upsizing because of small pressure loss, but the I-V characteristics with the IDD is inferior to that with the FTD with the same flow rate of the electrolyte, as described above. Therefore, it is necessary to improve the I-V performance of the IDD with keeping the pressure loss low. In this study, we tried to optimize the electrode structure by combining the two types of electrodes having opposite properties. The carbon paper electrode having a low porosity has an advantage that the surface area can be secured even if it is thin. On the other hand, the carbon felt electrode having a small pressure loss has an advantage that it can suppress the pump power. Figure 4 shows results of the I-V measurement with the IDD using four types of electrode structures. In addition to the previous structures, the combination of carbon paper and felt, and two 4.0mm thick two carbon felts are compared. In the combination, one carbon paper was stacked on one carbon felt electrode at the current collector side. In the case with the combination structure, the I-V performance is improved compared to that with the carbon felt electrode. The pressure loss can be also maintained small. This suggests that combination of various types of carbon electrode is effective to improve the cell performance with the ID. Detailed investigations on the mechanism and further improvements of the cell performance with the IDD will be conducted. Reference (1) M. M. Mench, et al. , Journal of Power Sources, 302, 369 (2016). (2) T. J. Schmidt, et al. , ECS Trans., 57, 535 (2018). Figure 1

The Effect of Potential Cycling on High Temperature PEM Fuel Cell with Different Flow Field Designs

AbstractDegradation of phosphoric acid doped polybenzimidazole membrane based fuel cells under accelerated potential cycling conditions is investigated in current study. Three unit cells with identical high temperature membrane electrode assembly were assembled with three different cathode flow field designs. The fuel cell is cycled between 0.5 V and 0.9 V with 3 min dwelling time for each voltage set point. Performance degradation mechanisms associated with differences in cathode flow design are identified. The fuel cell with multiple serpentine design is operated for a maximum of 4,821 potential cycles with only 38.6% of initial performance remaining at the end‐of‐test (EoT), whereas straight and parallel design operated for only 3,188 cycles. The electrochemical characterization studies reveal the cause of observed performance losses from polarization curves. Irrespective of the design type used there are very high activation losses observed which accelerated with accelerated stress tests (AST) testing. The impedance studies reveal high charge transfer resistance related to increased platinum crystal growth on cathode and reduced electrochemical surface area (ECSA) of catalyst. Overall the AST results in irreversible performance loss and severe degradation of the cathode catalyst support and catalyst itself.

A two-dimensional model for the design of flow fields in vanadium redox flow batteries

In this work, we report a two-dimensional mathematical model for the design of flow fields in vanadium redox flow batteries (VRFBs). The model is validated by calculating the pressure drop, distribution uniformity of vanadium ions in an interdigitated flow field and a serpentine flow field for a 9-cm2 cell. The model is then used to simulate interdigitated and a series of parallel serpentine design of flow fields in a 410-cm2 cell. It is demonstrated that with an increase in the number of parallel serpentine channels, the pumping power decreases while the distribution of vanadium ions becomes less uniform. Among the design of flow fields studied in this work, the interdigitated design performs the lowest pumping power and the most uniform distributions of vanadium ions.

A Detailed Optimisation of Solar Photovoltaic/Thermal Systems and its Application.

Abstract There have been various studies and experimental results analysing the operational behaviour of PVT, most of which has been done at steady state or quasi-state. Variable factors can be controlled to optimise the PVT output such as mass flow rate, irradiation falling on the PVT through tracking or incidence angles in a day and fixed factors that depend on the design of the chosen PVT system as well as location parameters such as ambient temperature, wind speed, Transport Fluid used, Difference in Structure, Packing Density, Nominal operating temperature, stagnation temperatures, Fill Factor, Thickness of each layer, Location and Latitude and Heat removal factor (harp or serpentine design). The aim of this research is to validate and predict the dynamic behaviour of PVT systems while accurately describing the factor responsible for the loss of efficiency at any point in time under various weather constraints. A commercial system was considered (Solar Angel PVT system) here and is simulated for an entire year. The system was modelled in MATLAB and solved in implicit RK-4 method. The research question finds out to establish the basis for a standard testing protocol for assessing PV-T performance throughout various differences. It also analyses the long-term dynamic performance of PV/T technology by providing evidential data analysis (solar irradiance, heat and electricity, ambient temperature, operational temperatures, flow rates and thermal storage capacity) while completing an assessment of PVT behaviour with respect to an equivalent PV under different weather conditions. The flow rates, heat removal factor and the location affect the thermal behaviour of the PV/T to a greater extent than nominal temperatures and stagnation temperatures.

Stainless-Steel Column for Robust, High-Temperature Microchip Gas Chromatography.

This paper reports the first results of a robust, high-performance, stainless-steel microchip gas-chromatography (GC) column that is capable of analyzing complex real-world mixtures as well as operating at very high temperatures. Using a serpentine design, a 10 m column with an approximately semicircular cross-section with a 52 μm hydraulic diameter ( Dh) was produced in a 17 × 6.3 × 0.1 cm rectangular steel chip. The channels were produced using a multilayer-chemical-etch and diffusion-bonding process, and metal nuts were brazed onto the inlet and outlet ports allowing for column interfacing with ferrules and fused silica capillary tubing. After deactivating the metal surface, channels were statically coated with a ≈0.1 μm layer of 5% phenyl-1% vinyl-methylpolysiloxane (SE-54) stationary phase and cross-linked with dicumyl peroxide. By using n-tridecane ( n-C13) as a test analyte with a retention factor ( k) of 5, a total of 44 500 plates (≈4500 plates per meter) was obtained isothermally at 120 °C. The column was thermally stable to at least 350 °C, and rapid temperature programming (35 °C/min) was demonstrated for the boiling-point range from n-C5 to n-C44 (ASTM D2887 simulated-distillation standard). The column was also tested for separation of two complex mixtures: gasoline headspace and kerosene. These initial experiments demonstrate that the planar stainless-steel column with proper interfacing can be a viable alternative platform for portable, robust microchip GC that is capable of high-temperature operation for low-volatility-compound analysis.

Performance study of solid oxide fuel cell with various flow field designs: numerical study

A comprehensive 3D mathematical model has been developed to study the performance of the planar anode-supported solid oxide fuel cell (SOFC) with different flow field designs such as helical, single-entry serpentine, traditional parallel, modified parallel design, double-entry serpentine and triple-entry serpentine. The model includes charge transport (electron and ion), conservation of mass, momentum, and energy. The developed model is numerically simulated and the predicted results are validated using the available experimental data from previous work. Results showed that single-entry cells suffer of back flow at the outlet of the cathode flow side in both helical and single-entry serpentine designs due to early full fuel consumption. To avoid back flow, increasing the number of entry ports at inlets and outlets in different designs is performed to increase the inlet mass flow rate. It is found that the triple-entry serpentine design attains good uniform distributions for both fuel and oxygen throughout the active surface area and achieves a high collected current of about 23.3 A with a percentage increase of 5.18% compared to the other designs at low voltage. Comparison with other designs indicates that the triple-entry serpentine gives better performance.

An investigational back surface cooling approach with different designs of heat-absorbing pipe for PV/T system

A solar photovoltaic panel accumulates substantial amount of heat, which deteriorates its performance. Thus, to minimize the panel temperature, 3 new designs (semioval serpentine, circular spiral, and circular spiral semiflattened) of absorbers for back surface cooling are introduced in this paper. Experimental investigations on the panel performances with and without the designed cooling systems are performed. A similar experiment with an existing serpentine design of absorbers is also conducted, and the results of all the experiments are compared. The circular spiral semiflattened design absorber has shown preeminent performance among all the absorbers in terms of the highest improvement in efficiency (4.32%), fill factor (19.80%), etc.

Effects of Flexible Dry Electrode Design on Electrodermal Activity Stimulus Response Detection.

The focus of this research is to evaluate the effects of design parameters including surface area, distance between and geometry of dry flexible electrodes on electrodermal activity (EDA) stimulus response detection. EDA is a result of the autonomic nervous system being stimulated, which causes sweat and changes the electrical characteristics of the skin. Standard silver/silver chloride (Ag/AgCl) EDA electrodes are rigid and lack conformability in contact with skin. In this study, flexible dry Ag/AgCl EDA electrodes were fabricated on a compliant substrate, used to monitor EDA stimulus responses and compared to results simultaneously collected by rigid dry Ag/AgCl electrodes. A repeatable fabrication process for flexible Ag/AgCl electrodes has been established. Surface area, distance between and geometry of electrodes are shown to affect the detectability of the EDA response and the minimum number of sweat glands to be covered by the electrodes has been estimated at 140, or more, in order to maintain functionality. The optimal flexible EDA electrode is a serpentine design with a 0.15cm2 surface area and a 0.20cm distance with an average Pearson correlation coefficient of . Fabrication of flexible electrodes is described and an understanding of the effects of electrode designs on the EDA stimulus response detection has been established and is potentially related to the coverage of sweat glands. This work presents a novel systematic approach to understand the effects of electrode designs on monitoring EDA which is of importance for the design of wearable EDA monitoring devices.

Low-cost origami fabrication of 3D self-aligned hybrid microfluidic structures

3D microfluidic device fabrication methods are normally quite expensive and tedious. In this paper, we present an easy and cheap alternative wherein thin cyclic olefin polymer (COP) sheets and pressure sensitive adhesive (PSA) were used to fabricate hybrid 3D microfluidic structures, by the Origami technique, which enables the fabrication of microfluidic devices without the need of any alignment tool. The COP and PSA layers were both cut simultaneously using a portable, low-cost plotter allowing for rapid prototyping of a large variety of designs in a single production step. The devices were then manually assembled using the Origami technique by simply combining COP and PSA layers and mild pressure. This fast fabrication method was applied, as proof of concept, to the generation of a micromixer with a 3D-stepped serpentine design made of ten layers in less than 8 min. Moreover, the micromixer was characterized as a function of its pressure failure, achieving pressures of up to 1000 mbar. This fabrication method is readily accessible across a large range of potential end users, such as educational agencies (schools, universities), low-income/developing world research and industry or any laboratory without access to clean room facilities, enabling the fabrication of robust, reproducible microfluidic devices.

Dielectric barrier discharge actuator for vehicle drag reduction at highway speeds

We propose and demonstrate reduction of aerodynamic drag for a realistic geometry at highway speeds using serpentine dielectric barrier discharge actuators. A comparable linear plasma actuator fails to reduce the drag at these speeds. Experimental data collected for linear and serpentine plasma actuators under quiescent operating conditions show that the serpentine design has profound effect on near wall flow structure and resulting drag. For certain actuator arrangement, the measured drag reduced by over 14% at 26.8 m/s (60 mph) and over 10% at 31.3 m/s (70 mph) opening up realistic possibility of reasonable energy savings for full scale ground vehicles. In addition, the power consumption data and drag reduction effectiveness for different input signals are also presented.

Serpentine Design on Forest Roads by the Internal Circular Curve Method: A Case Study in Serbia

Serpentine Design on Forest Roads by the Internal Circular Curve Method: A Case Study in Serbia

Influence of architecture and material properties on vanadium redox flow battery performance

This publication reports a design optimization study of all-vanadium redox flow batteries (VRBs), including performance testing, distributed current measurements, and flow visualization. Additionally, a computational flow simulation is used to support the conclusions made from the experimental results. This study demonstrates that optimal flow field design is not simply related to the best architecture, but is instead a more complex interplay between architecture, electrode properties, electrolyte properties, and operating conditions which combine to affect electrode convective transport. For example, an interdigitated design outperforms a serpentine design at low flow rates and with a thin electrode, accessing up to an additional 30% of discharge capacity; but a serpentine design can match the available discharge capacity of the interdigitated design by increasing the flow rate or the electrode thickness due to differing responses between the two flow fields. The results of this study should be useful to design engineers seeking to optimize VRB systems through enhanced performance and reduced pressure drop.

Performance testing of thermal and photovoltaic thermal solar collectors

AbstractThis work details a methodology to characterize the performance of solar thermal and photovoltaic thermal (PVT) collectors using an indoor solar simulator. In this study, several cases have been compared to show that the methodology can be used to extract fundamental performance characteristics from a solar collector. In the first case, a serpentine collector was compared against a header riser collector using the same mass flow rate. It was found that the header riser was less efficient, with a 34% increase in the overall loss coefficient. The experimental results were compared with commonly used empirical models and showed a close agreement. In the second case, the impact on performance of using a polycarbonate cover is presented. The results show that the optical efficiency of the collector is reduced by 12% when using a cover; however, because the loss coefficient is reduced by 53%, the covered collector performs better when there is a large temperature difference between the absorber and the ambient. The third case investigates the combined performance of a PVT collector, that produces both heat and electricity from a single device. By placing photovoltaic (PV) laminates on top of the serpentine absorber, the thermal efficiency is reduced by 15%. When electricity is generated by laminates, the thermal efficiency is reduced by a further 3.5%; this drop in thermal efficiency is a result of the incident radiation producing electricity before reaching the thermal absorber. The combined efficiency of the PVT collectors was compared at controlled inlet temperatures. The serpentine design had the highest combined efficiency of 61% with 8% electricity at the lowest inlet temperature (21°C). The dominant form of loss in the PVT system is temperature driven; as the thermal efficiency decreases, electricity generation makes up a larger percentage of the combined output. This study highlights the potential for manufacturers of bespoke thermal absorbers and PV devices to combine their products into a single PVT device that could achieve improved efficiency over a given roof area.

Mechanics Design for Stretchable, High Areal Coverage GaAs Solar Module on an Ultrathin Substrate

The trench design of substrate together with curvy interconnect formed from buckling provides a solution to stretchable electronics with high areal coverage on an ultrathin substrate, which are critically important for stretchable photovoltaics. In this paper, an improved trench design is proposed and verified by finite element analysis (FEA), through use of a heterogeneous design, to facilitate strain isolation and avoid possible fracture/delamination issue. A serpentine design of interconnect is also devised to offer ∼440% interconnect level stretchability, which is >3.5 times that of previous trench design, and could transform into 20% system-level stretchability, even for areal coverage as high as ∼90%.

Assessing the performance of reactant transport layers and flow fields towards oxygen transport: A new imaging method based on chemiluminescence

A new, simple and precise ex-situ optical imaging method is developed which allows indirect measurement of the partial pressure of oxygen (as ozone) within fuel cell components. Images of oxygen distribution are recorded with higher spatial (∼20 μm) and time (40 ms) resolutions. This approach is applied to assess oxygen concentration across the face of a pseudo polymer electrolyte fuel cell (PEFC), with a serpentine design flow field. We show that the amount of light produced is directly proportional to the partial pressure of ozone, in the same way as the local current density in a PEFC is proportional to the partial pressure of bimolecular oxygen. Hence the simulated system provides information relevant to a PEFC with the same geometry operating at the same stoichiometric ratio. This new approach allows direct imaging of flow under lands due to pressure gradients between the adjacent channels and non-laminar flow effects due to secondary flow around U-turns. These are major discoveries of fundamental importance in guiding materials development and in validating modelling studies. We find that contrary to many simulation papers, advection is an important mechanism in both the gas diffusion layer (more properly “reactant transport layer”) and the microporous layer. Models which do not include these effects may underestimate reactant transport to the catalyst layer.

Polymer-bridging flocculation performance using turbulent pipe flow

Hydraulic flocculation has attracted the attention of many researchers and designers due to its potential applications, simple design, small foot print and reduced electrical/mechanical energy consumption. Flocculation studies were conducted with two types of equipment, namely the Flocs Generator Reactor (FGR) and the Flocculation–Flotation (FF), comparing both aggregation devices. FGR is a compact system whereby the flocculation of particles occurs through a helical reactor and FF has a serpentine design. Both devices have plug flow regimes with suitable hydrodynamics to disperse the polymer and also to generate flocs, enabling solid/liquid separation. This work summarizes recent results on hydraulic flocculation as a function of particle type and concentration (colloidal Fe(OH)3 and coal particles as suspension models), polymer type and dosage. The FF and the FGR were evaluated individually and with the FF placed ahead of the FGR. The effectiveness of the process was measured by indirect performance criteria such as solid/liquid separation. Best efficiency for the Fe(OH)3 flocs generation was obtained using the FGR, reaching settling rates of 22mh−1. Best results for coal dispersions were obtained with the FF ahead to the FGR, reaching settling rates of 30mh−1. In all cases, flocculation degrees were higher than 98% and showed that efficiency is largely dependent on flocs characteristics (size, mass density and water contents). These data show a high performance of polymer-bridging flocculation efficiency for both hydraulic flocculation devices evaluated, considering two suspension models (Fe(OH3) and coal particles), and validate the potential of the in-line flocs formation prior to solid/liquid separation at high rates.

Treatment of landfill leachate using microbial fuel cells: Alternative anodes and semi-continuous operation

Microbial fuel cells were designed and operated to treat landfill leachate while continuously producing power. Two different anodes were tested in batch cycles using landfill leachate as a substrate without inoculation: an activated carbon anode and biochar anode. In addition, a semi-continuous serpentine design was evaluated. No significant difference of the mean was found for the peak voltage, current density or power densities between the batch cell with activated carbon or biochar. Similar COD reduction occurred at both the batch (with biochar) and semi-continuous scale (28% ± 8.8% and 21.7% ± 12.2%, respectively). The batch MFC with activated carbon anode had significantly higher COD removal (74.7% ± 5.5%). BOD was removed by the semi-continuous MFC, but ammonia was not removed in four of the five cycles. The results provide further information on the possibility of using MFCs in landfill leachate treatment systems.

Continuous-flow synthesis of [11C]raclopride, a positron emission tomography radiotracer, on a microfluidic chip

11C-labelled radiotracers such as [11C]raclopride are produced in a process that can take between 45 and 60 min to complete. These conventional approaches can consume upwards of 75% of the 11C (t1/2 = 20 min) due to radioactive decay alone, even more if synthesis losses are considered. To compensate, a large starting quantity of radioactive precursors such as [11C]methyl iodide is required to produce an adequate amount of the tracer for injection. In this investigation, a continuous-flow microchip is explored for the purpose of synthesizing 11C radiotracers in a shorter time by exploiting the favorable reaction kinetics of using smaller reaction volumes. To enhance the mixing of reagents within the microchannel, a micromixer “loop” design was used in fabricating various polydimethylsiloxane chip styles. With a loop design implemented in an abacus-style chip for the production of nonradioactive raclopride, shorter reaction times, reduced precursor use, and improved yields were possible when compared with the use of a simple serpentine design (no loop-style chip). However, when performing the equivalent radiochemical reaction, the results were not as favorable. Using the loop design in a full loop-style chip, parameters such as premixing the reagents, reducing flow rate, and varying reagent concentrations were explored to improve the yields of [11C]raclopride (in terms of relative radioactivity) formed. The full loop chip design produced the best results, and future work will see the polydimethylsiloxane prototype chip design translated into a glass chip for further optimization.

Numerical simulations of carbon monoxide poisoning in high temperature proton exchange membrane fuel cells with various flow channel designs

The performance of high temperature proton exchange membrane fuel cell (HT-PEMFC) is significantly affected by the carbon monoxide (CO) in hydrogen fuel, and the flow channel design may influence the CO poisoning characteristics by changing the reactant flow. In this study, three-dimensional non-isothermal simulations are carried out to investigate the comprehensive flow channel design and CO poisoning effects on the performance of HT-PEMFCs. The numerical results show that when pure hydrogen is supplied, the interdigitated design produces the highest power output, the power output with serpentine design is higher than the two parallel designs, and the parallel-Z and parallel-U designs have similar power outputs. The performance degradation caused by CO poisoning is the least significant with parallel flow channel design, but the most significant with serpentine and interdigitated designs because the cross flow through the electrode is stronger. At low cell voltages (high current densities), the highest power outputs are with interdigitated and parallel flow channel designs at low and high CO fractions in the supplied hydrogen, respectively. The general distributions of absorbed hydrogen and CO coverage fractions in anode catalyst layer (CL) are similar for the different flow channel designs. The hydrogen coverage fraction is higher under the channel than under the land, and is also higher on the gas diffusion layer (GDL) side than on the membrane side; and the CO coverage distribution is opposite to the hydrogen coverage distribution.