Channel Configuration Research Articles

A novel wake control strategy for a twin-rotor floating wind turbine: Mitigating wake effect

As one of the most promising alternatives to large wind turbines, twin-rotor floating wind turbines enables a significant reduction in the cost of power generation. An appropriate wake control strategy for twin-rotor floating wind turbines can contribute to the reduction of wake effect in wind farms. In the current study, aerodynamics and wake characteristics of twin-rotor floating wind turbine under four different yaw configurations are demonstrated. In detail, the variation of power and thrust of the twin-rotor at different yaw angles (0°, 5°, 10°, 15°, 20°, 30°) are analyzed, and the effect of the surge motion amplitude on the torque and thrust of twin-rotor in yaw are considered, and the wake dynamics under four different configurations are compared. The power gain of a twin-rotor floating wind turbine is about 5 % compared to a DTU 10 MW wind turbine at yaw angle of 15°. When the twin-rotor wind turbine is in wake channeling configuration, optimum wake recovery performance with the lowest level of turbulent kinetic energy is achieved. This study provides a scenario for optimizing the framework of floating wind farms.

Topology optimization and numerical analysis of cold plates for concentrating photovoltaic thermal management

Continuous advances in concentrating photovoltaic (CPV) panel efficiency are increasingly affected by cell temperature. Improving PV panel cooling performance is critical. This application optimizes the internal flow channel structure of PV panel cooling systems using topology optimization techniques like multi-objective and multi-stage optimization with penalty factors. Three-dimensional CFD simulation is used to compare the heat transfer performance of topology optimized channel cooling configuration and traditional straight channel cooling configuration for photovoltaic panel systems. Effects of inlet flow rates, concentration ratios, and other parameters on cooling performance are investigated. Results show the topology optimized flow channel configuration has better cooling than the straight channel. At different concentration ratios, the solar cell temperature reduces 13.85%–23.45%. The optimized application also has lower inlet and outlet pressure drops for the same operating conditions, requiring less external power. Compared to the straight channel, the topology optimized flow channel increases net PV system output power 3.00%–19.37% at different concentration ratios. Applying topology optimization provides new ideas for optimizing PV cooling system designs.

Method for retrieval of aerosol optical depth from multichannel irradiance measurements.

We present, to the best of our knowledge, a new method for retrieval of aerosol optical depth from multichannel irradiance measurements. A radiative transfer model is used to simulate measurements to create the new aerosol optical depth retrieval method. A description of the algorithm, simulations, proof of principle, merits, possible future developments and implementations is provided. As a demonstration, measurements in the New York City area are simulated based on the specific channel configuration of an existing multichannel irradiance instrument. Verification of the method with irradiance measurement data is also provided.

Heat transfer enhancement by inserting a radiation-turbulence component in a wedge channel

This study proposed the concept of coupled convective and radiative heat transfer enhancement to improve the internal cooling near turbine blade's trailing edge. An original method, which employed a radiation-turbulence component inside a wedge-shaped channel was developed. Flow and heat transfer for four channel configurations were studied numerically. The results indicated that, in condition of Re=10,000 and q = 10,000 W·m−2, compared with the existing channel's configuration merely with pin-fins and without considering radiation (Model NN), the total Nusselt number ratio of the channel using the radiation-turbulence component (Model YY) increased by 48.10 %. The maximum temperature dropped by 354.73 K and the average temperature dropped by 38.59 K. This was attributed to extension of cold surfaces for enhancement of radiative heat transfer and change of flow disturbance distribution for improvement of convective heat transfer uniformity, both of which were induced by using the radiation-turbulence component. Furthermore, the influences of the Reynolds number as well as the wall heat flux were explored. This method was proved to have an excellent self-adaptive ability, which showed that the increase of the thermal load resulted in the growth of the total Nusselt number.

Effects of nutrient concentration and scaffold elasticity on the tissue growth in a tissue engineering scaffold channel

Tissue-engineering scaffolds contain channels lined by cells that allow nutrient-rich culture medium to pass through to encourage cell proliferation. Several factors have significant impacts on the tissue growth, including the nutrient flow rate, concentration in the feed, scaffold elasticity, and cell properties. Recent studies have investigated these effects separately; however, in this work, we examine all of them simultaneously. Our objectives in this work are as follows: (i) developing a mathematical model describing the nutrient flow dynamics and concentration, scaffold elasticity, and cell proliferation; (ii) solving the model and then simulating the cell proliferation process; and (iii) optimizing the initial configuration of the scaffold channels to maximize the cell growth. The results of our study demonstrate that the rate of nutrient consumption by the cells (cell hunger rate) and the scaffold elastic compliance have an impact on tissue growth, with higher cell hunger rates leading to longer incubation periods, while scaffold elastic compliance slightly affects overall growth. Furthermore, decreasing the scaffold elastic compliance while maintaining a constant nutrient consumption rate results in an optimal funnel-shaped channel geometry, where the upper part of the channel is larger than the downstream, promoting enhanced tissue integration and functionality.

Remote Sensing of Snow Parameters: A Sensitivity Study of Retrieval Performance Based on Hyperspectral versus Multispectral Data

Snow parameters have traditionally been retrieved using discontinuous, multi-band sensors; however, continuous hyperspectral sensors are now being developed as an alternative. In this paper, we investigate the performance of various sensor configurations using machine learning neural networks trained on a simulated dataset. Our results show improvements in the accuracy of retrievals of snow grain size and impurity concentration for continuous hyperspectral channel configurations. Retrieval accuracy of snow albedo was found to be similar for all channel configurations.

How multiple anthropic pressures may lead to unplanned channel patterns: Insights from the evolutionary trajectory of the Po River (Italy)

The aim of this work is to investigate how a sequence of anthropic pressures that occurred on a river sector can generate mutual feedback that determines unplanned channel configurations. We reconstructed the evolutionary trajectory and historical human impacts on a sector of the Po River (Italy). A training scheme was implemented from the 1930 s to the 1950 s along a multi-thread sector of the river to ensure its navigability by bent navigation structures. Other human activities were carried out from the 1960 s to the 1970 s for the exploitation of sediment and water resources, inducing a dramatic reduction in sediment availability along the Po River. Our results show an evolution from multi-thread configurations in the 1950 s to single-thread configurations at the beginning of the 21th century, accompanied by remarkable channel narrowing (-50 %). This evolution has been interpreted as follows: Riverbed lowering occurred exclusively in the main channel during the 1970 s, and the training works enhanced the disconnection and deactivation of the secondary channels that were located behind navigation structures. This localised incision of the active channel (-4 m) was determined by the sediment starvation. In the absence of navigation structures, it is likely that the channel adjustments would have been less profound. The current single thread sinuous pattern is the result of these two anthropic pressures, with the training works defined as an anthropic predisposing condition and the sediment starvation recognised as the triggering factor generating morphological modifications. The channel rearrangement that resulted from these processes can accordingly be defined as unplanned, that is, not designed but caused by diachronous impacts acting on the same river sector for different purposes. The lesson learned from the Po River suggests that anthropogenic, unplanned channel configurations can represent a common type of riverscape in densely inhabited areas significantly affecting recovery potential and future geomorphological trajectories.

Assessment of Changes in Brahmaputra River Course at the Pagladia Confluence Point using Remote Sensing and GIS Techniques

The river Brahmaputra is a large alluvial river that is prone to frequent bank erosion and channel pattern changes, leading to significant shifts in its course. This study aimed to analyze these changes along a 56-kilometer stretch of the river using a combined approach of remote sensing and GIS techniques. This study utilized USGS and Landsat 8 satellite imagery to map the river's channel configuration from 1985 to 2022, providing valuable insights into the river's morphology and the stability of its banks. Additionally, the analysis provided information on changes in the river's main channel which can help in predicting future behavior and mitigating the impact of these changes. The findings of this study have significant implications for river management, allowing for informed decision-making and improved strategies for protecting communities and infrastructure located along the river's course.

Direct numerical simulations and spectral proper orthogonal decomposition analysis of shocklet-containing turbulent channel counter-flows

Counter-flow configurations in a confined channel flow provide an efficient framework to study high intensity turbulent mixing processes. In a previous study (Physical Review Fluids, 6(9), p.094603), a wall-bounded counter-flow turbulent channel configuration was presented as an effective framework for addressing certain challenges related to the study of compressibility effects on turbulence as an alternative to free shear layer and Poiseuille/Couette type flows. Here, the previous direct numerical simulations are extended to a higher Mach number (M=0.7) to quantify direct and indirect effects of compressibility. It is found that the configuration is able to produce large numbers of embedded shocklets, leading to significant asymmetry in probability density functions of dilatation. Reducing the Prandtl number from 0.7 to 0.2 increases the compressibility effect further by reducing the bulk heating in the channel. A peak turbulent Mach number close to unity is obtained, for which the contribution of the dilatational dissipation to the total dissipation is nevertheless found to be limited to ∼6%. Indirect effects of compressibility are much larger, with changes of up to 40% in Favre normal stresses, despite the mean flow and shear stress being almost unaffected by compressibility in this configuration. Given the inflectional nature of the turbulent mean flow it is also interesting to identify large structures. Spectral Proper Orthogonal Decomposition (SPOD) reveals a full spectrum with a slow decay of energy with mode number. Mode shapes are three-dimensional with the low frequencies displaying elongated streaks in the velocity field at the channel centre plane.

Inspired biomimetic design for efficient fluid channel configuration based on leaf vein structures

Efficiency of heat and mass transfer is critical for vapor chambers (VCs), but conventional designs often encounter problems with heat transfer and liquid distribution. The hierarchical branch network and heat dissipation function of leaf veins share certain similarities with the wick structure employed in vapor chambers (VCs). Therefore, to explore the potential of biomimetic design for optimizing fluid channel configuration, we investigated the heat transfer and capillary flow performance of symmetric and asymmetric leaf vein (SLV and ALV) networks. Our investigation reveals that the SLV exhibits the best heat transfer and flow characteristics among the ALV and tree branch structure. Additionally, the relationship between the distribution patterns and natural structures of leaf veins was also elucidated. Our findings suggest that the leaf vein network may offer a promising template for designing more efficient liquid channels in VCs and other engineering applications.

Effect of UV-C LED arrangement on the sterilization of Escherichia coli in planar water disinfection reactors

In this study, a planar UV reactor with five distinct UV-C LED arrangements was proposed to treat drinking water. The particle tracing method combined with computational fluid dynamics were used to simulate water velocity field, microbial trajectory and residence time. The ray tracing method was used to determine the irradiance distribution in water. The simulated variables were then integrated to determine the distribution of fluence in water. Both experimental and theoretical results among the five distinct UV light modules used in this study, turn-enhanced emission exhibited the highest efficiency in sterilizing Escherichia coli owning to the synergic effect of hydrodynamics and UV radiation. Turn-enhanced emission combined with turn-induced secondary flow effectively improved the reactor performance. At a flow rate of 300 mL/min, turn-enhanced emission resulted in an inactivation value of 4.56 log, which was approximately 0.90, 0.82, 0.84, and 2.41 log higher than the values obtained with top, staggered, lined, and side emission, respectively. According to the particle count and cumulative count of the fluid particles, turn-enhanced emission effectively enhanced the UV fluence to which microbes in water were subjected. In conclusion, optimal combinations of LED arrangements and channel configurations effectively improve the sterilization efficiency of UV reactors.

A critical review on single-phase thermo-hydraulic enhancement in geometrically modified microchannel devices

The usage of liquid-cooled microchannel heat dissipation devices is gaining importance in thermal management of electronic components owing to miniaturization. The development of such devices requires a deeper knowledge of the flow characteristics within geometrically modified microchannels. This article critically examines the research on modifications in geometry of channels for thermo-hydraulic performance enhancement. The article aims to determine the best channel configuration with optimal parameters that can maximize the overall performance of the device. For this purpose, collected research have been scrutinized in ascending order of the complexity in channel design. This article explores various designs and their influencing parameters, starting with linear and non-linear microchannel shapes, followed by bifurcated and connected secondary channels and, in the end, configurations with structured roughness such as cavities, ribs and cavity-rib combinations in it. Finally, conclusions of the examined research are presented with an analysis of their implications as well as gaps and potential recommendations for future research.

Two-phase flow structures in a helically coiled microchannel: An experimental investigation

At the microfluidic scale, the utilization of helically coiled channels (HCCs), also known as a spiral channel, for two-phase flow offers numerous advantages in various applications. Existing articles mainly focus on the macro-scale transport, examining secondary flows induced in curved channels. The increasing demand, however, for innovative miniature equipment for thermal energy management emphasizes the importance of comprehending gas–liquid micro-scale flow in curved channels. Unfortunately, despite a vast body of literature on this paradigm, there is still a lack of systematic investigations into the underlying facets of two-phase micro-scale transport in HCCs. To address this gap, our study conducted experiments on adiabatic two-phase air–water flow inside an up-flow helical micro-scale tube. The tube had a hydraulic diameter of 0.87 mm, a coil diameter of 50 mm, and a helical pitch of 20 mm. The primary aim was to explore the impact of centrifugal force on flow pattern, void fraction, and frictional pressure drop characteristics. Additionally, we carefully examined the phase separation phenomenon influenced by the secondary flows induced by the curved channel. In particular, we compared the gas-core flow pattern (either throat-annular flow or annular flow), void fraction, and frictional pressure drop obtained from our experiments on the helical tube with corresponding results based on straight micro-scale channel configurations for an Eötvös number of approximately 0.01. In summary, this study delves deep into the crucial aspects of two-phase micro-scale transport in HCCs, contributing to a better understanding of these systems for future advancements in micro-channel applications.

The Eruption of a Magnetic Flux Rope Observed by Solar Orbiter and Parker Solar Probe

Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope’s handedness and the number of turns that any helical field lines make is difficult without magnetic field modeling or in situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 2022 September 4 and 5 made using the Solar Orbiter spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within ∼5 hr of the second plasma flow. The erupting flux rope then passed over the Parker Solar Probe spacecraft during its encounter (13), enabling in situ diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the in situ measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun.

CFD investigation of the effect of flow field channel design based on constriction and enlargement configurations on PEMFC performance

In this study, a three-dimensional CFD, non-isothermal model was developed to identify an optimal layout for key geometrical parameters of PEMFC flow field designs with constriction and enlargement cross-sections located at the middle of the channel. For this purpose, the effect of channel configurations with both constriction and enlargement cross-sections was explored and compared with a conventional constant channel segment, under varying hydraulic diameter and lengths. As results, the constriction configuration channel with a hydraulic diameter reduction of 50% has shown the best performance among the enlargement and straight channels for all considered lengths. The constriction configuration enhances fluid velocity, resulting in improved flow distribution and relatively increased pressure drop across the flow channels. Moreover, a better temperature distribution, higher oxygen consumption, improved membrane humidification, and water removal were observed. This leads to an increased net power output of the PEMFC. However, considering different hydraulic diameters of the constriction geometry, the best performance of the cell was achieved at a hydraulic diameter reduction of 60%, combined with a length of 4/7 of the total channel length. This optimal balance between pressure drops and reactants’ flow has enhanced the net power of the proposed geometry by 26.30 %, compared to the straight channel. The novel proposed single-channel configuration based on a simple constriction, is a low-cost design that has significantly improved cell performance compared to the straight one. Since operating conditions are crucial for cell performance, the effects of operating temperature and relative humidity were investigated, and the optimum conditions were determined.

Supramolecular Transistors with Quantum Interference Effect.

The charge transport through supramolecular junctions exhibits unique quantum interference (QI) effects, which provide an opportunity for the design of supramolecular transistors. Benefiting from the configuration dependence of QI, configuration control of the supramolecular assemblies to demonstrate the QI features is a key but challenging step. In this work, we fabricated the supramolecular transistors and investigated the charge transport through the conducting channel of the individual π-stacked thiophene/phenylene co-oligomers (TPCOs) using the electrochemically gated scanning tunneling microscope break junction technique. We controlled the configuration of the supramolecular channel and switched the QI features between the anti-resonance and resonance states of the supramolecular channels. We observed the supramolecular transistor with its on/off ratio above 103 (∼1300), a high gating efficiency of ∼165 mV/dec, a low off-state leakage current of ∼30 pA, and the channel length scaled down to <2.0 nm. Density functional theory calculations suggested that the QI features in π-stacked TPCOs vary depending on the supramolecular architecture and can be manipulated efficiently by fine-tuning the supramolecular configurations. This work reveals the potential of the supramolecular channels for molecular electronics and provides a fundamental understanding of intermolecular charge transport.

Effect of channel configuration on the water sterilization efficiency of a photoreactor with ultraviolet C light-emitting diodes

This study investigated the effect of flow channel configuration on the water disinfection efficiency of a photoreactor with ultraviolet (UV) C light-emitting diodes (LEDs). The synergistic effect of UV radiation and hydrodynamics on microbial inactivation was analyzed to obtain the UV fluence distribution for five channel configurations. Simulations revealed that the serpentine and spiral configurations led to similar microbial residence times. However, the high mixing efficiency in the serpentine configuration resulted in the efficiency of Escherichia coli inactivation being higher in this configuration than in the spiral configuration. Although the pin configuration achieved the highest average UV fluence of the five channel configurations, the E. coli inactivation value in this configuration was low because approximately 25 % of the microbes received UV fluence of less than 5 mJ/cm2. This study modified the pin configuration, and the results revealed that this configuration effectively increased the UV fluence received by microbes and eliminated low-fluence particles. At a flow rate of 120 mL/min, the average UV fluence in the modified pin configuration was 43 %, 52 %, and 72 % higher than those in the serpentine, spiral, and bioinspired configurations, respectively. Experimental findings indicated that at a maximum flow rate of 160 mL/min, the E. coli inactivation value achieved in the modified pin configuration was 3.3 log, which was approximately 0.4, 1.2, 1.5, and 1.8 log higher than those achieved in the serpentine, spiral, pin, and bioinspired configurations, respectively. The results of this study provide insights regarding enhancement of the UV exposure of microorganisms and can be used as a guideline in flow channel design for water disinfection reactors with UV-C LEDs.

Elementary intracellular Ca signals approximated as a transition of release channel system from a metastable state.

Cardiac muscle contraction is initiated by an elementary Ca signal (called Ca spark) which is achieved by collective action of Ca release channels in a cluster. The mechanism of this synchronization remains uncertain. We approached Ca spark activation as an emergent phenomenon of an interactive system of release channels. We constructed a weakly lumped Markov chain that applies an Ising model formalism to such release channel clusters and probable open channel configurations and demonstrated that spark activation is described as a system transition from a metastable to an absorbing state, analogous to the pressure required to overcome surface tension in bubble formation. This yielded quantitative estimates of the spark generation probability as a function of various system parameters. We performed numerical simulations to find spark probabilities as a function of sarcoplasmic reticulum Ca concentration, obtaining similar values for spark activation threshold as our analytic model, as well as those reported in experimental studies. Our parametric sensitivity analyses also showed that the spark activation threshold decreased as Ca sensitivity of RyR activation and RyR cluster size increased.

Optimization strategies to mitigate reactant starvation in a dead-ended hydrogen–oxygen proton exchange membrane fuel cell during cyclic loading

Investigating the dynamic characteristics in hydrogen–oxygen proton exchange membrane fuel cells (PEMFCs) can provide valuable insights into the coupling degradation mechanism present within the fuel cell, which can help avoid reactant starvation and voltage decline. In this study, a recirculation subsystem is integrated into the cathode of the PEMFC to alleviate gas starvation due to water flooding. The impact of pump speed on dynamic loading is also examined. Furthermore, obstacle devices are incorporated into the cell flow channel to enhance mass transfer. The effects of flow channel configuration under the exhaust gas recirculation mode on cell performance and dynamic characteristics are investigated as well. Our findings indicate that blockage of the gas transport channel due to accumulated liquid water is the primary issue during the loading process of PEMFCs. The cathode recirculation pumps set at 600 rpm improves cell performance by 30.6% compared to the dead-ended mode at 1000 mA·cm−2. However, excessively high pump speeds lead to an increase in voltage undershoot during the loading process. Exhaust gas recirculation is found to significantly alleviate gas starvation and water flooding during the cyclic loading process and the cathode recirculation is the primary mitigation strategy for improving dynamic characteristics.

Effects of bipolar plate flow channel configuration on thermal-electric performance of direct ammonia solid oxide fuel cell: Part I - Numerical study of channel section geometry

Direct ammonia SOFCs (DA-SOFCs) are numerical studied to investigate the effects of bipolar plate flow channel configuration on thermal-electric performance. This study establishes a planar DA-SOFC model and investigates triangular, quadrangular, and oval flow channel configurations’ impact using numerical simulations. Results reveal oval cross-section channels outperform trapezoidal and triangular ones, achieving power density increases of 15.6%, 16.1%, and 18.6%, respectively, compared to rectangular channels at 0.6V. The oval channel displays superior velocity and vorticity, enhancing mass transfer between the main flow and reaction zone. Increasing channel width reduces rib width, promoting O2 distribution, temperature improvement via exothermic reactions, NH3 decomposition into H2, and improved cell performance. Rib width increase shortens diffusion and reduces concentration polarization, but increases ion transport and ohmic polarization. A theoretical formula for optimal rib width (Wrib0) to minimize polarization loss is provided. These findings offer a comprehensive reference for optimizing DA-SOFC design.