Channel Configuration Research Articles

Long Propagating Polaritonic Heat Transfer: Shaping Radiation to Conduction.

Surface phonon polaritons (SPhPs) originate from the coupling of mid-IR photons and optical phonons, generating evanescent waves along the polar dielectric surface. The emergence of SPhPs gives rise to a phase of quantum matter that facilitates long-range energy transfer (100s μm-scale). Albeit of the recent experimental progress to observe the enhanced thermal conductivity of polar dielectric nanostructures mediated by SPhPs, the potential mechanism to present the high thermal conductivity beyond the Landauer limit has not been addressed. Here, we revisit the comprehensive theoretical framework to unify the distinct pictures of two heat transfer mechanisms by conduction and radiation. We first designed our experimental platform to distinguish contributions of two distinct fundamental modes of SPhPs, resulting in far-field radiation and long propagating conduction, respectively, by tuning the configuration of a nanostructured heat channel integrated into the thermometer. We could effectively control the transmission of long-propagating SPhPs to influence the apparent thermal conductivity of the nanostructure. This study reveals the high thermal conductance of 1.63 nW/K by a fast SPhP mode comparable to that by classical phonons, with measurements showing apparent conductivity values of up to 2 W/m·K at 515 K. The origin of the enhanced thermal conductivity was exploited by observing the interference of dispersive evanescent waves by double heat channels. Furthermore, our experimental observations of length-dependent thermal conductance by SPhPs are in good agreement with the revisited Landauer formula to illustrate a polaritonic mode of heat conduction, considering the dispersive nature of radiation not limited to the physical boundaries of a solid object yet directionally guided along the surface.

On the selection of Saffman–Taylor viscous fingers for divergent flow in a wedge

We study self-similar viscous fingering for the case of divergent flow within a wedge-shaped Hele-Shaw cell. Previous authors have conjectured the existence of a countably infinite number of selected solutions, each distinguished by a different value of the relative finger angle. Interestingly, the associated solution branches have been posited to merge and disappear in pairs as the surface tension decreases. For the first time, we demonstrate how the selection mechanism can be derived based on exponential asymptotics. Asymptotic predictions of the finger-to-wedge angle are additionally given for different sized wedges and surface-tension values. The merging of solution branches is explained; this feature is qualitatively different to the case of classic Saffman–Taylor viscous fingering in a parallel channel configuration. Moreover, because the asymptotic framework does not highly depend on specifics of the wedge geometry, the proposed theory for branch merging in our self-similar problem likely relates much more widely to tip-splitting instabilities in time-dependent flows in circular and other geometries, where the viscous fingers destabilise and divide in two.

Antijamming Schemes for the Generalized MIMO Y Channel.

Signal space alignment (SSA) is a promising technique for interference management in wireless networks. However, despite the excellent work done on SSA, its robustness against jamming attacks has not been considered in the literature. In this paper, we propose two antijamming strategies for the SSA scheme applied in the multiple-input-multiple-output (MIMO) Y channel. The first scheme involves projecting the jamming signal into the null space of each source's precoding vectors, effectively eliminating it entirely. The second scheme removes interference originating from the jammer by subtracting the disturbance estimate from the incoming signal. The estimate is derived on the basis of the criterion of minimizing the received signal energy. The block error rate (BLER) performance of the proposed strategies in various channel configurations is verified by link level simulations and is presented to show the efficiency in mitigating jamming signals within the SSA-based MIMO Y channel.

Numerical Study On the Effect of Channel Configuration On Mixture Formation of an Axial Flow Wave Rotor Combustor

Abstract Wave rotor combustor technology is a new technical means to improve the thermal efficiency of aero-engine by using unsteady flow and constant volume combustion. In this article, the influence of wave rotor combustor channel structure on the mixture formation in the channel was studied by numerical simulation. The results showed that the internal flow field structure and change of any structure channel are similar. Flow separation will occur in all channels, and wake regions will be formed in the channels. The turbulence kinetic energy in the wake region was increased, and the velocity and pressure were decreased, resulted in the vortex in the channel. When the channel width was reduced to half of the original design, the Relative Standard Deviation (RSD) of the mixture was reduced by at least 54.92% compared to the original design, and the global fuel mass fraction in the channel was increased by at least 27.32%. In addition, the fluctuation of discharge pressure was also reduced. The reduction of the channel height does not lead to a significant improvement in the aforementioned results. This study can provide guidance for the structural design of wave rotor combustor channel.

Effect of coil diameter on water disinfection efficiency in a helical photoreactor using ultraviolet-C light emitting diodes

ABSTRACT This study investigated the disinfection efficiency of a photoreactor equipped with a helical water flow channel and ultraviolet-C (UV-C) light emitting diodes (LEDs). Theoretical simulations and biodosimetry tests were conducted to investigate the effects of coil diameter and flow rate on the reactor’s performance in inactivating Escherichia coli. The interplay between hydrodynamics and UV radiation was analyzed to determine the UV fluence absorbed by the microbes. The simulations revealed that, primarily due to the specific radiation pattern of the UV LEDs, the coil diameter strongly influenced the distribution of irradiance in the water and the UV fluence received by microbes. The experimental results indicated that the photoreactor achieved the highest inactivation value of 2.8 log when the coil diameter was 48 mm for a flow rate of 40 mL/min; this log value was superior to those for coil diameters of 16, 32, 64, and 80 mm by approximately 1.9, 0.4, 0.5, and 0.7 log units, respectively. This optimal coil diameter leading to the maximal UV irradiance and the highest degree of irradiance uniformity along the flow channel. This study offers design guidelines for constructing a high-efficiency water disinfection reactor with a helical flow channel configuration.

Modeling of Additively Manufactured Ceramic Heat Exchangers with Semi-Elliptical Cross-Section Flow Channels

An approximate and easily applied analytical model was developed for heat transfer calculations of heat exchangers consisting of multiple rows and columns of heat transfer fluid flow channels with semi-elliptical cross sections. Heat exchangers of this type are being developed by using ceramic material and additive manufacturing for high temperature and pressure-concentrating solar electric power plants. Calculations using the model require only the geometrical dimensions and flow conditions of the heat exchanger. Comparisons of modeling predictions, with both simulation results and experimental data, were conducted to verify the viability of the model. The results showed good agreement where almost all the modeling predictions were within 20% of the simulation results or the experimental data. The proposed modeling approach is more generally applicable to heat transfer analysis of heat exchangers with similar flow channel configurations to those considered in this study.

Improving phase change heat transfer in an enclosure partially filled by uniform and anisotropic metal foam layers

Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.

Hydrothermal analysis of parallel and symmetric microchannels with phase change slurry and porous fin designs

The dynamic information of microchannel systems with parallel and symmetric configurations is insufficient, which limits our ability to compare and optimize these systems in all directions. In this study, thermal and hydraulic characteristics in parallel and symmetric microchannel heat sinks (MCHSs) with porous fins cooled by phase change slurry are investigated. A 3-D steady state conjugate model is adopted to compare the effects of fin configuration, coolant type and structural parameters on hydrothermal properties of wavy MCHS. The variations of dimensionless parameters involving Nu, f, η (temperature control effectiveness) and PEF (performance evaluation factor) are considered to demonstrate the effectiveness of combined design on overall performance enhancement of wavy MCHS. Results indicate that lower temperature increment and higher pressure loss appear in wavy configuration with porous fins than in straight mode, and lowest thermal resistance arises in parallel porous fin design. At the narrow position of symmetric channel, the fluid changes from the low-speed drop-shaped micelle to high-speed bullet-shaped one with increasing A, which leads to higher Nu with larger pressure drop penalty. Due to the extended flow route and improved fluid mixing, η increases with decreasing wavelength in all cases, and η of porous microchannels with both phase change slurry and parallel fins is much larger than that of symmetric one and the one with only base fluid. Compared with wavy fin configurations with small and large ε, lower temperature and its more uniform distribution happen in the mode with medium porosity. In comparison with basic configuration, the parallel configuration with slurry as cooling medium has the maximum PEF value when the pore size is 0.14 mm, up to 1.64. Larger f increase occurs in wavy channel with increasing N, and the space shortening between adjacent channel cavities in symmetric mode makes the adjoining Dean vortices easier to contact and repel, thus making it appear larger rise of f than parallel mode. Compared with other channel parameters, it is not effective to improve the overall performance of wavy MCHS with porous fins by adjusting α. Overall, the throat effect of symmetric MCHS significantly occurs in channel configuration with larger A, bigger λ, lower ε, smaller dp, more N, and lesser α, leading to higher f rise than the parallel mode.

Enhancing fuel transport and cell performance by an anodic wedge-shaped channel in a paper-based microfluidic fuel cell

Paper-based self-pumping microfluidic fuel cells (PMFCs) typically exploit the wicking effects in porous papers to enable passive reactant delivery and co-laminar flow, eliminating micro pumps and physical membranes. PMFCs have been regarded as promising micro-power sources for next-generation paper-based electrochemical microfluidic assays for biomedical applications. However, the PMFC performance is fundamentally limited by the low capillary flow velocity and ineffective diffusive fuel transport. In this study, a novel PMFC with an anodic wedge-shaped channel is developed. The anodic wedge-shaped channel enables reactant convection at improved fuel flow velocity. Visualization experiments suggest that the fuel flow velocity can be improved by about 23 times in this anodic wedge-shaped channel configuration as compared to that in conventional single-layer paper-based flow channel. In addition, favorable features like localized enhancement of fuel transport and reduced fuel crossover are also observed in this novel configuration. Due to enhanced convective-diffusive fuel transport, the cell performance can be improved 245.8 % as compared to the single-layer case. The peak power density reaches 59.9 mW cm−2 and the limiting current density achieves 305.9 mA cm−2, outperforming most of the previous PMFCs. This anodic wedge-shaped channel configuration can also be potentially used in paper-based assays to enhance reactant delivery.

On the corrugation effect on thermo-fluids characteristics and entropy generation in channels equipped with wavy and straight sections

A numerical simulation was performed to investigate the characteristics of thermo-fluids and the irreversibility generation of laminar forced convection through three different channel designs. This article first presents a comprehensive study of combination of straight and wavy sections in order to create a balance between improved thermal performance from the wavy design and optimized flow properties from the straight section, leading to an overall enhancement in cooling efficiency. A novel design has been considered using a channel configuration that consists of different lengths of wavy and straight sections and is named (cases I, II, and III). The outcomes are shown in terms of average Nu, enhancement ratio (ER), performance factor, total irreversibility generation, as well as the contours of streamlines, isothermal, and Bejan numbers for different values of the Reynolds number range of 5≤Re≤400 and dimensionless wave amplitude 0.3≤α≤0.6. The results were compared of the three cases with the plane channel, revealing an augmentation in HTR of 73.7%, 64.9%, and 43.3% for cases III, II, and I, respectively. On the other hand, with both Re and α, the total irreversibility generation increases continuously.

Air trap and removal on a pressure driven PDMS-based microfluidic device.

With the development of microfluidic technology, microfluidic chips have played a positive role in applications such as cell culture, microfluidic PCR, and nanopore gene sequencing. However, the presence of bubbles interferes with fluid flow and has a significant impact on experimental results. There are many reasons for the generation of bubbles in microfluidic chips, such as pressure changes inside the chip, air vibration inside the chip, and the open chip guiding air into the chip when driving fluid. This study designed and prepared a microfluidic device based on polydimethylsiloxane. First, air was actively introduced into the microfluidic chip, and bubbles were captured through the microfluidic device to simulate the presence of bubbles inside the chip in biological experiments. To remove bubbles trapped in the microfluidic chip, distilled water, distilled water containing surfactants, and mineral oil were pumped into the microfluidic chip. We compared and discussed the bubble removal efficiency under different driving fluids, driving pressures, and open/closed channel configurations. This study helps to understand the mechanism of bubble formation and removal in microfluidic devices, optimize chip structure design and experimental reagent selection, prevent or eliminate bubbles, and reduce the impact of bubbles on experiments.

High-Voltage Discharge Optimization of a Hybrid-Wall Hall Thruster

A segmented discharge channel is generally adopted in a hybrid-wall Hall thruster. A metallic wall is situated in the upstream portion of the channel, while a boron nitride ceramic wall is retained in the downstream portion of the channel. This hybrid-wall design avoids the disadvantages of the mechanical properties of boron nitride ceramic. Moreover, the channel can be widened by reducing the thickness of the metallic wall upstream of the channel. In this study, the width and configuration of a discharge channel based on a hybrid-wall Hall thruster are investigated, and a convergent channel configuration is adopted. The experimental results show that the configuration of the channel significantly affects the discharge process, and the ionization and acceleration efficiency of the HEP-100HW are substantially improved using the convergent hybrid channel. The specific impulse and efficiency of the HEP-100HW with the optimal convergent hybrid channel are 210 s/2.5% and 270 s/6% higher than those of the HEP-100HW with a straight hybrid channel and the HEP-100 with a straight-configuration ceramic channel at the discharge voltage of 900 V, respectively. Furthermore, from experiments and supporting simulations, it was found that the convergent hybrid-wall design resulted in an increase in the number of ions created further upstream in the channel compared to a conventional design. This led to more efficient acceleration and ejection of the ions out of the channel, resulting in the observed performance improvement. The results from this study provide valuable guidance for the design of high-power and high-voltage Hall thrusters.

FATE: A Flexible FPGA-Based Automatic Test Equipment for Digital ICs

The limits of chip technology are constantly being pushed with the continuous development of integrated circuit manufacturing processes and equipment. Currently, chips contain several billion, and even tens of billions, of transistors, making chip testing increasingly challenging. The verification of very large-scale integrated circuits (VLSI) requires testing on specialized automatic test equipment (ATE), but their cost and size significantly limit their applicability. The current FPGA-based ATE is limited in its scalability and support for few test channels and short test vector lengths. As a result, it is only suitable for testing specific chips in small-scale circuits and cannot be used to test VLSI. This paper proposes a low-cost hardware and software solution for testing digital integrated circuits based on design for testability (DFT) on chips, which enables the functional and performance test of the chip. The solution proposed can effectively use the resources within the FPGA to provide additional test channels. Furthermore, the round-robin data transmission mode can also support test vectors of any length and it can satisfy different types of chip test projects through the dynamic configuration of each test channel. The experiment successfully tested a digital signal processor (DSP) chip with 72 scan test pins (theoretically supporting 160 test pins). Compared to our previous work, the work in this paper increases the number of test channels by four times while reducing resource utilization per channel by 37.5%, demonstrating good scalability and versatility.

Performance uniformity analysis in polymer electrolyte fuel cell using long-term dynamic simulation

The temporal stability and spatial homogeneity of current density are key factors in Polymer Electrolyte Fuel Cell (PEFC) performance and durability. Temporal and spatial variations of relative humidity, fuel concentration, and water droplets in the channels are the principal causes of non-homogeneous current density. A dynamic pseudo-3D model was previously proposed by the authors and has been extended and improved to perform the long-term and intensive simulations of PEFC with low computational cost, which allows to study of the performances homogeneity with different experimental configurations and flow field topologies. The model considers important phenomena in the homogeneity analysis, such as gases and liquid water movement in diffusion layers and flow field, electrochemical reactions, and others. Model validation has been performed using experimental data obtained from a 25 cm2 cell with a single serpentine, which has allowed studying the model transient response and spatial representation. The simulations have been used to study the homogeneity and stability of 36 setups of PEFC, varying the rib/channel width ratio, the stoichiometric ratio, and the number of parallel serpentine channels. The results show the importance of a properly flow field design to control gas flow, remove the channels’ liquid water, and keep a homogeneous feeding. The study evaluated a set of channel configurations that show the improved temporal voltage stability and current density spatial homogeneity. The results show the impact of channel gas speed and ratio channel/rib width in liquid droplets removal and the proper fuel spatial distribution; and how configurations with a lesser number of channels in serpentine design require a lower stoichiometric ratio to perform better temporal and spatial uniformity. In the case of the cell configurations simulated, the optimum design was achieved using between 5 and 7 parallel serpentine channels and a channel/rib ratio 3/5.

Specific and Label‐Free bioFET Sensing of the Interaction Between the Electrically Neutral Small Estriol Molecule and Its Antibody in a Microliter Drop of Diluted Plasma

AbstractThe sensing of small molecules is important to a variety of fields and particularly to clinical diagnostics. Estriol is an important small chemical molecule, as it is one of three markers measured during mid‐gestation for the Down syndrome. Point‐of‐care testing of estriol will increase maternal compliance for aneuploidy mid‐gestation screening. A bioFET technology is a promising point‐of‐care platform. The meta‐nano‐channel (MNC) bioFET is employed with its tunable channel configuration to optimize the coupling between the electrostatics of the estriol‐receptor interactions and the electrodynamics of the conducting readout current. Also, the MNC bioFET receptor layer is composed of anti‐estriol antibodies to address the high structural similarity of estriol to other estrogens. Despite the small size and the electrical neutrality of estriol, real‐time is demonstrated, specific, and label‐free sensing of estriol in 0.5 µL of 1:100 diluted plasma with excellent linearity, sensitivity, dynamic range extending to ten orders of magnitude in estriol concentration and limit‐of‐detection of 1 fg mL−1. Extensive control and non‐specific measurements are reported including the response to other neutral members of the estrogen family.

Experimental and model study of swirling fluid flow in a converging channel as a simulation of blood flow in the heart and aorta

The study of swirling flows in channels corresponding to the static approximation of flow channels of the heart and major vessels with a longitudinal-radial profile zR2 = const and a concave streamlined surface at the beginning of the longitudinal coordinate has been carried out. A comparative analysis of the flow structure in channel configurations zRN = const, where N = –1; 1; 2; 3, in the absence and presence of a concave surface was carried out. The numerical modelling was compared with the results of hydrodynamic experiments on the flow characteristics and the shape of the flow lines. The numerical model was used to determine the velocity structure, viscous friction losses and shear stresses. Numerical modelling of steady-state flows for channels without a concave surface showed that in the channel zR2 = const there is a stable vortex flow structure with the lowest viscous friction losses. The presence of a concave surface of sufficient size significantly reduces viscous friction losses and shear stresses in both steady state and pulsed modes.

Maze-solving in a plasma system based on functional analogies to reinforcement-learning model.

Maze-solving is a classical mathematical task, and is recently analogously achieved using various eccentric media and devices, such as living tissues, chemotaxis, and memristors. Plasma generated in a labyrinth of narrow channels can also play a role as a route finder to the exit. In this study, we experimentally observe the function of maze-route findings in a plasma system based on a mixed discharge scheme of direct-current (DC) volume mode and alternative-current (AC) surface dielectric-barrier discharge, and computationally generalize this function in a reinforcement-learning model. In our plasma system, we install two electrodes at the entry and the exit in a square lattice configuration of narrow channels whose cross section is 1×1 mm2 with the total length around ten centimeters. Visible emissions in low-pressure Ar gas are observed after plasma ignition, and the plasma starting from a given entry location reaches the exit as the discharge voltage increases, whose route converging level is quantified by Shannon entropy. A similar short-path route is reproduced in a reinforcement-learning model in which electric potentials through the discharge voltage is replaced by rewards with positive and negative sign or polarity. The model is not rigorous numerical representation of plasma simulation, but it shares common points with the experiments along with a rough sketch of underlying processes (charges in experiments and rewards in modelling). This finding indicates that a plasma-channel network works in an analog computing function similar to a reinforcement-learning algorithm slightly modified in this study.

Investigating peristaltic flow of Newtonian fluid in a permeable channel: Effects of nonlinear curvature and wall properties

This investigation delves into the peristaltic flow characteristics of a Newtonian fluid within a permeable channel, emphasizing the influence of nonlinear curvature and wall properties. The study employs wave trains of varying amplitudes and phases to induce an asymmetric configuration along the channel boundaries. The curvature effects are contingent upon the ratio of channel width to wavelength, and the accuracy of results is maintained up to the second order in δ. To facilitate the derivation of closed-form solutions at higher levels, a domain transformation is executed, converting a channel with a variable cross section into one with a uniform cross section. To impose constraints on parameters and achieve a singular flux in the presence of a specified pressure gradient, a distinctiveness criterion is formulated. This study investigates the interplay of inertia and curvature on pumping and trapping, examining both symmetric and asymmetric channels. The pressure difference escalates with wave number in both channel configurations. Moreover, in the absence of inertial forces and flux, the impact of curvature on the pressure difference demonstrates a direct proportionality. Conversely, an augmentation in the permeability of the porous channel correlates with a reduction in the pressure difference. An intriguing observation arises as phase differences increase: the visibility of the bolus diminishes, and the streamlines become more prominent. This establishes a favorable environment for fluid flow, enhancing our understanding of the intricate dynamics at play in peristaltic flow within permeable channels.

Optimal flow channel structure selection for hybrid locomotive battery pack liquid cooling system

Simulation studies were performed on the power battery pack to determine the most suitable flow channel configuration for the liquid cooling system. The study involved conducting thermal simulation analysis on four different channel types with varying structures under specific conditions, including an ambient temperature of 25°C, coolant inlet speed of 2L/min, and inlet temperature of 25°C. Based on a comparative analysis, it can be inferred that an increase in the number of parallel flow channels leads to a degradation in the temperature performance of the battery pack while concurrently enhancing the pressure performance of the coolant. After considering all evaluation factors, the liquid cooling channel structure design for the battery pack was determined to consist of two parallel channels.

Quantitative assessment of the erosion and deposition effects of landslide-dam outburst flood, Eastern Himalaya

Both regular flow and infrequent outburst floods shape the mountain landscape, but their relative contributions have been widely debated, in part due to the paucity of quantitative data on historical outburst floods. In June 2000, an outburst flood was triggered by a landslide-dam failure in a rapidly exhumed region of the Eastern Himalaya. To investigate the role of this kind outburst flood on landscape evolution, we employ topographic differencing, satellite imagery, and 2D hydraulic simulations to quantify the equivalent erosion and deposition within ~ 80 km flood route downstream of the breach. The flood lasted for ~ 10 h, with a peak discharge of 105 m3/s, leading to average erosion of 10 m, and contributed ~ 1–2 × 103 times more sediment than over long-term mean fluvial processes. The flood produced extensive lateral erosion, which triggered a threefold widening of the valley floor and abundant subsequent landslides. The ubiquitous boulder bars deposited in the channel inhibited incision, and facilitated lateral erosion after the flood. The resulting channel configuration and extensive bank erosion continue to affect fluvial dynamics until the next catastrophic flood that remobilizes the boulders. Our quantitative findings highlight the profound importance of recurrent outburst floods for gorge development and landscape evolution in Eastern Himalaya.