Constant Channel Research Articles

Effect of amplitude of walls on thermal and hydrodynamic characteristics of laminar flow through an asymmetric wavy channel

In this work, we investigate the hydrothermal characteristics for laminar forced convective flow of water through sinusoidal asymmetric wavy channel of three types: linearly increasing amplitude channel (LIAC), linearly decreasing amplitude channel (LDAC) and constant amplitude channel (CAC). The computed velocity and temperature fields are analyzed by varying the Reynolds number (Re) and slope (A) of the linearly varying amplitude in the following ranges: 5 ≤Re≤ 200 and 0.02≤A≤ 0.04. The value of average Nusselt number is almost independent on the geometry of the channel at lower values of Re and A. At higher Re values, the average Nusselt number is the highest for LIAC followed by LDAC, and CAC. The combined effects of heat transfer increase in the wavy channel compared to plane channel and the associated pumping power is assessed using performance parameter (PF). For lower Re values the highest PF is obtained for CAC. For higher values of Re the PF is the largest for LDAC at A = 0.02 and 0.03, and the value of PF for A = 0.04 is the highest for CAC.

Experimental Study of Methane Combustion Efficiency in a High-Enthalpy Oxygen-Containing Flow

The article presents the experimental study analysis results of the methane combustion efficiency in a high-enthalpy oxygen-containing flow (HOF) inside of constant cross-section channel, finite along the length. The range of initial HOF enthalpies was considered from 350 to 700 kJ/kg. The regularities of the HOF initial enthalpy influence on the methane combustion efficiency were obtained. The values of the fuel excess coefficient under which the maximum coefficients of methane combustion completeness in the HOF are realized were determined. The data obtained indicate the realization of transitional diffusion-kinetic modes of methane combustion and make it possible to assess the factors limiting the combustion process.

Modelling the fluid mechanics in single-flow batteries with an adjacent channel for improved reactant transport

Redox flow batteries (RFBs) are an emerging electrochemical technology envisioned towards storage of renewable energy. A promising sub-class of RFBs utilizes single-flow membraneless architectures in an effort to minimize system cost and complexity. To support multiple functions, including reactant separation and fast reactant transport to electrode surfaces, electrolyte flow must be carefully designed and optimized. In this work, we propose adding a secondary channel adjacent to a permeable battery electrode, solving for the flow field and analysing the effects on the reactant concentration boundary layer at the electrode. We find that an adjacent channel with gradually changing thickness leads to a desired nearly uniform flow through the electrode to the adjacent channel. Consequently, the thickness of the concentration boundary layer is significantly reduced, increasing reactant transport to the electrode surface to 140% of the rate of a battery with a constant width adjacent channel, and 350% of the rate with no adjacent channel. Overall, this theory provides insight into the important role of flow physics for this promising sub-class of flow batteries, and can pave the way to improved energy efficiency of such flow batteries.

The Effect of Time Delay on the Average Data Rate and Performance in Networked Control Systems

This paper studies the performance of a feedback control loop closed via an error-free digital communication channel with transmission delay. The system comprises a discrete-time noisy linear time-invariant (LTI) plant whose single measurement output is mapped into its single control input by a causal, but otherwise arbitrary, coding and control scheme. We consider a single-input multiple-output (SIMO) channel between the encoder-controller and the decoder-controller which is lossless and imposes random time delay. We derive a lower bound on the minimum average feedback data rate that guarantees achieving a certain level of average quadratic performance over all possible realizations of the random delay. For the special case of a constant channel delay, we obtain an upper bound by proposing linear source-coding schemes that attain desired performance levels with rates that are at most 1.254 bits per sample greater than the lower bound. We supplement our results with a numerical experiment demonstrating that the obtained bounds and operational rates are increasing functions of the constant delay.

Performance Analysis of Multilayer Coil Based MI Waveguide Communication System

In the non-conventional media like underwater and underground, the Radio Frequency (RF) communication technique does not perform well due to large antenna size requirement and high path loss. In such media, magnetic induction (MI) communication technique is very promising due to small coil size and constant channel behavior. Unlike the RF technique, the communication range in MI technique is relatively less. To enhance this range, a waveguide technique is already brought in practice. This technique employs single layer coils to enhance the performance of MI waveguide. To further enhance the system functioning, in this paper, we investigated the performance of multi-layer coil (MLC) antenna based MI waveguide communication system in terms of transmission range, path loss, bit error rate (BER) and bandwidth. Besides, the system performance is quantitatively evaluated in three different non-conventional media viz., dry soil, fresh water and wet soil. As compared with the single layer counterpart, the MLC system shows a significant improvement in transmission range, BER even in loosely coupled scenarios and shows a corresponding reduction in path loss. However, the bandwidth is observed to be low (< 1 KHz). In this analysis, the eddy current effects and parasitic capacitance are compared for single and multi-layer coils. It is observed that the proposed system performs better in dry soil medium due to less medium conductivity.

Secure Information Transfer Using Two Keyless Cryptography Methods

In the current paper, some methods of information security protocols based on physical layer security are considered. It is proved that well known Shamir’s protocol can be applied to RSA cryptosystem but not to Rabin, Mac-Ellice and trellis based cryptosystems.The main stream of this paper is a description of key sharing protocol on constant public and noiseless channels (like Internet). It is shown that it is able to provide a high reliability and control of security in terms of Shannon’s information providing nothing-additional requirements to communication channels and without any cryptographic assumptions.

Annual thermal performance assessment of a regenerative evaporative cooling system under different climate conditions in Mexico

A numerical heat and mass transfer model with thermophysical properties dependent on the temperature, humidity ratio and atmospheric pressure was developed. The numerical model was verified and validated against literature, and it showed good agreements. The pseudo-transient model provides a low-cost computational tool to evaluate the potential and performance of a dew point evaporative cooling system for a wide range of extreme climate conditions (BWh, BSh, Cw and Aw from Köppen classification). A parametric analysis of different operational and design conditions in the evaporative cooler was conducted. Results show that there is an optimal channel length for given climatic conditions. The Dew-point evaporative cooling (DPEC) system showed that the best thermal performance corresponds to the climate very arid (Hermosillo – BWh) with 4018 comfort hours (83.1%) followed by the climate arid (Monterrey – BSh) with 3470 comfort hours (90.9%), the mild climate (Puebla – Cw) with 295 comfort hours (100%) and the warm climate (Cancun – Aw) with 3452 comfort hours (62.3%). Finally, an engineering correlation for constant atmospheric pressure and channel length was obtained ([Formula: see text] of 93%).

Channel/rib patterns optimization of a proton exchange membrane fuel cell by combining down-the-channel performance model and genetic algorithm

It is necessary to establish an effective method to guide the flow channel design of the bipolar plate (BPP) to obtain the optimal performance of the proton exchange membrane fuel cells (PEMFC). Most of the existing works focused on the optimization of constant channel dimensions and structures without considering achieving the flow channel's optimal local performance. In this study, an approach combining the down-the-channel performance model and genetic algorithm (GA) is developed to optimize BPP channel/rib patterns for fuel cells. A flow channel is divided into several segments, and the channel dimensions of each segment are brought into the down-the-channel performance model as variables to obtain the optimal parameter design by GA. The model and the optimization results are validated by the CFD and local current density experiment. The performance results of both CFD and local current density experiments are in good agreement with the results of the down-the-channel performance model. It is found that the cell performance of variable rib to channel width ratio (RCWR) design along the flow channel is better than the performance of constant RCWR design. Performance improvements are more significant when the sum of rib and channel width (SRCW) is higher, and the output voltage is lower. Smaller SRCW design can effectively reduce the ohmic losses and concentration polarization which is beneficial to cell performance, and as the SRCW is reduced, the performance improvement of variable RCWR design along the flow channel is less necessary. A guide for the design of the cathode flow channel RCWR from upstream to downstream is provided.

Colonialism, Collective Memory, and Memory Politics: Critical Reflections on Narratives and Public Archives of the Algerian War

Purpose: The article examines the trial of French General Paul Aussaresses (b. 1918, d. 2013) in the 2000s for war crimes committed during the Algerian War (1954 to 1962). Approach/Methodology/Design: A historiographical analysis covering topics such as colonialism, public memory, collective memory, counter-narratives, education, forgetting, and authenticity. Findings: Public history without individual memories or lived experiences of communities that have survived historical events can be viewed as inauthentic. It might even be called propaganda to present only state state-sanctioned accounts of historical events. Many governments will consequently enact laws to distinguish between what constitutes official national narratives—and what remains peripheral, or perhaps extremist individual, historical accounts. Practical Implications: This paper contributes to the scholarly literature examining oral testimonials in political and war crime tribunals, and the ethics of conducting public history research using media archives. Originality/value: Towards a greater understanding of collective memory processes, the case of the Algerian War reveals the constant negotiations, formal networks, and informal channels used to distinguish between legitimate and illegitimate sources of historical memory—and the consequences on culture, law, and society.

Comparative assessment among several channel designs with constant volume for cooling of pouch-type battery module

Liquid cooling is an effective thermal management technique in reducing the peak temperature of lithium-ion batteries. To meet the development of the battery thermal management system's compact design, a liquid-based mini channel cold plate is utilised. Although several researchers proposed numerous designs of mini channels across the cold plate, a comparative assessment among these designs is limited. Therefore, a three-dimensional numerical method is introduced to explore the laminar flow of liquid coolant in six distinct mini channel designs. This includes serpentine, U-bend, straight, pumpkin, spiral, and hexagonal designs under a constant channel volume. Their cooling ability is evaluated in terms of pressure drop, temperature variation, a non-dimensional j/f factor, average temperature, uniformity factor, and cooling performance factor for varying mass flow rate and a fixed discharge rate of 3C. Results signify that the serpentine and hexagonal geometries could significantly improve temperature homogeneity, whereas the pumpkin model maintains a lower pressure drop and pumping power. Furthermore, a detailed analysis is conducted with all the channel designs for an ambient temperature and discharge rate varying from 25 °C to 45 °C and 1C to 5C, respectively. Also, a realistic drive cycle data US06 is utilised to assess the performance of optimal design serpentine channel-based battery module for on-road driving conditions.

Adaptive Neural Network Control of Time Delay Teleoperation System Based on Model Approximation.

A bilateral neural network adaptive controller is designed for a class of teleoperation systems with constant time delay, external disturbance and internal friction. The stability of the teleoperation force feedback system with constant communication channel delay and nonlinear, complex, and uncertain constant time delay is guaranteed, and its tracking performance is improved. In the controller design process, the neural network method is used to approximate the system model, and the unknown internal friction and external disturbance of the system are estimated by the adaptive method, so as to avoid the influence of nonlinear uncertainties on the system.

A simulation study of the impact of traps in the GaN substrate on the electrical characteristics of an AlGaN/GaN HEMT with a thin channel layer

Gallium nitride (GaN) substrates are promising candidates for GaN high-electron-mobility transistors (HEMTs) because of their epitaxial layer growth with low defect density. We perform device simulations to study the influence of substrate acceptor traps in GaN HEMTs on semiinsulating GaN substrates with a thin (0.02 μm) channel layer. When the trap concentration in the GaN substrate increases at a constant channel trap concentration of 1.0 × 1015 cm−3, the drain leakage current decreases but the transient response worsens. These phenomena result from an increase of the conduction-band energy due to ionized acceptor traps with negative charge. For GaN buffer structures, we obtain moderate suppression of the drain leakage current (1.7 × 10−9 A/mm) and a good transient response (with a normalized drain current of 0.86 at 1 ms for the transient response from the off- to on-state condition) at a substrate trap concentration of 5.0 × 1015 cm−3. The aluminum gallium nitride (AlGaN) back-barrier structure is highly effective for suppressing the drain leakage current at a low trap concentration of 1.0 × 1015 cm−3 in GaN substrates. Although its maximum drain current is decreased, this structure exhibits a low drain leakage current (4.7 × 10−11 A/mm) and a high normalized drain current (0.95) in the transient response. Increasing the Al content in the barriers of the GaN HEMT structure increases its maximum drain current to 1.2 A/mm, whereas the drain leakage current and transient response are well maintained. Moreover, the traps in the GaN substrate affect the low-frequency S21, which is important for the linearity of power amplifiers, and the characteristics of S21 are similar to those of the transient responses.

The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of Dh = 50, 100, 150, and 200 μm with constant channel aspect ratio of 0.5 and length of 2.4 mm were examined. Due to the different Dh, the applied heat and mass flux values varied between 20 to 200 kW/m2 and 150 to 2400 kg/m2s, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number Nuglob was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with Dh of 200 μm and four-parallel rectangular microchannels, each having a hydraulic diameter Dh of 50 μm. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance R¯l compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the R¯l by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms.

Riding Stress Wave: Underwater Communications Through Pipeline Networks

The majority of research works on underwater communications have been struggling against the water medium for a long time. Either acoustic, electromagnetic, or optical waves suffer from specific propagation defects in the water. Briefly, acoustic waves suffer from long propagation delay and frequency-selective fading. Electromagnetic waves are susceptible to the significant attenuation in the conductive seawater. Strong absorption and severe Rayleigh scattering make wireless optical communication vulnerable. Therefore, a reliable, long-range (up to kilometer), and high data-rate (up to megabits per second) wireless communication is still unavailable in the underwater environments so far. Fortunately, in the past few decades, massive offshore pipeline networks have been deployed for oil and gas transportation. These pipelines provide a new medium for realizing underwater communications, in which the acoustic wave propagates in the pipe wall (also known as stress wave). This stress wave assisted communication scheme overcomes some drawbacks within the aforementioned modalities. So, in this article, we propose a brand new underwater communication paradigm, namely underwater stress wave communications, which utilizes stress wave and offshore pipeline networks for underwater data transmission. Fundamentally different from the conventional underwater communication schemes, stress wave signals propagate through the solid pipe instead of water. Therefore, underwater stress wave communications exhibit several unique and promising features, including 1) lower latency and higher bandwidth compared with acoustic communications; 2) longer communication range than electromagnetic and optical communications; and 3) nearly deterministic and constant channel conditions. To fully utilize these promising features to establish reliable, secure, and high-data-rate communication links along offshore pipelines, this article investigates the stress wave channel characteristics including path loss, available bandwidth, and channel response. Furthermore, we demonstrated a stress wave communication along a steel pipe both in the air and water, and experiment results indicated the feasibility of stress-wave-based communications.

Information theoretically secure key sharing protocol executing with constant noiseless public channels

Предлагается новый протокол обмена ключами, работающий с постоянными общедоступными каналами без шумов (по крайней мере, без шумов для перехватчиков) и не использующий стандартные сложностные предположения. Протокол основан на схеме EVSKey, недавно предложенной Цинем и Дингом. Показано, что такая схема нестойкая, для повышения ее стойкости вводятся искусственный шум и процедура повышения конфиденциальности. Вероятности ключевых битовых ошибок как для законных, так и для нелегальных пользователей оценены с помощью моделирования. Вероятности декодирования ошибок рассчитаны для кодов LDPC. Оценен объем утечки информации Шеннона злоумышленникам. Приведен также канальный трафик, необходимый для выполнения предложенного протокола.

Optimization of a Fractal Treelike Microchannel Network with Uniform Roughness for Laminar Flow

AbstractConsidering the excellent transport performance of treelike networks and the effect of roughness on fluid flow in a microchannel, the present work studied the optimization of a symmetric treelike roughened network with minimum hydraulic resistance under constant total channel base volume. It was found that there is an optimal base diameter ratio βm of channels at two successive branching levels that minimizes the hydraulic resistance of the network. The βm value increases with increasing average roughness height. A larger βm value is needed to minimize the hydraulic resistance of the network with larger branching number N, branching level m, and channel length ratio γ, because the increases in N, m, and γ reduce the channel diameter and magnify the influence of roughness on the fluid flow.

Hardships of drugs monitoring - Ambiguities in pharmacovigilance rules 2018 and guidelines 2019 in the Pakistan.

Introduction: Pharmacovigilance is the monitoring of drugs in and after post marketing surveillance phase of drug development and clinical trials. The phases in clinical trials is restricted to a certain population size under some conditions therefore all effects of medicine which is under trials is limited to the involved participants and it needs to be monitored through a constant channel later for eliminating the adverse events of drugs, when it is ready to be used by general consumers. In a country like Pakistan where self-medication and over the counter (OTC) medicine rate is already very high 25-75%, the regulations to control this health threat is weak due to the weak regulations. This paper is aimed to address the critical analysis on the pipeline draft of Pharmacovigilance Rules 2018 and Guidelines 2019 of Pakistan. Methodology and Rationale: The qualitative document analysis has been done by using National PV guidelines and Rules 2018 draft of Pakistan. The culture of reporting adverse events of medicines in Pakistan is not followed because of no awareness and no PV training of Pharmacists and Physicians in healthcare settings who could disseminate PV and understand the need of this hence. Pharmaceutical industries also do not adopt and accept this subject properly because of no regulations by the government and regulatory authorities. They do not have proper workforce and departments for PV.

Numerical and Theoretical Study of Performance and Mechanical Behavior of PEM-FC Using Innovative Channel Geometrical Configurations

Proton exchange membrane fuel cell (PEM-FC) aggregation pressure causes extensive strains in cell segments. The compression of each segment takes place through the cell modeling method. In addition, a very heterogeneous compressive load is produced because of the recurrent channel rib design of the dipole plates, so that while high strains are provided below the rib, the domain continues in its initial uncompressed case under the ducts approximate to it. This leads to significant spatial variations in thermal and electrical connections and contact resistances (both in rib–GDL and membrane–GDL interfaces). Variations in heat, charge, and mass transfer rates within the GDL can affect the performance of the fuel cell (FC) and its lifetime. In this paper, two scenarios are considered to verify the performance and lifetime of the PEM-FC using different innovative channel geometries. The first scenario is conducted by adopting a constant channel height (H = 1 mm) for all the differently shaped channels studied. In contrast, the second scenario is conducted by taking a constant channel cross-sectional area (A = 1 mm2) for all the studied channels. Therefore, a computational fluid dynamics model (CFD) for a PEM fuel cell is formed through the assembly of FC to simulate the pressure variations inside it. The simulation results showed that a triangular cross-section channel provided the uniformity of the pressure distribution, with lower deformations and lower mechanical stresses. The analysis helped gain insights into the physical mechanisms that lead to the FC’s durability and identify important parameters under different conditions. The model shows that it can assume the intracellular pressure configuration toward durability and appearance containing limited experimental data. The results also proved that the better cell voltage occurs in the case of the rectangular channel cross-section, and therefore, higher power from the FC, although its durability is much lower compared to the durability of the triangular channel. The results also showed that the rectangular channel cross-section gave higher cell voltages, and therefore, higher power (0.63 W) from the fuel cell, although its durability is much lower compared to the durability of the triangular channel. Therefore, the triangular channel gives better performance compared to other innovative channels.

A Numerical Model of Bank Collapse and River Meandering

AbstractMeander migration results from the interaction between inner bank accretion and outer bank erosion/collapse. This interaction has been usually treated as a long‐term average of a sequence of erosion events determined by flow hydrographs. Little attention has been paid to the role that individual bank collapse events play on meander evolution. To fill this gap, we developed a numerical model of river meandering that describes explicitly bank collapse. Results show that as bend curvature increases due to meander migration and elongation, the initially scattered locations of bank collapse events converge toward the channel section where bed shear stress attains a maximum. Simulations illustrate the observed catch‐up behavior between inner and outer banks, driven by intermittent bank collapse events. Moreover, bank collapse is found to speed up short‐term meander migration and, consistent with field observations, meanders turn out to evolve toward a state characterized by constant channel width.

Width variation around submarine channel bends: Implications for sedimentation and channel evolution

Submarine-fan channels can build the largest sediment accumulations on Earth, but our understanding of flow and sedimentation processes related to channel evolution remains limited. Results from physical and numerical modelling predict dominantly downstream channel bend migration. However, observations and evolutionary models for aggradational submarine channels on passive margins suggest that bends are dominated by lateral expansion. This paradox may be due to limitations induced by the use of constant width channels in process studies. Constant width has been used for two reasons: partly because this is the simplest possible case, but primarily because the width variation around submarine channel bends is unknown. Channel width variations are examined from an active channel reach with 49 bends and three inactive but unfilled channel reaches with a total of 35 bends from the Congo Fan. Each bend was divided into 13 cross-sections, and for each cross-section, channel width was measured for the channel base, and at 10 m vertical increments up to the height of the channel banks. The results indicate that channels are typically wider around bend apices than around inflections. We argue that this morphology suggests that channels are controlled by bank-pull (outer bank erosion), with later deposition at the inner bend, similar to many rivers. The implications of these spatial changes in channel width around bends for sedimentation and channel evolution are explored, and we suggest that such changes may account for the contradictions between physical and numerical modelling, and seafloor observations. Integration of these channel width data with the known climate history of the Congo Fan, further suggests that the magnitude of channel width variation at bend apices may be controlled by allogenic forcing, with larger flows associated with greater width variations around bends.