Channel Cross-sectional Shape Research Articles

Performance of proton exchange membrane fuel cell system by considering the effects of the gas diffusion layer thickness, catalyst layer thickness, and operating temperature of the cell

BackgroundIn this research, the effect of anode and cathode channel cross-sectional shape on the performance of PEM fuel cell was investigated and the appropriate length and dimensions of the channel were determined. Finally, for the determined geometric conditions, the cell performance at different voltages was investigated. MethodsThe purpose of this study was to investigate the structural characteristics of the fuel cell on its performance. The results show that the pressure and temperature in the catalyst layer (CL) of the cathode side are greater than the anode, and the temperature in the central regions of the catalyst layer is higher than the lateral regions. Also, the channel with a length of 100 mm is optimal in terms of producing the maximum current density and the amount of pressure drop is much lower than the channel with a length of 150 mm, which reduces the power consumption of the cell. Significant findingsIn general, a higher electric current is produced by increasing the thickness of the gas diffusion layer (GDL) and the catalyst layer. At a voltage of 0.8 V, with increasing thickness from 0.25 mm to 0.5 mm, the current density increases above 6 %. The percentage increase in current density at 60 °C–80 °C for 0.85 V and 0.75 V voltages is 42.1 % and 9.28 %, respectively.

Impact of the flow-field distribution channel cross-section geometry on PEM fuel cell performance: Stamped vs. milled channel

Polymer electrolyte membrane fuel cells (PEM FCs) represent an essential part of the emerging hydrogen economy. Metallic bipolar plates (BPs) allow high speed and capacity production using established industrial technologies, like mechanical stamping. Stamping, however, leads to different cross-sectional shapes of flow-field (FF) channels as compared to milled or compression-moulded bipolar plates. The impact of these changes on the resulting fuel cell performance is not yet fully understood. This study employs an experimentally validated three-dimensional, isothermal, steady-state, continuum-mechanics based mathematical model to gain a deeper insight into this issue and to identify optimal stamped BP channel cross-sectional shapes for parallel and serpentine FF. The uniformity of the local distribution of the physico-chemical quantities and the resulting load curves are analysed. The results obtained confirm that stamped BPs with channels of the trapezoidal cross-section are a viable alternative to the traditional milled or moulded BPs with channels of the rectangular cross-section. The observed differences in performance of FC with stamped and milled channels can be mitigated by optimization of the channel cross-section geometry parameters. As an optimal rib width 0.4 mm and an optimal channel ground width 1 mm for milled and 0.2 mm for stamped BPs are suggested.

Numerical simulation of all-vanadium redox flow battery performance optimization based on flow channel cross-sectional shape design

This paper numerically investigates optimizing trapezoidal flow channel cross-sectional shapes to improve all‑vanadium redox flow battery performance. A 3D steady-state multiphysics model coupling fluid dynamics, mass transfer, and electrochemistry was developed in COMSOL. Eight trapezoidal and one rectangular cross-section serpentine flow fields were simulated at varied flow rates. Results showed the TCS-T06 design reduced pressure drop by 12 % and pump power by 12 % versus the RCS. The concentration distribution of VO2+ was also improved, enhancing mass transfer. At 60 mA/cm2, TCS-T06 achieved 0.9 % higher pump power-based voltage efficiency. The optimized trapezoidal cross-section was proven to minimize losses, improve electrolyte distribution, and enhance VRFB performance. This work provides guidance for optimizing trapezoidal flow channel cross-sections to improve VRFB performance via enhanced mass transfer and reduced pressure drop.

Tunable viscoelastic size-based particle separation in straight microchannels with triangular cross-sections

In recent years, viscoelastic particle manipulation within microfluidic systems has received much attention due to the ease with which micron-sized objects may be maneuvered and isolated on the basis of size. While several factors, including both fluid and particle properties, regulate the precise locations and trajectories of micron-sized species flowing along a microchannel, the role of channel cross-section shape is critical, since it directly influences the fluid velocity profile and thus the direction and magnitude of hydrodynamic forces. It is therefore surprising that this parameter has not been comprehensively investigated for cell-based separations, especially since most viscoelastic microfluidic systems are only able to efficiently sperate cells over limited size ranges. To address this shortcoming, we present a viscoelastic microfluidic system integrating a triangular cross-section microchannel, for efficient and tunable size-based separations of micron-sized species. We find that particle focusing patterns can be controlled by simple variation of volumetric flow rates, which allows for the efficient separation of particles and cells of variable size. To showcase the efficacy of the approach, we present a size-based separation of various blood components, including white blood cells, platelets, and rare cells. By quantifying the number of particles collected at the outlets, we achieve recovery efficiencies of over 98%.

Ice shelf basal channel shape determines channelized ice-ocean interactions

Growing evidence has confirmed the critical role played by basal channels beneath Antarctic ice shelves in both ice shelf stability and freshwater input to the surrounding ocean. Here we show, using a 3D ice shelf-ocean boundary current model, that deeper basal channels can lead to a significant amplification in channelized basal melting, meltwater channeling, and warming and salinization of the channel flow. All of these channelized quantities are also modulated by channel width, with the level of modulation determined by channel height. The explicit quantification of channelized basal melting and the meltwater transport in terms of channel cross-sectional shape is potentially beneficial for the evaluation of ice shelf mass balance and meltwater contribution to the nearshore oceanography. Complicated topographically controlled circulations are revealed to be responsible for the unique thermohaline structure inside deep channels. Our study emphasizes the need for improvement in observations of evolving basal channels and the hydrography inside them, as well as adjacent to the ice front where channelized meltwater emerges.

Effect of flow channel cross-section shape on the performance of proton exchange membrane electrolysis cell

To study the thermal and mass distribution in proton exchange membrane electrolytic cells (PEMEC), a two-phase numerical model of a single-channel electrolytic cell was established. The polarization performance and gas-heat distribution in a single-channel electrolytic cell under five different flow channel cross-sections (rectangle, trapezoid, inverted trapezoid, triangle, and circle) were studied. The findings indicate that the inverted trapezoidal flow channel’s gas buildup effect is rather severe in both the catalytic and diffusion layers. In the trapezoidal flow channel, the temperature of the proton exchange membrane region is lower, and the electrochemical performance of the rectangular flow channel electrolytic cell is the best, with an improvement rate of up to 11.47%. The electrochemical performance of the triangular and circular flow channels is the worst.

Design and Optimization of Heat Sinks for the Liquid Cooling of Electronics with Multiple Heat Sources: A Literature Review

This paper presents a detailed literature review on the thermal management issue faced by electronic devices, particularly concerning uneven heating and overheating problems. Special focus is given to the design and structural optimization of heat sinks for efficient single-phase liquid cooling. Firstly, the paper highlights the common presence and detrimental consequences of electronics overheating resulting from multiple heat sources, supported by various illustrative examples. Subsequently, the emphasis is placed on single-phase liquid cooling as one of the effective thermal management technologies for power electronics, as well as on the enhancement of heat transfer in micro/mini channel heat sinks. Various studies on the design and structural optimization of heat sinks are then analyzed and categorized into five main areas: (1) optimization of channel cross-section shape, (2) optimization of channel flow passage, (3) flow distribution optimization for parallel straight channel heat sinks, (4) optimization of pin-fin shape and arrangement, and (5) topology optimization of global flow configuration. After presenting a broad and complete overview of the state of the art, the paper concludes with a critical analysis of the methods and results from the literature and highlights the research perspectives and challenges in the field. It is shown that the issue of uneven and overheating caused by multiple heat sources, which is commonly observed in modern electronics, has received less attention in the literature compared to uniform or single-peak heating. While several design and structural optimization techniques have been implemented to enhance the cooling performance of heat sinks, topology optimization has experienced significant advancements in recent years and appears to be the most promising technology due to its highest degree of freedom to treat the uneven heating problem. This paper can serve as an essential reference contributing to the development of liquid-cooling heat sinks for efficient thermal management of electronics.

Estimating river bathymetry from multisource remote sensing data

River bathymetry is a key variable in estimating river discharge by remote sensing. However, traditional methods of mapping river bathymetry are expensive and time-consuming, which hinders the estimation of river discharge. In this study, we propose and test a method for estimating river bathymetry by combining remotely sensed observations of water level (z) and river width (w) with a nonlinear z-w relationship derived from a generalized channel cross-sectional shape. The results from five reaches of the upper Yangtze River show that the absolute relative error for the estimate is between 1.25% and 6.18%, indicating the ability of this method to provide accurate estimates. The channel exposure (e) is the main limitation of the proposed method, and the river bathymetry estimates improve significantly with increasing e. For the upper Yangtze River, averaging reaches over an appropriate length can reduce variability in river bathymetry estimate, especially when data are reach-averaged over a length of 10 km. Considering that a priori bathymetric information is not required and its computational process is relatively simple, the proposed method could open up the possibility of bathymetry modeling of global rivers.

Supercritical Heat Transfer and Pyrolysis Characteristics of n-Decane in Circular and Rectangular Channels

In this research, the effects of different channel cross-section shapes on the flow, heat transfer and pyrolysis characteristics of n-decane were analyzed and compared based on CFD simulations. The interactions between cracking, heat transfer and flow field in a circular tube and a rectangular tube were studied. The results showed that the mean pressure drop in the rectangular channel is 1.18 times as high as that in the circular channel with pyrolysis due to its smaller equivalent diameter. The maximum value of the chemical heat sink in the rectangular channel is 1.6 times as high as that in the circular channel. The high temperature zone of any cross section in the rectangular channel is much larger than that in the circular channel due to the superposition of the boundary layer and lower turbulent kinetic energy in the corners of the rectangular channel. The maximum value of the Nu in the circular channel is 1.3 times as high as that in the rectangular channel with pyrolysis due to larger heat capacity, lower viscosity and higher wall shear stress.

Effect of manufacturing deviations on the thermohydraulic performance of printed circuit heat exchangers with zigzag channels

• The etching-induced deformations have subtle effects on thermo-hydraulics; • The bonding-induced deformations is closely related to PCHE thickness; • An estimation model for bonding-induced deformation is proposed and validated; • The semicircular microchannel deformation mechanism is proposed and validated. A printed circuit heat exchanger (PCHE) is an essential component of the supercritical carbon dioxide Brayton cycle ( sCO 2 -BC ), but the effect of manufacturing deviations of PCHEs on thermohydraulic performance is seldom reported. To quantitatively analyse the etching-induced and bonding-induced deformations, 19 test plates/blocks are manufactured for measurement. Numerical simulations are performed to investigate the effects of these geometric deformations. The results indicate that the influences of etching-induced deformations are relatively small, the effect of the channel cross-section shape is more significant than the zigzag angle, and the longitudinal pitch is the weakest contributor. For the oval-shaped channel, the channel width plays a leading role in influencing the heat transfer, while the pressure drop is affected more severely by the channel depth. The channels tend to be narrower and shallower after diffusion bonding, and the bonding-induced channel cross-section deformation can cause large deviations in thermal-hydraulic characteristics, especially for those with thin blocks and few layers. Based on the measurement data, an estimation model for the relative deviation of the channel hydraulic diameter after bonding is proposed for the present manufacturing process.

Theoretical investigation of dam-break waves in frictional channels with power-law sections

Both the hydraulic resistance and the channel cross-sectional geometry have significant effect on the propagation of the dam-break waves. Analytical models including either of them have been available. However, it is not feasible to assess the comprehensive influence using the existing solutions. The present study considers a resistance-dominated wave tip region followed by an ideal fluid flow region in a dry horizontal channel whose cross-sectional shape is controlled by a power-law index n. Laboratory experiments and numerical simulations are conducted to measure/predict the water surface profiles of the dam-break flows in five types of flumes. The water depth, location and celerities of the wave front predicted by the analytical model agree well with the experimental and numerical results. The quantitative effects of the bottom resistance and the channel cross-sectional shape on the wave properties are investigated. Results show that the spatio-temporal variation in the wave feature of the dam-break flows strongly depends on the channel cross-sectional geometry; while the retardation effect of the bottom resistance becomes more significant as n increases. Furthermore, the derived analytic solution as well as the experimental data can be used for evaluating numerical solutions considering the hydraulic resistance and cross-sectional geometry.

The Effect of Geometric Parameters on Flow and Heat Transfer Characteristics of a Double-Layer Microchannel Heat Sink for High-Power Diode Laser.

The effect of the geometric parameters on the flow and heat transfer characteristics of a double-layer U-shape microchannel heat sink (DL-MCHS) for a high-power diode laser was investigated in this work. FLUENT 19.2 based on the finite volume method was employed to analyze the flow and heat transfer performance of DL-MCHS. A single variable approach was used to fully research the impact of different parameters (the number of channels, the channel cross-sectional shape, and the aspect ratio) on the temperature distribution, pressure drop, and thermal resistance of the DL-MCHS. The rectangular DL-MCHS heat transfer performance and pressure drop significantly increased with the rise in the channel's aspect ratio due to there being a larger wet perimeter and convective heat transfer area. By comparing the thermal resistance of the DL-MCHS at the same power consumption, it was found that the rectangular DL-MCHS with an aspect ratio in the range of 5.1180-6.389 had the best overall performance. With the same cross-sectional area and hydraulic diameter (AC = 0.36 mm, Dh = 0.417 mm), the thermal resistance of the trapezoidal microchannel heat sink was 32.14% and 42.42% lower than that of the triangular and rectangular ones, respectively, under the condition that the pumping power (Wpp) was 0.2 W. Additionally, the thermal resistance was reduced with the increment of the number of channels inside the DL-MCHS, but this would induce an increased pressure drop. Thus, the channel number has an optimal range, which is between 50 and 80 for the heat sinks in this study. Our study served as a simulation foundation for the semiconductor laser double-layer U-shaped MCHS optimization method using geometric parameters.

Stiffening optimisation of conventional cold-formed steel cross-sections based on a multi-objective Genetic Algorithm and using Generalised Beam Theory

This paper reports the development, numerical implementation and application of a novel methodology to perform a multi-objective stiffening optimisation of conventional cold-formed steel (CFS) cross-section shapes with longitudinal intermediate stiffeners, manufactured by bending the steel sheets with roll-forming machines. The methodology is based on a Genetic Algorithm (GA) and aims at maximising the compressive and/or flexural ultimate strength of CFS members currently used in industry with respect to local, distortional and local-distortional interactive failures. The design approach adopted to estimate the member ultimate strengths is based on the Direct Strength Method (DSM) and Generalised Beam Theory (GBT) is used to calculate the elastic buckling loads and moments. The proposed methodology consists of adding small intermediate stiffeners, whose possible locations are pre-defined in accordance with a map of executable fold-line positions, thus leading to an optimisation procedure whose output are alternative (stiffened) cross-sections that (i) outperform the original conventional/plain cross-section and (ii) can be fabricated with a minimal additional cost – the original cross-section typology, overall dimensions and wall angles are retained. The application and potential of the developed GA-based code is illustrated by addressing the stiffening optimisation of conventional lipped channel, lipped zed and rack cross-section shapes for CFS members subjected to compression, bending or compression and bending – the numerical results are presented in terms of cross-section families belonging to the optimal Pareto Front. For validation and assessment purposes, some optimised cross-sections obtained are compared with the “exact” solutions provided by a “brute-force search”.

Investigation, Analysis and Optimization of PEMFC Channel Cross-Section Shape

In this study, a three-dimensional (CFD) model is employed to simulate and optimize the CCS (Channel Cross-Section) shape of the single straight channel PEMFC. Four CCS shapes, namely trapeze, inverted trapeze, half of ellipse and inverted half of ellipse, are investigated using ANSYS-FLUENT software and compared to the rectangular and triangular CCS shapes. The results obtained from the simulation are compared to the experimental results of the literature. A good agreement is observed between the numerical and experimental results. From the obtained results, it appears that the best delivered power density is reported by the trapeze CCS configuration, whereas, the worst delivered power density is obtained by the inverted half of ellipse CCS configuration. The highest pressure-drop and pumping power are obtained with the triangular CCS configuration and the smallest are resulted by the rectangular CCS configuration. Finally, the highest net power output is reported by the trapeze channel cross-section configuration, while, the lowest one is yielded by the inverted half of ellipse CCS configuration.

Experimental investigation of two-phase flow regimes in rectangular micro-channel with two mixer types

This study primarily aimed to explore the two-phase flow characteristics in a rectangular channel with a hydraulic diameter of 1.33 mm. High-speed video imaging techniques were used to capture two-phase flow behavior corresponding to different superficial gas and liquid velocities. To examine the effect of the gas–liquid mixer configuration on two-phase flow patterns, experiments were conducted using two types of mixers. The results show that the mixer configuration can affect the flow structure only in the slug flow regime. The present study provides a more detailed classification of flow regimes than previous studies. The flow regimes observed were classified into seven categories: slug, aerated-slug, transition, multiple, wavy-annular, smooth-annular, and dispersed-annular flows. Moreover, the quantitative characterization of flow regimes and transition boundaries in micro-channel flows using the standard deviation of differential pressure fluctuations was attempted. This study comprehensively reviews and assesses previous two-phase flow regime maps for both macro-channels and mini/micro-channels. It is shown that the two-phase flow pattern in mini/micro-channels is influenced by various factors, such as the channel hydraulic diameter, the channel cross-sectional shape, the gas–liquid mixer configuration, the difference in the hydraulic diameters between the mixer outlet and test channel, and the thermophysical properties of the working fluids. The comparison between the present experimental data and predictions of the previous flow regime maps demonstrates the necessity of developing a new flow regime map to accurately predict two-phase flow regimes in micro-channels.

Correlation between pressure loss and heat transfer coefficient in boiling flows in printed circuit heat exchangers with semicircular and circular mini-channels

• Boiling flow heat transfer coefficient and pressure drop were evaluated. • Printed circuit heat exchangers with semicircular and circular channels were employed. • Nucleate boiling in corners affected the heat transfer and flow resistance. • Heat transfer coefficient in semicircular channel was twice as high at low quality. • Increase in pressure drop was suppressed by effect of corners at a low quality. In this study, we investigated the correlation between the pressure loss and heat transfer coefficient for boiling flows in printed circuit heat exchangers. The effect of channel cross-sectional shapes—semicircle and circle—was evaluated. The hydraulic diameters of the semicircular and circular channels were 1.04 mm and 1.0 mm, respectively. A subcooled liquid with a subcooling temperature of 10 K was heated with hot water, and the saturation temperature was 30 °C. The refrigerant mass flux was set in a range of 100–400 kg/m 2 ·s. Consequently, despite the lower pressure drop, for low outlet quality, the heat transfer coefficient was higher for the semicircular channel than for the circular channel. The heat transfer was enhanced by the promotion of bubble nucleation in the thick liquid film at the corners, and the flow resistance was suppressed by the decrease in the vapor shear stress. However, for high outlet quality, the difference in the heat transfer coefficient decreased with an increase in the outlet quality. The experimental results were compared with the results obtained by correlation equations. The lowest mean absolute error of heat transfer coefficient and pressure drop for the semicircular mini-channel were 15.1 % and 26.7 %, respectively.

Rapid assembly of PMMA microfluidic devices with PETE membranes for studying the endothelium

Biomicrofluidic devices and organ-on-a-chip (OOC) systems with integrated membranes are often fabricated from two different thermoplastic materials but bonding of such dissimilar thermoplastics remains challenging to manufacture at scale. Here, we present a method to bond poly(methylmethacrylate) layers to a polyethylene terephthalate porous membrane to create membrane-based microfluidic devices for biological barrier modeling. By combining milling, laser cutting and chlorocarbon-based solvent bonding supported by retention grooves, we achieved a fabrication rate of 36 devices in 5 h. Chlorocarbon-based solvent bonding resulted in bond strength of ~10 J/m2 and did not adversely affect the membrane pore structure or the channel cross-sectional shape. The bonded devices were found to support long term culture of human endothelial cells that developed expected morphology and cell-cell adhesion contacts as evidenced by immunofluorescent labeling of VE-cadherin. Barrier permeability was measured to be 3.38 × 106 cm/s for 10 kDa dextran using a sampling-based method compatible with mass spectrometry and scintillation techniques and was in agreement with literature. To validate the devices for cell migration experiments, THP-1 monocytes were introduced into devices with confluent endothelial monolayers. Monocytes adhered to and migrated through the endothelium. Activation of the endothelium with TNF-α prior to introducing monocytes significantly increased monocyte adhesion. Overall, the rapid device fabrication method achieved medium-volume production rates and was found to support both cell culture and experiments associated with measuring barrier and endothelial function. This fabrication method has potential to both accelerate biomicrofluidics and OOC research in the lab and accelerate development of commercialized microfluidic membrane devices.

Determination of Dimensional and Shape Parameters of CRoss-sections of Natural Torrents in Small Mountain Watersheds

The aim of this article is to assess the accuracy of estimates of geometric and shape parameters in cross-sections of natural mountain torrents using the equations of regional downstream hydraulic geometry. Equations of regional hydraulic geometry were derived for 19 natural torrents of the Western Tatras in the geomorphological unit of the Tatras. The equations for the relations between the watershed area AW (km2) and the bankfull channel width inside the banks Bbf (m), channel depth Hbf (m), channel cross-section area Abf (m2) and shape characteristics of the cross-section Bbf : Hbf and Hbf : Bbf, were ascertained. At the same time, equations for the relationships between the length of the main stream LT (km) and aforementioned dimensional and shape parameters were derived. Subsequently, the measured geometric and shape parameters of the natural cross sections of torrents were compared with the calculated values. Differences between measured and calculated characteristics were found and confirmed by pairwise selection testing.

A Double-Bridge Channel Shape of a Membraneless Microfluidic Fuel Cell

A double-bridge shape is proposed as a novel flow channel cross-sectional shape of a membraneless microfluidic fuel cell, and its electrochemical performance was analyzed with a numerical model. A membraneless microfluidic fuel cell (MMFC) is a micro/nano-scale fuel cell with better economic and commercial viability with the elimination of the polymer electrolyte membrane. The numerical model involves the Navier–Stokes, Butler–Volmer, and mass transport equations. The results from the numerical model were validated with the experimental results for a single-bridge channel. The proposed MMFC with double-bridge flow channel shape performed better in comparison to the single-bridge channel shape. A parametric study for the double-bridge channel was performed using three sub-channel widths with the fixed total channel width and the bridge height. The performance of the MMFC varied most significantly with the variation in the width of the inner channel among the sub-channel widths, and the power density increased with this channel width because of the reduced width of the mixing layer in the inner channel. The bridge height significantly affected the performance, and at a bridge height at 90% of the channel height, a higher peak power density of 171%was achieved compared to the reference channel.

Effect of Flow Channel Cross Section Shape on the Performance of Heat Storage Structure

A numerical simulation is carried out for the thermal storage process in a heat storage device with magnesia bricks as thermal energy storage medium. Three types of cross section shapes (square, hexagon, circle) of the flow channel are considered with the inlet air temperature as high as 1023K. The perssure drop, temperature distribution and temperature uniformity of the flow channel are obtained. The results show that the pressure drop of the flow channel with circle cross section is the lowest when the Reynolds number is less than 2300 (in this case the inlet velocity is 5m/s), While when the Reynolds number is more than 2300, the flow channel with square cross section has the lowest pressure drop. The thermal storage time of the heat storage device decreases with the increase of air velocity. The temperature distribution of the flow channel indicates that the flow channel with hexagon cross section has the best comprehensive performance.