Channel Orientation Research Articles

Artificial Water Channels—Progress Innovations and Prospects

Artificial Water Channels—Progress Innovations and Prospects

Phase Change and Heat Transfer Analysis of Different Refrigerants During Condensation in Minichannel Using a Novel Numerical Approach

Abstract This paper analyses the condensation heat transfer phenomena in minichannel using acetone, ammonia, propylene, and R134a as the working fluids used in new-age space applications. A novel numerical model is developed considering the changes in local vapor pressure in the channel established due to shrinking in the flow passage by the gradual formation of the liquid layer. The present developed numerical model is compared with the available numerical and experimental results. The impacts of different inlet mass fluxes (250, 500, and 750 kg/m2 s), channel heights (1, 4, 6, and 8 mm), applied heat loads (10, 100, 250, and 500 W), and channel orientations (0 deg, 30 deg, 45 deg, 60 deg, and 90 deg) on the performance of the condensation heat transfer process are investigated. The formation of the thin liquid film layers and evaluation of the liquid–vapor interface profiles are examined. The study reveals that the channel orientation has a marginal influence on the flow pattern for the considered channel length of 20 mm. The maximum change in pressure loss is found at the channel orientation of 45 deg, and the average heat transfer coefficient is almost the same for all the considered orientations. The flow pattern is affected by the increase in mass flux resulting in the delay of heat transfer coefficient fluctuations. The average heat transfer coefficient decreases with increasing heat load, and the minimum average heat transfer coefficient is obtained for heat load, Q = 500 W.

Influence of secondary flow channels on heat transfer and fluid flow characteristics in curved microchannel

AbstractMicrochannel‐assisted cooling technologies have found extremely suitable for compact heat exchangers surpassing conventional fan‐assisted heat sink solutions. Though extensive research was done on straight channels, research on curved microchannel is scant. In the present study, hydraulic flow characteristics and cooling performance of curved microchannel with secondary flow (CMCSF) with four different oblique angles are investigated numerically and compared with conventional curved microchannel (CCMC). A 3D conjugate heat transfer analysis is performed for four CMCSFs and CCMC using commercial software ANSYS Fluent with Reynolds number (Re) ranging between 125 and 325. A part of fluid from main channel is diverted into the secondary channels, leading to re‐initialization of boundary layers. Also, this diverted flow that is fed into adjacent main channels consecutively results in better fluid mixing. Owing to these two phenomena, there is a huge enhancement in heat dissipation through the channel. The results revealed a Nusselt number increment of up to 80.12% for CMCSF in comparison with CCMC. Moreover, the average wall temperature was recorded lowest for CMCSF with oblique angle 30°, which is 8.83°C lower in comparison with CCMC for same Re. For the entire range of Re considered, the overall performance of all CMCSFs was found better than CCMC with maximum performance factor of 1.62 being achieved with secondary channel orientation of 24°.

Performance of a fuel cell‐based proton battery with varied designs of micro‐flow channel for enhanced hydrogen storage

AbstractWe present an experimental investigation on a proton battery, that could run both as electrolyser and fuel cell, using six different flow channel orientations viz. pin‐type, parallel, interdigitated, spiral, serpentine, and parallel serpentine. The battery stores energy in the form of hydrogen ions and its performance is determined in terms of hydrogen wt. % stored in an integrated carbon‐based electrode. In this paper, the fabrication of electrode, development of an experimental proton battery and its testing are disclosed. The characterization of the employed activated carbon electrode is done using scanning electron microscopy, X‐ray diffraction analysis, energy dispersive spectroscopy, and fourier transform infrared spectroscopy. The fabricated proton battery is tested by charging (E‐mode operation) and discharging (FC‐mode operation) subsequently at normal temperature and pressure conditions. In the E‐mode operation, electrochemical hydrogen storage of the battery with six different flow channels is found to be in the range of 1.36–1.97 wt. %. The corresponding desorption of hydrogen in the FC‐mode operation is found to be in the range of 1.047–1.479 wt. %, respectively, for six different flow channels. The comparative result analysis revealed that parallel serpentine flow channel outperformed, with energy storage capacity of 1.97 wt. %; and pin type channel design showed comparatively low performance with energy storage capacity of 1.36 wt. %. The presented research work is an effort towards meeting the set targets of hydrogen storage set by the U.S. Department of Energy to make the hydrogen technology commercially viable.Statement of Industrial RelevanceThe presented research work has relevance with the power industry as it reveals the optimum design of flow channels for enhanced hydrogen adsorption. It is a way forward towards developing a fuel‐cell based proton battery that does not emit harmful fumes like lithium batteries and therefore, is environmentally friendly.Novelty or SignificanceThe presented research work is a maiden attempt of testing different designs of micro‐flow channels in an experimental proton battery that is a single unit capable of performing dual tasks i.e., electrolyser and fuel cell to store energy and give out power when required.

β-Ga2O3 FinFETs with ultra-low hysteresis by plasma-free metal-assisted chemical etching

In this work, β-Ga2O3 fin field-effect transistors (FinFETs) with metalorganic chemical vapor deposition grown epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are demonstrated. β-Ga2O3 fin channels with smooth sidewalls are produced by the plasma-free metal-assisted chemical etching (MacEtch) method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages is also characterized. The FinFET with channel perpendicular to the [102] direction is found to exhibit the lowest subthreshold swing and hysteresis.

A multiscale LBM–TPM–PFM approach for modeling of multiphase fluid flow in fractured porous media

AbstractIn this paper, we present a reliable micro‐to‐macroscale framework to model multiphase fluid flow through fractured porous media. This is based on utilizing the capabilities of the lattice Boltzmann method (LBM) within the phase‐field modeling (PFM) of fractures in multiphase porous media. In this, we propose new physically motivated phase‐field‐dependent relationships for the residual saturation, the intrinsic as well as relative permeabilities. In addition, an anisotropic, phase‐field‐dependent intrinsic permeability tensor for the fractured porous domains is formulated, which relies on the single‐ and multiphasic LBM flow simulations. Based on these results, new relationships for the variation of the macroscopic theory of porous media (TPM)–PFM model parameters in the transition zone are proposed. Whereby, a multiscale concept for the coupling between the multiphasic flow through the crack on one hand and the porous ambient, on the other hand, is achieved. The hybrid model is numerically applied on a real microgeometry of fractured porous media, extracted via X‐ray microcomputed tomography data of fractured Berea Sandstone. Moreover, the model is utilized for the calculation of the fluid leak‐off from the crack to the intact zones. Additionally, the effects of the depth of the transition zone and the orientation of the crack channels on the amount of leakage flow rates are studied. The outcomes of the numerical model proved the reliability of the multiscale model to simulate multiphasic fluid flow through fractured porous media.

Giant Osmotic Energy Conversion through Vertical-Aligned Ion-Permselective Nanochannels in Covalent Organic Framework Membranes.

Nanofluidic membranes have been demonstrated as promising candidates for osmotic energy harvesting. However, it remains a long-standing challenge to fabricate high-efficiency ion-permselective membranes with well-defined channel architectures. Here, we demonstrate high-performance osmotic energy conversion membranes based on oriented two-dimensional covalent organic frameworks (COFs) with ultrashort vertically aligned nanofluidic channels that enabled efficient and selective ion transport. Experiments combined with molecular dynamics simulations revealed that exquisite control over channel orientation, charge polarity, and charge density contributed to high ion selectivity and permeability. When applied to osmotic energy conversion, a pair of 100 nm thick oppositely charged COF membranes achieved an ultrahigh output power density of 43.2 W m-2 at a 50-fold salinity gradient and up to 228.9 W m-2 for the Dead Sea and river water system. The achieved power density outperforms the state-of-the-art nanofluidic membranes, suggesting the great potential of oriented COF membranes in the fields of advanced membrane technology and energy conversion.

Discourse Analysis of TV News Headlines

This study investigates features of TV news headlines. Discourse analysis is used as a method for studying news headlines in question. The model adopted is an eclectic one. The approaches of Olowe (1993), Van Dijk (2000), Van Dijk (2013) on text analysis were utilized to examine the data. The analysis involves three levels of analysis: Grammatical, linguistic and ideological. The study aims to explore whether the linguistic features of TV headlines among different news channels vary according to the channel orientation or not. It also seeks to highlight the grammatical structure of news headlines and examine the various TV headlines' differences with their respective ideologies. It is hypothesized that through the sample channels have different orientations, they use the same structures and techniques in their headlines. Moreover, due to this difference, it is hypothesized that there is a difference in the ideologies. Consequently, the headlines will have sometimes hidden meanings to be conveyed indirectly to their readers. In addition, the study sheds light on discourse markers used in news headlines. Data analysis shows that most headlines carry the same linguistic and grammatical features with little focus. Diversity in orientation has its obvious effect in some channels. A small number of discourse markers is used in news headlines. The researcher has come up with findings that validate the set hypotheses.

Fabrication of Irregularity-Free, Highly Circular Cross-Sectional Microchannel

Microchannels typically have rectangular cross-sections, whereas biological channels, such as blood vessels and airways, have circular cross-sections. The difference in cross-sections causes different fluidic behaviors, resulting in differences between fluidic behavior in microchannels and biological channels. To simulate fluidic behavior in vitro, circular cross-sectional microchannels are required. We developed a circular cross-sectional microchannel with a smooth channel wall, free from cracks and irregularities. In the fabrication process of the circular cross-sectional microchannel, uncured polydimethylsiloxane (PDMS) was inserted into a rectangular cross-sectional microchannel. Then, the PDMS was pushed out by the introduction of compressed air before the curing process. During the introduction of compressed air, we observed the behavior of the uncured PDMS and found the formation and movement of protrusions along the microchannel. After pushing out the uncured PDMS, the residual PDMS was cured, resulting in a circular cross-sectional microchannel. The fabrication method was examined by varying the channel orientation and airflow direction. In the case of the horizontal orientation and airflow in an opposite direction, the circularity of the microchannel was greater than 0.99 at the centimeter scale in all cross-sections along the microchannel.

Adiabatic two-phase pressure drop of carbon dioxide in different channel orientations

Adiabatic pressure drop measurements of two-phase Carbon Dioxide (CO2) have been carried out in horizontal, vertical upward and downward direction with a dedicated test facility at the European Organization for Nuclear Research (CERN). A database of more than 1100 measurements, consisting of 512 data points in horizontal and 295 data points for each vertical up- and downflow respectively, has been compiled within this study. The experiments cover saturation temperatures from -25°C⩽Tsat⩽+5°C, mass velocities from 100kgm-2s-1⩽G⩽450kgm-2s-1 and are carried out in test sections with an inner diameter of 8 mm. The analysis of the pressure drop signals reveals that pressure fluctuations are increasing around the slug flow regime and the oscillation effects get magnified in vertical direction. The measurements in horizontal direction are compared to 18 frictional pressure drop models. For the comparison of the vertical data, 21 void fraction correlations accounting for the static head have been combined with the frictional models. The data sets of the horizontal and vertical upflow measurements are well predicted by several pressure drop models with an acceptable statistical significance. However, the prediction models perform less accurately for vertical downflow and it has been found that the static head is not well described by the void fraction correlations. In particular at low mass velocities, the effects of phase separation due to dominant buoyancy forces are not well incorporated by the void fraction models considered. In addition to the comparison of the entire data sets, subdivided analyses accounting for the flow patterns are provided within the present work.

Alternative designs and technological advancements of phase change material integrated photovoltaics: A state-of-the-art review

Photovoltaics (PV) is the most established renewable energy technology of sunrays to electricity conversion, which converts only a fraction of the solar radiation to electricity. The remaining sunlight causes the heating of PV modules which significantly mitigates their performance and life-span. To minimize the temperature-dependent power degradations, various PV cooling techniques have been proposed in the literature. Utilisation of PCM as a cooling system is found an attractive way of photovoltaics thermal management. Present article demonstrates a state-of-the-art review of technological advancements of PCM integrated photovoltaics. Concentrated and non-concentrated PV modules integrated with PCM are discussed in detail. The extracted heat from PV panels is harnessed for domestic and industrial purposes through hybrid systems such as PCM integrated photovoltaic-thermal (PVT/PCM) systems and thermoelectric module integrated PCM regulated photovoltaic (PV/PCM-TE) systems. The effect of ambient temperature, sunlight intensity, PCM melting point temperature, PCM channel orientation, various heat transfer enhancement configurations, etc., on PV panel performance is studied. Moreover, a complete methodology for the numerical solution of a conventional PV/PCM system, along with the governing equations and boundary conditions, is discussed.

Effect of channel orientation on heat transfer in a rotating impingement cooling channel

The jet impingement cooling technology is usually applied in the turbine blade leading edge which suffers high thermal loads. In a high-speed rotating turbine blade, however, the channel orientation (β, the angle between the direction of the jet and the rotating plane) could alter the jets and heat transfer. Therefore, the effects of channel orientation (from 90∘ to 180∘) on heat transfer of confined jet impingement cooling are experimentally studied under an iso-thermal boundary. Both the jet-to-target surface distance and the jet-to-jet spacing are 3 times of the jet diameter. The jet Reynolds number varies from 5000 to 15,000, and the maximum jet rotation number reaches 0.24. The results show that the rotational effect on heat transfer is different in each channel orientation. In the cases of 90∘≤β≤ 135∘, a large vortex generated by the Coriolis force in the supply channel significantly changes the mass-flowrate distribution in each jet orifice. Hence, the heat transfer in the middle part decreases with the rotation number whereas the heat transfer at both ends increases, resulting in a “U-shape” pattern of heat transfer in the impingement channel. In the cases of 135∘<β≤ 180∘, however, the heat transfer throughout the stagnation zone decreases with the rotation number. The rotation-induced jet diversion is the primary factor that weakens the heat transfer, and jets are driven away from the target surface at high rotation numbers. Moreover, the heat transfer correlation on the stagnant zone is developed, which considers the effects of channel orientation and rotation number.

Formula omitted]-plume geothermal in fluvial formations: A 2D numerical performance study using subsurface metrics and upscaling

CO2-plume geothermal (CPG) operations are considered for sufficiently permeable formations due to their superiority compared to conventional water-based geothermal systems. The fluvial heterogeneity in sedimentary reservoirs can significantly affect the pumping energy losses and heat extraction from hot sedimentary aquifers. In the present study, we have implemented the braided type of fluvial channels to account for the geological uncertainty, and investigated the subsurface performance metrics of a CPG system with a checkers-board pattern. An optimization of doublet/well spacing is performed based on the coefficient of performance (CoP), energy sweep parameter, and an objective function (f) defined specifically for optimization of the process. In addition, a sensitivity analysis on the grid resolution, braided channel thickness and orientation, and the injection flow rate and span of the supercritical (sc)-CO2 is performed. The upscaled grid resolution mainly affects the pressure-related parameters, including CoP and f, resulting in an average error of 80% and 60% between the fine- (120 × 120) and the coarse-scale (15 × 15), respectively. As a result, the grid resolution of 60 × 60 with dx≈16.5 m is found to have both acceptable average error and optimum runtime. The optimum doublet/well spacing for the present case is about L=450 m, in which the CPG system provides about 9 to 13 times higher values of f compared to cases with doublet/well spacing higher or lower than the optimum value. Moreover, injection wells with I1-I2 line parallel to channels’ orientation, provide about 30% higher f compared to the perpendicular case. However, channels’ orientation does not change the optimum doublet/well spacing (L=450 m).

Hierarchically porous biochar derived from orthometric integration of wooden and bacterial celluloses for high-performance electromagnetic wave absorption

Inspired by the natural growth of wooden cellulose (WC) and bacterial cellulose (BC), we integrated the two categories of cellulosic materials by static fermentation. BC networks created in plane are intimately integrated with the wooden chip (cross section of wood, CW) and are perpendicular to the orientation of the cellular channels along the growth of the trees. The as-prepared BC/CW composites were converted into the interconnected carbon monoliths with hierarchically porous structure (CBC/CCW) by a one-step carbonization. The complementarity of WC and BC in spatial orientation created more mixed meso/macropores. Upon EMW irradiation, the wood-derived carbonaceous cellular wall attenuates EM energy by multiple reflection, while CBC networks further dissipate EMW by conduction loss. Additionally, the abundant voids inside of the wooden channels are beneficial to impedance matching. As a result, the as-fabricated three-dimensional CBC/CCW composites infiltrated with polydimethylsiloxane delivered strong EMW absorption performance with minimum reflection loss of −57.97 dB, broad absorption bandwidth of 6.28 GHz, and ultralow filler loading of 3.5%. Moreover, the elastomer CBC/CCW can still maintain 90% EMW absorption capability even after 500 bending-releasing cycles. The ingenious integration of wooden and bacterial celluloses provides a new sight for designing high-performance EMW absorbers with low-cost and sustainable resources.

The quantitative 6H-SiC crystal damage depth profiling

The hexagonal silicon carbide (6H-SiC) is one of materials used in nuclear applications, and as such is exposed to crystal damage inducing by variety of energetic particles like neutrons. In this article the 6H-SiC crystal lattice damage was introduced by the 4 MeV C3+ and 4 MeV Si3+ channelling ion implantation at the room temperature. The implantation of C and Si ions (so called self-ions) to the set of different fluences, achieves a 6H-SiC crystal lattice damage more similar to what the exposure to neutrons would produce. The 6H-SiC crystal damage has been investigated by the Elastic Backscattering spectra taken in the channeling orientation (EBS/C). EBS/C spectra of the implanted 6H-SiC samples were taken with 1.725 MeV and 1.860 MeV protons. By fitting the EBS/C spectra, the quantitative 6H-SiC crystal damage depth profiles were obtained. Further, the cross section of crystal's implanted region has been scanned with the micro-Raman (μR) technique for a comparison. In this way, the qualitative analysis of a non-crystalline phase as a function of the crystal depth was independently determined. Additionally, a scanning electron microscopy (SEM) image was taken of the implanted crystal cross sections. The comparison of the crystal damage profiles obtained by fitting EBS/C spectra with the corresponding ones obtained with the μR and SEM techniques shows very good consistency between them.

An investigation of horizontal and vertical flow boiling in a single channel with a confinement number beyond the threshold of micro-scale flow

The gravitational force effect is of concern when designing flow boiling systems deployed on Earth and in space. A study of the R-134a flow boiling inside the horizontal and vertical channels was experimentally performed to explore the flow orientations' effect on flow pattern and heat transfer characteristics. The test section was a 0.5 mm diameter tube from which the corner effect was excluded. The single channel was used to avoid disturbances that flow maldistribution could possibly cause in the multiple channels. The experimental two-phase flow corresponded to a 1.75 confinement number, which was above the threshold for micro-scale flow. The results indicated the flow regime map, which was less affected by the channel orientation except for that slug flow pattern that was unable to survive during the vertical downflow and vertical upflow. Also, based on the present micro-scale flow, the heat transfer results were mostly independent of the gravitational force effect, and the nucleate boiling and convective mechanisms tended to govern them.

Proton Conductive Composite Membranes with Stable Anisotropic Though-Plane Conductivity: A New Preparation Approach

In common PEMFCs, a polymer electrolyte membrane selectively conducts protons but blocks passage of electrons and reactants. Nafion, current benchmark membrane material, offers a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels within a Teflon-like matrix. Nanochannel orientation is a promising approach to enhance Nafion conductivity, yet there has been no facile method to induce a strong and stable alignment within membranes in the most desired through-plane (TP) direction.Here we report a novel and facile preparation approach based on dual electrospun Nafion-PVDF nanofiber composite that yields a stable TP alignment. The preparation starts from electrospinning of a mixed fiber mat, which is subsequently converted to a solid membrane by plunging the mat into a thin slit. Due to extreme thinness, the electrospun nanofiber readily buckle into a folded structure, thereby a strong inherent microscopic channel orientation within nanofibers is readily converted to macroscopic TP channel alignment. Ultimately, the folded nanofibers fuse, consolidating the membrane.A pronounced TP alignment of ion channels in the membranes, sustaining fusion and annealing, is demonstrated using TEM and SAXS. The analysis also highlights the importance of PVDF fiber as a stabilizing and confining component. Electrospun PVDF fibers within consolidated Nafion-PVDF composite preserve channel orientation upon annealing both in TP and in-plane (IP) aligned membranes, while pure Nafion membranes, similarly prepared from electrospun Nafion fibers, rapidly lose structural anisotropicity. Finally, the impedance measurements demonstrate highly anisotropic conductivity of both TP- and IP-aligned membranes, consistent with their anisotropic structure. Thus, measured TP conductivity of TP-aligned 46% Nafion composite is nearly three times its IP conductivity and about 70% that of Nafion 212, thereby the conductivity normalized to Nafion content exceeds that of pure Nafion. The approach, still leaving much room for optimization, holds potential to advance PEMFC technology by overcoming current limitations and fully utilizing advantageous features of Nafion membranes. Figure 1

Mechanistic critical heat flux prediction for in-vessel retention conditions

In-vessel retention (IVR) is considered a feasible technique to keep reactor pressure vessel (RPV) integrity in a severe reactor accident. For light water reactor (LWR), the effectiveness of this strategy relies soundly on the critical heat flux (CHF) distribution over the external surface of the lower plenum of RPV, whose orientation varies gradually from downward-facing horizontal to vertical. The CHF prediction capability of the liquid sublayer dryout model is efficient for high mass flux in vertical flow boiling conditions. This paper focuses on how to adapt the model to the changed orientation of the heating surface. Bubble departure diameter (dB) and net vapor generation point (NVG), the starting point for the void fraction developing in a heating channel, is one of the important key points in the CHF prediction. Therefore, to assess the predictive potential of CHF under IVR, experimental research was performed to measure bubble departure diameter and NVG for a changing heating surface orientation from downward-facing horizontal to vertical with a mechanistic model basing on the force balance. A modified liquid sublayer dryout model was then proposed where the channel orientation effect is considered to measure the bubble departure diameter (vapor blanket diameter) using the improved force balance model. The NVG is modified according to the departure diameter. The predicted departure diameter and subcooling at NVG show good consistency with the experimental data, and the modified liquid sublayer dryout model can predict the CHF data with an average relative error of 18.36% in IVR.

Significant k-point selection scheme for computationally efficient band structure based UTB device simulations

The accurate calculation of channel electrostatics parameters in ultra-thin body devices requires self-consistent solution of the Poisson’s equation and the full-band structure of the thin channel. For silicon channel, the full-band structure is obtained using the semi-empirical tight-binding model. To make this approach computationally tractable for a wide range of channel thicknesses, in terms of time and resource, only significant k-points in the irreducible Brillouin zone need to be considered. In this work, we present a scheme for precisely identifying the significant k-points based on Fermi–Dirac probability and show that the band-structure approach using those significant k-points can be applied over a wide range of channel thicknesses, oxide thicknesses, device temperatures and different channel orientations. The benchmarking of the obtained channel electrostatics parameters is performed with the results from accurate full-band structure simulations showing excellent agreement (maximum error within ) along with significant reduction in computational time.

Guiding cellular channels of artificial nanohybrid woods for anisotropic properties and solar-thermal evaporation

Natural evolution offers woods with intriguing multicomponent and anisotropic cellular structures, and endows super physicochemical properties. In order to compete with natural woods, many types of artificial woods were endeavored from polymers to achieve on-demand structures and functionalities. In most cases, production of oriented channels in mimic of wood lumina relied on a delicate unidirectional freeze-drying approach and utilization of volatile solvents. Herein we showed that artificial woods with controllable channel orientation could be produced from polymers in involatile solvents without particular control of freezing parameters. By dissolving cellulose in ionic liquid, oriented channels (diameter of 250–540 μm) were produced through diffusion-induced phase separation and strengthened through a facile freezing and air-drying process. The compressive strength could reach 5.5 MPa at the strain of 15% along the channel direction. With the presence of structural anisotropy, incorporation of low-dimension nanomaterials offered the design flexibility in adding super properties in mechanics, water transportation, solar-thermal effect, thermal and photo conductance. For example, artificial hybrid woods with carbon nanotubes showed super solar-thermal property. When combining with the water-transporting ability of oriented channels, it was promising to design an efficient solar-thermal evaporator (5.88 kg m−2 h−1 under equivalent 3-sun irradiation). Thus, this study not only suggests an unprecedented approach of producing artificial woods from polymers in involatile solvents, but also offers the flexibility of designing microstructures and functionalities of artificial woods for various applications.