Velocity Layer Research Articles

Spontaneous ignition and flame propagation in hydrogen/methane wrinkled laminar flames at reheat conditions: Effect of pressure and hydrogen fraction

Direct numerical simulations (DNS) with detailed chemical kinetics and chemical explosive mode analysis (CEMA) are performed to investigate the effect of operating pressure and hydrogen–methane blending on laminar wrinkled flames at reheat combustion conditions. Building upon previous three-dimensional DNS datasets of reheat hydrogen flames, the present work considers two-dimensional configurations that render computationally-feasible simulations of high-pressure combustion and significantly more complex hydrocarbon chemistry. A geometrically-simplified representation of the reheat combustor is adopted and the thermodynamic states considered in the simulations are carefully chosen to mimic gas turbine operation conditions, which are constrained to achieve a target flame position and flame temperature. The two-dimensional DNS results are first assessed against the available three-dimensional data and then analyzed to extract the main trends exhibited by the reheat combustion process with respect to the fraction of the fuel consumed by spontaneous ignition and flame propagation, for increasing pressures and hydrogen fractions. Due to significant differences in the characteristic features of the velocity and thermal boundary layers between the three-dimensional and the two-dimensional configurations, a different global flame shape is observed (V-shaped flame vs W-shape flame) together with a ∼10% bias in the fraction of fuel consumed by spontaneous ignition. Crucially, results from the scaling studies reveal very clear trends with a significant decrease in the fuel consumption by spontaneous ignition for increasing pressures and hydrogen fractions, at the conditions investigated. Finally, this study highlights the important role that first-principle direct numerical simulations, even when conducted in computationally affordable two-dimensional simplified geometrical configurations, can play in obtaining detailed insights and quantitative trends useful for the characterization of complex reactive flows.Novelty and significanceThe reheat burners of the two-stage sequential gas turbine combustors are designed to stabilize flames primarily due to spontaneous ignition. However, prior numerical simulations revealed the presence of an additional assisted-ignition mode aided by recirculation zones. In this study, we used practically feasible two-dimensional direct numerical simulations of premixed hydrogen–air mixtures under lean conditions to quantify the roles of the two flame stabilization modes at different operating pressures. Achieving fundamental understanding of the effect of pressure and hydrogen fraction on flame stabilization is crucial to the development of two-stage sequential combustion and the present two-dimensional calculations provide important new insights. We show that at high pressures, both modes consume fuel to a similar extent. We also investigated the effect of methane blending on flame stabilization. This study also discusses how two-dimensional direct numerical simulations can be leveraged in the design optimization of reheat burners at low technology readiness levels.

Characterization of Shallow Sedimentary Layers in the Oran Region Using Ambient Vibration Data

This study investigates the structure of shear-wave velocities (Vs) in the shallow layers of the Oran region, north-west of Algeria, using non-invasive techniques based on ambient vibration arrays. The region has experienced several moderate earthquakes, including the historical Oran earthquake of 1790. Ambient vibration measurements were carried out at 15 sites throughout the study area. Two methods were used: spatial autocorrelation (SPAC) and frequency–wavenumber analysis (f-k), which allowed us to better constrain Rayleigh wave dispersion curves. The inversion of the dispersion curves derived from the f-k analysis allowed for estimating the shear-wave velocity profiles and the Vs30 value at the sites under study. The other important result of the present study is an empirical equation that has been proposed to predict Vs30 in the Oran region. The determination of near-surface shear-wave velocity profiles is an important step in the assessment of seismic hazard. This study has demonstrated the effectiveness of using ambient vibration array techniques to estimate the soil Vs structure.

Experimental and Numerical Study on the Plasma-Laser-Induced Ignition of Strut Stabilizer at Different Locations

The minimum ignition equivalence ratio of the strut stabilizer is an important parameter in the design of integrated afterburners. The ignition location significantly affects the ignition equivalence ratio and flame propagation, and therefore, it should be deeply studied. The ignition equivalence ratio and flame propagation at different axial ignition locations downstream of the strut stabilizer are studied in this paper. When the ignition distance is approximately the bluff body trailing edge width, a lower ignition equivalence ratio is required for ignition, and the flame propagates faster through the entire combustion chamber. For different ignition locations, the generated flame kernel at different locations all first propagates to the shear layer. Subsequently, the unilateral flame rapidly extends, ultimately igniting the entire combustion chamber. The flame propagation trajectory depends on the ignition location controlled by the non-reacting flow field and the distribution of kerosene concentration. The flame propagation trajectory mainly includes three paths: (1) the flame kernel is directly downstream the shear layer when the ignition location is close to the tail edge of the stabilizer, (2) the flame propagates upstream into the shear layer in a U-shape when the ignition location is far from the stabilizer but still in the recirculation zone, and (3) the flame propagates upstream into the recirculation zone and shear layer in a U-shape when the ignition location is outside the recirculation zone. In addition, the time for flame propagation to the shear layer is directly related to the ignition performance when the ignition location is within the recirculation zone. If the flame reaches the shear layer in a longer time, there will be more energy loss during the flame propagation process, and the ignition performance will deteriorate. The speed of the flame-trailing edge extension is directly related to the ignition fuel-air ratio, and the downstream extension of the flame is mainly affected by the turbulence velocity in the shear layer.

Multi-cycle Direct Numerical Simulations of a Laboratory Scale Engine: Evolution of Boundary Layers and Wall Heat Flux

AbstractMulti-cycle direct numerical simulations (DNS) of a laboratory-scale engine at technically relevant engine speeds (1500 and 2500 rpm) are performed to investigate the transient velocity and thermal boundary layers (BL) as well as the wall heat flux during the compression stroke under motored operation. The time-varying wall-bounded flow is characterized by a large-scale tumble vortex, which generates vortical structures as the flow rolls off the cylinder wall. The bulk flow is found to strongly affect the development of the BL profiles, especially at higher engine speeds. As a result, the large-scale flow structures lead to alternating pressure gradients near the wall, invalidating the flow equilibrium assumptions used in typical wall modeling approaches. The thickness of the velocity BL and of the viscous sublayer was found to scale inversely with engine speed and crank angle. The thermal BL thickness also scales inversely with engine speed but increases with in-cylinder temperature. In contrast, thermal displacement thickness, which is sometimes used as a proxy for thermal BL thickness, was found to decrease with increasing temperature in the bulk. Examination of the heat flux distribution revealed areas of increased heat flux, particularly at places characterized by strong flow directed towards the wall. In addition, significant cyclic variations in the surface-averaged wall heat flux were observed for both engine speeds. An analysis of the cyclic tumble ratio revealed that the cycles with lower tumble ratio values near top dead center (TDC), indicative of an earlier tumble breakdown, also exhibit higher surface averaged wall heat fluxes. These findings extend previous numerical and experimental results for the evolution of BL structure during the compression stroke and serve as an important step for future engine simulations under realistic operating conditions.

Investigations into dynamic variation characteristics of near-bottom boundary flows over a long term at strait areas

Dynamic processes at the bottom boundary layers are crucial for various marine applications such as marine energy exploration and environmental protection. This paper explored hydrodynamic characteristics of near-bottom boundary currents based on the continuous measured velocity data at a site near the bottom boundary layer in the Strait of Georgia. Previous studies on the bottom boundary layer encompasses various aspects, including physical, chemical, and biological dimensions. However, the mechanism underlying the hierarchical structure of flow velocity remain poorly understood. Thus, the power spectrum and wavelet analysis were used to analyze the significant period of the averaged velocity and tidal characteristics, and to calculate the thickness of near-bottom boundary layer. The results indicate that the current velocities at the boundary layer tend to flow in south-eastern and north-western directions. There is a significant period of 15 days in August and September. At a depth of 301 m, the vertical velocities are stratified, indicating different velocity layers. The boundary layer thickness varies from 5.23 to 14.74 m, as indicated by the vertical structural characteristics. The structural characteristics of the seabed boundary layer are conducive to deepening our understanding of sediment's incipient motion, transport, and sedimentation process. The findings provide a theoretical foundation for future studies on sediment movement and the numerical simulation analysis of the bottom boundary layer. It is of great significance for the study of wave flow interaction and marine dynamic structure, and can provide scientific support for the development and utilization of the strait area.

Deep low velocity layer in the sublithospheric mantle beneath India

SUMMARY Globally, there is now a growing evidence for a low velocity layer in the deeper parts of the upper mantle, above the 410 km discontinuity (hereafter called LVL-410). The origin of this layer is primarily attributed to interaction of slabs or plumes with a hydrous mantle transition zone (MTZ) that results in dehydration melting induced by water transport upward out of the MTZ. However, the ubiquitous nature of this layer and its causative remain contentious. In this study, we use high quality receiver functions (RFs) sampling diverse tectonic units of the Indian subcontinent to identify Ps conversions from the LVL-410. Bootstrap and differential slowness stacking of RFs migrated to depth using a 3-D velocity model reveal unequivocal presence of a deep low velocity layer at depths varying from 290 to 400 km. This layer appears more pervasive and deeper beneath the Himalaya, where detached subducted slabs in the MTZ have been previously reported. Interestingly, the layer is shallower in plume affected regions like the Deccan Volcanic Province and Southern Granulite Terrane. Even though a common explanation does not appear currently feasible, our observations reaffirm deep low velocity layers in the bottom part of the upper mantle and add to the list of regions that show strong presence of such layers above the 410 km discontinuity.

Evolution of relative density and shear wave velocity in non-compacted embankment layers: Geological long-term monitoring

This study proposes a novel method for assessing the evolution of relative density and shear wave velocity that vary with depth and effective stress in non-compacted embankment layers. Embedded soil stiffness measurement devices were used to monitor the shear waves at each stage of filling at the test site, and comprehensive laboratory compaction tests were conducted using a floating ring oedometer cell to reproduce real field conditions with minimal friction. Assuming a constant soil unit weight γ with 7% water content, the effective stress σ’ is proportional to depth z (i.e., σ’ = γ·z). Field test results were compared with the shear wave velocity relationships determined in laboratory tests for four samples of differing relative density (30%, 50%, 70%, and 90%), indicating that the relative density at the bottom of the embankment varied between 15% and 48%. However, the constant soil unit weight applied in this study can underestimate the relative density of the embankment, causing a prediction error if the self-weight compaction of the embankment is not minute. Therefore, this study provides guidelines based on a physics-inspired and data-based approach and anticipates the relative density and shear wave velocity analyzed in the context of depth in non-compacted embankment layers. The physics-based data analyses suggested in this study can be used in first-order estimations to assess the relative density and shear wave velocity evolution in non-compacted embankment layers.

Investigation into the nocturnal ozone in a typical industrial city in North China Plain, China

Ozone (O3) concentrations usually peak at midday by photochemical reactions and gradually decline after sunset due to chemical destruction and dry deposition. However, an increase in the frequency of elevated nocturnal ozone enhancement (NOE) and high nocturnal ozone value (HNOV) has been frequently observed in urban areas of eastern China, but the reasons are not well understood. In this study, taking a typical industrial city, ZiBo as a case study, we analyzed the trends, characteristics, and causes of the NOE and HNOV events in historical years by combining observations and model simulations. During the warm season (April–September) of 2017–2023, HNOV events are accompanied by low humidity, high temperature, large friction velocity, and a high boundary layer (52 days in total), whereas NOE events coincide with increases in humidity, wind speed, friction velocity, and boundary layer height (141 days in total). During the HNOV and NOE events, the nighttime average concentrations of Ox were 77 ± 7 and 12 ± 6 μg m−3 higher than the non-nocturnal O3 period, indicating enhanced atmospheric oxidizing capacity during nighttime. The modeling results indicate that both the HNOV and NOE events were mainly driven by vertical mixing and regional transport. We selected a typical period with high O3 pollution and frequent NOE and HNOV events to conduct the modeling study. Three typical nocturnal O3 events are identified: Case I was mainly driven by horizontal transport; while in the two subsequent cases, the vertical transport contribution was 80 μg m−3 h−1 (20:00 LT on June 21, 2021) and 35 μg m−3 h−1 (02:00 LT on June 26, 2021), respectively. Our study reveals that the O3 pollution in industrial cities has been extending to nighttime, primarily attributed to vertical mixing and horizontal transport within the boundary layer. This highlights the critical role of implementing regional joint control action to reduce primary emissions and eliminate residual ozone.

Small-time global approximate controllability for incompressible MHD with coupled Navier slip boundary conditions

We study the small-time global approximate controllability for incompressible magnetohydrodynamic (MHD) flows in smoothly bounded two- or three-dimensional domains. The controls act on arbitrary nonempty open portions of each connected boundary component, while linearly coupled Navier slip-with-friction conditions are imposed along the uncontrolled parts of the boundary. Some choices for the friction coefficients give rise to interacting velocity and magnetic field boundary layers. We obtain sufficient dissipation properties of these layers by a detailed analysis of the corresponding asymptotic expansions. For certain friction coefficients, or if the obtained controls are not compatible with the induction equation, an additional pressure-like term appears. We show that such a term does not exist for problems defined in planar simply-connected domains and various choices of Navier slip-with-friction boundary conditions.

Evidence of low velocity layers at the top and bottom of the Mantle Transition Zone (MTZ) below the Uttarakhand Himalaya, India

The Mantle Transition Zone (MTZ) beneath the Uttarakhand Himalaya has been modelled using Common Conversion Point (CCP) stacking and depth-migration of radial P-receiver functions. In the Uttarakhand Himalaya region, the depths of the 410-km discontinuity (d410) and the 660-km discontinuity (d660) are estimated to be approximately 406 ± 8 km and 659 ± 10 km, respectively. Additionally, the thickness of the mantle transition zone (MTZ) is modelled to be 255 ± 7 km. The average arrival times for d410 and d660 conversions are (44.47 ± 1.33) s and (71.08 ± 1.29) s, respectively, indicating an undisturbed slightly deeper d410 and a deformed noticeably deeper d660 in the area. The model identifies the characteristics of the d410 and d660 mantle discontinuities beneath the Lesser Himalayan region, revealing a thickening of the MTZ towards northeast, which could be due to gradual cooling or thickening of the Indian lithosphere towards its northern limit. We simulate a low-velocity layer (perhaps partially molten) above the d410 discontinuity at depths of 350 to 385 km, indicating the presence of a hydrated MTZ beneath the area. We also interpret a negative phase at d660 as a low-velocity layer between 590 and 640 km depths, which could be attributed to the accumulation of old subducted oceanic materials or increased water content at the bottom of the MTZ. Our results suggest the presence of residues from paleo-subducted lithospheric slabs in and below the mantle transition zone underlying the Uttarakhand Himalayas.

Variability of saltwater flow in the Hoburg Channel, Baltic Sea: in situ measurements vs NEMO modelling

A half-year long time series of the bottom layer velocity measured in situ in the Hoburg Channel displayed seven-day oscillations of the saltwater flow. The flow was characterized by alterations of surges with the increase of northward velocity to approximately 0.2–0.3 m/s and blockages when the northward velocity vanishes or becomes small negative. The measured time series of the northward velocity component was surprisingly highly correlated with the simulation by NEMO reanalysis at the correlation coefficient of 0.82 and the 95 % confidence limits of 0.76–0.86. The seven-day oscillations were accompanied by almost synchronous oscillations of the southeast component of the wind vector. It can be considered convincing evidence that the seven-day oscillations in the saltwater flow were caused by wind forcing.

A transcranial multiple waves suppression method for plane wave imaging based on Radon transform

Transcranial ultrasound imaging presents a significant challenge due to the intricate interplay between ultrasound waves and the heterogeneous human skull. The skull’s presence induces distortion, refraction, multiple scattering, and reflection of ultrasound signals, thereby complicating the acquisition of high-quality images. Extracting reflections from the entire waveform is crucial yet exceedingly challenging, as intracranial reflections are often obscured by strong amplitude direct waves and multiple scattering. In this paper, a multiple wave suppression method for ultrasound plane wave imaging is proposed to mitigate the impact of skull interference. Drawing upon prior research, we developed an enhanced high-resolution linear Radon transform using the maximum entropy principle and Bayesian method, facilitating wavefield separation. We detailed the process of wave field separation in the Radon domain through simulation of a model with a high velocity layer. When plane waves emitted at any steering angles, both multiple waves and first arrival waves manifested as distinct energy points. In the brain simulation, we contrasted the characteristic differences between skull reflection and brain-internal signal in Radon domain, and demonstrated that multiples suppression method reduces side and grating lobe levels by approximately 30 dB. Finally, we executed in vitro experiments using a monkey skull to separate weak intracranial reflection signals from strong skull reflections, enhancing the contrast-to-noise ratio by 85 % compared to conventional method using full waveform. This study deeply explores the effect of multiples on effective signal separation, addresses the complexity of wavefield separation, and verifies its efficacy through imaging, thereby significantly advancing ultrasound transcranial imaging techniques.

Assessing foundation characteristics at the war dam site, lake tana basin, Ethiopia: A geophysical and geotechnical perspective

An integrated geophysical and geotechnical study evaluated the foundation conditions at the War dam site in northwest Ethiopia. This investigation included the classification of rock quality, shallow seismic refraction, and magnetic approaches. The dam's location comprises quaternary soil deposits and rhyolite rock units that have undergone varied weathering and fracturing. The shallow seismic refraction method distinguishes three layers of p-wave velocities that are less than 1.5 km per second with a depth range of 2–6 m, 1.5–2.5 km per second at a depth range of 15–20 m, and 2.5–3.5 km per second ranging from 20 to 40 m, respectively. Magnetic data were used to identify lineaments, and the RQD value acquired from boreholes ranged from extremely poor to excellent. Lineaments were recognized using the tilt angle approach. The results of the permeability tests demonstrated that the rock mass that serves as the dam's foundation had characteristics that are resistant to low permeability. The maximum and minimum lugeon values obtained from the testing were 9Lu and 0.81Lu, respectively. There are weak zones at and below the surface of the dam site, according to the overall findings acquired from seismic refraction, magnetic, and discontinuity surveying. These results were obtained from monitoring the dam site. These significant structures are directed towards a SW-NE, NE-SW, NNW-SSE, and SSW-NNE orientation. The study assessed the geological suitability of a proposed dam site using seismic refraction and magnetic survey methods. Significant geological variations were observed, particularly in the right abutment and valley floor, indicating the need for targeted grouting. The findings suggest that while the site is generally suitable for dam construction, specific areas require further ground improvement to ensure stability.

Turbulence Analysis From Long-Exposure-Time Acquisitions With Interferometric Rayleigh Scattering

This study focuses on the analysis of long-exposure-time interferograms obtained with an Interferometric Rayleigh Scattering (IRS) set-up pointing at a high subsonic isothermal jet flow. The objectives are twofold: retrieve from seeding-free optical measurements the mean characteristics of this flow - in particular the mean velocity profile in the jet shear-layer - and determine higher order statistics for the flow velocity in the shear layer. The results are compared to those obtained on the same test bench by use of hot wire anemometry, and conclusions about the relevancy of the approach together with potential improvements are deduced therefrom.

Near-Wall Flow Measurements Using Frequency-Modulating Filtered Rayleigh Scattering (FM-FRS)

The frequency-modulating filtered Rayleigh scattering (FM-FRS) technique has been developed and applied for the boundary layer measurements. The FM-FRS technique effectively extracts Rayleigh scattering information from noisy low SNR signals caused by intense wall glare. The boundary layer velocity profiles measured by FM-FRS show excellent agreement with an independent pressure probe measurement and the law-of-the-wall, including approximately 100 μ m above the wall. This technique is desirable for the practical applications of the Rayleigh scattering technique for flow diagnostics to regions that were limited due to strong background and low signal-to-noise ratio.

Выбор сорбента для элиминации ионов железа из сточных и природных вод

Natural waters and wastewaters often contain heavy metals, e.g., iron. Iron ore mining contaminates groundwater with iron up to 30 maximal permissible concentrations (MPC) as this element gets washed out from rock and soil. Adsorption is the most effective and economically feasible method of additional purification of natural and wastewater from iron. Its efficiency depends on the type of adsorbent. The research objective was to select the most efficient sorption material to eliminate water from iron, as well as to establish the adsorption patterns for different sorbents, thus creating sustainable and effective purification. The study featured carbonaceous sorbent of the SKD-515 grade, mineral sorption materials with aluminosilicate of the AC grade, and silicate-based sorbent of the ODM-2F grade. The porous structure was studied by porometry methods while the surface image was obtained using scanning electron microscopy. Other indicators included equilibrium, kinetics, and dynamics of iron adsorption by various sorbents. The Freundlich and Langmuir equations made it possible to calculate the key adsorption parameters. The Gibbs energy values were obtained from the Langmuir equation and equaled 11.93–20.66 kJ/mol, which indicated the physical nature of the adsorption process. Under static conditions, the sorbents demonstrated a high adsorption capacity with respect to iron, depending on the structure, and could be arranged as AC > SKD-515 > ODM-2F. In SKD-515, iron adsorption occurred in micropores; in AC and ODM-2F, it took place in mesopores. The kinetics of iron extraction showed that the adsorption process was limited by external mass transfer. The research provided a new understanding of iron adsorption by materials of various structures. The conclusions were supported by scanning electron microscopy images. Initial concentration, flow velocity, and loading layer height were studied in dynamics, i.e., during continuous operation of the adsorption column. The system proved extremely effective and reached 99.0% Fe3+ extraction under the following conditions: flow rate = 1 L/min, loading column height = 0.15 m, column diameter = 0.05 m, initial concentration = 0.5 mg/L (5 MPC). The column performance was tested at an initial concentration of iron ions of 50 MPC, which simulated the wastewater treatment at industrial enterprises. This comprehensive study of iron adsorption from wastewater proved the efficiency of the mineral sorption materials with aluminosilicate of AC grade.

Comparative analysis of selected machine learning techniques for predicting the pull-off strength of the surface layer of eco-friendly concrete

With recent trends reducing the carbon footprint of concrete, more novel materials are designed. It's mostly done by replacing cement with admixtures that are wastes in industrial processes. There is a need to provide reliable and accurate models to estimate the properties of the material. In this case the selected ML algorithms such as ANN, RF and DT were used for estimating the pull-off strength of the surface layer of cement mortar containing granite powder, fly ash and ground granulated blast furnace slag. The focus was on the cement-sand ratio of 1:3, replacing up to 30 % of the binder. Ultrasonic pulse velocity and pull-off strength of the surface layer. The analyses were performed in comparative manner and proved the accuracy of the designed models. The error values (MAPE, NRMSE and MAE) of the most effective model is below 3,5 %, indicating an extremely high success rate in prediction. An R2 ratio of 0.9436 confirms the very good fit of the model. Parametric tests were performed and SHAP analysis gave a better understanding of the models. The main conclusion of the study is to identify the possibility of replacing destructive testing with non-destructive testing supported by machine learning and material information to determine the pull-off strength of the subsurface layer at a selected depth for cement mortars containing waste materials. A particular advantage of the presented approach is the possibility of reducing the time to determine selected desired material parameters and the amount of testing required compared to the traditional approach.

Evaluation of WRF Cloud Microphysics Schemes in Explicit Simulations of Tropical Cyclone ‘Fani’ Using Wind Profiler Radar and Multi-Satellite Data Products

Extremely severe cyclonic storm (ESCS) ‘Fani’ formed in the North Indian Ocean and crossed at Puri in Orissa State on the east coast of India on 03 May 2019. In this study, we examine the sensitivity of convection permitting WRF simulations (3 km) of ‘Fani’ to cloud microphysics (CMP) schemes using radar and multi-satellite data products. Five CMP schemes, namely Thompson, Goddard, WSM6, Morrison and Lin are tested in WRF. Results show that the changes in the CMP schemes primarily affect the simulated intensity and have lesser impact on the track predictions. Simulations with Thompson followed by Goddard produced the best predictions for both track and intensity estimates. Our analysis reveals significant variations in vertical motions associated with Fani across different CMP schemes; the WSM6, Goddard and Lin schemes produced relatively stronger vertical motions. The explicit WRF simulations could reproduce the wind profiler radar observed intense convective motions during the transit of Fani between 1 and 2 May 2019 at Gadanki station. Experiments with Thompson and Goddard schemes simulated the mean vertical velocities in lower, middle and upper layers in better agreement with radar data. The Lin, WSM6 and Goddard CMP predicted stronger updraft velocities (~ 0.35 m/s); Thompson produced moderate updraft velocities (~ 0.25 m/s) in the upper troposphere over a relatively wider area of high theta-e (385–390 K) indicating the simulation of a convectively stronger and warmer core compared to Morrison. Our analysis suggests that the differences in vertical motions in various CMP simulations are mainly due to the variations in the warming in simulations. It has been found that WSM6, Lin and Goddard produced a deeper core (up to 200 hPa) with a stronger diabatic heating of ~ 6° C followed by Thompson, which simulated a moderately deep core extending to ~ 250 hPa with moderate heating of ~ 5 °C whereas Morrison produced a relatively weak core with a heating of ~ 4 °C limited to 300 hPa. The stronger simulated diabatic heating in Lin, WSM6 and Goddard produces stronger inflow, moisture convergence in the lower levels and stronger outflow and divergence in the upper levels leading to stronger convection in the core region in these cases. The Lin, WSM6 and Goddard mixed phase schemes with more solid hydrometeors simulated stronger radar reflectivities, and stronger eyewalls, due to more latent heat release leading to the development of a strong warm core in the upper troposphere and thus a stronger TC.

Experimental and numerical study of structural parameters on the heat transfer performance of submerged cooling system

Immersion direct contact cooling effectively transfers heat from electronic components to a cooling solution without additional thermal resistance, due to its high energy density, low power consumption, system simplicity, and integrated thermal management for electronic devices. Current scholarly research on immersed structures predominantly focuses on surface temperature effects, with a scant investigation into internal flow and temperature field distributions concerning boundary layers. This study addresses structural optimization in immersion cooling systems, employing experimental and simulation methods to elucidate the thermal mechanisms by which structural optimization impacts the performance of chip immersion cooling systems. The research examines the impact of panel spacing and liquid level height on the thickness of velocity and thermal boundary layers, as well as the combined effects of natural and forced convection under three distinct cooling modes. Analysis reveals that heat pipe immersion cooling can reduce the heat source junction temperature to 40.7 °C under a 60 W power dissipation, a 47.2 % decrease from the bare heat source temperature. Reducing panel spacing disrupts the thermal boundary, enhancing forced convection and lowering the junction temperature by up to 10.1 % (6.5 °C). As liquid level height increases, the junction temperature initially decreases and then rises, with an optimal height of 175 mm for the best overall heat transfer effect. At low flow velocities (0.04 m/s), the vertical buoyancy-induced flow velocity at the heat source surface (24.2 × 10-6 m/s) exceeds the horizontal forced convection velocity (0.78 × 10-6 m/s), indicating that buoyancy changes due to density differences are significant and must be considered.

Comprehensive evaluation of the influence of PEM water electrolyzers structure on mass transfer performance based on entropy weight method

The proton exchange membrane water electrolyzer (PEMWE) has broad prospects in hydrogen production due to its green and efficient advantages. This paper comprehensively analyzes the performance and water-gas transport characteristics of PEMWE with different cell structures, in which polarization curves, flow velocity distribution, oxygen concentration, temperature, liquid water saturation, and pressure are investigated. Simultaneously, the study explores the effects of variations in inlet velocity, inlet temperature, porosity, and thickness of the anode porous transport layer (APTL) on the four flow fields. Finally, the technique for order preference by similarity to ideal solution (TOPSIS) based on entropy weight method is employed for a comprehensive evaluation of the flow fields. The results indicate that, compared to parallel flow field (PFF), sinusoidal wave flow field (SWFF), intercepted flow field (ICFF), and single-serpentine flow field (SSFF) exhibit stronger exhaust capabilities, with temperature uniformity increasing by 83.65 %, 59.24 %, and 70.15 %, respectively. However, the longer flow channel of SSFF results in a high pressure drop and lower liquid water saturation. An increase in inlet velocity leads to a decrease in temperature, causing an increase in voltage, as higher temperatures reduce activation and ohmic overpotentials. Additionally, an increase in the porosity and thickness of APTL deteriorates the polarization performance of PEMWE. The research results of this study can provide valuable assistance for the future design of PEMWE.