Position Of Front Research Articles

Inversely estimating flow characteristics of geopolymer paste based on the MPH-I calculations

A method for inversely predicting the flow properties of Bingham fluid, i.e., yield stress and plastic viscosity of the geopolymer paste, from a simple dam-break experiment was developed based on the MPH-I ((Moving Particle Hydrodynamics for Incompressible flows) calculations. In the decommissioning of Fukushima-Daiichi nuclear power plant, geopolymer is one of the candidate materials for stabilizing the fuel debris and for sealing the PCV (Primary Containment Vessel), where it is important to predict and control the fluidity of the paste of the material. Therefore, the flow property is to be confirmed just before practically pouring the paste. In the inverse estimation, the MPH-I calculations are used only in the preparation phase to obtain the base curve of the front position history with respect to the various yield stresses. Then, both the yield stress and plastic viscosity are estimated using the base curve with an assumption that the inertial force is negligible. Since no additional calculation is needed in the prediction phase, it is applicable for the checking before the pouring. In this study, the methodology was tested against the geopolymer pastes with adding various amount of silica sand for enlarging viscosity. It was confirmed that the front position history obtained from the experiment was well reproduced by the predicted flow properties. This indicates that the Bingham parameters were inversely estimated well.

Impact of the ITF Relationship and the Onset of Rainfall on Precipitation in the Republic of Guinea

Republic of Guinea is one of the West African countries which share form a border with the southern. The rainfall onset in this country is one of the major problems that the farmers face. For it, we determined with more precision, the rainy season onset in eight synoptic stations in Republic of Guinea: Boke, Conakry, Faranah, Kankan, Koundara, Labe, Mamou and NZerekore. Then, we studied the InterTropical Front (ITF) position compared to each station at the onset date. This work better analyses the atmospheric dynamics leading to rainfall particularity. We used the daily rainfall data provided by the National Meteorological Service of Guinea for (1991-2020) years and the dekadal (10-day) ITF position data produced by the National Oceanic and Atmospheric Administration (NOAA) for (1990-2021) years. Using these daily rain of the eight stations and the ITF data, we calculated, the dekadal, monthly and annual rain amount, then we established a relation between the ITF position and the precipitation for each station. Results obtained show that the rainy season begins on May 18th, April 20th, May 4th, May 14th, June 8th, May 12th, April 28th and March 20th in Boké, Conakry, Faranah, Kankan, Koundara, Labe, Mamou and NZerekore regions, respectively. Compared to these dates, the ITF is located 2247.77 km north of Boke, 2136.13 km north of Conakry, 2121.24 km north of Faranah, 2136.13 km north of Kankan, 2236.61 km north of Koundara, 2247.77 km north of Labe, 2236.61 km north of Mamou and 2136.13 km north of NZerekore. The good correlation is obtained between the ITF position and the monthly precipitations for eight regions. This study will allow farmers to know with more precision the rainfall onset in Republic of Guinea.

Tensile Fracture Initiation and Propagation of Granite and Gneiss at Wedge Splitting Tests: Part 2—Fracturing Studies Based on Digital Image Correlation and Thin Section Analysis

AbstractThe crack development in quasi-brittle granite and brittle gneiss under mode I loading condition was monitored using digital image correlation (DIC) technique during wedge splitting tests. The cracking behavior was studied on granite specimens that were split in one material direction, perpendicular to the rift plane, and gneiss specimens that were split in three different material directions, parallel and perpendicular to the foliation (along and across a lineation). The granite specimens had a saw cut 5 mm-wide notch and a blunt round notch in form of a 32 mm borehole. The gneiss specimens had a saw cut notch. The results from the DIC measurements revealed a meandering and branching crack path for the granite, whereas a smoother crack path for the gneiss with almost no branching. This behavior was confirmed by microscopy images from thin sections taken from specimens after testing. The thin sections showed that the fractures were prone to propagate across grains in the more coarse-grained granite than in the fine-grained gneiss, where the fractures propagated almost entirely along grain boundaries. The crack initiation occurred mainly in the corner of the saw cut notches and centrally in the round notch. However, the initiation locations in the granite were affected by the medium- to coarse-grained microstructure with grains preventing initiation and propagation which yielded displaced positions out from the ideal ones with respect to the highest stress in some cases. The crack opening displacement was determined along the crack path from the DIC measurements at 12 stages on each specimen of the advancing crack during the splitting progress. The critical crack opening displacement and length of the fracture process zone were assessed and the crack front position yielding the crack length along the tests was determined. The results showed a critical crack length when the deformations in the ligament (also called plastic hinge) affected the cracking process. The average crack velocity in gneiss during the test was more than twice as high as in the granite. This is attributed to a combined effect of the higher brittleness in the gneiss and the effect of a too large elastic energy in the specimen and test setup in relation to the dissipated fracture energy which made the initial crack propagation in the gneiss specimens nearly unstable. The strain energy release rate was calculated along the crack propagation and showed a lower value when the crack lengths were less than 40–60 mm. The calculation of the strain energy release rate was made on crack length measurements from DIC results. The results from the investigation were discussed in relation to the few other similar results found in the literature. The findings give an insight and understanding of the cracking process via both qualitative and quantitative results. Several used methods were novel or not used together in a single study as in this one.

Moisture Distribution and Ice Front Identification in Freezing Soil Using an Optimized Circular Capacitance Sensor.

As the interface between frozen and unfrozen soil, the ice front is not only a spatial location concept, but also a potentially dangerous interface where the mechanical properties of soil could change abruptly. Accurately identifying its spatial position is essential for the safe and efficient execution of large-scale frozen soil engineering projects. Electrical capacitance tomography (ECT) is a promising method for the visualization of frozen soil due to its non-invasive nature, low cast, and rapid response. This paper presents the design and optimization of a mobile circular capacitance sensor (MCCS). The MCCS was used to measure frozen soil samples along the depth direction to obtain moisture distribution and three-dimensional images of the ice front. Finally, the experimental results were compared with the simulation results from COMSOL Multiphysics to analyze the deviations. It was found that the fuzzy optimization design based on multi-criteria orthogonal experiments makes the MCCS meet various performance requirements. The average permittivity distribution was proposed to reflect moisture distribution along the depth direction and showed good correlation. Three-dimensional reconstructed images could provide the precise position of the ice front. The simulation results indicate that the MCCS has a low deviation margin in identifying the position of the ice front.

Frozen autocatalytic fronts in a radial flow

Autocatalytic reaction-diffusion fronts are localized reaction zones propagating at a constant speed with a constant width. We show both theoretically and experimentally that, if the reactant Y of the autocatalytic reaction is injected radially at a constant flow rate in a sea of the autocatalytic species X, a stationary front can be maintained at a fixed position that scales linearly with the flow rate. When this reaction front is about to reach a stationary state, a second outward traveling front emerges to adapt the outer concentration of the autocatalytic species to the stoichiometry ratio between X and Y. Simple analytical solutions to the reaction-diffusion-advection equations governing the dynamics are computed for both fronts. The analytical predictions for the stationary front position and moving front dynamics as a function of injection flow rate, reactant concentration, and gap of the quasi-two-dimensional reactor agree well with experimental results obtained with the autocatalytic chlorite-tetrathionate reaction. Published by the American Physical Society 2024

The Importance of Solving Subglaciar Hydrology in Modeling Glacier Retreat: A Case Study of Hansbreen, Svalbard

Arctic tidewater glaciers are retreating, serving as key indicators of global warming. This study aims to assess how subglacial hydrology affects glacier front retreat by comparing two glacier–fjord models of the Hansbreen glacier: one incorporating a detailed subglacial hydrology model and another simplifying the subglacial discharge to a single channel centered in the flow line. We first validate the subglacial hydrology model by comparing its discharge channels with observations of plume activity. Simulations conducted from April to December 2010 revealed that the glacier front position aligns more closely with the observations in the coupled model than in the simplified version. Furthermore, the mass loss due to calving and submarine melting is greater in the coupled model, with the calving mass loss reaching 6 Mt by the end of the simulation compared to 4 Mt in the simplified model. These findings highlight the critical role of subglacial hydrology in predicting glacier dynamics and emphasize the importance of detailed modeling in understanding the responses of Arctic tidewater glaciers to climate change.

A New Model for Steam Cavity Expansion in Vertical Wells of Heavy Oil Reservoirs

Summary Steamflooding is one of the most effective and mature methods for developing heavy oil. However, existing research has not fully explained the phenomena of steam overburden and heat loss, particularly overlooking the steam velocity loss at the steam cavity front. Therefore, the condensation heat transfer coefficient (CHTC) was introduced to describe the decrease in steam velocity at the steam cavity front. A steam cavity front expansion model, considering shape factor, pseudofluidity ratio, and CHTC ratio (CHTCR), was established and validated by using mine monitoring data. The research results show that the steam cavity of the revised model is in the shape of a “funnel,” and the steam overburden phenomenon is more pronounced at the steam cavity front. Through comparison with the field data of the P6 and P612-1 well groups, it is observed that the average displacement error of the steam cavity front of the two is only 6.58%. As steam injection progresses, the steam cavity is more degraded, and the steam overburden phenomenon is more intensified compared with the initial stage. Taking into account the phenomenon of kinetic energy loss, a higher formation heat loss rate is calculated during the middle and late stages of steam injection in the modified model. The pressure gradient at the steam cavity front is analyzed to determine an optimal displacement radius of 40 m for vertical well steamflooding in heavy oil reservoirs. When parameters such as shape factor, steam injection rate, and CHTC are increased, the development shape of the steam cavity is more ideal, but the convexity of the steam cavity front is increasingly pronounced as the pseudomobility ratio increases. The CHTC was incorporated into the steam cavity expansion model, elucidating the steam overburden phenomenon and advancing the theoretical understanding of steamflooding. By improving the existing model, the analytical formula can be used to rapidly predict the position of the steam cavity front and estimate of the steam-saturated zone, even in the absence of some field data or numerical models. Practical guidance for optimizing steam injection strategies is provided, with the potential to significantly enhance the recovery of heavy oil reservoirs.

X-ray phase-contrast imaging of strong shocks on OMEGA EP.

The ongoing improvement in laser technology and target fabrication is opening new possibilities for diagnostic development. An example is x-ray phase-contrast imaging (XPCI), which serves as an advanced x-ray imaging diagnostic in laser-driven experiments. In this work, we present the results of the XPCI platform that was developed at the OMEGA EP Laser-Facility to study multi-Mbar single and double shocks produced using a kilojoule laser driver. Two-dimensional radiation-hydrodynamic simulations agree well with the shock progression and the spherical curvature of the shock fronts. It is demonstrated that XPCI is an excellent method to determine with high accuracy the front position of a trailing shock wave propagating through an expanding CH plasma that was heated by a precursor Mbar shock wave. The interaction between the rarefaction wave and the shock wave results in a clear signature in the radiograph that is well reproduced by radiation-hydrodynamic simulations.

The Parameterized Oceanic Front-Guided PIX2PIX Model: A Limited Data-Driven Approach to Oceanic Front Sound Speed Reconstruction

In response to the demand for high-precision acoustic support under the condition of limited data, this study utilized high-resolution reanalysis data and in situ observation data to extract the Kuroshio Extension Front (KEF) section through front-line identification methods. By combining the parameterized oceanic front model and the statistical features of big data, the parameterized oceanic front was reconstructed. A proxy dataset was generated using the Latin hypercube sampling method, and the sound speed reconstruction model based on the PIX2PIX model was trained and validated using single sound speed profiles at different positions of the oceanic front, combined with the parameterized oceanic front model. The experimental results show that the proposed sound speed reconstruction model can significantly improve the reconstruction accuracy by introducing the parameterized front model as an additional input, especially in the shallow-water area. The mean absolute error (MAE) of the full-depth sound speed reconstruction for this model is 0.63~0.95 m·s−1, and the structural similarity index (SSIM) is 0.76~0.78. The MAE of the sound speed section within a 1000 m depth is reduced by 6.50~37.62%, reaching 1.95~3.31 m·s−1. In addition, the acoustic support capabilities and generalization of the model were verified through ray tracing models and in situ data. This study contributes to advancing high-precision acoustic support in data-limited oceanic environments, laying a solid groundwork for future innovations in marine acoustics.

Pressure Analysis of Vertical-Wells with the Hydraulic Fracturing Assisted Water Injection in Low-Permeability Hydrogen and Carbon Reservoirs.

Enhancing the energy of hydrogen and carbon reservoirs is crucial for the extraction of these resources. Currently, the conventional water-flooding technology faces challenges in replenishing the energy of hydrogen and carbon reservoirs due to the low injection rates caused by their low-permeability properties. To address this, hydraulic fracturing-assisted water injection technology has been employed to enhance the energy of these reservoirs. However, there has been a lack of research on pressure analysis for vertical wells using this technology. Existing studies on pressure analysis are not applicable to this scenario due to the unique behavior of dynamic fracture propagation. In this article, we present a pressure analysis model for vertical wells with hydraulic fracturing-assisted water injection in low-permeability hydrogen and carbon reservoirs, considering dynamic fracture propagation. The model examines the effects of key parameters on the pressure and fluid flow fronts, and it is applied to field wells for validation. Our findings include the following: the typical pressure response curve for vertical wells with hydraulic fracturing-assisted water injection in low-permeability hydrogen and carbon reservoirs can be divided into six stages: dynamic fracture propagation region, linear flow region in hydrogen and carbon reservoirs, bilinear flow region, radial flow region, transition flow region, and boundary control flow region. The production rate affects the pressure and pressure derivatives in the later stages of the process. However, reservoir permeability influences all flow regions, causing the pressure and pressure derivative curves to shift left with increasing permeability. Increases in both the injection rate and production rate result in a rise in the position of fluid fronts. The impact of permeability on fluid fronts is more significant in the early stages than in later stages. This work is of great significance for the development of low-permeability hydrogen and carbon reservoirs, providing a deeper understanding of the pressure dynamics involved in hydraulic fracturing-assisted water injection.

Characteristics of dynamic thickness change across diverse outlet glacier geometries and basal conditions

Abstract Outlet glaciers in Greenland are undergoing retreat and diffusive thinning in response to external forcings, but the rates and magnitudes of these responses differ from glacier to glacier for unclear reasons. We test how changes in ice overburden pressure and basal lubrication affect diffusive thinning rates and their spatial patterns by conducting numerical experiments over various idealized Greenland-like glacier domains. We find that ~10 km frontal retreat over a decade can produce sustained thinning rates as large as 16 m a−1 due to ice overburden pressure changes, at outlet glaciers with high basal drag (>60 kPa) and lateral resistive stress (>70 kPa). Localized basal lubrication perturbations induce upstream thinning and downstream thickening up to 12 m a−1; the duration of the lubrication forcing generally has a greater effect than its intensity on induced thickness changes. Lastly, episodic grounding line retreats over a rough bed produce a stepped time series of thinning broadly consistent with observations of dynamic elevation change on multiple Greenland glaciers. Our findings highlight the critical role of the total grounding zone – not ice front position – through the resistive stress change in relation to total glacier thinning.

Enhancing ignition stability in an annular combustor using a pre-chamber ignition system

The traditional method using spark electrode ignition in annular combustors lacks safety due to its long ignition delay and deficiencies in reliability and repeatability. The present work investigates the ignition characteristics of a premixed annular combustor using pre-chamber combustion (PCC) as an ignition source. The ignition process of the annular combustor is studied experimentally with PCC and is compared to the one with the traditional spark electrode ignition under the same equivalence ratio and bulk velocities. The ignition process is recorded using a high-speed camera. The two-dimensional time-resolved Mie scattering technique is employed to determine the flame front position in the annular combustor. It was found that the jet issued from PCC generates hot radicals associated with strong turbulence, exhibiting distributed ignition sites along the jet trajectory inside the annular combustor. Introducing PCC to the annular combustor increases the ignition probability and burning rate, as well as reduces the light-round time by about 24 % compared to the spark electrode at a thermal power of 18.6 kW. Moreover, the experimental results indicate that flame propagation in the annular combustor is significantly influenced by the PCC operating parameters. In contrast, combustion within the PCC is less affected by the local flow structure in the annular combustor, making the PCC a favourable solution for various operating conditions. Additionally, a slightly rich mixture in the PCC increases the burning rate, whereas a very rich mixture decreases the burning rate.

General integration method for system configuration of organic Rankine cycle based on stage-wise concept

Organic Rankine Cycle (ORC) integrated systems with heat sources consist of heat exchange processes and thermodynamic power conversion processes. Fully exploring feasible system configuration while considering fluid selection is crucial for enhancing ORC power generation and balancing economic costs. This study innovatively proposes a theoretical framework that decomposes the Rankine cycle into basic thermodynamic processes. The design of system configuration is regarded as the adjustment of the series-parallel relationships of these basic processes, aiming to achieve simultaneous optimization of the cycle structure and the HEN structure, thereby greatly expanded the search space for feasible ORC system configurations. The optimization problem is solved using a bi-level strategy, The outer layer determines the number of thermal power conversion components, operating parameters, and working fluid selection, then provides the associated stream information to the inner layer for optimizing the heat exchange scheme. Applying this method to two different case studies from the literature validated its effectiveness in optimizing scenarios with single and complex heat sources. The Pareto frontier obtained under the conditions of Case I indicates that the investment cost can be reduced by $33.04 k/yr while maintaining the same net power output. In exchange for an increase of $1.51 k/yr in investment cost, the maximum net power output can be improved by 124.74 kW. Under the conditions of Case II, the maximum net output power can increase by 9.71 %–52.5 %, and the Pareto frontier featuring outputs exceeding 50 kW is provided. By analyzing the relative positions of literature schemes and Pareto front within the solution space, the impact of system configuration improvements on the objective functions is explained. These results confirm the effectiveness of the proposed approach for designing optimal ORC energy recovery systems for heat sources. This contribution advances optimization methods for similar closed cycle configurations, which is significant for advancing the utilization of waste heat and addressing sustainability challenges.

Three-dimensional Thermodynamic Structures of the Intracluster Medium across Edges in the X-Ray Surface Brightness of Massive, Bright, Dynamically Active Galaxy Clusters

We present a detailed study of three-dimensional (3D) thermodynamic structures of the intracluster medium (ICM) across edges in the X-ray surface brightness of four massive, bright, dynamically active galaxy clusters (A3667, A2319, A520, and A2146), with the Chandra X-ray Observatory. Based on a forward modeling approach developed in previous work, we extend this approach with more generalized ICM density and temperature profiles, allowing us to apply uniformly to the observed X-ray surface brightness profiles to detect edges and measure the 3D thermodynamic profiles of the ICM simultaneously and self-consistently. With the forward modeling analysis, we find, in agreement with previous works, that the obtained 3D thermodynamic structures of the ICM across the edges in A3667 and A2319 are consistent with the characteristics of cold fronts, whereas those in A520 and A2146 are consistent with the nature of shock fronts. We find that the azimuthal distribution of the pressure ratio at the cold front in A3667 shows a different trend from that in A2319. For the shock fronts in A520 and A2146, the observed 3D temperature profiles of the ICM indicate that the temperature is highest at the position of the shock front. In the case of the sector exhibiting M=2.4 in A520, the ICM temperature appears isothermal with a temperature of ∼10 keV until ∼300 kpc away from the shock front in the post-shock region, being consistent with the hypothesis of the instant-equilibration model for shock heating.

Ecological patterns of benthic foraminiferal communities driven by seasonal and spatial environmental gradients in an Arctic fjord

AbstractArctic fjords, being transitional areas between glacier‐covered land and the ocean, are characterized by strong environmental gradients. The seasonal melting of glaciers generates strong turbidity and primary production antagonist gradients, which can affect benthic habitats. Two sampling campaigns were carried out in Kongsfjorden (Svalbard, Arctic Ocean) in May and August 2021 to investigate seasonal changes in benthic foraminifera spatial distribution and ecosystem functioning along a longitudinal transect of 10 km from the Kronebreen tidewater glacier front. Concurrently, organic matter quantity and biochemical composition, sediment grain size, and physical parameters of the water masses were investigated as possible driving factors of benthic ecosystem responses. In a previous study, three statistically determined foraminiferal biozonations (glacier proximal, medial, and distal) were observed on the basis of their species content within the closest 10 km from the glacier front, presenting similar assemblages in both seasons. Our results indicate that foraminiferal distribution at the local scale is mainly driven by physical and geochemical gradients induced by melting waters and sediment discharges from the tidewater glacier occurring during summer. Due to the climate change, the melting season is expected to last longer and increasing global temperature will much probably accelerate the melting processes. Our findings strongly support the use of foraminifera as bioindicators to monitor the effects of ongoing climate change on the benthic ecosystems of Arctic fjords and, accessorily, as proxies for reconstructing glacier front positions in the recent past.

Local Vorticity and Flow Heat Transfer Mechanism Analysis in Micro-Cylinder-Groups Based on Field Synergy Principle

In this paper, local vorticity distribution in micro-cylinder-groups was investigated by finite volume method and the mechanism of local heat transfer around cylinders was explored by using field synergy analysis. The vorticity distribution and local heat transfer performance are different at different positions around the cylinders. In front of micro cylinders, the vorticity has a positive correlation with heat transfer coefficient, and the average field synergy angle is close to 65° with good synergy effect. The vertical and spanwise vortices are generated on the top and side positions, respectively, which are negatively correlated with the heat transfer coefficient. Affected by the end-wall and boundary layer, the vorticity behind the micro cylinders varies at different heights and the vertical vorticity appears near the root position. The vertical and spanwise vortices account for a similar proportion near the upper part of the micro cylinders, and both of them are positively correlated with heat transfer coefficient. Due to the stagnation effect, the heat transfer coefficient in the rear position has been weakened by about 40% compared with the front position.

The impact of predators and vegetation on shoaling in wild zebrafish.

In their natural habitats, animals experience multiple ecological factors and regulate their social responses accordingly. To unravel the impact of two ecological factors on the immediate behavioural response of groups, we conducted experiments on wild zebrafish shoals in arenas with vegetation, predator cues, and both factors simultaneously or neither (control treatments). Analysis of 297 trials revealed that while shoals formed significantly larger subgroups in the presence of predator cues, their subgroup size was comparable to control treatments when they faced predator cues and vegetation. Shoals were highly polarized in open arenas, in the absence of either ecological factors and in the presence of predator cues (with/without vegetation). The presence of vegetation alone, however, significantly reduced shoal polarization. Furthermore, food intake was significantly reduced when predator cues and/or vegetation were present. Tracking individuals revealed that (i) individuals within shoals receiving predator cues had a significantly higher probability to continue being in a group compared with control treatments and (ii) individuals occupying the front positions deviated less from their median position within a shoal as compared with other individuals regardless of predator cues. The adaptability of animals depends on behavioural responses to changing environments, making this study significant in the context of environmental changes.

High-resolution UK’37 sea surface temperature reconstruction in the southwestern Atlantic Ocean during the Holocene

Modern sea surface temperatures (SST) were assessed using the alkenone calibration index (UK′37; SST-UK′37) values from twenty-one core-top sediment samples collected along the Southwestern Atlantic Ocean and validated by comparison with satellite-derived SSTs. The SST-UK′37 values revealed an annual signal between 28 and 30°S and a winter signal (83% of the region samples) between 30 and 34° S, with deviations falling within the UK′37 calibration error range. The paleotemperature (SST-UK′37) reconstruction through the Holocene was performed using two high-resolution marine sediment cores from 33 to 34°S latitude band. Millennial-scale variations dominate most of the SST-UK′37 results with changes up to ∼6 °C. Considering the modern ocean circulation dynamics, the SST-UK’37 in our records likely stems from the combined influence of the Subtropical Shelf Front (STSF) position and the interaction between the warm, salty, and nutrient-poor Subtropical Shelf Water (STSW) and the cold, fresh, and nutrient-rich Subantarctic Shelf Water (SASW). Our SST-UK’37 results also suggest that the northernmost position limit of the STSF reached around 33°S during the mid-to-late Holocene, while after ∼5500 cal yr BP the Plata Plume Water became the dominant influence on the regional SST-UK’37 signal. Spectral analyses revealed statistically significant oscillations of ∼8600 and ∼ 2250 years in record MDBT 557, and ∼ 5300 and ∼ 2600 years in record MDBT 561 which suggests the influence of Southern Westerly Winds (SWW) on the SST-UK’37, and therefore, on the STSF dynamic through the Holocene.

Influence of Voltage Rising Time on the Characteristics of a Pulsed Discharge in Air in Contact with Water: Experimental and 2D Fluid Simulation Study

In the context of plasma–liquid interactions, the phase of discharge ignition is of great importance as it may influence the properties of the produced plasma. Herein, we investigated the influence of voltage rising time (τrise) on discharge ignition in air as well as on discharge propagation on the surface of water. Experimentally, τrise was adjusted to 0.1, 0.4, 0.6, and 0.8 kV/ns using a nanosecond high-voltage pulser, and discharges were characterized using voltage/current probes and an ICCD camera. Faster ignition, higher breakdown voltage, and greater discharge current (peak value) were observed at higher τrise. ICCD images revealed that higher τrise also promoted the formation of more filaments, with increased radial propagation over the water surface. To further understand these discharges, a previously developed 2D fluid model was used to simulate discharge ignition and propagation under various τrise conditions. The simulation provided the spatiotemporal evolution of the E-field, electron density, and surface charge density. The trend of the simulated position of the ionization front is similar to that observed experimentally. Furthermore, rapid vertical propagation (<1 ns) of the discharge towards the liquid surface was observed. As τrise increased, the velocity of discharge propagation towards the liquid increased. Higher τrise values also led to more charges in the ionization front propagating at the water surface. The discharge ceased to propagate when the charge number in the ionization front reached 0.5 × 108 charges, irrespective of the τrise value.

Evaluation of melting front kinetics in cylindrical phase change materials module using infrared thermography and digital imaging

An experimental study examined buoyancy-driven convection in the unconstrained melting of PCM within a cylindrical module. Melting progress and PCM fraction were analyzed using IRT and digital imaging. Initial symmetric melting led to accelerated phase change at the bottom and a rippled PCM surface. Thermal stratification in the lower module was evident, with molten liquid displacing colder fluid. Observations underestimated bottom PCM waviness and melting. As the melt zone expanded, buoyancy-driven convection intensified, speeding up melting at the top while the bottom relied more on conduction. The study details transient front positions, temperature profiles, solid PCM amounts, and melting times. Unstable fluid layers near the bottom caused waviness due to chaotic fluctuations. Nucleation rates critically impacted PCM crystallization kinetics and properties.