Low Flux Research Articles

Fabrication of composite ceramic polymeric membranes for agricultural wastewater treatment

Humans have contaminated water supplies with harmful compounds, including different heavy metals. Heavy metals can interfere with human and animal vital organs and metabolic processes. They are also persistent and bioaccumulative. So, this study aimed to fabricate composite ceramic membranes (CCM) from Egyptian raw substances to eliminate heavy metals from agricultural wastewater. A ceramic supporting (CS) filter constructed from ball clay, kaolin, feldspar, and quartz using corn starch flour as a pore-developing agent. CS fired at two different temperatures and soaking times. Then, a thin polyamide 6 (PA6) coating was dip-coated over the upper layer of the support membranes. The raw materials and prepared CCM were subjected to characterization and applied to treat agricultural wastewater from the Kitchener drain in Kafr El-Sheikh Governorate, Egypt. The results showed that the CCM (M2) (membrane sintered at 1000 °C/30 min soaking time and modified with PA6) had a higher pure water permeability of 558.5 L h−1 m−2 than the membrane (M4) (membrane sintered at 1100 °C/180 min soaking time and modified with PA6). The study examined how effectively the membranes removed toxic substances from wastewater. The findings exhibited an excellent removal of > 80% and up to 97.02%, > 80% and up to 99.97% of the heavy metals, and optimum fluxes of 341.07 and 276.35 L h−1 m−2 were achieved in the cases of M2 and M4, respectively. Furthermore, with a low flux decline ratio and a high permeate recovery of 92.3% for wastewater, the modified M4 membrane demonstrated remarkable antifouling capabilities.

Improvement of MoS2 film quality using sputtering processes controlling particle- and energy-flux followed by sulfur-vapor annealing

Abstract Molybdenum disulfide (MoS2) deposited by sputtering holds promise for applications in areas such as three-dimensional (3D)-stacked field-effect transistors (FETs) and human-interface devices. The quality of the MoS2 film is enhanced by maintaining a low particle flux with sufficient energy flux during sputtering. Furthermore, the sulfur defects in the MoS2 films were suppressed by annealing in a sulfur-vapor atmosphere, leading to an improvement in the film quality. This technology has great potential for the development of high-performance FETs based on MoS2 channels using sputtering.

From data to insights: Upscaling riverine GHG fluxes in Germany with machine learning.

Global fluvial ecosystems are important sources of greenhouse gases (CO2, CH4, and N2O) to the atmosphere, but their estimates are plagued by uncertainties due to unaccounted spatio-temporal variabilities in the fluxes. In this study, we tested the potential of modeling these variabilities using several machine learning models (ML) and three different input datasets (remotely sensed vegetation indices, in-situ water quality, and a combination of both) from 20 headwater catchments in Germany that differ in catchment land use and stream size. We also upscaled fluvial GHG fluxes for Germany using the best ML model and explored the role of catchment land use on the GHG spatial-temporal trends. Model performance depended on the choice of ML model, input data and GHG type. Complex decision-tree-based models better predicted GHG concentrations and fluxes than other ML model types (r2=0.33 to 0.72). Our upscaled fluxes from catchment scale remotely sensed vegetation indices showed that total annual riverine CO2 equivalent fluxes from 2934 catchments in Germany ranged from 1.7 to 96.4kgm-2yr-1 (mean±SE: 23.2±0.001). The highest fluxes came from urban and intensively cropped catchments, while lower fluxes came from extensively cropped, forestry, and pasture-dominated catchments. Our study demonstrates that spatially and temporally resolved catchment vegetation indices from remotely sensed data in conjunction with machine learning models can be applied to upscale all three GHG concentrations and fluxes from diverse catchments, revealing important spatio-temporal trends associated with catchment land use.

Numerical study of turbulent flow boiling heat transfer in structured cooling channels using lattice Boltzmann method with advanced outlet boundary conditions

This study investigated the application of the lattice Boltzmann (LB) method to simulate turbulent flow boiling in structured cooling channels. The simulation used a central moment-based pseudopotential LB model with advanced characteristic boundary conditions to address numerical instabilities associated with turbulent multiphase flow. This approach ensures prolonged stability, facilitating the accurate modeling of complex flow boiling dynamics. The simulation results revealed that structured cooling channels considerably enhanced thermal performance, achieving a 27.3% increase in critical heat flux compared to flat channels. This improvement is induced by the fin structure of structured cooling channel, which makes heat distribution and promotes lower local wall heat flux compared with incident heat flux. Moreover, the simulations showed that fin structures manage bubble detachment more effectively, thereby enhancing heat transfer during the phase-change process. The study suggests that advanced outlet boundary conditions are crucial in stabilizing simulations for fin-structured channels, and the findings provide significant insights into heat dissipation mechanisms in high-heat-flux applications.

Experimental Study on Liquid Jet Trajectory in Cross Flow of Swirling Air at Elevated Pressure Condition

Abstract Motivated by fuel atomization applications in gas turbine combustors, this paper presents an experimental examination of liquid jet trajectory and spray dynamics in crossflow of swirling air, at elevated pressure conditions. The study was conducted within an annular passage and was focused on momentum flux ratio and swirl number as the main parameters. The momentum flux ratio was varied from 2 to 25 through incremental adjustments to the liquid injection velocity and the swirl number values of 0.42 and 0.74 were used, representing typical gas turbine fuel atomization conditions. The jet trajectories were captured by imaging the three-dimensional (3D) helical path traced by the liquid jet using two mutually perpendicular optical windows. Radial penetration was quantified by solving the equations of a helix. The key findings revealed that radial penetration of the liquid jet is larger for higher momentum flux ratios and is influenced by the helical arc length. Notably, the radial penetration observed at low momentum flux ratios was larger for crossflow with lower swirl number and the radial penetration observed at high momentum flux ratios was more for crossflows with higher swirl number. In comparison to the spray characteristics in swirling crossflows at atmospheric pressure, condition of elevated gaseous pressure resulted in lower radial penetration, jet spread and jet area. The jet trajectory correlations for elevated pressure conditions are additionally presented, developed using curve fitting to the experimental data, which will be useful to the industry for estimation of spray trajectory in swirling crossflows at elevated pressure conditions.

Seasonal Analysis of Planetary Boundary Layer and Turbulence in Warsaw, Poland Through Lidar and LES Simulations

We analyzed the planetary boundary layer (PBL) characteristics in Warsaw, Poland for a day of summer, autumn, winter, and spring of 2021 by integrating and comparing measured and simulated data. Using remote sensing lidar sensor data, the PBLH was calculated using wavelet covariance transform (WCT) and the gradient method (GM). Also, simulations of turbulent fluxes were performed utilizing the large eddy simulation (LES) from the Parallel Large Eddy Simulation Model (PALM) to better understand how turbulence and convection behave across different seasons in Warsaw. The PBLH diurnal cycles showed pronounced changes in their vertical structure as a function of the season: the winter heights were shallow (~0.7 km), while summer heights were deeper (~1.7 km). The spring and autumn presented transient characteristics of PBLH around 1.0 km. This study is crucial for enhancing urban air quality and climate modeling. The PBLH simulations from PALM showed agreement with the measured data, with an underestimation of approximately 10% in both methods. Through PALM, it was possible to observe that summer exhibited increased convection, enhanced mixing efficiency, and a deeper boundary layer compared to other seasons throughout the daily cycle. Winter has a lower sensible heat flux and little convection throughout the day. Spring and autumn showed intermediate characteristics. In this way, the effectiveness of the applicability of the PALM model to obtain flows within the PBL and their heights is highlighted, because correlations ranged from strong to very strong (r ≥ 0.70).

Application of Active Heating Tests with the Distributed Temperature Sensing to Characterize Flow Dynamics in a Tidal-Influenced Coastal Aquifer

Aquifer storage and recovery have gained attention as a solution that utilizes submarine groundwater discharge (SGD) as a surrogate water resource to alleviate water scarcity and fill the demand gap. Characterizing SGD is crucial for using coastal groundwater and improving understanding of the interaction between continental water and seawater. This study employs fiber-optical distributed temperature sensing (FODTS) and the heat tracer to quantify the groundwater flux in a coastal aquifer in northern Taiwan. The fluxes in different sections along the borehole were estimated from the temperature response caused by the active heating tests and campier groundwater flux under different tidal conditions, providing information on potential water resources for water resource planning and management. According to the active heating tests, the material of the sections with high-temperature response mainly consists of a gravel–sand mixture. Based on the estimations of groundwater fluxes along the well, the sections with low sensitivity of temperature response have low hydraulic conductivity and low groundwater flux. The estimated thermal parameters at the site are consistent with those obtained from the borehole samples in the laboratory tests. The groundwater fluxes in different sections are calculated based on the temperature response observed from the FODTS. The groundwater fluxes along the well vary between 0.02 and 1.77 m/day. There are considerable differences between the estimated fluxes during the tidal cycle in a heterogeneous coastal aquifer, indicating the high uncertainty of estimated SGD along coastlines.

Thermo-Magnetic properties of non-relativistic particles under the effect of energy-dependent Hellmann potential

This manuscript presents an analysis of the thermal and magnetic properties of particles moving in two dimensions under the influence of an external magnetic field and Aharanov-Bohm flux, considering an energy-dependent Hellmann potential. The energy eigenvalue is obtained using the asymptotic iteration method. Next, we model the system as a canonical ensemble and derive the partition function to acquire analytical expressions for the Helmholtz free energy, entropy, mean energy, and specific heat. We observe that an increase in the external magnetic field and AB flux generally increases the energy eigenvalues, with a stronger effect at lower flux values, while energy eigenvalues decrease with an increase in the screening parameter. Additionally, Helmholtz free energy and entropy functions are sensitive to temperature, particularly in the low-temperature regime, while specific heat exhibits a Schottky anomaly. We also compute the magnetisation and susceptibility functions, finding that both magnetisation and susceptibility increase with the external magnetic field strength and the AB flux.

Rising water levels increase CH4 emissions and decrease CO2 exchange in a temperate salt marsh

AbstractSaline wetlands play a crucial role in climate regulation through their robust cooling effect, attributed to rapid carbon sequestration and minimal methane production. However, a comprehensive understanding of the mechanisms controlling their greenhouse gas (GHG) balance is lacking, particularly in salt marshes that are fully or partially submerged due to rising sea levels. We conducted a controlled manipulative experiment to test the effect of water levels on GHG emissions, including four water table levels: ‐10, 0, +5 cm and a fluctuating water table. We used soil cores from a Spartina anglica‐dominated salt marsh and examined the CO2 and CH4 fluxes over a growing season. Daylight CO2 uptake and dark CO2 emission were highest at the ‐10cm water table, while CH4 emissions were lowest at this water table. CO2 and CH4 fluxes were primarily driven by air and water temperature and solar irradiance. Our results indicate that salt marshes with near‐surface water levels (‐10 to 5 cm) function as potent CO2 sinks and minor sources of CH4 during the growing season. The high photosynthetic carbon assimilation combined with low CH4 fluxes resulted in a Global Warming Potential value of ‐326 g CO2eq m−2 on a 100‐year scale. Our study accounted for CH4 fluxes, CO2 uptake and emission together, and identified the mechanisms controlling CO2 and CH4 exchange. This approach is crucial for evaluating the potential of saline tidal wetlands as net carbon sinks and for developing scientifically sound climate mitigation policies.

Comprehensive Investigation of Partitioned Thermal Barrier Coating: Impact on Thermal and Mechanical Stresses, and Performance Enhancement in Diesel Engines

The thermal barrier coating method is applied using materials with low thermal conductivity to increase the efficiency and improve the emissions of internal combustion engines. However, coated surfaces may be damaged due to the high thermal and pressure stresses encountered by the piston surface in the combustion chamber during engine operation. In this study, experiments and analysis were carried out for four piston models to analyze the coating layer and increase its strength: two partially coated piston surface models, a fully coated model, and an uncoated piston model. The results of the transient thermal analysis revealed that the fully coated piston model exhibited the highest surface temperature. Additionally, heat losses were observed to be lower in the fully coated model compared to the other piston models. Partially coated piston models exhibited lower heat flux on the coated surface but higher heat flux on the uncoated combustion chamber surfaces. Combustion analysis indicated that the fully coated piston model exhibited the highest in-cylinder temperature and pressure values, while the uncoated model had the lowest values. When comparing heat transfer rates on the walls, the uncoated piston model exhibited the highest transfer, whereas the fully coated piston model exhibited the lowest. Finally, the fully coated piston demonstrated the highest combustion efficiency.

ДОСЛІДЖЕННЯ ТЕМПЕРАТУРНИХ ПОЛІВ НА СТАЛЯХ З УРАХУВАННЯМ КІНЦЕВОЇ ШВИДКОСТІ РОЗПОВСЮДЖЕННЯ ТЕПЛА ПРИ МОДЕЛЮВАННІ УМОВ ОТРИМАННЯ НАНОСТРУКТУР У ПЛАЗМОВОМУ СЕРЕДОВИЩІ

The primary objective of the study was to determine the impact of variations in maximum temperatures and thermal stresses during laser radiation exposure on the material being processed (steel 38Х), taking into account the finite speed of heat propagation. The research was conducted on the material surface and its near-surface layer under a specified heat flux. A comparison of the obtained results showed that certain temperature variations occur in the area of heat propagation. When the finite speed of heat propagation was considered, additional temperature jumps were identified, which, during the development of the temperature fields, shifted from the central part to the edges. Thermal stresses were calculated considering thermal conductivity and thermoelasticity. Analyzing the changes in certain physical parameters revealed the nature of the temperature distribution on the material surface and in its near-surface layers. It was found that there is an increase in thermal stresses of up to 10% in regions of maximum temperature gradients and up to 30% in cases of sharp temperature jumps. These circumstances create favorable conditions for nanostructure formation. When determining the thermal conditions for the formation of nanostructures, especially in the case of short-term laser radiation exposure and high-energy heat fluxes of 10¹⁰ W/m² and above, considering the finite speed of heat propagation results in an increase in thermal stresses up to 10-20%, which can significantly affect the determination of the technological parameters required for nanostructure formation. At the same time, for lower heat flux values and longer laser radiation exposure times, the increase in thermal stresses will be less than 10%, which will not significantly influence the determination of laser radiation technological parameters. The conducted research is important for further theoretical studies on the creation of nanostructures on steels in a plasma environment.

Integrated System of Reverse Osmosis and Forward Pressure-Assisted Osmosis from ZrO2 Base Polymer Membranes for Desalination Technology

In this work, reverse osmosis and forward osmosis membranes were prepared using base cellulosic polymers with ZrO2. The prepared membranes were rolled on the spiral-wound configuration module. The modules were tested on a pilot unit to investigate the efficiency of the RO membrane and the hydraulic pressure effect on both sides of the FO membranes. The RO membrane provided a rejection of 99% for the seawater desalination, and the brine was used as a draw solution for the FO system. First, seawater was used as a draw solution to indicate the best hydraulic pressure, where the best one was 3 bar for the draw solution side, and 2 bar for the feed side, where the water flux reached 48.89 L/m2·h (LMH) with a dilution percentage of 80% and a low salt reverse flux of 0.128 g/m2·h (gMH) after 5 h of operation time. The integrated system of RO and forward-assisted osmosis (PAO) was investigated using river water as a feed and RO brine as a draw solute, where the results of PAO indicate a high-water flux of 68.6 LMH with a dilution of 93.2% and a salt reverse flux of 0.18 gMH. Therefore, using PAO improves the performance of the system.

Identification of Priority Supply Areas for Carbon Sinks Based on Ecosystem Service Flow: A Case Study for the Hexi Region in Northwestern China

The development and implementation of regional protection plans for ecosystem carbon storage services have been recognized as crucial actions for mitigating global climate change. However, the supply areas of carbon sequestration in terms of ecosystem service flows in inland regions are still less evaluated. The goal of this study is to identify the priority-ranked supply areas for carbon sinks. Here, we conducted a case study in the Hexi Region of northwestern China and proposed a framework to quantify the priority supply areas for carbon sinks from the perspective of ecosystem service flows. Firstly, we quantified the carbon service supply and demand areas by combining carbon models (i.e., the Carnegie–Ames–Stanford Approach model and soil respiration models) with socioeconomic and natural factors. Then, we introduced a breaking point formula to estimate ecosystem service flow, specifically focusing on distance or range. Finally, we determined priority supply areas for carbon sinks based on the Zonation model. The results showed that significantly higher carbon sequestration values were detected in the Qilian Mountains, ranging from 2.0 to 3.0 t hm−2, in comparison with desert oasis areas, where the supply values ranged from 0 to 0.01 t hm−2. The urban areas and rural settlements within the study area are characterized by higher values of carbon emissions compared to those in the Qilian Mountains and deserts. The carbon flow analysis demonstrated that the middle and northern parts of the study area, being characterized by lower precipitation and sandy landscapes, were identified as locations with low carbon sequestration fluxes (<1.0 t hm−2). In addition, the mountainous regions were identified as the main highest priority area for ecosystem carbon sequestration, covering 8.33% of total area of the Hexi Region. Our findings highlighted the importance of the Qilian Mountains in terms of sustaining carbon sequestration service supply in the Hexi Region and targeted ecological protection practices to be implemented going forward.

System‐Wide Greenhouse Gas Emissions From Mountain Reservoirs Draining Permafrost Catchments on the Qinghai‐Tibet Plateau

AbstractReservoirs influence the global climate by exchanging greenhouse gases (GHGs) of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) with the atmosphere. Few studies, however, quantify emissions of all three GHGs from reservoirs, particularly in permafrost‐affected mountain regions where ecosystems are highly vulnerable to climate change. This study presents three‐year direct measurements of CO2, CH4, and N2O concentrations and fluxes upstream, within, and downstream from two reservoirs draining permafrost catchments on the Qinghai‐Tibet Plateau, including periods of reservoir drawdown. Comparing GHG fluxes across space and time exhibits a general pattern of lower fluxes at the two reservoirs relative to up‐ and downstream channels. Ebullitive fluxes contributed to 36.7% and 9.4% of total CH4 and N2O fluxes, respectively. CO2 has no response to drawdown, but CH4 and N2O display synchronous drawdown‐associated increase within the reservoir, constituting 57.5% and 32.8% of the annual reservoir emissions in just 2 months, respectively. Riverine emissions from up‐ and downstream channels accounted for an outsized fraction (55.5% for CH4, 17.3% for CO2 and 16.5% for N2O) of the system‐wide GHG budget. Compared with global reservoirs, the two reservoirs have high CO2 and N2O but low CH4 fluxes in CO2 equivalents. Upscaling shows that the two reservoirs emit the same magnitude of carbon as thermokarst lakes, and four times higher N2O than Finnish lakes on an areal basis. This article shows that alpine reservoirs draining permafrost catchments are unrecognized atmospheric sources in current reservoir GHG inventories, but also emphasizes the importance of system‐wide emissions when assessing total GHG evasion from reservoir systems.

Design of transient thin film heat flux sensor based on the transverse thermoelectric effect

Abstract Accurate heat flux measurement is critical for evaluating thermobaric elastic thermal damage, and acquiring heat flux at the time of explosion provides an important foundation for estimating damage sverity. To suit the test requirement, a transient thin film heat flux sensor (THFS) using the transverse thermoelectric effect was developed. The THFS offers the benefits of small size and rapid reaction time. The sensitive element of the THFS is made up of a lead telluride (PbTe) film, a sapphire substrate, gold electrodes, and a heat-absorbing coating. PbTe films were created on the sapphire surface using magnetron sputtering, and gold electrodes were grown on both sides of the film by electron beam evaporation. The THFS, which was evaluated for static and dynamic performance throughout a laser-generated heat flux range of 1.2-3.8 MW/m2, had its static performance test results revealing an excellent linear connection between the THFS response voltage and the laser applied heat flux, with a sensitivity of 1.40 μV/(kW/m2). The dynamic performance test, which demonstrated that THFS can get a full heat flux curve under the excitation of a low pulse width heat flux signal, showed a measured time constant of 10 μs. The novel heat flux sensor is intended for high reaction speed and dependability, providing a dependable new approach for measuring heat flux during thermobaric bomb explosions.

Slag rim structure and phase formation mechanism in molds during the continuous casting of high-Mn high-Al steel

The slag–steel reaction between low basicity mold flux and high-Mn and high-Al steel results in changes to the composition and properties of the mold flux, forming a slag rim at the meniscus of the mold during continuous casting. In this study, the slag rim was divided into five layers comprising the glass, columnar crystals, fine crystals, coarse crystals, and sinter layers from mold to molten steel based on their morphological features. Compared to the original slag, the Al2O3 content in the slag rim significantly increased and the SiO2 content decreased, thereby increasing the Al2O3/SiO2 mass ratio from 0.05 to 5.52. Phases with high melting points, such as Na2O·CaO·2Al2O3 and LiAlO2, were identified in the slag rim. According to crystallization process calculations using FactSage, these phases were the primary causes of slag rim formation. Thus, new slags with a low O/F mass ratio were subsequently designed to mitigate the generation and growth of Na2O·CaO·2Al2O3. These new compositions reduced the melting point and viscosity, thereby ensuring sufficient fluidity in slags with a high Al2O3/SiO2 mass ratio.

Optimisation Studies on Performance Enhancement of Spray Cooling - Machine Learning Approach

The performance optimisation of spray cooling heat transfer systems has been identified as a significant step in improving process efficiency, and the application of machine learning tools is a recent development that has enhanced this. This study aims to maximise the heat transfer coefficient for spray cooling at low heat flux levels. The effects of nozzle inclination angle, water pressure, and spray height on heat transfer coefficient were studied. Taguchi L27 orthogonal array technique was used to perform the experiments. A maximum heat transfer coefficient of 181.4 kW/m2K was obtained at a nozzle inclination angle of 60o, spray height of 4 cm, and water pressure of 15 psi. Analysis of variance was performed to find the significance of each variable and its interactions. The results show that for the maximum heat transfer coefficient (181.4 kW/m2K), the optimum levels of the independent variables were A3H1P3, i.e., the highest level of nozzle inclination angle (60o), the lowest level of spray height (4 cm), and the highest level of water pressure (15 psi). The support vector machine outperformed the Random Forest algorithm and Multiple Regression analysis regarding prediction accuracy with a maximum error of 0.15% and root mean squared error of 0.01.

Damage regularity and multifractal analysis of sol-gel reflection coating of KDP crystal under low UV irradiation flux.

This study employed multifractal analysis to investigate the changes in surface morphology of SiO2 anti-reflective coatings prepared on KDP substrates using the sol-gel method, under various conditions of ultraviolet (UV) irradiance. The coatings were successfully fabricated, and the chemical structure of the SiO2 sol was comprehensively characterized using Solid-State Nuclear Magnetic Resonance (SSNMR) technology. Under low UV irradiance (4 J/cm2), repeated experiments revealed a crack-induced mechanism of surface fatigue damage. Utilizing Scanning Electron Microscopy (SEM), the study discovered the induction effect of initial crack defects in UV-damaged coatings and established a damage model. Furthermore, Atomic Force Microscopy (AFM) was used to acquire images of the coatings' surface morphology at different damage levels, which were analyzed using the multifractal spectrum f(α). This analysis confirmed the multifractal nature of the coatings both before and after damage. This study identified significant effects of UV irradiation on the width of the multifractal spectrum and Δf, indicating that the SiO2 anti-reflective coatings exhibit multifractal characteristics under various damage states. The coatings displayed a pattern of decreasing and then increasing singularity spectrum width, height distribution unevenness, and surface roughness with increasing damage. This study demonstrates that multifractal analysis is an effective tool for describing the complexity of the surface morphology of sol-gel-derived anti-reflective coatings for the first time and for validating their multifractal properties across different stages of UV damage. HIGHLIGHTS: Damage dynamic process of KDP crystal sol-gel coating was described by SEM&AFM; The crack propagation mechanism of sol-gel coating under UV radiation is proposed; The damage evolution of sol-gel coating was described by multifractal analysis.

Dynamic analysis of the bubble's spatiotemporal evolution on a microheater under microsecond pulse heating

Transient heating of liquids upon a microheater surface manifests an exceedingly rapid temperature escalation, inducing a pronounced superheating at the onset of nucleation. Rare study focuses on the spatiotemporal behavior of subcooled boiling bubbles on a thin-film microheater surface. The present study experimentally explores the subcooled pool boiling heat transfer process on a platinum thin-film microheater with dimensions of 1000 μm × 1000 μm under microsecond pulse heating conditions. The visualized results indicate that three typical heat transfer regimes related to various heating scenarios can be identified, including the single-phase, nucleate boiling and film boiling heat transfer regimes. Consequently, the boiling incipience moment and the corresponding average microheater temperature are meticulously discussed and compared with analogous scholarly contributions. Moreover, the rapid bubble lifecycle involving nucleation, growth, coalescence and collapse within approximate 130 μs under microsecond pulse heating is captured and detailly analyzed. At lower heat flux, the boiling process is distinctly classified into five phases: (I) single-phase heat transfer, (II) isolated bubbles nucleation, growth and coalescence, (III) formation and growth of vapor blanket, (IV) shrinkage and collapse of vapor blanket, followed by (V) microbubbles condensation. As the vapor blanket nearly envelops the microheater completely, the temperature dramatically surges, with the increase rate markedly surpassing that observed during phase II. When further raising the heat flux, the regrowth of main bubble locating at the central area can be observed. Meanwhile, the nucleation and growth of numerous microbubbles in the peripheral zones after the collapse of vapor blanket are identified.

Dust mass in protoplanetary disks with porous dust opacities

Atacama Large Millimeter/submillimeter Array surveys have suggested that protoplanetary disks are not massive enough to form the known exoplanet population, based on the assumption that the millimeter continuum emission is optically thin. In this work, we investigate how the mass determination is influenced when the porosity of dust grains is considered in radiative transfer models. The results show that disks with porous dust opacities yield similar dust temperatures, but systematically lower millimeter fluxes, as compared to disks that incorporate compact dust grains. Moreover, we have recalibrated the relation between dust temperature and stellar luminosity for a wide range of stellar parameters. We also calculated the dust masses of a large sample of disks using the traditionally analytic approach. The median dust mass from our calculation is about six times higher than the literature result, and this is mostly driven by the different opacities of porous and compact grains. A comparison of the cumulative distribution function between disk dust masses and exoplanet masses shows that the median exoplanet mass is about two times lower than the median dust mass when grains are assumed to be porous and there are no exoplanetary systems with masses higher than the most massive disks. Our analysis suggests that adopting porous dust opacities may alleviate the mass budget problem for planet formation. As an example illustrating the combined effects of optical depth and porous dust opacities on the mass estimation, we conducted new IRAM/NIKA-2 observations toward the IRAS 04370+2559 disk and performed a detailed radiative transfer modeling of the spectral energy distribution (SED). The best-fit dust mass is roughly 100 times higher than the value given by a traditionally analytic calculation. Future spatially resolved observations at various wavelengths are required to better constrain the dust mass.