Influence of liquid film on fuel consumption behavior in paraffin-based hybrid rocket engines at low mass flux

Determining mass fluxes of space debris upon demise in the atmosphere

Novel continuous production of single-cell proteins from purple non-sulfur bacteria using gaseous volatile fatty acids by closed-loop membrane contactor system.

Abstract Strong updrafts in deep convective clouds can quickly transport aerosol and chemical species from the planetary boundary layer (PBL) to the upper troposphere and lower stratosphere (UTLS), influencing weather, air quality, and climate by altering trace gas composition. This study examines two cases from the Deep Convective Clouds and Chemistry (DC3) campaign: a supercell cluster and a mesoscale convective system (MCS). Simulations using the Weather Research and Forecasting model with Chemistry (WRF-Chem) are used to assess key processes in parameterized convection including mass flux, subgrid scale transport, and entrainment rate to understand their roles in trace gas transport. Results show that the supercells transport carbon monoxide (CO) more efficiently than the MCS, which is impacted by a mid-tropospheric rear inflow jet that reduces the overall mass flux density of transported CO. In the supercell cluster, 35.3% of the total transported CO reaches above the lapse rate-derived tropopause (LRT) compared to 24% for the MCS. The supercell clusters exhibit smaller net CO mass flux than the MCS, but greater flux density (~15.5 t h −1 km −1 vs ~3.5 t h −1 km −1 ), indicating that the supercells produced more than four times stronger vertical transport than the MCS. The subgrid contribution of supercell convective transport to the UTLS is found to be greater than that of the MCS, with supercell contributions ranging from ~60–80%, while the MCS contributes ~40%. A mean fractional entrainment rate exceeding 0.1 km −1 at higher altitudes results in less subgrid CO transport to the lower stratosphere for both cases.

Microplastic (MP) mass is a key metric for understanding transport and fate of MPs in the environment, yet reliable estimation methods remain limited, particularly when detailed morphological data are unavailable. To address this, a size-probability distribution method is proposed that integrates empirical size distribution characteristics with volume-density models. The optimal configuration was identified by combining a conditional fragmentation distribution (CFD)-based size model with suitable volume approximations and evaluating it against measured mass from balance and mass spectrometry data. This method outperformed coefficient-based conversion approaches and achieved comparable accuracy with the results of direct volume-density calculations. When applied to empirical MP data from the Yangtze River, the method estimated annual mass fluxes ranging from 1950.00 to 12,655.58 tons, with a mean of 6895.90 ± 3763.24 tons. Overall, the proposed method provides a reliable and efficient means of estimating MP mass from particle counts data, yielding accurate, comparable mass estimates across different size classes.

We present a study of the gas kinematics within the Hestia project, a state-of-the-art set of simulations of the Local Group, with a particular focus on the velocity patterns of different ions and the large-scale motion of gas and galaxies towards the Local Group's barycentre. Using two of the Hestia i , C, iv , Si, iii , O, vi , O, vii , and O, viii and their imprints on sightlines observed from the Sun's location in different reference frames. To mimic observational strategies, we assessed the contribution of rotating disc gas, assuming simple kinematic and geometrical considerations. Our results indicate that local absorption features in observed sightlines most likely trace material in the circumgalactic medium of the Milky Way. Some sightlines, however, show that intragroup material could be more easily observed towards the barycentre, which defines a preferred direction in the sky. In particular, H, i , Si, iii , and C, iv roughly trace cold gas inside Milky Way and Andromeda haloes, as most of their mass flux occurs within the virial region of each galaxy, while oxygen high ions mostly trace hot halo and intragroup gas, with comparable mass fluxes in the Local Group outskirts and the circumgalactic medium of the two main galaxies. Additionally, we find that pressures traced by different ionic species outside the Milky Way's halo show systematically higher values towards the barycentre direction in contrast to its antipode in the sky. Kinematic imprints of the global motion towards the barycentre can be seen at larger distances for all ionic species as the Milky Way rams into material in the direction of Andromeda, with gas towards the anti-barycentre lagging behind.

Abstract Idealized numerical simulations using a climatological composite sounding of significant tornadoes within China failed to produce a sustained storm. An increase in vertical wind shear showed minimal impact on storm longevity. The simulated storms exhibited very high sensitivity to environmental humidity near the cloud base, at 1 to 2 km above ground. Increasing humidity within this layer led to the formation of long-lived (≥ 2 hours) and more intense supercells, even though the increase did not change much standard environmental parameters including the lifting condensation level (LCL) and convective available potential energy (CAPE). LCL and CAPE are important environmental parameters that are components of the significant tornado parameter (STP) used in tornado forecasting operations. This strong sensitivity is investigated. Instead of calculating air mass fluxes, water vapor entrainment into storms is calculated as moisture fluxes across the interface between the storm updraft core and its surrounding environment, which also includes that at the cloud base. Results show that more environmental moisture is entrained into the updraft core of simulated storms when the humidity in the 1–2 km layer AGL is increased. The resulting greater positive buoyancy due to the release of more latent heat leads to larger vertical acceleration and steeper slopes of the air parcel trajectories and therefore more upright updrafts. The generation of positive inflow shear due to the enhanced near-surface inflow further increases the uprightness of updraft at the lower levels. As a result, the convective cells stay close to the low-level gust fronts and intense supercell storms are sustained throughout the two-hour simulation.

Abstract In this study, two types of brazed ribbed-array channel structures with wall surface roughness values of 0.28μm and 10μm were fabricated. Experimental investigations were conducted to evaluate the natural circulation phase-change cooling performance in ribbed-array channel under various subcooling conditions. The working fluid was a new dielectric coolant, PFO-50, and the heating power ranged from 1.2 to 9.6 kW. The results show that, at subcooling levels of 5 K to 20 K, the maximum heat transfer coefficient per unit mass flux in the 10μm ribbed-array channel increased by 62.0 to 95.3% compared to that in the 0.28μm ribbed-array channel. In the 10μm ribbed-array channel, the average heat transfer coefficient increased by 68.77% as subcooling rose from 5 K to 20 K, while the corresponding thermal resistance decreased from 5.95 K/kW to 3.52 K/kW. As the heating power increased from 2.67 to 9.05 kW, the coolant mass flow rate increased approximately linearly from 82.6 to 313.6 kg/h. Notably, the mass flow rate was found to be independent of the inlet subcooling temperature. Finally, a correlation for the natural circulation immersion boiling heat transfer coefficient of PFO-50 was proposed. The model yields a maximum relative error of 24.2% and a minimum of only 0.29%, with a high confidence level achieved within 20% relative error range.

Abstract The ENSO Transition Mode (ETM) is a distinct Southern Hemisphere mode characterised by a multidecadal see-saw in boreal spring sea-level pressure about the dateline in the Southern Pacific Ocean. ETM significantly influences the equatorial winds and plays a key role in shaping ENSO’s boreal winter-to-summer seasonal transition. This study combines observational data and climate model simulations to examine how ETM affects global rainfall during boreal summer at multidecadal timescales. During its positive phase, ETM is linked to a cooler Northern Hemisphere, especially the Northern Pacific, and a warmer Southern Hemisphere with maximum warming over the Southern Indian Ocean. This creates an unfavourable inter-hemispheric sea surface temperature (SST) gradient, weakening the large-scale atmospheric circulation by reducing cross-equatorial mass flux and decreasing rainfall over the regions such as South Asia and the Sahel. These results underscore the significant impact of the Southern Hemisphere variability on the global climate patterns at multidecadal timescales.

Parboiling remains a critical pre-processing stage in rice production, especially in Nigeria, where traditional methods are inefficient, labour-intensive, and often result in poor rice quality. This study presents the design and computational fluid dynamics (CFD) analysis of a novel rice parboiling boiler intended to improve energy efficiency and product quality for small-scale rural processors. Using PTC Creo for 3D modelling and ANSYS Fluent 2021 R1 for simulation, the thermal and fluid dynamic performance of the proposed boiler was evaluated under steady-state conditions. Tetrahedral meshing with boundary layer refinement was employed to resolve critical flow gradients, while a realizable k–ε turbulence model was adopted to capture complex internal flow characteristics. Simulation results revealed improved temperature uniformity, smoother fluid flow, and enhanced heat transfer due to the presence of internal baffles. Key performance parameters—including temperature distribution, pressure profile, turbulence kinetic energy, enthalpy, and mass flux—were analysed to validate the design’s effectiveness. The boiler achieved a thermal efficiency of 89.95%, demonstrating significant improvements over conventional parboiling systems. This research fills a notable gap in the application of CFD for rice parboiling boiler optimization, offering a cost-effective and energy-efficient solution tailored for rural deployment in developing countries. The findings provide a foundation for future design enhancements and sustainable agro-processing technologies.

Abstract Per- and polyfluoroalkyl substances (PFAS) are persistent and potentially toxic compounds increasingly detected in aquatic environments, yet their occurrence, sources, and health risks in major watersheds remain under-characterized. This study provides a comprehensive assessment of PFAS contamination in the Nakdong River Basin, South Korea, through integrated analysis of spatial distribution, source apportionment, mass fluxes, and age-stratified human health risks. Surface water samples were collected from 23 sites across the mainstem and major tributaries during high-flow conditions. A total of 11 PFAS compounds were detected, with ΣPFAS concentrations (sum of PFAS) ranging from 9.28 to 171.40 ng/L. Concentrations of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) exceeded the United State environmental protection agency (USEPA) maximum contaminant levels at several sites. Land-use analysis revealed that industrial and wastewater treatment plant (WWTP) affected tributaries showed the highest PFAS levels and detection frequencies. Positive matrix factorization (PMF) modeling identified four source profiles linked to domestic wastewater, industrial discharge, electronics manufacturing, and secondary re-entry. Mass flux calculations indicated that tributaries such as GA-3 and IG-3 contribute disproportionately to basin wide PFAS transport. Human health risk assessment using mixture hazard quotients (HQ mix ) showed that children (0–5 years) exceeded the precautionary risk threshold of 0.1 at six sites, despite all values remaining below 1.0. These findings highlight the need for integrated monitoring and land-use-informed management strategies to mitigate PFAS exposure, especially in vulnerable populations. The study provides critical insights for targeted regulation and sustainable watershed protection in PFAS impacted regions.

Steady-state solutions to the Navier-Stokes equations are a valuable tool for constructing quasi-steady models of the solar wind and exploring the various factors that affect the fluxes of mass, energy, and momentum into the heliosphere. These models typically omit the effects of viscosity, which is assumed to be negligible under most coronal and heliospheric conditions; however, the inviscid Navier-Stokes equations are known to admit solutions that are singular at the sonic point, where the solar wind speed becomes equal to the relevant acoustic speed. Consequently, inviscid solar wind models require special treatment of the solution near the sonic points, and this has proven to be a significant impediment to efficient modeling of the solar wind. In this paper we revisit the governing hydrodynamic equations for the expanding solar wind, with the inclusion of the viscous stress as defined by the classical (Newtonian) closure, and we show how this inclusion eliminates the singularities that emerge from the inviscid equations. This result has been previously reported and used to generate steady-state solar wind profiles from initial conditions in the asymptotic limit (outside of the Sun's gravitational well); however, those studies did not include realistic treatments of the inner corona, and generally rejected the prospect of extrapolating solutions outward from the Sun into the heliosphere, which they deemed to be computationally unfeasible. Our aim, therefore, is to expand this method to include external heating and optically thin radiative losses and show that solutions can be computed outward from initial conditions near the solar surface, thereby capturing the entire range of scales from below the transition region to the outer heliosphere in a single solution. Our the steady-state, field aligned Navier-Stokes equations as a system of five coupled, first order, ordinary differential equations (ODEs) describing the spatial evolution of the mass density, pressure, speed, conductive heat flux, and viscous stress. These equations were then solved approach was to cast using conventional methods, without any special treatment of the governing equations in the vicinity of the sonic point. Physically meaningful solutions were identified by varying the initial conditions at the lower boundary until the solution obtained the correct asymptotic form, which we derived for the particular closures that we employed. The representative solutions that we present here demonstrate the utility and efficiency of this extrapolation method, which is considerably more realistic than commonly used analytical or empirical models. This method provides a direct approach to generating accurate solar wind profiles subject to motivated initial conditions near the solar surface, at a fraction of the computational cost of comparable relaxation-based models. The this method can be used to initialize time-dependent simulations, to large families of steady-state solutions that can then be used to populate the hydrodynamic variables along individual magnetic field lines in , observationally solutions obtained from generate global magnetic field models and to explore how the properties of the quasi-steady solar wind are affected by changes in magnetic geometry and different coronal heating models.

Enhancing the evaporator configuration of plate heat exchangers is essential for improving the overall efficiency of organic Rankine cycle (ORC) systems. To investigate the evaporator’s heat transfer characteristics, an experimental ORC test rig was developed. The experiments were conducted at saturation temperatures of 62.8–86.2 °C, mass fluxes of 5.0–16.6 kg/(m2·s), and heat fluxes of 3.1–9.2 kW/m2, spanning subcooled boiling, saturated two-phase, and superheating regions. The heat flux showed minimal variation with heat source temperature, whereas higher mass fluxes resulted in substantial increases in generator power and thermal efficiency due to enhanced convection and vaporization. The overall and refrigerant heat transfer coefficients rise with heat source temperature and mass flux, peaking under moderate conditions and declining as the superheating region becomes constrained. Comparison with existing correlations reveals pronounced deviations, indicating their limited applicability under the present operating conditions. A nondimensional correlation was established using dimensional analysis and multivariate regression to predict heat transfer across the subcooled boiling, saturated two-phase, and superheating regions. The proposed correlation yielded a mean absolute percentage error of 15.9%, demonstrating good predictive accuracy and providing a reliable theoretical basis for performance evaluation and design optimization of plate evaporators in ORC systems.

Abstract In this study, we have characterized the convective heat transfer due to the movement of particles through a lattice frame configuration comprised of an array of 5 × 5 unit cells of Octet topology. The unit cell porosity was varied between 0.75 and 0.88. The test coupons were additively manufactured using Binder jet technique in stainless steel 316 L. The convective heat transfer coefficients were determined via quasi-steady-state experiments conducted on a particle elevator and heat exchanger test facility, which provided a continuous supply of particles at desired flowrates. The heat transfer experiments were conducted for particle mass flux upto ∼100kg/m2s, which encompassed both packed bed and loose bed flow configurations. The heat transfer experiments were conducted with two different sets of CARBOBEAD particles, with mean diameters of 266 µm and 397 µm. Further, to understand the particle movement near the endwall, optical flow experiments were also conducted for the 397 µm particles to determine the near-wall particle velocity field using the Farneback algorithm. The results indicate that lattice porosity has a dominant effect on the convective transport, while smaller-sized particles supported better heat transfer.

This paper investigates the flow of a second-grade hybrid nanofluid through a Darcy–Forchheimer porous medium under Cattaneo–Christov heat and mass flux models. The hybrid nanofluid, composed of alumina and copper nanoparticles in water, enhances thermal and mass transport, while the second-grade model captures viscoelastic effects, and the Darcy–Forchheimer medium accounts for both linear and nonlinear drag. Using similarity transformations and the spectral quasilinearisation method, the nonlinear governing equations are solved numerically and validated against benchmark results. The results show that hybrid nanoparticles significantly boost heat and mass transfer, while Cattaneo–Christov fluxes delay thermal and concentration responses, reducing the near-wall temperature and concentration. The distributions of velocity, temperature, concentration, and microorganism density are markedly affected by porosity, the Forchheimer number, the bio-convection Peclet number, and relaxation times. The results illustrate that hybrid nanoparticles significantly increase heat and mass transfer, whereas thermal and concentration relaxation factors delay energy and species diffusion, thickening the associated boundary layers. Viscoelasticity, porous medium resistance, Forchheimer drag, and bio-convection all have an influence on flow velocity and transfer rates, highlighting the subtle link between these mechanisms. These breakthroughs may be beneficial in establishing and enhancing bioreactors, microbial fuel cells, geothermal systems, and other applications that need hybrid nanofluids and non-Fourier/non-Fickian transport.

Supercritical fluids such as water or CO2 are an attractive choice for future nuclear reactor systems. The exact knowledge of the heat transfer in a trans-critical pressure is important for the design of those systems. In subcritical pressure, knowing how to avoid the reduction of heat removal when exceeding the critical heat flux (CHF) is of critical importance. A series of experiments is carried out with the SCARLETT (Supercritical CARbon dioxide Loop at IKE StuTTgart) test facility at the Institute of Nuclear Technology and Energy Systems of the University of Stuttgart, focusing on investigations of CHF and post-CHF heat transfer with CO2 as a working fluid. Two test sections have been used – each with a different internal diameter - to investigate CHF and post-CHF heat transfer. Both test sections with 10 mm and 6 mm internal diameters and heated lengths of 2000 mm are equipped with glass fiber in a stainless-steel capillary for semi-continuous wall temperature measurement and thermocouples for the reference temperature measurement. The test sections are instrumented accordingly for pressure, differential pressure, mass flow, inlet, and outlet temperature measurements. The paper presents CHF, upstream CHF, and boiling heat transfer measurements in selected experiments in the 10mm tube at subcritical pressures of pr=0.7 and pr=0.98, mass fluxes of 1000 kg/m2s, and heat fluxes from 80 to 200 kW/m2.

To investigate the variation characteristics of heat transfer performance in plate evaporators within the ocean thermal energy conversion (OTEC) systems of underwater unmanned vehicles (UUVs) under marine motion conditions, a flow boiling experimental system integrated with a six-degree-of-freedom motion platform was designed and established. This study examined the effects of sloshing modes (heaving, pitching, and rolling), mass velocity, sloshing amplitude, sloshing frequency, and sloshing intensity on the heat transfer characteristics of the plate evaporator. The results indicate the following: (1) Heaving motion exerts a significant enhancement effect on the heat transfer performance of the plate evaporator. Under conditions of a heaving amplitude of 100mm and a frequency of 0.6Hz, the convective heat transfer coefficient of R134a increases by up to 61.8%; (2) Pitching motion exhibits a noticeable enhancement effect on heat transfer performance at small sloshing amplitudes (2.5° amplitude), with the convective heat transfer coefficient of R134a increasing by up to 34.75% at a frequency of 0.2Hz; (3) Rolling motion demonstrates a significant weakening effect on heat transfer performance, with the convective heat transfer coefficient of R134a decreasing by up to 31.8% under conditions of a rolling amplitude of 7.5° and a sloshing frequency of 1Hz. It should be noted that the inlet working fluid of the plate evaporator in this experiment is saturated, and the vapor quality of the outlet working fluid is 0.3-0.4. Furthermore, a heat transfer correlation applicable to plate evaporators under heaving, pitching, and rolling conditions was developed in this study. Validation results demonstrate that the proposed correlation exhibits excellent predictive performance, with prediction deviations within ± 15%. It should be noted that the applicable range of the heat transfer correlation established in this study is for pitching and rolling amplitudes of 2.5° to 7.5°, heaving amplitudes of 50 to 100mm, frequencies of 0 to 1Hz, mass fluxes of 125 to 225kg·m-2·s-1, and the working fluid being R134a.

Abstract Over tropical oceans, cumulus convection is triggered by updrafts from the atmospheric boundary layer (BL). Given mutual interactions between cumulus convective ensembles and synoptic‐ to global‐scale atmospheric phenomena, it seems important to quantitatively evaluate the updraft on spatiotemporal scales relevant to the interactions and understand its variability, which have been rarely explored through observational studies. Therefore, this study attempts to estimate daily mean updraft mass flux across the BL top from in situ observation data obtained during a shipborne observation campaign over the tropical Western North Pacific and examines its variation associated with changes in circulation fields. It is found that the updraft mass flux ranges from a few to several tens of g m −2 s −1 and is tightly correlated with low cloud amount. From this relationship, the mean updraft intensity, the updraft mass flux averaged only over updraft areas, can be roughly estimated at ∼80 g m −2 s −1 . Variation of the daily mean mass flux associated with the passage of a northwestward‐migrating tropical depression is examined in detail. The updraft mass flux starts to increase ∼5 days before the passage and reaches its maximum at the time of the passage. Large‐scale (∼100‐km scale) horizontal convergence in the BL primarily leads to the increase of the flux in the first half of the increasing period. In contrast, variation of local‐scale mass exchange should be considered for understanding the increase in the second half.

Abstract. Observations from airborne field campaigns are used to study the interplay between boundary-layer thermals and clouds in the trades. The size distributions of thermal and cloud-base chords inferred from turbulence and horizontal lidar-radar measurements are robustly described by the sum of two exponentials. Analytical calculations and statistical simulations show that the merging of objects is sufficient to explain the two exponentials, representing, respectively, the populations of merged- and unmerged-object chords. They also show how circulations induced by convective objects facilitate the merging process. The observed day-to-day variability of these populations at cloud base can thus be tied to the variability of thermal merging across the depth of the subcloud layer. Clouds rooted in unmerged thermals are small and shallow while those rooted in merged thermals are wider and deeper. An intricate interplay between thermal- and cloud-merging arises: when thermal merging is weak, thermal number density is high and cloud bases merge easily, leading to strong mesoscale mass fluxes and “Gravel” shallow mesoscale organizations. In contrast, when thermal merging is strong, clouds are fed by sparser but wider thermals, leading to longer cloud lifetimes but weaker cloud merging, weaker mesoscale mass fluxes, and “Flower” mesoscale organizations. This interplay between thermal- and cloud-merging imposes an upper bound on cloud coverage and suggests a negative feedback on the growth of mesoscale circulations. Thermal merging also controls observed size distributions of thermals in deep convective regimes. The merging process thus appears to be a fundamental player in the mesoscale organization of convection.

Abstract. This study introduces a helicopter-borne mass balance approach, utilizing the HELiPOD platform, to accurately quantify methane (CH4) emissions from coal mining activities. Compared to conventional research aircraft, the use of an external sling load configuration eliminates the need for aeronautical certifications, facilitates easier modifications and enables local helicopter companies to conduct flights. Furthermore, it allows for plume probing as close as several hundred meters downwind of an emission source and offers comprehensive vertical coverage from 50 m to 3 km altitude, making the HELiPOD an ideal tool to distinguish, capture, and quantify emissions from single sources in complex emission landscapes worldwide. Our approach serves as an independent emission verification tool, bridging the gap between ground-based, drone, near-field and far-field airborne measurements and supports identification of CH4 emission mitigation opportunities. Nineteen mission flights were conducted in the Upper Silesian Coal Basin of Southern Poland in June and October 2022 that targeted CH4 emissions from multiple coal mine ventilation shafts and several drainage stations. The comparison of top-down HELiPOD mass flux estimates against those calculated from bottom-up in-mine CH4 safety sensor and air flow measurements revealed very good agreement with relative deviations of 0 % to 25 %. This indicates, notwithstanding associated uncertainties, that the two independent approaches are capable of estimating CH4 emissions from coal mine ventilation shafts accurately. However, the accuracy and representativeness of derived in-mine data is application-specific and should be evaluated by independent measurements. With measured CH4 emission rates up to 3000 kg h−1 from individual coal mine ventilation shafts we confirm prior research, while revealing that emission strengths from drainage stations can be of comparable magnitude and should be investigated further. The possibility to detect emissions at rates as low as 20 kg h−1 with the HELiPOD was demonstrated through a controlled release experiment. This emphasises the wide range of potential applications in quantifying sources within a wide range of CH4 emission rates, i.e. from relatively small sources, e.g. biodigesters, landfills, cattle feedlots and manure pits to larger industrial sources including those from the coal, oil and gas sectors.