Evaporation Conditions Research Articles

Surface processes and drivers of the snow water stable isotopic composition at Dome C, East Antarctica – a multi-dataset and modelling analysis

Abstract. Water stable isotope records in polar ice cores have been largely used to reconstruct past local temperatures and other climatic information such as evaporative source region conditions of the precipitation reaching the ice core sites. However, recent studies have identified post-depositional processes taking place at the ice sheet's surface, modifying the original precipitation signal and challenging the traditional interpretation of ice core isotopic records. In this study, we use a combination of existing and new datasets of precipitation, snow surface, and subsurface isotopic compositions (δ18O and deuterium excess (d-excess)); meteorological parameters; ERA5 reanalyses; outputs from the isotope-enabled climate model ECHAM6-wiso; and a simple modelling approach to investigate the transfer function of water stable isotopes from precipitation to the snow surface and subsurface at Dome C in East Antarctica. We first show that water vapour fluxes at the surface of the ice sheet result in a net annual sublimation of snow, from 3.1 to 3.7 mm w.e. yr−1 (water equivalent) between 2018 and 2020, corresponding to 12 % to 15 % of the annual surface mass balance. We find that the precipitation isotopic signal cannot fully explain the mean, nor the variability in the isotopic composition observed in the snow, from annual to intra-monthly timescales. We observe that the mean effect of post-depositional processes over the study period enriches the snow surface in δ18O by 3.0 ‰ to 3.3 ‰ and lowers the snow surface d-excess by 3.4 ‰ to 3.5 ‰ compared to the incoming precipitation isotopic signal. We also show that the mean isotopic composition of the snow subsurface is not statistically different from that of the snow surface, indicating the preservation of the mean isotopic composition of the snow surface in the top centimetres of the snowpack. This study confirms previous findings about the complex interpretation of the water stable isotopic signal in the snow and provides the first quantitative estimation of the impact of post-depositional processes on the snow isotopic composition at Dome C, a crucial step for the accurate interpretation of isotopic records from ice cores.

Impact of Comb Cell Diameter on Nectar Evaporation Efficiency in Honey Bees

Honey bees transform nectar into honey through a combination of physical and chemical processes, with the physical process primarily involving the evaporation of excess water to concentrate the nectar. However, the factors affecting evaporation efficiency, such as evaporation duration, cell type, and bee species, remain incompletely understood. This study aimed to examine how these factors affect nectar evaporation efficiency during honey production. We measured the sucrose content in solutions subjected to combined active and passive evaporation, as well as passive evaporation alone. The results showed that eastern honey bee (EHB; Apis cerana) colonies were more efficient at concentrating sucrose solutions in worker cells than in drone cells under both combined active and passive evaporation conditions, as well as passive evaporation alone. Conversely, western honey bee (WHB; Apis mellifera) colonies exhibited greater efficiency in drone cells. Additionally, EHB colonies were more effective than WHB colonies in converting sucrose into fructose and glucose. Under passive evaporation, EHB colonies required at least 48 h to significantly concentrate the sucrose solution, while WHB colonies achieved similar concentrations in just 24 h. Sucrose content increased with the duration of passive evaporation. These findings provide insights into how honey bee colonies can efficiently produce mature honey during periods of abundant nectar flow.

Sustainable solar-powered seawater desalination enabled by phosphorene-decorated watermelon-like phase-change microcapsules

Solar-powered interfacial evaporation is considered as an emerging innovative technology for seawater desalination; however, it suffers from insufficient evaporation efficiency under intermittent solar irradiation. Aiming at realizing sustainable solar-powered seawater desalination for clean water production, we have designed a new type of watermelon-like phase-change microcapsules as a photothermal absorbent material for a solar interfacial evaporator. This type of phase-change microcapsules was prepared through rational layer-by-layer microencapsulation with a ZrO2 nanoparticle-containing n-docosane core as a phase-change material (PCM) for solar photothermal harvest and prompt thermal response, a ZrO2 shell for the leakage prevention of the molten n-docosane core, and a polydopamine coating layer together with its surface-decorated phosphorene nanoflakes for high-efficient sunlight absorption and fast water transportation. The resultant microcapsules are featured by a watermelon-like microstructure as confirmed by transmission electron and scanning electron microscopy. They also exhibit a high light absorption efficiency of 84.95 %, a high latent heat capacity of 146.2 J g−1, and good wettability. Equipped with the watermelon-like phase-change microcapsules, the developed solar interfacial evaporator obtained an evaporation rate of 3.09 kg m−2 h−1 under one-sun illumination for seawater desalination. The PCM core within the microcapsules can store solar photothermal energy as latent heat under sufficient solar irradiation and then release it under evaporation conditions without sunlight illumination, thus enhancing the water evaporation efficiency. This enables the developed evaporator to increase its total evaporation mass by 31.5 % on a cloudy day in comparison with the conversional solar evaporator without a PCM, indicating a remarkable enhancement in the evaporation performance under intermittent solar irradiation. The developed solar interfacial evaporator exhibits great potential for application in sustainable solar-powered seawater desalination.

Void fraction of R32 in microfin tube under evaporation conditions using capacitance-based sensor

Void fraction of R32 in microfin tube under evaporation conditions using capacitance-based sensor

Evolution features and corrosion behavior of (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7 environmental barrier coatings under water vapor conditions at 1400 °C

Evolution features and corrosion behavior of (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7 environmental barrier coatings under water vapor conditions at 1400 °C

New data of deuterium excess values of glacial ice of Kamchatka

The isotopic signature (δ18О, δ2Н, d-excess) of the ice of the Ushkovsky volcano in Kamchatka were studied. A new shallow ice core was obtained in 2022 in the Gorshkov crater. The 14 m long ice core was dated by counting annual layers, which were also compared with known eruptions in recent years. The upper 14 m of the glacier were formed over the last 16 years (from 2006 to 2022). The values of δ18О very from −16 to −24‰, δ2Н from −110,5 to −177,7‰, the averaged values are −20,5 and −150,2‰, respectively. The d-excess value varies with depth from 8,7 to 21,3‰, the average value is 13,7‰. For winter horizons at low values of δ18О and δ2Н, an increase in d-excess is noted. Such features are associated with the origin of moisture brought to Kamchatka. The source of moisture is the Pacific Ocean, the Sea of Okhotsk and the Sea of Japan, for which there are pronounced differences in the conditions of moisture evaporation between summer and winter. The increasing trends in δ18О and δ2Н values from 2006 to 2022 are accompanied by a decrease in deuterium excess, indicating an increase of summer precipitation. However, in addition to changes in seasonal proportions of precipitation, ice d-excess values may reflect climatic changes in the source of moisture.

Oxidative Dissolution of Sulfide Minerals in Porous Media Under Evaporative Conditions: Multiphase Experiments and Process‐Based Modeling

AbstractThe dissolution of sulfide minerals in subsurface porous media has important environmental implications. We investigate the oxidative dissolution of pyrite under evaporative conditions and advance a mechanistic understanding of the interactions between multiple physical processes and mineral/surface reactions. We performed a set of experiments in which initially water saturated and anoxic soil columns, containing a top layer of pyrite, are exposed to the atmosphere under no evaporation (single‐phase) and natural evaporative (two‐phase) conditions. The oxidative dissolution of pyrite was monitored by non‐invasive high‐resolution measurements of oxygen and pH. Additionally, we developed and applied a multiphase and multicomponent reactive transport model to quantitatively describe the experimental outcomes and elucidate the interplay between the physico‐chemical mechanisms controlling the extent of pyrite dissolution. The results confirm that the extent of pyrite dissolution under single‐phase conditions was constrained by the slow diffusive transport of oxygen in the liquid phase. In contrast, during evaporation, the evolution of fluid phases and interphase mass transfer processes imposed distinct physical constraints on the dynamics of pyrite oxidation. Initially, the invasion of the gaseous phase led to a fast delivery of high oxygen concentrations in the reactive zone and thus markedly increased pyrite oxidation and acidity/sulfate production. However, such enhanced release of reaction products was progressively limited over time as drying conditions prevailed in the reactive zone and inhibited pyrite oxidation. The transient phase displacement was also found to control the distribution of aqueous species and formation of secondary minerals by creating spatio‐temporally variable redox conditions.

Active Interfacial Perimeter in Pt/CeO2 Catalysts with Embedding Structure for Water-Tolerant Toluene Combustion.

Supported Pt catalysts are often subjected to severe deactivation under the conditions of high temperature and water vapor in catalytic oxidation; thus, the superior stability and water-resistant ability of catalysts have great significance for the effective degradation of volatile organic compounds (VOCs). Herein, we constructed a Pt/CeO2-N catalyst with an active interfacial perimeter, in which Pt species were partially embedded in the defective CeO2-N support to prevent the sintering. A significant charge transfer between Pt species and ceria in the embedding structure occurred via the Pt-CeO2 interface, which induced the formation of a Pt4+-Ov-Ce3+ interfacial structure. Experimental research and theoretical calculations demonstrated that the active Pt4+-Ov-Ce3+ interface promoted the activation and migration of lattice oxygen, thus facilitating the participation of oxygen species in toluene oxidation. Consequently, Pt/CeO2-N showed excellent catalytic performance for toluene degradation. In situ DRIFTS and DFT calculation proved that the Pt4+-Ov-Ce3+ interfacial sites served as the intrinsic active center in the dissociation of H2O to generate ·OH, which contributed to the formation of benzaldehyde, thus remarkably improving the water-resistant property. This study provided a facile strategy for fabricating the interfacial embedding structure to enhance the catalytic activity and water tolerance for eliminating VOCs in practical application.

Numerical simulation of CuCr alloys vacuum arc under conditions of arc contraction, deflection, and anode vapor

In practical arc ignition processes of high-current vacuum arcs, despite the calibration effect of the axial magnetic field, the strong magnetic constriction force still causes the arc to contract. Additionally, during the actual electrode opening process, due to the random nature of the arcing position, the center of the arc column is often not located at the center of the electrode. At this point, the behavior of the vacuum arc can be understood as an asymmetric three-dimensional (3D) process under the influence of the spatial magnetic field, affecting the generation of anode vapor and the characteristics of arc species. Therefore, it is useful to conduct simulation studies on multi-species vacuum arc behavior considering arc contraction and arc deflection. In this paper, the spatial magnetic field distribution under different electrode effective areas and different arc center deflection distances have been simulated, and the influence of actual magnetic field-induced by arc contraction and deflection on 3D spatial distribution characteristics of arc plasma has been studied based on a 3D multi-species (CuCr alloys) vacuum arc model with anode vapor. The simulation results show that with the contraction of the arc column, the area occupied by neutral atomic vapor decreases correspondingly, but the ionization and recombination process between the arc column regions becomes more intense. The axial current density and electron temperature distribution around the neutral atomic vapor area become more non-uniform. When the arc column deviates from electrode center, the neutral atomic vapor area shows an asymmetrical distribution on both sides of the arc column center axis, and the axial current density and electron temperature gather and enhance in the opposite direction of the arc deflection, thereby significantly affecting the distribution of arc species.

The effect of ion solvation on ion-induced nucleation—A generalized Thomson model

We present a model for ion-induced nucleation, focusing on the effect of dissociated ions embedded in the fluid surrounding a charged core or colloid. The model includes the ions' direct electrostatic energy and preferential solvation. The integrated ions' free energy has two terms: The first can be short- or long-range, depending on their density. The second is proportional to the nucleus' volume and can shift the state from undersaturation to supersaturation at high ion concentration. The inclusion of the Gibbs transfer energies of ions in the free energy leads to a modified Poisson-Boltzmann equation for the potential around the core. The integrated ions' free energy is added to the fluids' interfacial and bulk terms to establish a generalized Thomson model. In the Debye–Hückel limit, the model is solved analytically, while in the nonlinear regime, it is solved numerically. The state diagram in the plane of saturation and core charge includes regions with a homogeneous phase, electro-prewetting, metastable vapor, metastable nucleus, and spontaneous nucleation states. The lines separating these regions depend sensitively on the preferential solvation. Our model shows nucleation asymmetry to the sign of the nucleus' charge. This sign asymmetry is due to the Gibbs transfer energies of ions.

δ13C and δ18O-based interpretation of Miocene carbonates of the Miranda-Trebiño basin, NE Iberia: preliminary insights

The stable isotopes (C and O), bulk mineralogy and sedimentary facies types of the Miocene lacustrine palustrine carbonates of the Cucho Section (Miranda-Trebiño basin, N Iberia) are studied. The results indicate deposition in a freshwater carbonate lake recording significant biogenic CO2 input, changing Precipitation/Evaporation rates and variations in vegetation cover and pedogenesis on palustrine areas. Short-lived stages of higher salinity and evaporative conditions are recorded by the relative abundance of fine-grained dolomite. The highest δ13C values suggest 12C sequestration in anoxic bottom waters due to water column stratification. These new data support the general deepening trend of the lake system established from previous sedimentological analyses.

Theoretical and Experimental Analysis of the Cathode-Vapour-Feed PEM-Electrolyser for Space Applications

Water electrolysis is experiencing growing interest due to its importance in the transition to a carbon-neutral transportation sector and even in spaceflight it can play a vital role. Here, its typical application has been the oxygen generation for the life support of astronauts onboard a spacecraft or the International Space Station. However, in recent years the application of electrolysis for a new form of spacecraft propulsion is receiving increasing attention, as well. This technology is called Water Electrolysis Propulsion (WEP).So far highly toxic and expensive propellants have been used for in-space propulsion, like hydrazine-derivatives and dinitrogen tetroxide. However, with a constantly growing number of satellite-launches per year, the spaceflight industry is searching for more inexpensive solutions which do not entail the corresponding safety hazards and engineering challenges of these conventional propellants. WEP is currently considered to be one of the most promising solutions for these issues. Within such a system a satellite is filled on ground with pure water. Once launched into space an electrolyser, powered by the satellite’s solar panels, is used to split the water into gaseous hydrogen and oxygen which are stored in intermediate storage tanks at pressures of up to 100 bar. Subsequently the gases can be combusted in a rocket engine to generate thrust and to propel the spacecraft for various propulsive needs.One of the core components of such a system is the electrolyser. In order to be competitive, an electrolyser type has to be found, which is lightweight, able to operate in zero-gravity and is able to pressurize the gases without the need for additional mechanical pumps. Currently the most promising electrolyser type is the so-called Cathode-Vapour-Feed (CVF) PEM electrolyser. Here a conventional PEM electrolyser is operated in cathode feed and modified by integrating a second membrane (Water Feed Barrier) between the electrolysis membrane and the water inlet. In order for the electrolyser to operate, the water has to diffuse through this Water Feed Barrier (WFB) and is subsequently present in a vapour state at the electrolysis membrane. Therefore, no phase separators are needed and the electrolyser is able to operate independently and unaffected by gravity. Furthermore, a low voltage is applied on the Water Feed Barrier slightly exceeding the Nernst-Voltage. Hence the WFB is effectively acting as an electrochemical pump which allows the generation of the gases at higher pressures than the water inlet pressure.This conceptual change is however introducing several unconventional mechanisms and phenomena that have to be considered during the design of such a device. However, previous research on the CVF technology has been very limited due to its niche application so far and most of these phenomena and mechanisms remain unanalysed. This paper is aiming to contribute towards the closure of this knowledge gap.The working principle and the theory behind these additional phenomena appearing in the CVF electrolyser are presented. These are the significantly affected mass transport of the water towards the anode side of the electrolysis membrane, the gas diffusion through both membranes and its effect on the electrolyser’s performance, as well as the mutual interaction between the applied voltages on the three electrodes. Furthermore, many researchers have used the same membrane type for the WFB as for the electrolysis membrane, although it serves a different purpose and is exposed to different operating conditions. Therefore, special attention will be devoted to the determination of the optimal membrane type for the WFB since barely any research has been conducted on this topic. In addition, a proof-of-concept electrolyser has been built and tested in a parameter study to validate the theoretical considerations. The experimental findings on the effect of membrane selection for the WFB, distance between the membranes and impact of flow field topology are presented and discussed. Therefore, the paper contributes towards a more targeted development of space electrolysers in the future. Figure 1

Demonstration of magnetically silent optically pumped magnetometers for the TUCAN electric dipole moment experiment

We report the performance of a magnetically silent optically pumped cesium magnetometer with a statistical sensitivity of 3.5 pT/Hz at 1 Hz and a stability of 90 fT over 150 s of measurement. Optical pumping with coherent, linearly-polarized, resonant light leads to a relatively long-lived polarized ground state of the cesium vapour contained in a measurement cell. The state precesses at its Larmor frequency in the magnetic field to be measured. Nonlinear magneto-optical rotation then leads to the rotation of the plane of polarization of a linearly polarized probe laser beam. The rotation angle is modulated at twice the Larmor frequency. A measurement of this frequency constitutes an absolute measurement of the magnetic field magnitude. Featuring purely optical operation, non-magnetic construction, low noise floor, and high stability, this sensor will be used for the upcoming TUCAN electric dipole moment experiment and other highly sensitive magnetic applications. Novel aspects of the system include commercial construction and the ability to operate up to 24 sensors on a single probe laser diode.

Balloon Baseline Stratospheric Aerosol Profiles (B2SAP)—Perturbations in the Southern Hemisphere, 2019–2022

AbstractVolcanic and pyrocumulonimbus (pyroCB) injections into the stratosphere perturb the aerosol layer and can have important radiative and chemical impacts on timescales spanning from months to several years. Repeated in situ balloon‐borne measurements of aerosol size and number concentration (>140 nm in diameter), ozone, water vapor, and atmospheric state variables made at midlatitudes in the southern hemisphere (SH) since 2019 enable us to better characterize such events. We use this record and coincident lidar extinction profiles to study several moderate to large stratospheric perturbations in the SH between 2019 and 2022 in detail, including the Australian New Year Super Outbreak (ANYSO) pyroCB in 2020. Median vertical profiles of aerosol number concentration, effective radius, and surface area in SH midlatitudes are also compared with those recorded in Northern Hemisphere midlatitudes under baseline conditions using an identical payload. These data depict the variability in stratospheric aerosol properties in the SH midlatitudes during this period and provide a benchmark for global sectional aerosol models. They reveal that sulfate particle size distributions under baseline conditions and in volcanic plumes are relatively well represented in the Community Earth System Model—Community Aerosol Radiation Model for Atmospheres (CESM‐CARMA), but more observations of biomass burning plumes are needed to improve model skill in simulating pyroCB. Comparisons between in situ and lidar observations also highlight a need for more observations of aerosol composition and refractive index in both fresh and aging biomass burning plumes.

Acidified biochar one-off application for saline-alkali soil improvement: A three-year field trial evaluating the persistence of effects

Salinization is a global soil degradation issue threatening agricultural productivity and environmental sustainability. Native biochar is a promising soil amendment, but its high alkalinity limits its use in saline-alkali lands. Acidified biochar, with a lower pH, is theoretically more suitable. This study aims to evaluate the persistence of effects of acidified biochar one-off application on soil particle size distribution, physicochemical properties, water retention, temperature regulation, and evaporation conditions of saline-alkali soil, thereby verifying its feasibility and exploring the optimal application range. We conducted a three-year cotton field experiment using palm fruit branch biochar as the raw material, acidified with ferrous sulfate, which involved four biochar applications (0, 10, 20, and 30 t ha−1) and four irrigation quotas (60 %, 80 %, 100 % and 120 % ETc). The results indicated that the initial acidified biochar application slightly increased surface soil (0–20 cm) pH by 0.1 %–3.9 %, this negative effect was nearly eliminated by the third year. Biochar application significantly altered surface soil particle size distribution, increasing sand content by 1.6 %–8.4 %, and persistently improved soil hydraulic properties, with water holding capacity still showing a 6.5 %–16.7 % increase in the third year. Biochar enhanced soil thermal insulation and suppressed soil evaporation, but these benefits gradually diminished with increasing cultivation years. Acidified biochar effectiveness was closely linked to irrigation quota. Significant differences in soil water and heat indicators were observed between the 20 and 30 t ha⁻¹ biochar treatments only under low irrigation quotas. Under sufficient irrigation (100 % and 120 % ETc), the optimal biochar application range was 15–20 t ha⁻¹, while under low irrigation (60 % and 80 % ETc), the optimal range was 20–25 t ha⁻¹. This study demonstrated that acidified biochar one-off application has significant multi-year benefits in improving soil structure and hydrothermal properties, providing a scientific basis for the improvement and sustainable utilization of saline-alkali soil.

Should we delay leaf water potential measurements after excision? Dehydration or equilibration?

BackgroundAccurate leaf water potential (Ψw) determination is crucial in studying plant responses to water deficit. After excision, water potential decreases, even under low evaporative demand conditions, which has been recently attributed to the equilibration of pre-excision Ψw gradients across the leaf. We assessed the influence of potential re-equilibration on water potential determination by monitoring leaf Ψw and relative water content decline after excision using different storage methods.ResultsEven though leaf Ψw declined during storage under low evaporative demand conditions, this was strongly reduced when covering the leaf with a hydrophobic layer (vaseline) and explained by changes in relative water content. However, residual water loss was variable between species, possibly related to morpho-physiological leaf traits. Provided water loss was minimized during storage, pre-excision leaf transpiration rate did not affect to the magnitude of leaf Ψw decline after excision, confirming that transpiration-driven Ψw gradients have no effect on leaf Ψw determination.ConclusionsDisequilibrium in water potentials across a transpiring leaf upon excision is dissipated very quickly, well within the elapsed time between excision and pressurization, therefore, not resulting in overestimation of leaf Ψw measured immediately after excision. When leaf storage is required, the effectiveness of a storage under low evaporative demand varied among species. Covering with a hydrophobic layer is an acceptable alternative.

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and anomalous negative geopotential height at 500 hPa and anomalous cyclone at 700 hPa control the entire Tarim Basin, favoring anomalous upward motion, and western and southwestern water vapor transport. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, the western part of the Tarim Basin is affected by the anomalous cyclone while the eastern part is affected by the amomalous anticyclone, leading to the east-west discrepancy. The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

Highly efficient iodine capture from vapor and water using UiO-66-X: Effects of functional group modifications

Radioactive iodine waste from the nuclear industry poses a critical threat to human health, and its effective capture has become an important research topic. In this study, modified UiO-66-X adsorbents (where X is ATA, BTA, or STA) were used to investigate the effects of the free functional groups in the UiO-66 skeleton on iodine capture in the vapor and solution states. The adsorption behavior revealed that the capture efficiency of UiO-66-ATA was substantially higher than that of UiO-66-BTA and UiO-66-STA because the electron-donating amino groups could enhance the I − I···π halogen bond interactions compared with the electron-withdrawing carboxyl and sulfonic acid groups. In addition, the pore volume of UiO-66-ATA was significantly higher than those of UiO-66-BTA and UiO-66-STA. In particular, the removal uptakes of UiO-66-ATA were 1108.1 mg/g (vapor phase) and 3601.9 mg/g (aqueous solution). This study is the first to investigate the effects of functional groups on the adsorption uptake of UiO-66 toward iodine. This efficient functional group modification strategy holds significant promise for the development of novel metal–organic framework adsorbents.

The effect of working fluid and compressibility on the optimal solidity of axial turbine cascades

The blade solidity, namely the blade chord-to-pitch ratio, largely affects the fluid-dynamic performance of turbomachinery and its cost. For turbo-machines operating with air or steam, the optimal value of the solidity which maximizes the efficiency is estimated with empirical correlations such as the ones proposed by <xref ref-type="bibr" rid="fn19">Zweifel (1945)</xref> and <xref ref-type="bibr" rid="fn17">Traupel (1966)</xref>. However, if the turbomachine operates with unconventional fluids, the accuracy of these correlations is questionable. Examples of such fluids are the organic compounds (e.g., hydrocarbons, siloxanes) used in organic Rankine cycle (ORC) power systems. This study concerns an investigation on how the working fluid, its thermodynamic state, and flow compressibility influence the optimum pitch-to-chord ratio of turbine stages. A first principle reduced-order model (ROM) for the computation of profile losses was developed for this purpose. The ROM results are compared with those obtained from numerical simulations of the flow over two axial turbine cascade geometries. The influence of both the working fluid, the flow compressibility, and the solidity value on both the boundary layer state at the blade trailing edge and the base pressure are evaluated. Models to compute mixing and passage losses in the compressible regime as a function of the axial solidity are proposed and discussed. Results show that the value of the optimal solidity of turbine cascades significantly increases with the flow compressibility, and mildly increases if the fluid is in the dense vapor state. Moreover, the optimal solidity value is strongly affected by the mixing process occurring downstream of the blade trailing edge. Therefore, currently available models for its estimation, which are solely based on the minimization of the profile losses, are inaccurate.

Large eddy simulation of droplet dispersion and deposition over street canyons

Predicting droplet transport in the atmosphere is a major issue for a large number of dispersion problems such as spray cooling systems in streets, urban lawn sprinklers [Milesi et al., “Interferometric laser imaging for respiratory droplets sizing,” Environ. Manage. 36, 426–438 (2005)], and dispersion of virus such as COVID or from a terrorist attack [Balachandar et al., “Host-to-host airborne transmission as a multiphase flow problem for science-based social guidelines,” Int. J. Multiphase Flow 132, 103439 (2020)]. Here, we investigate the propagation of droplets issued from a source near the ground between square obstacles with different spacings. The aerodynamic field is determined by large eddy simulation coupled with an immersed boundary method for the obstacles. Droplets are tracked by a Lagrangian approach. An evaporation model is used to account for varying humidity conditions. Droplet concentration, mass flux, and deposition rates are obtained for different evaporation conditions and obstacle spacings. The results show high deposition rates on the internal wall of the first obstacle due to droplet advection by the reverse flow of the primary vortex. In addition to this, droplets may escape the canyon and propagate downstream as far as eight times the obstacle distance (8H). The concentration of air-borne droplets downstream the canyon is higher for smaller street canyon openings. When evaporation is accounted for, the ground-level droplet concentration may be reduced by up to 30% in the case of small canyon openings.