Intermittent Mixing Research Articles

A case study analysis of the impact of a new free tropospheric turbulence scheme on the dispersion of an atmospheric tracer

AbstractMost Lagrangian dispersion models represent free tropospheric turbulence as a homogeneous steady‐state process. However, intermittent turbulent mixing in the free troposphere may be a significant source of mixing. We test a new parametrization scheme that represents spatial‐ and temporal‐varying turbulence in the free troposphere in the Met Office's Numerical Atmospheric‐dispersion Modelling Environment. We use semi‐idealized emissions of radon‐222 (Rn) from rocks and soil in the United Kingdom to evaluate the impact of using a variable free tropospheric turbulence parameterization on the dispersion of Rn. We performed two experiments, the first using the existing steady‐state scheme and the second using the newly implemented spatio‐temporal‐varying scheme, for two case periods July 2018 and April 2021. We find that the turbulence in the varying scheme (represented by the vertical velocity variance) can range by two to three orders of magnitude (10 to 10 m s) when compared with the steady‐state scheme (10 m s). In particular, low‐altitude turbulence is enhanced when synoptic conditions are conducive to forming low‐level jets. This leads to a greater dispersion in the free troposphere, reducing the mean monthly Rn concentration above the boundary layer by 20–40% relative to the steady‐state scheme. We conclude that without a space–time‐varying free tropospheric turbulence scheme atmospheric dispersion may be significantly underestimated under synoptic conditions that are favourable for low‐level jet formation. This underestimation of dispersion may potentially result in inaccurate estimations of local emissions in top‐down greenhouse gas inventory studies.

Biogas Production in a Variety of Sawdust and Cow Dung Mixtures Using the Intermittent Mixing Method

Cow dung is livestock waste that is very useful for renewable energy sources. The acceleration of the gas rate in cow dung biogas fermentation can be accelerated by the addition of secondary material, sawdust is one of the organic materials that can accelerate the rate of gas production in the formation of cow dung biogas. This study used a mixture composition: (B1) 675 g cow dung and 0 g sawdust, (B2) 472.5 g cow dung and 202.5 sawdust, (B3) 450 g cow dung and 225 g sawdust, and (B4) 427.5 g cow dung and 247.5 g of sawdust by fermentation for 20 days. In the research process, measurements of pH at the beginning and at the end of the study, gas pressure, gas volume, biodigester temperature, production rate, methane gas content, and flame test were carried out. In this study, the pH values ranged from 7-7.5 and the biodigester temperature was 27.5-31°C. The results of this study indicate that an organic mixture with a mixture of sawdust can accelerate production faster than without organic sawdust. Optimal results are found in the variation of the organic mixture of sawdust with a mixture of 450 g cow dung and 250 g sawdust having the highest production rate of 281.72 ml/day.

Observations of strong turbulence and mixing impacting water exchange between two basins in the Baltic Sea

Abstract. Turbulent diapycnal mixing is important for the estuarine circulation between basins of the Baltic Sea as well as for its local ecosystems, in particular with regard to eutrophication and anoxic conditions. While the interior of the basins is overall relatively calm, stratified flow over steep bathymetric features is known as a source of strong turbulent mixing. Yet, current in situ observations often cannot capture the spatio-temporal development of dynamic and intermittent turbulent mixing related to overflows over rough bathymetry. We present observational oceanographic data together with openly accessible high-resolution bathymetry from a prototypical sill and an adjacent deep channel in the sparsely sampled Southern Quark located in the Åland Sea, connecting the northern Baltic Proper with the Bothnian Sea. Our data were acquired during two 1-week cruises on R/V Electra in February–March 2019 and 2020. We collected high-resolution broadband acoustic observations of turbulent mixing together with in situ microstructure profiler measurements, and current velocities from acoustic Doppler current profilers. We found that a temporally reversing non-tidal stratified flow over the steep bathymetric sill created a dynamic and extremely energetic environment. The observed flow reversed during both cruises on timescales of a few days. Saltier, warmer, and less oxygenated deep water south of the sill was partly blocked, the reversing flow was at times hydraulically controlled with hydraulic jumps occurring on both sides of the sill, and high spatial variability occurred in the surface layer on small scales. Dissipation rates of turbulent kinetic energy, vertical turbulent diffusivities, and vertical salt flux rates were increased by 3–4 orders of magnitude in the entire water column in the vicinity of the sill compared to reference stations not directly influenced by the overflow with average dissipation rates near the sill between 10−7 and 10−6 W kg−1, average vertical diffusivities of 0.001 m2 s−1 in the halocline and up to 0.1 m2 s−1 below the halocline, and average vertical salt flux rates around 0.01 g m−2 s−1 in the halocline and between 0.1 and 1 g m−2 s−1 below the halocline. We suggest, based on acoustic observations and in situ measurements, that the underlying mechanism for the highly increased mixing across the halocline is a combination of shear and topographic lee waves breaking at the halocline interface. We anticipate that the resulting deep- and surface-water modification in the Southern Quark directly impacts exchange processes between the Bothnian Sea and the northern Baltic Proper and that the observed mixing is likely important for oxygen and nutrient conditions in the Bothnian Sea.

Three-Dimensional Printing of Biomass–Fungi Biocomposite Materials: The Effects of Mixing and Printing Parameters on Fungal Growth

Biomass–fungi biocomposite materials are derived from sustainable sources and can biodegrade at the end of their service. They can be used to manufacture products that are traditionally made from petroleum-based plastics. There are potential applications for these products in the packaging, furniture, and construction industries. In the biomass–fungi biocomposite materials, the biomass particles (made from agricultural waste such as hemp hurd) act as the substrate, and a network of fungal hyphae grow through and bind the biomass particles together. Typically, molding-based methods are used to manufacture products using these biocomposite materials. Recently, the authors reported a novel extrusion-based 3D printing method using these biocomposite materials. This paper reports a follow-up investigation into the effects of mixing parameters (mixing time and mixing mode) on fungal growth in biomass–fungi mixtures prepared for 3D printing and the effects of printing parameters (printing speed and extrusion pressure) on fungal growth in printed samples. The fungal growth was quantified using the number of fungal colonies that grew from samples. The results show that, when mixing time increased from 15 to 120 s, there was a 52% increase in fungal growth. Changing from continuous to intermittent mixing mode resulted in an 11% increase in fungal growth. Compared to mixtures that were not subjected to printing, samples printed with a high printing speed and high extrusion pressure had a 14.6% reduction in fungal growth, while those with a low printing speed and low extrusion pressure resulted in a 16.5% reduction in fungal growth.

Mixing effect on bio-methanation, settleability and dewaterability in the anaerobic digestion of sewage sludge fractions

Biomethanation and dewaterability characteristics of primary sludge (PS), secondary sludge (SS) and mixed sludge (MS) fractions were assessed after anaerobic stabilization under parallel batch and continuous mixing conditions at 35℃ in order to investigate the performance of the separate digestion system. Similar methane conversion/yield values were obtained in PS, SS and MS digestion with continuous mixing’s positive effect only in PS digestion. Continuous mixing resulted in 50% increase in the methane yield (600(+/-100) mL/g VSadd.d. SS digestion produced a comparable methane yield at 650(+/-100) mL/g VSadd.d showing no effect due to mixing pattern. Settling and dewaterability characteristics of the stabilized PS were superior to stabilized SS samples. A reverse relationship was obtained between settling and dewaterability characteristics where intermittent mixing enhanced settling ability while continuous mixing resulted in higher dewaterability of the stabilized sludges. Polyelectrolyte (PE) addition showed a negative effect on the settleability of the sludges. Low degree mixing resulted in 50% sludge volume reduction and an SVI of 64 mL/g VS compared to 25% volume reduction and 82 mL/g SVI in the continuous mixing mode for the stabilized PS. A similar trend for the stabilized SS but weaker values with 25% volume reduction and an SVI 182 mL/g in the intermittent mixing mode compared to 15% volume reduction and 200 mL/g VS SVI indicated a much lower settleability in the continuous mixing mode and compared to stabilized PS.

Kinematic Parameters of the Biplanetary Mechanism (Intermittent Mixing Machines)

Kinematic Parameters of the Biplanetary Mechanism (Intermittent Mixing Machines)

Intermittent mixing facilitates energy recovery and low carbon emissions from high-solids anaerobic co-digestion of food waste and sewage sludge

Mixing inside high-solids anaerobic co-digestion (HS-AcoD) is essential for process feasibility and economic sustainability. This study developed a proper energy assessment for a high solids anaerobic digestion-combined heat and power (AD-CHP) system to clarify the impact of mixing on methane production, energy recovery and carbon emission reduction during HS-AcoD of food waste (FW) and sewage sludge (SS). Results indicated that intermittent mixing enhanced methane production and shortened the lag phase compared with unmixing and continuous mixing. The modified Gompertz model yielded better fitting than the logistic and transfer function models via kinetic analysis. In the case of a scaled-up AD-CHP system, intermittent mixing with 15 min/h boosted energy output (2.14 × 103 kWh/tonne VS) at 21 d. Compared with continuous mixing, 15 min/h intermittent mixing at 13 d improved the energy recovery ratio from 31% to 45% and carbon emissions reduction from 0.25 t CO2/t VS to 0.35 t CO2/t VS. For a high availability of FW and SS in China, the AD-CHP system with intermittent mixing would have higher net energy output (128.4 × 109 kWh) and carbon emission reduction (15.3 million tonnes) by the full utilization of these biomasses. These results are expected to provide theoretical support for the high solids AD-CHP system in determining the optimal mixing strategy with maximum energy production for FW and SS disposal.

Effect of mixing intensity on volatile fatty acids production in sludge alkaline fermentation: Insights from dissolved organic matter characteristics and functional microorganisms

Alkaline fermentation for volatile fatty acids (VFAs) production has shown potential as a viable approach to treat sewage sludge. The hydrolysis and acidogenesis of sludge are greatly influenced by mixing. However, the effects of mixing intensity on VFAs production in sludge alkaline fermentation (SAF) remain poorly understood. This study investigated the impacts of mixing intensity (30, 90 and 150 rpm continuous mixing, and 150 rpm intermittent mixing) on VFAs production, dissolved organic matter (DOM) characteristics, phospholipid fatty acid profiles and microbial population distribution in SAF. Results showed that 150 rpm continuous and intermittent mixing enhanced the hydrolysis of sludge, while 150 rpm intermittent mixing resulted in the highest VFAs production (3886 ± 266.1 mg COD/L). Analysis of fluorescent and molecular characteristics of DOM revealed that 150 rpm intermittent mixing facilitated the conversion of released DOM, especially proteins-like substances, into VFAs. The abundance of unsaturated and branched fatty acids of microbes increased under 150 rpm intermittent mixing, which could aid in DOM degradation and VFAs production. Firmicutes and Tissierella were enriched at 150 rpm intermittent mixing, which favored the maximum VFAs yield. Moreover, Firmicutes were found to be the key functional microorganisms influencing the yield of VFAs during SAF. This study provides an understanding about the mixing intensity effects on VFAs production during SAF, which could be helpful to improve the yield of VFAs.

Strong positive fractionation of chromium isotopes in iron formation of the Jacadigo Group (Brazil) – A link to enhanced atmospheric oxygenation during the Late Neoproterozoic

Cr isotopes recorded in iron formations (IF) are considered to have the potential to reflect the isotope signatures in respective ambient surface seawater. The ∼600 Ma Fe and Mn deposits pertaining to the Banda Alta Formation (Urucum district, Mato Grosso do Sul, Brazil), comprise the world’s youngest and largest Neoproterozoic sedimentary Fe and Mn formations (MnF). Shale normalized Rare Earth Element and Yttrium (REY) patterns of drillcore samples show flat, positively sloped patterns with absent Europium anomalies and near- to supra-chondritic Yttrium-Holmium ratios with negative Cerium anomalies, which imply intermittent mixing of freshwater with seawater. Redox sensitive element enrichment factors (MoEF, UEF, CrEF) show positive correlation, indicating varying redox conditions across the Jacadigo Basin, with ephemeral euxinic conditions. The Cr isotope signatures across the Urucum IF (δ53Crauth at: Morraria Grande + 0.93 ± 0.34 ‰, 2σ, n = 28; Morro do Rabichão + 0.5 ± 0.4 ‰, 2σ, n = 3; and Morro do Urucum ca. + 0.64 ‰, n = 1) are statistically indistinguishable from previously published surface outcrop samples at Morro do Urucum. Our new data support: (1) a stable supply of oxidized Cr potentially from continental sources at the time of deposition, implying high atmospheric O2 levels in the Late Neoproterozoic; (2) insignificant alteration of the authigenic Cr isotope signals by tropical weathering despite surface iron up-concentration and leaching of carbonates, and (3) lack of isotope effects that would be associated with non-quantitative reduction processes and accompanying particulate transport to the chemical sediments in the Jacadigo Basin. The combined information from (isotope)geochemical data presented herein speak for a deposition of the Urucum IFs in restricted, periodically ice-covered and stratified sub-basins with partial connection to the open ocean, and for the presence of a sufficiently oxidative atmosphere which promoted a continuous supply of the surface waters with isotopically heavy Cr from the weathering landmasses at this time.

Energy-saving in fucoxanthin production by Chaetoceros gracilis in a flat-bag photobioreactor with intermittent mixing

To save energy in the production of high-value products with antioxidant properties such as fucoxanthin by Chaetoceros gracilis, the effect of mixing frequency (once every 18 min and once every 9 min) on fucoxanthin productivity was examined using a flat bag photobioreactor. The mixing frequency of once every 9 min resulted in a significantly higher (p < 0.01) areal fucoxanthin productivity of 28.9 mg m−2 d−1 than mixing once every 18 min (13.7 mg m−2 d−1). The fucoxanthin productivity at the mixing frequency of once every 9 min was comparable to that in previous studies of diatoms cultured using continuous mixing. Moreover, intermittent mixing reduced the energy required for mixing and biomass productivity per mixing energy of 20.5-21.2 g-DW kWh−1 d−1 was achieved. The present study showed that mixing frequency affected the cell density and light intensity per dry weight of C. gracilis which means the light intensity received by individual cells. The fucoxanthin content increased exponentially with decreasing light intensity per dry weight due to the decrease of the light intensity received by individual cells. Thus, mixing frequency is an essential parameter for high fucoxanthin productivity. Light intensity per dry weight and mixing frequency should be considered in combination to achieve energy savings in fucoxanthin production by C. gracilis.

Restoring capacity and efficiency of vanadium redox flow battery via controlled adjustment of electrolyte composition by electrolysis cell

One of the major challenges in vanadium redox flow batteries (VRFB) is a gradual decrease of available capacity over operation time. The VRFB capacity fade is a complex issue that affects volume, total content, and average valence of vanadium ions in posolyte and negolyte. Imbalances that occur due to crossover of vanadium ions, osmosis and electroosmosis of water can be dealt with by intermittent mixing of posolyte and negolyte, thereby prolonging VRFB operation at high capacity rates. However, the change in the average oxidation state (AOS) should be considered for stable VRFB operation. The imbalance of vanadium valence arises due to side reactions during charge–discharge processes. This work proposes a novel operando method for restoration of the initial VRFB capacity. Partial posolyte reduction on the cathode and oxygen evolution reaction on the RuO2/Ti electrode of the electrolysis cell, following which electrolytes mix and recharge, allow to recover initial performance parameters. Optimizing electrolysis conditions ensures high energy efficiency of the rebalancing procedure. Coulometric sensors data provide the charge required for posolyte reduction. The proposed approach for VRFB capacity recovery allows for complete restoration of performance parameters regardless of the magnitude of a capacity drop.

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m−3.d−1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10–0.05 m3.kgTVSfed−1.d−1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS−1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

The effect of intermittent mixing on particle heat transfer in an agitated dryer

Intermittent mixing, alternating agitation and no agitation, is an approach to maintain a high drying rate while minimizing particle breakage in agitated filter drying of the active pharmaceutical ingredient. In this study, the effect of intermittent mixing on heat transfer of particles was examined using DEM simulations. The agitation ratio (the fraction of time the agitator is on) and intermittent cycle number (the number of on/off cycles) represent the extent and allocation of agitation, respectively. It was observed that as the agitation ratio increases from the static bed, the rate of heat transfer and temperature uniformity initially increased sharply, and then more gradually for high agitation ratios. Additionally, the rate of heat transfer and temperature uniformity initially increased with intermittent cycle number, then reached a plateau. The results were fitted using a power law which predicted the rate of heat transfer as a function of the intermittent mixing parameters.

High cell density culture of Neochloris oleoabundans in novel horizontal thin-layer algal reactor: Effects of localized aeration, nitrate concentration and mixing frequency

A horizontal thin-layer algal reactor was designed, constructed and tested for high cell density culture of an oil-rich green alga, Neochloris oleoabundans, at a thickness of 6 mm. A hollow fiber membrane sparger was used for localized aeration with CO2-enriched air, which allowed control of culture pH at a narrow range of pH 7.0–7.5. The optimal nitrate concentration under the investigated conditions was 345 mg-N/L with a cell density of ∼6.6 × 108 cells/mL and biomass concentration of ∼8 g/L. The volumetric and areal biomass productivities were 1.81 g/L/day and 10.85 g m− 2/day, respectively, and the maximum volumetric and areal productivities 3.57 g/L/day and 21.42 g m− 2/day, respectively. Intermittent mixing at a frequency of once every two hours (five min mixing each time) produced a cell growth profile similar to that of continuous mixing. Such intermittent mixing resulted in 98.38 % saving on mixing energy and 33.9 % reduction in water evaporation. It was observed that metabolic stress such as high pH and high nitrate concentration could inhibit cell division while causing cell size to enlarge abnormally. The results indicate that it is technically feasible to have high cell density culture of photoautotrophic microalgae with intermittent mixing and no culture circulation, opening the door towards the development of open algal farming systems of low capital, operational, and maintenance costs.

Simplified Modeling of High-Solids Anaerobic Digestion of Dairy Manure in a Pilot-Scale Stirred Tank Anaerobic Digester

Highlights HSAD is a cost-effective approach for managing high-solids manure. Batch digestion of HSAD at a low inoculum ratio is unsuitable. Mixing once a day was enough to maintain a stable digestion process. The stoichiometric method with an appropriate biodegradability factor provided perfect prediction. Simplified biokinetics can predict methane productivity at steady-state conditions. Abstract. Anaerobic digestion (AD) is considered one of the most effective methods of managing dairy manure. To effectively and economically treat the huge volumes of manure produced by commercial dairy farms, high-solids anaerobic digestion (HSAD) is to be encouraged. In this manuscript, batch and semi-continuous anaerobic digestion experiments of dairy manure with a high volatile solid (VS) content were conducted in a pilot-scale stirred digester with an effective volume of 1.63 m3, operated under mesophilic temperature conditions. Three intermittent mixing treatments (50, 100, and 150 rpm) were mixed once a day during feeding with a constant mixing duration of 5 minutes, including a non-mixed experiment, operating at a 30-day hydraulic retention time. The objectives were to determine an optimum mixing intensity to enhance HSAD efficiency and economy and to apply simplified models to model the digestion process. The simplified kinetic models were modified to accurately predict methane growth, yield, and production rates. The modified Gompertz growth model predicted the methane growth at the batch experiment perfectly. The first-order kinetic model predictions of the biodegradability factor, the specific methane yield, and the specific methane production rate were consistent with the batch experimental results. The stoichiometric method and the Karim model were modified to accurately model the effect of mixing intensity on the methane yield and the specific methane production rate. Three linear equations were successfully developed to predict the methane production rate. Optimized mixing intensity and organic loading rate are critical for high methane production rates. This study contributes to the ongoing research to improve the efficiency of HSAD. Keywords: Dairy manure, High-solids anaerobic digestion, Methane productivity, Mixing intensity.

Significance of Intermittent Mixing in Mesophilic Anaerobic Digester

The mixing of slurry in an anaerobic digester (AD) is one of many key parameters, which have a significant effect on specific biogas yield (BY) and volatile solid (VS) removal rate. The determination of the optimum mixing regime in a digester is very complex as it depends on a large number of internal and external factors such as microbial community, the rheology of slurry, digester and impeller design, mixing intensity, and mixing intervals. The novelty of this study is the investigation of the optimum mixing regime in a lab-scale digester under semi-continuous mixing regimes by the continuous monitoring of the physicochemical properties of the digestate. In this study, a helical ribbon (HR) impeller was used for the agitation of the slurry operated at 67 rpm for 5 min under various agitation intervals (1 h, 2 h, 3 h, and 4 h). The results showed a 6–12% reduction in BY as the time between mixing operations increased. The highest BY was observed at a mixing frequency of 5 min/h, which produced a total of 54.1 L of biogas as compared to the mixing frequencies of 2 h, 3 h, and 4 h, where the BYs were recorded as 51.2 L, 49.8 L, and 47.3 L, respectively. Volatile fatty acids (VFAs) and FOS/TAC ratio were stabilized at 5–7 Gl−1 and 0.3–0.5, respectively. The appropriate mixing intensity was determined to obtain the highest biogas production, which could lead to lower power consumption for mixing operations.

Effect of different mixing modes on the abundance of Microcystis in Lake Taihu under green light.

Light and hydrodynamic force are important physical factors affecting growth of Microcystis. The most recent study found that green light has good effect in inhibiting growth of Microcystis. To understand the effect of mixing modes on Microcystis under the green light, we investigated the effects of continuous mixing and intermittent mixing on the abundance of Microcystis in Taihu Lake under field conditions. The study results found that abundance of Microcystis in control, intermittent mixing group, and continuous mixing group decreased 76.62%, 40.36%, and 95.18% on day 7 compared with that on day 1 in this experiment. At the end of the experiment, abundance percentages of diatoms and green algae to total phytoplankton abundance were 1.57% and 0.48% in control, 2.32% and 0.67% in intermittent mixing group, and 22.47% and 20.27% in continuous mixing group. The results indicated that continuous mixing favored the removal of Microcystis under green light conditions and was helpful for the growth of green algae and diatoms. The results provide a new approach for the control of Microcystis blooms.

Effect of optimized intermittent mixing during high-solids anaerobic co-digestion of food waste and sewage sludge: Simulation, performance, and mechanisms

Inadequate mixing has been proven to be a major cause of anaerobic digester failure. This study revealed the mechanism of mixing intervals on high-solids anaerobic co-digestion (HS-AcoD) of food waste (FW) and sewage sludge (SS). Optimized intermittent mixing time (15 min/h) was determined through computational fluid dynamics (CFD) simulation. Experimental results indicated that the simulated intermittent mixing could shorten digestion time and increase cumulative methane output (366.8 mL/gVS) compared with continuous mixing and unmixing. Mixing could considerably accelerate substrate solubilization and hydrolysis. Maximum rates of acidogenesis (53.35 %) and methanogenesis (49.41 %) were observed with an optimized intermittent mixing (15 min/h). Vigorous mixing induced apoptosis and disrupted syntrophic metabolism, whereas intermittent mixing promoted the syntrophic metabolism between Syntrophomonas and Methanobacterium, and led to an enrichment of genes involved in acidogenic and methanogenic pathways. These findings have important implications for the development of an optimized intermittent mixing strategy for maximizing HS-AcoD efficiency of FW and SS.

Microphysical timescales and local supersaturation balance at a warm cloud top boundary

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud–clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction, and condensation times within the cloud–clear air interface for the size distributions of the initial monodispersed and polydisperse droplets. For the monodisperse population, a clustering of the values of the reaction, phase, and evaporation times, that is around 20–30 s, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities.

Automated Tethered Profiler for Hydrophysical and Bio-Optical Measurements in the Black Sea Carbon Observational Site

Biogeochemical cycles of carbon transformation throughout the euphotic zone of the sea are controlled by physical processes, e.g., daily thermocline, variation in solar irradiance, thermohaline convection, and intermittent mixing. These processes should be regularly observed with sufficient time resolution at fixed geographical locations. This study provides a brief overview of the carbon observational site in the Northeastern Black Sea. The focus is on the design of a new tethered profiler Winchi for the inner continental shelf part of the site. The profiler hull and two outriggers comprise an open trimaran platform that is positively buoyant and tends to maintain a horizontal position in the water. The lower end of the winch wire is secured to the bottom anchor. By unwinding/winding the wire, the profiler ascends/descends while measuring the depth profiles of marine environment parameters ranging from the seafloor to air–sea interface. After surfacing, the profiler determines its location using the Global Positioning System (GPS) and transmits data to (and from) a server on land through the Global System for Mobile Communications (GSM). Initial field tests with the Winchi profiler at the Northeastern Black Sea shelf exhibited promising results. We report these early tests to demonstrate the use of Winchi.