Poor Mixing Research Articles

Evaluation and Simulation Analysis of Mixing Performance for Gas Fuel Direct Injection Engine under Multiple Working Conditions

Gas fuel direct injection (DI) technology can improve the control precision of the in-cylinder mixing and combustion process and effectively avoid volumetric efficiency reduction in a compressed natural gas (CNG) engine, which has been a tendency. However, compared with the port fuel injection (PFI) method, the former’s mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. What is worse, the in-cylinder mixing performance would be seriously affected by engine working conditions, such as engine speed and load. Based on this situation, the fluid mechanics software FLUENT is used in this article, and the computational fluid dynamics (CFD) model of the injection and mixing process in a gas-fueled direct injection engine is established. A quantitative evaluation mechanism of the in-cylinder mixing performance of the CNG engine is proposed to explore the influencing rule of different engine speeds and loads on the mixing process and performance. The results indicate that phase space analysis can accurately reflect the characteristics of the mixture mixing process. The gas fuel mixture rapidly occupies the cylinder volume in the injection stage. During the transition stage, the gas fuel mixture is in a highly transient state. The diffusion stage is characterized by the continuous homogenization of the mixture. The in-cylinder mixing performance is linearly dependent on the engine’s working condition in the phase space.

Atmospheric CO2 Depletion Near the Surface in the Martian Polar Regions

AbstractThe kinetic temperature of the Martian seasonal caps is controlled by the partial pressure of atmospheric CO2 at the surface. When carbon dioxide condenses, typically near the poles, light non‐condensable species (Ar, N2, CO, etc.) accumulate in the atmosphere, resulting in a decrease of the CO2 partial pressure and depressing the local frost point temperature. The buoyant air should mix laterally and vertically within the polar vortices. Observations show that the Martian seasonal caps' kinetic temperatures are ∼0–4 K below the expected CO2 frost point, depending on latitude and season, indicating atmospheric CO2 gas depletion at the surface/atmosphere interface. In the North and South, we find relatively similar non‐condensable peak enhancement factors (e.g., EFNC ∼ 6–8, up to ∼8.7 in the North) at most latitudes, confirming the efficient meridional mixing within the polar vortices, despite steep surface condensation gradients. In the South, this surface enhancement is similar to column‐integrated values derived from Gamma Ray Spectrometer data, indicating efficient vertical mixing. But in the North, the surface depletion is much larger than in the entire column, suggesting poor vertical mixing. Reduced infrared emission of the seasonal caps stemming from CO2 depletion is not a major energy balance factor. This work illustrates how the atmosphere's composition at the surface can be significantly different from column‐integrated values.

Sub-10 nm Mixing and Alloying of Cu-Ag and Cu-Ni via Accelerated Solid Diffusion.

Development of nanoscale multicomponent solid inorganic materials is often hindered by slow solid diffusion kinetics and poor precursor mixing in conventional solid-state synthesis. These shortcomings can be alleviated by combining nanosized precursor mixtures and low temperature reaction, which could reduce crystal growth and accelerate the solid diffusion at the same time. However, high throughput production of nanoparticle mixtures with tunable composition via conventional synthesis is very challenging. In this work, we demonstrate that ∼10 nm homogeneous mixing of sub-10 nm nanoparticles can be achieved via spark nanomixing at room temperature and pressure. Kinetically driven Spark Plasma Discharge nanoparticle generation and ambient processing conditions limit particle coarsening and agglomeration, resulting in sub-10 nm primary particles of as-deposited films. The intimate mixing of these nanosized precursor particles enables intraparticle diffusion and formation of Cu/Ni nanoalloy during subsequent low temperature annealing at 100 °C. We also discovered that cross-particle diffusion is promoted during the low-temperature sulfurization of Cu/Ag which tends to phase-segregate, eventually leading to the growth of sulfide nanocrystals and improved homogeneity. High elemental homogeneity, small diffusion path lengths, and high diffusibility synergically contribute to faster diffusion kinetics of sub-10 nm nanoparticle mixtures. The combination of ∼10 nm homogeneous precursors via spark nanomixing, low-temperature annealing, and a wide range of potentially compatible materials makes our approach a good candidate as a general platform toward accelerated solid state synthesis of nanomaterials.

Unleashing the Influence of High-Throughput Flow Process Optimization on Luminescent Behavior of Engineered ZnO Quantum Dots

Engineered ZnO quantum dots (E-QDs) are sought-after nanostructures in healthcare and optoelectronic industries, necessitating a paradigm shift toward high-throughput continuous flow platforms, the crux to whose successful design and performance lies in comprehending the nucleation-growth kinetics, defect engineering, and reaction dynamics. This work investigates the synergistic interplay of enhanced hydrodynamics and heat–mass transfer in the helical coil reactor, fostering rapid nucleation-growth-driven E-QDs fabrication. We integrated computational fluid dynamic modeling, and comprehensive experimentation for producing E-QDs with record-high photoluminescence quantum yield (PLQY) (∼89% in the yellow-green spectrum) by carefully creating oxygen vacancies via a novel reproducible protocol. Dean vortices formed due to the helical geometry facilitated ultrafast mixing and accelerated reaction kinetics, yielding colloidally stable E-QDs in gram-scales [ζ = −39.7 mV, polydispersity index (PDI) ∼0.22] with a narrow particle size distribution (average particle size ∼4.5 nm). Contrastingly, the conventional batch route produced less stable E-QDs with ζ value of −15.3 mV, PDI ∼0.41, and diminished PLQY (∼40%) because of inadequate process control, batch-to-batch variability due to poor mixing, and heat transfer. The simple, economical, in-house-fabricated flow reactor manifested ∼90% increment in yield and reduced product cost. Thus, this research demonstrated the benefits of simulation-driven process engineering and reactor design in catalyzing QDs-based innovations.

Accelerated Solid Phase Glycan Synthesis: ASGS.

Solid phase synthesis is the most dominant approach for the preparation of biological oligomers as it enables the introduction of monomers iteratively. Accelerated solid phase synthesis of biological oligomers is crucial for chemical biology, but its application to the synthesis of oligosaccharides is not trivial. Solid-phase oligosaccharide assembly is a slow process performed in a variety of conditions and temperatures, requires an inert gas atmosphere, and demands high excess of glycosyl donors. The process is done in special synthesizers and poor mixing of the solid support increases the risk of diffusion-independent hydrolysis of the activated donors. High shear stirring is a new way to accelerate solid phase synthesis. The efficient mixing ensures that reactive intermediates can diffuse faster to the solid support thereby increasing the kinetics of the reactions. We report here a stirring-based accelerated solid-phase oligosaccharide synthesis. We harnessed high shear mixing to perform diffusion-dependent glycosylation in a short reaction time. We minimized the use of glycosyl donors and the need to use an inert atmosphere. We showed that by tailoring the deprotection and glycosylation conditions to the same temperature, assembly steps are performed continuously, and full glycosylation cycles are completed in minutes.

Study on Scale-Up of Anaerobic Fermentation Mixing with Different Solid Content

The scale-up technology of anaerobic fermentation stirring equipment is worthy of attention. Computational fluid dynamics (CFD) simulations were used to study the scale-up of anaerobic fermentation mixing under different solid content conditions. The applicability of different scale-up criteria was analyzed by investigating the relative parameters, such as the blade tip speed and the Reynolds number. On this basis, the scale-up index was optimized and verified. The results revealed the applicability of five common scale-up criteria under different solid content conditions. When the solid content is less than 5%, the anaerobic fermentation tank should be scaled up according to the same Weber number. When the solid content is between 5% and 10%, the anaerobic fermentation tank should be scaled up according to the same blade tip speed; it was especially suitable for anaerobic fermentation and other conditions that limit the shear rate. Scaling up according to the Reynolds number was not recommended due to the poor mixing effect. When the scale-up index x reached 0.75, there was no need to further reduce it. For anaerobic fermentation systems, the suitable scale-up indices selected for 5%, 10%, and 15% solid content were 1.1, 1, and 0.75, respectively.

Combustion dynamics of high Mach number scramjet under different inflow thermal nonequilibrium conditions

To characterize the impact of thermal nonequilibrium conditions in shock-induced combustion in high Mach number scramjet engines, a comparative numerical investigation has been performed. The combustor configuration was based on the HyShot II scramjet while the total enthalpy is 3.3 MJ/kg which resembles Mach 8 flight condition. The improved delay detached eddy simulation with Park two-temperature approach in combination with the vibration-chemical coupling model was employed in the nonequilibrium simulations. It is shown that under thermal nonequilibrium inflow conditions, noticeable stratification in the thermal state exists in the circumferential direction both in the combustor section and exhaust nozzle. In the inner core where the fuel mixes with the mainstream, flow deceleration caused by the heat release leads to a sufficient transformation of energy between the vibrational and translational-rotational modes approaching the thermal equilibrium state. However, the τv,mix is quite large in the supersonic mainstream, whereby the thermal nonequilibrium dominates. For the case with higher Tv in the inflow, the fuel jet's penetration height is lower while the local viscosity is higher which results in poor mixing between the fuel and air stream. Nevertheless, a 400 K increase in inflow Tv gives a higher effective temperature, which promotes the dissociation reactions, shortens the ignition distance and yields an 8% increase in the overall combustion efficiency. With better combustion performance, an additional 6% deceleration in the supersonic mainstream and the energy exchange rate between vibrational and translational-rotational modes becomes almost four times faster at the combustor outlet, which promotes the restoration of the thermal equilibrium state. Furthermore, under higher inflow vibrational temperature, the shock-induced combustion in supersonic crossflow becomes less stable with noticeable fluctuations in combustion heat release and local static pressure.

A CFD coupled photo-bioreactive transport modelling of tubular photobioreactor mixed by peristaltic pump

Optimisation and upscaling of biohydrogen production in externally pumped-recirculated photobioreactors (PBRs) are hampered by the infeasible computational cost of coupling hydrodynamics, to light transmission and bioreaction transport, through the column and peristaltic pump. This study approximates the complexities of peristaltic pump with inlet-outlet boundary conditions (BCs), introduces mean residence time (tm) for updating BCs, and unifies tm-dependent accelerated growth kinetics to parallelised Computational Fluid Dynamic (CFD) environment. Due to superior cost-savings compared to previous CFD studies, the bioprocess reliability under 5% coupled CFD-photo-bioreaction parameter uncertainties was investigated for the first time, and thoroughly validated with literature bioreaction data for a 1L PBR. The results agreed to within 10% of error for simulated velocities, identifying undesired regions with poor radial mixing, and showed similar output uncertainties between the coupled CFD-photo-bioreactions and pure photo-bioreactions models, indicating absence of numerical diffusion. Therefore, this approach has great potentials for modelling other similar biosystems.

Electric Arc Furnace Stirring: A Review

Thermodynamics and kinetics are affected by the stirring conditions. Higher‐stirring intensities promote conditions closer to equilibrium and increase the mass‐transfer coefficients. A major limitation of the conventional electric arc furnace (EAF) is the low velocities of liquid steel which result in very poor mixing conditions. The practical consequences are lower decarburization rates and lower melting rates. Herein, the forces that operate and promote the motion of liquid steel in a conventional EAF are reviewed in detail; buoyancy forces, momentum transfer by the oxygen jets, drag forces by CO bubbles are produced by decarburization and local electromagnetic forces at the electrode regions. It is shown in the short range and limited intensity of the previous forces. Bottom gas injection and electromagnetic stirring are the main methods that can induce forced convection in the EAF. The information available is summarized and analyzed to describe the results obtained at laboratory level and industrial scale using different stirring mechanisms. Finally, guidelines are provided in this review for further research on the basis of the limitations of the current results.

Evaluation of a computational strategy to model transitory injection in rotating detonation combustors

The efficiency of a Rotating Detonation Combustor (RDC) strongly depends on the transitory injection process of fresh reactants in the combustion chamber: poor propellant mixing induces losses of combustion efficiency and consequently low detonation speed and unstable detonation propagation. Moreover, dilution of fresh reactants with burnt gases during injection increases the deflagration losses and decreases the pressure gain provided by the detonation. Numerical simulation can help design an efficient injector to reduce these losses. In this study, the modeling strategy previously proposed by ONERA to simulate the transitory injection process is applied to two existing experimental RDC (from Nagoya University and TU Berlin) and one in-development RDC from ONERA. The computational domain represents only one injection element, convenient for a parametric study at low computational cost. A custom initial condition is used to model the expansion process of burnt gases past a detonation wave. The initial condition parameters are discussed and a method is proposed to correctly set them. The TU Berlin RDC is studied in more detail: mixing efficiency up to 70% is obtained, and 5% of deflagration losses are estimated according to the assumptions of the simulation. Based on the numerical results, detonation speed was evaluated at various distances from the injection plane taking into account the heterogeneities of the fresh mixture. The measured speed lies within the predicted range.

Numerical investigation of a large bore, direct injection, spark ignition, hydrogen-fuelled engine

This paper presents Unsteady Reynolds Averaged Navier Stokes (URANS) simulations of a large bore, hydrogen-fuelled direct injection spark ignition (DISI) engine at different spark and start of injection (SOI) timings. Six cases are simulated, including three with various spark timings at a low boost level and three with advanced to late injection timings at a higher boost level. The numerical simulations are validated with experimental data for four out of six cases, while the other two are considered blind computational fluid dynamics (CFD) simulations. It is shown that the autoignition occurs with advanced spark timing due to high in-cylinder pressure and unburnt temperature. For different SOIs, it is demonstrated that flame propagation involves a spark-initiated flame combined with an autoignition generated flame. The case with the late injection timing features poor mixing and slower combustion due to the presence of lean mixtures near the spark plug. As a result, this case features the lowest thermal efficiency when SOI is varied. In all cases, both mixture and temperature stratification are present. Simulations of zero-dimensional chemical reactors demonstrate that this stratification must be correctly captured for accurate prediction of autoignition timing.

The critical role of swirl in high-specific-output diesel engines

In-cylinder flows are critical for the understanding of the combustion process in internal combustion engines. Although swirl flow has been extensively employed as the primary in-cylinder flow motion in diesel engines, it is usually accompanied with reduced intake mass, and the necessity and the role of swirl flow in high-specific-output diesel engines still remain inadequately understood. In this work, the combustion process of a high-specific-output diesel engine is numerically investigated under different swirl ratios (SR). Results show that the indicated work exhibits a nonmonotonic variation of “increase–decrease” with increasing SR, peaking at SR = 1 with the shortest combustion duration yet slightly higher heat loss compared to the non-swirl condition. The introduction of swirl is capable of reducing high-equivalence-ratio regions through enhanced transport and turbulent diffusion, while the spray-spray interaction may be too strong to yield a rich region in the central cylinder when the swirl is excessively high. The chemical reaction pathway analysis indicates that a moderate swirl ratio could promote mixing, yielding an improved utilization of fresh O2 that further affect the reactions. Specifically, the highly reactive mixture enlarges the radical pool and yields a higher reaction rate during the mixing-controlled combustion stage; While an overlarge swirl ratio may cause excessive mixing, leading to reduced local availability of fresh O2 in the mixing-controlled combustion stage, thereby suppressing the oxidation of small molecule hydrocarbon and hence reducing the global heat release rate. Compared to the spray-induced turbulent mixing for the non-swirl case, the turbulence intensity is significantly increased through swirl-spray interaction under a moderate SR, which could preserve throughout late-cycle combustion and yield improved soot oxidation rate, while an excessive swirl would trap some soot within the central cylinder region and suppress late-cycle soot oxidation. According to the present results, solely high-pressure injection is not sufficient to control the combustion, particularly due to the poor late-cycle mixing and combustion, and an adequate swirl flow is still indispensable in high-specific-output diesel engines.

Thermal Stress Analysis and Optimization of FSW Process on UHMWPE by Using Hexagonal Tool Profile

Abstract: The use of polymeric materials has grown widely in various sectors such as packaging, building, electronic, automotive, and aerospace industries. Particularly, Ultra-High Molecular Weight Polyethylene has wide engineering applications and is used in large quantities in automotive oil pans, gears, slides, cams, bearings, fluid reservoirs, and the sports industry. Friction Stir Welding (FSW) is a solid-state process in joining thermoplastic materials. In this investigation, FSW process must be applied to join a UHMWPE plate of 8 mm thickness with specially designed hexagonal tool pin profile. The aim of this study is to examine the effect of main friction stir welding (FSW) parameters on the quality of UHMWPE plate welds. FSW machine, using a tool with a stationary shoulder and no external heating system. The welding parameters studied were the tool rotational speed which varied between 1300 and 1500 (rpm); the traverse speed which varied between 15 and 25 (mm/min), and the axial force ranging from 8 to 10 (KN). Good quality welds are achieved without using external heating, when the tool rotational speed and axial force are above a certain threshold. For high rotational speed and axial force welds have poor material mixing at the retreating side and mild voids at the nugget, tensile strength also obtained very poor. The hardness angle distortion and bead geometry also evaluated. Taguchi design optimum parameters and ANNOVA were found.

Numerical study on the internal fluid mixing and its influencing mechanisms of the wave-driven floating photobioreactor for microalgae production

The wave-driven floating photobioreactors (PBRs) with advantages of easy in scaling-up, low energy inputs and low fabricating cost, hold great potential for massive and cost-energy effective microalgae production. However, their applications may be seriously challenged by intermittent waves that could produce very poor mixing under poor wave conditions, leading to a significant reduction of biomass productivity or even collapse of the cultures. To improve the utilization efficiency of waves for efficient and stable microalgae production in the floating PBRs, this work aims at numerically studying the fluid-dynamics of the floating PBRs, as well as the effects from wave conditions, culture depth and three different PBRs’ structures of square, rectangular and circular types. The results showed that the liquid inside the floating PBRs follow a periodic sinusoidal and reciprocating flow, and the square PBR had aggressive mixing characteristics at high wave excitation frequency, while the rectangular PBR produced more intense mixing at low wave excitation frequency. Regarding the culture depth, the dependence of liquid mixing on the culture depth showed a decreasing trend. Moreover, the results indicated that the PBRs with a high culture depth had several dead zones, although there was apparent upward flow at the high excitation frequency. This work provides valuable insight into increasing the utilization efficiency of wave energy for mixing enhancement in the floating PBRs and their design.

Power Consumption and Fluid Mixing in a Scale-Down Geometry of a Stirred Digester for Biogas Production

A unconventional stirred tank of geometry typically adopted for the production of biogas is experimentally investigated with pseudo-plastic model fluids. The apparent viscosities of the fluids, based on the Metzner–Otto method, are in the range of 39–264 mPa·s, resulting in a range of rotational Reynolds number equal to 17–648. The power consumption of the three top-entering agitators is measured by a strain gauge technique, and the power number curve is obtained in the full range of flow regimes, going from laminar to fully turbulent conditions. The flow field measured by particle image velocimetry allows us to observe the fluid circulation patterns and their variations in different operative conditions. The measurements reveal relatively low axial and radial velocities, especially toward the bottom of the tank, that may hinder solid feedstock suspension and subsequent biogas production. Significant changes in the flow patterns are observed with small variations in the impeller speed and the mixture viscosity. The homogenization dynamics of a tracer obtained by planar laser-induced fluorescence leads us to estimate the dimensionless mixing time, a trend similar to that observed for conventional stirred vessel geometries. The detailed fluid dynamics information collected by a combination of different techniques can contribute to optimize the energy requirement and to avoid failure of the biogas production due to poor fluid mixing.

Numerical and experimental investigations on enhancement mixing performance of multi-blade stirring system for fluids with different viscosities

Abstract The poor mixing caused by zinc powder deposition in purification process is a serious problem which can’t be avoided in treatment of zinc-containing solid waste. Here, to enhance the purification efficiency of zinc-containing solid waste treatment reactor, two kinds of multi-blade combined stirring systems are compared with single layer four straight-blade and double-layer straight-blade (DFB) stirring systems which are traditionally chosen by industry. This study simulated and explored the flow field characteristics and purification effects of these four kinds of stirred-tank reactor, further proposes the unit ion purification energy (UIPE) as a criterion for purification energy consumption and effect evaluation. The results show that multi-blade combined (MBC) stirring system enhances axial flow by 12.56% in water. Meanwhile it effectively inhibits the growth of isolated mixing region which scope has decreased by 56.25%. In high viscosity Carboxymethylcellulose sodium solution, the fluid axial speed can be increased by up to 1407 times with MBC. MBC can increase the purification rate by 24.79% while the UIPE decreases by 29.45% compared with DFB which is used in industrial purification process. MBC paddle has exhibited a wide range of fluid viscosity applicability and axial velocity improvement effect. The improvement increases collisions between the impurity particles and the zinc powder particles, which increased rate of substitution reactions. The application of MBC solves the purification problem in the process of treating zinc-containing solid waste.

Climate Patterns Affecting Cold Season Air Pollution of Ulaanbaatar City, Mongolia

Many studies have been conducted on air pollution in Ulaanbaatar city. However, most have focused on the sources of pollutants and their characteristics and distribution. Although the location of the city subjects it to unavoidable natural conditions where air pollution accumulates during the cold season, nature-based solutions have not yet been considered in the projects implemented to mitigate air pollution levels. Therefore, this study aims to determine the combined influence of geography and atmospheric factors on cold season air pollution. The spatiotemporal variations in the variables were investigated using meteorological observation data from 1991 to 2020 in the different land-use areas. Then, atmospheric stagnation conditions and air pollution potential parameters were estimated from daily radiosonde data. Subsequently, the temporal variations in air pollutants were studied and correlated with estimates of the above parameters. In the Ulaanbaatar depression, the stable cold air lake (colder than −13.5 °C), windless (34–66% of all observations), and poor turbulent mixing conditions were formed under the near-surface temperature inversion layer in the cold season. Moreover, due to the mountain topography, the winds toward the city center from all sides cause polluted air to accumulate in the city center for long periods. Air pollution potential was categorized as very high and high (<4000 m2·s−1), in the city in winter, indicating the worst air quality. Thus, further urban planning policy should consider these nature factors.

Evaluating Fouling Control and Energy Consumption in a Pilot-Scale, Low-Energy POREFLON Non-Aerated Membrane Bioreactor (LEP-N-MBR) System at Different Frequencies and Amplitudes.

Continual aeration, a fouling control strategy that causes high energy consumption, is the major obstacle in the deployment of membrane bioreactors (MBRs) for wastewater treatment. In recent years, a technology has been developed which adopts mechanical reciprocity for membrane vibration, and it has been proven efficient for membrane scouring, as well as for saving energy: the low-energy POREFLON non-aerated membrane bioreactor (LEP-N-MBR). In this study, a pilot-scale LEP-N-MBR system was designed, established, and operated at various frequencies and amplitudes, and with various membrane models, so as to evaluate energy usage and membrane fouling. The results showed that a slower TMP rise occurred when the frequency and amplitude were set to 0.5 Hz and 10 cm, respectively. Under a suitable frequency and amplitude, the TMP increasing rate of model B (sealed only with epoxy resin) was slower than that of model A (sealed with a combination of polyurethane and epoxy resin). The average specific energy demand (SED) of the LEP-N-MBR was 0.18 kWh·m-3, much lower than the aerated MBR with 0.43 kWh·m-3 (obtained from a previous study), indicating a significant decrease of 59.54% in the SED. However, the uneven distribution of sludge within the membrane tank indicated that the poor hydraulic mixing in the reactor may result in sludge accumulation, which requires further operational optimization. The findings of this pilot-scale study suggest that the LEP-N-MBR system is promising and effective for municipal wastewater treatment with a much lower level of energy usage. More research is needed to further optimize the operation of the LEP-N-MBR for wide application.

Likelihood-free Hamiltonian Monte Carlo for modeling piping degradation and remaining useful life prediction using the mixed gamma process

The gamma process is a popular model to characterize the temporal uncertainty in degradation processes. According to this model, degradation occurs in tiny independent increments creating a monotonic non-decreasing trend. Mechanical components or units are often repetitively observed over time for measuring the extent of degradation; apparently, they degrade at different rates although operating in the same environment. The mixed gamma degradation process is suitable for capturing these unexplained differences. However, statistical estimation of its parameters and subsequent prediction of remaining useful life (RUL) turn challenging with limited and noisy measurements.While limited observations bring uncertainties to the model parameters, noisy data turns the likelihood function intractable. In such cases, approximate Bayesian computation (ABC) methods are widely applicable for their ability to bypass the likelihood evaluation and generate samples from an approximate target posterior distribution. The currently available Markov chain Monte Carlo (MCMC) based ABC method shows promising results, although it requires significant thinning due to poor mixing of samples. A new ABC method is derived in this paper which imitates the sampling process of the Hamiltonian Monte Carlo (HMC) method. The proposed ABC-HMC algorithm explores a target probability space more effectively — generating better mixing of samples and requiring less thinning than the MCMC based ABC method. Proof of convergence of ABC-HMC is shown by fulfilling the detailed balance condition. The application of the method is shown using real degradation data of piping components of the heat transport system of a nuclear reactor.

Environmental DNA Metabarcoding Reflects Fish DNA Dynamics in Lentic Ecosystems: A Case Study of Freshwater Ponds

Environmental DNA (eDNA) is a good indicator of fish diversity and distribution in aquatic environments. This study used metabarcoding to assess fish diversity and distribution in two connected ponds during two sampling periods. The eDNA analysis of surface samples displayed differences in the fish communities between the two connected ponds, while within each sampling site the species detected across the two time points were not always the same. These results revealed poor horizontal transport of eDNA between the two connected ponds alongside poor mixing of eDNA for a single pond’s stocked fish. Additionally, water temperature, pH, and total nitrogen were the key environmental factors affecting fish eDNA spatial and temporal distribution. These findings have important implications for designing eDNA sampling strategies in lentic ecosystems; for example, complete fish diversity in a lentic ecosystem cannot be detected by collecting only surface samples and in only one sampling period.