Primary Flow Research Articles

Photovoltaic Systems through the Lens of Material-Energy-Water Nexus

Solar photovoltaics (PV) has emerged as one of the world’s most promising power-generation technologies, and it is essential to assess its applications from the perspective of a material-energy-water (MEW) nexus. We performed a life cycle assessment of the cradle-to-grave MEW for single-crystalline silicon (s-Si) and CdTe PV technologies by assuming both PV systems are recycled at end of life. We found that the MEW network was dominated by energy flows (>95%), while only minor impacts of materials and water flows were observed. Also, these MEW flows have pyramid-like distributions between the three tiers (i.e., primary, secondary/sub-secondary, and tertiary levels), with greater flows at the primary and lower flows at the tertiary levels. A more detailed analysis of materials’ circularity showed that glass layers are the most impactful component of recycling due to their considerable weight in both technologies. Our analysis also emphasized the positive impacts that increased power-conversion efficiency and the use of recycled feedstock have on the PV industry’s circularity rates. We found that a 25% increase in power-conversion efficiency and the use of fully recycled materials in PV panel feedstocks resulted in 91% and 86% material circularity for CdTe and s-Si PV systems, respectively.

Pulsatile Blood Flow Simulation for Subject-Specific Geometry of a Human Aortic Arch

Pulsatile blood flow in a subject-specific human aortic arch and its major branches is studied computationally for a peak Reynolds number of 1553 and a Womersley number of 22.74. The aortic geometry is constructed from the CT-scan images of a subject. The aorta has out-of-plane curvature and significant area variation along the flow direction. A physiologically representative pulsatile velocity waveform is applied as boundary condition at the inlet of the aorta. The primary velocity profiles are skewed towards the inner wall of the ascending aorta during the entire cardiac cycle. In the decelerating phase, reverse flow is noted along the inner wall and the magnitude of maximum velocity is about 50 % of the peak flow condition. Flow separation is observed in the inner wall of the ascending aorta during the decelerating and reverse flow phases of the cardiac cycle. In the accelerating phase, however, flow separation does not occur. The major observation of the present work is the existence of complex and asymmetrical vortical flow structures which are not observed either in simple curved pipes or in idealized aortic arch computational studies. The relative strength of the secondary flow with respect to the primary flow is quantified by means of Relative Secondary Kinetic Energy whose highest value is evaluated to be 1.202 occurring near the entrance of the right carotid artery during the maximum reverse flow condition. High values of wall shear stress is observed at distal of the left and right subclavian arteries, the bifurcation of brachiocephalic artery between right subclavian artery and right carotid artery, and proximal inner wall of descending aorta during the cardiac cycle. The wall shear stress at the bifurcations of the branches are low and oscillatory and generally correlates with the preferential sites for atherosclerosis. The flow structures on the aorta wall are explicitly highlighted by the limiting streamlines. The application of limiting streamlines to clearly elucidate the complex on-wall flow structures is one of the key contributions of the present study. During the decelerating and reverse flow phases several critical points are observed on the aortic wall. These complex flow structures vanish during the accelerating phase. The observations made in the present study will be helpful in creating accurate and clinically useful computational models.

Prediction of the primary dendritic arm spacing in the laser metal deposition of Inconel 718 superalloy using the numerical and experimental techniques

In order to obtain the knowledge about the formation of the oriented structure in the additive manufacturing process, it is required to gain an accurate understanding about the formation and growth of grains. Hence, in this paper, the simulation of laser metal deposition was performed by the volume of fluid technique to predict the primary dendritic arm spacing, fluid flows, and geometry of the deposited layer. Moreover, the laser metal deposition of the Inconel 718 superalloy was performed experimentally to verify the results of simulation. From the results of simulation, a maximum error of about 8% was observed in the prediction of the geometry of the deposited layer. In addition, the difference between the value of primary dendritic arm spacing in the experimental and simulation results was about 14%. The results have also shown that a cellular dendritic structure was formed when the ratio of the temperature gradient to the cooling rate was more than 9 × 108, while when this ratio was less than 9 × 108, a columnar dendritic structure was formed. The results of simulations and experiments showed that an increase in the laser power from 350 to 450 W led to an improvement of about 9.5% in the size of primary dendrite arms due to the reduction in the temperature gradient, while the increase in the scanning speed from 3 to 5 mm/s resulted in a reduction of about 21% in the size of primary dendrite arms due to the faster cooling rate.

Combustion behavior study and flame zone analysis of biogas-fueled gas turbine combustor under O2/CO2 and O2/H2O oxidizing modes

Environmental problems resulting from the increment of greenhouse gases have raised the tendency toward using renewable energy sources alongside carbon-capturing technology via oxyfuel combustion. In this regard, numerical simulation on the feasibility of using renewable biogas in the gas turbine combustor under two combustion modes, namely, O2/CO2 and O2/H2O, at high operating pressure is investigated in the current research. Considering that conventional air-based combustion systems are not suitable for oxyfuel combustion regimes, the modification of the gas turbine combustor will be addressed to provide the necessary conditions for proper operation at higher power densities on an industrial scale. In this study, the focus is on investigating the influences of the primary diluent mass flow rate ratio (PDR) and the O2 content in the oxidizer composition on combustion and thermal behaviors of biogas flame such as distribution of reaction zone and temperature, combustion species, pattern factor, combustion efficiency, CO pollutant emission, and as well as flame stability in different combustion modes. The results indicated that the PDR parameter plays an essential role in the combustion stability within the gas turbine combustor due to its direct exposure to the vortices created in the recirculation zone. Moreover, combustion instabilities were observed for biogas flame at PDR = 15% in both combustion modes and in O2/H2O case at PDR < 25%. It was also found that CO emissions decrease significantly with increasing PDR, so in higher PDR values, CO pollutant levels were observed at 39 ppm and 21 ppm in O2/CO2 and O2/H2O cases, respectively.

An equivalent analysis of non-linear flow along rough-walled fractures based on power spectrum and wavelet transform

The classical cubic law deviates from the estimation of the flow rate because of the surface roughness distributed along the fracture surface, which can be decomposed as the primary and the secondary roughness. A piecewise equivalent model is developed to characterise the relationship between primary and secondary roughness and flow rate inside the fracture, setting the fractal dimension 2.0 as the piecewise point. The rough-walled fracture influenced by the primary and secondary roughness is quantitatively evaluated based on the wavelet transform and the power spectrum method. A classification criterion is then proposed to accurately capture the secondary roughness by investigating the non-linear flow behavior along rough-walled fractures using the lattice Boltzmann method. The results found that secondary roughness greatly enhances the flow non-linearity when the fracture fractal dimension exceeds 2.0, while secondary roughness has little effect on non-linear flow behavior with the fracture fractal dimension less than 2.0. The developed piecewise equivalent model shows that the non-linear flow pattern is affected by both fracture primary and secondary roughness. The flow variation along fractures with identical fracture apertures and primary roughness is greatly related to the influence of the secondary roughness. The increase of secondary roughness greatly decreases the hydraulic aperture and the permeability. This work provides an improved equivalent model which can be potentially used in field practices to precisely predict the non-linear flow property by emphasising the great impacts of the secondary roughness.

Enhancement of Control Jet Performance in Supersonic Crossflows Through Pilot Injection

Injection of a control jet into a supersonic crossflow creates a large region of separated flow in the vicinity of injection, altering the pressure distribution on the parent body, and consequently the effectiveness of the injected jet in producing the desired control forces and moments. In the case of an axisymmetric parent body, this disruption typically results in a loss of effectiveness due to the spillover of the shock structures around the parent body. In this study, a novel technique for enhancing this jet effectiveness on bodies of revolution by means of employing a pilot injection upstream of the main control jet is proposed and evaluated at different external flow conditions. We show that diverting a small fraction () of the primary control jet mass flow rate through an orifice situated five to 10 jet diameters upstream causes an earlier disruption of the external flow, leading to a weaker shock system around the primary injector. This reduces the extent of adverse interaction region and results in a lower spillover of the shock and vortical structures to the bottom side, leading to a significant improvement of the control effectiveness.

Large-eddy simulation of separated turbulent flows over a three-dimensional hill using WRF and OpenFOAM

It is not clearly known about the limitations of the large-eddy simulation (LES) mode of an atmospheric model (WRF) in predicting the microscale flows for engineering purpose. This study chooses a typical separated turbulent flow past a three-dimensional axisymmetric hill and investigates the performance of WRF-LES in comparison with the popular CFD solver (OpenFOAM). The numerical models and conditions are set similarly between the two codes. The instantaneous visualization shows that both WRF-LES and OpenFOAM-LES can produce the primary flow features, including hairpin vortices, horseshoes, and surface-shear-induced vortices at different scales, with high similarity. Nevertheless, the turbulent kinetic energy in the near wake produced by WRF-LES is underestimated, in comparison with WRF-LES. The energy spectra suggest that WRF-LES using the high-order advection schemes has a stronger capacity of generating and maintaining small-scale turbulent motions than OpenFOAM-LES. Furthermore, the deviation of numerical dissipation behavior is examined between the two solvers.

Structured porous blunt trailing edge with uniform and non-uniform parameters for vortex shedding noise reduction

Aiming at reducing the blunt trailing edge noise of flat plate, three-dimensional structured porous media with uniform and non-uniform porosities are designed. Acoustics and flow measurement using far-field microphone and particle image velocimetry (PIV) respectively have been implemented in the anechoic wind tunnel to investigate the mechanisms of noise reduction and flow manipulation. The chord-based inflow Reynolds numbers range from 4.8 × 105 to 1.5 × 106. The present work reveals that the regularized structured porous media could provide an effective noise reduction for the blunt trailing edge of flat plate similar to conventional randomized porous media (e.g. metal foam). When the uniform porosity is larger than 0.73, the tonal noise is suppressed significantly and the overall sound pressure level is decreased by 10 dB at least. However, some unexpected additional noise in the mid-to-high frequencies (1500–9000 Hz) occurs, which is associated with primary flow interactions inside the pore structures (cavity resonance). Further, four non-uniform porosity cases are studied to explore the optimization of porosity distribution. Not only is the tonal noise significantly reduced but also the additional noise is lower than that of uniform cases, which indicates that non-uniform porosity has more potential advantages for noise reduction. It is interestingly discovered that for the non-uniform porous trailing edge, the volume-average porosity and distribution trend play important roles respectively in suppressing the tonal noise and the additional mid-to-high-frequency noise. The PIV results demonstrate that 3D printed structured porous media can significantly weaken the vortex intensity of the shear layer and delay the generation of vortex shedding downstream, which are the critical underlying mechanisms for noise reduction. The porosity of uniform cases and the volume-average porosity of non-uniform cases are closely associated with the vortex shedding and the high-values benefit of suppression. And the analysis of wake velocity spectrum indicates that the additional noise is not correlated to the wake flow, but the cavity resonance might be the main reason.

Reverse engineering environmental metatranscriptomes clarifies best practices for eukaryotic assembly

BackgroundDiverse communities of microbial eukaryotes in the global ocean provide a variety of essential ecosystem services, from primary production and carbon flow through trophic transfer to cooperation via symbioses. Increasingly, these communities are being understood through the lens of omics tools, which enable high-throughput processing of diverse communities. Metatranscriptomics offers an understanding of near real-time gene expression in microbial eukaryotic communities, providing a window into community metabolic activity.ResultsHere we present a workflow for eukaryotic metatranscriptome assembly, and validate the ability of the pipeline to recapitulate real and manufactured eukaryotic community-level expression data. We also include an open-source tool for simulating environmental metatranscriptomes for testing and validation purposes. We reanalyze previously published metatranscriptomic datasets using our metatranscriptome analysis approach.ConclusionWe determined that a multi-assembler approach improves eukaryotic metatranscriptome assembly based on recapitulated taxonomic and functional annotations from an in-silico mock community. The systematic validation of metatranscriptome assembly and annotation methods provided here is a necessary step to assess the fidelity of our community composition measurements and functional content assignments from eukaryotic metatranscriptomes.

Abstract Number ‐ 131: Microsurgical Clipping and Endovascular Treatment of Paraclinoid Aneurysms: A Systematic Review and Meta‐Analysis

Introduction Paraclinoid aneurysms (PAs) have traditionally been treated with clipping. However, with the emergence of new techniques, endovascular treatment (EVT) has supplanted surgical treatment in recent years. We aimed to determine the safety and efficacy of EVT and microsurgical clipping for PAs. Methods A systematic review was performed in Scopus, Embase, Medline, Web of Science, and Cochrane from inception to March 2022 for all studies that tested the safety and efficacy of EVT or microsurgical clipping of PAs. Efficacy outcomes included complete aneurysm occlusion at last follow‐up, immediate complete occlusion, and an mRS 0–2 at last follow‐up. Safety outcomes included mortality, intraoperative and postoperative complications. We performed a random‐effects meta‐analysis of proportions and assessed the statistical heterogeneity across studies with I2 statistics. Results Eighty‐nine studies included 6496 patients, 3682 treated with EVT and 2814 with microsurgical clipping. Immediate complete occlusion rates were 92% (95% CI 88 – 96%; I2 = 60%) and 46% (95% CI 34 – 59%; I2 = 93%) for clipping and EVT, respectively. The rate of complete occlusion at last follow‐up was 94% (95% CI 91 – 96%; I2 = 0%) and 69% (95% CI 63 – 74%; I2 = 79%) for microsurgical clipping and EVT, respectively. Among EVT studies, the rate of complete occlusion was 54% (95% CI 48 – 59%; I2 = 50%), 52% (95% CI 39 – 64%; I2 = 73%), and 77% (95% CI 54 – 91%; I2 = 91%) for primary coiling, stent‐assisted coiling, and flow diversion, respectively. Among clipping studies, the rate of last follow‐up mRS 0–2 was 86% (95% CI 76 – 92%; I2 = 72%). Among EVT studies, the rate of last follow‐up mRS 0–2 was 94% (95% CI 86 – 98%; I2 = 93%). Mortality rate was 4% (95% CI 3 – 7%; I2 = 57%) and 1% (95% CI 0 – 3%; I2 = 0%) for clipping and EVT, respectively. Among EVT studies, the mortality rate was 3% (95% CI 1 – 6%; I2 = 0%) and 3% (95% CI 1 – 9%; I2 = 39%) for primary coiling and flow diversion, respectively. Intraoperative and postoperative complications were present in 9% (95% CI 6 – 14%; I2 = 68%) and 21% (95% CI 17 – 26%; I2 = 87%) among clipping studies, respectively. Intraoperative and postoperative complications were present in 6% (95% CI 4 – 9%; I2 = 64%) and 9% (95% CI 6 – 13%; I2 = 72%) among EVT studies, respectively. Conclusions In conclusion, microsurgical clipping and EVT for PAs are both safe and effective treatment modalities. Treatment via either approach should be determined on a case‐by‐case basis and according to institutional experience and resources.

Low-frequency unsteadiness of recompression shock structures in the diffuser of supersonic ejectors

Supersonic ejectors are passive gasdynamic devices that compress a low-pressure fluid by utilizing the kinetic energy of a high-pressure fluid in a variable area duct. The ejector consists of a primary supersonic nozzle in a mixing duct where the secondary flow is entrained and mixed. The mixed flow can undergo a series of recompression shocks resulting in a subsonic flow in the diverging portion to aid pressure recovery. Recompression shocks usually lead to unsteady shock boundary layer interactions. The performance of the ejector is influenced by shear layers, shock and expansion waves, and their mutual interactions. While existing literature has extensively dealt with mixing of the primary and secondary flows, the unsteadiness in flow resulting from recompression shocks has been seldom investigated. Fluctuations in pressure due to the unsteadiness of the shock often lead structural fatigue issues. This paper reports a detailed investigation on low-frequency unsteadiness of recompression shock using high-speed schlieren images and dynamic pressure measurements. Modal analyses using proper orthogonal decomposition and dynamic mode decomposition techniques are used to determine the dominant spatial modes and associated frequencies. Multimodal frequencies ranging between 80 and 300 Hz are observed. These findings are further corroborated by Fourier and wavelet transformations of the experimentally measured wall static pressure signals. Subsequently, scaling parameter is established for the dominant frequencies based on flow velocities upstream of the shock and the distance between two consecutive shocks. This results in a unique scaling frequency of 4.58% ± 18%, for the recompression shock independent of operating conditions.

Magnetic fabrics reveal three-dimensional flow processes within elongate magma fingers at the margin of the Shonkin Sag laccolith (MT, USA)

Unravelling magma flow in ancient sheet intrusions is critical to understanding how magma pathways develop and feed volcanic eruptions. Analyzing the shape preferred orientation of minerals in intrusive rocks can provide information on magma flow, because crystals may align parallel to the primary flow direction. Anisotropy of magnetic susceptibility (AMS) is an established method to quantify such shape preferred orientations in igneous sheet intrusions with weak or cryptic fabrics. However, use of AMS data to characterize how magma flows within the individual building blocks of sheet intrusions (i.e., magma fingers and segments), hereafter referred to as elements, has received much less attention. Here we use a high spatial resolution sampling strategy to quantify the AMS fabric of the Eocene Shonkin Sag laccolith (Montana, USA) and associated elongate magma fingers. Our results suggest that magnetic fabrics across the main laccolith reflect sub-horizontal magma flow, and inferred flow directions are consistent with an underlying NE-SW striking feeder dyke. Within the magma fingers, we interpret systematic changes in magnetic fabric shape and orientation to reflect the interaction between competing forces occurring during finger-parallel magma flow (i.e., simple shear) and horizontal and vertical inflation (i.e., pure shear flattening). For example, we highlight how local crossflow of magma between coalesced fingers increases the complexity of magma flow kinematics and related fabrics. Despite these complexities, the AMS data in coalesced magma fingers maintain their internal flow- and inflation-related fabrics, which suggests that magma flow within the fingers remains channelized after coalescence. Given that many sheet intrusions consist of amalgamated elements, our findings highlight the need to carefully consider element distribution and sample locations when interpreting magma flow based on AMS measurements.

Multilayered membrane spacer: does it enhance solution mixing?

AbstractThe present review systematically investigates and illustrates the effect of multilayered membrane spacers on the features of fluid dynamics that influence all performance metrics. Multilayer spacers are frequently composed of three sets of filaments (i.e., top, middle, and bottom layers), which has the benefit of increasing mass transfer and decreasing membrane surface fouling when compared to ordinary monolayer (e.g., extruded spacer) and two‐layer spacers. The review found that the multilayer spacer's middle layer disperses primary flow to the thin side spacers placed near the membrane's surfaces. The thin side spacers will then form narrow passageways to keep the solution in situ for as long as mass transfer is achievable. The employment of thin spacers close to the membranes at satisfactory operational conditions (e.g., adequate flow velocity) results in swirling flows and incorporation of transverse and longitudinal eddies near to the membranes, reducing the boundary layer's width and making the associated ion concentration domain at the membranes much more consistent. The concept and implementation of multilayer geometry in feed channels appears to be promising, since a multilayered spacer can function at a lower maximum flow velocity than normal two‐layer spacers, saving operational energy while minimizing concentration gradients at the membrane surfaces. Furthermore, the multilayer structure's durability and mechanical strength may help to reduce membrane deformation and maintain long processes. Future studies might look at significantly reducing spacer thickness for industrial uses. © 2023 Society of Chemical Industry (SCI).

Structural optimization of hydrogen recirculation ejector for proton exchange membrane fuel cells considering the boundary layer separation effect

Ejectors can greatly improve the efficiency of proton exchange membrane fuel cells (PEMFCs) by pumping unreacted hydrogen, and boundary layer separation (BLS) significantly impacts the recirculation performance of an ejector. However, current studies usually focus on improving ejector performance without considering the effect of the BLS. Therefore, this paper focuses on the influence of the key structural parameters of the ejector on the BLS and the recirculation performance of the ejector. A mathematical model of the hydrogen recirculation ejector is established. Considering the BLS effect, the influence of the ejector structure parameters on the BLS and the performance of the ejector are studied under the design condition. To ensure the high performance of the ejector in a wide working range, the structure of the ejector is optimized in the full working range. The results show that when the backpressure is less than the reflux point (3.47 bar), the ejector works in the subcritical mode, and the hydrogen recirculation ratio decreases rapidly with increasing backpressure. When the backpressure is 3.35 bar, the BLS appears, and the separation area increases with increasing backpressure. The optimized ejector has good hydrogen recirculation performance in a specific range of throat diameters (6.2–7.2 mm), constant-area mixing chamber lengths (26.8–33.5 mm), and nozzle exit positions (−8–2 mm). When the throat diameter is less than 13.4 mm or greater than 33.5 mm, the degree of BLS is intensified, and the recirculation performance of the ejector decreases sharply. When the primary flow pressure is 6 bar, the efficiency of the optimized hydrogen recirculation ejector is significantly improved by 33.2%.

Performance improvement of continuous horizontal fluidised bed dryer based on computational fluid dynamics

The fluidisation quality of a horizontal fluidised bed dryer (HFBD) is determined by the uniformity of airflow distribution in the distributor plates, which affects its drying efficiency. Based on predictions, the addition of baffles to the HFBD chamber increases the uniformity of airflow distribution, eliminates the primary vortex flow, and generates a uniform airflow distribution along the distributor plate. In this study, the airflow distribution of an HFBD with a baffle is investigated both numerically and experimentally. Simulations are conducted for an HFBD without baffles, with baffles, and with the new design based on five baffle inclination angles of 42.5°, 45°, 47.5°, 50°, and 52.5° under isothermal conditions. The k–ε turbulence model is used to simulate fluid flow to obtain the airflow distribution, vortex flow, and fluidisation direction. The minimum fluidisation velocity, derived analytically based on the particle size distribution, is used to estimate the fluidisation conditions along the distributor plate. Verification is performed by measuring the velocity distribution at five points along the bed using a hot-wire anemometer. A similar trend is indicated between the experimental and numerical simulation results, with a maximum error of 14.11%. The appropriate addition of baffles can eliminate backflow and increase the uniformity of airflow distribution. The results of this study show that improved airflow uniformity increases the effective drying area by 83.2% at the maximum, whereas the HFBDs with and without a baffle provide effective drying areas of 57.52% and 21.95%, respectively.

Improvement of drug processability in a connected continuous crystallizer system using formulation additive

Continuous crystallization in the presence of polymer additives is a promising method to omit some drug formulation steps by improving the technological and also pharmacological properties of crystalline active ingredients. Accordingly, this study focuses on developing an additive-assisted continuous crystallization process using polyvinylpyrrolidone in a connected ultrasonicated plug flow crystallizer and an overflow mixed suspension mixed product removal (MSMPR) crystallizer system. We aimed to improve the flowability characteristics of small, columnar primary plug flow crystallizer-produced acetylsalicylic acid crystals as a model drug by promoting their agglomeration in MSMPR crystallizer with polyvinylpyrrolidone. The impact of the cooling antisolvent crystallization process parameters (temperature, polymer amount, total flow rate) on product quality and quantity was investigated. Finally, a spatially segmented antisolvent dosing method was also evaluated. The developed technology enabled the manufacture of purified, constant quality products in a short startup period, even with an 85% yield. We found that a higher polymer amount (7.5–14%) could facilitate agglomeration resulting in “good” flowability without altering the favorable dissolution characteristics of the primary particles.

Experimental investigation on the performance of a novel resonance-assisted ejector under low pressurization

It is of great significance and value to apply different techniques to optimize the entrained performance of an ejector. In this paper, a novel resonance-assisted ejector is proposed by applying a mixing enhancement technique. Experimental studies were conducted to investigate the oscillation effect on the performance of the ejector under different geometries and operating conditions. The results show that adding high-frequency oscillations to the primary flow can provide up to a 14% improvement in entrainment performance. As the length of the resonance tube increases, the performance tends to increase and then decrease. The performance is sensitive to variations in the distance between the nozzle of the resonance generator and the inlet of the resonance tube. The shorter the distance, the greater the performance improvement. The critical pressure ratio of the resonance generator is approximately 5.5. The entrained performance enhancement rate increases gradually over the critical pressure ratio. Entrainment enhancement caused by resonance generator can be eliminated with small mixing cross-sectional areas. The oscillation effect enhances the entrained performance at different backpressures, and the higher the pressure the greater the enhancement rate. This paper provides new ideas for the optimization of ejector performance.

Assessment of Thermodynamic Efficiency of the Belarusian Energy System. Part 1

The energy system is one of the foundations of a modern state, so, the need for its successful development and functioning is beyond doubt. In this regard, an objective assessment based on a set of indicators (viz. economic, energy and thermodynamic) is relevant. However, the traditional assessment of the operation of the energy system is carried out on the basis of such characteristics as the specific consumption of conventional fuel for electricity generation and heat release, which does not provide a comprehensive picture and is not always applied correctly. In this article, for the first time on the basis of the exergetic method, the calculation of the exergetic efficiency is considered. The use of this indicator makes it possible to obtain an objective assessment of the thermodynamic efficiency of such a complex formation as the energy system of a modern country in the easiest way. As an example, the unified energy system of Belarus in general and condensing power plants in particular have been analyzed for a fairly long period (2000–2021) and in various characteristic time periods. The method of calculating the exergetic efficiency is described. The results obtained are presented graphically. Attention is paid to the issue of the acceptability of the error when generalizing data on the initial flows of primary energy resources and product flows of centralized generating sources of the energy system. The contribution of condensing power plants to the total volume of electricity generation is analyzed, the most advanced of them are determined from a thermodynamic point of view. The calculation of their energy and exergetic indicators was carried out; the changes associated with the commissioning of the Belarusian NPP were considered. The conclusion is made that further reconstruction of energy sources of the power system in order to reduce the relative weight of natural gas in the incoming part of the energy balance to 50 % is expedient. This can be achieved by increasing the thermodynamic efficiency.

Similarity characteristics of qualitative and quantitative regulation for adjustable ejector

Abstract In the new era of ejector technology entering into system scale from device scale. The methodology of regulation mode of an adjustable ejector has been summarized in this paper. The similarity in characteristics of qualitative and quantitative regulation under different operating modes are researched. The results show that both qualitative and quantitative regulation have the characteristics of ‘constant capacity’. Three different ‘constant-capacity’ phenomena in ejectors have been found, and the similarity indicates that the turbulent flow in ejectors has some statistical invariances in the form of mass flow rate of jetting flow. The ejector has the similar entrainment ability by increasing primary pressure by 43% in the qualitative regulation mode or enlarging the nozzle throat opening by 47% in the quantitative regulation mode under critical mode with similar underexpanded state. The advantages of adjustable ejectors have been promoted, in particular ±5% regulation accuracy or constant regulation ability, discharging improved ability by 80% in flow rate or 10% in pressure lifting ability in subcritical mode or primary flow rate saving ability by 25% or 13% in pressure lifting ability in critical mode.

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.