Volumetric Flow Rate Research Articles

Automated Gas Influx Handling Model and Mechanisms During Deep High-Temperature and High-Pressure Well Drilling

The exploration and development of oil and gas resources in deep formations is a key strategic priority for national energy production. However, manual methods for handling gas kicks suffer from low operating accuracy and inefficiency during high-temperature and high-pressure deep well drilling. To address the need for real-time bottomhole pressure prediction and control, an efficient gas–liquid–solid computing model was developed based on the gas slip model and cuttings settling velocity model. By integrating this model with an automatic choke adjustment system, an automatic gas kick attenuation model for deep well drilling was established. Results show that, compared to the driller’s and wait-and-weight methods, the automatic gas kick attenuation method significantly reduces peak choke pressure due to its larger frictional pressure drop and higher cuttings hydrostatic pressure. The automatic attenuation method not only leads to an average reduction of 28.42% in maximum choke/casing pressure but also accelerates gas removal, achieving gas kick attenuation ten times faster than the driller’s method and seven times faster than the wait-and-weight method. The study also investigates the influence of gas solubility, well depth, gas influx volume, formation permeability, and drilling fluid volumetric flow rate on gas kick attenuation characteristics. The findings provide a solid foundation for improving the efficiency of gas kick management in deep well drilling operations.

Flagellum pumping efficiency in shear-thinning viscoelastic fluids

Microorganism motility often takes place within complex, viscoelastic fluid environments, e.g. sperm in cervicovaginal mucus and bacteria in biofilms. In such complex fluids, strains and stresses generated by the microorganism are stored and relax across a spectrum of length and time scales and the complex fluid can be driven out of its linear response regime. Phenomena not possible in viscous media thereby arise from feedback between the swimmer and the complex fluid, making swimming efficiency co-dependent on the propulsion mechanism and fluid properties. Here, we parameterize a flagellar motor and filament properties together with elastic relaxation and nonlinear shear-thinning properties of the fluid in a computational immersed boundary model. We then explore swimming efficiency, defined as a particular flow rate divided by the torque required to spin the motor, over this parameter space. Our findings indicate that motor efficiency (measured by the volumetric flow rate) can be boosted or degraded by relatively moderate or strong shear thinning of the viscoelastic environment.

Characterization of artesian flow and heat transition in an ATES research wellbore using DTS monitoring and numerical modelling

Abstract. In the practice of Aquifer Thermal Energy Storage (ATES), the hydraulic connection to the wellbore of any other aquifers besides the planned thermal storage should be identified and prohibited in order to operate the ATES system in a sustainable way. The present study was aimed at locating an artesian aquifer other than the planned thermal storage in an ATES research wellbore (Berlin, Germany). Therefore, we analysed the wellbore temperature as monitored with a single fiber optic cable using the Distributed Temperature Sensing (DTS) technique in a series of artesian flow tests. The change in the wellbore temperature, the depth-dependent thermal gradients and the isotherms as derived from the DTS-monitored data helped positioning the artesian aquifer in the depth interval from 220 to 230 m. In addition, the transition from cooling to heating in the wellbore sections above the depth of 40 m was applied calculating the velocity of the artesian flow. A numerical model accounting for such artesian flow was built via matching the simulated volumetric flow rate to the wellhead measurements. The consistency of the simulated wellbore temperature with the DTS measurements validated this numerical model as well as the positioning of the artesian aquifer. These simulates extensively visualized the effect of the artesian flow on the near-wellbore temperature field.

Pulse electroosmotic flow of Newtonian fluids in parallel plate microchannels under triangular and half-sinusoidal pulse electric fields

Unlike the conventional electroosmotic flow (EOF) driven by direct current and alternating current electric fields, this study investigates the pulse EOF of Newtonian fluids through a parallel plate microchannel actuated by pulse electric fields. Specifically, the pulses considered encompass triangular and half-sinusoidal pulse waves. By applying the Laplace transform method and the residual theorem, the analytical solutions for the velocity and volumetric flow rate of the pulse EOF associated with these two pulse waves are derived, respectively. The influence of pulse width a¯ and electrokinetic width K on velocity is further considered, while the volumetric flow rate as a function of time t¯ and electrokinetic width K is examined separately. A comparison of the volumetric flow rates related to these two pulse waves under varying parameters is also conducted. The research findings indicate that irrespective of the pulse wave, a broader pulse width results in a prolonged period and increased amplitude of the velocity profile. Elevating the electrokinetic width yields higher near-wall velocities, with negligible effect on near-center velocities. It is noteworthy that regardless of the electrokinetic width, the near-wall velocity exceeds that of the near-center during the first half-cycle, while the situation reverses during the second half-cycle. The volumetric flow rate varies periodically with time, initially surging rapidly with electrokinetic width before gradually stabilizing at a constant level. More interestingly, independent of pulse width and electrokinetic width, the volumetric flow rates linked to the half-sinusoidal pulse wave consistently surpass those of the triangular pulse wave. For any pulse width, the volumetric flow rates corresponding to the two pulse waves grow with higher electrokinetic widths, especially prominent at alternating intervals of the two half-cycles within a complete cycle. These findings have important implications for improving the design and optimization of microfluidic devices in engineering and biomedical applications utilizing pulse EOF.

The Electrooxidation of Synthetic Bipyridyl Herbicide Wastewaters with Boron-Doped Diamond Electrodes: A Technical and Economic Study to Boost Their Application for Pollution Prevention in the Agricultural Sector

Boron-doped diamond electrodes (BDDEs) offer a highly efficient pathway to mineralize recalcitrant compounds due to their reduced energy requirements, fewer chemical inputs, and mechanical stability. In this work, the electrochemical degradation of paraquat (PQ) and diquat (DQ) was studied using an undivided cell (Condiacell®-type) at circumneutral pH, and under galvanostatic control. The roles of applied current density, volumetric flow rate, and herbicide concentration were systematically studied through a central composite design (CCD) using a closed-flow reaction setup. Under the best operating conditions (i.e., for PQ: 1.6 mA/cm2, 80 mL/min, and 70 mL/min, and 70 mg/L; and for DQ: 1.5 mA/cm2, 80 mL/min, and 73 mg/L), a spectrophotometric analysis evidenced that the herbicides were satisfactorily removed (ca. 100%) while mineralization degrees were above 90%. Furthermore, the produced effluents yielded significant increases in seed germination and root length, which suggest a reduction in toxicity. Energy consumptions of 0.13 and 0.18 kWh/g of TOC are reported with the electrochemical cells for the PQ and DQ treatments, respectively. The PQ and DQ treatments by electrooxidation are estimated to emit nearly 2.7 and 38.9 kg CO2/m3 of water treated, with a cost around USD 250/m3. Carbon emissions could be greatly decreased for PQ (0.28 kg CO2/m3) and DQ (0.40 kg CO2/m3) if electricity were generated from renewable resources. Although this study suggests that the use of BDDE can be considered as a green alternative for agrochemical removal due to lower carbon emissions, the environmental profile of the process is determined by the degree of renewability of the electrical grid of each country or region.

IMPROVING METHODS FOR PREDICTING THE STRUCTURE OF GAS-LIQUID FLOW IN HORIZONTAL PIPES

Analysis of existing research on the hydrodynamics of two-phase mixtures allows us to trace the main trends in the development of engineering calculation methods, as well as identify the most promising approaches for developing algorithms for predicting the patterns of gas-liquid flows in horizontal pipes. Predicting the patterns of two-phase flows is necessary to solve a number of applied problems related to the design of field pipeline systems, monitoring of operational parameters during the transportation of well products, calculation of hydraulic pressure drop in pipes, etc. Conventionally, in creating methods for predicting flow regimes in horizontal pipes, there are stages based on empirical approaches, mechanistic modeling and unification of hydrodynamic criteria for assessing the processes of patterns transformations of two-phase flows. Approaches based on the unification of hydrodynamic models of gas-liquid flows are noted as promising directions in the development of hydrodynamic forecasting criteria. The principles of unification consist in bringing to uniformity a mathematical apparatus capable of predicting all possible patterns of gas-liquid flow in vertical, inclined and horizontal pipes based on known volumetric flow rates of liquid and gas. The article proposes the improvement of known unification approaches in the development of criteria for predicting the annular and dispersed-bubble patterns of gas-liquid flow in field pipes. The verification of the obtained algorithms for pattern prediction of annular and dispersed-bubble modes of horizontal gas-liquid flow was carried out.

Unsteady flow rate in transient, incompressible pipe flow

AbstractKnowledge regarding current flow rates through pipes and other components is crucial for most hydraulic systems. The hydraulic power can be computed in combination with the pressure, which may be used in many applications, such as predictive maintenance. Most flow rate sensors used in the field of fluid power operate invasively. Therefore, the measurement process itself alters the flow rate. Furthermore, most sensors operate accurately for stationary flow but produce inaccurate measurements for transient flow. A well‐known method of determining the flow rate is to measure the pressure difference between two points along a pipeline and calculate the flow rate based on the law of Hagen and Poiseuille. However, since the relation mentioned above only applies to laminar, steady, and incompressible flow, its usefulness for transient flows is limited. This paper derives a system equation based on the fundamental laws of fluid mechanics, which describe transient, incompressible pipe flow. As a result, the fundamental equations are solved in the Laplace domain and subsequently transformed back into the time domain. The four‐pole theorem relates the pressure difference and the volumetric flow rate. The analytical solution consists of a convolution integral containing a weighting function and the pressure difference. Compared to a simulation, the novel equation displays high accuracy for transient and stationary incompressible pipe flow. This equation paves the way for a soft sensor, which allows the noninvasive measurement of arbitrary volumetric flow rates within pipes.

Ultrasonic-assisted radial jet reattachment atomizer

Ultrasonic atomization, a powerful method using high-frequency sound waves, has gained notable significance across diverse industries due to its capacity to disintegrate liquids into very fine droplets. The use of ultrasonic vibrations for spray formation can effectively address the challenges associated with conventional methods, including the requirement for high temperatures and high-pressure fluids. Compared to conventional methods, ultrasonic atomizers can deliver a spray with lower velocity, operate at lower temperatures, produce smaller particle sizes, achieve high evaporation rates, and impose low mechanical stress. The radial jet reattachment (RJR) nozzle is a unique design to modify a jet’s flow and improve its transport characteristics, especially in air drying and cooling processes. In this paper, a novel technology is utilized with the combination of an RJR nozzle and ultrasonic atomization to atomize most liquids. The corresponding atomization rate, mist droplet size distribution, and mist droplet velocity distribution, influenced by liquid properties, temperature change, transducer mesh pore size, and applied voltage have been investigated in this paper. The energy consumption ratios, defined as the ratio of thermal energy required to evaporate liquid divided by ultrasonic energy, are analyzed based on atomization rate and applied power, showing very promising results among atomizing methods. Furthermore, the results in terms of the droplet average diameter and mean velocity as well as the resultant volumetric flow rate under different operating conditions and for all working fluids considered have been correlated with the aid of non-dimensional parameters. In addition, certain potential applications based on the remarkable characteristics of the ultrasonic-assisted RJR atomizer such as misting liquids and spray drying are highlighted.

Electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid through parallel plate microchannels with surface charge-dependent asymmetric slip

The investigation of electromagnetohydrodynamic (EMHD) flow of non-Newtonian fluids in microchannels represents a compelling intersection of fluid dynamics, electromagnetism and materials science, particularly demonstrating significant potential and importance in contemporary microfluidic applications. This work delves into the intricate mechanisms governing the EMHD flow of non-Newtonian Jeffrey fluids within parallel plate microchannels, with a specific focus on the influence of asymmetric slip boundary conditions that depend on surface charge. The EMHD flow is propelled by the amalgamation of the Lorentz force and a consistent pressure gradient. Analytical solutions for the velocity and volumetric flow rate of this problem are derived employing both the method of separation of variables and Cramer's rule. Initially, this study undertook comparisons with prior research, leveraging pertinent assumptions to validate the precision of our findings. Subsequently, the discussion shifts to the examination of how velocities are affected by surface charge effects under various slip boundary conditions at different Reynolds numbers. The results suggest that velocities are significantly influenced by surface charge effects under asymmetric slip boundary conditions compared to scenarios involving symmetric and single-wall type, irrespective of the Reynolds number, thereby highlighting the importance of this study. Finally, the relationships among key parameters such as surface charge density, Hartmann number, relaxation time and retardation time affecting volumetric flow rate are analyzed, while approaches and specific percentages for increasing or decreasing volumetric flow rate are provided. One of the more interesting findings is that the volumetric flow rate is expected to experience a 3.9% reduction, considering the influence of the surface charge effect. These findings are not only vital for advancing microfluidics but also have the potential to drive new innovations in related medical technologies, given the notable similarities in the physical properties of Jeffrey fluid and blood.

Electro-osmotic flow and heat transfer in Jeffery fluid: A multi-membrane microchannel model

Microscale heat transfer is vital for the performance of smart thermal devices like heat sinks, thermosyphons, and microheat pipes. This study introduces a biothermal pumping flow model based on a multi-membrane pumping mechanism that leverages microscale heat transfer. The model describes rhythmic contraction and relaxation of membranes, combined with electro-osmosis in Jeffery fluid flow within a vertical microchannel of finite length. Two membranes on the microchannel walls, with varying amplitudes, diameters, and phase lags, generate pressure that moves fluid in both directions through contraction and expansion cycles. The model is based on the conservation of mass and momentum, using a low Reynolds number approximation to capture microscale transport phenomena at biomedical scales. Dimensionless conservation equations are analytically solved under no-slip boundary conditions, with results computed in MATLAB for clarity. Axial velocity results are simulated and verified using the optimal homotopy analysis method. The model explores the influence of key parameters (UHS, me, λ, Gr, β) on pressure gradient, velocity distribution, volumetric flow rates, skin friction, Nusselt number, and stream function. The findings demonstrate that pressure from membrane motion is significantly affected by thermal effects and buoyancy forces, and flow and pumping characteristics are largely determined by the fluid's rheological qualities and the geometrical features of the membrane. This study provides novel ideas for enhancing the functionality and design of smart thermal devices while also advancing microscale heat transfer technology.

Robust bilinear tracking control of a parabolic trough solar collector via saturation

This paper investigates the problem of robust tracking control of heat transport in a Parabolic Trough Solar Collector (PTSC), where the output has to track a desired reference trajectory. In this work, the PTSC is modeled by state-space bilinear dynamics. The manipulated variable is the pump volumetric flow rate, and the source term, i.e., solar irradiance, is assumed to be unmeasured. In addition, the actuator’s physical constraints induce saturation bounds on the manipulated variable and need to be considered explicitly in the controller design. To deal with these challenges, we first propose a saturated state-feedback law that meets the control objectives. Then, we reconstruct the unknown time-varying source term using an adaptive estimator. Later, through Lyapunov stability analysis, we prove that the closed-loop system and the output tracking error are uniformly ultimately stable. Numerical simulations attest to the performance of the proposed control strategy.

Thermal Characterization Methodologies for Experimental Minichannel Heat Sink Designs in Printed Circuit Board Assemblies

There has been a growing demand for novel, highly efficient, power-saving cooling solutions in recent years. In many cases, standard cooling techniques offer only limited opportunities to prevent the overheating of circuits. Such issues concern high-speed Printed Circuit Board Assemblies (PCBA) in data centers and telecommunication racks, where the flow of the cooling medium is obstructed due to the lack of space. Size limitations can also be a serious problem when cooling high-power devices because the devices consume a large space. Since the heat sink-based cooling solutions and the sophisticated IC packages only deal with one possible heat flow path, we were given the idea of enhancing the secondary heat flow path towards the Printed Circuit Board (PCB). Led by this intention, the idea of creating an embedded minichannel system inside the circuit board and circulating the cooling agent was realized. Through this method, we could decrease the board-to-ambient thermal resistance significantly. This paper presents the demonstration and feasibility study of this method. One of the main aims of this study is to demonstrate the applicability of the proposed concept in PCBAs, where the primary concerns are the low-cost manufacturability and available space. The other goal is to create an adaptation of the standard thermal characterization methodologies to deal with the specific dissipating components in the PCBA demonstrators. In the first part, the manufacturing technology is elaborated on, and its efficiency is characterized by thermal transient testing and Computational Fluid Dynamics (CFD) simulations. For these use cases, it was noted that the cumulative thermal resistance decreased by approximately 60% when a volumetric flow rate of 100 ccm was applied in the minichannels. In the second part, a more sophisticated technology demonstration is realized and characterized by adding the proposed embedded minichannel heat sink to an existing high-speed PCBA. A specific thermal transient testing was implemented specifically for this use case, and it was carried out on programmable logic devices by utilizing general-purpose programmable logic to construct the necessary measurement methods. In the future, this feature can be used in different logic circuit designs where it is not possible to determine the junction temperature directly.

An Automated Computational Fluid Dynamics Workflow for Simulating the Internal Flow of Race Car Radiators

In this article, we present a software tool developed in Python, named T-WorkFlow. It has been devised to meet some of the design needs of Tatuus Racing S.p.a., a leading company in the design and production of racing cars for the FIA Formula 3 Regional and Formula 4 categories. The software leverages the open-source tools OpenFOAM and FreeCAD to fully automate the fluid dynamics simulation process within car radiators. The goal of T-WorkFlow is to provide designers with precise and easily interpretable results that facilitate the identification of the geometry, ensuring optimal flow distribution in the radiator channels. T-WorkFlow requires the radiator’s geometry files in .stp and .stl formats, along with additional user inputs provided through a graphical interface. For mesh generation, the software leverages the OpenFOAM tools blockMesh and snappyHexMesh. To ensure uniform mesh quality across different configurations, and thus, comparable numerical results, various pre-processing operations on the specific geometry files are needed. After generating the mesh, T-WorkFlow automatically defines a control surface for each radiator channel to monitor the volumetric flow rate distribution. This is achieved by combining the OpenFOAM command topoSet with specific geometric information directly obtained from the radiator’s CAD through FreeCAD. During the simulation, the software provides various outputs that automate the main post-processing operations, enabling quick and easy identification of the configuration that ensures the desired performance.

Evaluation of the effect of viscosity on blood flow using viscosity models

The study of blood hemodynamics and rheological properties, particularly blood viscosity, is essential for understanding and treating certain cardiovascular conditions. Blood is a non-Newtonian fluid, meaning its viscosity varies with shear rate, a behavior driven by the aggregation and deformation of red blood cells (RBCs). Accurate modeling of blood viscosity is therefore critical for simulating blood flow in both physiological and pathological states. In this work, various viscosity models were assessed to identify the most suitable that represents the blood’s behavior in relation to shear rate. Although the Newtonian model is simple, it fails to capture the non-Newtonian characteristics of blood, particularly at varying shear rates. In comparison, the Power Law, Walburn-Schneck, and Carreau-Yasuda models offer more detailed and complex approaches to modeling blood viscosity. The Effect of blood viscosity on the overall blood flow was evaluated based on the four viscosity models. The work was carried out in a MATLAB Simulation Environment. The Volumetric blood flow rate was evaluated from the Poiseuille’s equation using three viscosity models whose values were defined by shear rates ranging from (217.5 – 226.5)s−1 . The percentage change in the blood volume resulting from changes in the viscosity was examined for each model. The two viscosity models (Power and Carreau models) concurrently reported equal percentage change of blood flux variation with the corresponding variation of the viscosity due to change in shear rate. This shows that any of the two models can be used to study the variation of blood flow to the viscosity with respect to cardiovascular complications.

Comprehensive validation of a compact laser speckle contrast imaging system for vascular function assessment: from the laboratory to the clinic.

Proper organ functioning relies on adequate blood circulation; thus, monitoring blood flow is crucial for early disease diagnosis. Laser speckle contrast imaging (LSCI) is a noninvasive technique that is widely used for measuring superficial blood flow. In this study, we developed a portable LSCI system using an 805-nm near-infrared laser and a monochrome CMOS camera with a 10 × macro zoom lens. The system achieved a high-resolution imaging (1280 × 1024 pixels) with a working distance of 10 to 35 cm. The relative flow velocities were visualized via a spatial speckle contrast analysis algorithm with a 5 × 5 sliding window. In vitro experiments demonstrated the system's ability to image flow velocities in a fluid model, and a linear relationship was observed between the actual flow rate and the relative flow rate obtained by the system. The correlation coefficient (R2) exceeded 0.83 for volumetric flow rates of 0 to 0.2 ml/min when channel widths were greater than 1.2 mm, and R2 > 0.94 was obtained for channel widths exceeding 1.6 mm. Comparisons with laser Doppler flowmetry (LDF) revealed a strong positive correlation between the LSCI and LDF results. In vivo experiments captured postocclusive reactive hyperemic responses in rat hind limbs and human palms and feet. The main research contribution is the development of this compact and portable LSCI device, as well as the validation of its reliability and convenience in various scenarios and environments. Future applications of this technology include evaluating blood flow changes during skin injuries, such as abrasions, burns, and diabetic foot ulcers, to aid medical institutions in treatment optimization and to reduce treatment duration.

Whole-channel acoustic energy and acoustophoretic efficiency frequency spectrum by the in-flow focusing method

The in-flow focusing method, introduced herein, enables rapid and straightforward measurements of the whole-channel acoustic energy of acoustic flow-through devices. The method is applied to assess the whole-channel acoustic energy and acoustophoretic efficiency frequency spectra of a bottom-actuated silicon-glass and a side-actuated glass chip. The input variables are the time-independent geometrical shape of the particle trajectories along the manipulation chamber, the channel cross-section geometry, the physical properties of the reference particles and fluid, and the volumetric flowrate. The outputs are the total acoustic energy, the acoustophoretic efficiency, as well as the acoustic energy density distribution along the channel, which provide a comprehensive overview of the performance of acoustically driven lab-on-a-chip setups. The acoustophoretic efficiency is an important parameter that relates the energy dissipation, and therefore the heat development in the device, to the useful acoustic energy in the channel. Unlike the current state-of-the-art methods such as particle image velocimetry, particle tracking velocimetry, and optical trapping, which are typically limited to small channel areas and are time-consuming, the in-flow focusing method can be applied to long channels and enables rapid measurements of the whole-channel acoustic energy. Published by the American Physical Society 2024

CFD investigations of a shape-memory polymer foam-based endovascular embolization device for the treatment of intracranial aneurysms.

The hemodynamic and convective heat transfer effects of a patient-specific endovascular therapeutic agent based on shape memory polymer foam (SMPf) are evaluated using computational fluid dynamics studies for six patient-specific aneurysm geometries. The SMPf device is modeled as a continuous porous medium with full expansion for the flow studies and with various degrees of expansion for the heat transfer studies. The flow simulation parameters were qualitatively validated based on the existing literature. Further, a mesh independence study was conducted to verify an optimal cell size and reduce the computational costs. For convective heat transfer, a worst-case scenario is evaluated where the minimum volumetric flow rate is applied alongside the zero-flux boundary conditions. In the flow simulations, we found a reduction of the average intra-aneurysmal flow of > 85% and a reduction of the maximum intra-aneurysmal flow of > 45% for all presented geometries. These findings were compared with the literature on numerical simulations of hemodynamic and heat transfer of SMPf devices. The results obtained from this study can serve as a guide for optimizing the design and development of patient-specific SMPf devices aimed at personalized endovascular embolization of intracranial aneurysms.

Assessment of different energy-based breakage distribution functions in population balance model of an industrial scale continuously operated wet stirred media mill

This study aimed at assessing various energy-based breakage distribution functions Bij within the context of a population balance model (PBM) of copper ore milling in a wet stirred media mill (WSMM). First, drop weight impact tests were performed to determine the size distribution parameters, tn. Second, various tn models called tn-fitted and tn-regenerated approaches were used to fit experimental tn, and their goodness-of-fits were compared. They were then used to construct the matrices of the cumulative breakage distributions, Bij, of the PBM, while a power-law form of the specific breakage rate function, Si, was assumed. By fitting the PBM to the product particle size distributions (PSDs) obtained under various rotor speeds, suspension volumetric flow rate, and solids content, we estimated the Si parameters. Results suggest that except the Napier-Munn model, all tn models fitted the experimental drop weight data reasonably well, which was reflected in the PBM fitting of the product PSDs. The PBM fits with Bij constructed with the tn-regenerated approach were more accurate than those with the tn-fitted approach. The PBM was validated with additional tests that were not considered in the parameter estimation. Overall, we have established that the choice of tn function and the methodology to determine Bij can affect the PBM predictions of the WSMM process significantly.

Comparative performance analysis of recuperative helium and supercritical CO₂ Brayton cycles for high-temperature energy systems

This study presents a comprehensive comparative analysis of recuperative Brayton cycles utilizing helium (He) and supercritical carbon dioxide (sCO2) as working fluids for high-temperature power generation, focusing on applications in next-generation concentrated solar power (CSP) systems. Thermodynamic cycle simulations were conducted across a temperature range of 1000 K–2000 K, exploring the effects of low-side pressure (1 bar–100 bar) and expansion ratio (1–5) on key performance indicators. These indicators included thermal efficiency, net specific work output, mass flow rate, volumetric flow rate, and system irreversibilities. Results demonstrate that helium-based Brayton cycles exhibit superior thermal efficiency at high temperatures, reaching up to 65 %, compared to sCO2 cycles, which achieve efficiencies up to 55 %. This advantage stems from helium's higher specific heat capacity and lower pressure drops within the cycle. Conversely, sCO2 cycles demonstrate higher net specific work output due to the fluid's higher density, leading to more compact turbomachinery. The study further investigates the impact of irreversibilities, including pressure losses, leakage losses, and heat transfer losses, on cycle performance. A detailed analysis of multi-stage Brayton cycles incorporating intercoolers and reheaters reveals the potential for further efficiency enhancements in both helium and sCO2 systems. This research provides valuable insights for the design and optimization of high-temperature power generation systems, particularly for next-generation CSP plants. The findings highlight the trade-offs between working fluid properties and cycle configurations, guiding the selection of optimal solutions based on specific application requirements and operating conditions.

Vortex Motion on the Surface of Shallow and Deep Water

The attenuation of vortex motion on the surface of shallow and deep water is investigated. The vortex flow was formed by two mutually perpendicular waves excited by plungers at a frequency of 6 Hz (wavelength λ = 5.6 cm) on the surface of water measuring 70 × 70 cm and depth h. After reaching a stationary state in the vortex system, the wave pumping was switched off, and the attenuation of the surface flow was recorded. On the surface of shallow water, λ/2π ≈ h, when the characteristic size of the vortices L exceeds the depth of the liquid, L h, the time dependence of the energy of the vortex flow Е(t) is described by an exponential function at all pumping levels, and the dependence of the enstrophy Ф(t) = Ω2(t) has an exponential dependence only in the range of wave vectors 0–0.3 см–1. On the surface of deep water λ/2π h, L ≈ h dependence Е(t) and Ф(t) are far from exponential in all ranges of wave numbers. At high pumping levels, the dependencies Е(t) and Ф(t) are nonmonotonic, which can be attributed to the influence of volumetric flows.