Energy Loss Regions Research Articles

Analysis of Flow Loss Characteristics of a Multistage Pump Based on Entropy Production

To reveal the internal flow loss characteristics of a multi-stage pump, the unsteady calculation of the internal flow field of a seven-stage centrifugal pump was carried out, and the entropy production theory and Q criterion were utilized to analyze the unsteady flow characteristics of each flow component under different flow rates. The research results show that as the flow rate increases, the entropy production value and the energy loss inside the flow components also increase accordingly. The viscous dissipation entropy production caused by fluid viscosity is very small, and the turbulent dissipation entropy production caused by turbulent fluctuations and wall dissipation entropy production are the main sources of energy loss. The impellers, diffusers, and outlet chamber are the main regions of energy loss in the multistage pump. The entropy production value of the first-stage impeller is significantly higher than that of other impellers, while the entropy production value of the first-stage diffuser is significantly lower than that of other diffusers. Through vortex structure analysis, it is found that the high entropy production regions in the impeller are concentrated in the impeller inlet area, the blade suction surface, and the impeller outlet area.

Research on the starting-up process of a prototype reversible pump turbine with misaligned guide vanes: An energy loss analysis

With fossil fuel depletion and rising demand for renewable energy, reversible pump turbines (RPTs) are crucial for balancing energy supply. Understanding the dynamics of RPTs during starting-up is essential for optimal performance and stability in renewable energy systems. The unique “S" curve of RPTs can lead to instability under transient conditions. This study aimed to investigate the impacts of misaligned guide vanes (MGV) devices on prototype RPT stability, pressure pulsation, and performance improvement during the starting-up process. Using CFD simulation, flow characteristics and energy loss during start-up were analyzed and validated against experimental data. The results show that MGV enhances stability but induces significant energy loss. The analysis of entropy production, vorticity transport, and pressure fluctuation revealed high energy loss regions and the evolution of vortices during the starting-up process. This study provides new insights into hydrodynamic challenges and energy loss with MGV in prototype RPT start-up, with implications for optimizing pumped storage hydropower operations. Overall, this study has valuable engineering significance for the development and application of RPT in renewable energy systems.

A setup for hard x-ray time-resolved resonant inelastic x-ray scattering at SwissFEL.

We present a new setup for resonant inelastic hard x-ray scattering at the Bernina beamline of SwissFEL with energy, momentum, and temporal resolution. The compact R = 0.5 m Johann-type spectrometer can be equipped with up to three crystal analyzers and allows efficient collection of RIXS spectra. Optical pumping for time-resolved studies can be realized with a broad span of optical wavelengths. We demonstrate the performance of the setup at an overall ∼180 meV resolution in a study of ground-state and photoexcited (at 400 nm) honeycomb 5d iridate α-Li2IrO3. Steady-state RIXS spectra at the iridium L3-edge (11.214 keV) have been collected and are in very good agreement with data collected at synchrotrons. The time-resolved RIXS transients exhibit changes in the energy loss region <2 eV, whose features mostly result from the hopping nature of 5d electrons in the honeycomb lattice. These changes are ascribed to modulations of the Ir-to-Ir inter-site transition scattering efficiency, which we associate to a transient screening of the on-site Coulomb interaction.

Characteristics of the axial compressor with different stator gaps in compressed air energy storage system

The axial compressor in compressed air energy storage (CAES) system needs to operate stably and efficiently within a wide working range. The stator gap plays a critical role in suppressing corner separation and enhancing blade throughflow. The primary objective of this study is to determine the optimal combination of stator gaps to further expand the stable working range of the compressor while ensuring high efficiency. In this study, the flow characteristics of different stator gaps of the five-stage axial compressor in a specific CAES system are researched numerically. Firstly, the impact of different stator gaps on the aerodynamic performance is analyzed. The stator gap effectively broadens the stable working range of the compressor, with the hub gap exhibiting greater potential for expansion compared to the shroud gap. Subsequently, a comparative analysis is conducted on the internal flow of the third stage stator under near-stall conditions. Different gap leakage forms different vortex structures, and the gap leakage can effectively eliminate the accumulation of low-energy fluid in the corner area, optimize the limit streamlines on the blade suction surface and the temperature distribution. The low-velocity area caused by different stator gaps is also different. Finally, energy loss and energy dissipation with different stator gaps are explored. The gap leakage flow results in high energy loss, and different stator gaps exhibit notable differences in distribution of the high energy loss regions. Different types of stator gaps exhibit consistent high energy dissipation areas, which include the leading-edge stagnation area, boundary layer area on blade surface, and wake area. It is important to note that the high energy loss area does not necessarily coincide with the high energy dissipation area. The combined application of two loss evaluation methods contributes to a more comprehensive investigation of the loss distribution characteristics of the compressor.

Numerical investigation of energy loss distribution in the cavitating wake flow around a cylinder using entropy production method

The wake flow of a circular cylinder is numerically investigated by Large Eddy Simulation (LES) combined with the Schnerr–Sauer cavitation model. By comparing entropy production in the presence or absence of cavitation, the energy loss distribution in the wake flow field of a cylinder is explored, shedding light on the interactions between multiscale vortex systems and cavitation. The comparative results reveal that, under non-cavitating conditions, the energy loss region in the near-wake area is more concentrated and relatively larger. Energy dissipation in the wake flow field occurs in regions characterized by very high velocity gradients, primarily near the upper and lower surfaces of the cylinder near the leading edge. The influence of cavitation bubbles on entropy production is predominantly observed in the trailing-edge region (W1) and the near-wake region (W2). The distribution trends of wall entropy production on the cylinder’s surface are generally consistent in both conditions, with wall entropy production primarily concentrated in regions exhibiting high velocity gradients.

Stain-free mapping of polymer-blend morphologies via application of high-voltage STEM-EELS hyperspectral imaging to low-loss spectra

Polymer blends composed of multiple types of polymers are used for various industrial applications; therefore, their morphologies must be understood to predict and improve their physical properties. Herein, we propose a spectral imaging method based on scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy to map polymer morphologies with nanometric resolution as an alternative to the conventional electron staining technique. In particular, the low-loss spectra of the 5–30 eV energy-loss region were measured to minimize electron irradiation damage rather than the core-loss spectra, such as carbon K-shell absorption spectra, which require significantly longer recording times. Medium-voltage (200 kV) and high-voltage (1000 kV) STEM was used at various temperatures to compare the degrees of electron-beam damage resulting from various electron energies and sample temperatures. A multivariate curve resolution technique was used to isolate the constituent spectra and visualize their distributions by distinguishing the characteristic peaks derived from various chemical species. High-voltage STEM was more useful than medium-voltage STEM for analyzing thicker samples while suppressing ionization damage.

Improvement of energy performance of the axial-flow pump by groove flow control technology based on the entropy theory

Energy loss is a key factor affecting the performance of the axial-flow pump, especially under the low flow conditions when sharply decrease of energy performance happens and strong vibration of the units poses great threats to the system safety. To address this problem, the entropy theory was utilized to quantitatively analyze and accurately locate the energy loss of axial-flow pump under different working conditions, and to analyze the improvement of energy performance of the axial-flow pump by groove flow control technology. The energy loss characteristics before and after the addition of grooves were compared under different flow rates, and the mechanism of improving energy performance of the axial-flow pump by groove flow control technology was revealed. 1) The impeller and guide vane are the main regions of energy loss in the flow passage under different flow conditions, which is of vital importance to the energy performance. Under the low flow conditions, the energy loss of the inlet pipe region is also nonnegligible, averagely accounts for 30% of the total entropy production in the saddle area. 2) The high entropy generation area in the impeller region is concentrated near the blade tip on the cylinder surface besides the shroud and the high entropy generation area in the inlet pipe region is besides the wall near inlet of the impeller under the low flow conditions. 3) After adding grooves, the total entropy production of axial-flow pump decreases under low flow conditions, especially under the deep stall condition, 5.32% in the impeller region and 17.26% in the inlet pipe region, leading to an increase of head by 65.77%. 4) Under the deep stall condition, the elimination of main passage vortex and the weakening of clearance vortex in the impeller region will lead to a significant decrease of the local entropy generation in the impeller, which is the underlying causes of the improvement of the energy performance in the saddle area of the axial-flow pump. The groove flow control technology applied in this paper can effectively improve the energy performance of the axial-flow pump, which provides valuable references for the improvement of energy characteristics in similar hydraulic machinery.

Investigation of energy loss mechanism of shroud region in A mixed-flow pump under stall conditions

The energy consumption of various pumps accounts for almost 20% of the world’s electricity production, and the improvement of pump efficiency could save enormous energy consumption globally. In a mixed-flow pump, the hydraulic loss within the shroud region accounts for almost 30% of the whole loss in the impeller, which is an inevitable factor. Therefore, in this study, the loss near the end wall of impeller caused by the tip leakage flow (TLF), secondary flow and disorder flow, etc., is quantitatively investigated by the entropy production loss theory. The purpose is to find out the serious region of energy loss and conduct the structure optimization in the future. The research shows that the tip leakage vortex (TLV) and the TLF “jet effect” are responsible for the hydraulic loss within the shroud region in the designed flow fields. In the stall flow fields, some unsteady flow components are the additional loss source, such as the secondary flow vortex, separation flow vortex, secondary TLV, and wake vortex. In the deep stall flow fields, the coupling effect between reverse flow near shroud and inlet swirling flow would be the source of periodicity stall characteristic with high possibility.

Flow-drag reduction performance of a resident electrolytic microbubble array and its mechanisms

This work examines the problem of stable high-efficiency flow drag reduction for underwater vehicles using microbubble arrays. To this end, test pieces for micropore arrays capable of forming self-stabilizing arrays of microbubbles via electrolysis have been prepared. The quantitative relationships between the electrolysis voltage, micropore size, and flow velocity (v) and the growth behaviors and residence stability of electrolyzed microbubbles were examined by experimental and numerical methods. The flow drag reduction performance and mechanisms of microbubble arrays were investigated. It has been shown that an electrode-wall micropore array can be used to achieve self-adaptive start-stop control of microbubble electrolysis. A micropore diameter-to-depth ratio of k = 2 was found to be optimal for generating arrays of electrolytic microbubbles with good stability in flow. Two types of microbubbles are generated: the air-film type exhibits greater resident stability than the protruding type. The average measured flow-drag-reduction rate of a microbubble array with 250 μm micropores was found to be around 26%. The energy-loss region of free-fluid flow with a solid wall was 0.037 mm thicker than that with a microbubble-array wall (v = 0.5 m/s), meaning that more energy is consumed, leading to greater flow drag. Significant up-thrown flow induced by elastic deformation of microbubbles and air/water interface forces can suppress turbulent coherent structural bursts and reduce near-wall Reynolds shear stress. The mean values of turbulence-related characteristic parameters (vorticity = 890.55 s−1, kinetic energy = 0.08096 m2/s2, shear stress = 17.75 Pa, and v = 0.5 m/s) of the boundary-layer flow over the microbubble-array wall were found to be greatly reduced. This demonstrates the good turbulent friction drag reduction performance of the resident microbubble array.

Evolution Characteristics of Energy Change Field in a Centrifugal Pump during Rapid Starting Period

Although the energy change field in the centrifugal pump has been investigated under quasi-steady conditions (QSC), equivalent information is not yet known during the rapid starting period (RSP). A centrifugal pump loop system is constructed to investigate the energy change field in the centrifugal pump during RSP. The RSP is selected as a linear rotational speed from 0 rev/min to 2900 rev/min (design rotational speed) and a constant valve opening of 0.569. Results show that the flow rate lags behind the pump head value with the linear increase in rotational speed. The large values of partial derivations of mechanical energy in normal and tangential components are mainly concentrated at the impeller outlet, whose position is insensitive to rotational speed. The region of dominant energy loss is negatively correlated with rotational speed, and an opposite phenomenon is observed in the region of dominant energy increase. With the rotational speed increasing, the mean energy gradient function in the pump impeller and pump volute gradually increases, and the slope of the former is less than that of the latter. After reaching the design rotational speed, the energy change field gradually approaches that under quasi-steady conditions.

Energy loss mechanisms of transition from pump mode to turbine mode of an axial-flow pump under bidirectional conditions

Pump-as-turbine stations with ultra-low head often face the deterioration risk during load rejection operations when the demands in water delivery and power generation are satisfied. In the course of load rejection, significant energy transfer and hydraulic instability may ensue from the pump-to-turbine transition mode, and vice versa. In order to investigate the variation of energy loss during the transition process of a bidirectional axial-flow pump, the entropy production method is herein utilized for visualization and quantitative analysis of high energy loss regions within key components. In the process of transient simulation, the torque balance equation is applied for calculating the rotational speed of impeller. Two-way transitions are considered with the bidirectional pump for comparing two distinct forms of pumps equipped with front and rear guide vanes. Results show that the simulated external characteristic curves and transition parameters of the pump are in good accordance with the experimental data. The transient process of the transition successively goes through four modes, i.e. pump, braking, turbine and runaway modes. In the process of the direction switch of the main flow and rotation, the different positions of guide vanes also deeply influence the inflow angle and flow pattern in impeller, and then change the distribution of the pressure coefficient, vorticity and entropy production rate. In pump mode, the entropy production rate and pressure coefficient at the impeller inlet edge under backward transition condition (BTC) is higher than that under forward transition condition (FTC), due to the smaller inflow angle caused by the front guide vanes under BTC. In runaway operation, the total entropy production (TEP) under FTC is obviously higher than that under BTC, because the energy loss is reduced by the broken shedding vortices caused by the obstruction of the guide vanes under BTC. This study's results can be referred to while seeking for the operation safety and stability of the pump stations consecutively used to pump and generate power.

Performance Characteristics and Energy Loss Analyses of a High-Speed Centrifugal Pump with Straight Blades

Along with the rapid growth of cutting-edge petrochemical technology and the pressing demand for efficiency improvement, evaluation of the performance characteristics of high-speed pump is becoming increasingly important. In this paper, numerical simulation is presented on the flow instability of a 16 straight-blade high-speed centrifugal pump with flow rate of 3 m3/h and rotating speed of 8500 rpm. Combined with the analysis of flow stability, the entropy production method is introduced to evaluate regions of high mechanical energy loss and its distribution at different flow rates. Results show that approximately 96% of the energy loss of the pump is produced in the volute, gap, and front and back chambers. Large energy loss is observed near the trailing edge of the blade and volute tongue, which are caused by the small region including both the high and low pressure gradients and large momentum exchange by the flow separation, respectively. Moreover, the rotor–stator interaction causes much energy loss at the wall of the volute and front and back chambers. Owing to the circumferential pressure gradient and the 90° leading edge of the straight blade, the fluid tends to form counter-rotating recirculation vortices. The large number of blades narrows the passage and limits the formation of large vortices in flow channels, thus the backflow phenomenon seems not to worsen with the rise of flow rates. Hence, the entropy production in most of the flow parts are insensitive to flow rates.

TEM analysis of radiation effects in ODS steels induced by swift heavy ions

Oxide dispersion strengthened steels ODS Eurofer and ODS 13.5Cr-0.3Ti were irradiated with 945 MeV Au ions and 167 MeV Xe ions at room temperature. Beam-induced microstructural changes were analyzed by high-resolution transmission electron microscopy in the region of maximum electronic energy loss of 55 and 30 keV/nm, respectively.In both ODS steels, an increase in the fraction of small oxide inclusions (<5 nm) was observed. In ODS Eurofer steel, the irradiation with Xe and Au ions leads to the formation of amorphous tracks in yttrium oxide inclusions larger than 8 nm with track diameters of 2 nm and 3–4 nm, respectively.

A theoretical and experimental investigation of Bragg's rule for energy-loss straggling in low mean energy loss regime in air and its constituents

A theoretical and experimental investigation of Bragg's rule in low energy loss region where charge exchange straggling can be ignored is presented. Energy-loss straggling of 5.486 MeV alpha particles in air and 5N purity constituent gases was measured using high-resolution alpha spectroscopy system. Measured values are compared with Bohr, Bethe-Livingston and Yang et al. formulations. An experimental investigation of Bragg's rule to estimate the energy-loss straggling in air using the experimental data of constituents is discussed.

Large eddy simulation of energy gradient field in a centrifugal pump impeller

Large eddy simulation of the fluid flow in a centrifugal pump impeller is conducted at design load and quarter load, and the energy gradient field is analyzed to reveal the behavior of internal flow. A universal equation for calculating the energy gradient function, which is defined as the ratio of energy increase (transversal gradient of the mechanical energy gradient) to energy loss (stream-wise gradient of the work done by shear stress), is adopted. Research results show that positive and negative 0.3 for the logarithm of energy gradient function are critical values that reflect dominant energy increase and dominant energy loss, respectively. The large eddy simulation results indicate that the magnitude and shape of energy gradient field are affected by turbulent fluctuation. The energy gradient field in the impeller at mid-height has more small-scale features than those in the impeller at zero and one heights. The regions of dominant energy increase and dominant energy loss are highly distinct at both design load and quarter load. In some large areas, neither dominant energy increase nor dominant energy loss is observed at quarter load in the impeller passage. These results, which are mainly attributed to a highly separated flow, are not evident at design load. The region of dominant energy increase at design load is larger than that at quarter load, particularly close to the volute. The magnitude of mean logarithm of energy gradient function at quarter load is evidently smaller than that at design load, but its value remains higher than 1.0.

An EELS signal-from-background separation algorithm for spectral line-scan/image quantification

Background removal is an important step in the quantitative analysis of electron energy-loss structure. Existing methods usually require an energy-loss region outside the fine structure in order to estimate the background. This paper describes a method for signal-from-background separation that is based on subspace division. The linear space is divided into two subspaces. The signal is recovered from a linear subspace containing no background information, and the other subspace containing the background is discarded. This method does not rely on any signal outside the energy-loss range of interest and should be very helpful for multiple linear least-squares (MLLS) regression analysis on experimental signals with little or no available smooth pre-edge region or with overlapping pre-edge features. Use of the algorithm is demonstrated with several practical applications, including closely overlapping core-loss spectra and zero-loss peak removal. Tests based on experimental data indicate that the algorithm has similar or better performance relative to conventional pre-edge power-law fitting methods in applications such as MLLS regression for electron energy-loss near-edge structure.

Biventricular vortex ring formation corresponds to regions of highest intraventricular viscous energy loss in a Fontan patient: analysis by 4D Flow MRI

Biventricular vortex ring formation corresponds to regions of highest intraventricular viscous energy loss in a Fontan patient: analysis by 4D Flow MRI

Extension and applications of switching model: Range theory, multiple scattering model of Goudsmit–Saunderson, and lateral spread treatment of Marwick–Sigmund

The switching model (PSM) developed in the previous paper is extended to obtain an “extended switching model (ESM). In the ESM, the mixt electronic-and-nuclear energy-loss region, in addition to the electronic and nuclear energy-loss regions in PSM, is taken into account analytically and appropriately. This model is combined with a small-angle multiple scattering range theory considering both nuclear and electronic stopping effects developed by Marwick–Sigmund and Valdes–Arista to formulate a improved range theory. The ESM is also combined with the multiple scattering theory with non-small angle approximation by Goudsmit–Saunderson. Furthermore, we applied ESM to lateral spread model of Marwick–Sigmund. Numerical calculations of the entire distribution functions including one of the mixt region are roughly and approximately possible. However, exact numerical calculation may be impossible. Consequently, several preliminary numerical calculations of the electronic, mixt, and nuclear regions are performed to examine their underlying behavior with respect to the incident energy, the scattering angle, the outgoing projectile intensity, and the target thickness. We show the numerical results not only of PSM and but also of ESM. Both numerical results are shown in the present paper for the first time. Since the theoretical relations are constructed using reduced variables, the calculations are made only on the case of C colliding on C.

Spatially Resolved Characterization of Phases in LiFePO4 Battery Cathodes Using Low Loss Electron Energy-loss Spectroscopy

Lithium iron phosphate (LiFePO4) has considerable potential for automotive applications due to its high rate capability, reasonable energy density and environmentally benign nature [1]. However, performance degradation seen after thousands of cycles at high charging-rates (C-rates) has been a point of major concern [2]. Studies of the aging mechanism suggest that phases (LiFePO4/FePO4) formed in the cathode during discharge influence the aging profile [3]. These phases have been investigated recently using x-ray and neutron diffraction [4, 5]. While these methods provide insights into crystal structure and unit cell volume changes associated with phase changes between LiFePO4 and FePO4, their ability to provide spatially resolved measurements of quantities such as Li and Fe concentration at the nanoscale is severely limited. Such measurements are key to confirming the presence or absence of the phases mentioned above and solid solution phases (LixFePO4). With recent advances in aberration corrected electron microscopy, electron energy-loss spectroscopy (EELS) performed in the scanning transmission electron microscope (STEM) has emerged as a leading technique to obtain spatially resolved measurements of chemistry, structure and bonding. Previously, researchers have used shifts observed in core-loss peaks of iron and oxygen to study the delithiation of FePO4 host lattice [6-8]. However, these ionization edges have relatively small inelastic scattering cross sections, and consequently, a relatively high electron dose is required to achieve acceptable signal-to-noise ratios in the data resulting in significant electron beam damage to the specimen. The low energy-loss region of the spectrum (0-40 eV) can be very useful since (i) the intensity is much larger compared to the coreloss spectrum and (ii) lesser collection time is required which significantly lowers the risk of beam damage to the material. In this study, we explore the use of low loss EELS to characterize the nominally pure LiFePO4 powder with trace amounts of FePO4 which is typical of phase mixtures that is present during phase transformation within the LiFePO4 battery cathode at the nanoscale during aging.

Optical and structural properties of 6H–SiC irradiated by [formula omitted] coimplantation

Single crystal 6H–SiC irradiated by Si3+⧹He+ coimplantation was studied to analyze changes in structural and optical properties by Raman spectroscopy, UV–visible transmittance spectroscopy and Fourier transform infrared reflectance. Four ion irradiation experiments were performed, He+ (single), Si3+ (single), Si3++He+ (successively) and Si3+ & He+ (simultaneously). The fluences for 18MeV Si3+ and 2.2MeV He+ at the damage peak are 0.55dpa and 35appm, respectively. The synergistic effect due to Si3+ and He+ simultaneously implanted into SiC is higher than that of sequential irradiation. Helium will aggravate irradiation damage when it is introduced into SiC. Defects such as vacancies due to displacement damage stabilized by helium are related to the optical absorption band. Optical defects induced by heavy ions are related to elastic collisions which occur at the nuclear energy loss region. Simultaneous recovery of defects due to dynamic annealing effects resulting from the excessive heat induced by dual-ion irradiation was observed.