Vacuum Level Research Articles

Influence of straw degradation on dredged sludge consolidation under vacuum preloading

Vacuum preloading with straw drainage has been used as an eco-friendly soil-reinforcement method to promote the consolidation of dredged sludge. In previous studies, the degradation of straw, an essential factor influencing dredged-sludge consolidation, has often been disregarded. In this study, laboratory tests were conducted to investigate the effects of straw degradation on the consolidation efficiency of dredged sludge. The vacuum level within the straw drainage decreased with increasing degradation time, causing a reduction in water discharge and settlement. Consequently, the moisture content increased and the shear strength of the soil decreased. After 60 days of degradation, the water discharge and settlement decreased by 46% and 25%, respectively. The impact of degradation time was most significant during the first 15 days, which was when most straw degradation occurred. The average moisture difference from 0-15 days was 5.0%, whereas from 45-60 days it was 0.8%, which was negligible. The increase in the organic matter content enhanced the Atterberg limits and hydrophilic properties of the soil. The findings of this study promote the engineering application of vacuum preloading with straw drainage and confirm it as an effective and eco-friendly method for consolidating dredged sludge.

Numerical Study on Composite Multilayer Insulation Material for Liquid Hydrogen Storage

This study investigated the heat transfer characteristics of composite multilayer insulation (MLI) materials used for the storage and transport of liquid hydrogen at cryogenic temperatures. This research focused on analyzing the effects of thermal boundary temperature, total layer count, and vacuum level on the heat flux through the insulation material. Based on the layer-by-layer model, a heat transfer model of composite MLI was constructed. This research introduces a novel method for analyzing the heat transfer properties of composite MLI in the liquid hydrogen temperature range. Results indicate that heat flux increases with higher thermal boundary temperatures, with the MLI layers near the cold boundary playing a critical role in overall insulation performance. Additionally, numerical analysis was conducted to examine the impact of different material combinations and variations in vacuum level on heat transfer characteristics. Findings reveal that adding spray-on foam insulation reduces heat flux by 20.76% compared to using MLI alone. Furthermore, increasing the total number of MLI layers effectively mitigates heat flux increase, achieving an optimal heat flux of 0.5377 W/m2 with a total of 50 layers.

Thermodynamic Modelling of a Twin-Stage Claw Vacuum Pump and Its Gas Pressurization Analysis

Multi-stage claw vacuum pumps are crucial in various industrial applications for efficiently achieving high vacuum levels compared to other positive displacement vacuum pumps. In order to elucidate the gas pressurization process of the multi-stage claw vacuum pump and clarify its structural design principles, the authors investigated a twin-stage claw vacuum pump as the main research subject, and analyzed its working characteristic. A thermodynamic model of the twin-stage claw vacuum pump describing the pressurization process was established, and the results were verified by means of experiments. Moreover, effects of the phase difference φⅠ-Ⅱ, the first-stage discharge port angle θd,Ⅰ and the thickness ratio B1:B2 on pump performance were discussed. Results show that as φⅠ-Ⅱ increases, the pump power of the first stage gradually increases, while the power of the second stage decreases and then increases. With the increase of θd,Ⅰ, the pump power decreases and then increases. When the suction pressure is 10kPa, the specific power reaches its minimum value under B1: B2=2:1. As the suction pressure increases, the pump power gradually increases, and its specific power fells substantially and then levels out. These contents are of great significance for the design and optimization of multi-stage claw vacuum pumps.

Aluminum droplets on Ni substrates: Evaluating high-temperature oxidation at the liquid/gas interface

In reactive wetting aluminum (Al)/nickel (Ni) systems, oxides at liquid/gas (L/G) interfaces received less attention compared to intermetallic compounds forming at liquid Al/solid Ni interfaces yet potentially significantly influencing wetting properties. Between 900 and 1250 °C, we observed that the shape of sessile Al droplets with dense oxides at the L/G interface and intense interactions at liquid Al/solid Ni interfaces deviates from a spherical cap and can be used as a way to characterize the oxide evolution. This approach reveals a critical temperature of 1100 °C under a PO2 level of 3.9 × 10−9 atm and a vacuum level of ∼2 × 10−2 mbar. Above it, Al2O3 oxides at the L/G interface are eliminated as Al2O gas, while at lower temperatures, they develop as a mixture of Al2O3 oxides and Al-Ni intermetallic compounds with Ni being dissolved from the substrate. At high temperatures (above 1200 °C), despite oxide-free L/G interfaces, non-spherical cap shapes were also obtained due to the formation of sharp edges at the contact line triggered by the growth of intermetallic compounds. The coupling between the droplet shapes and the interfacial interactions is further confirmed by in-situ observation of oxides, analysis of quenched samples and thermodynamic calculations. The proposed method can be potentially applied to multiple reactive wetting systems (e.g. Sn/Cu, Al/Fe, Mg/Ni systems), which are crucial for high-temperature processes such as soldering, coating, and processing of metal matrix composites.

Heat transfer performance and startup characteristics of separated gravity heat pipe

Separated gravity heat pipes, with distinct arrangements of evaporating and condensing sections, offer low thermal resistance, high heat transfer efficiency, and a simple structure, making them suitable for passive cooling of spent fuel pools through gravity-driven processes. In this study, a steady-state, one-dimensional, two-phase flow model is developed to analyze phase change heat transfer in a separated gravity heat pipe. The research investigates the impact of liquid filling rate and vacuum level on heat pipe operation. The findings reveal a notable increase in pressure drop inside the tube with higher liquid filling rates, which diminishes the adaptability of the heat pipe as pressure rises, resulting in a narrower range of effective liquid filling rates. Specifically, the liquid filling rate of the heat pipe ranges from 38 % to 72 % at P = 13.75 kPa and from 44 % to 68 % at P = 15.75 kPa. Additionally, a startup prediction model is formulated based on a thermal resistance network model using the ideal gas assumption. Two startup states—namely, the initial startup state and the subsequent startup state—are proposed for large-scale separated gravity heat pipe arrays. The heat pipe achieves the large-temperature-difference initial startup state at a 50 % liquid filling rate within 7 min before transitioning to the subsequent startup state. The vapor mass, heat transfer coefficient, and working fluid temperature initially increase and then decrease over time, with varying peak times. As the liquid filling rate increases, the maximum vapor mass also increases. The heat transfer coefficient peaks at a 60 % liquid filling rate before subsequently declining. The optimal liquid filling rate of 60 % is identified based on startup time, heat transfer coefficient, and overall heat transfer efficiency.

Tip-induced local Fermi level alignment: A Stark shift in vacuum level in scanning tunneling microscope configurations

Electric fields in the junction of a scanning tunneling microscope (STM) are generally considered to have a negligible impact on the vacuum level (VL) of materials. We employed field emission resonance (FER) in the STM, combined with the triangular potential model, to measure the VL of the Ag(100) surface under varying electric currents. Unexpectedly, our results reveal that the VL exhibits a linear positive energy shift with increasing electric field strength. We suggest that this Stark shift in the VL arises from local Fermi level alignment induced by the STM tip. Additionally, we examined the VL of Ag islands grown on Cu(111) and Au(111) surfaces under different currents. Despite the Ag island having a lower work function than the Cu(111) and Au(111) surfaces, the energy shift in the VL with respect to the electric field on the Ag island is almost identical to that on the substrate under the same tip structure. This suggests that the Stark shift of the VL is insensitive to the work function. These findings are crucial for utilizing FER to measure local work function variations on surfaces, as the measured value is not influenced by the STM tip structure or the tunneling current, both of which can alter the electric field.

An upgrade of the radial probes for HIRFL-SFC

SFC (Sector Focusing Cyclotron) is essential to the Heavy Ion Research Facility in Lanzhou (HIRFL). Its beam extraction efficiency is directly related to the overall operational efficiency of the accelerator. The original radial probes of the SFC, due to its outdated equipment, no longer meet the requirements for beam tuning in terms of mechanical precision, vacuum level, and local noise. Three new sets of radial probes have been developed in phases. These devices were installed at the accelerator site during annual maintenance, providing axial and radial beam distribution during acceleration. Since 2020, the system has been operating without any failures, providing corresponding beam parameters for the accelerator's operation and ensuring the normal functioning of the accelerator.

Method for Quantitative Analysis of Vitreoretinal Adhesion in Ex Vivo Model.

Posterior vitreous detachment (PVD) is implicated in numerous retinal pathologies. A necessary step in developing new therapies, an area of significant interest, is a quantifiable assessment of posterior vitreous adhesion (PVA) that is also clinically relevant. A 23-gauge vitrector was used at varying levels of vacuum to attempt PVD induction in a porcine eye model injected with either balanced salt solution (BSS) (control) or plasmin (2, 3, or 5 U), which can pharmacologically induce PVD. The average minimum vacuum necessary to induce a PVD was 395 ± 28 mm Hg for BSS alone, 385 ± 58 mm Hg for 2 U of plasmin, 265 ± 53 mm Hg for 3 U of plasmin, and 145 ± 28 mm Hg for 5 U of plasmin. We demonstrated a dose-dependent response curve with increasing amounts of plasmin, leading to a statistically significantly lower minimum vacuum necessary to induce a PVD except between BSS and 2 U plasmin. A dose-dependent relationship between plasmin concentration and PVD was demonstrated. We believe that this model offers significant benefits over prior work as it minimizes confounding manipulations and offers a quantitative assessment that is translatable to in vivo surgical models. This is the first methodology to quantitatively assess the degree of vitreous adhesion in situ.

Experimental study on the vacuum dehumidification performance of PVA/CaCl2 selective permeation membrane under vortex conditions

Vacuum membrane dehumidification is a promising power-saving isothermal dehumidification technology, and the development of low-cost and efficient selective permeation membranes is beneficial to its application. In this study, the dehumidification performance and mechanism of the PVA/CaCl2 water vapor selective permeation membrane are investigated experimentally. The effects of the CaCl2 concentration in the casting membrane solution, the permeation side vacuum level, and the inlet air flow rate and relative humidity on the dehumidification performance are discussed. In addition, the effect of the deflector fins on the dehumidification performance is analyzed. The results show that the vortex coupled dissolution-diffusion theory can explain the experimental results. In addition, from the point of view of dehumidification capacity per unit power consumption, the best concentration of CaCl2 in casting membrane solution is 2.08 %, and the worst permeation side vacuum level is 60 kPa. The higher the inlet air flow rate and relative humidity under the deflector fins, the better the dehumidification performance. The dehumidification performance can be significantly improved by the deflector fins, which increase the COP by 38.31 %∼146 % and the selectivity by 35.85 %∼147 %.

Different Types of Milk Flow Curves and Factors Affecting Milkability in Buffalo Species

Buffaloes are characterized by longer teats and teat canals and stronger muscular resistance of the teat wall than cattle; it is necessary to have a high vacuum level to open the teat canal and begin milk ejection. In buffalo milking management, milk yield, and flow profiles are essential parameters to record and evaluate. The milking machine is a critical point, and the characteristics of the milking vacuum and the pulsation rate are closely related to milk flow observations. In Italy, the most used vacuum levels are 44-46 kPa (range 40-53 kPa). The data on the milkability traits of the Mediterranean Italian breed made it possible to classify eight different types of milk flow curves due to anatomical, physiological, and management differences. This study aims to evaluate the main factors influencing milkability in dairy buffaloes. The results suggest the detachment of the milking cluster to reduce the decreasing and blind phases with the following advantages: reduction of the total milking time and consequently of the worker's time, improvement of the farmer's profitability and milk quality through decreasing the incidence of mastitis. Milk ability is influenced by physiological, sanitary, management, and genetic factors. In Mediterranean Italian buffaloes milked with the Automatic Milking System (AMS), a considerable variation in milk ejection and, consequently, in the milk flow curve was found compared to the conventional one, with better pre-stimulation, independent milk ejection for each teat, optimal milking of all quarters. In conclusion, continuous milkability monitoring will help optimize milking practices by reducing labor time and increasing farmers’ income through better milk quality. In addition, the identification of buffaloes with desirable types of milk flow curves could be helpful for buffalo breeders’ associations to address farmer management and to define potential new breeding objectives.

Exploring the effects of increased socket-residual limb coupling integrity via vacuum assisted suspension on prosthetic control: a preliminary study in transtibial prosthesis users.

The prosthetic socket provides the critical interface between prosthesis and residuum. The purpose of this pilot study was to explore the effect of altering socket-residuum coupling integrity on limb and body control, through the use of vacuum-assisted suspension. A secondary purpose was to explore the potential use of two measurement tools designed to assess mobility in a clinical context. Individuals with unilateral transtibial amputation performed intentional sway (n = 7) and treadmill walking (n = 6) tasks at three vacuum levels. Sway deviation from a straight-line path to peripheral targets was measured using an instrumented balance platform. Step width variability and targeting accuracy were measured using an augmented reality treadmill. There was a significant difference in intentional sway performance toward the target on the anterior diagonal toward the prosthetic side (p = 0.036); higher vacuum levels tended toward less deviation from a straight-line path. We found no group differences between total intentional sway deviation, step width variability or stepping accuracy across vacuum levels. Improved socket-residuum coupling integrity via vacuum may have measurable effects on functional control that warrant further investigation. We highlight limitations of the clinical testing paradigms to inform future work.Implications for rehabilitationThe fit of the socket is a critical factor in the success of lower limb prosthesis use.Vacuum-assisted suspension modifies the coupling between the residuum and socket.Changes in socket-residuum coupling may lead to measurable differences in control; however, these may be activity and person-specific.Clinically intended instrumented tests of movement function derived for an intact anatomy should be used with caution when assessing prosthesis users.

Fabrication of Wafer-Level Vacuum-Packaged 3C-SiC Resonant Microstructures Grown on <111> and <100> Silicon

In this work, the fabrication of wafer-level vacuum packaged 3C-SiC resonators obtained from layers grown on <100> and <111> silicon is reported. The resonant microstructures are double-clamped beams encapsulated by glass-silicon anodic bonding using titanium-based vacuum gettering. Open-loop resonance frequency measurements are performed on the vacuum-packaged devices showing Q-factor values up to 292,000 for <100> and 331,000 for <111> substrates, with a maximum vacuum level around 10-2 mbar inside the encapsulations with Ti getter.

(Invited) Upconverted Hot Electrons from Semiconductor Nanocrystals for Enhancing Photocatalysis

The exciton-to-hot electron upconversion phenomenon in Mn-doped semiconductor quantum dots (QDs) produces highly energetic hot electrons. These electrons have an average energy just a fraction of 1 eV below the vacuum level, with a subpopulation of hot electrons existing above the vacuum level. This hot electron upconversion process is similar to photon upconversion in lanthanide-doped nanoparticles. However, the final state here is a highly excited hot electron in the conduction band of the host QDs, not a state emitting higher-energy photons. These upconverted hot electrons can be harnessed to carry out thermodynamically and kinetically challenging reduction reactions, benefiting from their high excess kinetic energy and long-range transfer capability. The presentation will discuss recent demonstrations of the benefits of these upconverted hot electrons in various photocatalytic reduction and redox-neutral reactions. Additionally, the development of new materials for more efficient hot electron upconversion and the potential to broaden the application of these energetic hot electrons beyond photocatalysis will be discussed.

(Invited) Consideration on Gate Stack Formation Processes of Ultrawide Bandgap Ga2O3 with SiO2 Dielectric Layer

MOSFETs on β-Ga2O3 are expected to be a high-efficient and cost-effective alternative option of high-voltage power devices. Taking account of the reliability and the large conduction-band offset against β-Ga2O3, it would be reasonable to employ SiO2 as the gate dieletric. In this study we investigated the effects of post-deposition annealing (PDA) on SiO2/β-Ga2O3 MOS gate stacks, in terms of the MOS electrical characteristics and the band alignment.β-Ga2O3 (001) wafers with ~2×1016 cm-3 n-type doped epitaxial layers were cleaned in diluted HF solution, and SiO2 films were deposited by electron-beam (EB) evaporation of Si in O2 ambient of ~1×10-2 Pa, followed by PDA at various temperatures from 600 to 1000℃ in either O2 or N2 ambient. Au was evaporated as gate electrode to form MOS capacitors. X-ray photoelectron spectroscopy (XPS) was conducted on the stacks with ~3nm-thick SiO2 for the evaluation of band alignment. Ultraviolet photoelectron spectroscopy (UPS) was also employed to determine the band diagram of β-Ga2O3 (001).Nearly-ideal capacitance-voltage characteristics were obtained for the MOS capacitor fabricated with O2-PDA at 1000℃. The interface state density (Dit) determined by conductance method decreased down to ~1010 cm-3 at the energy level of EC−0.2 eV by PDA at higher temperature. The hysteresis width (ΔVhys) of C-V curves was smaller for the samples annealed at higher temperatures. The flatband voltage (VFB) shift after O2-PDA resulted in VFB close to the ideal value estimated from the physical properties of Au and Ga2O3, suggesting that fixed charge density at the interface would be minimized. However, PDA in N2 at 1000℃ resulted in a negative shift of VFB, which indicates the formation of positive fixed charges in the stack. The beneficial influences of O2-PDA on those characteristics suggest that an oxygen deficiency introduced near the interface is one of the origins of interface defect states. It is noteworthy that Ga3d XPS on the surface of Ga2O3 substrate always shows a tailing in lower binding energy side, which is indicating oxygen deficiency on the surface. The intensity of this lower-binding-energy component reduced significantly when a bare-Ga2O3 substate was annealed in O2, however, it did not decrease efficiently even after O2-PDA when the surface was covered with SiO2. This is probably due to the oxygen rearrangement at SiO2/Ga2O3 interface determined by the difference of material properties of those oxides. This fact suggests that the Ga2O3 surface easily forms oxygen vacancies when it is covered with SiO2. This would be the reason why the formation of interface defect states is not suppressed without O2-PDA.Next the band diagram of β-Ga2O3 (001) substrate was investigated by UPS analysis where the energy level of valence band edge referring to the vacuum level was evaluted from the energy difference between minimum (cut-off) and maximum edges of the obtained kinetic energy spectra of photoelectrons. As a result we found the valence band edge of of β-Ga2O3 (001) was ~8.2 eV below the vacuum level, where the influences of O2 annealing at 1000℃ on the valence band edge energy level was limited to the shift within ~0.1eV. This would tell us the valence band offset between SiO2 and Ga2O3 should be around ~1.1eV, and the conduction band offset between them is to be around 2.8-2.9eV, by taking account of the well-reported SiO2 band diagram and assuming the bandgap of β-Ga2O3 as 4.7eV. On the other hand, the valence band offset estimated from the deconvolution of the XPS valence band spectrum for a ~3nm-thick SiO2/β-Ga2O3 stack from the energy edge difference between the deconvoluted spectra corresponding to SiO2 and Ga2O3, was a few hundreds of mV smaller than the above expected value (~1.1eV). This discrepancy is indicating the formation of an interface dipole layer between SiO2 and Ga2O3 with a pair of nagative and positive charges aligned at the interface to cause a shift in the band alignment. The magnitude of such dipole was indicated to be more significant (~0.5eV) for the stack after PDA at 1000℃, whereas it was less (0.2~0.3eV) after PDA at 600℃.In conclusion, we demonstrated that SiO2/β-Ga2O3 (001) MOS capacitors showed nearly-ideal electrical characteristics with significantly reduced interface defect density and small fixed charge density by applying O2-PDA. The band alignment of SiO2/β-Ga2O3 (001) MOS stack was clarified by photoelectron spectroscopy to confirm a very large conduction band offset of the stack, but an influence of the formation of interface dipole layer between SiO2 and Ga2O3 on the band alighment was also indicated.

Edge-enriched CeO2/MoS2 heterostructure with coupled interface for enabling selective room-temperature NO2 detection

Endowed with abundant oxygen vacancy and excellent redox properties, CeO2 has attracted extensive attention for potential application in gas sensing, while it suffers from high working temperature and low sensing response. Herein, the MoS2 nanoflowers with abundant edges are coupled with CeO2 nanoparticles and the edge-enriched heterostructure is formed at interface. Owing to the synergistic effects of strong adsorption, abundant adsorption sites, and coupled interface, the CeO2/MoS2 compounds behave excellent room-temperature NO2 sensing performance. The 5 ppm NO2-sensing response of compounds is enhanced by 1033 % and 450 % in company with pure CeO2 and MoS2, respectively and the low detection limit of 1 ppm, high recovery rate, excellent long-term stability and selectivity are also obtained at room temperature. According to first-principles calculation, the binding energy of CeO2 for NO2 is much more negative than that of MoS2. Functionalization of MoS2 with CeO2 substantially improves NO2 adsorption. The Fermi level of MoS2 is nearer to the vacuum level than that of CeO2. The electrons are transferred from MoS2 to CeO2 at interface to create an electric field and an electron accumulation layer is formed on CeO2 to promote electron exchange between NO2 and the sensor and the NO2-sensing response. The results promote the application of two-dimensional materials to gas sensing boding well for the wireless sensing systems development in environmental and safety monitoring.

Additive manufacturing and mechanical performance of short fiber reinforced PEEK (polyether ether ketone) thermoplastic composites in a vacuum environment

Short fiber reinforced thermoplastic composites (SFRTC) have gained popularity in the material extrusion (MEX) method, which is an additive manufacturing (AM) technology, allowing for the simpler and more cost-effective production of polymer composites. However, parts produced using MEX 3D printing technology often exhibit poor mechanical properties and surface quality compared to products manufactured using injection molding, which is one of the main disadvantages of this method. Various methods are used to overcome these challenges, such as production in a vacuum environment, heat-based processes, ultrasonic vibrations, and others. The objective of this study was to achieve parts with lower porosity and improved mechanical properties when printed in a vacuum environment compared to an atmospheric environment. Additionally, an investigation into the optimization of printing parameters was conducted to determine the parameters that yield the highest mechanical properties. For this purpose, SFRTC parts were printed at different vacuum levels (0.5, 10, 100 mbar), and they were subjected to flexural tests to determine their mechanical properties. The results showed that the flexural stress and elastic modulus of the samples produced in a 0.5 mbar vacuum environment increased by 79.75% and 39.41%, respectively, compared to samples produced in an atmospheric environment. Furthermore, the cross-sectional images of the samples were examined using an optical microscope, revealing the lowest porosity in the samples printed in 0.5 mbar vacuum environment.

A Case Study of Diagnosis & Treatments How is Functional Abdominal Pain Diagnosed?

Abstract: Vacuum levels are commonly measured in terms of in. Hg (inches of mercury), mm Hg (Torr), and microns. We monitor motor cortical excitability, brain stimulation-induced neuroplasticity. The most common causes of abdominal pain and diarrhea are infections, such as gastroenteritis (stomach flu), and food allergies, lactose intolerance, and stress. Common bowel disorders, such as IBS and Crohn's disease, can also cause these symptoms. Viral gastroenteritis is an infection of your intestines that typically causes watery diarrhea, pain or cramping in your abdomen, nausea or vomiting, and sometimes fever. People commonly call viral gastroenteritis “stomach flu,” but the term is not medically correct. Flu viruses do not cause viral gastroenteritis. The most common symptom of chronic pancreatitis is long-standing pain in the middle of your abdomen. If you have chronic pancreatitis, you might get repeated episodes of acute pancreatitis, where your pain gets worse. Your pain may get worse with eating, drinking and drinking alcohol. You may also develop jaundice.

Strain Effects in the Work Function and Charge Transfer of the Au(111) Surface.

Work function (WF) is one of the most fundamental physical parameters of metal surfaces, which can not only reflect the electronic structure of metal surfaces but is also very sensitive to the surface microstructure. In this paper, we use first-principles calculations to systematically study the strain effects on the vacuum level, Fermi level, and WF of the Au(111) surface. We find that the vacuum level and Fermi level of the Au(111) surface increase under compressive strain and decrease under tensile strain, and the effects of biaxial strain on the vacuum level and Fermi level can be equivalent to the superposition of two perpendicular uniaxial strains. These strain effects are attributed to the charge transfer induced by the strain. However, the change of WF with strain is the result of the competition between the strain effects of the vacuum level and Fermi level. That leads to the WF increasing with compressive uniaxial strain and decreasing with tensile uniaxial strain. Moreover, because the Fermi level is more responsive to compressive uniaxial strain, the Fermi level changes faster than the vacuum level under compressive biaxial strain. Consequently, the WF decreases with increasing tensile biaxial strain and slightly increases before decreasing with increasing compressive biaxial strain.

A MEMS resonant vacuum gauge for high vacuum measurement

In this paper, a MEMS resonant vacuum gauge (MRVG) based on the squeezed film damping is proposed and its theoretical measurement model is established. The sensitive structure and electrodes of the MRVG were fabricated on SOI wafers and were wafer level packaged including intake hole. An resonance excitation and capacitive detection circuit consists of capacitive voltage converter (C/V) module, PLL and modulation and demodulation module was designed. Experimental tests were carried out in a standard vacuum calibration chamber, and the measurement results verified the theoretical model. The indication accuracy of the MRVG is less than ±20% in the vacuum range of 9×10−5 Pa ∼ 1 Pa. Moreover, the output voltage is still not saturated at the highest vacuum level (9×10−5 Pa), which lays the foundation for subsequent measurement of higher vacuum levels.

Windage loss characterisation for flywheel energy storage system: Model and experimental validation

In this paper, a windage loss characterisation strategy for Flywheel Energy Storage Systems (FESS) is presented. An effective windage loss modelling in FESS is essential for feasible and competitive design. Unlike generic aerodynamic loss models, FESS require particular attention to their unique characteristics i.e., vacuum, small airgaps, high angular speed, and presence of low friction rotor supports.The proposed model is based on several analytical and semi-empirical windage loss solutions for cylindrical and planar surface interactions, harmonised to manage the transition between laminar and turbulent flows. Also, the model is enriched by introducing corrections for rarefied gasses, using kinetic gas theory formulation. Therefore, it is possible the reduce the windage overestimation occurring with Navier–Stokes equation solutions for laminar flow. The model is compared to case studies from the literature featuring different boundary and operating conditions, to check consistency of all the harmonised models. A dedicated experimental test-rig is developed to validate the corrections to the model for rarefied gas at different vacuum levels. Then, a non-invasive characterisation approach for FESS windage losses in self-discharge phase is proposed and validated on the test-rig.