Two-phase Mode Research Articles

Droplet sizes and delivery rates from film breakup aerosolisation mode in porous materials

Abstract A novel two-phase aerosolisation mode utilizing porous materials is investigated, aiming to improve aerosol delivery for medical inhalation. Sintered stainless steel filters with varied pore sizes (PS) from 0.2 μm to 7 μm were used to generate aerosols from a 0.9 wt.% sodium chloride solution. Droplet sizes and delivery rates were measured using laser diffraction spectroscopy. Further measurements included shadow imaging. Results indicate that aerosolisation occurs within a specific range of PS with droplet sizes increasing with increasing PS. The droplets generated are suitable for inhalation therapies. A hypothesis is established about the process of droplet formation which states that different PS within the porous material serve distinct functions that contribute to the breakup of liquid films into aerosol particles. Droplet formation is the result of film breakup in pores filled with fluid. This low-energy aerosolisation method has the potential to be used in handheld devices for sensitive drug formulations, overcoming the limitations of current technologies. Further research is needed to optimize the pore size distribution and enhance aerosol generation efficiency.

Research on operating characteristics of V-shaped ultrasonic motor based on improved electromechanical coupling model

Abstract As a complex electromechanical coupling system, evaluating the motion characteristics of an ultrasonic motor via an accurate theoretical model is challenging due to the strong coupling between its electrical and mechanical properties. To address this issue, the paper first establishes a complete dynamic model of the V-shaped ultrasonic motor (VUSM). In contrast to the traditional dynamic model, the proposed model incorporates the centroid vibration of the stator and applies the weighted residual method to reduce the computational complexity by simplifying the dynamic model from infinite-dimensional degrees of freedom to two degrees of freedom. Subsequently, the finite element method is employed to determine the vibration mode of the stator structure and derive the two-phase operational mode of the motor. Using these two-phase working modes, the model is then solved to predict the motor's output characteristics under any operational condition. Furthermore, an electrical model accounting for preload nonlinearity was developed based on the dynamic model and compared with the model without considering preload nonlinearity, supported by experimental verification. The findings demonstrate that the established dynamic model and electrical model can accurately simulate the changing laws of the input and output characteristics of the motor, which provides assistance for the subsequent operation status evaluation of the motor and fault diagnosis during operation.

Harmonic Self-Compensation Control for Bidirectional Grid Tied Inverter Based on Crown Porcupine Optimization Algorithm

A self-compensating control strategy for harmonic parameters based on the crown porcupine optimization algorithm is proposed for the single-phase rectifier and two-phase inverter operation mode of the bidirectional converter. In order to improve the response speed of the inverter voltage, the instantaneous expressions of the phase angle coefficient and amplitude coefficient of the dc-side voltage doubling fluctuation are derived, and the third harmonic is calculated based on the crown porcupine optimization algorithm according to the Proportional Integral (PI) + Quasi-Proportional Resonance (QPR) double closed-loop control method and injected into the input voltage of the inverter side to offset the influence of the bus-doubling fluctuation on the output voltage of the two-phase inverters of B and C so that the total harmonic content of the two-phase output voltages of the two-phase inverters of B and C can be reduced. The total harmonic content of the B and C inverter output voltages is reduced. The effective control of the control method for single-phase rectifier two-phase inverter mode is verified through simulation. Finally, the effectiveness of the control strategy is verified by experimenting with a 15 kW LCL-type bi-directional converter prototype.

Damage classification and evolution in composite under low-velocity impact using acoustic emission, machine learning and wavelet packet decomposition

The primary objective of this research is to conduct an exhaustive experimental investigation into the damage identification and damage evolutionary mechanisms in laminated CFRP under low-velocity impact. The recorded acoustic signals were classified by Principal Component Analysis, Pearson correlation analysis and K-means++ clustering algorithm and four damage modes including matrix cracking, delamination, fiber–matrix debonding and fiber failure are identified. The Wavelet Packet Decomposition is used to analyze the characteristics of the signal in the time–frequency domain. Matrix cracking is the fundamental damage mode, with its characteristic frequency band being FB1. An increase in the FB3 of matrix cracking signals indicates the tendency to the inter-laminar region, leading to delamination damage. Fiber-matrix debonding is a two-phase damage mode. The transition of the energy components from FB1 to FB7, as indicated by the scanning electron microscopy (SEM) results, signifies the evolution of Fiber-matrix debonding. The initial stage is dominated by matrix peeling off the fiber surface, while the second half of the loading shows matrix peeling accompanied by fiber fracture. Fiber breakage failure is caused by local stress concentrations due to matrix cracking. In the later stages of loading, fibers fail by brittle fracture due to mutual compression without the involvement of matrix cracking as reflected by SEM and WPD.

Theoretical analysis of the three-stage phase transition process of alkane droplet under supercritical conditions

With the development of heavy-duty diesel engines, the in-cylinder ambient conditions of the diesel engine are well above critical points of the main components of the diesel fuel. Therefore, significant changes arise in the phase transition process of the liquid fuels. However, the entire phase transition process of the liquid fuels in such supercritical environments is not well understood compared with that under subcritical conditions. In this work, A high-pressure transient droplet evaporation model was presented for the theoretical analysis of phase transition processes of the heptane/dodecane/hexadecane-nitrogen binary system under supercritical conditions. Analysis of the thermodynamic pseudo-trajectories reveals that the alkane droplets will undergo a three-stage phase transition process when the ambient condition is much higher than the critical point of alkanes, including classical two-phase mode, transitional two-phase mode, and supercritical single-phase mode. The evaporation dominates the phase transition process in the classical two-phase mode, and the transition from classical two-phase modes to transitional two-phase modes occurs when gas-liquid interfaces deviate from the global thermal equilibrium. In transitional two-phase modes, a gas-liquid interface still exists and separates the liquid phase and vapor phase, but with a questionable adoption of vapor-liquid equilibrium. The transition from the transitional two-phase mode to the supercritical single-phase mode occurs when the thermodynamic state of the binary mixture in the interface reaches the critical mixing state. We distinguished the phase states for the whole phase transition process according to the thermodynamic analysis of binary systems. Analogous to the immiscible interface in classical two-phase mode, a miscible boundary layer containing supercritical fluids exits between the liquid core and gas in the initial period of the supercritical single-phase mode. The pseudo-boiling phenomenon occurs in this boundary layer.

Promoting fucoxanthin accumulation in Phaeodactylum tricornutum by multiple nitrogen supplementation and blue light enhancement

The aim of this study was to promote fucoxanthin accumulation in Phaeodactylum tricornutum by photo-fermentation through optimizing the mode of multiple nitrogen supplementation and blue light enhancement. The results showed that the mixed nitrogen source (tryptone: urea=1:1, N mol/N mol; total nitrogen concentration at 0.02 mol/L) added to the culture system by six times was the best mode in shake flasks. Two-phase culture with light adjustment was then carried out in 5 L photo-fermenter with an enhanced blue light (R: G: B=67.1:16.7:16.3) in the second phase, leading to improved cell density (1.12×108 cells/mL), biomass productivity (330 mg/(d·L)), fucoxanthin content (19.62 mg/g), titer (69.71 mg/L) and productivity (6.97 mg/(d·L)). Compared with one-phase culture under red/blue (R: G: B=70.9:18.3:10.9) light and six-times nitrogen supplementation, the fucoxanthin content was significantly increased by 7.68% (P < 0.05) but the productivity did not change significantly (P > 0.05). Compared with one-phase culture under red/blue (R: G: B=70.9:18.3:10.9) light and one-time nitrogen supplementation, the content and productivity of fucoxanthin were significantly increased by 45.98% and 48.30% (P < 0.05), respectively. This study developed a two-phase culture mode with multiple nitrogen supplementation and blue light enhancement, which effectively promoted the accumulation of fucoxanthin and improved the efficiency of nitrogen source utilization, thus providing a new approach for fucoxanthin accumulation in P. tricornutum by photo-fermentation.

A face image classification method of autistic children based on the two-phase transfer learning.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, which seriously affects children's normal life. Screening potential autistic children before professional diagnose is helpful to early detection and early intervention. Autistic children have some different facial features from non-autistic children, so the potential autistic children can be screened by taking children's facial images and analyzing them with a mobile phone. The area under curve (AUC) is a more robust metrics than accuracy in evaluating the performance of a model used to carry out the two-category classification, and the AUC of the deep learning model suitable for the mobile terminal in the existing research can be further improved. Moreover, the size of an input image is large, which is not fit for a mobile phone. A deep transfer learning method is proposed in this research, which can use images with smaller size and improve the AUC of existing studies. The proposed transfer method uses the two-phase transfer learning mode and the multi-classifier integration mode. For MobileNetV2 and MobileNetV3-Large that are suitable for a mobile phone, the two-phase transfer learning mode is used to improve their classification performance, and then the multi-classifier integration mode is used to integrate them to further improve the classification performance. A multi-classifier integrating calculation method is also proposed to calculate the final classification results according to the classifying results of the participating models. The experimental results show that compared with the one-phase transfer learning, the two-phase transfer learning can significantly improve the classification performance of MobileNetV2 and MobileNetV3-Large, and the classification performance of the integrated classifier is better than that of any participating classifiers. The accuracy of the integrated classifier in this research is 90.5%, and the AUC is 96.32%, which is 3.51% greater than the AUC (92.81%) of the previous studies.

Semi-continuous production of polyhydroxybutyrate (PHB) in the Chlorophyta Desmodesmus communis

Polyhydroxyalkanoates (PHAs) are promising alternatives that accumulate as energy and carbon storage material in various microorganisms, including bacteria and microalgae, being biodegradable and suitable for a wide variety of applications. Among these compounds, the most prevalent and well-characterized biopolymer is polyhydroxybutyrate (PHB), which belongs to the short-chain PHAs.The present study was designed to evaluate algae-based PHB production in two Chlorophyta (Desmodesmus communis and Chlorella vulgaris) under a two-phase nutritional mode of cultivation, namely a phototrophic growth phase (PGP) and a mixotrophic stress phase (MSP) with N,P-depleted media and organic carbon supply (i.e., glucose or sodium acetate, NaOAc). The highest PHB productivity (0.11 g PHB/g biomass/d; 0.015 g PHB/L/d), corresponding to 32.1 % w/w of intracellular PHB, was observed for D. communis after 3 days of cultivation under mixotrophic conditions in batch cultures (e.g., low light, phosphorus-free medium, 1 g/L of NaOAc). A scaled-up cultivation (10 L) was set up to evaluate for the first time PHB yields and biomass composition in a semi-continuous system. A PHB content of 34 % w/w was achieved on day 8, corresponding to a maximum PHB productivity of 0.10 g PHB/g biomass/d (or 0.011 g PHB/L/d), which increased up to 54 % w/w on day 15. The biomass was composed of about 30 % w/w proteins, 6 % w/w polysaccharides, and 11 % w/w lipids, which can be valorised from a biorefinery perspective. The scaled-up D. communis cultivation in 10 L PBRs confirmed the potential utilization of this algal species for PHB production with productivity up to 2-times higher than those reported for several cyanobacterial species and similar to the maximum value obtained with batch cultures in previous works performed with Scenedesmaceae.

Mechanisms and inhibition method investigation on condensation induced water hammer in an equal-height-difference passive heat removal system

The equal-height-difference passive heat removal system utilizes the ocean as an ultimate heat sink for residual heat removal, demonstrating obvious advantages for ocean nuclear power plant applications. However, the structure with a zero-height difference can trigger the reverse flow of subcooled water. This could cause serious condensation induced water hammer events. In this study, a fully visual experimental setup was established to investigate the occurrence features. First, two kinds of formation mechanisms were defined by the visual experimental results. In this regard, the subcooling and the isolated steam slug are the necessary conditions for the formation and development. In addition, the occurrence positions were found to be concentrated in the test pipe section near the water tank. Then, a butterfly check valve was designed to avoid the condensation induced water hammer events based on the formation mechanisms. The experimental results showed that the check valve usage can effectively inhibit the reverse flow of the subcooled water and thus achieve its purpose of eliminating condensation induced water hammer events. Moreover, the check valve transforms the two-phase natural circulation flow from the condensation oscillation mode to the stable boiling two-phase flow mode. As a result, it enhances the two-phase natural circulation capacity.

Characterization of bubble population morphology in direct contact heat transfer process under different flow regimes and its influence on heat transfer performance

In this study, the effect of bubble population morphological characteristics and heat transfer performance in the direct contact boiling heat transfer process under two different flow modes are comparatively investigated. Based on the visualization method and homogeneity theory, the relationships between the bubble population morphological characteristics, distribution homogeneity, specific interface area, and volumetric heat transfer coefficient were investigated. The obtained results show that the bubble morphology tends to flatten with the increase of the dispersed phase flow rate in both flow modes. The more uniform the distribution of the bubble population, the better the specific interface area, and the trend is more obvious in the two-phase reverse flow mode. In addition, it was found that the specific interface area was positively correlated with the volumetric heat transfer coefficient. The synergistic relationship between the uniformity of bubble population distribution and the improvement of heat transfer is explained from the perspective of a specific interface area. It is concluded that different flow patterns affect the morphological characteristics of the bubble population and its distribution, which in turn affects the specific interface area of the two-phase contact heat transfer and ultimately the heat transfer performance. The morphology of the bubble population and its uneven distribution has a strong correlation with the flow pattern. This thesis provides a new idea to study the influence of bubble cluster morphology characteristics and heat transfer performance in direct contact boiling heat transfer process under different flow patterns and provides a new way for heat exchanger design.

Research on Low Switching Loss Control Strategy of High-Speed FESS Based on NPC Three-Level Converter

The high-speed flywheel energy storage system (FESS) has been used in urban rail transit system to provide network stability and regenerative braking energy recovery due to its merits of high-power density, almost infinite charging–discharging cycles, nonexistent capacity deterioration, and environmental friendliness. The electrical fundamental frequency of the FESS motor/generator will be significantly increased when the rotor is mainly composed of carbon fiber composites to achieve higher speed. In addition, in view of the 1500-VDC power supply of the urban rail transit system, the switching loss of the power switching devices will be significantly increased or the system failure may be occurred when the high switching-to-fundamental frequency ratio (SFFR) control strategy is applied. Therefore, a low SFFR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$=$ </tex-math></inline-formula> 1 control strategy of the I-type neutral point clamped (NPC) three-level converter for the high-speed FESS with brushless direct current (BLDC) motor in two-phase conduction mode is designed, and the matching midpoint voltage balance strategy is proposed. The effectiveness of the proposed control strategy is verified by simulation and experiments. The stable and low switching loss operation of the high-speed FESS rated at 1500 VDC, 330 kW, and 36 000 r/min is realized, and the midpoint voltage balance is strongly controlled.

Two-phase dual-signal-readout immunosensing platform based on multifunctional carbon nano-onions for ovarian cancer biomarker detection.

In order to detect early tumor markers and gain valuable time for treatment, there is an urgent need to develop a fast, cheap, and ultrasensitive multi-reading sensing platform. Herein, a solid/liquid two-phase dual-output biosensor was explored based on a sensitized sonochemiluminescence (SCL) strategy and a multifunctional carbon nano-onion (CNO) probe. It is clear that ultrasonic radiation caused the formation of hydroxyl radicals (˙OH), triggering the SCL signal of the emitter lucigenin (Luc2+). Meanwhile, titanium carbide nanodots and ethanol were used to enhance the SCL signal, and an astonishingly linear enhancement of the SCL intensity was produced with increasing ethanol concentration. More importantly, the CNOs, with their excellent photothermal properties and adsorption capacity, can output both the temperature signal and an enhanced SCL strength from the solid-liquid phase. Through inter-calibration of the signals from the two-phases, this biosensor shows excellent analytical performance for the detection of the ovarian cancer biomarker, human epididymis-specific protein 4, from 10-5 to 10 ng mL-1 with a low detection limit of 3.3 fg mL-1. This work not only provides a novel two-phase signal-output mode that broadens the scope of multiperformance joint applications of CNOs, but also enriches the quantitative detection of point-of-care testing.

A Novel Two-Phase Mode Switching Control Strategy for PMSM Position Servo Systems With Fast-Response and High-Precision

In this article, a novel mode switching control (MSC) strategy is proposed containing a fast-response phase and a high-precision settling phase to meet the requirement of high-quality point-to-point permanent magnet synchronous motor servo systems. In the fast-response stage, an adaptive trajectory planning method is developed to program the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current profile online based on the reference for the motor to reach the neighborhood of the reference position in minimum time. The chattering in the conventional time-optimal control is overcome and the idea that skipping speed and position loop with preplanned <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current trajectory is first attempted. After switching, the high-precision settling stage that is responsible for improving the transient performance in terms of reducing the overshoot and settling time is built with the proposed robust composite nonlinear feedback (RCNF) control law. This RCNF method cancels the overall disturbance through an extended state observer. The switching condition for the proposed MSC controller is clarified. Afterward, the whole closed-loop system's stability is strictly proved. Experiments are then conducted based on different scenarios to prove the effectiveness and robustness of the proposed MSC method.

Two-Phase Stator Vibration Amplitude Compensation of Traveling-Wave Ultrasonic Motor

The consistency of the two-phase mode responses is essential to ensure the mechanical performance and stability of traveling-wave ultrasonic motors. Due to the asymmetry of the stator, inevitable manufacturing errors, or imbalance of the excitation voltages, the amplitudes of the two-phase standing waves cannot be exactly the same, resulting in unstable operating of USM. To improve the stability of the motor and decrease the velocity fluctuation, a closed-loop velocity control scheme considering two-phase consistency compensation based on the vibration amplitude of the stator is proposed. This scheme is implemented under the framework of the stator vibration amplitude-based velocity control and parallel resonance frequency tracking (VCBVF). Based on the relationship between the velocity and stator vibration amplitude (SVA), two-phase excitation signals are adjusted individually and simultaneously. Compared with the single-phase feedback VCBVF control scheme, experimental results show that the proposed scheme can reduce the overshoot from 17.50% to 6.90% and velocity fluctuations from 7.69 rpm to 2.40 rpm, under different load torques. The proposed scheme can compensate for the two-phase electrical inconsistency and improve the velocity stability and output power of motor operation under various conditions.

ADAPTATIONS OF RESULTS OF EXPERIMENTAL QUALIFICATION OF PASSIVE SAFETY SYSTEMS OF NUCLEAR POWER PLANTS

Problems. An urgent issue of ensuring the safety of nuclear power plants is the adaptation of the results of experimental qualification of the fittings of passive safety systems in a single-phase environment to emergency conditions of two-phase flows. For most of the equipment of systems important for the safety of nuclear power plants, there is no principled possibility of qualification through direct tests in emergency conditions. The experience of operating nuclear power plants, as well as the results of simulations after design accidents, determined the possible inconsistency of the operating conditions of the fittings in emergency situations and in the modes of operational tests with a single-phase steam-gas environment.Thus, it is necessary to adapt the results of the experimental qualification of the fittings of the emergency steam and gas removal systems in a single-phase environment to the emergency conditions of two-phase flows. The aim of the study. The purpose of this article is sufficient justification of the adaptation of test results on a single-phase environment to the conditions of emergency processes with a two-phase environment. Methodology of implementation. To achieve the goals of the study, deterministic modeling of the conditions and criteria of operation/testing of valves of emergency steam and gas removal systems was used. Research results. T An analysis of the validity of the results of the experimental qualification was performed for the dynamic pressure pressure on the closing device in the test mode (single-phase flow mode) and the dynamic pressure pressure on the closing device in the emergency mode (two-phase flow mode). The adaptation of the results of the experimental qualification for closing the valves of the emergency steam and gas removal systems in a single-phase environment to the emergency conditions of two-phase flows was carried out under the conditions of subsonic and supersonic flow regimes. Conclusions. The conditions for adapting the results of the experimental qualification for closing the valves of the emergency vapor gas removal systems to the emergency conditions of subsonic and transonic flows of two-phase flow in the flow part of the valves have been determined. The dynamic pressure on the closing device of the valve in single-phase flows of operational tests and the dynamic pressure in two-phase flows of emergency modes are considered qualification criteria.

The Role of Scintigraphy and Hybrid Single-Photon Emission Tomography in Comparison with Laboratory Data in a Comprehensive Examination of Patients with Secondary Hyperparathyroidism

Objective:to estimate the possibilities and determine the diagnostic value of scintigraphy and single-photon emission computed tomography combined with computed tomography (SPECT/CT) in the assessment of the functional state of parathyroids in comparison with laboratory data in patients with secondary hyperparathyroidism (SHPT). Material and methods.The study consistently included 64 patients with the established diagnosis of SHPT due to the acquired vitamin D deficiency or with terminal chronic kidney disease (CKD), with the presence of ultrasound data and laboratory tests of calcium-phosphoric exchange indicators. Neck and mediastum nuclear study with 99mTc-methoxy-isobutyl-isonitrile (MIBI) was performed in the planar two-phase scintigraphy mode according to the standard protocol with an estimation of parathyroid visualization intensity, as well as in SPECT/CT performed 1 hour after MIBI injection. Results. In the group of patients with CKD as a cause of SHPT (n = 14), the most pronounced increase of parathyroid hormone (PTH) level (210.8 ± 103.0 vs. 107.0 ± 40.2 pg/ml in patients with vitamin D deficiency (n = 50, p &lt; 0.001)) and phosphorus (mean 1.39 ± 0.51 mmol/l), as well as excess of normal levels of alkaline phosphatase (407.7 ± 338.1 units/l) were noted. In patients with vitamin D deficiency, impaired parathyroids according to SPECT/CT data was visualized in 8 % of cases, and in patients with CKD in 14.3 %. No significant differences in the mean levels of vitamin D in patients with (n = 46) and without (n = 4) modified parathyroids according to scintigraphy were detected: 26.06 ± 13.19 vs. 25.82 ± 18.80 ng/ml, respectively (p = 0.97). Differences in PTH and calcium levels were not observed: 91.3 ± 39.2 vs. 89.2 ± 29.5 pg/ml (p = 0.90), 2.53 ± 0.21 vs. 2.58 ± 0,15 mmol/l (p = 0.64), respectively. Conclusion.The neck SPECT/CT is a key method of topical imaging of impaired parathyroids in preoperative preparation of patients with SHPT caused by CKD. The method may have a diagnostic value in treatment-resistant patients with vitamin D deficiency and upper-normal PTH and calcium levels in terms of detection of the nodular form of parathyroid hyperplasia. The implementation of SPECT/CT after 1 hour after MIBI injection increases the sensitivity of the study.

A bearingless flux-switching permanent magnet memory machine

A bearingless flux-switching permanent magnet memory machine (BFSPMMM) is proposed, which demonstrates the advantages of good suspension performance and wide-ranging speed regulation. The bias magnetic field of the radial force generated by the motor is provided by the permanent magnet, which can flexibly decide whether to adopt a single-phase or two-phase mode of conduction according to the needs of radial levitation force in the X- and Y-directions, so as to ensure the tracking of radial levitation forces therein. This paper introduces its structure, which lays a foundation for the subsequent establishment of an accurate mathematical model of a BFSPMMM.

Low salinity water flooding: Evaluating the effect of salinity on oil and water relative permeability curves using coupling of DLVO and geochemical reactions

Enhancing the oil recovery of carbonate reservoirs with acidic oil depends on injected brine composition and salinity throughout the low salinity water flooding. The typical description of this phenomenon on oil and water relative permeability curves is being put forward by the process-dependent interpolation function, which barely addresses the underlying fundamentals governing the direct impact of wettability alteration and geochemical reactions on flow saturation functions. The main objective of this work is to perform an integrated investigation of the effect of salinity on oil and water relative permeability curves by dynamic coupling of the Derjaguin, Landau, Verwey, and Overbeek (DVLO) theory and geochemical reactions. We studied both the single and two-phase systems using the basis of the geochemical reactions to track the variations of the wetting and non-wetting phase relative permeability curves. In the single-phase scenario, the results show the superiority of the reactive flow modeling technique with kinetic-controlled reactions, in the range between [2–4] of the Damkohler number, to yield a better result for the experimental effluent ions' concentrations than the equilibrium approach. In addition, the single-phase results under dynamic conditions propose Civan correlation as the best predictor of residual resistance factor (RRF) by numerically adjusting the correlation of coefficients based on the physical variables - salinity, dimensionless consumed ion concentration, and Peclet number. Accordingly, the results indicate a novel linkage between the single-phase and two-phase results in the sense that RRF under single-phase mode can be used to estimate the change in the wetting phase relative permeability under the two-phase mode. The single-phase methodology provides the capability for an improvement – up to 15% - in the prediction of the pressure drop curve. For two-phase cases, our procedure involved coupling the characterized geochemical reactions and the DLVO theory to consider the effect of injected water composition on contact angle as the static two-phase parameter. The phase-field method is coupled with DLVO theory to calculate the relative permeability curves for the non-wetting phase, which corresponds to the contact angle at each simulation time step. The two-phase results indicate an improvement – up to 30% - in the prediction of the recovery factor curve, on a history-matching basis, using the DLVO theory with contact angle-dependent correlation of non-wetting phase relative permeability curve. The main novelties of this study are using the single-phase dynamic permeability impairment results in calculating the variation of the wetting-phase relative permeability curve. Moreover, dynamic coupling of DLVO and non-linear contact angle-dependent correlation is used to calculate the non-wetting phase relative permeability curve. According to these novelties, more accurate prediction of the laboratory production profiles can be obtained.

A Novel Step Current Excitation Control Method to Reduce the Torque Ripple of Outer-Rotor Switched Reluctance Motors

Featured in low-speed and high-torque operation, outer-rotor switched reluctance motors (OSRMs) have the potential to be widely deployed in low-speed commuter and logistics vehicle applications. In this paper, a five-phase OSRM and the control method featuring torque ripple reduction has been proposed, which can be applied as the wheel hub motor in the electric vehicles. The simulation was carried out to analyze the OSRM operation. The electromagnetic characteristics of single-phase and two-phase hybrid excitation mode, as well as step current excitation mode, were compared and analyzed. To solve the problem of the large torque ripple of OSRMs under traditional excitation modes, the torque ripple suppression method based on step current excitation was also studied. The experiment design, including motor start-up control, speed control, and torque ripple reduction, are presented to verify the system torque ripple mitigation method.

CFD investigation of flow reversal in inverted U-tube steam generator under two-phase natural circulation

In this paper, a critical mass flow rate (CMFR) has been obtained for three different steam generators (i.e. two marine-type and one commercial) at different inlet void fractions using the CFD method to study the sustainability of natural circulation (NC) due to depressurization in two-phase NC mode. Because of depressurization, the transients in the inlet void fraction have been considered as multiple steady-state inputs, and the range of safe operating mass flow rate has been obtained. The results show that the characteristics curves shift with inlet void fraction thus limiting the operating mass flow rate range between 0.046 kg/s to 0.050 kg/s for M_SG1 and 0.051 kg/s to 0.055 kg/s for M_SG2. The effect of pipe roughness on CMFR has also been studied. The results can be used for the optimized design of the U-tube steam generator (UTSG) that will safely perform the heat removal operation during a small break loss of coolant accident (SBLOCA).