Search Results (39)

This study takes four parallel axial-flow pumps (three in operation + one on standby) as the research object. Using a 1D–3D coupling method, it explores the flow characteristics of axial-flow pumps under different startup strategies during multi-pump parallel operation. Through comparative analysis, the following conclusions are drawn: when all three pumps start simultaneously, the internal pressure exceeds the rated head by 23.43%, and the reverse flow reaches 10.57% of the rated flow. When starting the pumps sequentially with 5 s intervals, the pressure can be reduced to 11.41% above the rated head, but the reverse flow increases to 13.87%. Further extending the startup interval to 15 s results in only minimal improvements compared to 5 s intervals: the maximum internal pressure and maximum reverse flow decrease by just 0.97% and 0.05%, respectively. When valve coordination is added to the 5 s sequential startup strategy (pre-opening the valve to 60% before pump startup), the pressure exceeds the rated head by 10.49%, and the reverse flow exceeds the rated flow by 6.04%. In this scenario, the high-pressure areas and high-turbulence zones on the blade back surfaces are significantly reduced, achieving optimal flow stability. Therefore, the parallel system startup should adopt a coordinated strategy combining moderate time intervals with 60% valve pre-opening. This approach can both avoid excessive pressure impact and effectively control reverse flow phenomena, providing an important basis for optimizing the startup of multi-pump parallel systems. Full article

In intermittent gas lift (IGL), not all the liquid initially in the tubing is usually produced at the surface in one cycle. This is due to a concept known as fallback, which occurs when some amount of the initial liquid column drops back to join the next slug. We conducted a review of earlier works on IGL and the behavior of the fallback factor. The dependence on the fallback factor on the operational conditions such as slug velocity, valve opening pressure, valve closing pressure, casing–tubing pressure ratio, diameter of tubing, and amount of gas injected during IGL are discussed in this paper. The effect on the shape and stability of the nose of the Taylor bubble on the lifting efficiency of the bubble is also explained. In trying to reduce the fallback factor per cycle, there have been recommendations to combine gas lift with plunger lift. We also present the results of this combination and the effects on the fallback factor in gas-assisted plunger lift (GAPL). More light is shed on the behavior of the velocity of the liquid slug and how it affects the fallback factor during IGL. The behavior of the fallback factor with an increase or decrease in plunger velocity during GAPL is also presented in this paper. This review is categorized into experimental and numerical studies on fallback factor to evaluate their impact on production efficiency in IGL and GAPL. Additionally, different formulas for fallback proposed by different literature are compiled. Full article

With the advantages of simple structure, low power consumption, no electromagnetic interference, and fast response, piezoelectric pumps (PPs) have been widely used in the fields of chip cooling, biomedical applications, chemical applications, and fuel supply applications. In recent decades, scholars have proposed various PPs, and this article reviews the recent research results. In this review, according to the “valve” structure, PPs are divided into valve-less piezoelectric pumps (VLPPs), valve-based piezoelectric pumps (VBPPs), and piezoelectric pumps with valve and valve-less state transitions (PPVVSTs). Firstly, the design methods of typical structures were discussed, and comparisons were made in terms of driving frequency, driving voltage, output pressure, flow rate, structure materials, and pump size. The advantages and disadvantages of VLPPs, VBPPs, and PPVVSTs were analyzed. Then, we compared the driving parameters, output performance, structure materials, and pump size of single-chamber piezoelectric pumps (SCPs) and multi-chamber piezoelectric pumps (MCPs) and analyzed the advantages and disadvantages of SCPs and MCPs. Optimization methods proposed in recent years have been summarized to address the issues of the cavitation phenomenon, the liquid back-flow problem, and low output performance in PPs. Subsequently, the application research of PPs and the distribution of academic achievements were discussed. Finally, this review was summarized, and future research hot spots for PPs were proposed. The main contribution of this review is to provide piezoelectric pump (PP) researchers with a certain understanding of the structural design, optimization methods, practical applications, and research distribution of PPs, which can provide theoretical guidance for future research. Full article

In this paper, a novel technical route, namely combining the low-pressure exhaust gas recirculation (LP-EGR) and variable compression ratio (VCR), is proposed to address the inferior fuel economy for marine dual-fuel engines of low-pressure gas injection in diesel mode. To validate the applicability of the proposed technical route, firstly, a zero-dimensional/one-dimensional (0-D/1-D) engine simulation model with a predictive combustion model DI-Pulse is established using GT-Power. Then, parametric investigations on two LP-EGR schemes, which is implemented with either a back-pressure valve (LP-EGR-BV) or a blower (LP-EGR-BL), are performed to qualitatively identify the combined impacts of exhaust gas recirculation (EGR) and compression ratio (CR) on the combustion process, turbocharging system, and nitrogen oxides (NOx)-brake specific fuel consumption (BSFC) trade-offs. Finally, an optimization strategy is formulated, and an optimization program based on response surface methodology (RSM)–particle swarm optimization (PSO) is designed with the aim of improving fuel economy while meeting Tier III and various constraint conditions. The results of the parametric investigations reveal that the two LP-EGR schemes exhibit opposite impacts on the turbocharging system. Compared with the LP-EGR-BV, the LP-EGR-BL can achieve a higher in-cylinder pressure level. NOx-BSFC trade-offs are observed for both LP-EGR schemes, and the VCR is confirmed to be a viable approach for mitigating the penalty on BSFC caused by EGR. The optimization results reveal that for LP-EGR-BV, compared with the baseline engine, the optimized BSFC decreases by 10.16%, 11.95%, 10.32%, and 9.68% at 25%, 50%, 75%, and 100% maximum continuous rating (MCR), respectively, whereas, for the LP-EGR-BL scheme, the optimized BSFC decreases by 10.11%, 11.93%, 9.93%, and 9.58%, respectively. Furthermore, the corresponding NOx emissions level improves from meeting Tier II regulations (14.4 g/kW·h) to meeting Tier III regulations (3.4 g/kW·h). It is roughly estimated that compared to the original engine, both LP-EGR schemes achieve an approximate reduction of 240 tons in annual fuel consumption and save annual fuel costs by over USD 100,000. Although similar fuel economy is obtained for both LP-EGR schemes, LP-EGR-BV is superior to LP-EGR-BL in terms of structure complexity, initial cost, maintenance cost, installation space requirement, and power consumption. The findings of this study provide meaningful theoretical supports for the implementation of the proposed technical route in real-world engines. Full article

The lymphatic system collects excess fluid and molecules from the interstitial space back into the venous system mainly via the thoracic duct (TD). Despite the importance of the lymphatic flow in health and disease, a validated pressure–flow relation of lymphatic fluid through the TD is lacking in a translational large animal model. The objective of this work was to establish a pressure–flow relationship for a TD segment with one valve in a swine model. Our methodology consisted of using a specialized bench experimental setup to measure the passive forward flow of 0.9% saline through single-valve TD segments (n = 5) under various pressure gradients. Using Poiseuille’s law, we computed the resistance to flow in the TD segment. Subsequently, we used a sigmoidal function to model the relation between valve resistance and pressure gradient across the valve. We estimated the model’s parameters using the Poiseuille-based resistance values and associated experimental pressure date then validated the model by comparing model predictions of flow to experimental measurements. We found that the model performs accurately ($R^2=0.985\pm 0.010$). The resistance model validated here for a single valve TD segment provides a fundamental element for computational simulations of lymphatic flow in the entire TD. Moreover, this work provides a baseline for future characterization of TD behavior under pathological conditions, such as congestive heart failure or hepatitis caused ascites. Full article

In this study, we analyzed changes in flow characteristics and energy-dissipation characteristics due to changes in hydrogen temperature and inlet/outlet differential pressure in a check valve, which affect the storage safety and reliability of high-pressure hydrogen refueling systems. The effects of flow separation and recirculation flow generation at the back end of the valve were investigated, and the pressure, flow rate, pressure coefficient, and energy dissipation at the core part (where the hydrogen inflow is blocked) and the outlet part (where the hydrogen is discharged) were numerically analyzed. The hydrogen-inlet temperature (T_in) was selected as 233 K, 293 K, and 363 K, and the differential pressure (∆P) was selected in the range of 2 to 10 MPa in 2 MPa steps. To ensure the reliability of the numerical results, mesh dependence was performed, and the effect of the mesh geometry on the results was less than 2%. The numerical simulation results showed that the hydrogen introduced into the core part is discharged into the discharge part, and the pressure decreases by up to 6% and the velocity increases by up to 16% at the 95 mm position of the L-shaped curved tube. In addition, for the hydrogen-inlet temperature of 233 K in the L-shaped curved tube, the flow velocity decreases by up to 60% and the pressure coefficient increases at the 2.3 mm point in the Y-axis direction, indicating that the main flow area is biased towards the bottom of the valve due to the constriction of the veins caused by flow separation. The TDR results showed that the hydrogen discharge to the discharge region increased by 96% at 95 mm compared to 90 mm, and the turbulent kinetic energy of the hydrogen was dissipated, resulting in a temperature increase of up to 4.5 K. The exergy destruction was maximized in the core region where flow separation occurs, indicating that the pressure, velocity, and TDR changes due to flow separation and recombination have a significant impact on the energy loss of the flow in the check valve. Full article

Methanol reforming is considered to be one of the most promising hydrogen production technologies for hydrogen fuel cells. It is expected to solve the problem of hydrogen storage and transportation because of its high hydrogen production rate, low cost, and good safety. However, the strong nonlinearity and slow response of the pressure and temperature subsystems pose challenges to the tracking control of the methanol reforming hydrogen production system. In this paper, two internal model-based temperature and pressure controllers are proposed, in which the temperature is adjusted by controlling the air flow and the pressure is adjusted by controlling the opening of the back-pressure valve. Firstly, a lumped parameter model of the methanol reforming hydrogen production system is constructed using MATLAB/Simulink^® (produced by MathWorks in Natick, Massachusetts, USA). In addition, the transfer function model of the system is obtained by system identification at the equilibrium point, and the internal model controller is further designed. The simulation results show that the control method achieves the robustness of the system, and the temperature and pressure of the reforming reactor can quickly and accurately track the target value when the load changes. Small-load step tests indicate stable tracking of the temperature and pressure for the reforming reactor, without steady-state errors. Under large-temperature step signal testing, the response time for the reforming temperature is about 148 s, while the large-pressure step signal test shows that the response time for the reforming pressure is about 8 s. Compared to the PID controller, the internal model controller exhibits faster response, zero steady-state error, and no overshoot. The results show that the internal model control method has strong robustness and dynamic characteristics. Full article

Proton exchange membrane fuel cells (PEMFCs), as a clean energy technology, show remarkable potential for a wide range of applications. However, high altitude regions pose significant challenges for PEMFC system operation due to thin air and low oxygen partial pressure. Existing logic judgement-based controls exhibit defects such as poor robustness and poor adaptability, which seriously restrict PEMFC system operation. In order to address this issue, this paper puts forth an intelligent control of a PEMFC system air compressor (AC) and back pressure valve (BPV) using an asynchronous advantage actor-critic (A3C) algorithm and systematically compares it with the logic judgement-based control. The application of an A3C-based control under three distinct high altitude test conditions demonstrated a notable enhancement in dynamic responsiveness, with an improvement of up to 40% compared to the results for the logic judgement-based control. Additionally, an improvement of 5.8% in electrical efficiency was observed. The results demonstrate that the A3C-based control displays significant robustness and control precision in response to altitude alterations. Full article

Short-circuit blowing is a crucial technical approach for ensuring the rapid surfacing of submersibles. In order to investigate the law, L₁₈(3⁷) orthogonal experiments based on a proportional short-circuit blowing model test bench were conducted. Subsequently, a Back Propagation Neural Network (BPNN) and Pearson correlation analysis were employed to train the experimental data; further examination of the correlation between individual factors and blowing served as an enhancement to the orthogonal experiments. It has been proved that both multi-factor combinations and personal factors, including blowing duration, sea tank back pressure, gas blowing pressure from the cylinder group, and sea valve flowing area, exert significant influence with Pearson correlation coefficients of 0.6535, 0.8105, 0.5569, and 0.5373, respectively. Notably, the F-ratio for blowing duration exceeds the critical value of 3.24. The statistical evaluation metrics for the BPNN ranged from 10⁻¹ to 10⁻¹², with relative errors below 3%, and achieving a prediction accuracy rate of 100%. Based on these findings, a robust predictive methodology for submersible short-circuit blowing has been established along with recommendations for engineering design and operational strategies that highlight its advantages as well as its initial condition settings. Full article

The counter-pressure casting (CPC) process has the technical advantages of smooth filling and solidification under pressure, which is conducive to obtaining high-quality castings. In the counter-pressure casting process, the way of fixed solenoid valve opening is used for synchronous pressurization at present. However, this synchronous pressurization method causes the melt to rise first in the transfer tube and then fall back. The falling process of the melt will lead to the formation of the double-layer oxide films on the melt surface. In the subsequent pouring stage, part of the double-layer oxide films will enter the inside of the casting to form defects. To solve this problem, the synchronous pressurization process was optimized. Combined with numerical simulation and measurement results, the influence of two kinds of processes on melt rise behavior in transfer tubes before and after optimization is compared. The optimized process can reduce the rise height of melt by about 90% in the process of synchronous pressurization and change the flow behavior of melt so that the melt is always filled forward and the fall of melt is eliminated. Furthermore, the formation of double-layer oxide films in the melt during synchronous pressurization is eliminated. Full article

The bypass valve of a positive displacement motor is a key component for regulating the bottom hole pressure and ensuring the normal circulation of drilling fluid during the drilling process. Severe erosion damage to the bypass valve significantly affects the service life of the positive displacement motor, yet there is currently a lack of related research. In this research, the flow characteristics of drilling fluid inside the valve core were analyzed through flow field simulation, and the main factors influencing erosion damage to the valve core were investigated. The results indicate that the side holes and flow channel structure of the valve core are the main causes of erosion. Based on this, two optimization schemes are proposed, namely, reducing the number of bypass side holes to 4 and optimizing the flow channel cone angle to 45°. The simulation results show that the erosion rate of the optimized valve core is significantly reduced, and the service life is effectively improved. Finally, a valve core life prediction model is established using a back propagation (BP) neural network to evaluate the optimization effect. The results show that the applicable flow range and maximum service life of the optimized valve core are increased by approximately 60% and 75.4%, respectively, validating the effectiveness of the optimization scheme. Full article

The exhaust back pressure of diesel engines is becoming increasingly higher nowadays. In order to keep discharging exhaust unhindered and operating smoothly under high exhaust back pressure, a large reduction in engine maximum brake output is often observed, as well as increased fuel consumption and lower combustion efficiency with heavy exhaust smokes. In our previous study, “Applicability of Reducing Valve Timing Overlap for Diesel Engines under High Exhaust Back Pressure”, a reduced valve timing overlap of 12 °CA partially improves the brake output and BSFC for a fixed-geometry turbocharged diesel engine under high exhaust back pressures. A potential solution for restoring the brake output under high exhaust back pressures could be the use of variable-geometry turbochargers. In this study, a variable-geometry turbocharger is applied to a diesel engine to study the engine performance characteristics and applicability, especially the further improvement of brake output and the brake-specific fuel consumption of the engine. Continuing with the results of our previous research, a basic setting of 12 °CA for the valve timing overlap is set up for the subsequent engine performance simulations in this study (using GT-Power SW). Via simulation, exhaust back pressures of 25 kPa, 45 kPa, and 65 kPa gauge are studied for a turbocharged diesel engine. The results for the engine parameters, including brake output, brake-specific fuel consumption, compressor outlet temperature, turbine inlet temperature, intake air mass flow rate, and exhaust mass flow rate are analyzed. The results of the variable-geometry turbocharger, including turbocharger speed, pressure ratios and efficiencies of compressor and turbine are also analyzed. The results indicate that the brake output and brake-specific fuel consumption are effectively improved under full-load operation with an adequate variable-geometry turbocharger rack position. Operable ranges of rack position are also set up for different back pressures. Full article

The intrusion of micrometer-sensitive contaminant particles into the clearance of sliding valves within hydraulic fluids is one of the root causes of valve sticking and reliability issues in hydraulic systems. To reveal the transient process and characteristics of particle intrusion into the clearance process, this paper proposes a numerical method for fluid–particle one-way coupling and verifies it through experimentation. Furthermore, a numerical simulation of the motion trajectory of spherical iron particles inside the valve chamber was conducted in a two-dimensional flow model. It was discovered that in a steady-state flow field with a certain valve opening, micrometer-sized particles in the valve chamber’s hydraulic fluid mainly move with the valve flow stream, and the number of micron particles invading the slide valve clearance and the probability of invasion is related to the slide valve opening and differential pressure. When the slide valve opening decreases, especially in the small opening state, the probability of particles invading the slide valve clearance will increase dramatically, and the probability of invading the clearance is as high as 27% in a valve opening of 50 μm; the larger the pressure difference between the valve ports, the more the number of particles invading the slide valve clearance increases; the particles in the inlet of the slide valve clearance are more prone to invade the slide valve clearance, and invade in an inclined way, touching the wall and then bouncing back. These findings are of great value for the design of highly reliable hydraulic control valves and the understanding of the mechanism of slide valve stalls and provide an important scientific basis for the optimization and improvement in the reliability of hydraulic systems. Full article

Background: In military flight operations, during flights, fighter pilots constantly work under hyperoxic breathing conditions with supplemental oxygen in varying hypobaric environments. These conditions are suspected to cause oxidative stress to neuronal organ tissues. For civilian flight operations, the Federal Aviation Administration (FAA) also recommends supplemental oxygen for flying under hypobaric conditions equivalent to higher than 3048 m altitude, and has made it mandatory for conditions equivalent to more than 3657 m altitude. Aim: We hypothesized that hypobaric–hyperoxic civilian commercial and private flight conditions with supplemental oxygen in a flight simulation in a hypobaric chamber at 2500 m and 4500 m equivalent altitude would cause significant oxidative stress in healthy individuals. Methods: Twelve healthy, COVID-19-vaccinated (third portion of vaccination 15 months before study onset) subjects (six male, six female, mean age 35.7 years) from a larger cohort were selected to perform a 3 h flight simulation in a hypobaric chamber with increasing supplemental oxygen levels (35%, 50%, 60%, and 100% fraction of inspired oxygen, FiO₂, via venturi valve-equipped face mask), switching back and forth between simulated altitudes of 2500 m and 4500 m. Arterial blood pressure and oxygen saturation were constantly measured via radial catheter and blood samples for blood gases taken from the catheter at each altitude and oxygen level. Additional blood samples from the arterial catheter at baseline and 60% oxygen at both altitudes were centrifuged inside the chamber and the serum was frozen instantly at −21 °C for later analysis of the oxidative stress markers malondialdehyde low-density lipoprotein (M-LDL) and glutathione-peroxidase 1 (GPX1) via the ELISA test. Results: Eleven subjects finished the study without adverse events. Whereas the partial pressure of oxygen (PO₂) levels increased in the mean with increasing oxygen levels from baseline 96.2 mm mercury (mmHg) to 160.9 mmHg at 2500 m altitude and 60% FiO₂ and 113.2 mmHg at 4500 m altitude and 60% FiO₂, there was no significant increase in both oxidative markers from baseline to 60% FiO₂ at these simulated altitudes. Some individuals had a slight increase, whereas some showed no increase at all or even a slight decrease. A moderate correlation (Pearson correlation coefficient 0.55) existed between subject age and glutathione peroxidase levels at 60% FiO₂ at 4500 m altitude. Conclusion: Supplemental oxygen of 60% FiO₂ in a flight simulation, compared to flying in cabin pressure levels equivalent to 2500 m–4500 m altitude, does not lead to a significant increase or decrease in the oxidative stress markers M-LDL and GPX1 in the serum of arterial blood. Full article

A hydraulic cavitation platform was developed in order to examine the occurrence of cavitation in the rectangular throttling groove spool and its correlation with noise characteristics. The test valve is constructed using PMMA material, which possesses excellent transparency. This transparency enables direct visual examination of cavitation occurring at the throttle slot. Additionally, high-speed photography is employed to observe the flow characteristics of the valve port, facilitating the analysis of cavitation morphology changes. Furthermore, a noise meter is utilized to measure and record the noise level and its corresponding spectrum. The flow field and flow phenomena at the rectangular throttling groove spool were studied using high-speed photography, noise spectrum analysis, and other methods. It is discovered that back pressure has the greatest influence on cavitation and flow separation, followed by the influence of intake pressure on cavitation morphology and noise. As the back pressure lowers, the cavitation morphology changes from flaky to cloudy, and the cavitation intensity, distribution area, and noise level increase. Background noise and cavitation noise have distinct frequency differences; cavitation noise in the rectangular throttling groove spool is high-frequency noise, with a frequency of more than 8 kHz, and the higher the frequency, the greater the difference in noise value. The magnitude of the alterations in noise intensity is minimal. The noise values exhibit slight variations of 2.3 dB, 4 dB, and 4.3 dB under varying back pressure circumstances of 3 MPa, 4 MPa, and 5 MPa inlet pressure, respectively. It is recommended to use the frequency of cavitation noise to detect the cavitation state and monitor the cavitation process. In the low-frequency region, the cavitation noise in the rectangular throttle groove valve core is not significantly different. Once the center frequency surpasses 3.15 kHz, a discernible distinction emerges, with the magnitude of the discrepancy in noise value increasing as the frequency rises. In other words, the cavitation cloud does not pulsate at one single frequency, but rather in a range of relatively high frequencies (more than 3.15 kHz). Full article