Large Pressure Variations Research Articles

Modelling the hydraulic performance of an array of centrifugal pumps operating under a variable pressure in a hydro-pneumatic energy storage system

Abstract The large pressure variation in hydro-pneumatic energy storage systems presents a major challenge for maintaining a high operating efficiency of the turbomachinery used in the hydro-electric energy conversion processes. This paper applies numerical modelling to compare the hydraulic performance of two pumping unit variants used for charging an offshore hydro-pneumatic energy storage (HPES) accumulator. The first unit consists of a single large centrifugal pump operated at variable speed while the second pumping unit is made up of an array of smaller, dynamically similar fixed-speed pumps. A number of series/parallel configurations for the latter option were derived in order to optimise the operational efficiency at various states of charge of a gas-charged accumulator, specifically between 80 and 200 bar. A comparative analysis of the operational hydraulic efficiencies for both pumping units shows that using an array of small fixed-speed pumps arranged in series/parallel configurations is more energy efficient than using a single large pump operated at variable speed.

Determination of Partial Propagation Velocity and Partial Isentropic Compressibility Coefficient in Water-Ethanol System.

This study introduces an innovative approach to the layered model, emphasizing the physical-chemical characterization of miscible liquid systems through ultrasonic techniques, with a specific focus on the water-ethanol system used in pharmaceutical formulations. Traditional characterization methods, while effective, face challenges due to the complex nature of solutions, such as the need for large pressure variations and strict temperature control. The proposed approach integrates partial molar volumes and partial propagation velocity functions into the layered model, enabling a nuanced understanding of miscibility and interactions. Ultrasonic techniques are used to calculate the isentropic compressibility coefficient for each component of the mixture as well as the total value using an additive mixing rule. Unlike conventional methods, this technique uses tabulated and experimental data to estimate the propagation velocity in the mixture, leading to a more precise computation of the isentropic compressibility coefficient. The results indicate a significant improvement in predicting the behavior of the water-ethanol system compared to the classical layered model. The methodology demonstrates the potential to provide new physicochemical insights that can be applied to other miscible systems beyond water-ethanol. This research has implications for improving the efficiency and accuracy of liquid medication formulations in the pharmaceutical industry.

Research on hydraulic variable pressure pumped compressed air energy storage system

Abstract To cope with the problems of large pressure variation, large throttling loss of the existing pumped compressed air energy storage system, a new hydraulic variable pressure pumped compressed air energy storage system is proposed in this paper. The key components include a variable-speed pump turbine, a hydraulic potential energy transfer device and a water-gas compatible tank. For the proposed system, a thermodynamic model is established. And its correctness is verified by comparing it with measured data. Then, the charging and discharging simulation is carried out. Finally, the variation process of each key parameter of the system is revealed. It is found that the energy efficiency of the system is high, reaching 58.2%, and the energy density is 0.36 kW·h/m3. Through the hydraulic potential energy transfer device, the pressure variation of 2.2 MPa in the tank is converted into the head variation of about 60 m (0.6 MPa) at the variable-speed pump turbine, which improves the operating efficiency of the hydraulic machinery. This technology can provide support for the development of energy storage technology.

Feasibility of Unobtrusively Estimating Blood Pressure Using Load Cells under the Legs of a Bed.

The ability to monitor blood pressure unobtrusively and continuously, even during sleep, may promote the prevention of cardiovascular diseases, enable the early detection of cardiovascular risk, and facilitate the timely administration of treatment. Publicly available data from forty participants containing synchronously recorded signals from four force sensors (load cells located under each leg of a bed) and continuous blood pressure waveforms were leveraged in this research. The focus of this study was on using a deep neural network with load-cell data as input composed of three recurrent layers to reconstruct blood pressure (BP) waveforms. Systolic (SBP) and diastolic (DBP) blood pressure values were estimated from the reconstructed BP waveform. The dataset was partitioned into training, validation, and testing sets, such that the data from a given participant were only used in a single set. The BP waveform reconstruction performance resulted in an R2 of 0.61 and a mean absolute error < 0.1 mmHg. The estimation of the mean SBP and DBP values was characterized by Bland-Altman-derived limits of agreement in intervals of [-11.99 to 15.52 mmHg] and [-7.95 to +3.46 mmHg], respectively. These results may enable the detection of abnormally large or small variations in blood pressure, which indicate cardiovascular health degradation. The apparent contrast between the small reconstruction error and the limit-of-agreement width owes to the fact that reconstruction errors manifest more prominently at the maxima and minima, which are relevant for SBP and DBP estimation. While the focus here was on SBD and DBP estimation, reconstructing the entire BP waveform enables the calculation of additional hemodynamic parameters.

Pore Pressure in Montmorillonite During Frictional Sliding

AbstractEarth's shallow crust is pervasively breached by fractures and faults that are often filled with saturated clays such as montmorillonite. Pore pressure in montmorillonite is difficult to measure due to its extremely low permeability, resulting in large uncertainties in its friction, which, in turn, may impact our understanding on the mechanical behaviors of the shallow crust. This difficulty motivates us to investigate pore pressure in montmorillonite during frictional sliding. Here we provide a first order understanding on the evolution of pore pressure in montmorillonite during frictional sliding by combining experimental data with an analytical consolidation model. Our result shows large variations in pore pressure in montmorillonite during frictional sliding, which need correction for the evaluation of friction of montmorillonite. We re‐visit this problem with the measured stresses at the end of our slow loading experiments where the modeled pore pressure approaches zero and obtain a new relation that shows a significant cohesive strength. The new relation may be united with our modeled pore pressure with a Biot‐Willis effective stress coefficient of α ∼ 0.5. X‐ray powder diffraction analysis of our samples shows evidence that intense deformation occurred during the frictional sliding with strain‐hardening, consistent with the occurrence of shear localization in the clay matrix following extended frictional sliding (Tembe et al., 2010, https://doi.org/10.1029/2009JB006383). These results suggest that our new relation may represent a constitutive relation for an intensely sheared, saturated montmorillonite in frictional sliding. Our result also suggests that substantial cohesion may appear on some natural clay‐rich faults.

Cavitation-Effect-Based Treatments and Extractions for Superior Fruit and Milk Valorisation.

Ultrasound generates cavities in liquids with high-energy behaviour due to large pressure variations, leading to (bio)chemical effects and material modification. Numerous cavity-based treatments in food processes have been reported, but the transition from research to industrial applications is hampered by specific engineering factors, such as the combination of several ultrasound sources, more powerful wave generators or tank geometry. The challenges and development of cavity-based treatments developed for the food industry are reviewed with examples limited to two representative raw materials (fruit and milk) with significantly different properties. Both active compound extraction and food processing techniques based on ultrasound are taken into consideration.

Dual titration of minute ventilation and sweep gas flow to control carbon dioxide variations in patients on venovenous extracorporeal membrane oxygenation

BackgroundThe implantation of venovenous extracorporeal membrane oxygenation (VV-ECMO) support to manage severe acute respiratory distress syndrome generates large variations in carbon dioxide partial pressure (PaCO2) that are associated with intracranial bleeding. We assessed the feasibility and efficacy of a pragmatic protocol for progressive dual titration of sweep gas flow and minute ventilation after VV-ECMO implantation in order to limit significant PaCO2 variations.Patients and methodsA protocol for dual titration of sweep gas flow and minute ventilation following VV-ECMO implantation was implemented in our unit in September 2020. In this single-centre retrospective before-after study, we included patients who required VV-ECMO from March, 2020 to May, 2021, which corresponds to two time periods: from March to August, 2020 (control group) and from September, 2020 to May, 2021 (protocol group). The primary endpoint was the mean absolute change in PaCO2 in consecutive arterial blood gases samples drawn over the first 12 h following VV-ECMO implantation. Secondary endpoints included large (> 25 mmHg) initial variations in PaCO2, intracranial bleedings and mortality in both groups.ResultsFifty-one patients required VV-ECMO in our unit during the study period, including 24 in the control group and 27 in the protocol group. The protocol was proved feasible. The 12-h mean absolute change in PaCO2 was significantly lower in patients of the protocol group as compared with their counterparts (7 mmHg [6–12] vs. 12 mmHg [6–24], p = 0.007). Patients of the protocol group experienced less large initial variations in PaCO2 immediately after ECMO implantation (7% vs. 29%, p = 0.04) and less intracranial bleeding (4% vs. 25%, p = 0.04). Mortality was similar in both groups (35% vs. 46%, p = 0.42).ConclusionImplementation of our protocol for dual titration of minute ventilation and sweep gas flow was feasible and associated with less initial PaCO2 variation than usual care. It was also associated with less intracranial bleeding.

Performance of a Closed Cycle Power Takeoff for a Shore-Based Wave Energy Device

A promising class of devices for ocean wave energy conversion is called the oscillating water column in which the wave power is transferred to an airflow that rotates a turbine. A closed cycle power takeoff (CCPTO), in which air is forced through two valves and a turbine, has two main benefits for such a system: it allows a unidirectional turbine, and it smooths the large variations in pressure due to irregular (i.e., polychromatic) seas. This paper presents the design of a CCPTO for a shore-based installation, with particular attention paid to the turbine. The entire system is simulated with a reduced order model for a range of sea states to estimate the operating conditions of the turbine. It is found that the pressure drop range is modest but strongly dependent on the tide and sea chamber geometry. The geometry of the turbine is initially developed with a 1D preliminary design of the blades and then the turbine performance is analysed and the design is refined using Reynolds Averaged Navier–Stokes simulations. The design process is conducted based on the geometry and the sea climate of a real-life wave energy installation located in Mutriku (Spain). A turbine that displays efficient performance over a wide range of sea states is obtained. The overall performance of this turbine as part of the entire CCPTO system is assessed and leads to an energy output of ∼1500 kWh for one month in sea conditions at Mutriku wave power plant in Spain. It is concluded that the CCPTO deserves further development in any fixed oscillating wave column system.

Experimental Investigation on Reversible Swelling Mechanisms of Lithium-Ion Batteries under a Varying Preload Force

The safety of lithium-ion batteries has to be guaranteed over the complete lifetime considering geometry changes caused by reversible and irreversible swellings and degradation mechanisms. An understanding of the pressure distribution and gradients is necessary to optimize battery modules and avoid local degradation bearing the risk of safety-relevant battery changes. In this study, the pressure distribution of two fresh lithium-ion pouch cells was measured with an initial preload force of 300 or 4000 N. Four identical cells were electrochemically aged with a 300 or 4000 N preload force. The irreversible thickness change was measured during aging. After aging, the reversible swelling behavior was investigated to draw conclusions on how the pressure distribution affected the aging behavior. A novel test setup was developed to measure the local cell thickness without contact and with high precision. The results suggested that the applied preload force affected the pressure distribution and pressure gradients on the cell surface. The pressure gradients were found to affect the locality of the irreversible swelling. Positions suffering from large pressure variations and gradients increased strongly in thickness and were affected in terms of their reversible swelling behavior. In particular, the edges of the investigated cells showed a strong thickness increase caused by pressure peaks.

Effect of gravity on phase transition for liquid–gas simulations

Direct simulations of phase-change and phase-ordering phenomena are becoming more common. Recently, qualitative simulations of boiling phenomena have been undertaken by a large number of research groups. One seldom discussed limitation is that large values of gravitational forcing are required to simulate the detachment and rise of bubbles formed at the bottom surface. The forces are typically so large that neglecting the effects of varying pressure in the system becomes questionable. In this paper, we examine the effect of large pressure variations induced by gravity using pseudopotential lattice Boltzmann simulations. These pressure variations lead to height dependent conditions for phase coexistence and nucleation of either gas or liquid domains. Because these effects have not previously been studied in the context of these simulation methods, we focus here on the phase stability in a one-dimensional system, rather than the additional complexity of bubble or droplet dynamics. Even in this simple case, we find that the different forms of gravitational forces employed in the literature lead to qualitatively different phenomena, leading to the conclusion that the effects of gravity induced pressure variations on phase-change phenomena should be very carefully considered when trying to advance boiling and cavitation as well as liquefaction simulations to become quantitative tools.

Modulating pipe-soil interface friction to influence HPHT offshore pipeline buckling

High-Pressure High-Temperature offshore pipelines laid on the seafloor are subject to large temperature and pressure variations which manifest as axial pipeline loading. Pipes become unstable in this condition and buckles form to relieve the axial stress. Considerable theoretical and experimental energy has been directed at establishing controlling mechanisms and parameters to predict buckling and design pipeline systems to be resilient and serviceable. The pipe-soil interface friction plays a pivotal role in the rate of build-up of axial loads and in controlling the critical buckling threshold. Pipes adopting smooth polymer coatings have very low friction coefficients but experimental work has shown that simple roughening techniques make greater friction coefficients available to a designer. Presented are a series of numerical analyses carried out using Abaqus to model a pipeline resting on the seabed subject to typical HPHT pipeline conditions. Global stability response is assessed with pipe-soil friction coefficients varying from 0.25 to 0.75 and differential friction regimes are adopted. It is shown that targeted application of pipe sections with greater interface friction may be a useful design tool for manipulating global buckling phenomena and could be a useful additional tool for influencing the spacing in Virtual Anchor Spacing analysis.

Flame stabilization of liquid oxygen/kerosene bi-swirl injector at elevated pressure

Throttleable liquid-propellant rocket engines have wide range and economical applications. However, low frequency combustion instabilities were often excited in the oxygen-rich preburners of liquid oxygen (LOx) and kerosene rocket engines as the engines throttling. To understand the mechanisms and eliminate these instabilities, the detail features of the instabilities need to be described. Bi-swirl injectors with deep recess are used in the oxygen-rich preburners to spray propellants. This paper presents the non-premixed flame dynamic of a LOx/kerosene bi-swirl injector under high-pressure conditions. High-speed cameras captured OH* and CH* chemiluminescence images of the oxygen-rich flame for the first time. Results indicate that a stable flame was anchored inside the recess region and featured by a V-shaped, swirl flame. The flame-spreading angle under supercritical conditions was slightly larger than the liquid spray angle. Intense low-frequency combustion instabilities at 16–37 Hz were developed when the LOx/kerosene mixing ratio (ROF) was greater than threshold value. The flame oscillation process was coupled to the oscillations of the mass flow rate and the ROF. As the oxygen-rich level decreased, the flame oscillation pattern gradually shifted from flame blow-out/auto-ignition mode to flame length oscillation mode. Both modes were characterized by violent flashback and blow-off movement of the flame and large pressure variations. The instability was one type of “lean-limit” instability. A discussion of the oscillation periods qualitatively explains why the oscillation periods were found to decrease as the ROF decreases. The axial velocity of the kerosene is a controlling parameter of the oscillation period.

Flow Stability in a Miniature Centrifugal Pump under the Periodic Pulse Flow

The flow behavior inside a miniature centrifugal pump, under a periodic pulse flow rate, was studied by means of numerical simulation. For a given incoming periodic pulse flow with a sine wave, the performance of the centrifugal pump was investigated in the section with increasing flow and the section with decreasing flow, and the special points of the flow rate and the periodic flow were identified. Further, the energy gradient method and the Q-criterion were adopted to analyze the internal vertical structure and flow stability. It was found that the regions with large variations in velocity and total pressure were mainly located at the leading edge of the suction surface and the middle area of the pressure surface of the blades. Irregular pressure fluctuation frequency under the periodic pulse flow was shown; this was mainly concentrated in the low-frequency zones close to the impeller’s rotational frequency. In addition, for the same flow rate in the periodic pulse flow, the pressure frequency fluctuation for the increasing flow rate section was higher than that observed for the decreasing flow rate section. It was found that the most unstable sections appeared in the first half-period of the flow rate variation (large flow rate), according to the distributions of the Q criteria of the vortex and the energy gradient function K. In this section, motions of strong vortices led to large gradients of the mechanical energy.

Non-axisymmetric complete flow conditioning gauzes

This paper presents a novel methodology for the design of a gauze that produces distributions of stagnation pressure, swirl angle, pitch angle and turbulence intensity, tailored in both the radial and circumferential directions. A distortion gauze is made from a large number of small-scale circumferential and radial blades with tailored thickness and camber distributions. By controlling the blade design independently in both the radial and circumferential directions, the target inflow pattern can be achieved. 1D correlations are used to initialise the blades and they are refined using full 3D CFD simulations. The final design is additively manufactured for use in rotating rigs. In this paper, the method has been used to reproduce four target inflow patterns with large variations in stagnation pressure and flow angularity. Two examples model the inlet flow distortion seen at the aerodynamic interface plane of an aft-mounted boundary layer ingesting fan. The final two examples model the inlet distortion at inlet to an axial compressor spool caused by upstream structural struts in a swan neck duct. The gauzes are shown to replicate the structures of the target flow in an experimental test. These kind of flow structures would be extremely difficult or impossible to replicate in an experiment in any other way.Graphical abstract

Episodicity and Migration of Low Frequency Earthquakes Modeled With Fast Fluid Pressure Transients in the Permeable Subduction Interface

AbstractIn many subduction zones, the plate interface hosts intermittent, low‐frequency, low‐magnitude seismic tremor and low‐frequency earthquakes (LFEs). Seismic activity clusters in episodic bursts that migrate along the fault zone in complex ways. Geological structures in fossil tremor source regions testify to large and pervasive variations of fluid pressure and permeability. Here, we explore the potential of fluid pressure transients in a permeable subduction interface to trigger seismic sources and induce interactions between them. We show how variations of pore pressure and permeability can act in tandem to generate tremor‐like patterns. The core feature of the model is that low‐permeability plugs behave as elementary fault‐valves. In a mechanism akin to erosive bursts and deposition events documented in porous media, valve permeability opens and closes in response to the local fluid pressure distribution. The rapid pressure release and/or mechanical fracturing associated with valve opening acts as the source of an LFE‐like event. Valves interact constructively, leading to realistic, tremor‐like patterns: cascades, synchronized bursts, and migrations of activity along the channel, on both short and long time and space scales. Our model predicts that the input fluid flux is a key control on activity occurrence and behavior. Depending on its value, the subduction interface can be seismically quiescent or active, and seismicity can be strongly time‐clustered, quasi‐periodic or almost random in time. This model allows new interpretations of low frequency seismic activity in terms of effective fluid flux and fault‐zone permeability.

Mediastinal effusion due to pericardiocentesis with cardiac tamponade: a case report

BackgroundPericardiocentesis is an effective treatment for cardiac tamponade, but there are risks, including haemorrhagic events, cardiac perforation, pneumothorax, arrhythmia, acute pulmonary oedema and so on. Mediastinal effusion caused by puncture is rarely reported.Case presentationA 47-year-old man who had a history of right leg deep vein thrombosis and pulmonary artery embolism with implantation of an inferior vena cava filter presented for inferior vena cava filter removal. Within 30 min after the procedure, he developed chest pain, nausea, vomiting and presyncope with shock. Echocardiography confirmed massive pericardial effusion with evidence of cardiac tamponade. Emergency pericardiocentesis was performed. Confusingly, only 3 mL of bloody pericardial effusion was drained in total, and subsequently, the patient’s symptoms rapidly improved with stable haemodynamics. Repeat echocardiography showed that the pericardial effusion had disappeared. Urgent computed tomography pulmonary angiography demonstrated localized effusion, which was not seen the previous computed tomography results and was noted around the left ventricle in the mediastinal apace. No intervention was performed, given that there was no bleeding tendency or further adverse events related to the mediastinal effusion. The patient was subsequently discharged in a stable condition a few days later, and outpatient follow-up was advised.ConclusionsMediastinal effusion is a rare complication of pericardiocentesis. In the case described herein, the most likely cause was pericardial effusion extravasated into the mediastinum through the needle insertion site in the puncture process due to large pressure variations in the intrapericardial space with tamponade, differing from cases of over-anticoagulation reported in the previous literature. Just as our case demonstrates that conservative treatment of an hemodynamic insignificant mediastinal effusion may be appropriate. Echocardiography is useful and effective to minimize complication rates.

Effects of intake conditions and octane sensitivity on GCI combustion at early injection timings

Gasoline compression ignition (GCI) engines favor low-octane fuels (RON = 60–80). However, low-octane fuels possessing low-temperature reactions strongly interact with in-cylinder thermodynamic conditions, which in turn significantly affect GCI combustion characteristics. In this work, using a toluene primary reference fuel (TPRF) with RON = 75, the effects of intake pressure and temperature on combustion evolutions, low-temperature heat release (LTHR), high-temperature heat release (HTHR), and indicated thermal efficiency were numerically investigated in a single-cylinder GCI engine, allowing for the role of octane sensitivity. An early injection timing was considered to obtain relatively homogeneous mixtures and large variations in intake pressure were employed to simulate low to medium loads. The results show that for a given equivalence ratio, the peak of the LTHR and HTHR and the main combustion phasing positively correlates with intake pressure. However, an opposite tendency in the peak of the HTHR is observed for a fixed amount of fuel injection. When octane sensitivity is elevated, the peak of in-cylinder pressure and heat release rate is reduced and ignition timing is retarded, especially for the HTHR. Elevating intake temperature facilitates high-temperature combustion while suppresses low-temperature reactions, which results in nonlinear variations in combustion phasing at a certain range of intake temperatures. The correlations of operating conditions and combustion evolutions are evaluated by pressure-temperature trajectory and Livengood-Wu integration, which indicates the significance of intake pressure in GCI combustion. Finally, combustion evolutions show that low-temperature reactions first take place at fuel-lean regions and hot flame pockets develop in fuel-rich regions, which suggests that low-temperature ignition is more sensitive to ambient temperatures while high-temperature ignition is more dependent on equivalence ratio.

Blast pressures and waveforms of consumer firecrackers

Current methods for testing blast pressures produced by fireworks are ad hoc and differ substantially from established methods for assessing injury risks from explosives. In this experimental study, pressure-versus-time waveforms were measured as a function of distance from the source for four consumer firecrackers and one consumer bottle rocket. Pressure-versus-time data were collected at 10 MHz using a piezoelectric blast pressure sensor at distances 75 mm, 150 mm, 225 mm, and 300 mm from the source. While large variations in peak pressure were observed, in some trials, peak blast pressures over 100 kPa were observed, which suggests a risk of primary blast injury. The results support analysis of pressure waves produced by consumer firecrackers using established methods to quantify blast waves and to evaluate the risk of primary blast injury by comparing peak pressure and positive pulse duration to injury thresholds for specific body systems. Similar methods can be applied to result in comparable measurements for other firework devices.

Quartz Vein Geochemistry Records Deformation Processes in Convergent Zones

AbstractIn several examples of subduction zones, we compared pairs of quartz veins formed either at the lower temperatures of the seismogenic zone (260°C or below), or at the higher temperatures of its downdip limit (∼330°C). All the veins analyzed here are mode I cracks that formed contemporaneously with the host‐rock main stage of deformation at peak burial conditions. Lower‐temperature veins show examples of quartz crystals with euhedral shapes and growth rims, while higher‐temperature veins contain crack‐seal microstructures. In the lower‐temperature realm, quartz growth rims have alternatingly either: (1) high cathodoluminescence (CL), CL‐blue color and high concentration in trace elements and fluid inclusions, or (2) low luminescence, CL‐brown color and low concentration in trace elements and fluid inclusions. In contrast, the quartz from higher‐temperature samples is homogeneously low luminescent and CL‐brown, except for very restricted domains of the crack‐seal microstructures where patches of CL‐blue quartz are present. The highly luminescent quartz contains high concentrations of aluminum and lithium, up to 3,000 and 400 ppm, respectively. Variations in Al and Li correlate well, so that Li appears as the main charge‐compensating cation for Al. We propose that the incorporation of Al and Li reflects the amplitude of the fluid pressure variations, which control crystal growth rates. Quartz geochemistry might therefore unravel the contrast between the seismogenic zone, where large fluid pressure variations are present, and its downdip limit, where fluid pressure variations are much more limited in amplitude.

Unsteady Effects on NOx Measurements in Pulse Detonation Combustion

Emission measurements from unsteady combustion systems such as Pulse Detonation Combustion (PDC) are challenging due to the inherently large variations in pressure, temperature, composition, and flow velocity of the exhaust gas. Comparison of experimental data is additionally complicated by differences in operating conditions and gas sampling setup between different facilities. Qualitative considerations with regard to the sampling process from PDC, based on one-dimensional simulations, indicate a systematic influence of the sampling setup and extraction process on the resulting concentration measurements. Therefore, operating frequency, sample time, fill time, as well as PDC outlet and probe geometry were varied experimentally in order to assess the degree to which each of these parameters impact the resulting measured {rm NO}_{rm x} in order to better inform researchers of these effects when making measurements. It was shown that measured {rm NO}_{rm x} emissions can vary significantly depending on the choice of these parameters and therefore care must be exercised in order to reduce the influence of the sampling technique when aiming for comparable results.