Pressure Decay Research Articles

Understanding perioperative risk determinants in carotid endarterectomy: the impact of compromised circle of Willis morphology on inter-hemispheric blood flow indices based on intraoperative internal carotid artery stump pulse pressure and backflow patterns.

Carotid artery stenosis (CAS) often requires surgical intervention through carotid endarterectomy (CEA) to prevent stroke. Accurate cerebrovascular risk assessments are crucial in CEA, as poor collateral circulation can lead to insufficient interhemispheric blood flow compensation, resulting in ischemic complications. Therefore, understanding perioperative risk determinants is vital. This study aims to determine the impact of compromised circle of Willis (CoW) morphology on inter-hemispheric blood flow, focusing on indices based on intraoperative internal carotid artery stump pulse pressure and backflow patterns. In 80 CAS patients who underwent CEA, preoperative CT angiography for CoW was conducted. Patients were categorized into five subgroups based on their CoW anatomy and three additional groups based on intraoperative internal carotid artery (ICA) stump backflow patterns evaluated by the surgeon. Continuous blood pressure signals, including systolic, diastolic, mean, and pulse pressure values, were recorded during the procedure. The relationship between CoW anatomical variants and the systolic and diastolic segments of the averaged pressure waveforms, particularly diastolic pressure decay, was analyzed. The correlation between CoW anatomy and stump backflow intensity was also examined. Significant variability in ICA stump backflow and pressure values was evident across CoW variants. Patients with compromised CoW morphology exhibited weaker backflow patterns and lower ICA stump pulse pressure values, consistent with impaired interhemispheric blood flow. Notably, ICA stump diastolic pressure decay was consistent across most CoW variant groups, indicating developed collateral circulation in cases with CoW anomalies. Thus, impaired CoW integrity is associated with compromised interhemispheric blood flow indices based on intraoperative ICA stump pulse pressure and backflow patterns during CEA. Integrating intraoperative pulse waveform analysis with preoperative CT angiography provides a more detailed assessment of cerebrovascular risk, guiding the selective use of shunts. This combined approach may improve surgical outcomes and patient safety by identifying patients at increased risk of perioperative neurological events due to CoW anomalies.

Impact of gas adsorption of nitrogen, argon, methane, and CO2 on gas permeability in nanoporous rocks

Gas adsorption on the surface of nanoporous rocks is an important process that occurs in many applied scenarios such as shale gas production or CO2 enhanced gas recovery or storage. While there are few theoretical considerations on the effect of gas adsorption on permeability, a systematic laboratory investigation of the impact of gas adsorption on gas flow and permeability is still lacking. In this paper, permeability of four adsorptive gases, i.e., nitrogen, argon, methane, and carbon dioxide, was measured, along with helium permeability, for two nanoporous rock samples that have high and low total organic carbon (TOC) content, respectively. The measurements were conducted at a range of pore pressures from 150 to 1500 psi (1.03–10.34 MPa). Gas adsorption isotherms were also measured at the same conditions. A mathematical model that considers adsorption with specific boundary conditions for the experimental setup was used for data analysis. The results show that gas adsorption causes larger drop in pressure decay and greater retardation in pressure equilibrium. However, the reduction of permeability relative to helium (25%–46%) is similar for gases with different levels of adsorption, indicating the occurrence of single-layer adsorption for these gases. Comparison between the two samples further supports the concept of single-layer adsorption and signifies the impact of pore size on the permeability reduction due to adsorption. These new findings deepen the fundamental understanding and provide important clarification on the effect of gas adsorption on gas flow and permeability in nanoporous rocks.

Sustainable biomass derived natural surfactant of soybean seeds in fly ash industrial waste utilization for carbon storage: Evaluation of environmental impact

The rising carbon emissions challenge global environmental sustainability and climate stability. This study aims to advance climate change mitigation by integrating fly ash and natural surfactant into CO2 sequestration strategies. Fly ash, a by-product of industrial processes, presents an opportunity for innovative reuse. By combining fly ash with a natural surfactant extracted from soybean seeds, both industrial waste management and greenhouse gas reduction can be addressed. The surfactant was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, surface tension, and electrical conductivity measurements, confirming saponin presence with a critical micelle concentration of 0.3 wt%. Pressure decay studies revealed that a (5 wt% fly ash + NS) demonstrated the highest CO2 absorption, supported by microscopic analysis. Further research on optimizing reaction conditions and kinetics of mineralization could enhance this method’s efficiency and scalability for broader application.

Air Leakages at Microvalves: Pressure Decay Measurements and Extended Continuum Modelling of Knudsen Flows

To improve the performance of valves in relation to the leakage rate, a comprehensive evaluation of the valve characteristics and behavior during pressure exposure is important. Often, these low gas flow rates below 0.1 cm3/min cannot be accurately measured with conventional flow sensors. This paper presents a small and low-cost test rig for measuring gas leakage rates accurately, even far below 0.1 cm3/min, with the pressure decay method. These leakage flows are substantiated with a flow model, where we demonstrate the feasibility of modeling those gas flows with an extended Navier–Stokes framework to obtain more accurate theoretical predictions. As expected, the comparison to the experimental results proves that the classical Navier–Stokes system is unsuitable for modeling Knudsen flows. Hence, self-diffusion of gas, a wall-slip boundary condition, and an effective mean free path model were introduced in a physically evident manner. In terms of the calculated mass flow, while self-diffusion and slip boundary conditions explain deviations from the classical Navier–Stokes equation for Knudsen numbers already smaller than 1, the effective mean free path model has an effect, especially when Kn > 1. For simplified conditions, an analytical solution was presented and compared to the results of an OpenFOAM CFD-solver for flow rates through more complex gap-flow geometries of the flap valve. Hereby, acceptable deviations between 10% and 20% were observed. A comparison with measurement results was carried out. The reproducibility of the measurement method was verified by comparing multiple measurements of one silicon microvalve sample to a state-of-the-art flow sensor. Three geometrically similar passive silicon microvalves were measured with air overpressure decreasing from 15 kPa relative to atmospheric pressure. Maximum gas volume flowing in a blocking direction of 1–26 µL/min with high reproducibility and marginal noise were observed.

Enhancing subjective spaciousness for stereo reproduction in car-size acoustical enclosures based on audio signal decorrelation

Audio signal decorrelation has been used for enhancing the spaciousness of auditory source width (ASW) in a stereo reproduction. However, the acoustic environment in car-size acoustical enclosures is quite different from that in a home theater or listening room. Due to the small cabin size and the substantial presence of absorptive surfaces, the reproduced sound field in car-size acoustical enclosures is characterized by the interior mode region up to some hundreds or one thousand hertz and fast decay of pressure at higher frequencies which could affect the perceived performance of audio signal decorrelation. Therefore, the present work evaluates the effect of reflections in an acoustical enclosure model with car-size on the ASW enhanced by decorrelated audio signals, which reproduced by a standard stereo system. The decorrelation algorithm is handled by all-pass filters sets based on a pair of reciprocal maximal length sequence (MLS). Last, a subjective assessment experiment of ASW validates that appropriate decorrelation method can improve perceived spaciousness for sound reproduction in car-size acoustical enclosures.

P166 EXPLORING AGE-ASSOCIATED CHANGES IN HEMODYNAMICS: INSIGHTS FROM 24-HOUR BLOOD PRESSURE MONITORING

Background and Objective: Aging is associated with progressive alterations in the structure and function of the heart and arteries, which can occur independently. This study aims to investigate the hemodynamic changes occurring in aging normotensive subjects concerning heart and arterial function. We employed a novel method based on blood pressure values obtained during 24-hour ambulatory blood pressure monitoring (24-h ABPM). Methods: A cross-sectional study was conducted involving 3,220 non-obese patients referred for 24-h ABPM, who did not have hypertension and were not taking any medications. 24-hour mean hemodynamics was obtained using a non-invasive method based on Ct. Ct was estimated as: Ct/BSA= 38/PPth+ 4/5 × Td/T - 3/7, where BSA: body surface area, Td: diastolic time, T: cardiac period, and PPth: theoretical pulse pressure. The stroke volume (SV) was estimation as: SV= Ct (PP+MSP ×Ts/τ), where PP: pulse pressure, MSP: mean systolic pressure, Ts: systolic time, τ: diastolic pressure decay time constant. Cardiac output (CO) and SVR were obtained using conventional formulas. Results: Among the participants, 64.6% were female, with an average age of 51.0±15.3 years, Ct of 0.96±0.21 mL/mmHg, CO of 5.2±0.68 L/min, and SRV of 1394±178 dyn.s/cm5. An age-related reduction in stroke index and cardiac index are noteworthy, stabilizing from the sixth decade of life onward (41.1±2.0 mL/m2 and 3.0±0.23 L/min/m2, respectively). Conversely, Ct exhibits an early increase from the third to fifth decades of life (1.04±0.18 mL/mmHg), followed by a continuous and gradual decline until the ninth decade (0.71±0.16 mL/mmHg). Meanwhile, SVR demonstrates an upward trend until reaching and maintaining high values from the sixth decade of life (1426±167 dyn.s/cm5) onward with a clear shift in arterial hemodynamics (Analysis of variance [ANOVA]; P value <0.001) (Figure). Conclusions: The current method based on 24-hour ABPM effectively portrays the cardiac and arterial hemodynamics that mirror age-related circulatory alterations. This method offers a valuable pathophysiological basis for understanding the aging blood pressure profile.

Controlling sonic rectangular jet with nozzle trailing edge modification

Sonic rectangular jet emanating from a convergent nozzle of aspect ratio 2 with modified trailing edge in the form of triangular extension on its widest side is investigated experimentally at different nozzle pressure ratios corresponding to underexpanded states of sonic jet. To assess the impact of trailing edge modification on jet mixing, the sonic rectangular jet from aspect ratio two plain convergent nozzle (without trailing edge modification) is also studied. The centerline pressure decay results at nozzle pressure ratios 2, 3, 4 and 5 confirm the superiority of modified jet (jet from trailing edge modified nozzle) over plain jet from the mixing point of view. At all the pressure ratios, the modified jet possessed shorter core and weaker shock and expansion waves compared to plain jet, which is an outcome of faster mixing of modified jet with ambient fluid. The enhanced mixing caused the modified jet to decay faster than the plain jet. An appreciable core length reduction of about 32% is noticed at pressure ratio of 5. The modified jet experienced increased spread along major axis than along minor axis owing to the restriction offered by the triangular extension on jet spread along minor axis. Thus, the axis switching was absent in modified jet compared to plain jet switching axes at all pressure ratios. The shadowgraph images confirmed the presence of weaker waves in the modified jet. Also, the images confirmed the absence of Mach disk in the modified jet at pressure ratio of 5 compared to plain jet.

A Novel Combined Approach to Better Predict Sealing Performance of Luer Lock Connectivity.

Luer systems, for example Luer-needle hub with syringe's Luer cone tip and its Luer lock Adapter, are common interface on medical devices. One of the key questions in this application is about the safety guaranty and dose accuracy. It is then crucial to study the sealing between these elements. In this study we combine the use of Finite Element Analysis (FEA) and Multiscale Contact Mechanics (MCM) to analyze the connectivity and sealing performance of a glass syringe and a plastic needle Luer hub.This methodology has been applied before to the contact between glass and rubber and this is the first time that it is used for the contact between glass and plastic materials. The use of FEA allows to calculate the contact pressures and the nominal area of contact. The surface topographies of the two surfaces were measured, over a wide wavelength range (mm to nm). Subsequently, the air and liquid interfacial flow (leakage) is calculated using Persson's MCM theory which considers the roughness and elasto-plasticity of the interfacial surfaces. The theoretical predictions are compared to experimental leak measurements by pressure decay method. Further analysis is conducted, evidencing the key features that are responsible for a good sealing.

Fast permeability measurement for tight reservoir cores using only initial data of the one chamber pressure pulse decay test

In this study, a mathematical model for fast determination of the permeabilities of tight rocks using measurements taken from the initial period of the One Chamber Pressure Pulse Decay (OC-PPD) test is presented. The model applies to measurements taken both before and after the pressure pulse front has reached the downstream end of the specimen. The analytical solutions for the pressure decay in the upstream chamber are derived based on a parabolic arc approximation of pore pressure distribution along the test specimen. This approximation allows converting the initial–boundary value problem of fluid diffusion in the specimen, governed by partial differential equations, to a system of ordinary differential equations that can be easily solved by explicit formulae. Thus, an explicit formula for the pressure decay rate is obtained, which enables inverse analysis of the initial experimental data to estimate the rock permeability. The proposed method expedites the pulse decay test as it does not require the system to reach equilibrium. The method is validated with three sets of experimental data of the OC-PPD test using helium as the diffusing fluid, for which the relative error of the permeability is found to be less than 6%. This method is particularly useful if the equilibrium time of the pulse decay test for rock specimens with permeabilities in the range of nano-Darcy takes hours or days.

Deep Learning Forecasts Caldera Collapse Events at Kı̄lauea Volcano

AbstractDuring the 3 month long eruption of Kı̄lauea volcano, Hawaii in 2018, the pre‐existing summit caldera collapsed in over 60 quasi‐periodic failure events. The last 40 of these events, which generated Mw > 5 very long period (VLP) earthquakes, had inter‐event times between 0.8 and 2.2 days. These failure events offer a unique data set for testing methods for predicting earthquake recurrence based on locally recorded GPS, tilt, and seismicity data. In this work, we train a deep learning graph neural network (GNN) to predict the time‐to‐failure of the caldera collapse events using only a fraction of the data recorded at the start of each cycle. We find that the GNN generalizes to unseen data and can predict the time‐to‐failure to within a few hours using only 0.5 days of data, substantially improving upon a null model based only on inter‐event statistics. Predictions improve with increasing input data length, and are most accurate when using high‐SNR tilt‐meter data. Applying the trained GNN to synthetic data with different magma‐chamber pressure decay times predicts failure at a nearly constant stress threshold, revealing that the GNN is sensing the underling physics of caldera collapse. These findings demonstrate the predictability of caldera collapse sequences under well monitored conditions, and highlight the potential of machine learning methods for forecasting real world catastrophic events with limited training data.

Determination of time lag by accurate monitoring of pressure decay in a new generation constant volume system

The time-lag method is the standard approach for evaluating membrane permeability, diffusivity and solubility in a single gas permeation experiment. The conventional time-lag method relies on accurately monitoring the pressure rise in a constant volume downstream from the membrane following a change in pressure upstream from the membrane. The same information could be extracted from the upstream pressure decay in the same time-lag experiment. However, accurately monitoring the pressure decay presents a challenge due to the resolution limitations of absolute pressure transducers. If the membrane was characterized based on pressure decay, a mass spectrometer could be used to simultaneously monitor the composition of the gas permeating from the membrane, opening the time-lag method to gas mixtures. Also, the simultaneous monitoring of pressure rise and decay could provide additional information about gas transport in the membrane, which is critical for more complex membrane materials.•The resolution challenge was overcome by splitting the upstream volume into the working and reference volumes and monitoring pressure decay using a differential pressure transducer between the two volumes.•The validity of the measured pressure decay was confirmed by the unique relation between the upstream and downstream time lags for a commercial PDMS membrane.

Cationic Imidazolium-Urethane-Based Poly(Ionic Liquids) Membranes for Enhanced CO2/CH4 Separation: Synthesis, Characterization, and Performance Evaluation.

The escalating emissions of CO2 into the atmosphere require the urgent development of technologies aimed at mitigating environmental impacts. Among these, aqueous amine solutions and polymeric membranes, such as cellulose acetate and polyimide are commercial technologies requiring improvement or substitution to enhance the economic and energetic efficiency of CO2 separation processes. Ionic liquids and poly(ionic liquids) (PILs) are candidates to replace conventional CO2 separation technologies. PILs are a class of materials capable of combining the favorable gas affinity exhibited by ionic liquids (ILs) with the processability inherent in polymeric materials. In this context, the synthesis of the IL GLYMIM[Cl] was performed, followed by ion exchange processes to achieve GLYMIM variants with diverse counter anions (NTf2-, PF6-, and BF4). Subsequently, PIL membranes were fabricated from these tailored ILs and subjected to characterization, employing techniques such as SEC, FTIR, DSC, TGA, DMA, FEG-SEM, and CO2 sorption analysis using the pressure decay method. Furthermore, permeability and ideal selectivity assessments of CO2/CH4 mixture were performed to derive the diffusion and solubility coefficients for both CO2 and CH4. PIL membranes exhibited adequate thermal and mechanical properties. The PIL-BF4 demonstrated CO2 sorption capacities of 33.5 mg CO2/g at 1 bar and 104.8 mg CO2/g at 10 bar. Furthermore, the PIL-BF4 membrane exhibited permeability and ideal (CO2/CH4) selectivity values of 41 barrer and 44, respectively, surpassing those of a commercial cellulose acetate membrane as reported in the existing literature. This study underscores the potential of PIL-based membranes as promising candidates for enhanced CO2 capture technologies.

Analytical and numerical studies of gas discharge out of gun barrel tube

Abstract This paper investigates the characteristics of the discharge of gases out of gun barrel tube. The paper gives an insight into the physical principles that govern gas discharge through the presentation of analytical and two different numerical approaches. The analytical model is based on the well-known Bravin’s model, whereas the numerical approaches involve single- and two-phase flow numerical simulations conducted by utilities of Computational Fluid Dynamics (CFD). The differences between analytical and numerical results are analysed, from which the numerical approach is found to be capable of capturing the interacting phenomena due to the discharge of hot and high-pressure gases. The visualisation of flow parameters manifests the complex dynamics evoked by flow patterns and the formation of Mach disc and shock waves. It is found that the analytical Bravin’s model underestimates the pressure decay inside the barrel due to gas discharge compared to both the single- and two-phase flow numerical approaches.

Insights into RC time curve fit analysis of pulmonary artery pressure decay

The notion of a constant relationship between resistance and capacitance (RC time) in the pulmonary circulation has been challenged by more recent research. The RC time can be obtained using either a simplified empirical approach or a semilogarithmic equation. Although direct curve-fit analysis is a feasible and ostensibly reference approach for RC analysis, it remains largely unexplored. We aimed to study the relationship between various RC methods in different states of pulmonary hemodynamics.Methods In total, 182 patients underwent clinically indicated right heart catheterization. The pressure curves were exported and processed using the MATLAB software. We calculated the RC time using the empirical method (RCEST), semilogarithmic approach (RCSL), and direct measurement of curve fit (RCFIT).Results Among 182 patients, 137 had pulmonary hypertension due to left heart disease (PH-LHD), 35 had pulmonary arterial hypertension (PAH), and 10 demonstrated normal hemodynamics (non-PH). RCEST consistently overestimated the RCFIT and RCSL measurements by a mean of 75%. With all three methods, the RC values were longer in the PAH (RCFIT = 0.36 ± 0.14 s) than in the PH-LHD (0.27 ± 0.1 s) and non-PH (0.27 ± 0.09 s) groups (p < 0.001). Although the RCSL and RCFIT values were similar among the three subgroups, they exhibited broad limits of agreement. Finally, the RCEST demonstrated a strong discriminatory ability (AUC = 0.86, p < 0.001, CI = 0.79–0.93) in identifying PAH.Conclusion RC time in PAH patients was substantially prolonged compared to that in PH-LHD and non-PH patients. The use of the empirical formula yielded systematic RC overestimation. In contrast, the semilogarithmic analysis provided reliable RC estimates, particularly for group comparisons.

Impact of the blockage ratio and void fraction of porous obstacle on gas explosion characteristics in semi-confined channel

This study conducted various explosion experiments under different porous obstacle conditions of blockage ratio (BR) and void fraction (Φf). The impact of porous obstacle on flame propagation velocity (v) and peak overpressure (Pop) were analyzed. The results indicate that an increase in the BR enhances explosion pressure near the blockage area for both porous and non-porous obstacles. However, it also increases the downstream pressure decline gradient. An increase in the Φf weakens the hindrance of porous obstacle on the flame propagation, allowing more flame to pass through the internal void channels of obstacles, thus delaying the downstream pressure decay. Compared to non-porous obstacles, gas explosions disturbed by porous obstacles with both high BR (BR＞75%) and high Φf (Φf＞0.55) exhibit a lower downstream pressure decline gradient and a longer positive pressure duration. As a result, the explosion can produce a broader range of destruction.

Long-Term Statistical Process Monitoring of an Ultrafiltration Water Treatment Process.

As water treatment technology has improved, the amount of available process data has substantially increased, making real-time, data-driven fault detection a reality. One shortcoming of the fault detection literature is that methods are usually evaluated by comparing their performance on hand-picked, short-term case studies, which yields no insight into long-term performance. In this work, we first evaluate multiple statistical and machine learning approaches for detrending process data. Then, we evaluate the performance of a PCA-based fault detection approach, applied to the detrended data, to monitor influent water quality, filtrate quality, and membrane fouling of an ultrafiltration membrane system for indirect potable reuse. Based on two short case studies, the adaptive lasso detrending method is selected, and the performance of the multivariate approach is evaluated over more than a year. The method is tested for different sets of three critical tuning parameters, and we find that for long-term, autonomous monitoring to be successful, these parameters should be carefully evaluated. However, in comparison with industry standards of simpler, univariate monitoring or daily pressure decay tests, multivariate monitoring produces substantial benefits in long-term testing.

In situ effective pumping speed measurements as a tool for non-evaporable getter activation and saturation monitoring

We have developed method of in situ effective pumping speed measurements based on injecting finite gas pulse into a vacuum volume and subsequent recording of pressure response using a Residual Gas Analyzer (RGA). The pressure burst caused by injected gas pulse falls exponentially in time and the exponential coefficient of such pressure decay is proportional to total effective pumping speed of all vacuum pumps acting on vacuum chamber volume. The effective pumping speed can be extracted from the dependence of injected gas species pressure vs time recorded by an RGA. Non-Evaporable Getters (NEGs) are widely used in multiple ultra and extremely high vacuum devices and applications during the last several decades. Areas of NEG applications were recently expanded into vacuum devices with relatively high-pressure levels (up to 10−7 Torr) by the invention of high capacity ZAO NEG which can be operated at elevated temperatures. The intrinsic property of all NEG-based vacuum pumps is the reduction of their pumping speed, called “NEG saturation”, after an extended period of operation. Typical time interval for such process can span from about a month and up to a few years depending on NEG type, vacuum level of NEG pump operation, and residual gas content. After that, the NEG pump will require a re-activation cycle to restore its pumping speed close to the initial value. For many applications it is difficult to realize what is the current pumping speed of NEG pump is and when the pump should be re-activated. A method for in situ effective pumping speed measurements developed in this study can be used as a tool for NEG-based pump activation and saturation monitoring. Application of such an approach to monitor pumping status of NEG pumps was utilized and will be continually used at Extended EBIS which was recently developed and commissioned for Relativistic Heavy Ion Collider (RHIC) and future Electron Ion Collider (EIC). The results obtained during commissioning are presented and discussed.

Air tab location effect on supersonic jet mixing

Abstract Mixing of Mach 2.1 circular, jet issuing from a straight convergent-divergent circular nozzle, in the presence of sonic air tabs at exit and shifted locations along the jet axis was investigated experimentally at nozzle pressure ratios (NPR) 3–6, insteps of 1. Two constant area tubes of 1 mm diameter positioned diametrically opposite, at 0 D, 0.25 D, 0.5 D and 0.75 D (where D is the nozzle exit diameter), were used for fluidic injection. The injection pressure ratio (IPR) of air tabs was maintained at 6. The Mach 2.1 jet operated at nozzle pressure ratio (NPR) in the range of overexpanded states corresponding to NPR 3–6 was controlled with the sonic air tabs operating at the underexpanded state corresponding to IPR 6. The impact of air tabs on jet mixing was studied from the measured Pitot pressure along the jet centerline. The centerline pressure decay of the jet confirms that the air tab promotes jet mixing with the entrained air mass, and the mixing promotion caused by the air tab is dependent on tab location as well as the NPR. In the presence of air tabs, the jet possesses shorter core and experiences faster decay than the uncontrolled jet. Also, the air tabs were effective in reducing the number of shock cells and rendering the waves weaker in the jet core. Among the tab locations, the mixing promoting effectiveness of air tabs at 0 D is better than the tabs at shifted locations. The jet core length reduction caused by the air tab at 0 D increases from 25.4 % to 77.2 %, with increasing NPR from 3 to 6. The same trend was noticed for tab location 0.75 D, but not for 0.25 D and 0.5 D locations. The core length reduction for 0.75 D tab location is about 61.4 %, at NPR 6, and 62.1 % and 55.8 %, for NPR 5 and 4 for tab locations 0.25 D and 0.5 D, respectively. Shadowgraph images of the waves present in the jet core confirms the findings of centerline pressure decay results.

Experimental study on the negative pressure loss generated by the gas influx process around a long borehole

In the process of gas extraction in long boreholes, gas influx in the radial direction causes a non-uniform variable mass flow field due to bore wall friction. This flow field can lead to a negative pressure decay along the hole length, thus affecting the gas extraction effect. With this effect in mind, a gas variation mass test was designed for pore-containing specimens with different pore wall roughnesses. It is also based on the variable mass flow pressure drop theory and analyzes the pressure variation, hole wall roughness, and gas influx rate inside the borehole. The result indicates that radial influx of gas along the borehole wall can interfere with the main flow in the borehole. The increase of the radial influx flow rate of the gas produces an obvious swirling phenomenon, which gradually makes the fluid mixing flow situation more and more complicated the more it differs from the mainstream velocity. The mainstream velocity and the pore wall influx velocity are the main factors causing mixing loss. The study results are important for understanding the long borehole gas sink process and the design of reasonable borehole parameters.

Numerical and experimental studies on the thermodynamic characteristics of post-buckling separate plate in the clutch

Considering the influence of the contact and friction for buckling deformation, a comprehensive model is proposed to study the timing-varying thermodynamic characteristics of the clutch. The mathematical model is developed to calculate the contact status of the post-buckling separate plate, which is testified by the finite element method and bench experiments. The post-buckling plate undergoes a five-stage deformation, and the radial contact pressure finally forms ‘M/W′ shape during engagements. With the increasing buckling angle, the plate flattening threshold and pressure decay increase gradually; meanwhile, the radial temperature distribution is sculptured as ‘W′ shape, creating larger thermal stress and thermal bending moment. Thus, the surface morphology is changed by the wear which related to the pressure and thermal distribution.