Absolute Pressure Values Research Articles

High-velocity compressible gas flow modelling through porous media considering the quadratic pressure gradient: Part 2. experimental investigations and numerical analysis

This research investigates reliability of existing methods for analysis of transient Pressure Pulse Decay (PPD) test results. Analysis of experimental data reported by previous studies using existing conventional analysis methods revealed significant discrepancies, in some cases with more than 300% error between different experiments on the same sample. New experiments (Knudsen number ranged from 0.22 to 0.34) were designed and conducted in our laboratory, reducing the uncertainty by eliminating slip flow and net stress effects under low and high-pressure conditions. These experimental results aligned much better with the recently proposed analytical solution for improved interpretation of PPD experimental results. The differences are around 25% between different pulses, confirming the reliability of the conducted experiments and newly proposed methodology.Numerical simulations using a commercial software package were conducted to complement experimental and analytical findings. The simulator, which demonstrated good agreement with the proposed analytical solution, facilitated conducting sensitivity analyses on permeability variations and compressive storage capacity effects. These simulations validated the findings of the proposed analytical solution, which accounts for both pressure difference and absolute pressure values, and explains the discrepancies observed in lower pressure scenarios using conventional methods.Overall, this study presents a comprehensive framework integrating experimental, analytical, and numerical approaches to enhance our understanding and better analysis of transient PPD test results for compressible gas flows. The findings also offer a more robust approach for analysing gas flow behaviour in porous media.

A new anal manometry technique for assessing the functional state of the rectal sphincter apparatus

Objective. To develop a new modern precession strain gauge sphincterometer for assessing the functional state of the sphincteric apparatus of the rectum in the normal state with an increase in the accuracy of the results of recording the absolute pressure values generated in it. Materials and methods. The results of anal manometry (sphincterometry) of 90 patients (45 men and 45 women) aged 18 to 72 years without anorectal pathology and manifestations of anal incontinence were analysed to establish normal indicators of the state of the sphincteric apparatus of the rectum using a newly developed modern precession strain gauge sphincterometer. Results. The conducted sphincterometric study allowed to establish the following indicators of the functional state of the sphincteric apparatus of the rectum in the norm for men: sphincter tone (26.7 ± 2.2) mm Hg, maximum contraction (35.6 ± 5.1) mm Hg, gradient of voluntary contraction (9 ± 4.9) mm Hg, cough test (36.5 ± 4.9) mm Hg, test with straining (38.2 ± 3.5) mm Hg; for women: sphincter tone (23.3 ± 2.5) mm Hg, maximum contraction (31.3 ± 4.3) mm Hg, voluntary contraction gradient (8.0 ± 3.6) mmHg, cough test (31.6 ± 3.0) mmHg, and expiratory test (32.4 ± 3.0) mmHg. Conclusions. The proposed method of anal manometry allows for a detailed study and objective assessment of the functional state of the sphincteric apparatus of the rectum in men and women in the normal state according to such indicators as sphincter tone and maximum contraction, gradient of voluntary contraction, as well as cough and straining tests.

Effect of runner radial installation deviation on the flow characteristics of the 1000MW turbine

Abstract The flow simulation of a hydraulic turbine is not limited to calculations and analyses under ideal conditions and simplified models, but it should also consider the existence of radial installation deviations in actual operating conditions and their influence on the flow of the turbine. Therefore, this study focuses on a 1000MW unit and analyzes the internal flow characteristics under actual operating conditions while considering the radial installation deviations of the turbine wheel. The results show that the absolute value of pressure increases with the increase of radial deviation, but the difference value remains almost constant. And it also indicates that the magnitude of the radial forces increases with the increase in radial installation deviations. There are two linear relationship curves, one before 0.5mm and one after 0.5mm, with the latter growing at a faster rate. Furthermore, taking the crown as an example, the influence of the wall velocity-generated dynamic pressure on the clearance is different. Lastly, considering the magnitude of the combined forces and vibration amplitude, the crown is the most critical part that should be given attention. The research findings can guide the high-quality installation of 1000MW units during major overhauls and provide valuable technical references for similar units. The research outcomes can also guide the initial installation and major overhaul stages of 1000MW units and offer beneficial technical references for other similar units.

A novel method for evaluating stack pressure in real high-rise buildings: Optimization of measurement points

Excessive stack pressure in a high-rise building always causes various problems, and the most direct way to understand the extent of the stack pressure across building components is to derive pressure distribution profiles for the entire buildings. As an alternative to measurement process, which is generally time-consuming and labor-intensive, an optimal field measurement method is proposed to investigate the real-time pressure distribution in operating high-rise buildings. The absolute pressure at unmeasured points can be accurately predicted from measured values at selected key points, both horizontally and vertically. Robust linear regression and the MARS model are applied to develop the related prediction models, and the number and positions of measurement points in the horizontal and vertical directions are optimized sequentially. Two high-rise buildings were selected to validate the applicability of the method, and five and six key pressure measurement points were finally determined, respectively. The measured and predicted absolute pressure values at unmeasured points were further compared, and the results showed a high goodness of fits as the R2 values were higher than 0.98 and the average MAE values were less than 2.0 Pa for all models. It is observed that the proposed method is suitable for engineering applications and demonstrates a practical method for investigating stack pressure distribution within high-rise buildings.

The degree of engagement of cardiac and sympathetic arms of the baroreflex does not depend on the absolute value and sign of arterial pressure variations

Objective. The percentages of cardiac and sympathetic baroreflex patterns detected via baroreflex sequence (SEQ) technique from spontaneous variability of heart period (HP) and systolic arterial pressure (SAP) and of muscle nerve sympathetic activity (MSNA) burst rate and diastolic arterial pressure (DAP) are utilized to assess the level of the baroreflex engagement. The cardiac baroreflex patterns can be distinguished in those featuring both HP and SAP increases (cSEQ++) and decreases (cSEQ−−), while the sympathetic baroreflex patterns in those featuring a MSNA burst rate decrease and a DAP increase (sSEQ+−) and vice versa (sSEQ−+). The present study aims to assess the modifications of the involvement of the cardiac and sympathetic arms of the baroreflex with age and postural stimulus intensity. Approach. We monitored the percentages of cSEQ++ (%cSEQ++) and cSEQ−− (%cSEQ−−) in 100 healthy subjects (age: 21–70 years, 54 males, 46 females), divided into five sex-balanced groups consisting of 20 subjects in each decade at rest in supine position and during active standing (STAND). We evaluated %cSEQ++, %cSEQ−−, and the percentages of sSEQ+− (%sSEQ+−) and sSEQ−+ (%sSEQ−+) in 12 young healthy subjects (age 23 ± 2 years, 3 females, 9 males) undergoing incremental head-up tilt. Main results. We found that: (i) %cSEQ++ and %cSEQ−− decreased with age and increased with STAND and postural stimulus intensity; (ii) %sSEQ+− and %sSEQ−+ augmented with postural challenge magnitude; (iii) the level of cardiac and sympathetic baroreflex engagement did not depend on either the absolute value of arterial pressure or the direction of its changes. Significance. This study stresses the limited ability of the cardiac and sympathetic arms of the baroreflex in controlling absolute arterial pressure values and the equivalent ability of both positive and negative arterial pressure changes in soliciting them.

Negative Linear Compressibility of Formate Crystals from the Viewpoint of Quantum Electronic Pressure

In order to understand the phenomenon of negative linear compressibility (NLC) in organic crystals, it is necessary to investigate not only the structural features but also the electronic changes taking place under external hydrostatic pressure. It is also necessary to clarify which electronic properties allow the quantification and comparison of the compressibility of crystals. In our study, the crystal structures of sodium and cadmium formates under hydrostatic compression were modeled, as well as the α and β-phases of calcium formate. The changes in cell parameters and spatial dependences of the linear compressibility were analyzed, and the ranges of external pressure, which must be applied for NLC onset, were predicted for the sodium and α-calcium formates. Although the behavior of chemical bonds is not predicted by the sign or absolute value of the quantum electronic pressure, its relative change under external pressure clearly distinguishes the soft and rigid regions in a crystal. The relationship between the NLC values and the changes in quantum electronic pressure in the cavities of formate crystals was established.

The effect of OSA on the negative pressure and acoustic compliance of middle ear cavity in children.

To explore the effect of obstructive sleep apnea (OSA) on the negative pressure and acoustic compliance of middle ear cavity in children. The clinical data of 258 children with suspected OSA, who complained of mouth breathing or snoring at night in the Department of Otolaryngology Head and neck surgery of the Second Affiliated Hospital of Xi'an Jiao Tong University from August 2020 to March 2022, were enrolled and analyzed retrospectively. The OSA and otitis media with effusion (OME) were determined by polysomnography (PSG) and acoustic immittance examination, respectively. Then, the parameters of tympanometry were compared between OSA and non-OSA children or among the children with various severity of OSA. There was no significant difference in the incidence of OME between children with OSA and those with non-OSA (15.80% vs 11.80%, P=0.422). Compared with non-OSA children, OSA children had lower negative pressure (-56.42 vs -12.38, P<0.001) and higher acoustic compliance (0.45 vs 0.38, P=0.030) in middle ear cavity. There were also significant differences in negative pressure and acoustic compliance among children with mild, moderate and severe OSA (P<0.001; P=0.001). However, only the absolute value of negative pressure was markedly decreased after surgical therapy accompanied with transformation from OSA to non-OSA (-156.67 vs -45.67, P<0.05), while this was not observed for acoustic compliance (0.48 vs 0.40, P>0.05). OSA may have an adverse influence on the negative pressure and acoustic compliance of middle ear cavity in children.

Sub-megahertz cavitation detection and characterization in mouse brains

A key consideration in ultrasound medical device safety is the potential for cavitation related bioeffects. Device testing should address possible cavitation pathways, such as bubble formation, either in the focal region or at the device-tissue interface along with possible consequences regarding both safety and effectiveness. This has been particularly important in a number of emerging transcranial therapies including ablation, neuromodulation, and targeted opening of the blood-brain barrier (BBB) in conjunction with microbubbles. Subharmonic, and ultraharmonic emissions have been identified as indicators of treatment outcome and are a basis for safety and feedback control in BBB disruption. However, there remains a scarcity of baseline cavitation threshold data in the living mammalian brain, particularly at lower ultrasound frequencies. In our ongoing study, we are measuring and evaluating in vivo cavitation response in mice using a passive cavitation detector (PCD) for ultrasound frequencies as low as 40 kHz. Additional measurements are being carried out using a hydrophone imbedded in the brain tissue of mouse cadavers to characterize absolute pressure values as well as evaluate the sensitivity and reliability of the PCD measurements. Analyzed data will be presented along with detailed methodology and potential implications in future product evaluation will be discussed.

A systematic review of methodologies used in calculation of pen pressure in FDE

Pen pressure is an important individual characteristic of the handwriting examination whose potential has not been fully utilized. Most of the times it is overlooked by experts because they do not think it has substantial value to be of forensic significance. Generally, it is thought to be of relevance in cases involving simple and traced forgery. One of the reasons behind pen pressure being ignored by the document examiners may be a lack of technique to calculate the absolute value of pen pressure. The existing methods require specialized setup, training, and are expensive in nature and can only be used to measure relative value of pen pressure. The aim of this paper is to discuss various methodologies used by document experts and researchers in past with an attempt to quantify pen pressure and critically analyze them to bring the reader’s and researcher’s focus on their advantages and disadvantages. The paper also discusses prospects of future works which may include techniques that can be used more routinely in handwriting examination and can also give an absolute measure of pen pressure. In this aspect, mathematical approaches can be further explored.

Comparison of oscillometric, non-invasive and invasive arterial pressure monitoring in patients undergoing laparoscopic bariatric surgery \u2013 a secondary analysis of a prospective observational study

BackgroundOscillometric, non-invasive blood pressure measurement (NIBP) is the first choice of blood pressure monitoring in the majority of low and moderate risk surgeries. In patients with morbid obesity, however, it is subject to several limitations. The aim was to compare arterial pressure monitoring by NIBP and a non-invasive finger-cuff technology (Nexfin®) with the gold-standard invasive arterial pressure (IAP).MethodsIn this secondary analysis of a prospective observational, single centre cohort study, systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP) were measured at 16 defined perioperative time points including posture changes, fluid bolus administration and pneumoperitoneum (PP) in patients undergoing laparoscopic bariatric surgery. Absolute arterial pressures by NIBP, Nexfin® and IAP were compared using correlation and Bland Altman analyses. Interchangeability was defined by a mean difference ≤ 5 mmHg (SD ≤8 mmHg). Percentage error (PE) was calculated as an additional statistical estimate. For hemodynamic trending, concordance rates were analysed according to the Critchley criterion.ResultsSixty patients (mean body mass index of 49.2 kg/m2) were enrolled and data from 56 finally analysed. Pooled blood pressure values of all time points showed a significant positive correlation for both NIPB and Nexfin® versus IAP. Pooled PE for NIBP versus IAP was 37% (SAP), 35% (DAP) and 30% (MAP), for Nexfin versus IAP 23% (SAP), 26% (DAP) and 22% (MAP). Correlation of MAP was best and PE lowest before induction of anesthesia for NIBP versus IAP (r = 0.72; PE 24%) and after intraoperative fluid bolus administration for Nexfin® versus IAP (r = 0.88; PE: 17.2%). Concordance of MAP trending was 90% (SAP 85%, DAP 89%) for NIBP and 91% (SAP 90%, DAP 86%) for Nexfin®. MAP trending was best during intraoperative ATP positioning for NIBP (97%) and at induction of anesthesia for Nexfin® (97%).ConclusionAs compared with IAP, interchangeability of absolute pressure values could neither be shown for NIBP nor Nexfin®, however, NIBP showed poorer overall correlation and precision. Overall trending ability was generally high with Nexfin® surpassing NIBP. Nexfin® may likely render individualized decision-making in the management of different hemodynamic stresses during laparoscopic bariatric surgery, particularly where NIBP cannot be reliably established.Trial registrationThe non-interventional, observational study was registered retrospectively at (NCT03184285) on June 12, 2017.

Real-time burst detection based on multiple features of pressure data

Abstract Pipe bursts are an essential issue for water loss in water distribution systems. This study proposes a real-time burst detection method that combines multiple data features of multiple time steps. The method sets burst thresholds in three dimensions according to different moments at a specific monitoring point, and achieves burst identification based on a classification model. First, three data features, namely, absolute pressure value, predicted deviation value obtained by pressure variation value, of historical pressure at each time step are scored based on the Western Electric Company rules. The scores represent different abnormalities. Then, the scores corresponding to the three features are used as input of the decision tree classification model. The trained model is used for detecting burst events. Results show that this method achieves 99.56% detection accuracy, indicating that it is effective for burst detection. The proposed method outperformed the single-feature-based method and provides good results in water distribution systems.

Comparison of Anorectal Function as Measured with High-Resolution and High-Definition Anorectal Manometry

Introduction: Anorectal manometry (ARM) provides comprehensive assessment of pressure activity in the rectum and anal canal. Absolute pressure values might depend on the catheter used. Objective: Our aim was to compare the results obtained by different anorectal catheters in children with functional anorectal disorders. Methods: Children diagnosed with functional defecation disorders based on the Rome IV criteria were prospectively enrolled. ARM was performed in the supine position successively using 2 different probes in each patient in random order. Resting, squeeze pressures, and bear-down maneuver variables obtained by high-resolution (2-dimensional [2D]) and high-definition (3-dimensional [3D]) catheters were compared. Results: We prospectively included 100 children {mean age 7.5 [standard deviation (SD) ± 4.3] years; 62 boys}. Mean resting pressures were significantly higher when measured with the 3D than with the 2D catheter (71 [SD ± 19.4] vs. 65 [SD ± 20.1] mm Hg, respectively; p = 0.000). Intrarectal pressure measured by 3D and 2D catheters was similar (35 vs. 39 mm Hg, respectively; p = 0.761), but the percent of anal relaxation appeared to be higher for the 3D than for the 2D probe (12 vs. 5%, respectively; p = 0.002). Dyssynergic defecation (DD) was diagnosed in 41/71 patients (57.7%) using the 3D probe and in 51/71 children (71.8%) using the 2D probe (p = 0.044). Cohen’s kappa showed only fair agreement between the catheters (κ = 0.40) in diagnosis of DD. Conclusions: Our study demonstrated significantly different values of pressures obtained with different types of catheters. Normal ranges for conventional manometry cannot be applied to high-resolution systems, and results obtained by different types of manometry cannot be compared without adjustments (NCT02812823).

Negative Pressure Provides Simple and Stable Droplet Generation in a Flow-Focusing Microfluidic Device.

Droplet microfluidics is an extremely useful and powerful tool for industrial, environmental, and biotechnological applications, due to advantages such as the small volume of reagents required, ultrahigh-throughput, precise control, and independent manipulations of each droplet. For the generation of monodisperse water-in-oil droplets, usually T-junction and flow-focusing microfluidic devices connected to syringe pumps or pressure controllers are used. Here, we investigated droplet-generation regimes in a flow-focusing microfluidic device induced by the negative pressure in the outlet reservoir, generated by a low-cost mini diaphragm vacuum pump. During the study, we compared two ways of adjusting the negative pressure using a compact electro-pneumatic regulator and a manual airflow control valve. The results showed that both types of regulators are suitable for the stable generation of monodisperse droplets for at least 4 h, with variations in diameter less than 1 µm. Droplet diameters at high levels of negative pressure were mainly determined by the hydrodynamic resistances of the inlet microchannels, although the absolute pressure value defined the generation frequency; however, the electro-pneumatic regulator is preferable and convenient for the accurate control of the pressure by an external electric signal, providing more stable pressure, and a wide range of droplet diameters and generation frequencies. The method of droplet generation suggested here is a simple, stable, reliable, and portable way of high-throughput production of relatively large volumes of monodisperse emulsions for biomedical applications.

Taking into account the spatial variability of the physical and mechanical properties of a hydraulic dump when flushing it

Introduction. Slope stability analysis reliability depends on the level of schematizing the results of engineering-geological survey, hydrogeological monitoring, electrical sounding, and mine surveying data generalization. In order to improve the stability analysis accuracy, it is relevant to use the geomechanical models, which take into account the spatial variability of the adjacent rock mass physical and mechanical properties, with further search for the most hazardous section in the plan. Research aim is to substantiate the relevance of slopes physical and mechanical monitoring by the methods of downhole control and further stability analysis with the use of the geological and geophysical models. Methodology includes the search for the most hazardous section of the rock mass by the ratio of the shearing and restraining forces within the limits of the established zones characterized by the variability of physical and mechanical properties. Results. As a result of generalizing the databases of the engineering and geological study, hydrogeological monitoring, electrical sounding and mine surveying, the volumetric geological and geophysical models were built of the technogenic massif formed at the dump, as well as the slopes of the hydraulic overburden face, represented by the three-level fill of dry overburden. Test areas stability has been analyzed for the actual position, and the comparative analysis of the results was made. Conclusions. When building volumetric geological and geophysical models of man-made rock masses formed at the areas of filled hydraulic waste diposals, in addition to the results of the traditional survey measurements and direct engineering and geological study, it is important to create informative databases on spatial and temporal variations of physical and mechanical properties of alluvial rock conditioned by their fluid loss and consolidation, which with in details at cross hole intervals may be obtained based on the statistical dependences on electrical conductive properties variation by the methods of electrical sounding or tomography; and when making enclosing embankments (bridges) of dry rocks – information about excess pore pressure under these facilities. When using the hydromechanized method for the alluvial rocks, relatively homogeneous in strength properties, the hydraulic overburden face slope stability is determined to the greatest extent by the absolute values of the accumulated strength indicators in the mined area and the unfavorable combination of the edge shape (the presence of protruding sections and face unevenness in the plan) with the entry height. The established range of the stability coefficient was n = 1.03–3.76. The stability of the enclosing structures made of dry rock to the greatest extent depends on weak alluvial layer depth and thickness and the absolute value of excess pore pressure in this layer. The established range of stability coefficient variation for this rock mass section is much narrower and amounted to n = 1.29–1.59.

A Numerical Case Study on Boundary Effect in Test and Simulation of Seismic Hydrodynamic Pressure on Pier

Total 12 finite element models are built for piers of rectangular and elliptical sections in water with infinite boundary condition or with elastic boundaries and longitudinal size 3 m, 5 m, 7.5 m, 10 m and 15 m respectively. Responses of the models are calculated by numerical water - pier interaction coupling procedure. The result hydrodynamic pressures of nodes on the central line of the pier upstream faces at 8 depths show that the pressures on models with elastic boundaries are getting close to that with infinite boundary as the longitudinal size increasing, and the 15 m length is long enough for tank in shaking table test to prevent the disturbance of boundary wave on the maximum absolute value of hydrodynamic pressure.

Bladder urine oxygen partial pressure monitoring: Could it be a tool for early detection of acute kidney injury?

ABSTRACT Acute kidney injury (AKI) necessitating renal-replacement therapy has been associated with high mortality rates in critically ill patients. Usual methods to study AKI encompass the assessment of serum and urine biomarkers. Hypoxia is a major pathophysiological feature of AKI, which necessitates continuous bedside monitoring of renal tissue oxygenation in intensive care unit (ICU) patients. Research has made continuous bladder urine oxygen pressure (PuO2) monitoring possible in humans. Although the value of bladder PuO2 does not represent an absolute value of medullary tissue oxygen pressure (Po2), bladder PuO2 can be considered a window into the renal medullary oxygenation. Bladder PuO2 can be monitored by using probes with oxygen sensors inserted into the urinary bladder. Additionally, PuO2 can be measured manually by using a blood gas analyzer machine. PuO2 monitoring can be potentially helpful in early diagnosis and/or prevention of AKI and guide therapeutic interventions aimed at improving renal oxygen delivery in those patients.

Investigation on subsurface vortices within a closed pump intake under different pressure conditions

An experimental study to investigate various features of subsurface vortices and their evolutions inside a closed pump intake under different pressure conditions at free surface, and to analyze the influence of a pipe bell with different mean axial velocities at the same water level on flow patterns is presented. For all cases, three different flow regimes are closely observed: various side-wall attached, back-wall attached and submerged vortices structures, and their evolutions are subject to the free-surface pressure for a critical flow rate, the number and strength of all these vortex rise as the absolute value of the pressure increases for a higher flow rate, for a lower flow rate, whether the side-wall vortices occur or not is related closely to the pressure magnitude, and there are no vortices for lower absolute pressure values, the number and the strength of the side-wall vortices increase as the absolute pressure values increase. Besides, based on statistical analyses, the side-wall vortex probability on the right side along the stream-wise direction is much higher than that on the opposite side for all operation cases, particularly single vortex probability, and the back-wall vortex probabilities are quite higher with values of more than 90%, meanwhile, the multi-vortices probability is much higher than that of the single-vortex. The captured vortices have been qualitatively classified into different “vortex zones”: no vortex zones and vortex zones including transition, single- and multi-vortex. The Reynolds number and the absolute value pressure are the most important parameters which influence the existence and the number of these vortices, and the increase of the two parameters reduces the no vortex transition zone and causes bigger difference in the back-wall and side-wall vortex zones.

Investigation on free-surface vortices within a closed pump intake under different pressure conditions using stereo PIV

ABSTRACT This paper examines free-surface vortices and the vorticity distribution with time-dependent evolution within a closed pump intake under five pressure conditions. The location and the strength of these vortices, occurrence probability and perspective statistics, as well as vortex probability distribution are all systematically analyzed. Three cases were observed and analyzed: (a) Subcritical (Q= 19.78 m3/h), whether vortices occur or not is related closely to the pressure magnitude. (b) Critical (Q= 22.61 m3/h), evolution of vortices was significantly impacted by the pressure applied. The number of vortices increases as the absolute pressure values increase, which was fluctuating and random. (c) Supercritical (Q= 25.43 m3/h), the spatial scale of the whole measurement section is occupied by the vortex when the highest absolute values of pressure conditions are reached. Based on statistical analyses, the probability of vortex occurrence within the measurement section was obtained. The captured vortices have been qualitatively classified into different ‘vortex zones’. The Re, We and the absolute value pressures are the most important parameters influencing the existence and the number of free-surface vortices. The experiment results may provide a reference for the actual operation of closed pump intake and the design guidelines for the installations with closed pump intakes.

Agricultural machinery used in the process of denaturation of minced fish proteine

The development of the marine industry and processing of raw materials is very important. Many floating marine transport platforms are engaged in processing and preparing raw materials. The paper presents an experimental study of the absorption method of the dependence of the degree of protein denaturation on the absolute value of external hydrostatic pressure, which was used to process minced fish for 5 minutes at a temperature of 295 K. A mathematical model of the process of denaturation of protein molecules in minced fish under the influence of high hydrostatic pressure has been developed. Based on experimental data, the equilibrium constant K = 0.0019439869 of denaturation of protein molecules after 5-minutes action of external hydrostatic pressure at room temperature was determined. Extrapolation of experimental data using a model curve determined the pressure P = 520 MPa, at which the concentration of denatured protein molecules in minced fish for 5 minutes at a temperature of 295 K becomes equal to the concentration of denatured protein molecules in boiled minced fish. These studies are very important for the food and transport industry.

Influences of negative pressure on air-leakage of coalseam gas extraction: Laboratory and CFD-DEM simulations

Comprehensive understandings of the influences of negative pressure on air-leakage and its driving mechanism are critical for controlling methane concentration during coal seam gas extraction. Laboratory experiments were conducted using an integrated apparatus to study the air-leakage process of coal seam gas extraction under different negative pressures. In addition, a coupled computational fluid dynamics-discrete element approach was used to simulate the process of air flow and particle transport in a natural coal fracture to understand the influential mechanism of negative pressure on air-leakage at the mesoscale. Experimental results show that with an increase in the absolute value of negative pressure, the air-leakage experiences three stages of increase, decrease and increase at Stage I, Stage II and Stage III, respectively. It is reported for the first time and in good agreement with field test data. From experimental and numerical results, at Stage I the air-leakage increases with the absolute value of negative pressure because there is no blockage in fractures around borehole. At Stage II, the further increased absolute value of negative pressure contributes to particles motion in fractures. It gradually leads to the formation of blockage structure composed of aggregated particles in fractures, and the decrease of fracture conductivity and air velocity. With the absolute value of negative pressure rising continuously, the contact forces between the aggregated particles increase. Therefore, the balance of the blockage structure tends to be broken, which helps to understand the air-leakage increase with the absolute value of negative pressure at Stage III. Between Stage II and Stage III, there is a valley point corresponding to the minimum air-leakage, which is important to the improvement of gas extraction performance. The contact forces on the aggregated soft particles are larger than those on the aggregated hard particles under the same negative pressure. Therefore, the blockage structure consisting of soft particles is much easier to be broken than that formed by hard particles. This explains why the absolute value of negative pressure corresponding to the valley point for hard coal model is larger than that for the soft coal model.