Increase In Pressure Gradient Research Articles

#1397 Predictive factors for bioprosthetic valve stenosis and prognostic factors for survival following TAVR in hemodialysis patients with severe AS

Abstract Background and Aims Transcatheter aortic valve replacement (TAVR) is a promising option for the treatment of severe aortic valve stenosis (AS) in patients undergoing hemodialysis. Although the incidence of bioprosthetic valve deterioration (SVD) after TAVR has been reported to be lower than after surgical aortic valve replacement (SAVR), hemodialysis itself is still associated with a high risk of SVD. Until now, the factors that determine the prognosis of TAVR in hemodialysis patients were unknown. We previously reported that preoperative hypomagnesemia was correlated with an increase in postoperative mean aortic valve pressure gradient (MPG), an index of bioprosthetic valve stenosis as one of the indicators of SVD, in hemodialysis patients (Ren Fail. 2022 Dec;44(1):1083-1089). However, the study had a limited sample size of 24 cases, which raised concerns about statistical power. Therefore, we re-evaluate predictors of SVD and life expectancy in a larger number of post-TAVR hemodialysis patients. Methods From April 2012 to November 2021, all 100 hemodialysis patients treated with TAVR at Osaka University Hospital were included in the analysis. Pre- and post-operative demographic and laboratory data were analyzed by linear mixed-effects model and cox proportional hazards model. Results During the follow-up period (maximum 7 years), 4 out of 100 patients required re-TAVR (valve-in-valve) due to valve stenosis. The MPG increased over time with the lower preoperative serum Mg concentration (linear mixed-effects mode; +1.40 mmHg/year per 1mg/dl lower in Mg, p=0.006). However, serum calcium, phosphate, and intact PTH levels had no significant effect on the increase in MPG. In addition, a higher preoperative left ventricular ejection fraction (LVEF) was associated with a lower risk of death in a multivariate Cox proportional hazards model (hazard ratio [HR] 0.97 per 1% increase in LVEF; P=0.02). Conclusions Consistent with our previous report, preoperative hypomagnesemia was associated with increased MPG after TAVR. In addition, preoperative low cardiac function (LVEF<40%) may be a risk factor for postoperative mortality in dialysis patients. This was a single-center observational study, and the number of patients was still small, so our data may not be necessarily applicable to every patient. Further research is needed to identify a prognostic predictor of SVD and mortality, that will lead to the prevention of adverse outcomes in hemodialysis patients.

Heat and concentration analysis of two-layered muco-ciliary third grade fluid flow in human airways

Understanding the mechanisms involved in the movement and clearance of mucus within the human airways is important from a physiological perspective. A mathematical model of muco-ciliary two-layered fluid flow in a finite two-dimensional channel is proposed. Due to the presence of both the airway ciliary layer (ACL) and the periciliary liquid layer (PCL) in airways epithelial cells, the two-layered model is adopted. The third grade fluid models is used to characterize the viscoelastic nature mucus secreted in the airways. The mathematical modelling of two-layer flow problem is simplified using long wavelength and small Reynolds number approximation. A formulated set of partial differential equations (PDEs) is solved for series-form solutions of velocity, temperature, concentration, and pressure gradient by using the Adomian decomposition method (ADM). The analysis delineated that with an increase in pressure gradient at airways entrance ξ the velocity and temperature increases while concentration decreases. Deborah numbers impact ACL and PCL velocities differently, with De(A) influencing flow direction and De(P) causing fluid to flow faster in the forward direction. It also emphasises the significance of the rate of thermal diffusion, viscous dissipation, and relaxation time. The results showed that the suggested two-layered muco-ciliary model provides a better description of mucus transport in the human airways. The pressure gradient at the airways entrance has a significant impact on mucus transport through the airways.

Evaluation and clinical significance of contrast-enhanced ultrasound on changes in liver blood flow perfusion after TIPS surgery.

To investigate the clinical value of contrast-enhanced ultrasound in the prediction of hepatic encephalopathy (HE) in patients with hepatitis B cirrhosis after intrahepatic portal-systemic shunt via jugular vein. In this retrospective study, we collected data from 75 patients with hepatitis B, cirrhosis, and portal hypertension who underwent jugular intrahepatic portosystemic shunt from February 2019 to February 2022. The diagnostic instrument used was the TOSHIBA Aplio500 color Doppler ultrasound with contrast-enhanced ultrasound capabilities. The trial group comprised 20 patients with HE within 3 months postsurgery, while the control group (CG) included 55 patients without HE within the same postoperative period. All patients underwent various examinations before and within 48 hours after surgery, including observation of liver and spleen size and stent position, as well as assessment of blood flow direction in portal and hepatic veins. Subsequently, contrast-enhanced ultrasound was employed to examine and observe perfusion changes of contrast agents in hepatic veins, hepatic arteries, and portal veins (PV). Changes in PV pressure gradient, intrahepatic, and stent blood flow perfusion (BFP) were explored in both postoperative trials and CGs. The trial group exhibited higher BFP volume, PV pressure gradient difference, and percentage decrease compared to the CG. A weak positive correlation was observed between blood flow within the liver stent and PV pressure gradient difference, as well as the percentage decrease in PV pressure gradient. The correlation coefficient between blood flowing perfusion volume within the stent and the difference in PV pressure gradient was R = 0.415 (P = .000). The correlating coefficient between BFP amount within the stent and the percentage decrease in PV pressure gradient was R = 0.261 (P = .027). The area under the receiver operating characteristic curve for stent perfusion volume, difference in PV pressure gradient, and percentage decrease in PV pressure gradient was 0.691, 0.759, and 0.742, respectively. An increase in PV pressure gradient accelerates blood flow within the stent, predisposing to HE. Changes in hepatic BFP following transjugular intrahepatic portosystemic shunt can effectively predict the occurrence of HE, demonstrating significant clinical relevance.

Fractal study on the nonlinear seepage mechanism during low-permeability coal water injection

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient.

Evaluation of Recovery of Tight Sandstone Gas Reservoirs Based on a Seepage Steady-State Model

As an important indicator for measuring the effectiveness and level of oil and gas field development, recovery rate has always been a focus in the research of oil and gas fields. Reservoirs of tight sandstone gas formations have significant characteristics of low porosity, high permeability, and high water content, which leads to greater difficulty in their development and makes it challenging to evaluate the recovery rate. Newtonian mechanics, as an important component of the mechanical system, is an innovative application of classical mechanics in the field of seepage mechanics when applied to the two-phase flow of gas and water. Firstly, starting from the perspective of mechanics analysis, we derive a steady-state model for gas–water two-phase infiltration and obtain the productivity equation based on this model. Then, according to the steady-state model, we establish a method to calculate the effective control radius of gas reservoirs under different production conditions and reservoir physical properties. Finally, using Matlab 2018a programming based on the productivity equation, we calculate the gas recovery under different conditions during constant pressure drop production and constant production rate production. The results indicate that the effective control radius of the reservoir decreases with an increase in the economic ultimate daily gas production, increases with an increase in production pressure difference, slightly decreases with an increase in startup pressure gradient, and correspondingly increases with an increase in microtube radius and quantity. Regardless of whether it is production with a fixed pressure drop or production with a fixed production rate, the gas recovery decreases as the production pressure drop and bottomhole abandonment pressure increase, but it increases as the proportion of the single-well control radius increases. In production with a fixed pressure drop, the gas recovery remains consistent across different reservoir quality indices. However, in production with a fixed production rate, the gas recovery initially increases rapidly and then gradually slows down as the reservoir quality index increases, and there is an obvious critical permeability (0.1 mD). The research findings are based on the mechanical analysis of porous media, delving into the laws governing fluid flow during infiltration. The derived infiltration model can be used to calculate the effective control radius and evaluate recovery rates, providing practical guidance for reservoir development.

A Model for Simulating the Upward Flow of a Viscous Fluid in a Fracture Network

Fluid migration in a fracture network plays an important role in the oil accumulation mechanism and hence is key to oil exploration. In this study, we build a model by combining one-dimensional (1D) Navier–Stokes equations, linear elastic equations, and energy equations, and validate the model by reproducing the thickness profile of a fluid-driven crack measured in an experiment. We employ this model to simulate the upward flow of viscous fluid in a single fracture during hydrocarbon migration. The simulation suggests that the parameters of both the fluid and the surrounding rock matrix, as well as the boundary condition imposed on the fracture outlet, affect the upward flow in the fracture. We then extend our model from the single fracture to the bifurcated fracture and the fracture network by maintaining homogeneous pressure and mass conservation at the connection of the channels. We find that the increase in network complexity leads to an increase in the inlet pressure gradient and inlet speed, and a decrease in the outlet pressure gradient and outlet speed. The effective area where the fluid is driven upward from the inlet to the outlet is offset toward the inlet. More importantly, the main novelty of our model is that it allows us to evaluate the effect of inconsistencies in individual branch parameters, such as matrix stiffness, permeability, temperature, and boundary conditions, on the overall upward flow of viscous fluid. Our results suggest that the heterogeneity enforces the greater impact on the closer branches.

Effects of implantation height on the performance of a redo transcatheter aortic valve replacement using a balloon-expandable valve

ObjectiveThe use of the transcatheter aortic valve in low-risk patients might lead to a second intervention due to the deterioration of the first 1. Understanding the implantation height is key to an effective redo transcatheter aortic valve replacement treatment. MethodsThe effects of implantation height on the performance of a balloon-expandable valve within a self-expandable valve were assessed using hemodynamic testing and particle image velocimetry. The hemodynamic performances, leaflet kinematics, and turbulent shear stresses were measured and compared. ResultsWhen a second balloon-expandable valve was positioned at varying heights relative to the first self-expandable valve, the leaflet motion of the first valve transitioned from free opening and closing to overhanging, and eventually to being entirely pinned to the stent, forming a neo-skirt. When the leaflets of the self-expandable valve could move freely, a decrease in regurgitation fraction was observed, but with an increased pressure gradient across the valve. Flow visualization indicated that the overhanging leaflets disrupted the flow, generating a higher level of turbulence. ConclusionsThis study suggests that the overhanging leaflets should be avoided, whereas the other 2 scenarios should be carefully evaluated based on an individual patient's anatomy and the cause of failure of the first valve.

Analysis of MHD boundary layer flow of a viscous fluid past a stretching sheet employing the Legendre wavelet method

The current work introduces a novel approach to analyse the non-linear Falkner–Skan equation from fluid dynamics by utilising the Legendre wavelet method. In this paper, we relied on the Legendre wavelet to generate a new functional integration matrix and presented a novel approach known as the Legendre wavelet approach (LWA). The primary goal of this study is to provide a unified method via LWA to compute an approximate solution to a non-linear differential equation for a viscous fluid over a stretching sheet. The Legendre wavelet method has been used for the first time to solve the stretching sheet problem. A viscous fluid across a stretching sheet has been explored for its stable laminar magnetohydrodynamic (MHD) flow, transportation of mass and heat characteristics in the context of an intermittent magnetic field. By specifying appropriate non-dimensional parameters, the governing boundary layer equation evolves into a dimension devoid of the Falkner–Skan equation. Using the Legendre wavelet approach, the resulting nonlinear equation modified to an algebraic equation is addressed. With LWA, the undershoots and overshoots for a set of factors are noted. The boundary layer thickness appears to decrease with increasing pressure gradient and magnetic field parameters. The graphical interpretation of the boundary layer flow’s features is done for a range of physical parameter values. To ensure the accuracy of the findings, local skin friction has been tracked and contrasted with other techniques that are already documented in the previous research.

Extended landslide velocity and analytical drag

The landslide velocity plays a dominant role in estimating the impact force and devastated area. Here, based on Pudasaini and Krautblatter (Earth Surf Dyn 10:165–189, 2022. https://doi.org/10.5194/esurf-10-165-2022), I develop a novel extended landslide velocity model that includes the force induced by the hydraulic pressure gradient, which was neglected by all the existing analytical landslide velocity models. By a rigorous conversion between this force and inertia, which facilitates constructing exact analytical solutions for velocity, I develop two peer systems expecting to produce the same result. However, this contradicts with our conventional wisdom. This raises a legitimate question of whether we should develop some new balance equations such that these phenomena can be better explained naturally. I compare the two velocity models that neglect and include the force induced by the hydraulic pressure gradient. Analytical solutions produced by the two systems are fundamentally different. The new model is comprehensive, elegant, and yet an extraordinary development as it reveals serendipitous circumstance resulting in a pressure–inertia paradox. Surprisingly, the mass first moves upstream for quite a while; then, it winds back and continues accelerating down slope. The difference between the extended and simple solution is significant, and widens strongly as the force associated with the hydraulic pressure gradient increases, demonstrating the importance of this force in the landslide velocity. The viscous drag is an essential dissipative force mechanism and plays an important role in controlling the landslide dynamics. However, no explicit mechanical and analytical model exists to date for this. The careful sagacity of the graceful form of new velocity equation results in a plain, yet mechanically extensive, analytical model for viscous drag, the first of this kind. It contains several physical and geometrical parameters, and evolves dynamically as it varies inversely with the flow depth. A dimensionless drag number is constructed characterizing the drag dynamics. Importance of the drag model is explained. In contrast with the prevailing practices, I have proved that drags are essentially different for the expanding and contracting motions. This is an entirely novel revelation. Drag coefficients are close to the empirical or numerical values often used in practice. But, now, I offer an innovative, physically founded analytical model for the drag that can be instantly applied in mass flow simulations.

Effect of Displacement Pressure Gradient on Oil–Water Relative Permeability: Experiment, Correction Method, and Numerical Simulation

Relative permeability is a fundamental parameter affecting reservoir development performance analysis. During the development of oil and gas fields, the displacement pressure gradient changes with time and space. This paper studies the effect of displacement pressure gradient on relative permeability. The oil–water relative permeability curves of a Bohai Oilfield under different displacement pressure gradients are obtained through experimental analysis. Based on the experimental data, a correction model of the permeability curve is established by regression of the Willhite model parameters. The correction model is introduced into the black oil numerical simulation, and the production performance and remaining oil are compared and analyzed. The results show that the displacement pressure gradient can have an obvious impact on the relative permeability curve. As the displacement pressure gradient increases, the two-phase span of the relative permeability curve increases, the oil displacement efficiency increases, and the water relative permeability increases. The relative permeability curves under different displacement pressure gradients can be accurately characterized by the Willhite model. The consideration of the displacement pressure gradient has an obvious impact on numerical simulation results. The conventional method of using a fixed relative permeability curve cannot truly reflect the production performance and the remaining oil distribution. This paper proposes a set of realization methods including obtaining laws from experiments, utilizing the empirical model to correct, and simulating to characterize reservoir changes.

Rates and Predictors of Structural Valve Degeneration and Failure of Trifecta Bioprosthetic Valve Over a 5-year Follow-up Period: A Single-center Experience

Abstract Introduction: The Trifecta bioprosthetic valve has been commonly used for surgical aortic valve replacement (SAVR). Multiple studies have been done to define the rate of structural valve degeneration (SVD) and failure (SVF), but the outcomes are still debatable. Therefore, we aim to conduct this single-center study to estimate the rate and predictors of SVD/SVF. Methodology: This retrospective observational cohort single-center study was conducted between 2014 and 2019 among Trifecta SAVR patients. Data were patient’s characteristics collected from electronic medical records at baseline and follow-up (3–5 years). Statistical analysis was performed with a significance level of P ≤ 0.05. Results: A total of 271 eligible patients were identified. Most of our sample were males (57.9%), with a mean age of 71.1 ± 10.6 years. The mean baseline preoperative ejection fraction (EF) was 53.0%, with no change (P = 0.88) in the immediate postoperative EF (53.6%). A most recent follow-up EF revealed a significant increase of EF (55.2%), P = 0.01. Furthermore, there was a significant increase from peak velocity to PVMRE (mean difference [MD] ± standard error of mean (SEM) [0.15 ± 0.04], P < 0.01), an increase in pressure gradient (PGIPE) to PGMRE (MD ± SEM [1.70 ± 0.49], P < 0.01), and a decrease in Doppler velocity index (DVIIPE) to DVIMRE (MD ± SEM [−0.037 ± 0.01], P = 0.01). Regarding the SVF rate, 13 (4.8%) patients had failed valves requiring replacement throughout the study period. Conclusions: Over a 5-year follow-up period, 4.8% had SVF with an SVD of 23.2%, with the majority of SVD not being clinically significant except in six patients. These results corroborate with a previously published study suggesting a bad clinical outcome of Trifecta valve placement.

Two-relaxation-time lattice Boltzmann model of the velocity profiles and volumetric flow rate of generalized Newtonian fluids in a single-screw extruder

Single-screw extruders and injection molding machines are essential equipment in polymer processing. It is of great importance for the optimization of operating parameters and the design of extrusion screw to predict the throughput of an extruder and the metering time of an injection molding machine according to the geometric parameters of the screw, operating parameters, and the rheological behavior of materials. Most polymer melts exhibit non-Newtonian behavior. The lattice Boltzmann method has many advantages in simulating the flow of non-Newtonian fluids. Herein, the dimensionless velocity profiles and dimensionless volumetric flow rate of generalized Newtonian fluids in a screw channel have been studied using the two-relaxation-time lattice Boltzmann method (TRT–LBM). The numerical results of power-law fluids are in good agreement with the analytical solutions, which verifies the validity of TRT–LBM. Through research, the change rule of the dimensionless volumetric flow rate of Bingham fluids with dimensionless pressure gradient has been obtained. It was found that the rheological properties of polymer melts and the dimensionless pressure gradient significantly affect the dimensionless velocity profiles and dimensionless volumetric flow rate. The dimensionless volume flow rate has some unexpected changes with the increase of the dimensionless pressure gradient. This study can provide theoretical guidance for the optimization of operating parameters and the design of extrusion screws.

Flow-dependent regulation of rat mesenteric lymphatic vessel contractile response requires activation of endothelial TRPV4 channels.

The objective of our study is to evaluate the involvement of the transient receptor potential vanilloid 4 (TRPV4) in the alteration of lymphatic pumping in response to flow and determine the signaling pathways involved. We used immunofluorescence imaging and western blotting to assess TRPV4 expression in rat mesenteric lymphatic vessels. We examined inhibition of TRPV4 with HC067047, nitric oxide synthase (NOS) with L-NNA and cyclooxygenases (COXs) with indomethacin on the contractile response of pressurized lymphatic vessels to flow changes induced by a stepwise increase in pressure gradients, and the functionality of endothelial TRPV4 channels by measuring the intracellular Ca2+ response of primary lymphatic endothelial cell cultures to the selective agonist GSK1016790A. TRPV4 protein was expressed in both the endothelial and the smooth muscle layer of rat mesenteric lymphatics with high endothelial expression around the valve sites. When maintained under constant transmural pressure, most lymphatic vessels displayed a decrease in contraction frequency under conditions of flow and this effect was ablated through inhibition of NOS, COX or TRPV4. Our findings demonstrate a critical role for TRPV4 in the decrease in contraction frequency induced in lymphatic vessels by increases in flow rate via the production and action of nitric oxide and dilatory prostanoids.

The Arctic Fjord Breeze: Characteristics of a Combined Sea Breeze and Valley Wind in a Svalbard Fjord Valley

Thermally-driven circulations are a frequent meteorological phenomenon in complex Arctic terrain, but the Arctic fjord breeze, a combined sea-breeze and up-valley wind, has received little attention. A field campaign was conducted in the valley Adventdalen in Svalbard in summer 2022 using a Scanning Doppler Lidar and automatic weather stations. It is shown that a local up-valley circulation occurred frequently in this valley, and that it was driven by the temperature and pressure gradient between valley and fjord, i.e., a fjord breeze. The fjord breeze existed in both large-scale up-valley and down-valley winds. Its strength, extent and depth varied due to the diurnal cycle of solar irradiation as well as the interaction with large-scale winds. In contrast to typical lower-latitude breezes, the Arctic fjord breeze could persist over several days. The breeze was found to be relatively strong even under small horizontal temperature contrasts and opposing large-scale winds, possibly due to an increase in the thermal pressure gradient by the surrounding topography.

Mechanism of width effects on cavity-induced transitions at hypersonic speed using direct numerical simulation

Cavities on the surfaces of hypersonic vehicles cannot be avoided easily. Moreover, they can trigger boundary layer transition under certain conditions. However, little progress has been reported on boundary layer transitions induced by a three-dimensional (3-D) shallow cavity. In this study, transitions induced by six 3-D shallow cavities with the same length–depth ratios of 20 and different widths of 0.25, 0.5, 0.75, 1.0, and 1.5 times the baseline width (W), as well as infinite width, were investigated. A direct numerical simulation was conducted using the Roe scheme with 4th-order minimum dispersion and controllable dissipation, and weighted essentially non-oscillatory reconstruction, based on our in-house code: Unsteady NavIer–STokes equations solver. Cavity width was observed to have non-monotonic influences on transition. Both the 0.25 and 1.0 W cavities could induce transition constantly. Moreover, flow was maintained as laminar past the 1.5 W and InfW cavities. For the 0.5 and 0.75 W cavities, intermittent transition was observed with different intermittency factors. The intermittent transition phenomenon was determined to be caused by the periodic increase and decrease in the adverse pressure gradient (APG) in the front part of cavity. Notably, the recirculation with a synchronic size change was the origin of the APG oscillation.

Zoning Productivity Calculation Method of Fractured Horizontal Wells in High-Water-Cut Tight Sandstone Gas Reservoirs under Complex Seepage Conditions

Tight sandstone gas reservoirs generally contain water. Studying the impact of water content on the permeability mechanism of tight gas reservoirs is of positive significance for the rational development of gas reservoirs. Selected cores from a tight sandstone gas reservoir in the Ordos Basin were used to establish the variation in its seepage mechanism under different water saturations. The experimental results show that the gas slip factor in tight water-bearing gas reservoirs decreases as the water saturation increases. The stress sensitivity coefficient and the threshold pressure gradient (TPG) increase with increasing water saturation, characterizing the relationships between stress sensitivity coefficients, TPG, permeability, and water saturation. As the water saturation gradually increases, the relative gas phase permeability of tight sandstone gas reservoirs will sharply decrease. When the water saturation exceeds 80%, the gas phase permeability becomes almost zero, resulting in gas almost ceasing to flow. Through the analysis of experimental results, we defined high-water-cut tight sandstone gas reservoirs and analyzed the permeability characteristics of high-water-cut tight sandstone gas reservoirs in different regions. Combining stress sensitivity coefficients and the TPG with permeability and water saturation relationships, we established a zoning productivity calculation method of fractured horizontal wells in high-water-cut tight sandstone gas reservoirs under complex seepage conditions and validated the practicality of the model through example calculations.

The peculiar wind and wave climatology of the Arabian Gulf

Based on a 40-year hindcast, we analyze the climatology and long-term trends of wind and waves in the Arabian Gulf. We identify and characterize four dominant wind systems, and their related mean wave conditions and long-term trends. Focusing on the summer Shamal wind, we observed a mild decrease in the number of Shamal events with time, whereas their intensity shows little to no variation. Further, we revealed a tendency toward an extension of the summer Shamal season from August to September. On a short time scale, the related wind fields show an evident daily oscillation associated with the daily heating of the Arabian Peninsula, with wind speeds peaking at 3:00 p.m. local time (UTC+3) on land and 12 h later on the sea. The long-term analysis conducted herein reveals limited, but significant, trends in surface pressure and related west-to-east pressure gradients in August. In September, the observed increasing number of Shamal storms is associated with an increase of the longitudinal local pressure gradient.

Flow regime transition of multicomponent oil in shale nanopores

Understanding the shale oil flow mechanism in nanopores is crucial for optimizing development strategies and enhancing recovery in shale oil reservoirs. Despite the widespread use of molecular dynamics simulations in studying shale oil flow, oversimplified shale oil and shale nanopore models compromise result reliability, and a definitive shale oil flow regime has yet to be established. This study, employing validated molecular models, investigated 26-component oil flow in authentic shale kerogen and quartz nanopores. For the first time, we elucidated the nonlinear flux increase due to flow regime transition with pressure gradient. At low pressure gradients, shale oil flux gradually increased with a parabolic velocity profile. With the increasing pressure gradient, the velocity profile shifted from parabolic to piston-like, especially in quartz nanopores, indicating a positive slip velocity. Consequently, the shale oil flux increased significantly. At high pressure gradients, the growth of shale oil flux decelerated while maintaining a piston-like velocity profile. Through analysis of density distribution and oil-wall interactions, we revealed that oil desorption and redistribution triggered the flow regime transition. The flow regime transition occurred with the widening of quartz nanopores. Increased nanopore width and temperature notably enhanced shale oil flow. This study underscored the importance of accounting for shale oil’s multicomponent properties and roughness and composition of shale nanopores. It determined shale oil flow regimes under various conditions, advancing our comprehension of shale oil flow mechanisms in realistic settings and furnishing a theoretical foundation for enhancing shale oil recovery.

Pressure gradient and an upstream cylinder on nanofluid flow around a heated cylinder: Heat transfer and entropy analysis

This study numerically investigates the nanofluid flow around a long heated cylinder of square cross-section (DSC) with height placed parallel to a cold wall at a fixed gap height The incident flow is Couette–Poiseuille (C–P) flow. Another cylinder of rectangular cross section (UREP) is placed on the upstream side in an inline arrangement with different gap spacings between the cylinders. The base fluid is chosen as the water and ethylene glycol–water mixture. Numerical experiments are made using staggered grid arrangement on non–uniform grid, finite volume methods, and Semi–Implicit Method for Pressure Linked Equations algorithm. Impact of pressure gradient at the inlet (due to C–P flow), position and shape (square/rectangular) of the UREP, nanoparticle concentration, and base fluid on the crowding of isotherms around edges of the DSC and hence to the heat transfer characteristics (Nusselt number and entropy generation rate density) is investigated. Bejan number is used to ratify that the irreversibility due to heat transfer is the major constituent of the total system irreversibility here. A reduction of heat transfer and entropy generation from the values of an isolated DSC is natural here due to the inline arrangement. An effort is made to improve the heat transfer by reducing the height of the UREP or/and by generating unsteadiness in the incoming flow to the DSC using a bluffer UREP or/and an increased pressure gradient. Finally, some scenarios are reported where the heat transfer decrement is less in comparison to that of the total system irreversibility.

Porcine or Bovine Tissue Valves: Which are Better for Surgical Aortic Valve Replacement?

Summary The choice between mechanical and bioprosthetic aortic valve implants is affected by relatively clear criteria. However, the choice between porcine or pericardial valve is more complex regarding bioprosthetic devices. We aimed to elucidate any hemodynamic and clinical difference between two widely used bioprosthetic valves: the Sorin Mitroflow bovine pericardial valve and the St. Jude Medical Epic Supra porcine valve. We retrospectively studied 71 consecutive patients separated into two groups based on the valve they received. Clinical outcomes included patient survival and hemodynamic performance of the implanted prostheses. Patients were assessed at one and five years postoperatively. Mean transprosthetic pressure gradients were used as a marker of hemodynamic performance. The Mitroflow valve exhibited lesser mean transvalvular gradients than the Epic valve for all labelled sizes at one and five years postoperatively. The 5-year survival was equal between groups. Both prostheses demonstrated a small but significant increase in mean pressure gradients in the fifth year. Most patients enjoyed significant clinical improvement as assessed by NYHA functional class. Both bioprostheses performed very well with excellent hemodynamic parameters. The pericardial valves are a safe and appropriate choice for surgical bioprosthetic aortic valve replacement.