Increase In Pressure Gradient Research Articles

A pressure-controllable bump based on the pressure-ridge concept

An innovative type of pressure distribution for the hypersonic aircraft forebody (bump) is presented, and this design is based on the newly established known as pressure ridge (PR) flow mechanism. Studies on the low-kinetic-energy fluid over the aircraft surface are summarized. Then, the challenges of the inlet–airframe integration at high speeds are discussed. The flow structure around the bump is analyzed in detail to eliminate the side-embedded shock (SES) effect at the inlet entrance. The concept of PR is proposed to improve the overall aerodynamic characteristics of the bump, namely, the boundary layer removal, the reduction of external drag, and the streamline direction at bump end-section. On the basis of the developed inverse method to generate the bump surface by the prescribed pressure distribution, the improved PR-derived bump is designed and numerically compared with the typical pressure-controllable bump (PCB) while the identical leading edge profile is imposed. Results demonstrate that the PR creates outward and inward pressure gradients. The removed amount of boundary layer increases with the increase in outward pressure gradient. Meanwhile, the inward pressure gradient determines the streamline pattern after the bump. The PR-derived bump is 29.2% lower in height than the typical one by using a proper outward pressure gradient. The uniform area of the new bump is 30% wider than that of the typical PCB. The near-wall streamlines of the new bump are adjusted from expanding to the parallel, thereby relieving the side-compression. Changing the location, width, and peak value of the PR can lead to great flexibility in the design and optimization of aircraft forebody subjected to hypersonic flow.

Magnetohydrodynamic (MHD) Boundary Layer Flow Past a Wedge with Heat Transfer and Viscous Effects of Nanofluid Embedded in Porous Media

The problem of two‐dimensional steady laminar MHD boundary layer flow past a wedge with heat and mass transfer of nanofluid embedded in porous media with viscous dissipation, Brownian motion, and thermophoresis effect is considered. Using suitable similarity transformations, the governing partial differential equations have been transformed to nonlinear higher‐order ordinary differential equations. The transmuted model is shown to be controlled by a number of thermophysical parameters, viz. the pressure gradient, magnetic, permeability, Prandtl number, Lewis number, Brownian motion, thermophoresis, and Eckert number. The problem is then solved numerically using spectral quasilinearization method (SQLM). The accuracy of the method is checked against the previously published results and an excellent agreement has been obtained. The velocity boundary layer thickness reduces with an increase in pressure gradient, permeability, and magnetic parameters, whereas thermal boundary layer thickness increases with an increase in Eckert number, Brownian motion, and thermophoresis parameters. Greater values of Prandtl number, Lewis number, Brownian motion, and magnetic parameter reduce the nanoparticles concentration boundary layer.

Effects of viscous dissipation and Joule heating on the Couette and Poiseuille flows of a Jeffrey fluid with slip boundary conditions

In this article, we have presented the exact solutions of the Couette, Poiseuille and generalized Couette flows of an incompressible magnetohydrodynamic Jeffrey fluid between parallel plates through homogeneous porous medium. The effects of slip boundary conditions and heat transfer are considered. Viscous dissipation, radiation and Joule heating are also considered in the energy equation. The governing equations of the Jeffrey fluid flow are modeled in Cartesian coordinate system. Analytical solutions for the velocity and temperature profiles are obtained for all mentioned cases. The influences of the sundry parameters on the velocity and temperature profiles are studied and the results are presented through graphs. It is noted that, with increase of slip parameter and pressure gradient increases the velocity. Temperature behaves as a decreasing function due to the impact of Hartmann number, non-Newtonian parameter and slip parameter in all noted problems.

Influence of Lubricant Pressure Response on Subsurface Stress in Elastohydrodynamically Lubricated Finite Line Contacts

In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity–pressure and compressibility–pressure behavior have been shown to influence the film thickness and pressure distribution in elastohydrodynamic lubrication (EHL) contacts, further influencing the durability. In this work, a finite line EHL contact is analyzed with focus on the oil compressibility–pressure and viscosity–pressure response, comparing two oils with relatively different behavior and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller.

Modelling Study on Internal Energy Loss Due to Entropy Generation for Non-Darcy Poiseuille Flow of Silver-Water Nanofluid: An Application of Purification.

In this paper, an analytical study of internal energy losses for the non-Darcy Poiseuille flow of silver-water nanofluid due to entropy generation in porous media is investigated. Spherical-shaped silver (Ag) nanosize particles with volume fraction 0.3%, 0.6%, and 0.9% are utilized. Four illustrative models are considered: (i) heat transfer irreversibility (HTI), (ii) fluid friction irreversibility (FFI), (iii) Joule dissipation irreversibility (JDI), and (iv) non-Darcy porous media irreversibility (NDI). The governing equations of continuity, momentum, energy, and entropy generation are simplified by taking long wavelength approximations on the channel walls. The results represent highly nonlinear coupled ordinary differential equations that are solved analytically with the help of the homotopy analysis method. It is shown that for minimum and maximum averaged entropy generation, 0.3% by vol and 0.9% by vol of nanoparticles, respectively, are observed. Also, a rise in entropy is evident due to an increase in pressure gradient. The current analysis provides an adequate theoretical estimate for low-cost purification of drinking water by silver nanoparticles in an industrial process.

Left ventricular outflow obstruction predicts increase in systolic pressure gradients and blood residence time after transcatheter mitral valve replacement

Left ventricular outflow tract (LVOT) obstruction is a relatively common consequence of transcatheter mitral valve replacement (TMVR). Although LVOT obstruction is associated with heart failure and adverse remodelling, its effects upon left ventricular hemodynamics remain poorly characterised. This study uses validated computational models to identify the LVOT obstruction degree that causes significant changes in ventricular hemodynamics after TMVR. Seven TMVR patients underwent personalised flow simulations based on pre-procedural imaging data. Different virtual valve configurations were simulated in each case, for a total of 32 simulations, and the resulting obstruction degree was correlated with pressure gradients and flow residence times. These simulations identified a threshold LVOT obstruction degree of 35%, beyond which significant deterioration of systolic function was observed. The mean increase from baseline (pre-TMVR) in the peak systolic pressure gradient rose from 5.7% to 30.1% above this threshold value. The average blood volume staying inside the ventricle for more than two cycles also increased from 4.4% to 57.5% for obstruction degrees above 35%, while the flow entering and leaving the ventricle within one cycle decreased by 13.9%. These results demonstrate the unique ability of modelling to predict the hemodynamic consequences of TMVR and to assist in the clinical decision-making process.

Hydrodynamic Study of AR Coupling Effects on Solid Circulation and Gas Leakages in a High-Flux In Situ Gasification Chemical Looping Combustion System

In situ gasification chemical looping combustion (iG-CLC) is a novel and promising coal combustion technology with inherent separation of CO2. Our previous studies demonstrated the feasibility of performing iG-CLC with a high-flux circulating fluidized bed (HFCFB) riser as the fuel reactor (FR) and a counter-flow moving bed (CFMB) as the air reactor (AR). As an extension of that work, this study aims to further investigate the fundamental effects of the AR coupling on the oxygen carrier (OC) circulation and gas leakages with a cold-state experimental device of the proposed iG-CLC system. The system exhibited favorable pressure distribution characteristics and good adaptability of solid circulation flux, demonstrating the positive role of the direct coupling method of the AR in the stabilization and controllability of the whole system. The OC circulation and the gas leakages were mainly determined by the upper and lower pressure gradients of the AR. With the increase in the upper pressure gradient, the OC circulation flux increased initially and later decreased until the circulation collapsed. Besides, the upper pressure gradient exhibited a positive effect on the restraint of gas leakage from the FR to the AR, but a negative effect on the suppression of gas leakage from the AR to the FR. Moreover, the gas leakage of the J-valve to the AR, which is directly related to the solid circulation stability, was exacerbated with the increase of the lower pressure gradient of the AR. In real iG-CLC applications, the pressure gradients should be adjusted flexibly and optimally to guarantee a balanced OC circulation together with an ideal balance of all the gas leakages.

Assessment of the changes in the Etesians in the EURO‐CORDEX regional model projections

The northerly Etesian winds blow persistently over the Aegean Sea and eastern Mediterranean (EM) during summer months (June, July and August). This study investigates the July–August (JA) characteristics of the Etesians for a present time period (1981–2000) from both ECMWF ERA‐Interim Reanalysis data set (observations) and 11 EURO‐CORDEX regional climate model (RCM) simulations and assesses future changes using the associated RCP8.5 simulations. An EOF analysis applied to observations near surface meridional wind component (v10) over eastern Mediterranean demonstrates its strength as the leading mode, which explains 43.6% of the total variance, as the principal component (PC) time series of EOF1 has a very high correlation (r = 0.98) with an index showing the intensity of the Etesians. A composite analysis involving the opposite phases in the PC time series reveals that the strong Etesians develop when high pressure takes place towards Balkans and the Black Sea, which increases the meridional pressure gradient over the Aegean Sea. Some of the RCMs reproduce quite realistically pressure system and its associated Etesian winds. However, the intensity of the Etesians in these simulations is usually not as high as that in observations despite their higher horizontal resolutions. In general, the Etesians are projected to be stronger in the future periods as a result of the increasing pressure gradient over the Aegean Sea. This result suggests that the wind energy potential of the region that already attracts investment from the energy sector will increase in the future.

Examination of disproportionate permeability reduction mechanism on rupture of hydrogels performance

In this paper, the overall performance of a disproportionate permeability reduction mechanism for a sulfonated polyacrylamide copolymer and the chromium triacetate crosslinker was investigated. A home-built gel filtration system was used for visual inspections and evaluations of the hydrogel performance. The experiments were conducted based on rheological test plans, energy-dispersive X-ray spectroscopy, and scanning electron microscope. Accordingly, quadratic equations based on the polymer and crosslinker concentrations were presented predicting the rupture pressure gradient of the hydrogel and the hydrogel output due to the oil and water injection through the hydrogel. It was indicated that the polymer concentration was the main effect on the rupture pressure gradient of the hydrogel and hydrogel output. Moreover, under constant concentration of crosslinker, increasing polymer concentration showed an increase in rupture pressure gradient and output of the hydrogel due to the increase of elastic modulus of hydrogel network and its strength as a viscoelastic material. As the hydrogel structure illustrated no rupture during the gel filtration experiments, a mechanism presented justifying the disproportionate permeability reduction phenomenon which in that under constant condition, the oil permeability through hydrogel was greater than the water permeability.

The cavitating Taylor-Couette flow

This work presents an investigation of a new phenomenon of the Taylor-Couette flow: the onset of Taylor vortices in a cavitating fluid. This particular form of the Taylor-Couette flow develops if the shear flow between a rotating inner and a fixed outer cylinder approaches the critical Taylor number and the vapor pressure of the fluid simultaneously. This process is achieved by increasing the rotational speed of the inner cylinder, which causes an increase of the radial pressure gradient inside the laminar flow. The fully developed Taylor vortex flow is characterized by a pressure distribution in the azimuthal plane showing a local minimum adjacent to the wall of the inner cylinder between a pair of vortices that form a radial flow towards the outer cylinder. Thence, cavitation occurs simultaneously if the local pressure minimum drops below the vapor pressure of the fluid. This transition from a two-dimensional (Couette) into a three-dimensional (Taylor) flow triggered the idea to apply a newly developed unsteady 2-phase 3D-computational fluid dynamics code by computing the generation of vapor that is coinciding with the formation of Taylor vortices at the critical Taylor number. Whereas the results of a numerical simulation prove the existence of toroidal vapor caused by cavitation, the experimental validation demands additionally the development of a special fluid. Thus, the present work describes this specifically tailored fluid, which not only fulfills Taylor and pressure analogy but also features a favorable refractive index and a chemical suitability for the task.

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

Discrete Subaortic Stenosis: Perspective Roadmap to a Complex Disease.

Discrete subaortic stenosis (DSS) is a congenital heart disease that results in the formation of a fibro-membranous tissue, causing an increased pressure gradient in the left ventricular outflow tract (LVOT). While surgical resection of the membrane has shown some success in eliminating the obstruction, it poses significant risks associated with anesthesia, sternotomy, and heart bypass, and it remains associated with a high rate of recurrence. Although a genetic etiology had been initially proposed, the association between DSS and left ventricle (LV) geometrical abnormalities has provided more support to a hemodynamic etiology by which congenital or post-surgical LVOT geometric derangements could generate abnormal shear forces on the septal wall, triggering in turn a fibrotic response. Validating this hypothetical etiology and understanding the mechanobiological processes by which altered shear forces induce fibrosis in the LVOT are major knowledge gaps. This perspective paper describes the current state of knowledge of DSS, articulates the research needs to yield mechanistic insights into a significant pathologic process that is poorly understood, and proposes several strategies aimed at elucidating the potential mechanobiological synergies responsible for DSS pathogenesis. The proposed roadmap has the potential to improve DSS management by identifying early targets for prevention of the fibrotic lesion, and may also prove beneficial in other fibrotic cardiovascular diseases associated with altered flow.

Quantitative Estimates of Nonlinear Flow Characteristics of Deformable Rough-Walled Rock Fractures with Various Lithologies

The existence of surface roughness, various contact conditions and the occurrence of flow nonlinearity make the flow process in natural rock fractures more complicated. To evaluate the fluid flow regimes in deformable rough-walled rock fractures, a great many hydromechanical tests were conducted on nine real fractures artificially produced from a wide range of lithological diversity. For fractures with a certain JRC (fracture roughness coefficient) value, the confining pressure varied from 5 to 20 MPa, and the hydraulic pressure was increased from 0.4 to 6.0 MPa. The experimental results display that (i) regression analyses of the raw experimental data indicate that the Forchheimer’s law provides a perfect description for flow process through the fractures. The coefficients of viscous and inertial pressure drops undergo a growth of 2–3 orders of magnitude with an increase in the confining pressure; (ii) the hydraulic aperture decreases by approximately 87.41–92.81% as the confining pressure increases, and experiences a decrease of 1.52–2.96 times with the JRC values. A power-law function is used to evaluate the hydraulic aperture as a function of the nonlinear coefficient. The nonlinear coefficient decreases with increasing hydraulic aperture; (iii) using Forchheimer equation, the critical Reynolds number Rec was successfully assessed by choosing E percentage (generally 10%) of the nonlinear effect as the critical value between the linear and nonlinear flow regimes. The obtained Rec steadily increases with increasing confining pressure, while it diminishes with the JRC values; and (v) the transmissivity decreases as the pressure gradient increases. Additionally, transmissivity also exhibits a decreasing trend with both the confining pressures and JRC values due to fracture closure and tortuous and channeling flow paths in rougher fractures, and the rate of its decrease for a smaller confining pressure (5, 10 MPa) is more significant.

Conventional cardiopulmonary resuscitation-induced refractory cardiac arrest due to latent left ventricular outflow tract obstruction due to a sigmoid septum: a case report

BackgroundPatients with left ventricular outflow tract obstruction who do not exhibit a dynamic pressure gradient at rest, experience pressure gradient increases of ≥ 30 mmHg only during specific situations; this is called latent left ventricular outflow tract obstruction. It is provoked by increased cardiac contraction and preload and afterload depletion. There are a few reports of patients with it developing cardiac arrest. We present a case of latent left ventricular outflow tract obstruction in which the patient with a sigmoid septum experienced refractory pulseless electrical activity due to conventional advanced cardiac life support.Case presentationA 73-year-old Asian woman on escitalopram and lorazepam was transported to our hospital for chest and back pain with altered consciousness. On arrival, she was in shock and developed pulseless electrical activity. After initiation of conventional cardiopulmonary resuscitation according to adult advanced cardiovascular life support guidelines, she could not regain spontaneous circulation. She was ultimately resuscitated via venoarterial extracorporeal membrane oxygenation initiation. The only abnormal laboratory result at admission was anemia. Her hemodynamic status stabilized after red blood cell transfusion, and venoarterial extracorporeal membrane oxygenation was subsequently terminated. Transthoracic echocardiography showed a sigmoid septum; dobutamine-infused Doppler echocardiography revealed a significant outflow gradient, and continuous monitoring showed Brockenbrough–Braunwald sign, which confirmed a diagnosis of latent left ventricular outflow tract obstruction due to a sigmoid septum. As a result, carvedilol and verapamil were initiated. A follow-up dobutamine-infused Doppler echocardiography showed a reduction of outflow gradient, and she was discharged without any sequelae. Latent left ventricular outflow tract obstruction worsened due to increasing cardiac contraction and the depletion of preload and afterload. Depleted preload occurred due to dehydration and anemia, whereas depleted afterload occurred due to the prescribed drugs, which subsequently caused pulseless electrical activity. Moreover, β-stimulation from the adrenaline probably enhanced the hypercontractile state and caused refractory pulseless electrical activity in our case.ConclusionsPatients with latent left ventricular outflow tract obstruction can progress to cardiogenic shock and pulseless electrical activity due to increased cardiac contraction and depletion of preload and afterload. We should consider the patient’s underlying conditions that induced pulseless electrical activity.

THE ROLE OF THE TRANSDIAPHRAGMATIC PRESSURE GRADIENT IN THE PATHOPHYSIOLOGY OF GASTROESOPHAGEAL REFLUX DISEASE.

Gastroesophageal reflux disease (GERD) is the most common disease of the upper gastrointestinal tract in the Western world. GERD pathophysiology is multifactorial. Different mechanisms may contribute to GERD including an increase in the transdiaphragmatic pressure gradient (TPG). The pathophysiology of GERD linked to TPG is not entirely understood. This review shows that TPG is an important contributor to GERD even when an intact esophagogastric barrier is present in the setting of obesity and pulmonary diseases.

Modeling the characteristics of Bingham porous-flow mechanics for a horizontal well in a heavy oil reservoir

In order to investigate hydrodynamic characteristics of Bingham porous-flow mechanics in a heavy oil reservoir, this paper originally proposes a physical model of Bingham fluid flow for a horizontal well in a heavy oil reservoir. A corresponding mathematical model is established and solved. A series of typical pressure and pressure derivative curves are drawn by the use of the semi-analytical solution of the mathematical model. Hydrodynamic flow characteristics of Bingham fluid are thoroughly analyzed. Through the recognition of flow regimes from the typical curves, it is found that the flow process of Bingham fluid mainly includes the early radial flow regime, linear flow regime and late pseudo-radial flow regime. The curves controlled by different boundary conditions are especially studied, and it is found that the late curve shape, especially the shape of pressure derivative curve, differs completely for the various property of boundary. The curve sensitivity to different model parameters, such as dimensionless threshold pressure gradient and horizontal wellbore length, is deeply discussed. The findings are as follow: except the pure wellbore storage regime, the threshold pressure gradient influences the hydrodynamic flow behavior in all the regimes; the curve of Bingham fluid governed by the threshold pressure gradient upward deviates from that of Newtonian fluid; and the deviation of the curves increases with the increase of the threshold pressure gradient and the elapsed time. The research results of this paper sufficiently demonstrate the essential property of non-Newtonian porous-flow mechanics.

Establishing a porcine model of “Small for Flow Syndrome”

Introduction The concept of "Small for Flow Syndrome” (SFFS) arises from the observation that the determining factor of the appearance of the “Small For Size Syndrome” (SFSS) and the posthepatectomy liver failure is the increase of portal inflow against a reduced hepatic mass. The criteria that define the SFFS are intraoperative and determined by: a portal pressure >20mmHg or a portal flow >250mL/min/100g. They indicate that we must take measures to prevent the development of the SFSS, as a consequence of the structural alterations caused by this inflow. Materials and Methods An experimental study (10 minipigs) of 24-hour survival was carried out. An hyperextended hepatectomy (90%) was performed. It consists on resecting the lateral and medial left lobes, and lateral and medial right lobes. Blood tests, hepatic and systemic hemodynamics, hepatic function (PDR), histology, and volumetry were assessed before and after the surgery. Intracranial pressure (ICP) and hepatocyte proliferation were evaluated. Results In all of the swines the surgery was completed with success and hemodynamic stability to start the postoperative observation period. The percentage of hepatic volume remaining after surgery was 8.85±2.59% (volumetry by CT). Hemodynamic data were measured at the beginning, after the hepatectomy, and 24 hours after. There was an increase in portal pressure after surgery, 20.90±4.50mmHg. Portal flow varies from 68'38±23’54ml/min/100g to 245’02±115’62ml/min/100g. This increase in portal flow through a reduced sinusoidal volume is reflected in the increase in the portosystemic pressure gradient, going from 1.11±1.90 to 13.20±7.16mmHg. PDR values went from?? 12.30±5.47 to 4.54±1.82 and R15 from 17.53±10’86 to 52’12±13'00 after surgery. There are significant histological damages, oscillating the score from 0.75±1.16 to 5.62±2.55. After surgery 75% of the animals had a Ki-67<2%. The ICP was monitored, observing a gradual increase in it. Discussion After the resection there is a deterioration in the liver function (decreases the PDR and increases the INR), similars to hepatic transplant models with reduced grafts. The histological disorders are compatible with those described in the literature in relation to the SFSS. Above 20 mmHg of portal pressure all animals showed histological damage. Since the aim of establishment of an animal model of SFFS is a better understanding of this clinical syndrome as well as studying the possible preventive and curative methods, we strongly believe that, in a porcine model with normal parenchyma, 90% liver resection can be considered as ideal model. Following 90% hepatectomy, we can render the hemodynamic, histological, and biochemical changes of the SFFS. Conclusion Hyperextended hepatectomy in porcine model is a feasible, reproducible and appropriate model to study the pathophysiology, prediction, prevention, diagnosis and management of SFFS.

Analyzing thermo-hydrodynamics of nanofluid flowing through a wavy U-turn channel

In this paper, the thermo-hydrodynamics of Al2O3-water nanofluid in a wavy U-turn channel with hot walls is numerically investigated by means of lattice Boltzmann modeling. At first, the numerical technique is validated by simulating fluid flow in a (non-)wavy straight channel. Then, the effects of various active parameters, e.g. pressure gradient in the channel, nanoparticles volume fraction, and number of sinusoidal waves along the channel, on the flow field and heat transfer is studied. Furthermore, the thermal–hydraulic performance factor is determined to investigate whether heat transfer enhancement outweighs the greater frictional losses caused by both complex wavy wall geometry and nanoparticles. The results show that the heat transfer rises by increasing pressure gradient in the channel while drops by increasing number of waves. Also, the effect of nanoparticles volume fraction on dimensionless Nusselt number becomes more pronounced at higher pressure gradients. The results indicate that the thermal–hydraulic performance factor grows by increasing nanoparticles volume fraction or decreasing the number of waves.

Correlation between angiographic stenosis and physiologic venous sinus outflow obstruction in idiopathic intracranial hypertension

IntroductionThe relationship between degree of angiographic venous sinus stenosis and the trans-stenosis pressure gradient magnitude in idiopathic intracranial hypertension (IIH) is poorly understood. The present study aimed to assess the...

Outgassing on stagnant-lid super-Earths

Aims. We explore volcanic CO2-outgassing on purely rocky, stagnant-lid exoplanets of different interior structures, compositions, thermal states, and age. We focus on planets in the mass range of 1–8 M⊕ (Earth masses). We derive scaling laws to quantify first- and second-order influences of these parameters on volcanic outgassing after 4.5 Gyr of evolution. Methods. Given commonly observed astrophysical data of super-Earths, we identify a range of possible interior structures and compositions by employing Bayesian inference modeling. The astrophysical data comprise mass, radius, and bulk compositional constraints; ratios of refractory element abundances are assumed to be similar to stellar ratios. The identified interiors are subsequently used as input for two-dimensional (2D) convection models to study partial melting, depletion, and outgassing rates of CO2. Results. In total, we model depletion and outgassing for an extensive set of more than 2300 different super-Earth cases. We find that there is a mass range for which outgassing is most efficient (~2–3 M⊕, depending on thermal state) and an upper mass where outgassing becomes very inefficient (~5–7 M⊕, depending on thermal state). At small masses (below 2–3 M⊕) outgassing positively correlates with planet mass, since it is controlled by mantle volume. At higher masses (above 2–3 M⊕), outgassing decreases with planet mass, which is due to the increasing pressure gradient that limits melting to shallower depths. In summary, depletion and outgassing are mainly influenced by planet mass and thermal state. Interior structure and composition only moderately affect outgassing rates. The majority of outgassing occurs before 4.5 Gyr, especially for planets below 3 M⊕. Conclusions. We conclude that for stagnant-lid planets, (1) compositional and structural properties have secondary influence on outgassing compared to planet mass and thermal state, and (2) confirm that there is a mass range for which outgassing is most efficient and an upper mass limit, above which no significant outgassing can occur. Our predicted trend of CO2-atmospheric masses can be observationally tested for exoplanets. These findings and our provided scaling laws are an important step in order to provide interpretative means for upcoming missions such as JWST and E-ELT, that aim at characterizing exoplanet atmospheres.