Function Of Pressure Difference Research Articles

Steady diffusion of an ideal fluid through a two-layer thick walled pre-stressed and fiber-reinforced hollow cylinder within the context of mixture theory

Within the context of mixture theory, an attempt is made to solve a particular problem of radially directed fluid diffusion through a two-layer thick-walled pre-stressed fibrous hollow cylinder submitted to combined large deformations. With respect to both limitations due to perfect interface hypothesis and particular properties of rubber-fluid mixture, our investigation exhibit new results, which show interesting effects of both arterial stiffness in each layer as well as stretching and torsion upon applied mass flux as a function of pressure difference, but also upon spatial variations of both radial and tangential stretch ratios. These results could easily be echoed as an effective aid to improve the methods of making prosthetic conduits for use with living tissue; and can potentially help in understanding de-stiffening therapy, which is appearing as a potential strategy to decrease the stroke incidence and enhance the functional prognosis.

Influence of Pressure Difference Between Reservoir and Production Well on Steam-Chamber Propagation and Reservoir-Production Performance

Summary Steam-assisted gravity drainage (SAGD) is the most-effective thermal recovery method to exploit oil sand. The driving force of gravity is generally acknowledged as the most-significant driving mechanism in the SAGD process. However, an increasing number of field cases have shown that pressure difference might play an important role in the process. The objective of this paper is to simulate the effects of injector/producer-pressure difference on steam-chamber evolution and SAGD production performance. A series of 2D numerical simulations was conducted using the MacKay River and Dover reservoirs in western Canada to investigate the influence of pressure difference on SAGD recovery. Meanwhile, the effects of pressure difference on oil-production rate, stable production time, and steam-chamber development were studied in detail. Moreover, by combining Darcy's law and heat conduction along with a mass balance in the reservoir, a modified mathematical model considering the effects of pressure difference is established to predict the SAGD production performance. Finally, the proposed model is validated by comparing calculated cumulative oil production and oil-production rate with the results from numerical and experimental simulations. The results indicate that the oil production first increases rapidly and then slows down when a certain pressure difference is reached. The pressure difference has strong effects on steam-chamber-rising/expansion stages. However, at the expansion stage, lower pressure difference can achieve the same effect as high pressure difference. In addition, it is shown that the steam-chamber-expansion angle is a function of pressure difference. Using this finding, a new mathematical model is established considering the modification of the expansion angle, which (Butler 1991) treated as a constant. With the proposed model, production performance such as cumulative oil production and oil-production rate can be predicted. The steam-chamber shape is redefined at the rising stage, changing from a fan-like shape to a hexagonal shape, but not the single fan-like shape defined by (Butler 1991). This shape redefinition can clearly explain why the greatest oil-production rate does not occur when the steam chamber reaches the caprock. Literature surveys show few studies on how pressure difference influences steam-chamber development and SAGD recovery. The current paper provides a modified SAGD production model and an entirely new scope for SAGD enhanced oil recovery (EOR) that makes the pressure difference a new optimizable factor in the field.

A one-dimensional model for compressible fluid flows through deformable microchannels

Fluid-structure interactions in low-Reynolds-number flows have received an increasing interest due to emerging bio-applications of deformable microfluidics. We utilize the lubrication theory and wide-beam framework to develop a one-dimensional coupled fluid-solid-mechanics model for the prediction of the characteristic behavior of compressible fluid flows through deformable microchannels. An explicit relationship is extracted for the mass flow rate as a function of pressure difference across a microchannel, undeformed channel dimensions, and properties of channel’s ceiling such as thickness, modulus of elasticity, and Poisson’s ratio. The resulting fifth-order algebraic equation is also solved numerically to obtain the pressure distribution within the microchannel. As a special case for compressible fluid flows, the characteristics of ideal gas flows are extracted from the general model. Rigid and deformable microchannels are fabricated, and the mass flow rates of air through the channels are measured under various pressure differences across the channels. The proposed model predicts the mass flow rate with an acceptable accuracy. Our experimental and theoretical results highlight the importance of fluid compressibility and microchannel deformability, demonstrating that neglecting either of them under sufficiently large pressure differences can lead to erroneous results. To the best of the authors’ knowledge, this is the first theoretical model simultaneously addressing both fluid compressibility and microchannel deformability for an equilibrium pressure-driven compressible fluid flow in microscale.

Hybrid Fickian–Darcian flow model for high pressure impregnation of fluids into porous biomaterials

Pressure-driven fluid flow is an inevitable consequence which occurs during the high pressure processing of porous biological materials confined in a fluid phase. A hybrid numerical model was adopted to simulate the mass flow of fluids into an enclosed biological porous matrix under constant high hydrostatic pressure treatments. The numerical model was based on the finite element simulation of time-dependent Fickian mass transfer represented as saturation rate of fluid flow in the unsaturated media. The Kozeny–Carman model was used for correction of relative permeability because of the pressure-induced textural changes. As a case study, the proposed methodology was applied to simulate the high pressure impregnation of apple cubes by ascorbic acid solution (1% by mass). The proposed model demonstrated the existence of a low-pressure zone in the geometrical centre of the computational domain associated with the operating pressure level which provides a sufficient driving force for liquid migration. The numerical results were corroborated through implementing gravimetric and image processing experiments. Finally, a linear flow front rate of 0.03 cm s−1 was estimated along the porous matrix, and the analytical solutions to the Darcian model were used to determine the lumped permeability as a function of pressure difference at the impregnation flow front.

Hydrogen production by steam methane reforming in a membrane reactor equipped with a Pd composite membrane deposited on a porous stainless steel

With the aim of producing hydrogen at low cost and with a high conversion efficiency, steam methane reforming (SMR) was carried out under moderate operating conditions in a Pd-based composite membrane reactor packed with a commercial Ru/Al2O3 catalyst. A Pd-based composite membrane with a thickness of 4–5 μm was prepared on a tubular stainless steel support (diameter of 12.7 mm, length of 450 mm) using electroless plating (ELP). The Pd-based composite membrane had a hydrogen permeance of 2.4 × 10−3 mol m−1 s−1 Pa−0.5 and an H2/N2 selectivity of 618 at a temperature of 823 K and a pressure difference of 10.1 kPa. The SMR test was conducted at 823 K with a steam-to-carbon ratio of 3.0 and gas hourly space velocity of 1000 h−1; increasing the pressure difference resulted in enhanced methane conversion, which reached 82% at a pressure difference of 912 kPa. To propose a guideline for membrane design, a process simulation was conducted for conversion enhancement as a function of pressure difference using Aspen HYSYS®. A stability test for SMR was conducted for ∼120 h; the methane conversion, hydrogen production rate, and gas composition were monitored. During the SMR test, the carbon monoxide concentration in the total reformed stream was <1%, indicating that a series of water gas shift reactors was not needed in our membrane reactor system.

Peristaltic Pumping of a Generalized Newtonian Fluid in an Elastic Tube

The paper investigates the peristaltic pumping of an incompressible non-Newtonian fluid in an elastic tube with long wavelengths and low Reynolds number approximations. Carreau fluid model is considered for present study to describe the peristaltic flow characteristics of non- Newtonian fluid in an elastic tube. Carreau fluid is a generalized Newtonian fluid which exhibits Newtonian behaviour for and it resembles as a power-law model at higher shear rates. For it exhibits shear-thinning property, i.e., the apparent viscosity reduces with increasing shear rate. The equations governing the fluid flow are solved with usual perturbation expansion by taking Weissenberg number as a perturbation parameter. The expressions for axial velocity, stream function and volume flow rate as function of pressure difference are derived. The effects of various pertinent parameters on variation of flux for a Carreau fluid flow through an elastic tube along with peristalsis are calculated and interpreted through graphs. The pressure rise per wavelength and shear stress distribution for different values of physical parameters are calculated and presented. Trapping phenomenon is presented graphically to understand the physical behaviour of various parameters. The difference in flux variation is examined by two different models of Rubinow and Keller (1972) and Mazumdar (1992). It is observed that in elastic tubes, the flux of Carreau fluid with peristalsis is more when the tension relation is a fifth degree polynomial as compared to exponential curve. When the power-law index or Weissenberg number and without peristalsis, the present results are similar to the observations of Rubinow and Keller (1972). Further, the relation between the function and radius of the elastic tube for both Newtonian, non-Newtonian cases are discussed graphically and these findings are identical with the investigations of Mazumdar (1992). The results observed for the present flow characteristics reports several interesting behaviours that warrant further study of physiological fluids in elastic tubes with peristalsis.

A CO2 tracer-gas method for local air leakage detection and characterization

A method for local measurement of air leakage rate is presented that can be used to accurately and quickly assess leakage rates across a surface, such as around a valve or hatch in a pressurized gas tank or a window in a building. The method uses a small local enclosure with constant volume placed about a region on the structure under investigation (e.g., a window), which is depressurized and injected with a small concentration of carbon dioxide as a tracer gas. The time variation of the pressure and carbon dioxide concentration inside the enclosure are monitored and used to quantify the leakage flow rate as a function of pressure difference. This method uses a small enclosure with internal mixing so that a quasi-steady-state condition is quickly achieved. Because of the small size of the enclosure, advanced data processing techniques are necessary to reduce uncertainty in determination of the rate of change of the carbon dioxide concentration that arises from sensor variability. Results of a laboratory demonstration of the proposed leakage detection and characterization device are reported for the problem of leakage through a circular hole in a plate with prescribed pressure differences. Experimental results from the laboratory tests are found to be in excellent agreement with results of a numerical simulation of leakage flow through a hole, as well as predictions from a number of empirical equations for this problem found in the literature.

Numerical Study of The Effect of Wall Injection on The Cavitation Phenomenon In Diesel Injector

Cavitation has an important effect on the performance of diesel injectors. It influences the nature of the fuel spray and formation of emissions. In contrast, cavitation increases the hydraulic resistance of the nozzle, creates flow instability, produces noise, and erodes the nozzle wall. In the present study, the effect of wall injection on the boundary layer separation in the cavitating and turbulent flow developing inside a diesel injector has been investigated numerically using two-phase mixture model. Simulations have been performed for different cavitation numbers, injection ratios and injection angles. Furthermore, the effects of various wall injection locations have been investigated and the results have been compared. The results indicated that for a particular injection angle, the highest discharge coefficient and the lowest number of cavitation bubbles were observed at a specific range of cavitation numbers. Also, with the injection from the orifice wall, the critical cavitation number diminishes, and only for a small interval of cavitation numbers, the discharge coefficient becomes a function of pressure difference between the two ends of injector. The idea of the current work could be a starting point for application of wall injection in injectors in order to increase the discharge coefficient, and, at the same time, to decrease the undesired effects of the cavitation phenomenon.

Analysis of Thermal Shock and Stress with Infrared Optical Domes

The development of infrared optical materials is always closely related to the research and exploration of material science. The infrared optical domes bears shock and produces stress when the infrared optical domes mounted on the missile moving at a high speed is shocked by high temperature. According to aerodynamics theory and thermo shock theory, the surge current will be transferred to optical parts through holding up layer and warms the surface of optical parts when infrared optical parts are shocked by high temperature. A compress stress is formed on the hot external surface of optical parts forms and a tension stress is formed on the internal surface or optical parts under the circumstance of the edge of optical parts being fixed. The windows of optical parts become curvature radius of lens with the function of pressure difference which can cause aberration change. The brittle fracture of material will be caused if peak stress is beyond the strength which is permitted for infrared materials. Therefore, limits to design of windows thickness is proposed in this paper.

PMMA가 코팅된 주름 구조를 갖는 다공성규소 격판을 이용한 광섬유 압력센서

In this research, fiber-optic pressure sensors were fabricated with rugate-structured porous silicon (RPS) diaphragms coated with PMMA (Polymethyl-Methacrylate). The reflectance spectrum of the PMMA/RPS diaphragm was almost the same as that of uncoated RPS diaphragm. However the mechanical strength of the PMMA/RPS diaphragm increased more than that of the uncoated diaphragm. As a result, the fiber-optic sensor fabricated with PMMA/RPS diaphragm could successfully detect more high pressure difference without diaphragm damage than the highest detectable pressure difference of the sensor with normal RPS diaphragm. The response data of the fiber-optic sensor recorded as a function of pressure difference were fitted by theoretical curves. During this process, elastic moduli of the used PMMA/RPS diaphragms were obtained numerically. The dynamic response properties of the fiber-optic sensor were also investigated under continuous variation of the pressure difference conditions.

An experimental investigation of swirl atomizer sprays

In our previous studies (Chu et al. in Heat Mass Transf 43(11):1213–1224, 2007), a theoretical model of swirl atomizers was successfully established. From the analysis, the equations for the droplet size, velocity components, the boundary layer thickness and the spray cone angle were deduced based on the fundamental governing equations. The purpose of this study is to further compare the experimental result with the theoretical one already gained by a satisfactory embodiment of series of experiments. The aim is to corroborate the analytical results of the influence of atomizer construction and controlled pressure difference on typical swirl chambers. The results provide the droplet diameter as a function of pressure difference, swirl atomizer geometry, flow rate, spray cone angle. The experimental outputs also show a good confirmation of theoretical results and can also be used for further optimization on existing swirl chambers. Based on the results obtained, an optimization methodology on characteristics of swirl atomizers is proposed with the adjustment of individual design parameter and the matching flow number.

Supersonic flow in miniature nozzles of planar configuration

Supersonic flow of nitrogen gas through miniature nozzles of planar configuration was investigated experimentally and compared with numerical simulations to assess the applicability and accuracy of the various viscous-flow models. The design Mach number of the nozzles is 3, and the inlet pressures range from 0 to 10 atm (gauge). The measured thrust of the meso nozzle with a throat area of 0.773 mm2 agreed well with the numerical solution (96%). The agreement of the micro nozzle, with a throat area of 0.0625 mm2, decreased to 80% for pressure differences beyond the design flow condition. At low-pressure differences, separated flow occurred after the shock in the nozzle, causing unstable and asymmetric velocity distributions on the nozzle exit plane. Thrust was found to be not only a function of pressure difference but also a function of the flow history. The numerical simulation was successful in modeling these effects, but at different pressures.

Gas permeability through thin-foil x-ray filters

We have measured the permeation rates of helium and water through thin-foil UV-blocking filters used in the ASTRO-E/X-Ray Spectrometer (XRS) instrument. In the XRS program, there is a concern that outgassed contaminants such as water could permeate through the outermost filter, which will be at room temperature, and freeze on the inner filters, which will be at cryogenic temperatures. The filters tested consisted of ~ 1000 A Al on ~ 1000 A of either Lexan or polyimide. Results discussed include the permeation rate as a function of pressure difference across a filter, the ratio of helium to water permeation rate, and the effect of the aluminum layer thickness on permeation.

Effect of pressure drop on performance of hollow-fiber membrane module for gas permeation

The pressure drop mainly due to viscous friction inside hollow fibers is taken into consideration by nondimensionalization and numerical simulation of governing equations. For pure gas, the permeation pressure and velocity of actual situations with a viscous fluid deviate significantly from those of the corresponding inviscid or no-pressure-drop cases. The apparent permeability estimated from the relation of permeate flow rate and pressure difference is considerably underestimated in actual situations, and more severely for the region of small pressure difference and large module length. Numerical simulation shows that the estimated permeability behaves as if it were an increasing function of pressure difference for a constant permeability and roughly a constant for a dual-sorption-type permeability, respectively. For binary-mixture permeation the cut ratio and purity of permeate stream are mainly governed by two dimensionless parameters standing for pressure drop and permeability, respectively. The cut ratio and corresponding product composition are predictable without the rigorous simulation of the governing equations.

The characteristic response curve, I(ΔP), of a 3He weak link

We report measurements of the mass current as a function of pressure difference, I(ΔP), for superfluid 3He flowing through an aperture whose dimensions are on the order of the temperature dependent coherence length. The goal of the experiment is to see to what extent this weak link behaves like a simple Josephson junction. A model has been developed which predicts I(ΔP) for the case where the weak link is analyzed as a series connection of resistance, inductance and ideal Josephson junction. This model is found to be inadequate to explain the central feature of the data, i.e. the current increases monotonically with ΔP.

Generalized hydrodynamics approach to the Knudsen problem.

It is shown that the Knudsen problem (``paradox'') can be resolved by the flow-rate formula for a non-Newtonian fluid flowing under a pressure gradient in a circular tube, as reported elsewhere. The flow-rate formula exhibits a minimum in the low-pressure regime but gives the Hagen-Poiseuille linear dependence on pressure in the high-pressure regime. Since the generalized hydrodynamic equations used for the derivation of the flow-rate formula are derived from the Boltzmann equation, the present solution of the Knudsen problem is well founded on the kinetic theory of gases. The nonlinear transport processes, which increasingly manifest themselves as the gas density decreases, are the cause for the emergence of a minimum in the flow rate for rarefied gases in circular tube flow. The entropy production and also the drag coefficient are calculated as a function of pressure difference, Reynolds number, and other parameters characteristic of the system.

Jet flutter at capillary entrance

Experiments on capillary flow of non-Newtonian liquids exhibit a pronounced jet instability at high enough flow rates. A simple criterion for the onset of instability is proposed. The physical model draws on analogies with elastic solids. The model predicts a pressure dependence that is not only a function of pressure difference.