Net Flow Of Fluid Research Articles

Numerical analysis of the axisymmetric lattice Boltzmann method for steady and oscillatory flows in periodic geometries

Compared to more typical computational fluid dynamics techniques, the lattice Boltzmann method (LBM) is relatively new and unexplored. In recent years, axisymmetric LBM formulations, which can simulate flow in rotationally symmetric 3D geometries, have been published. Here we verify a novel axisymmetric LBM implementation using numerical criteria. Hagen–Poiseuille and Womersley flow are considered within a straight tube where analytic solutions are available. With this, we establish sufficient accuracy of the approximated flow and study the effects of changing simulation parameters (e.g. Reynolds number, Womersley number) and spatial/temporal parameters (e.g. relaxation time, mesh nodes, time steps). Furthermore, steady and oscillatory flows within a periodically-varying, longitudinally asymmetric geometry are considered. Analytic solutions are not available in these cases; however, the validity of the axisymmetric LBM for curved boundaries is ensured through convergence, mesh independence and qualitative observations. Guaranteeing reasonable flow field determination for the aformentioned geometry is relevant to a larger problem where particulate suspension is pumped back and forth through a membrane of axisymmetric micropores. In these circumstances, experiments have induced directed particle transport even though there is no net flow of the carrier fluid. Hence, our work aims to improve current numerical simulations of these flow problems to better understand the factors that facilitate particle transport.

ILEOSTOMY AND RISK OF ACUTE KIDNEY INJURY IN PATIENTS WITH CROHN'S DISEASE

Chron’s disease is an inflammatory disorder that can involve any part of GI tract but most commonly involves the small intestine. Many of the patients with Cohn’s disease end up requiring surgery, and the 10-year risk of requiring surgery is estimated to be around 50%. The most common type of surgery in patients with Crohn’s disease is ileocecal resection. More than 40,000 ileostomies are formed annually in the United States. Up to 15% of patients who receive ileostomy experience a de novo or community-onset AKI within 90 days. Oral rehydration with iso-osmolar fluids is the mainstay of outpatient management. Both hypotonic fluids, and hypertonic fluids can cause a net flow of fluid into the bowel lumen increasing the ostomy output. We aimed to study the risk of AKI within 30 days in CD patients after an ileostomy procedure.

ILEOSTOMY AND RISK OF ACUTE KIDNEY INJURY IN PATIENTS WITH CROHN'S DISEASE

Abstract BACKGROUND Chron's disease is an inflammatory disorder that can involve any part of GI tract but most commonly involves the small intestine. Many of the patients with Cohn’s disease end up requiring surgery, and the 10-year risk of requiring surgery is estimated to be around 50%. The most common type of surgery in patients with Crohn’s disease is ileocecal resection. More than 40,000 ileostomies are formed annually in the United States. Up to 15% of patients who receive ileostomy experience a de novo or community-onset AKI within 90 days. Oral rehydration with iso-osmolar fluids is the mainstay of outpatient management. Both hypotonic fluids, and hypertonic fluids can cause a net flow of fluid into the bowel lumen increasing the ostomy output. We aimed to study the risk of AKI within 30 days in CD patients after an ileostomy procedure. METHODS We collected data from the Healthcare Cost and Utilization Project- (HCUP) Nationwide Readmission Database- 2016- 2018. CD patients were identified and those who received an ileostomy procedure were identified using ICD-10 and PCS-10 codes respectively. Median and IQR were used to describe Continuous variables, and proportions were used with categorical variables. Comparison between groups was performed by Mann Whitney test for continuous variables and the Chi-Square test for Categorical variables. RESULTS We identified 214,622 index hospitalizations with CD, 3,789 of whom received an ileostomy procedure. Of those who received ileostomy, 2.1% were readmitted within 30 days for a primary diagnosis of AKI while 2.9% had 30-day readmission with a secondary diagnosis of AKI. CD patients admitted for AKI after ileostomy had a median length of stay of 14 days (IQR: 8-24). CD patients who received ileostomy had a higher rate of 30-day admission for AKI (2.1% vs. 0.3%, P <0.001) and a higher rate of 30-day readmission with a secondary diagnosis of AKI (2.9% vs. 1.5%, P <0.001) compared to CD patients who didn’t receive ileostomy during the index hospitalization. CD patients who received an ileostomy procedure and were readmitted for AKI within 30 days had an average cost of hospitalization of $140,544 (IQR: $85,072 - $242,059). CD patients admitted for AKI within 30 days after an ileostomy were older (59, IQR: 48-69 vs. 47, IQR: 33-61, P <0.001) compared to those who didn’t have a 30day readmission for AKI respectively. CONCLUSION In a nationwide cohort of patients hospitalized with Crohn’s disease, patients who received ileostomy had a significant risk of AKI within 30-days. The development of AKI was associated with significant morbidity, hospital readmission, and elevated costs of hospitalization. Further studies are needed to investigate novel measures to decrease the risk of AKI in this patient population.

Measuring intra-articular synovial fluid pressure in cadaveric scapholunate joints under radioulnar deviation

Multiple imaging modalities have been used to investigate normal wrist mechanics or detect wrist instabilities. While synovial fluid aspiration and biochemical analysis have also been used to study synovial fluid properties in normal and diseased wrist joints, this study aims to measure dynamic changes in intra-articular synovial fluid pressure of the scapholunate joint during repetitive radioulnar deviation. Cadaveric wrist specimens were mounted onto a custom-made motion simulator and moved at 0.5 Hz, from 20° ulnar deviation to 10° radial deviation and back. With guidance of a mini C-arm, a 25-gauge needle was inserted into the scapholunate joint and 0.5 mL of commercially available synovial fluid was injected into the joint. An external pressure transducer was connected to the needle and five sets of intra-articular synovial fluid pressure data were recorded over a period of 8 s. Periodical changes in intra-articular synovial fluid pressure were observed. The mean synovial fluid pressure changes of 4 specimens were 50.7 ± 9.0 Pa, 8.6 ± 3.7 Pa, 49.2 ± 8.8 Pa and 10.1 ± 2.2 Pa. We believe that the periodical changes in intra-articular synovial fluid pressure could be due to the net flow of synovial fluid and hysteresis effect of the scaphoid and lunate movements during radioulnar deviation.

Experimental Study on Net Flow Rate Generation Inside Closed Loop Mechanical Circulatory System Using Impedance Pump

This present study focused on the performance of net flow rate inside closed loop mechanical circulatory system with single and double pinching impedance pumps which generates a unidirectional flow of fluid around closed loop of soft viscoelastic tubing. The experimental setup consisted of viscoelastic tubing connected between two ends of rigid tube which was compressed rhythmically or squeezed asymmetrically at various frequencies by motorized pinching. Hence, net flow of fluid around the tubing can occur without valves. Experiment was done on two different fluid, namely Newtonian and Non-Newtonian. Result showed that the flow rate inside closed loop system for non-Newtonian fluid and Newtonian fluid were in good agreement with each other. Single pinching showed a lower flow rate compared to double pinching at higher frequency. The results could be used as a model for a new Mechanical Circulatory Support System used by cardiac patients. Factors influencing the performance of valveless impedance pump was also explained.

Quantum turbulence of bellows-drivenHe4superflow: Decay

We report on studies of quantum turbulence with second sound in superfluid $^{4}\mathrm{He}$ in which the turbulence is generated by the flow of the superfluid component through a wide square channel, the ends of which are plugged with sintered silver superleaks, the flow being generated by compression of a bellows. The superleaks ensure that there is no net flow of the normal fluid. In an earlier paper [S. Babuin et al., Phys. Rev. B 86, 134515 (2012)] we have shown that steady flow of this kind generates a density of vortex lines that is essentially identical to that generated by thermal counterflow, when the average relative velocity between the two fluids is the same. In this paper we report on studies of the temporal decay of the vortex-line density, observed when the bellows is stopped, and we compare the results with those obtained from the temporal decay of thermal counterflow remeasured in the same channel and under the same conditions. In both cases there is an initial fast decay which, for low enough initial line density, approaches for a short time the form ${t}^{\ensuremath{-}1}$ characteristic of the decay of a random vortex tangle. This is followed at late times by a slower ${t}^{\ensuremath{-}3/2}$ decay, characteristic of the decay of large ``quasiclassical'' eddies. However, in the range of investigated parameters, we observe always in the case of thermal counterflow, and only in a few cases of high steady-state velocity in superflow, an intermediate regime in which the decay either does not proceed monotonically with time or passes through a point of inflexion. This difference, established firmly by our experiments, might represent one essential ingredient for the full theoretical understanding of counterflow turbulence.

Propulsion by a helical flagellum in a capillary tube

We study the microscale propulsion of a rotating helical filament confined by a cylindrical tube, using a boundary-element method for Stokes flow that accounts for helical symmetry. We determine the effect of confinement on swimming speed and power consumption. Except for a small range of tube radii at the tightest confinements, the swimming speed at fixed rotation rate increases monotonically as the confinement becomes tighter. At fixed torque, the swimming speed and power consumption depend only on the geometry of the filament centerline, except at the smallest pitch angles for which the filament thickness plays a role. We find that the “normal” geometry of Escherichia coli flagella is optimized for swimming efficiency, independent of the degree of confinement. The efficiency peaks when the arc length of the helix within a pitch matches the circumference of the cylindrical wall. We also show that a swimming helix in a tube induces a net flow of fluid along the tube.

The Effects of Exogenous Crosslinking on Hydration and Fluid Flow in the Intervertebral Disc Subjected to Compressive Creep Loading and Unloading

In vitro study of genipin crosslinking effect on disc water content changes under compressive loading and unloading. To investigate the influence of collagen crosslinking on hydration and fluid flow in different regions of intact discs, and to evaluate the nutritional implications. Age-related reductions of nutrient supply and waste product removal are critically important factors in disc pathogenesis. Diffusion and fluid flow are blocked by subchondral bone thickening, cartilaginous endplate calcification, loss of hydrophilic proteoglycans, and clogging of anular pores by degraded matrix molecules. Previous studies demonstrated increased hydraulic permeability and macromolecular transport through crosslinked collagenous matrices. Genipin has also demonstrated the capability to increase retention of proteoglycans. A total of 57 bovine lumbar motion segments were divided randomly into phosphate buffered saline and 0.33% genipin-soaked treatment groups. Water content changes were measured using a mass-loss technique in 3 intervertebral disc regions following successive stages of compressive loading and unloading (post-treatment, after 1 hour 750 N compression, and after a subsequent 24-hour period of nominal loading). Net flow of fluid into or out of a region was determined from the percentage change in mean water content from successive groups. Fluid flow to and from the nucleus doubled with genipin crosslinking. Relative to the buffer-only controls, overall net fluid flow increased 103% in the nucleus pulposus, 36% in the inner anulus, and was 31% less in the outer anulus of genipin treated discs. The effects of genipin crosslinking on matrix permeability and proteoglycan retention can alter hydration levels and fluid flow in the intervertebral disc. Resulting increases in fluid flow, including a doubling of flow to and from the nucleus, could lead to enhanced nutritional inflow and waste product outflow for the disc, and may have implications for emerging cell-based therapies.

Case Scenario: Acute Postoperative Negative Pressure Pulmonary Edema

A 25-yr-old man (weight, 68 kg; height, 183 cm) presentedto the surgery center for excision of back and thigh schwan-nomas on the same day. The patient’s medical history wassignificant only for his history of multiple schwannoma re-sections and a history of smoking one pack of cigarettes perweek for the past 5 yr. He denied previous problems withgeneral anesthesia, and his baseline peripheral oxygen satu-ration was 99% on ambient air.Thepatientwaspremedicatedwith2mgmidazolam,andanesthesia was induced with 250 mg fentanyl, 500 mg thio-pental, and 8 mg vecuronium given for facilitation of tra-cheal intubation. He was atraumatically intubated with a7-mm ID endotracheal tube using a no. 3 Macintosh laryn-goscope (Teleflex Medical, Research Triangle Park, NC) onthe first attempt with direct visualization of the vocal cords.The patient was turned prone, bilateral breath sounds werereconfirmed, and schwannoma excisions were performed ontheleftthighandtheleftflank.Atotalof0.5mghydromor-phone was administered for analgesia. The intraoperativecoursewasunremarkable.Thepatientwashemodynamicallystable with minimal blood loss and was easily ventilated andoxygenated. A total of 500 ml lactated Ringer’s solution wasadministeredduringthe65-minsurgicalprocedure.Thepa-

Mechanical stretching forces oppose osmotic lens swelling

Mechanical stretching forces oppose osmotic lens swelling

Behavior of a viscoelastic valveless pump: a simple theory with experimental validation

BackgroundA valveless pump generates a unidirectional net flow of fluid around a closed loop of soft viscoelastic tubing that is rhythmically compressed at one point. The tubing must have at least two sections with two different stiffnesses. When a short segment of the tube is squeezed asymmetrically at certain frequencies, net flow of fluid around the loop can occur without valves.MethodsPartial differential equations for the pressures, volumes, and flows define a simple one-dimensional model of such a pump, based upon elementary physical principles. Numerical computations on a personal computer can predict measured net flows.ResultsNet flow varies with the frequency and waveform of compression used to excite the pump, as well as with the site of compression and the stiffness and viscosity of the tubing. Net flows on the order of 1 ml/sec are obtained in a water-filled loop including 46 cm of stiffer plastic (Tygon) laboratory tubing and 70 cm of softer latex rubber tubing.ConclusionsThe heretofore mysterious phenomenon of valveless pumping can be described in terms of classical Newtonian physics, in which viscous damping in the walls of the pump is included. Studying valveless pumps in the laboratory and modeling their behavior numerically provides a low-cost, engaging, and instructive exercise for research and teaching in biomedical engineering.

Arteriovenous Differences in Plasma Dilution and the Distribution Kinetics of Lactated Ringer′s Solution

Conventional concept suggests that infused crystalloid fluid is first distributed in the plasma volume and then, since the capillary permeability for fluid is very high, almost instantly equilibrates with the extracellular fluid space. We challenge whether this view is consistent with findings based on volume kinetic analysis. Fifteen volunteers received an IV infusion of 15 mL/kg of lactated Ringer's solution during 10 min. Simultaneous arterial and venous blood hemoglobin (Hgb) samples were obtained and Hgb concentrations measured. The arteriovenous (AV) difference in Hgb dilution in the forearm was determined and a volume kinetic model was fitted to the series of Hgb concentrations in arterial and venous blood. The AV difference in plasma dilution was only positive during the infusion and for 2.5 min thereafter, which represents the period of net flow of fluid from plasma to tissue. Kinetic analysis showed that volume expansion of the peripheral fluid space began to decrease 14 min (arterial blood) and 20 min (venous blood) after the infusion ended. Distribution of lactated Ringer's solution apparently occurs much faster in the forearm than in the body as a whole. Therefore, the AV difference in the arm does not accurately reflect the distribution of Ringer's solutions or whole-body changes in plasma volume. The relatively slow whole-body distribution of lactated Ringer's solution, which boosts the plasma volume expansion during and for up to 30 min after an infusion, is probably governed by a joint effect of capillary permeability and differences in tissue perfusion between body regions.

Pumping of liquids with ac voltages applied to asymmetric pairs of microelectrodes.

The net flow of electrolyte induced by an ac electric potential applied to an array of asymmetric pairs of microelectrodes has recently been reported. The interaction between the oscillating electric field and the oscillating induced charge at the diffuse double layer on the electrodes results in a steady electro-osmotic velocity distribution on top of the electrodes. This slip velocity distribution is anisotropic and produces a net flow of fluid. This paper presents a theoretical analysis of the pumping phenomena based upon an electro-osmotic model in ac fields. The electrical equations are solved numerically using the charge simulation method. The bulk flow generated by the electro-osmotic slip velocity is calculated. The dependence of the fluid flow on voltage and frequency is described and compared to experiments.

Process intensification of biodiesel production using a continuous oscillatory flow reactor

AbstractOscillatory flow reactors (OFRs) are a novel type of continuous reactor, consisting of tubes containing equally spaced orifice plate baffles. An oscillatory motion is superimposed upon the net flow of the process fluid, creating flow patterns conducive to efficient heat and mass transfer, whilst maintaining plug flow. Unlike conventional plug flow reactors, where a minimum Reynolds number must be maintained, the degree of mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length‐to‐diameter ratio. Many long residence time processes are currently performed in batch, as conventional designs of plug flow reactor prove to be impractical due to their high length‐to‐diameter ratios, which lead to problems such as high capital cost, large ‘footprint’, high pumping costs and, also control is difficult. The OFR allows these processes to be converted to continuous, thereby intensifying the process. The transesterification of various natural oils to form ‘biodiesel’ is a ‘long’ reaction, usually performed in batch. Conversion to continuous processing should improve the economics of the process, as the improved mixing should generate a better product (rendering the downstream separation processes easier), at lower residence time (reduction in reactor volume). These improvements can decrease the price of ‘biodiesel’, making it a more realistic competitor to ‘petrodiesel’. This paper shows that it is feasible to perform this reaction in an OFR at a lower residence time. The reaction was performed in a pilot‐scale plant, using rapeseed oil and methanol as the feedstocks, and NaOH as the catalyst.© 2003 Society of Chemical Industry

Formation and malformation of the vertebrate left-right axis.

Despite an externally symmetric body plan, the internal viscera of all vertebrates are asymmetric with respect to the left-right body axis. Determination of the handedness of this asymmetry is nonrandom and highly conserved among vertebrates. Errors in patterning along the left-right axis, which occur in about 1 in 10,000 human births, may result in significant morbidity and mortality. During early embryonic development, midline structures, in particular the node, coordinate patterning of the three main embryonic axes: anterior-posterior, dorsal-ventral, and left-right. A current model for specification of the handedness of left-right axis asymmetry invokes the activity of embryonic cilia in the node that create a net leftward flow of extraembryonic fluid. This flow is proposed to provide a signal for subsequent asymmetric gene expression. Signaling from the node defines patterns of asymmetric gene expression on the left and right sides of the embryo. These signals for "left" and "right" are ultimately interpreted by organ primordia during later development. Complex activating and inhibiting interactions involving TGF-beta family members, as well as homeobox transcription factors, mediate these asymmetric patterns of gene expression. The identification of the genes regulating left-right axis patterning in model organisms has resulted in the characterization of human mutations associated with left-right axis malformations.

Operation and Optimization of an Oscillatory Flow Continuous Reactor

Oscillatory flow reactors (OFRs) are a novel type of continuous reactor, in which tubes fitted with orifice plate baffles have an oscillatory motion superimposed upon the net flow of the process fluid. The combination of baffles and the oscillatory motion creates a flow pattern conducive to efficient heat and mass transfer while maintaining plug flow. Unlike conventional tubular reactors, where a minimum Reynolds number must be maintained, tube-side mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio. We have evaluated a pilot-scale OFR as a method for continuous production of sterols in an ester saponification reaction. The OFR achieved the required product specification, in a residence time one-eighth that of a full-scale batch reactor. To better understand the effect of the process variables on the reactor performance, the OFR was modeled using a tanks-in-series residence time distribution, combined with the saponification reaction kinetics, giving a “flow-conversion” model which predicted conversion based on flow and feed parameters. This simple model has led to a number of insights into the optimal operation of the OFR, one of which was that the OFR could give desired conversion selectivity at a lower reaction temperature without significant alteration to other process variables. Also, the current product specification could be surpassed, if necessary. These predictions were verified by experiment. A full-scale OFR design based on these results would be less than one-hundredth the volume of a full-scale batch reactor, assuming the same production rate and product quality. The construction of such an industrial-scale OFR for the saponification reaction is now being considered by an industrial collaborator.

Pumping of water with ac electric fields applied to asymmetric pairs of microelectrodes.

Bulk fluid flow induced by an ac electric potential with a peak voltage below the ionization potential of water is described. The potential is applied to an ionic solution with a planar array of electrodes arranged in pairs so that one edge of a large electrode is close to an opposing narrow electrode. During half the cycle, the double layer on the surface of the electrodes charges as current flows between the electrodes. The electrodes charge in a nonuniform manner producing a gradient in potential parallel to the surface of the electrodes. This gradient drives the ions in the double layer across the surface of the electrode and this in turn drags the fluid across the electrode surface. The anisotropic nature of the pairs of electrodes is used to produce a net flow of fluid. The flow produced is approximately uniform at a distance from the electrodes that is greater than the periodicity of the electrode array. The potential and frequency dependence of this flow is reported and compared to a simple model. This method of producing fluid flow differs from electrical and thermal traveling-wave techniques as only a low voltage is required and the electrode construction is much simpler.

Dynamic response of a neonatal catheter-manometer system in situ

The purpose of this study was to develop, validate, and apply a flush-pulse method to determine the dynamic response of a neonatal catheter-manometer system (CMS) in situ. In the flush-pulse method, the opened fast-flush valve of the CMS is closed; as a result, the fluid column in the CMS is impacted. This procedure can be done without affecting the net flow of infusion fluid. We validated the method in laboratory conditions by comparing 14 paired results obtained with this method to the results obtained using a generally accepted step-response method. The measurable values are the resonance frequency (fr) and the damping coefficient (delta). The analysis of the flush-pulse method in situ is complicated by the patient's blood pressure wave. A remedy for this problem that is based on the first derivative of the pressure signal has been developed. The flush-pulse method is applied 14 times in situ. In laboratory settings, the fr ranged from 12.5 to 64.0 Hz and delta ranged from 0.14 to 0.32. The correlation coefficient was 0.99 for fr and 0.91 for delta. We found four overdamped systems in situ (delta > 1). In other systems fr values between 8.5 and 41.0 Hz and delta values between 0.16 and 0.72 were observed. The dynamic response in situ appeared to deteriorate with time due to routine intensive care procedures. The flush-pulse method proved to be a valid test for determining the dynamic response. The results obtained in situ emphasize the need for a regular evaluation of the dynamic response of the neonatal CMS in order to assess the shape of the pressure wave.

A Hydrodynamic Theory of Radial-Face Mechanical Seals

The existence of a lubricating fluid film between the faces of a mechanical seal has been amply demonstrated, but the mechanisms of lubrication and sealing have yet to be convincingly established. Experimental evidence to show that mechanical seal faces are most probably lubricated by a hydrodynamic action induced by the waviness of one of the surfaces has recently been published by the authors. Following this work a modified form of the narrow bearing approximation to Reynolds' equation for hydrodynamic lubrication has been applied to an idealized wavy faced seal. The resulting theory of seal face lubrication has been extended to include radial flows in the fluid film and predicts a net inward flow of fluid which may be utilized to oppose the flow due to the sealed fluid pressure. Predicted lubrication and sealing characteristics are in substantial agreement with measured values. It is suggested that the performance of mechanical seals can be improved by giving one face an appropriately wavy surface at the time of manufacture; a number of other observations on mechanical seal design are also made.

Onset of Convection in a Porous Channel with Net Through Flow

The critical Rayleigh number for convective flow in a porous two-dimensional channel is found when there is a net flow of fluid up through the channel.