A Study of Optimum Conditions for Electrospinning Cellulose Acetate Nanofibers in Trifluoroacetic Acid Solvent

2013 ◽  
Vol 750-752 ◽  
pp. 323-327
Author(s):  
Edison Omollo ◽  
Chu Yang Zhang ◽  
Wan Jun Liu ◽  
Ncube Sizo
Keyword(s):  
Cellulose Acetate ◽  
Flow Rate ◽  
Trifluoroacetic Acid ◽  
Low Flow ◽  
Optimum Conditions ◽  
Flow Rates ◽  
Medium Voltage ◽  
Wide Range ◽  
Viscous Solution

Cellulose acetate (CA) nanofibers were electrospun in trifluoroacetic acid (TFA) under various conditions of concentration, voltage and dope flow rate while tip to collector distance (TCD) kept constant. Results showed that concentrations lower than 8 wt. % could only be electrospun at low flow rates. Bead free fibers were easily electrospun from higher CA concentrations 13 wt. % to 15 wt. %. Concentrations greater than 15 wt. % formed a viscous solution that could not be uniformly dispersed, thus impeding electrospinning. Medium voltage 20KV was found to produce good fibers while flow rates of 0.5ml/h and above, produced non-uniform fibers with a wide range. Average fiber diameters of 104nm and 129nm were formed at 13 wt. % and 15 wt. % (0.4ml/h, 20KV) respectively.

Air handling characteristics of five membrane oxygenators

Perfusion ◽  
1994 ◽  
Vol 9 (5) ◽  
pp. 357-362 ◽  
Author(s):  
AP Mehra ◽  
A. Akins ◽  
A. Maisuria ◽  
BE Glenville
Keyword(s):  
Flow Rate ◽  
Venous Drainage ◽  
Clinical Situation ◽  
Low Flow ◽  
Time Interval ◽  
Arterial Line ◽  
Flow Rates ◽  
Handling Characteristics ◽  
Wide Range ◽  
Membrane Oxygenators

This project looked at the potential of five different membrane oxygenators to allow passage of catastrophic quantities of air in a clinically simulated environment. All the oxygenators were set up in an identical circuit using heparinized human blood as the perfusate. The study was carried out at flow rates ranging from 1.0 to 6.0 I/min. The clinical situation of obstructed venous drainage was simulated by clamping the venous return line at each respective flow rate, while the initial level of blood in the open system hard shell venous reservoir was maintained at 600 ml. The time interval between the application of the clamp on the venous line and the first appearance of macroscopic air in the arterial line was recorded at each level of flow rate. A graph of time versus flow rate was plotted for each oxygenator type. At a flow rate of 6 I/min, the Safe II oxygenator took 20 seconds to allow passage of air after the venous line was clamped, while it took the Bentley Univox Oxygenator only 10 seconds. The Dideco oxygenator, which has a valve incorporated in its reservoir, did not, however, allow any air to be pumped forward at all. At low flow rates, some of the oxygenators offered protection against passage of air into the arterial line. Thus the Cobe oxygenator offered protection at flow rates of less than 2 I/min, the Safe II oxygenator at flow rates of up to 2.5 I/min and the Bard oxygenator at flow rates up to 3 I/min. This study has demonstrated the potential of membrane oxygenators to allow passage to clinical quantities of air into the arterial line. This study also has demonstrated that the top to bottom flow feature offers protection against passage of air at low flow rates only, while a simple valve is quite effective in preventing passage of air at a wide range of clinically relevant flow rates.

Assessment of the Use of Humidified Nasal Cannulas for Oxygen Therapy in Patients with Epistaxis

ORL ◽  
2021 ◽  
pp. 1-5
Author(s):  
Jingjing Liu ◽  
Tengfang Chen ◽  
Zhenggang Lv ◽  
Dezhong Wu
Keyword(s):  
Flow Rate ◽  
Oxygen Therapy ◽  
Preliminary Investigation ◽  
Nasal Cannula ◽  
Low Flow ◽  
Antiplatelet Drugs ◽  
Flow Rates ◽  
The Past ◽  
Oxygen Inhalation ◽  
Significant Difference

<b><i>Introduction:</i></b> In China, nasal cannula oxygen therapy is typically humidified. However, it is difficult to decide whether to suspend nasal cannula oxygen inhalation after the nosebleed has temporarily stopped. Therefore, we conducted a preliminary investigation on whether the use of humidified nasal cannulas in our hospital increases the incidence of epistaxis. <b><i>Methods:</i></b> We conducted a survey of 176,058 inpatients in our hospital and other city branches of our hospital over the past 3 years and obtained information concerning their use of humidified nasal cannulas for oxygen inhalation, nonhumidified nasal cannulas, anticoagulant and antiplatelet drugs, and oxygen inhalation flow rates. This information was compared with the data collected at consultation for epistaxis during these 3 years. <b><i>Results:</i></b> No significant difference was found between inpatients with humidified nasal cannulas and those without nasal cannula oxygen therapy in the incidence of consultations due to epistaxis (χ<sup>2</sup> = 1.007, <i>p</i> &#x3e; 0.05). The same trend was observed among hospitalized patients using anticoagulant and antiplatelet drugs (χ<sup>2</sup> = 2.082, <i>p</i> &#x3e; 0.05). Among the patients with an inhaled oxygen flow rate ≥5 L/min, the incidence of ear-nose-throat (ENT) consultations due to epistaxis was 0. No statistically significant difference was found between inpatients with a humidified oxygen inhalation flow rate &#x3c;5 L/min and those without nasal cannula oxygen therapy in the incidence of ENT consultations due to epistaxis (χ<sup>2</sup> = 0.838, <i>p</i> &#x3e; 0.05). A statistically significant difference was observed in the incidence of ENT consultations due to epistaxis between the low-flow nonhumidified nasal cannula and nonnasal cannula oxygen inhalation groups (χ<sup>2</sup> = 18.428, <i>p</i> &#x3c; 0.001). The same trend was observed between the 2 groups of low-flow humidified and low-flow nonhumidified nasal cannula oxygen inhalation (χ<sup>2</sup> = 26.194, <i>p</i> &#x3c; 0.001). <b><i>Discussion/Conclusion:</i></b> Neither high-flow humidified nasal cannula oxygen inhalation nor low-flow humidified nasal cannula oxygen inhalation will increase the incidence of recurrent or serious epistaxis complications; the same trend was observed for patients who use anticoagulant and antiplatelet drugs. Humidification during low-flow nasal cannula oxygen inhalation can prevent severe and repeated epistaxis to a certain extent.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

Subsynchronous Vibration Patterns Under Reduced Oil Supply Flow Rates

2017 ◽  
Author(s):  
B. R. Nichols ◽  
R. L. Fittro ◽  
C. P. Goyne
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Operating Conditions ◽  
System Stability ◽  
Supporting Evidence ◽  
Test Rig ◽  
Flow Rates ◽  
Oil Supply ◽  
Bending Mode ◽  
Wide Range

Many high-speed, rotating machines across a wide range of industrial applications depend on fluid film bearings to provide both static support of the rotor and to introduce stabilizing damping forces into the system through a developed hydrodynamic film wedge. Reduced oil supply flow rate to the bearings can cause cavitation, or a lack of a fully developed film layer, at the leading edge of the bearing pads. Reducing oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses due to shear forces. While machine efficiency may be improved with reduced lubricant flow, little experimental data on its effects on system stability and performance can be found in the literature. This study looks at overall system performance of a test rig operating under reduced oil supply flow rates by observing steady-state bearing performance indicators and baseline vibrational response of the shaft. The test rig used in this study was designed to be dynamically similar to a high-speed industrial compressor. It consists of a 1.55 m long, flexible rotor supported by two tilting pad bearings with a nominal diameter of 70 mm and a span of 1.2 m. The first bending mode is located at approximately 5,000 rpm. The tiling-pad bearings consist of five pads in a vintage, flooded bearing housing with a length to diameter ratio of 0.75, preload of 0.3, and a load-between-pad configuration. Tests were conducted over a number of operating speeds, ranging from 8,000 to 12,000 rpm, and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings under each condition. For nearly all operating conditions, a low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain from approximately 0–75 Hz. When the test rig was operated at running speeds above its first bending mode, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. This vibration signature is often considered a classic sign of rotordynamic instability attributed to oil whip and shaft whirl phenomena. For low and moderate load conditions, the amplitude of this 0.5x subsynchronous peak increased with decreasing oil supply flow rate at all operating speeds. Under the high load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results. Implications of reduced oil supply flow rate on system stability and operational limits are also discussed.

Effects of short blades on performance and inner flow characteristics of a low-specific-speed centrifugal pump

2017 ◽  
Vol 231 (4) ◽  
pp. 290-302 ◽  
Author(s):  
Can Kang ◽  
Ning Mao ◽  
Chen Pan ◽  
Yang Zhu ◽  
Bing Li
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Low Flow ◽  
Back Surface ◽  
Flow Rates ◽  
Pump Operation ◽  
Low Specific Speed ◽  
Specific Speed

A low-specific-speed centrifugal pump equipped with long and short blades is studied. Emphasis is placed on the pump performance and inner flow characteristics at low flow rates. Each short blade is intentionally shifted towards the back surface of the neighboring long blade, and the outlet parts of the short blades are uniformly shortened. Unsteady numerical simulation is conducted to disclose inner flow patterns associated with the modified design. Thereby, a comparison is enabled between the two schemes featured by different short blades. Both practical operation data and numerical results support that the deviation and cutting of the short blades can eliminate the positive slope of pump head curve at low flow rates. Therefore, the modification of short blades improves the pump operation stability. Due to the shortening of the outlet parts of the short blades, velocity distributions between impeller outlet and radial diffuser inlet exhibit explicitly altered circumferential flow periodicity. Pressure fluctuations in the radial diffuser are complex in terms of diversified periodicity and amplitudes. Flow rate influences pressure fluctuations in the radial diffuser considerably. As flow rate decreases, the regularity of the orbit of hydraulic loads exerted upon the impeller collapses while hydraulic loads exerted upon the short blades remain circumferentially periodic.

Cerebral Hyperperfusion Syndrome by the Numbers: Transient Focal Neurological Deficit, Imaging-Proven Focal Hyperperfusion, and High Graft Flow Rate Following Superficial Temporal Artery-Middle Cerebral Artery bypass in a Patient With Symptomatic Carotid Occlusion—Case Report

2018 ◽  
Vol 15 (6) ◽  
pp. E94-E99 ◽  
Author(s):  
Ralph Rahme ◽  
Tejaswi D Sudhakar ◽  
Marjan Alimi ◽  
Timothy G White ◽  
Rafael A Ortiz ◽  
...  
Keyword(s):  
Middle Cerebral Artery ◽  
Flow Rate ◽  
Perfusion Imaging ◽  
Superficial Temporal Artery ◽  
Temporal Artery ◽  
Low Flow ◽  
Flow Rates ◽  
Cerebral Hyperperfusion Syndrome ◽  
Cerebral Hyperperfusion ◽  
Graft Flow

Abstract BACKGROUND AND IMPORTANCE Cerebral hyperperfusion syndrome (CHS) is a well-known complication of superficial temporal artery (STA) to middle cerebral artery (MCA) bypass for ischemic cerebrovascular disease. While this argues against “low flow” in the bypass construct, flow rates in the graft have not been previously quantified in the setting of CHS. CLINICAL PRESENTATION A 58-yr-old man presented with recurrent left hemispheric ischemic strokes and fluctuating right hemiparesis and aphasia. Vascular imaging revealed left cervical internal carotid artery occlusion and perfusion imaging confirmed left hemispheric hypoperfusion. After failing to respond to maximal medical therapy, the patient underwent single-barrel STA-MCA bypass. Postoperatively, his symptoms resolved and blood pressure (BP) was strictly controlled within normal range. However, 2 d later, he developed severe expressive aphasia. CTA demonstrated a patent bypass graft and SPECT showed focal hyperperfusion in Broca's speech area. Seizure activity was ruled out. A high graft flow rate of 52 mL/min was documented by quantitative magnetic resonance angiography (MRA). Thus, the diagnosis of CHS was made and managed with strict BP control. The patient exhibited complete recovery of speech over a period of days and was discharged home. Repeat SPECT at 4 mo showed resolution of hyperperfusion and quantitative MRA demonstrated reduction of graft flow rate to 34 mL/min. CONCLUSION This is the first case of perfusion imaging-proven CHS after STA-MCA bypass, where high graft flow rates are objectively documented. Our observations constitute irrefutable evidence challenging the classic belief that the STA-MCA bypass is a low-flow construct.

Interaction between CO2 concentration and flow rate on peripheral airway resistance

1991 ◽  
Vol 70 (6) ◽  
pp. 2514-2521 ◽  
Author(s):  
A. Kaise ◽  
A. N. Freed ◽  
W. Mitzner
Keyword(s):  
Flow Rate ◽  
Airway Resistance ◽  
Co2 Concentration ◽  
Low Flow ◽  
Flow Rates ◽  
Peripheral Airway ◽  
Residual Capacity ◽  
Local Ventilation ◽  
End Tidal ◽  
The Relationship

In the present study, we investigated the interaction between CO2 concentration and rate of delivered flow on peripheral airway resistance (Rp) in the intact canine lung. Dogs were anesthetized, intubated, paralyzed, and mechanically ventilated with room air to maintain end-tidal CO2 between 4.8 and 5.2%. Using a wedged bronchoscope technique, we measured Rp at functional residual capacity. The relationship between CO2 concentration and Rp was measured at flow rates of 100 and 400 ml/min with 5, 3, 2, 1, and 0% CO2 in air. Measurements were made at the end of a 3-min exposure to each gas. At low flow rates (100 ml/min) responses to hypocapnia were small, whereas at high flow rates (400 ml/min) responses were large. The PC50 (defined as the CO2 concentration required to produce a 50% increase in Rp above baseline Rp established on 5% CO2) at 400 ml/min (1.73%) was significantly larger than that at 100 ml/min (0.38%). We also directly measured the relationship between Rp and flow rate with 5% CO2 (normocapnia) or 1% CO2 (hypocapnia) delivered into the wedged segment. Increases in normocapnic flow caused small but significant decreases in Rp. In contrast, increases in hypocapnic flow from 100 to 400 ml/min caused a 108% increase in Rp. Thus the response to hypocapnia is augmented by increasing flow rate. This interaction can be explained by a simple model that considers the effect of local ventilation-perfusion ratio and gas mixing on the local CO2 concentration at the site of peripheral airway contraction.

Determinants of flow across isolated gastroduodenal junctions of cats and rabbits

1983 ◽  
Vol 245 (2) ◽  
pp. G257-G264 ◽  
Author(s):  
K. Schulze-Delrieu ◽  
J. P. Wall
Keyword(s):  
Flow Rate ◽  
High Yield ◽  
Pressure Waves ◽  
Base Line ◽  
Tonic Activity ◽  
Flow Rates ◽  
Wide Range ◽  
Line Flow ◽  
Pressure Resistance ◽  
Unidirectional Valve

The resistance generated by the gastroduodenal junction was measured in isolated cat and rabbit preparations. Cannulas were tied into the antrum and duodenum. Yield pressures were determined by increasing the pressure in one of the cannulas until flow occurred. The junctional segment of the cat maintained a high yield pressure. Yield pressures were similar in the antroduodenal and the duodenogastric direction (12.5 +/- 5.7 vs. 14.8 5.8 cmH2O) and increased on both sides to the same degree following exposure of the preparation to 100 mM [K+] and to 10(-6) M carbachol. These experimental manipulations also led to the occurrence of pressure waves in the antral cannula. Yield pressures were diminished but not abolished by exposure of the preparation to 0 [Ca2+] solution or 10(-6) M isoproterenol. Junctional segments from the rabbit did not maintain a yield pressure. Resistance across the junctional segment of both species was also measured by channeling the outflow of one of the cannulas to a flowmeter. Over a wide range of pressures, flow rates across the junctional segment of the rabbit exceeded those across the junctional segment of the cat. Carbachol and 100 mM [K+] decreased the base-line flow and increased the amplitude of intermittent decreases of flow. Isoproterenol and 0 [Ca2+] had opposite effects. Inflation of a balloon decreased the flow rate across the rabbit but not the cat junctional segment. Flow rates across the junctional segment did not differ in the antroduodenal and duodenogastric direction. The gastroduodenal junction does not act as an unidirectional valve. Pyloric resistance relates to the structure of the pyloric segment and to phasic and tonic activity of its musculature.

Turbulence Measurements in a Centrifugal Pump With a Synchronously Orbiting Impeller

1991 ◽  
Author(s):  
Ronald D. Flack ◽  
Steven M. Miner ◽  
Ronald J. Beaudoin
Keyword(s):  
Centrifugal Pump ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Cross Product ◽  
Design Flow ◽  
Low Flow ◽  
Rate Variation ◽  
Flow Rates ◽  
The Individual ◽  
Design Flow Rate

Turbulence profiles were measured in a centrifugal pump with an impeller with backswept blades using a two directional laser velocimeter. Data presented includes radial, tangential, and cross product Reynolds stresses. Blade to blade profiles were measured at four circumferential positions and four radii within and one radius outside the four bladed impeller. The pump was tested in two configurations; with the impeller running centered within the volute, and with the impeller orbiting with a synchronous motion (ε/r2 = 0.016). Flow rates ranged from 40% to 106% of the design flow rate. Variation in profiles among the individual passages in the orbiting impeller were found. For several regions the turbulence was isotropic so that the cross product Reynolds stress was low. At low flow rates the highest cross product Reynolds stress was near the exit. At near design conditions the lowest cross product stress was near the exit, where uniform flow was also observed. Also, near the exit of the impeller the highest turbulence levels were seen near the tongue. For the design flow rate, inlet turbulence intensities were typically 9% and exit turbulence intensities were 6%. For 40% flow capacity the values increased to 18% and 19%, respectively. Large local turbulence intensities correlated with separated regions. The synchronous orbit did not increase the random turbulence, but did affect the turbulence in the individual channels in a systematic pattern.

Suppression of Self-Excited Flow Instability in a Radial Diffuser Using Rough Surfaces

2006 ◽  
Author(s):  
Saad A. Ahemd ◽  
Hayder Salem
Keyword(s):  
Flow Rate ◽  
Smooth Surface ◽  
Flow Instability ◽  
Rough Surfaces ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Flow Limit ◽  
Stable Operating

Flow instabilities in a compression system at low flow rates set the flow limit of the stable operating range. Experiments to investigate the feasibility of controlling the stall in the radial diffuser of a low speed centrifugal compressor were carried out. The technique was very simple and involved using rough surfaces (i.e., sand papers) attached to the diffuser shroud. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the mass flow rate could be reduced to 70% of its value with the smooth surface) when the rough surfaces were positioned on the diffuser shroud.

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