A Fast Method for Determining the Flow Conductance of Gas Microfluidic Devices

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Matteo Martinelli ◽  
Vladimir Viktorov
Keyword(s):  
Pressure Ratio ◽  
Time Derivative ◽  
Microfluidic Devices ◽  
Low Flow ◽  
Thermal Bath ◽  
Fast Method ◽  
Flow Rates ◽  
Pressure Drops ◽  
Upstream Pressure ◽  
Computerized Data Processing

This paper presents a fast method for determining the conductance of gas microfluidic devices with low flow rates and very small pressure drops starting from 30 Pa, corresponding to Re=0.3. This method is based on discharging a gas-pressurized chamber through the microfluidic device under test. The microfluidic device’s conductance can be estimated as a function of inlet pressure and the Reynolds number of the flow by recording the upstream pressure during the discharging process and calculating the time derivative of the gas pressure. The pressurized chamber is considered as an isothermal chamber. Experimental results show that a sufficiently accurate isothermal discharging process up to an upstream-to-downstream pressure ratio of 0.8 can be achieved by immersing the chamber in a thermal bath. The method presented here is very fast, requiring only a few seconds for the acquisition procedure and computerized data processing.

scholarly journals Study of Transmissivity of a Fracture Under Shearing

2018 ◽  
Author(s):  
Amir A. Mofakham ◽  
Goodarz Ahmadi ◽  
Matthew Stadelman ◽  
Kevin Shanley ◽  
Dustin Crandall
Keyword(s):  
Surface Roughness ◽  
Rock Fracture ◽  
Marcellus Shale ◽  
Ct Scans ◽  
Navier Stokes ◽  
Fast Method ◽  
Flow Rates ◽  
Pressure Drops ◽  
Fracture Pressure ◽  
Cubic Law

A Marcellus shale rock fracture was subjected to four shearing steps and at the end of each shearing step CT (computed tomography) scans with resolution of 26.8 μm were obtained. The CT images were used to generate full aperture maps of the fracture configuration at the end of each shearing phase. The pressure drops along the fracture were also measured for different water flow rates through the fracture. The aperture map of the fracture was used to generate the geometry of the fracture for use in numerical simulations. The water flows and pressure drops in the fracture were simulated with different computational methods that included the full Navier-Stokes simulation, Modified Local Cubic Law (MLCL), and Improved Cubic Law (ICL) methods. Full 3-D Navier-Stokes simulation is the most accurate computational approach which was done with use of the ANSYS-Fluent software for each shear step and different flow rates. The MLCL is a 2-D relatively fast method which is commonly used for prediction of transmissivity of fractures. ICL is a 1-D method proposed in this study in which the effects of surface roughness and tortuosity were included in calculation of the effective aperture height of fractures. To provide an understanding of the accuracy of each of these models their predictions were compared with each other and with the experimental data. Also, to examine the effects of resolution of CT scans and the surface roughness on prediction of fractures transmissivity, similar simulations were performed on average aperture maps. Here the fracture of the full resolution data was averaged over 10 × 10 pixels. Comparing the results of the average aperture maps with those of the full maps showed that the lower resolution of CT scans led to underestimation of the fracture pressure drop due to missing the small features of the fracture surfaces and smoothing out their roughness.

The Role of Turbomachinery in Enabling the Hydrogen Economy

2021 ◽  
Author(s):  
Simone Corbò ◽  
Tommaso Wolfler ◽  
Nicola Banchi ◽  
Ippolito Furgiuele ◽  
Majid Farooq
Keyword(s):  
Centrifugal Compressor ◽  
High Pressures ◽  
Pressure Ratio ◽  
Optimal Solution ◽  
Low Flow ◽  
Process Conditions ◽  
Flow Rates ◽  
Rotating Speed ◽  
High Compression ◽  
Delivery Pressure

Abstract The purpose of this paper is to present the various technological solutions optimized for the use of hydrogen, in transport, distribution, storage and utilization, analyzing their criticalities and advantages. Hydrogen compression is a fundamental step in the transportation and storage segments and continuous improvement are required. The greatest technological challenges are certainly the high pressures required for the various fields of use, the need to maintain a clean gas and to use materials that are not subject to embrittlement. The choice between the different compression technologies is based on the need for pressures and flow rates; in the case of high flow rates and low compression ratios a centrifugal compressor is preferable, while for low flow rates and high compression ratios the choice goes to piston compressors. To prevent gas contamination, dry reciprocating compressor are preferred because they allow to avoid an oil separator filter on the discharge. Current technology of reciprocating compressors allows to compress hydrogen up to 300 bar with lubricated machines, while with dry technology it is possible to reach up to 250 bar. A second criticality on reciprocating compressors is maintenance: the parts subject to wear need to be serviced every 8000 hour of operation. The use of innovative materials will increase the maintenance intervals reaching higher pressures without lubrication. To increase the pressure ratio with centrifugal compressor, it's needed to increase the rotating speed, therefore the peripheral speed, with materials suitable for H2, stages get high compression to reduce the number of compressor bodies. If the process conditions require high delivery pressures combined with large flow rates, a solution of centrifugal compressors alone would be able to manage the flow rate but not the required delivery pressure. On the other hand, the use of reciprocating compressors would require a considerable number of units. In this case, therefore, the optimal solution is to combine the two technologies, centrifugal and pistons, using the best features. A case study in which the superior performances of the hybrid solution in terms of total cost of ownership will be described and compared with traditional single technology compression train

High Flow Rate Circulating Tumor Cell Capture Device

2011 ◽  
Author(s):  
Taehyun Park ◽  
Daniel Sangwon Park ◽  
Michael C. Murphy
Keyword(s):  
Flow Rate ◽  
Early Stage ◽  
Human Peripheral Blood ◽  
Capture Rate ◽  
Microfluidic Devices ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Cell Capture ◽  
Flow Rates

Circulating tumor cells (CTCs) may become a new foundation for early stage cancer diagnosis requiring minimal patient effort [1]. This approach can overcome the limitations of current diagnostic technologies, including computer-aided tomography (CT), magnetic resonance imaging (MRI), X-ray mammography, and ultrasound (UR) which can detect only highly calcified tumors at relatively high cost. Several studies have demonstrated CTC capture using microfluidic devices to identify the presence of human breast cancer, and the CellSearch™ immunomagnetic system (Johnson & Johnson, New Brunswick, NJ) is approved by the Food and Drug Administration (FDA) for monitoring post-treatment therapy, but all of the systems reported have either a long diagnosis time or unacceptable capture rates [2, 3]. CTCs in human peripheral blood are very rare events, typically 1 ∼ 2 CTCs in 1 mL of circulating blood. This low concentration of CTCs requires a large sample volume (∼7.5 mL) to ensure detection. However, current affinity-based microfluidic devices for cell capture usually operate at very low flow rates to increase the capture rate. Therefore, developing high flow rate microfluidic devices for CTC capture is essential and challenging. A new concept of high flow rate device is introduced, simulated, and tested at high flow rates.

Experimental Evaluation of Cavitating Venturi as a Passive Flow Controller in Different Sizes

2010 ◽  
Author(s):  
Hamidreza Farshi Fasih ◽  
Hojat Ghassemi
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Water Flow Rate ◽  
Constant Mass ◽  
Flow Rates ◽  
Passive Flow ◽  
Upstream Pressure ◽  
Pressure Changes

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. A cavitating venturi is a converging-diverging nozzle with a suitable throat area for passing flow. The flow rate is a function of the upstream pressure, the throat area, the density and saturated pressure of the liquid. An experimental setup with the capability of supplying constant water flow rate, upstream pressure and temperature was designed and manufactured. Three cavitating venturies were designed and built to investigate the effect of cavitating venturi size on its mass flow rate and capability of performance venturi in wide ranges of flow rates. Three different sets of experiments were conducted to ensure the performance of the venturi to keep constant mass flow rate independent of downstream pressure. In the experiments, under different downstream and upstream pressure conditions, the mass flow rates were examined. The results show that if the ratio of downstream pressure to upstream pressure is less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever pressure ratio exceeds from 0.8, the venturi acts like an orifice.

3D CFD Approach to Predict the Performance of a Centrifugal Compressor With Surge and Choke Limits

2021 ◽  
Author(s):  
Abishek Sriram ◽  
Jeff Schlautman ◽  
Mehul Varshney ◽  
Dipak Maiti ◽  
Shyam Sundar Pasunurthi ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Low Flow ◽  
Design Stage ◽  
Test Bed ◽  
Process Industries ◽  
Flow Rates ◽  
Compressor Surge ◽  
Wear And Tear

Abstract Centrifugal compressor has widespread applications in areas such as aerospace, automotive, power and process industries and hence the prediction of its performance is crucial at the design stage. Traditional design, build and test are accelerated through numerical simulation as a virtual test bed for compressor development. In this work, a CFD methodology has been developed to predict the performance of a centrifugal compressor with its surge and choke limits. The transient, compressible flow in a moving domain with body-fitted unstructured mesh is solved in Simerics-MP. The distributed parallel solver of Simerics-MP enables to perform the complete performance map of a centrifugal compressor in a day. The phenomena of surge and choke in a centrifugal compressor is of paramount importance as it determines the limiting points of operation for a particular speed of the compressor. Surge occurs at low flow rates, and it is characterized by instabilities causing undesirable noises that lead to drop in the operational efficiency. It can also result in wear and tear of the impeller blades. Whereas choke occurs at high flow rates with no further increase in pressure and it is accompanied by aberrant vibrations. The CFD simulation predicts the instabilities occurring at surge such as pressure oscillations and flow reversal accurately, which is used as a criterion for the prediction of surge point. The choke phenomenon is characterized by fluid attaining sonic velocity in the impeller or diffuser region of the compressor. The CFD predicted results showed a fair comparison with the experimental results of pressure ratio, power, and efficiency at different speeds.

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 and Computational Analyses of Pressure Differentials in Flexible Ducts With Different Bent Angles

2007 ◽  
Author(s):  
Ray R. Taghavi ◽  
Wonjin Jin ◽  
Mario A. Medina
Keyword(s):  
Pressure Drop ◽  
Static Pressure ◽  
Complex Geometry ◽  
Analysis Data ◽  
Secondary Flows ◽  
Low Flow ◽  
Pressure Drops ◽  
Pressure Distributions ◽  
Geometrical Effects ◽  
Cfd Analyses

A set of experimental analyses was conducted to determine static pressure drops inside non-metallic flexible, spiral wire helix core ducts, with different bent angles. In addition, Computational Fluid Dynamics (CFD) solutions were performed and verified by comparing them to the experimental data. The CFD computations were carried out to produce more systematic pressure drop information through these complex-geometry ducts. The experimental setup was constructed according to ASHRAE Standard 120-1999. Five different bent angles (0, 30, 45, 60, and 90 degrees) were tested at relatively low flow rates (11 to 89 CFM). Also, two different bent radii and duct lengths were tested to study flexible duct geometrical effects on static pressure drops. FLUENT 6.2, using RANS based two equations - RNG k-ε model, was used for the CFD analyses. The experimental and CFD results showed that larger bent angles produced larger static pressure drops in the flexible ducts. CFD analysis data were found to be in relatively good agreement with the experimental results for all bent angle cases. However, the deviations became slightly larger at higher velocity regimes and at the longer test sections. Overall, static pressure drop for longer length cases were approximately 0.01in.H2O higher when compared to shorter cases because of the increase in resistance to the flow. Also, the CFD simulations captured more pronounced static pressure drops that were produced along the sharper turns. The stronger secondary flows, which resulted from higher and lower static pressure distributions in the outer and inner surfaces, respectively, contributed to these higher pressure drops.

Effect of Tip Clearance on Suction Performance at Different Flow Rates in a Mixed Flow Pump

2014 ◽  
Author(s):  
Yo Han Jung ◽  
Young Uk Min ◽  
Jin Young Kim
Keyword(s):  
Performance Test ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Low Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Flow Rates ◽  
Suction Performance ◽  
Flow Pump

This paper presents a numerical investigation of the effect of tip clearance on the suction performance and flow characteristics at different flow rates in a vertical mixed-flow pump. Numerical analyses were carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations. Steady computations were performed for three different tip clearances under noncavitating and cavitating conditions at design and off-design conditions. The pump performance test was performed for the mixed-flow pump and numerical results were validated by comparing the experimental data for a system characterized by the original tip clearance. It was shown that for large tip clearance, the head breakdown occurred earlier at the design and high flow rates. However, the head breakdown was quite delayed at low flow rate. This resulted from the cavitation structure caused by the tip leakage flow at different flow rates.

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.

EFFECT OF AXIAL CASING GROOVE GEOMETRY ON ROTOR-GROOVE INTERACTIONS IN THE TIP REGION OF A COMPRESSOR

2021 ◽  
pp. 1-54
Author(s):  
Subhra Shankha Koley ◽  
Huang Chen ◽  
Ayush Saraswat ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Low Flow ◽  
Flow Angle ◽  
Flow Rates ◽  
Piv Measurements ◽  
Tip Leakage ◽  
Large Vortex ◽  
Blade Leading Edge

Abstract This experimental study characterizes the interactions of axial casing grooves with the flow in the tip region of an axial turbomachine. The tests involve grooves with the same inlet overlapping with the rotor blade leading edge, but with different exit directions located upstream. Among them, U grooves, whose circumferential outflow opposes the blade motion, achieve a 60% reduction in stall flowrate, but degrade the efficiency around the best efficiency point (BEP) by 2%. The S grooves, whose outlets are parallel to the blade rotation, improve the stall flowrate by only 36%, but do not degrade the BEP performance. To elucidate the mechanisms involved, stereo-PIV measurements covering the tip region and interior of grooves are performed in a refractive index matched facility. At low flow rates, the inflow into both grooves, which peaks when they are aligned with the blade pressure side, rolls up into a large vortex that lingers within the groove. By design, the outflow from S grooves is circumferentially positive. For the U grooves, fast circumferentially negative outflow peaks at the base of each groove, causing substantial periodic variations in the flow angle near the blade leading edge. At BEP, interactions with both grooves become milder, and most of the tip leakage vortex remains in the passage. Interactions with the S grooves are limited hence they do not degrade the efficiency. In contrast, the inflow into and outflow from the U grooves reverses direction, causing entrainment of secondary flows, which likely contribute to the reduced BEP efficiency.

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