Boiling Crisis of Nitrogen in a Channel at Low Flow Rates and High Pressures

2001 ◽  
Vol 32 (1-3) ◽  
pp. 6
Author(s):  
A. V. Klimenko ◽  
A. M. Sudarchikov ◽  
V. V. Klimenko
Keyword(s):  
High Pressures ◽  
Low Flow ◽  
Flow Rates ◽  
Boiling Crisis

High Pressure Fan Design for Biogas Plants

2009 ◽  
Author(s):  
Philipp Epple ◽  
Mihai Miclea ◽  
Harald Schmidt ◽  
Antonio Delgado ◽  
Hans Russwurm
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Thermal Power ◽  
Flow Analysis ◽  
Single Stage ◽  
Low Flow ◽  
Operating Point ◽  
Flow Rates ◽  
New Class ◽  
Biogas Plants

High pressure fans for thermal power generation stations, especially biogas plants, usually operate in a spiral casing at high pressures of about p = 12.000–15.000 Pa and low flow rates of around Q = 100–600 m3/s. The motor drive has a constant speed of 3.000 l/min. This corresponds to specific speeds of nq = 3–6 min−1, which is already beyond the conventional range of single stage radial machines. Nowadays these fans for biogas plants usually operate at higher flow rates than specified or are multiple stage radial fans. Therefore a new class of radial impellers has been developed. These single stage impellers have a unique high pressure at a low flow rate operating point. In this work several impellers of this new class have been designed and validated with a commercial Navier-Stokes solver (ANSYS CFX). The design process is described in detail. It is based on a new extended analytical and numerical design method. It is shown that the prescribed unusual operating point can be achieved with single stage radial impellers. An in detail flow analysis is given showing the fundamental flow physics of these impellers.

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

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.

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.

Hydrogen Generation in an Annular Micro-Reactor: an Experimental Investigation of Water Splitting Reaction Using Aluminum in Presence of Potassium Hydroxide

2018 ◽  
Vol 17 (2) ◽  
Author(s):  
Shyam P. Tekade ◽  
Diwakar Z. Shende ◽  
Kailas L. Wasewar
Keyword(s):  
Water Splitting ◽  
Potassium Hydroxide ◽  
Hydrogen Generation ◽  
Energy Content ◽  
Average Rate ◽  
High Energy ◽  
Low Flow ◽  
Flow Rates ◽  
Metal Aluminum ◽  
Micro Reactor

Abstract Hydrogen is one of the important non-conventional energy sources because of its high energy content and non-polluting nature of combustions. The water splitting reaction is one of the significant methods for hydrogen generation from non-fossil feeds. In the present paper, the hydrogen generation has been experimentally investigated with water splitting reaction using metal aluminum in presence of potassium hydroxide as an activator under flow conditions. The rate of hydrogen generation was reported in the annular micro- reactor of 1 mm annulus using various flow rates of aqueous 0.5 N KOH ranging from 1 ml/min to 10 ml/min. The complete conversion of aluminum was observed at all the flow rates of aqueous KOH. The hydrogen generation rate was observed to depend on the flow rate of liquid reactant flowing through the reactor. At 1 ml/min of 0.5 N KOH, hydrogen generates at an average rate of 3.36 ml/min which increases to 10.70 ml/min at 10 ml/min of aqueous KOH. The Shrinking Core Model was modified for predicting the controlling mechanism. The rate of hydrogen generation was observed to follow different controlling mechanisms on various time intervals at low flow rates of aqueous KOH. It was observed that chemical reaction controls the overall rate of hydrogen generation at higher flow rates of aqueous KOH.

Leach Behavior of SRL TDS-131 Defense Waste Glass in Water at High&Low Flow Rates

1983 ◽  
Vol 26 ◽  
Author(s):  
Aaron Barkatt ◽  
William Sousanpour ◽  
Alisa Barkatt ◽  
Morad A. Boroomand ◽  
Pedro B. Macedo
Keyword(s):  
Contact Time ◽  
Protective Layer ◽  
High Flow ◽  
Low Flow ◽  
Matrix Elements ◽  
Flow Rates ◽  
Low Concentrations ◽  
Controlling Mechanism ◽  
The Matrix ◽  
Leach Behavior

ABSTRACTLeach tests carried out on SRL TDS-131 Defense Waste Class indicate that at high flow rates the controlling mechanism is simple corrosion. The matrix elements (Si, Al) are leached out at rates similar to those of the leaching of the alkalis and of boron, and the leaching process is nearly linear with time. At slow flow rates (below 1 m/yr) leaching becomes controlled by the build-up of a protective layer. Al and most of the Si remain in the leached surface layer. The leach rates decrease in the course of the test before leveling off at constant values which are almost inversely proportional to the contact time, indicating that leachate concentrations have become solubility-limited. The low concentrations observed at this stage indicate the formation of alteration products.

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