Vaneless diffuser for low flow rate centrifugal compressor stage

One of the rational ways of creating low-emission combustion chambers is the organization of low-temperature lean combustion with external heating of the components before they are fed into the combustion chamber. When organizing lowtemperature lean combustion with large excess air ratios, problems may arise with ensuring a stable position of the flame front. Combustion stability to a large extent depends on the ratio of the average flow rate and the rate of turbulent combustion. The rate of turbulent combustion depends on the composition, pressure and temperature of the components supply and the degree of turbulence in the combustion chamber. The average flow rate depends on the excess air ratio (oxidizer and fuel consumption) and the geometric dimensions of the chamber. Earlier it was shown that when developing a low-emission combustion chamber with low-temperature lean combustion, it is advantageous to use the relative flow rate as a generalized characteristic of the intra-chamber process, which takes into account the consumption, geometric and thermodynamic parameters in the combustion chamber. This work is devoted to the analysis of stable combustion of a fuel composition natural gas + air based on the experimental data available in the public domain by the authors from the University of Michigan (USA). With the help of the methods developed by the authors, the experimental data on the limiting feed rates of the components into the atmospheric burner were processed. The limiting flow rates of air and natural gas, the limiting values of the excess air ratio, the longitudinal values of the speed of the fuel-air mixture and the limiting values of the relative flow rate are obtained and analyzed. Areas of stable combustion by the listed parameters at different degrees of air swirl are graphically presented.

Acta PaediatricaVolume 54, Issue 5 p. 439-445 Peak Flow Rate in Relation to Age, Sex and Anthropometric Measurements S. T. CHIANG, S. T. CHIANG Pulmonary Function Laboratory, Department of Medicine, National Defense Medical Center; The Cardiopulmonary Function Laboratory, Department of Medicine, Taiwan Veterans' General Hospital; and the Department of Health Education, Taiwan Normal University, Taipei, Taiwan Downstate fiIrcIira1 Ccnter 450 Clarkson Ave. Brooklyn 3, N.T. U.S.A.Search for more papers by this authorT. S. HAN, T. S. HAN Pulmonary Function Laboratory, Department of Medicine, National Defense Medical Center; The Cardiopulmonary Function Laboratory, Department of Medicine, Taiwan Veterans' General Hospital; and the Department of Health Education, Taiwan Normal University, Taipei, Taiwan Downstate fiIrcIira1 Ccnter 450 Clarkson Ave. Brooklyn 3, N.T. U.S.A.Search for more papers by this author S. T. CHIANG, S. T. CHIANG Pulmonary Function Laboratory, Department of Medicine, National Defense Medical Center; The Cardiopulmonary Function Laboratory, Department of Medicine, Taiwan Veterans' General Hospital; and the Department of Health Education, Taiwan Normal University, Taipei, Taiwan Downstate fiIrcIira1 Ccnter 450 Clarkson Ave. Brooklyn 3, N.T. U.S.A.Search for more papers by this authorT. S. HAN, T. S. HAN Pulmonary Function Laboratory, Department of Medicine, National Defense Medical Center; The Cardiopulmonary Function Laboratory, Department of Medicine, Taiwan Veterans' General Hospital; and the Department of Health Education, Taiwan Normal University, Taipei, Taiwan Downstate fiIrcIira1 Ccnter 450 Clarkson Ave. Brooklyn 3, N.T. U.S.A.Search for more papers by this author First published: September 1965 https://doi.org/10.1111/j.1651-2227.1965.tb06399.xCitations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume54, Issue5September 1965Pages 439-445 RelatedInformation

The relevance of the study is due to the need to organize stable low-emission low-temperature combustion of a lean mixture in a single-zone uncooled combustion chamber, which is an integral part of a micro-gas turbine power plant. The stable position of the flame front in combustion chambers of this type mainly depends on the ratio between the average flow rate of the combustible-air mixture and the rate of turbulent combustion. This ratio depends on many factors, the main of which are the pressure and temperature of the components supply, the excess air ratio, the pulsating speed of the gas flow and autoturbulization of the flame, the consumption of the combustible-air mixture. In this work, we investigate the effect of external heating of the components on the expansion of the lower combustion limit and on the stable position of the flame front. The aim of the study is to obtain areas of breakthrough, stable position and flame blowout when organizing low-temperature lean combustion with large values of the excess air ratio; determination of the ranges of relative flow rate, at which a stable position of the flame front is observed, using experimental data and the results of numerical modeling; development of recommendations for determining the geometric appearance of a single-zone uncooled chamber of a micro-gas turbine power plant in the presence of air and fuel gas recuperators. As a result, the dependences of the normal combustion rate on the excess air ratio were obtained taking into account the lower combustion limit, the relationship between the average flow rate and the turbulent combustion rate in various combus-tion modes, and ranges for the relative flow rate in the region of low-temperature stable combustion. Based on the developed gas-dynamic model, the geometric and gas-dynamic parameters and characteristics of turbulent combustion in the flow in the combustion chambers of micro-gas turbine power plants with a capacity of 100 and 300 kW with external heating of air and fuel gas using a turbocompressor with a compression ratio of 3.0 are determined and analyzed.

Quantitative assessment for stimulated saliva flow rate and buffering capacity in relation to different ages

In this study, the voiding phase of the micturition cycle in the anesthetized rat and guinea pig is analyzed. In both animals, voiding is characterized by an increase in intravesical pressure and then a decrease, which is accompanied by flow through the urethra and emission of urine. An ultrasonic flow probe was used in both species to measure the flow rate in relation to the intravesical pressure. In the (male) rat, so-called high-frequency oscillations are superimposed on the decreasing bladder pressure. These oscillations do not occur in the guinea pig. It is concluded that the high-frequency oscillations are caused by intermittent flow and not by variations in the bladder contraction. The intermittent flow most likely is caused by the relaxation and contraction of the external urethral sphincter and may have a function in territory marking. In our view, it is not likely that the oscillations enhance bladder emptying, as has been suggested in the literature.

The paper presents the results of CFD-calculations of a centrifugal compressor stage with a high-pressure 3D impeller and a vaneless diffuser. The stage was designed by Prof. A. M. Simonov in the Problem Laboratory of Compressor LPI according to the following design parameters: flow rate coefficient 0.080, loading factor 0.74, and the relative Mach number 0.78. Two design grids were used: 2.4 and 4.4 million cells for the sector with one blade. The entire stage was calculated with a sparser grid. Special “Stage” interface conditions are used to interface the gas-dynamic parameters at the boundary regions. The SST turbulence model was used in the calculations. The results of efficiency characteristics and work coefficient comparison showed the following: in design flow rate all three variants of the calculation overstate the loading factor by 14.3%; the calculated characteristics of polytrophic work coefficient in the staging of 360 degrees are closest to the experimental characteristics, but the absolute value is greater than 12% at a flow rate coefficient of 0.085; the maximum calculated efficiency of a stage (the circle of 360 degrees) is almost equal to the measured maximum efficiency.

Experimental investigation on adiabatic transient flow fluctuation characteristics in a 3 × 3 rod bundles subjected to rolling motion in normal pressure and temperature was carried out. Single-phase flow as well as gas parameters under stagnant liquid condition were concerned. Ranges of liquid Reynolds number and gas flow rate were 657–3 328 and 0.079–0.2 m3/h, respectively. Rolling period and amplitude range from 8 s to 16 s and from 5° to 15°, respectively. Fluctuation amplitudes of transient parameters such as flow rate, pressure drop, void fraction and gas rising velocity were focused on this study. The results indicate that flow rate and frictional pressure drop present obvious fluctuations after rolling motion, and the fluctuation amplitudes decrease with the decrease of bypass valve opening. Flow rate reaches to peak at the positive rolling amplitude and it reaches to trough at the negative rolling amplitude, and there is no obvious phase difference between the fluctuation and rolling angle. Periodical fluctuation of gas flow rate was weakened with the increase of gas inlet pressure and valve opening under experimental conditions, while the variations of void fraction and gas rising velocity were limited. Transient parameter fluctuations correspond to the rolling period at low gas flow rate, whereas their periodical fluctuations are inconspicuous in relative high gas flow rate. Amplitudes of void fraction and gas rising velocity increase with increasing the rolling amplitude while the amplitudes of void fraction and gas rising velocity are nearly invariable with the rolling period no matter if gas flow rate oscillates.

The third era in olive oil extraction sees a new generation of decanter that give the operator the possibility to chose time by time the type of working: two or three phase shifting from one solution to the other without stopping the machine and even intermediate solutions between two or three phase, making the most suitable adjustments, following olive variety, just as the machine works. A decanter centrifuge was employed during the experimental tests with variable differential speed between bowl and screw conveyor (􀀀n) and with regulation capability of oil-pulp ring levels. Thus permit to shift from three to two phase, reducing water added and discharging the following byproducts: dehydrated husk similar to that of three-phase and recovers a wet pulp that is the between the liquid phase and the solid phase. This paper aims to report the preliminary results of the energy and functional efficiency of the decanter when it works in the industrial scale plant and using a continuous method. The tests were carried out at two different flow rate values; for each flow rate the different variable differential speed between bowl and screw conveyor was varied at 15,50, 17,50 and 19,50. Quality olive, operating speed of the crusher machine and relative feed flow rate of the machine, the malaxing time and the degree of dilution of the paste, as well as the oil-pulp ring level were the same for all the trials. Irrespective of the flow rate and 􀀀n used, the machine tends to stabilize energy consumption in a very short time and values were quite similar to each other. The reductions in flow rate do not involve reductions of energy consumption indeed lead to the increase of absorption per unit mass of product worked. For all thesis studied, no significant changes of the oil recovery efficiency were found, indeed changing the flow rate and the 􀀀n a different distribution of the not extracted oil was found in the pulp and in the husk. To complete the knowledge, a set of tests changing also the oil-pulp ring levels, has been provided for the next olive oil season.

Late‐stage seismic slip in geothermal reservoirs has been shown as a potential mechanism for inducing seismic events of magnitudes to ~2.6 as late as two decades into production. We investigate the propagation of fluid pressures and thermal stresses in a prototypical geothermal reservoir containing a centrally located critically stressed fault from a doublet injector and withdrawal well to define the likelihood, timing, and magnitude of events triggered by both fluid pressures and thermal stresses. We define two bounding modes of fluid production from the reservoir. For injection at a given temperature, these bounding modes relate to either low‐ or high‐relative flow rates. At low relative dimensionless flow rates the pressure pulse travels slowly, the pressure‐driven changes in effective stress are muted, but thermal drawdown propagates through the reservoir as a distinct front. This results in the lowest likelihood of pressure‐triggered events but the largest likelihood of late‐stage thermally triggered events. Conversely, at high relative non‐dimensional flow rates the propagating pressure pulse is larger and migrates more quickly through the reservoir but the thermal drawdown is uniform across the reservoir and without the presence of a distinct thermal front, and less capable of triggering late‐stage seismicity. We evaluate the uniformity of thermal drawdown as a function of a dimensionless flow rate QD that scales with fracture spacing s (m), injection rate q (kg/s), and the distance between the injector and the target point L∗ (QD ∝ qs2/L∗). This parameter enables the reservoir characteristics to be connected with the thermal drawdown response around the fault and from that the corresponding magnitude and timing of seismicity to be determined. These results illustrate that the dimensionless temperature gradient adjacent to the fault dTD/dxD is exclusively controlled by the factor QD. More significantly, this temperature gradient correlates directly with both the likelihood and severity of triggered events, enabling the direct scaling of likely magnitudes and timing to be determined a priori and directly related to the characteristics of the reservoir. This dimensionless scaling facilitates design for an optimum QD value to yield both significant heat recovery and longevity of geothermal reservoirs while minimizing associated induced seismicity.

The results of an experimental investigation of the flow-field within a low solidity inducer at design and off design flow rate are presented and discussed; particular attention is devoted to the analysis of the flow-field, at the tip in front of the leading edge, for the flow rate close to the back-flow onset. The flow-field was measured by means of a laser doppler velocimeter at four different axial positions: upstream, within and downstream of the inducer. Axial, tangential and relative flow angle distributions, in the measuring planes, are presented for three different flow coefficients. At the lower flow rate, the plots show the presence of reverse flow in the region close to the hub downstream of the trailing edge. For the same flow rate, quite low axial velocities are detected at the tip. This is in agreement with pressure probe traverses carried out in a slightly downstream section; these measurements also show radial inward velocities of the same order of magnitude as the axial velocities. Circumferentially averaged losses were evaluated from specific work and total head rise given by pressure probes.

A centrifugal compressor requires a wide operating range as well as a high efficiency. At high pressure ratios, the impeller discharge velocity becomes transonic and effective pressure recovery in a vaned or vaneless diffuser is necessary. At high pressure ratios, a vaned diffuser is used as it has high pressure recovery, but may have a narrow operating range. At low flow, diffuser stall may trigger surge. At high flow, choking in the throat of the vanes may limit the maximum flow rate. A low solidity diffuser allows a good pressure recovery because it has vanes to guide the flow and a wide operating range as there is no geometrical throat to limit the maximum flow. In experimental studies at a pressure ratio around 4:1, the author has replaced vaned diffusers with a range of low solidity diffusers to try to broaden the operating range. The test results showed that the low solidity diffuser also chokes. In this paper, a virtual throat is defined and its existence is confirmed by flow visualization and pressure measurements. A method to select low solidity diffusers is proposed based on test data and the fundamental nature of the flow. The extension of the proposed method to the selection of a vaneless diffuser is examined and a design approach for a vaneless diffuser system to minimize surge flow rate without limiting the attainable maximum flow rate is proposed.

We have developed hydrodynamic filtration method in microfluidic device for the efficient size-selection of polydisperse lipid vesicles for giant unilamellar vesicles (GUVs), in which vesicles were formed by electroformation method. Combining pinched flow channel design before hydrodynamic filtration, GUVs were flowed and guided to filtration channels, in which small lipid vesicles were further filtered and GUV were remained in main flow channels. For increasing the selectivity of GUV in outlets, length of slit section, or relative flow rate were controlled and drain channels were introduced for avoiding back flow. At higher flow rate in a pinched flow, the fraction of recovered GUVs (>10 microm) were increased, in which most of small vesicles were filtered.

This study will be described details on influence of movable diffuser such as local reverse flow patterns and pressure fluctuation in a vaneless diffuser during unstable operation of a centrifugal compressor. The experimental study is carried out in centrifugal compressor immersed into a water reservoir. Particle Image Velocity (PIV) is used to observe a secondary flow pattern and pressure transducer is used for investigating the onset and development of rotating stall inside vaneless diffuser. The reverse flow zone observes near hub wall of impeller exit at relatively low flow rate. This reverse flow on hub side wall brings about the rotating stall. This paper be simultaneously discussed on the effects of diffuser contraction to remove local reverse flow zone near hub wall, which are including variation of flow field in a vaneless diffuser and the influence on the pressure fluctuation. A contraction due to movable diffuser three cases (40%, 53% and 86% of diffuser width) was inserted into vaneless diffuser from a shroud wall. According to the results, the rotating stall involving single and two cells is enveloped by the outer lobe of the Rossby wave. Under the rotating stall onset, the stall propagation rate is 1.25Hz, 25% of the impeller speed in the same direction as the impeller in case of no contraction. In case of 40% contraction, onset of rotating stall is not delayed. In contrast of that, onset of rotating stall is delayed in case of 53%, 87% contraction. There exist several secondary vortices inside vaneless diffuser under onset of rotating stall. The size and location of them vary as flow rate decreases.

The liquid phase oxidations of p-xylene with cobalt ion as an catalyst and acetaldehyde as its promoter were carried out in various types of bubble reactors with different producibility of gas-liquid contact surface area. By comparison of the reactor performances, the following information was obtained.Both the perforated plates and the rotary distributor accelerate the exidation of P-xylene, In the case of continuous operation, the rotary with the buMes is superior to that with the perforated plates which tend to be pluged by the sparingly soluble final product, terephthalic acid. At the moderate flow rate of acetaldehyde, the induction period ef the oxidation decreases with increasing flow rate, whereas acetaldehyde retards the reaction at the relative high flow rate.

The cover shows an optical image of co‐electrospun nanofibers of poly(vinyl pyrrolidone) (outside) and hydrophobic oil (inside), irradiated by UV light. The resulting non‐woven mats present monosized beads regularly distributed along the nanofibers in work reported by Loscarteles and co‐workers on p. 2110. Only the beads fluoresce, due to special markers added to the oil, indicating that the oil is indeed wholly encapsulated inside the beads.There are many technical situations, such as various biological or medical applications, in which a hydrophobic fluid must be encapsulated inside a hydrophilic polymer shell in the form of tiny microscopic pieces. A novel approach is presented, based on the co‐electrospinning of the hydrophilic polymer melt (outside) and the hydrophobic fluid (inside), which results in beaded micro‐ and nanofibers, such that the hydrophobic fluid is efficiently encapsulated inside the beads. For the selected fluid couple, the low liquid–liquid surface tension and the high viscosity of the melt prevent the varicose break‐up of inner fluid in the coaxial electrified jet until the very end of the co‐electrospinning process. The resulting fibers present beads filled with the hydrophobic fluid, separated by a rather uniform distance whose length depends partially on the melt flow rate. The bead diameter grows with the inner flow rate, going from a monosized to a bisized distribution. In the case under study, the maximum relative (inner‐to‐outer) flow rate is one. The diameter of the solid fibers between beads scales well with existing theories for simple electrospinning.