scholarly journals Method for Predicting Choke Flow in Vaned Radial Diffusers Based on Thermodynamic and Gas Dynamic Criteria

1994 ◽  
Author(s):  
U. Seidel ◽  
M. Rautenberg
Keyword(s):  
Flow Rate ◽  
State Variables ◽  
Flow Conditions ◽  
Pressure Losses ◽  
Gas Dynamic ◽  
Wide Range ◽  
Method Of Solution ◽  
Mach Numbers ◽  
Dynamic Relationships ◽  
Experimental And Theoretical Studies

Conventional vaned diffusers have the disadvantage of extremely high total pressure losses in the region of choke, resulting from channel constrictions in the diffuser cascade. This effect is closely related to increasing impeller tip Mach numbers Mu,2 or increasing diffuser inlet flow Mach numbers. This aspect demands very special attention in diffuser design. On the basis of experimental and theoretical studies a hypothetical description of flow conditions within the diffusor was undertaken. The key feature of the working hypothesis is a one-dimensional loss model which is formulated in terms of thermodynamic and gas dynamic relationships. In conjunction with an appropriate application of the laws of conservation, this formulation leads to a method of solution for determining the aerodynamic conditions at the choke condition. Moreover, the method of analysis presented here is also applicable to a wide range of problems in fluid dynamics. In view of the fact that the position of the compressor choke flow rate is physically defined at the cascade inlet and the minimum cascade crossection, this work concentrates thematically on the formulation of the state variables at these locations. The method of analysis was illustrated by way of examples, and the theoretical approach was verified on the basis of experimentally determined flow conditions at choke flow rate.

INFLUENCE OF GAS-DYNAMIC TESTING RIG PIPELINES MATERIAL ON THEIR DYNAMIC CHARACTERISTICS

2021 ◽  
pp. 118-125
Author(s):  
А.В. Саврико ◽  
С.Н. Лымич ◽  
К.В. Кружаев ◽  
В.С. Левин ◽  
А.В. Москвичев
Keyword(s):  
Flow Rate ◽  
Dynamic Characteristics ◽  
Dynamic Testing ◽  
Analytical Calculation ◽  
Working Fluid ◽  
Factors Affecting ◽  
Pressure Losses ◽  
Steel Pipes ◽  
Gas Dynamic ◽  
Friction Pressure

Приведено исследование зависимости газодинамических характеристик стенда от применяемого материала трубопровода. Oсновополагающими факторами, влияющими на работоспособность стенда, являются выходные параметры - давление и расход рабочего тела, которые напрямую зависят от потерь давления на трение, создаваемого элементами стенда. Для оценки степени влияния материалов на потери стенда выбраны два вида труб: полипропиленовые и металлические. Аналитические расчёты потери давления рассматриваемых трубопроводов из различного материала показали, что трубопроводы из полипропилена предпочтительнее. Однако при проведении эксперимента получены противоположные данные, которые показали, что в полипропиленовых магистралях возможно присутствие значительного количества диафрагм: в местах пайки труб, образовавшихся в процессе изготовления. Именно этот факт способствует существенному повышению значений сопротивлений в полипропиленовых трубопроводах на 20 % по сравнению со стальными трубами, где диафрагмы отсутствуют. В результате проведения исследования был введен коэффициент, учитывающий влияние диафрагм полипропиленового трубопровода при аналитическом расчете на сопротивление. Для сохранения более точных снимаемых значений с газодинамических стендов целесообразнее использовать трубопроводы из металла, в которых рассчитать потери возможно с отклонениями до 3 % Here we give the study of the dependence of the gas-dynamic characteristics of the stand on the pipeline material used. The fundamental factors affecting the performance of the stand are the output parameters-the pressure and flow rate of the working fluid, which directly depend on the friction pressure losses created by the elements of the stand. To assess the degree of influence of materials on the losses of the stand, we selected two types of pipes: polypropylene and metal. Analytical calculations of the pressure loss of the considered pipelines made of various materials have shown that pipelines made of polypropylene are preferable. However, during the experiment, we obtained the opposite data, which showed that a significant number of diaphragms may be present in polypropylene pipelines: in the places of soldering of pipes formed during the manufacturing process. This fact contributes to a significant increase in the resistance values in polypropylene pipelines by 20 % compared to steel pipes, where there are no diaphragms. As a result of the study, we introduced a coefficient that takes into account the influence of polypropylene pipeline diaphragms in the analytical calculation of resistance. To preserve more accurate values taken from gas-dynamic stands, it is more expedient to use metal pipelines in which it is possible to calculate losses with deviations of up to 3 %

The Effect of Reynolds and Mach Number on End-Wall Profiling Performance

2010 ◽  
Author(s):  
Rau´l Va´zquez ◽  
Vicente Jerez Fidalgo
Keyword(s):  
Pressure Loss ◽  
Reynolds Numbers ◽  
Stagnation Pressure ◽  
Airfoil Surface ◽  
Pressure Losses ◽  
Physical Mechanisms ◽  
Wide Range ◽  
Mach Numbers ◽  
Turbine Airfoils ◽  
End Wall

This paper shows an experimental back-to-back comparison carried out between two annular cascades of identical turbine airfoils operating at the same flow conditions; one of them had axysimmetric endwalls and, the other, non-axysimmetric. The annular cascades consisted of 100 high lift, high aspect ratio and high turning blades that are characteristic of modern low pressure (LP) turbines. Upstream and downstream data were obtained with miniature pneumatic probes. The static pressure fields on the airfoil surface and the end-walls were measured with more than 200 sensors. The motivation of this work is to improve the understanding of profiled end-wall performance in the following three aspects: A. Explore the performance of profiled non-axysimmetric end-walls at off design conditions, namely its sensitivity to Reynolds and Mach numbers, analyzing how the turbine characteristics are modified. For that purpose, the experiment was carried out for a wide range of Reynolds numbers, extending from 120k to 315k, and exit Mach numbers, extending from 0.5 to 0.9. B. Determine experimentally the stagnation pressure loss improvement due to profiled non-axysimmetric end-walls in a relevant environment. C. Investigate further the physical mechanisms that govern the variation of stagnation pressure losses of profiled end-walls. CFD results are presented and are compared with experimental results in terms of total pressure loss, helicity and SKEH.

scholarly journals Physical and Mathematical Modeling of the Interaction of Water Droplets and High-Speed Gas Flow

2021 ◽  
Vol 11 (23) ◽  
pp. 11146
Author(s):  
Aleksandr Minko ◽  
Oleg Guskov ◽  
Konstantin Arefyev ◽  
Andrey Saveliev
Keyword(s):  
Mathematical Modeling ◽  
High Speed ◽  
Gas Flow ◽  
Reynolds Numbers ◽  
Droplet Breakup ◽  
Flow Conditions ◽  
Two Phase ◽  
Gas Dynamic ◽  
Physical And Mathematical Modeling ◽  
Mach Numbers

Present work is devoted to physical and mathematical modeling of the secondary disintegration of a liquid jet and gas-dynamic breakup of droplets in high-speed air flows. In this work the analysis of the experiments of water droplet breakup in the supersonic flow with Mach numbers up to M = 3 was carried out. The influence of shock wave presence in the flow on the intensity of droplets gas-dynamic breakup is shown. A developed empirical model is presented. It allows to predict the distribution of droplet diameters and velocities depending on the gas flow conditions, as well as the physical properties of the liquid. The effect of the Weber and Reynolds numbers on the rate of droplets gas-dynamic breakup at various Mach numbers is shown. The obtained data can be useful in the development of mathematical models for the numerical simulation of two-phase flows in the combined Lagrange-Euler formulation.

The generation of feeding currents by flagellar motions

1979 ◽  
Vol 94 (2) ◽  
pp. 305-330 ◽  
Author(s):  
J. J. L. Higdon
Keyword(s):  
Cell Body ◽  
Flow Rate ◽  
Optimum Number ◽  
Mean Flow ◽  
Maximum Slope ◽  
Approximate Form ◽  
Wide Range ◽  
Method Of Solution ◽  
Optimal Efficiency ◽  
Calculated Velocity

The use of flagella by sessile organisms to generate feeding currents is analysed. The organism consists of a spherical cell body (radius A) to which a smooth flagellum (radius a, length L) is attached radially. The cell body is a height H above the plane substrate to which it is rigidly attached via a stalk. The organism propagates plane sinusoidal waves (amplitude α, wavenumber k) from base to tip. The flagellum is represented by distributions of stokeslets and dipoles along its centre-line. The cell body and substrate are modelled by employing an approximate form of the Green's function for the sphere in the half space. The error terms in the model are O(a/L) and O(A2/H2). The analysis and method of solution are adapted from Higdon (1979).The mean flow rate and power consumption are calculated for a wide range of parameters. Optimal motions are determined with the criterion of minimizing the power required to achieve a given flow rate. The optimum wave has maximum slope in the range 2 < αk < 2·5 (compared to the optimum value αk = 1 for swimming). The optimum number of waves Nλ increases linearly with flagellar length for L/A > 10 and is approximately constant, Nλ = 1, for shorter flagella. The optimum flagellar length is in the range 5 < L/A < 10. There is no optimum flagellar radius a/A. For optimal efficiency, the height H should be greater than or equal to the length of the flagellum.The optimum values of the parameters are compared to the values for the choano-flagellates described by Lapage (1925) and Sleigh (1964). Excellent agreement is found between the predicted optima and the observed values. The calculated velocity field closely resembles the flow described by Sleigh and Lapage.

The Stabilizing Effect of Pre-Equilibria: A Trifluoromethyl Complex as CF2 Reservoir in Catalytic Olefin Difluorocarbenation

2020 ◽  
Author(s):  
Thomas Louis-Goff ◽  
Huu Vinh Trinh ◽  
Eileen Chen ◽  
Arnold L. Rheingold ◽  
Christian Ehm ◽  
...  
Keyword(s):  
High Selectivity ◽  
Side Reactions ◽  
Theoretical Studies ◽  
Attractive Feature ◽  
Catalyst Recovery ◽  
Wide Range ◽  
Stabilizing Effect ◽  
Experimental And Theoretical Studies

A new, efficient, catalytic difluorocarbenation of olefins to give 1,1-difluorocyclopropanes is presented. The catalyst, an organobismuth complex, uses TMSCF<sub>3</sub> as a stoichiometric difluorocarbene source. We demonstrate both the viability and robustness of this reaction over a wide range of alkenes and alkynes, including electron-poor alkenes, to generate the corresponding 1,1-difluorocyclopropanes and 1,1-difluorocyclopropenes. Ease of catalyst recovery from the reaction mixture is another attractive feature of this method. In depth experimental and theoretical studies showed that the key difluorocarbene-generating step proceeds through a bismuth non-redox synchronous mechanism generating a highly reactive free CF<sub>2</sub> in an endergonic pre-equilibrium. It is the reversibility when generating the difluorocarbene that accounts for the high selectivity, while minimizing CF<sub>2</sub>-recombination side-reactions.

Calculation of plasma centrifugal spraying parameters of fine granules of heat-resistant nickel alloys

2020 ◽  
pp. 471-474
Author(s):  
M.G. Yagodin ◽  
E.I. Starovoytenko
Keyword(s):  
Powder Metallurgy ◽  
Nickel Alloys ◽  
Dynamic Pressure ◽  
Calculated Data ◽  
Powder Size ◽  
Metal Powders ◽  
Heat Resistant ◽  
Gas Dynamic ◽  
Spraying Parameters ◽  
Wide Range

The equipment for the production of wide range of metal powders purposed for powder metallurgy is described. The possibility for producing of powders by the plasma centrifugal spraying is considered taking into account the gas dynamic pressure. The calculated data on the powder size for different materials are given.

Hydraulic model of a water cooling system in a chemical plant

1988 ◽  
Vol 53 (4) ◽  
pp. 788-806
Author(s):  
Miloslav Hošťálek ◽  
Jiří Výborný ◽  
František Madron
Keyword(s):  
Flow Rate ◽  
Cooling System ◽  
Cooling Water ◽  
Graph Algorithm ◽  
Automatic Generation ◽  
Hydraulic Calculation ◽  
Return Flow ◽  
Flow Rates ◽  
Pressure Losses ◽  
Controlled Flow

Steady state hydraulic calculation has been described of an extensive pipeline network based on a new graph algorithm for setting up and decomposition of balance equations of the model. The parameters of the model are characteristics of individual sections of the network (pumps, pipes, and heat exchangers with armatures). In case of sections with controlled flow rate (variable characteristic), or sections with measured flow rate, the flow rates are direct inputs. The interactions of the network with the surroundings are accounted for by appropriate sources and sinks of individual nodes. The result of the calculation is the knowledge of all flow rates and pressure losses in the network. Automatic generation of the model equations utilizes an efficient (vector) fixing of the network topology and predominantly logical, not numerical operations based on the graph theory. The calculation proper utilizes a modification of the model by the method of linearization of characteristics, while the properties of the modified set of equations permit further decrease of the requirements on the computer. The described approach is suitable for the solution of practical problems even on lower category personal computers. The calculations are illustrated on an example of a simple network with uncontrolled and controlled flow rates of cooling water while one of the sections of the network is also a gravitational return flow of the cooling water.

scholarly journals Effect of Fluid Flow on the Corrosion Performance of as-Cast and Heat-Treated Nickel Aluminum Bronze Alloy (UNS C95800) in Saline Solution

2021 ◽  
Vol 2 (1) ◽  
pp. 61-77
Author(s):  
Hamid Reza Jafari ◽  
Ali Davoodi ◽  
Saman Hosseinpour
Keyword(s):  
Corrosion Resistance ◽  
Corrosion Behavior ◽  
Flow Rate ◽  
Solution Temperature ◽  
Aluminum Bronze ◽  
Nickel Aluminum ◽  
Nacl Solution ◽  
Flow Conditions ◽  
Heat Treated ◽  
Nickel Aluminum Bronze

In this work, the corrosion behavior and surface reactivity of as-cast and heat-treated nickel aluminum bronze casting alloy (UNS C95800) in 3.5 wt% NaCl solution is investigated under stagnant and flow conditions. Increasing flow rate conditions are simulated using a rotating disk electrode from 0 to 9000 revolutions per minute (rpm). Optical micrographs confirm the decrease in the phase fraction of corrosion-sensitive β phase in the microstructure of C95800 after annealing, which, in turn, enhances the corrosion resistance of the alloy. Electrochemical studies including open circuit potentiometry, potentiodynamic polarization, and electrochemical impedance spectroscopy are performed to assess the effect of flow rate and heat treatment on the corrosion of samples at 25 and 40 °C in 3.5 wt% NaCl solution. For both as-cast and heat-treated samples, increasing the flow rate (i.e., electrode rotating rate) linearly reduces the corrosion resistance, indicating that the metal dissolution rate is significantly affected by hydrodynamic flow. Increasing the solution temperature negatively impacts the corrosion behavior of the as-cast and heat-treated samples at all flow conditions.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Haemorheological Effects on Thrombocyte Adhesion and Aggregation Found Under Controlled Flow Conditions

1979 ◽  
Author(s):  
P.D. Richardson
Keyword(s):  
Rate Of Change ◽  
Continuous Observation ◽  
Flow Conditions ◽  
Wide Range ◽  
Stream Migration ◽  
Local Shear ◽  
Videotape Recording ◽  
Controlled Flow ◽  
A Site

Thrombocyte adhesion and aggregation in a vessel or on a chamber wall can be measured most readily if the flow is controlled and steady, and continuous observation is used. Videotape recording is very helpful for subsequent quantification of the dynamics. The adhesion of each thrombocyte can occur for a finite time interval:this interval has been observed to have a wide range. Platelets which escape often leave open a site which attracts other platelets preferentially. The rate of change of adhesion density (platelets/mm2) is affected by the local shear rate and the shear history upstream. Aggregation is affected similarly, and also proceeds with some platelet turnover. The role of erythrocytes in facilitating cross-stream migration of thrombocytes (which can enhance the growth rate of large thrombi) appears due in part to convective flow fields induced by the motion of erythrocytes in a shear flow, which can be demonstrated theoretically and experimentally. Observations of the phenomenlogy of adhesion and aggregation under controlled flow conditions and comparison with fLu id-dynamically based theory allows representation in terras of a small number of parameters with prospects of prediction of behaviour over a wide range of haemodynamic conditions; biochemical changes lead to changes in values of the parameters, so that activating agents and inhibiting agents modify values in different directions.

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