Numerical Investigation of Rotating Stall Characteristics and Active Stall Control in Centrifugal Compressors

2014 ◽  
Author(s):  
Taher Halawa ◽  
Mohamed Alqaradawi ◽  
Osama Badr ◽  
Mohamed S. Gadala
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotating Stall ◽  
Air Injection ◽  
Tip Leakage Flow ◽  
Centrifugal Compressors ◽  
Flow Rates ◽  
Injection Angle ◽  
Mass Flow Rates

This paper focuses on providing better view for the understanding of rotating stall phenomenon in centrifugal compressors by using numerical simulations and presents a study of the role of air injection method in delaying stall inception by using different injection parameters aiming at increasing the efficiency of this method. Results showed that the formation of stall begins at the impeller inlet due to early flow separation at low mass flow rates and due to the increase of the turbulence level and the absence of fluid orientation guidance at the vaneless region. The flow weakness causes back flow that results in the formation of the tip leakage flow which causes stall development with time. Results also showed that using air injection at specified locations at the vaneless shroud surface at injection angle of 20° and with injection mass flow rate of 1.5% of the inlet design mass flow rate, can delay the stall onset to happen at lower mass flow rate about 3.8 kg/s comparing with using injection with angle of 10° with different injection mass flow rates and also comparing with the case of no injection.

Numerical Investigation of Steady Air Injection Flow to Control Rotating Stall in Centrifugal Compressors

2014 ◽  
Author(s):  
Taher Halawa ◽  
Mohamed Alqaradawi ◽  
Osama Badr ◽  
Mohamed S. Gadala
Keyword(s):  
Kinetic Energy ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotating Stall ◽  
Air Injection ◽  
Centrifugal Compressors ◽  
Injection Angle ◽  
Injection Method ◽  
Vane Angle

This paper concerns the role of air injection method in stabilization and stall control in centrifugal compressors. The main aim is to find the best arrangement of air injection parameters such as injection angle and injection mass flow rate in order to optimize the injection performance for stabilizing the compressor and increasing the surge margin. Numerical model was built to simulate high speed transonic centrifugal compressor working at an operating point close to surge. Air was injected at 12 locations at the vaneless region between the impeller and the diffuser at shroud surface with 5 different injection angles and 3 different injection mass flow rates. Results showed that the best injection method is when using an injection angle of 30° with injection mass flow rate of 1.5% of the design mass flow rate and the worst injection method is the injection at angle of 180° (reverse tangent injection). Results also indicated that by using air injection, the number of stalled diffuser passages is decreased compared to the case of no injection. The most significant result of this paper is that using an angle of injection around twice the value of the diffuser vane angle gives the best results and makes the ideal correction of the fluid kinetic energy and fluid angle at the diffuser inlet. It was found that injecting air at an angle less than the diffuser vane angle weakens the effect of injection and doesn’t increase kinetic energy of the fluid at diffuser inlet. It was also found that injecting air at an angle larger than the diffuser vane angle corrects the fluid direction but, at the same time, decreases the fluid kinetic energy at diffuser inlet.

Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors—Additional Findings

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Taher Halawa
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Stable Condition ◽  
Tangential Direction ◽  
Air Injection ◽  
Centrifugal Compressors ◽  
Injection Angle ◽  
Stall Control

This study presents additional important findings to the results of the research paper; “Optimization of the efficiency of stall control using air injection for centrifugal compressors” published in the Journal of Engineering for Gas Turbines and Power in 2015 (Halawa, T., Gadala, M. S., Alqaradawi, M., and Badr, O., 2015, “Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072604). The aim of this study is to make a fine determination of the injection angle, which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper, which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.

An Experimental Study of the Flow of R-407C in an Adiabatic Spiral Capillary Tube

2009 ◽  
Vol 1 (4) ◽  
Author(s):  
M. K. Mittal ◽  
R. Kumar ◽  
A. Gupta
Keyword(s):  
Experimental Data ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Capillary Tube ◽  
Flow Characteristics ◽  
Flow Rates ◽  
Tube Test ◽  
Mass Flow Rates ◽  
R 134A

The objective of this study is to investigate the effect of coiling on the flow characteristics of R-407C in an adiabatic spiral capillary tube. The characteristic coiling parameter for a spiral capillary tube is the coil pitch; hence, the effect of the coil pitch on the mass flow rate of R-407C was studied on several capillary tube test sections. It was observed that the coiling of the capillary tube significantly reduced the mass flow rate of R-407C in the adiabatic spiral capillary tube. In order to quantify the effect of coiling, the experiments were also conducted for straight a capillary tube, and it was observed that the coiling of the capillary tube reduced the mass flow rate in the spiral tube in the range of 9–18% as compared with that in the straight capillary tube. A generalized nondimensional correlation for the prediction of the mass flow rates of various refrigerants was developed for the straight capillary tube on the basis of the experimental data of R-407C of the present study, and the data of R-134a, R-22, and R-410A measured by other researchers. Additionally, a refrigerant-specific correlation for the spiral capillary was also proposed on the basis of the experimental data of R-407C of the present study.

Permeability and Inertial Coefficients of Porous Media for Air Bearing Feeding Systems

2007 ◽  
Vol 129 (4) ◽  
pp. 705-711 ◽  
Author(s):  
G. Belforte ◽  
T. Raparelli ◽  
V. Viktorov ◽  
A. Trivella
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Darcy’S Law ◽  
Darcy's Law ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Thrust Pad ◽  
Gas Bearing ◽  
Forchheimer’S Law

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing and thrust pad supply systems. The porous resistances considered in the investigation were made by sintering bronze powders with different grain sizes to produce cylindrical inserts that can be installed in bearing supply devices. The paper describes the test setup and experimental results obtained for: (i) mass flow rate through single porous resistances at different upstream and downstream pressures and (ii) mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from setup (i) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from setup (ii) were compared to those from setup (i) at the same pressure differentials across the resistance.

First and second thermodynamic law analyses applied to a solar dish collector

2014 ◽  
Vol 39 (4) ◽  
Author(s):  
Vahid Madadi ◽  
Touraj Tavakoli ◽  
Amir Rahimi
Keyword(s):  
Heat Transfer ◽  
Solar Radiation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Exergy Efficiency ◽  
Exergy Destruction ◽  
Flow Rates ◽  
Energy And Exergy ◽  
Mass Flow Rates

AbstractThe energy and exergy performance of a parabolic dish collector is investigated experimentally and theoretically. The effect of receiver type, inlet temperature and mass flow rate of heat transfer fluid (HTF), receiver temperature, receiver aspect ratio and solar radiation are investigated. To evaluate the effect of the receiver aperture area on the system performance, three aperture diameters are considered. It is deduced that the fully opened receivers have the greatest exergy and thermal efficiency. The cylindrical receiver has greater energy and exergy efficiency than the conical one due to less exergy destruction. It is found that the highest exergy destruction is due to heat transfer between the sun and the receivers and counts for 35 % to 60 % of the total wasted exergy. For three selected receiver aperture diameters, the exergy efficiency is minimum for a specified HTF mass flow rate. High solar radiation allows the system to work at higher HTF inlet temperatures. To use this system in applications that need high temperatures, in cylindrical and conical receivers, the HTF mass flow rates lower than 0.05 and 0.09 kg/s are suggested, respectively. For applications that need higher amounts of energy content, higher HTF mass flow rates than the above mentioned values are recommended.

Effect of nozzle angle, turbine inlets and mass flow rate on the performance of a bladeless turbine

2019 ◽  
Vol 234 (8) ◽  
pp. 1101-1107
Author(s):  
Muhammad Ali Kamran ◽  
Shahryar Manzoor
Keyword(s):  
Experimental Study ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Working Fluid ◽  
Operating Parameters ◽  
Lower Mass ◽  
Flow Rates ◽  
Significant Parameter ◽  
Mass Flow Rates

A comprehensive experimental study on the effects of different operating parameters on the efficiency of tesla turbine is reported. A bladeless turbine with nine discs and up to four turbine inlets was used, with water as the working fluid. The parameters investigated are the nozzle angle, number of turbine inlets and mass flow rates. Contrary to earlier studies, an effort was made to determine the performance under varying loading conditions, and hence identify the complete performance characteristics. The study revealed that efficiency of the turbine increases at lower nozzle angles and higher number of turbine inlets. It was observed that the nozzle angle becomes a significant parameter when the number of turbine inlets is increased. Efficiencies up to 78% were achieved when the working fluid entered the turbine through two nozzles at an angle of 7°. It was also noted that the turbine is most efficient at the designed mass flow rate, and the efficiency reduces appreciably if lower mass flow rates are fed to the turbine. The results obtained are an important contribution to the available knowledge and can be used as design references for further studies.

scholarly journals Experimental Study of the Slit Spacing and Bed Height on the Thermal Performance of Slit-Glazed Solar Air Heater

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Seyyed Mahdi Taheri Mousavi ◽  
Fuat Egelioglu
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Ambient Air ◽  
Solar Air Heater ◽  
Outlet Temperature ◽  
Flow Rates ◽  
Air Mass ◽  
Bed Height ◽  
Mass Flow Rates

The thermal performances of three slit-glazed solar air heaters (SGSAHs) were investigated experimentally. Three SGSAHs with different bed heights (7 cm, 5 cm, and 3 cm) were fabricated with multiple glass panes used for glazing. The length, width, and thickness of each pane were 154 cm, 6 cm, and 0.4 cm, respectively. Ambient air was continuously withdrawn through the gaps between the glass panes by fans. The experiments were conducted for four different gap distances between the glass panes (0.5 mm, 1 mm, 2 mm, and 3 mm) and the air mass flow rate was varied between 0.014 kg/s and 0.057 kg/s. The effects of air mass flux on the outlet temperature and thermal efficiency were studied. For the SGSAH with bed height of 7 cm and glass pane gap distance of 0.5 mm, the highest efficiency was obtained as 82% at a mass flow rate of 0.057 kg/s and the air temperature difference between the inlet and the outlet (∆T) was maximum (27°C) when the mass flow rate was least. The results demonstrate that for lower mass flow rates and larger gaps, the performance of SGSAH with a bed height of 3 cm was better compared to that of others. However, for higher mass flow rates, the SGSAH with 7 cm bed height performed better.

Optimization of an Intermittent Slug Injection System for Sawdust Biomass Pyrolysis

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Federico M Berruti ◽  
Lorenzo Ferrante ◽  
Franco Berruti ◽  
Cedric Briens
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Feeding Tube ◽  
Operating Conditions ◽  
Injection System ◽  
Flow Rates ◽  
Pinch Valve ◽  
Mass Flow Rates ◽  
Biomass Materials

Among many other potential applications, intermittent solid slug feeders can be used to effectively inject biomass materials into fluidized bed reactors for pyrolysis. In particular, these feeders can be used to convey biomass materials that are highly cohesive to prevent plugging or undesirable reaction in the feeding tube. Although feeders of this design have been shown to work very effectively, they have not been studied in detail or optimized for the pyrolysis process. In addition, the operating conditions required to obtain predictable and consistent mass flow rates and slugs of desirable characteristics need to be established.The purpose of this work was to design, build and demonstrate the operation of a horizontal intermittent solid slug feeder and to test it with sawdust as the feed material. Sawdust is an extremely cohesive and difficult biomass to inject, but one that holds great potential as an important renewable feedstock for pyrolysis.The intermittent feeder designed for this work consisted of a pressurized vertical solids storage silo leading to a pneumatic pinch valve. The pinch valve, controlled by solenoid valves connected to a relay timer, released the feed into a horizontal feeding tube at a ninety degree angle. Within the silo, a rotating mixer prevented the bridging of solids. Intermittent pulses of gas from a control volume were fed into the horizontal feeding tube, as well as, in some cases, a continuous gas flow. The timing of the pulses was controlled by solenoid valves with a relay timer. While the pinch valve is opened, solids fall into the horizontal feeding tube forming a plug, which is then propelled by the pulsating gas into the reactor. The solid mass flow rate was experimentally measured by collecting the solids and continuously measuring the mass using a digital balance.Several variables were tested in order to optimize the performance of the feeder and the consistency of the feeding rate. They included the silo pressure, mixing rate, gas pulse pressure and volume, continuous gas mass flow rate, and the open pinch-valve time interval. The goals of this optimization were (a) to maximize the solid-to-gas ratio of mass flow rates, since the gas mass flux must be minimized to avoid wasting energy, and (b) to define operating conditions required to inject consistent biomass mass flow rates suitable for a laboratory scale pyrolysis reactor, and (c) to propose initial design criteria and a calibration procedure for intermittent solid slug feeders.The results demonstrated that the intermittent solid slug feeder system successfully achieved the desired objectives and showed how to efficiently select its optimum operating conditions.

scholarly journals ŠILUMNEŠIO DEBITO ĮTAKOS FAZINIO VIRSMO MEDŽIAGOS VEIKIMUI TYRIMAS / INVESTIGATION OF THE INFLUENCE OF MASS FLOW RATE ON PHASE CHANGE MATERIAL BEHAVIOUR

2019 ◽  
Vol 11 (0) ◽  
pp. 1-5 ◽  
Author(s):  
Saulius Pakalka ◽  
Kęstutis Valančius ◽  
Matas Damonskis
Keyword(s):  
Experimental Study ◽  
Phase Change ◽  
Mass Flow Rate ◽  
Phase Change Material ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Transfer Fluid ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Change Material

The paper presents an experimental study of the influence of heat transfer fluid (HTF) mass flow rate on phase change materials (PCM) behaviour. The experimental study was performed on a specially designed test bench. Research object – PCM based thermal energy storage unit which consists of a stainless steel tank with dual circuit tube-fin copper heat exchanger. The tank (storage volume) was filled with phase change material RT82. The experiment was carried out using three different mass flow rates of HTF: high – 0.25 kg/s, medium – 0.125 kg/s, low – 0.05 kg/s. The analysis showed that in the case of high and medium mass flow rates the melting/solidification process highly depends on the temperature of inlet HTF. Influence of mass flow rate is higher in the case of low mass flow rate.

scholarly journals The Leakage of Steam Mass Flow Rate through the Gland Seals – Influence on Turbine Produced Power

2020 ◽  
Vol 58 (1) ◽  
pp. 39-56
Author(s):  
Vedran Mrzljak ◽  
Jan Kudláček ◽  
Đerzija Begić-Hajdarević ◽  
Jelena Musulin
Keyword(s):  
Steam Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Rates ◽  
Turbine Performance ◽  
Gland Seal ◽  
Mass Flow Rates ◽  
Marine Applications ◽  
Main Operating

In this paper is presented an analysis of gland seals operation and their influence on the performance of low power steam turbine with two cylinders and steam reheating, which can be used in marine applications. Performed analysis presents a comparison of steam turbine main operating parameters when gland seals operation is neglected (as usual in the most of the literature) and when steam mass flow rates leaked through all gland seals are taken into consideration. Steam mass flow rate leakage through all gland seals reduces produced power of the whole turbine and both of its cylinders. Operation of gland seal mounted at the inlet in the first cylinder of any steam turbine (cylinder which operates with the steam of the highest pressure) has the most notable influence on the reduction of the whole turbine produced power. Gland seal mounted at the outlet of the last turbine cylinder (cylinder which operates with the steam of the lowest pressure) did not have any influence on the reduction of steam turbine produced power. In any detail analysis of a steam turbine (especially the complex turbine with multiple cylinders), gland seals operation should be considered due to their notable influence on the turbine performance.

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