Centrifugal Stage Research Articles

Mathematical models for optimization of the centrifugal stage of a refrigerating compressor

The authors describe a general approach to the creating of mathematical models of energy and head losses in the flow part of the centrifugal compressor. The mathematical model of the pressure head and efficiency of a two-section stage proposed in this paper is meant for determining its characteristics for the assigned geometric dimensions and for optimizing by variance calculations. Characteristic points on the plot of velocity distribution over the margin of the vanes of the impeller and the diffuser of the centrifugal stage with a combined diffuser are presented. To assess the reliability of the mathematical model the authors compared some calculated data with the experimental ones.

Isolation of hemopoietic pluripotent stem cells from spleens of thiamphenicol-pretreated mice

The present report describes the bulk isolation of pluripotent stem cells (PSC) (assayed as day-9 CFU-S, colony-forming-units-spleen). As starting material, spleens, highly enriched with PSC, were used from mice that were bled and treated with thiamphenicol (TAP). In subjecting the spleen cells to a two-stage centrifugal elutriation procedure and a subsequent Percoll gradient centrifugation stage a 30-fold enrichment in the CFU-S concentration was achieved. The splenic PSC seeded with a characteristic low efficiency in the spleens of irradiated mice ( f = 2%). Correcting the colony number for this, we obtained a cell mixture consisting of 88% PSC, contaminated with 4% committed precursor cells and about 10% ganuloid cells.

Calculation of axial forces in the centrifugal stage with a view to the curving of the flow at the inlet

The authors propose a new system of equations for calculating the axial forces acting on the rotors of centrifugal compressors, taking into account the radial nonuniformity of the flow parameters at the inlet. They conclude that when the operation of a single-phase centrifugal blower is controlled by an inlet guide vane, the range of the change of axial force is approximately twice as large as the nominal range. Therefore, in practical calculations the additional component of the total axial force in the stage arising in consequence of the curving of the flow at the inlet has to be taken into account.

Computation of axial forces in the centrifugal stage with allowance for leakage through seals

This article considers fluid leakage due to the lack of airtightness in the seals of high-pressure centrifugal compressors. Disregard of this leakage may result in the wear and even the failure of support bearings. The proposed method for computing the axial forces with allowance for radial leakage of fluid is based on the combination of computational-theoretical analysis and experimental data. The flow in the chamber is axisymmetric and the fluid is incompressible. The leakage coefficient depends on the pressure in advance of the seal. Includes a diagram showing pressures and additional forces acting on outer surfaces of rotor disks.

18:1 pressure ratio axial/centrifugal compressor demonstration program

The results of a component technology demonstration program to design and test an advanced axial/centrifugal compressor for industrial gas turbine applications are presented. Objectives were to demonstrate 18:1 pressure ratio at 90% polytropic efficiency with 80% fewer parts as compared to current industrial gas turbine compressors. The compressor design approach utilizes low-aspect-ratio/highly loaded axial compressor blading combined with a centrifugal backend stage to achieve the 18:1 design pressure ratio on a single spool in only seven stages. Demonstrated design point performance was 91.5% polytropic efficiency at 14% stall margin and 70 Ibm/s flow. This represents the highest known demonstrated performance in this pressure ratio and flow class. The results are particularly significant in that they were accomplished at axial compressor aerodynamic loading levels approximately 15% above current production engine design practice.

In-line unit for large-scale condensate pumps

An in-line unit has been tested in the VNIIAEN for a screw centrifugal stage, Three alternative preincorporated axial impellers designed by the Voznesenskii-Pekin method for the sleeve action were tested with two types of centrifugal impellers. The optimum values of relative vortex current, mean peripheral component of the absolute velocity, and mean peripheral velocity are obtained. The existence of an optimum value for the mean relative vortex is explained. Results of tests lead to the design of a third alternative CI and AI No. 4 as specified. As a result of the tests, a screw centrifugal state with high energy and cavitational indices, a unit needed for the development of large scale condensate pumps, was obtained.

Effect of Gaseous Fluids on Submersible Pump Performance

Summary This paper reports the results of two independent laboratory investigations on the effect of free gas on centrifugal submersible pump performance. One investigation used air and water as the working fluids, with the free gas allowed to escape out an annulus. A separate investigation was conducted using diesel fuel and CO as the working fluids with intake pressures up to 400 psi. The results of the two investigations agreed in general at low pressures, where gas volumes exceeding 10% by total volume began to cause serious reduction in pump performance curves. Better performance at higher pressures with the same gas volumes present was found to occur at higher pump intake pressures. Introduction The presence of free gas has been recognized as having, in general, a detrimental effect on the performance of a submersible centrifugal pump. This paper describes two independent test programs undertaken to define the effect of the gas on the performance of this type pump. The effects of the free gas show up as a deterioration of the head-capacity curve, such as areas of unstable head production, and effects similar to cavitation at higher flow rates. Depending on the amount of free gas through the pump, these effects may vary from slight interference to gas locking. Gas interference is indicated on the surface amp chart by rapid variation of the motor loading. Gas locking occurs when the pump ingests too much gas and actually stops pumping because its head (or pressure) production is drastically decreased. This causes the motor to unload and to shut down because of excessive underload (control protection). When designing an electric submersible pump for a gassy application, it is very desirable to know the amount of free gas the pump can tolerate and to compare this to the downhole gas conditions. Test Facilities and Procedures Test facilities, methods of data collection and reduction, and results are presented for two independent test programs. Tests conducted by Amoco Production Research Co. involved using water and air. A separate program was conducted for Centrilift Hughes Inc. at the R.C. Ingersoll Research Center using diesel fuel and CO. In both programs, the purpose of the tests, was to define the performance of typical submersible centrifugal pump stages when free gas volumes were introduced at the pump suction under various flow and pressure conditions. If this information is available and can be shown to be extended to field use in the petroleum industry, improved pump design or selection of gas separation equipment can be made for the many cases where pumps are needed to handle gassy fluids. The two test facilities and programs are described, and results from each are presented and discussed. Facilities and Procedures for Air/Water Tests The test facility at Amoco was an aboveground installation, in which the flow patterns and distribution of air volumes could be viewed. For simplicity, water and air were chosen as working fluids. A schematic of the test loop is shown in Fig. 1. The pump housing, containing five Centrilift I-42 pump stages, was installed in an 8-in.-OD, 7-in.-ID plexiglass tube. JPT P. 2922^

Elevation of efficiency of feed pumps for large power generators

The elevation of key parameters of feed pumps raises the power input, the shaft diameter, and the hub ratio of the rotor. Data obtained during the development of a flow part by VNIIAEN for a turbopump can be used for designing centrifugal stages with a specific given speed. Guide devices (GD) were built, and the key geometric characterizations are shown. The guide test results indicate that the efficiency of the stage with GD 2 is 1-1.5% higher than that of the stage with GD 1 because of the increase of the diffuser expansion angle in the axial direction. Investigations performed show that this new stage device is more efficient than current well-known designs because of the uniaxial diffuser channels.

Effectiveness of using jet control blowers to change the characteristics of a centrifugal stage

Jet blowers that are used to change the twist of a stream at the inlet to a turbomachine rotor by blasting the stream at an angle to its main flow possess a series of advantages over control devices with rotating vanes. In order to make a preliminary evaluation of the effectiveness of jet blowers, several models of control devices of axial and radial configuration were produced and tested. The gas-dynamic characteristics of the axial stage were obtained for fixed mounting angles and relative injection gas flow rate, regulating operating modes of the stage by changing the resistance of the circuit with the aid of barriers in the exit sleeve. In the radial stage, the characteristics were varied by varying the value of the gas flow rate with a constant value of the mounting angle. An analysis of the static blast tests of the first axial stage modification showed that the gas current does not flow satisfactorily around an array of cylindrical elements because of the high frontal resistance. The maximum efficiencies and head coefficients for the two-level stage turn out to be 1-2% higher than in the single-level devices and the flow rate control limits are not changed. It ismore » concluded that the design modifications of the jet blowers are as a whole less efficient than vane devices.« less

Disk losses in centrifugal stages with allowance for leakage in packings

This article considers the disk-liquid-wall surface system keeping in view the whole liquid volume confined between the disk, wall, and reference sections. It applies the well-known theorem of mechanics which claims that the sum of power of all external and internal forces applied to this system is equal to the time derivative of the whole kinetic energy of the system. It reports that at the Special Design Office for Compressors (SKBK) the method developed for calculating disk losses has been used in the calculation of the centrifugal stage of the compressor on a computer.

Simplified modification of the macrophage migration inhibition method in mice

Simplified modification of the macrophage migration inhibition method is suggested. The simplification is achieved by omitting the capillary centrifugation stage.

Effect of the rotor-blade: Armature-vane ratio on the pressure pulse level in a centrifugal pump stage

Effect of the rotor-blade: Armature-vane ratio on the pressure pulse level in a centrifugal pump stage

Investigation into the head characteristic of a sectional low-speed centrifugal pump stage

Investigation into the head characteristic of a sectional low-speed centrifugal pump stage

Hydraulically driven installation for investigating the operation of submerged centrifugal pump stages

Hydraulically driven installation for investigating the operation of submerged centrifugal pump stages

Calculation of heat transfer in the elements of a centrifugal compression stage with internal cooling

Calculation of heat transfer in the elements of a centrifugal compression stage with internal cooling

Evaluation of a High Hub/Tip Ratio Centrifugal Compressor

A centrifugal compressor stage with an unusually high inlet hub/tip ratio of 0.87 was designed for a pressure ratio of 2.0 at a corrected mass flow of 2.45 lb per sec. The geometry was selected so that the centrifugal stage could replace several of the last stages of a multistage axial compressor. The stage was tested with two diffuser schemes. One diffuser consisted of a series of drilled conical pipes, whereas the other employed multirow vaned cascades. Sea level aerodynamic tests of the compressor stage with each diffuser showed a peak total-to-total efficiency at design speed of 83.8 percent for the pipe diffuser and 82.9 percent for the vaned cascade diffuser. Additional tests were conducted with a vaneless diffuser to determine effects of impeller discharge tip clearance and inlet prewhirl on impeller performance.

Gas-core nuclear rocket engine.

The major components of a gas-core nuclear rocket engine are studied, on the assumption of satisfactory hydrodynamic containment of the core. The core cavity was assumed to have a diameter and length of 60 in., a hydrogen cavity temperature of 12,000°R, a hydrogen flow rate of 200 Ib/sec, and a chamber pressure of 10,000 psia. A topping cycle was chosen to supply energy at a turbine inlet temperature of 2975°R. The turbopump has six impulse turbine stages and four centrifugal pump stages to deliver propellant at 15,000 psia. The modified plug-type nozzle must have regenerative and transpiration cooling. Its tungsten tubes must operate at about 4000°R, and seed must be injected in the exhaust stream along the walls to absorb thermal radiation. The pressure vessel requires cooling of the internal walls, and it can be made of titanium. The resulting engine has an Isp of 1730 sec with a thrust of 405,000 Ib and a weight of 92,000 Ib. The turbopump and pressure vessel look attractive for these service requirements though they call for advances in the state-of-the-art in order to be completely successful.

The Turbomeca Astazou XIV Powerplant

THE Sociéte Turbomeca Astazou, shown in the cutaway drawing, fig. 2, is a fixed shaft engine, running at the constant speed of 43,000 r.p.m. It has a three‐stage compressor, two axial stages followed by a centrifugal stage, after which there is the annular combustion chamber and finally the three‐stage turbine. The reduction gear, a two‐stage step‐down spur gear with three layshafts (or ‘stationary planets’), delivers 1,783 r.p.m. at the propeller shaft. Fuel flows along the main shaft from the front and enters the combustion chamber via a slinger ring, thus giving adequate vapourisation without the need for unduly small injection nozzles.

ADVANCE NOTES ON RESEARCH

Tilley et al. (1) have clearly demonstrated that their rumen liquor and pepsin procedure for the determination of digestibility of herbage is useful and precise. The method has, however, the disadvantage that the equipment required for the centrifugation stages is relatively expensive and, moreover, when using one centrifuge only the procedure is somewhat tedious. The method outlined below completely eliminates centrifugation; the rumen‐liquor stage is terminated by acidification and the residues from the pepsin stage is recovered by filtration, using a filter aid. Digestible dry matter or digestible organic matter may be determined; results for the former estimation on thirteen samples already examined at Hurley have given satisfactory results.