Centrifugal compressor

Summary

Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. They achieve pressure rise by adding energy to the continuous flow of fluid through the rotor/impeller. The equation in the next section shows this specific energy input. A substantial portion of this energy is kinetic which is converted to increased potential energy/static pressure by slowing the flow through a diffuser. The static pressure rise in the impeller may roughly equal the rise in the diffuser. Components of a simple centrifugal compressor A simple centrifugal compressor stage has four components (listed in order of throughflow): inlet, impeller/rotor, diffuser, and collector. Figure 1.1 shows each of the components of the flow path, with the flow (working gas) entering the centrifugal impeller axially from left to right. This turboshaft (or turboprop) impeller is rotating counter

Official source

https://en.wikipedia.org/wiki/Centrifugal_compressor

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related publications (23)

Related publications

Related people (5)

Related people

Related units (2)

Related units

Related concepts (8)

Related concepts

Related courses (7)

Related courses

Related lectures (22)

Related lectures

A numerical and experimental investigation of the shock-IGV (inlet guide vane) interaction in a transonic compressor is conducted at the Laboratoire de Thermique Appliquée et de Turbomachines (LTT) at the Ecole Polytechnique Fédérale de Lausanne (EPFL). The objective of the presented research work is to determine the impact of the upstream propagating shock pattern of an axial transonic compressor rotor on an aerodynamically loaded IGV and the influence of this interacting process on the compressor flow field for different operating points and aerodynamic setups. For the approach to the subject, a literature review shed light on the different research efforts over the past years. A large numerical study is conducted including the work with two different flow solvers. A numerical 3D transient analysis (commercial code) was conducted in order to provide information about the influence of the axial spacing on the overall mass flow through the stage. A numerical Q-3D transient analysis (industry owned code) on one streamline at a constant rotor inlet Mach number is performed in order to compare the shock-IGV interaction for different vane types similar to what is known in literature. A semi-analytical model was developed in order to evaluate in a fast approach the impact of a rotor bow shock on an upstream situated vane. The results of the numerical investigation can be summarized as following: The overall results of this investigation show that the upstream vane of a transonic compressor rotor transforms the rotor forcing function into an excitation with vane shape depending orientation and force. The time averaged flow field of the IGV does not show a measurable change of the exit flow angle due to the shock-IGV interaction for the studied operating points and axial distances. The 3D transient calculations do not show any influence of the examined axial spacing between vane and blade on the mass flow rate through the stage. The results of the Q3D analysis are compared with the semi-analytic approach and the measurements, both showing with some restrictions good accordance to the model. The results of the numerical investigation give an accurate prediction of the transient aerodynamic load of the upstream vane. An analytic tool was developed which uses three input parameters, the rotor relative inlet Mach number, the stagger angle of the rotor and the axial spacing between vane and rotor in order to provide an estimation of the amplitude of the pressure variation on the upstream situated vane. An extensive modification of the existing test facility of the LTT precedes the experimental study. The main steps of the approach are: A subsonic axial compressor test facility was modified to allow test runs at transonic rotor inlet conditions. A perfect leak tightness of the closed circuit was accomplished to enable its operation in heavy gas. Heavy gases like refrigerants have been used in many studies for compressor testing. While respecting certain restrictions during the use of heavy gas, a reduction of operation and manufacturing costs of the facility is beneficial. A high molecular weight of the gas reduces the sonic speed to the half of that of air thus reducing the dimension and the rotational speed of the rotor significantly and consequently reduces the demand in the material quality of the blading. A 1.5 stage transonic compressor had been designed and manufactured for the heavy gas (R134a) in a first step. Preliminary measurements showed that the influence of the downstream stator makes it difficult to separate the influence of shock-IGV interaction on the compressor flow field from loss generation mechanisms downstream of the rotor. Thus, the stator was removed and measurements were conducted in a one stage transonic compressor. Modifications on the construction of the testing setup are done in a way that the distance between IGV and rotor can be varied by means of spacers. Thus the flow can be determined for up to four different axial distances at varying rotational speed for different operating points. For transonic operation the time-dependent load of the IGV (inlet guide vane) due to the forcing function of the rotor bow shock was recorded with a high speed data acquisition system. The results of the experimental investigation can be summarized as following: No influence of the axial spacing on the efficiency and the mass flow was observed in the investigation. The operation characteristics remained equal between the minimum and the maximum vane-blade spacing. The measured global values of the stage are close to the values the design was made for, although the overall efficiency was generally lower than predicted. The experimental results of the pressure variation on the upstream vane agree well with the predicted values. The study in general showed a good matching between the numerical and the experimental investigation taking into account a rotor blade shape which is not optimized to the extend. The shock-vane interaction is responsible for an excitation of the entire vane blade. With decreasing distance between the rotor leading edge and vane trailing edge the excitation increases. The strength and orientation of the reflected shock/pressure wave part depends upon the vane shape. A more sophisticated design of the rotor blade shape should be in the focus of further investigations using this test facility at transonic rotor inlet conditions. Within this investigation a tool was developed in order to predict the load variation on the vane driven by the transient rotor forcing function. The tool maps the fact that the pressure on the vane surface oriented against rotational direction of the rotor exceeds the pressure of the passage shock due to the amplification effect of the reflection of the shock on a surface. Its possible application not only for compressors but also for turbine related topics should be an objective for similar investigations.

EPFL2008

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

François Avellan, Xiaoran Zhao

Dredge pumps are usually operated at part-load conditions, in which the low-solidity centrifugal impeller could experience large internal energy dissipation, related to flow separation and vortices. In this study, SST k- and SAS-SST turbulence models were used, in steady and unsteady simulations, for a low-head centrifugal pump with a three-bladed impeller. The main focus of the present work was to investigate the internal energy dissipation in rotating an impeller at part-load operating conditions, related to flow separation and stall. The unsteady nature of these operating conditions was investigated. Performance experiments and transient wall pressure measurements were conducted for validation. A methodology for internal energy dissipation analysis has been proposed; and the unsteady pressure fluctuations were analyzed in the rotating impeller. The internal power losses in the volute and the impeller were mostly found in the centrifugal pump. The rotating stall phenomenon occurred with flow separation and detachment at the part-load operating condition, leading to a dissipation of the internal energy in the impeller. The rotating impeller experienced pressure fluctuations with low frequencies, at part-load operating conditions, while in the design operating condition only experienced rotating frequency.

2019

, , ,

Multistage heat pumps are one of the most efficient technologies for delivering heat at temperatures below 100°C, Thanks to their fairly high exergy efficiency. In the recent years the development of radial compressors mounted on gas bearings have unlock the possibility of a downsizing of multistage heat pumps to the capacity range of domestic applications. Such small scale multistage heat pumps are expected to have increased efficiency at nominal and part load conditions, to be fully hermetic and to be more compact thanks to their oil free operation and the use of dynamic machines. As a result of an industrial collaboration, an experimental two-stage heat pump with flash economizer was built and tested in a previous work. It used radial oil free compressors arranged on a single shaft rotating on gas bearings. A dynamic simulation model has been developed in order to better understand the behavior of the aforementioned prototype, as well as to preliminary test control strategies. As a result, a whole range of dynamic models, including the evaporator, condenser, flash economizer, and compressors were developed using the modeling and simulation software gPROMS. They rely on simple two and three zone models for the evaporator and condenser respectively. Zero dimensional models were used for the compressors, two different types of which were implemented. One is a volumetric compressor with a fixed built-in volume ratio, connected to an asynchronous electric motor the other one is a variable speed radial type based on a simplified compressor map deduced from experimental data. As much as possible, the aforementioned models have been inspired from components available in the base library of gPROMS. The results showed that a two stage heat pump based on quasi constant speed volumetric compressors poses problem at low temperature lift, when the top part of the cycle is degenerated, making it close to a single stage machine. The version with the dynamic compressors does not exhibit any problem of degeneration of the cycle, while having a better performance and load characteristic curve. Both systems showed an insensitivity of the performances to the charge of refrigerant due to the buffering effect of the flash economizer. As a conclusion, a simple dynamic model was developed for simulating various types of two-stage heat pumps with flash economizer. It confirmed the potential of performance improvement of radial compressors based heat pumps over volumetric ones.

2013

, , ,

2013

EPFL2008