Compressor Applications Research Articles

Structure design and simulation research of active magnetic bearing for helium centrifugal cold compressor

Helium centrifugal cold compressors are utilized to pump gaseous helium from saturated liquid helium tank to obtain super-fluid helium in cryogenic refrigeration system, which is now being developed at TIPC, CAS. Active magnetic bearing (AMB) is replacing traditional oil-fed bearing as the optimal supporting assembly for cold compressor because of its many advantages: free of contact, high rotation speed, no lubrication and so on. In this paper, five degrees of freedom for AMB are developed for the helium centrifugal cold compressor application. The structure parameters of the axial and radial magnetic bearings as well as hardware and software of the electronic control system is discussed in detail. Based on modal analysis and critical speeds calculation, a control strategy combining PID arithmetic with other phase compensators is proposed. Simulation results demonstrate that the control method not only stables AMB system but also guarantees good performance of closed-loop behaviour. The prior research work offers important base and experience for test and application of AMB experimental platform for system centrifugal cold compressor.

Design Aspects of High-Speed Electrical Machines With Active Magnetic Bearings for Compressor Applications

Two-stage oil-free centrifugal air compressors can bring significant advantages and open new market opportunities for compressor manufacturers. One of the core technologies behind this compressor type is the high-speed electrical machine supported by active magnetic bearings. In this paper, the requirements set by the compressor on the electrical machine design are presented. The design solutions aimed to satisfy these requirements are discussed. Two case studies illustrate possible design approaches for the target application with examples of a 120-kW, 60 000-r/min induction machine with a solid rotor and a 225-kW, 50 000-r/min permanent-magnet synchronous machine (PMSM) with a full cylindrical magnet. The system design and simulation results are confirmed by measurements of a PMSM prototype.

Energy conservation in domestic refrigerators by cooling compressor shell – A case study

Application of energy efficient compressors, air handling units (AHUs), condensers and evaporators of high effectiveness are the some of the measures towards energy conservation in refrigeration systems. Cooling of compressor shell with the defrost drips is an energy saving measure which is explored in this paper. In tropical countries which have 70–80% RH year round, the quantity of defrost formation is significant while refrigeration systems are on. This defrost water is dripped on the compressor's shell, which in turn cools the compressor oil and hence reduces the friction losses and winding temperature of the motor. Once winding temperature is reduced the compressor's ampere rating is reduced which ultimately reduces the energy consumption of the compressor. For given conditions of refrigerator function, the compressor shell temperature and ampere rating of compressor are tabulated and investigated before and after compressor shell cooling. The investigation reveals that around 8–10% energy savings are achieved for the given conditions.

Energy potential of dual lead rotors for twin screw compressors

The paper deals with a theoretical investigation into the ways in which fluid properties influence the optimal geometrical parameters of dry running twin screw compressors with uniform and dual lead rotors. Dual lead rotors possess two segments with different rotor leads in order to optimise the progression of chamber volume, clearance size and outlet area. Optimal geometry parameters are determined by means of a multi-chamber model simulation. Fluids are treated as an ideal gas and fluid properties are varied systematically in order to provide guidance on how the machine should be designed for a particular application. The optimal geometry parameters mainly depend on the speed of sound and isentropic exponent of the fluid, because they influence outlet throttling during discharge, and pressure progression due to volumetric compression. In particular, the values for the rotor wrap angle and the internal volume ratio need to be adjusted individually for each compressor application. The results reveal that dual lead compressors possess most potential for fluids with low speed of sound and isentropic exponent.

Improved compressor corner separation prediction using the quadratic constitutive relation

This work presents the implementation and study of the quadratic constitutive relation nonlinear eddy-viscosity model with representative compressor application, for which the corner separation has been poorly predicted with the widely used linear Boussinesq eddy-viscosity model. With the introduction of the Reynolds stress anisotropy, the secondary flow of the second kind and its effect on the corner flow can be well captured and this results in greatly improved prediction of pressure coefficient, total pressure loss coefficient and the corner separation size. Without the quadratic constitutive relation model, the separation size and loss are generally over-estimated. The mechanism of the improvement is studied using both the vortex dynamics and the momentum equation. It is proved that quadratic constitutive relation model consumes low CPU time and provides much improved compressor corner separation prediction without worsening the convergence property.

Dynamic Analysis of a Novel Moving Magnet Linear Actuator

A novel moving magnet linear actuator is proposed for linear oscillations in the linear resonant compressors for household refrigerators. This paper provides stator and armature design including CAD model and geometric parameters. Furthermore, the working principle of the proposed actuator is explained. The stator assembly is composed of two reversely wound coils, which are electrically excited with single phase ac power and oscillates the radially magnetized armature. With the help of the electromechanical analytical model, the dynamic parameters such as stroke, velocity, and acceleration of the armature are derived. Additionally, the time-dependent current model of the stator winding is proposed. An experimental setup is used to validate these responses at the resonance excitation frequency with the help of sensors. The system kinetics are discussed to estimate the spring, damping, inertial, and magnetic forces. A simulation is executed to estimate the time-domain responses of these dynamic parameters and the effects of excitation frequency are discussed. The force models are experimentally validated at the resonance frequency excitation. In order to evaluate the performance of the proposed actuator, a comparison of the performance parameters, such as efficiency, stroke, current, and mass flow rate is demonstrated with the conventional rotary as well as the linear motors for linear compressor application.

Exhaust System for Radial and Axial-Centrifugal Compressor with Pipe Diffuser

Abstract The application of radial and axial-centrifugal compressors in turboprop, turboshaft and turbofan engines may require the construction of small diameters diffuser in order to obtain lower weight and smaller frontal area. Conventional exhaust diffusers typically have large outlet diameters for exit Mach numbers lower than 0,2 and low swirl flow to the combustor, hence the design of channel of the low-diameter diffusers called controlled-contour, fishtail-shaped diffuser or diffusing trumpet is complex. The cross-sectional shape of these channels is varied from circular to oval to elliptic and to rectangular. The paper presents an original method for determining the flow parameters in the channel and at the outlet section of the downstream diffusing trumpet for a pipe diffuser, which constitutes the downstream duct of the radial or axial-centrifugal compressor with the pipe diffuser. It also illustrates a new method for determining the geometrical parameters of the diffuser. Mentioned methods (for conceptual design of a compressor with pipe diffuser) are based on Pythagorean theorem, properties of ellipse, equation of continuity, energy equation, first law of thermodynamics, Euler’s moment of momentum equation, gasdynamics functions and definitions used in theory of turbo-machines.

Total Temperature Measurement of Fast Air Streams With Fiber-Optic Bragg Grating Sensors

The suitability of using fiber Bragg gratings (FBG) as sensor elements in total temperature probes for turbine compressor applications is shown. A series of five FBG-based probes was built and characterized experimentally in the harsh environment of an open-jet test bench at air stream velocities of up to Mach 0.8. The performances of the FBG-based probes were compared with that of a conventional thermocouple-based total temperature sensor. All fiber-optic probes showed good mechanical robustness and recovery factors in the range of 0.79–0.99. Employing fiber-optic sensor elements allowed a significant reduction of the diameters of the stagnation tubes of the transducers. Because of the smaller probe design and thinner signal transmission cables, less distortion of the air stream is expected with the fiber-optic sensors, when compared with the conventional instrumentation.

An approach for establishing the performance maps of the sc-CO2 compressor: Development and qualification by means of CFD simulations

One of the challenges in the performance prediction of the supercritical CO2 (sc-CO2) compressor is the real gas behavior of the working fluid near the critical point. This study deals with the establishment of an approach that allows coping with this particularity by dressing compressor performance maps in adequate reduced coordinates (i.e., suitable dimensionless speed and flow parameters inputs and pressure ratio and enthalpy rise outputs), while using CFD for its validation. Two centrifugal compressor designs have been considered in this work. The first one corresponds to a 6kW small scale component implemented in a test loop at Tokyo Institute of Technology. The second one corresponds to a 38 MW scale 1:1 design considered at an early stage of a project that investigates sc-CO2 cycle for a Small Modular Reactor application. Numerical results on the former have been successfully confronted with the experimental data to qualify the ability of CFD to provide a performance database. Results on the latter have revealed a significant decrease in the static temperature and pressure during flow acceleration along the leading edge of the impeller blades. In this line, the increased risk of vapor pockets appearance inside a sc-CO2 compressor has been highlighted and recommendations regarding the choice of the on-design inlet conditions and the compressor design have been given to overcome this concern. CFD results on the scale 1:1 compressor have then been used to evaluate the relevancy of some previous performance maps approaches for a sc-CO2 compressor application. These include the conventional approach for ideal gas and its derivation, as well as a reference approach from the literature that was previously applied to model a sc-CO2 test compressor. As the dimensionless parameters of these approaches are found to yield discrepancies on the compressor performance, a revised approach that incorporates real gas formulations into turbomachinery key similarity parameters has been finally proposed. In support, an extensive number of CFD case studies has been carried out at various compressor inlet conditions, providing numerical results for its qualification. Accordingly, the proposed approach has been found to succeed in consistently representing and accurately predicting the sc-CO2 compressor performance over a wide operating range.

Electromagnetic Design and Loss Calculations of a 1.12-MW High-Speed Permanent-Magnet Motor for Compressor Applications

Electromagnetic design of a 1.12-MW, 18 000-r/min high-speed permanent-magnet motor (HSPMM) is carried out based on the analysis of pole number, stator slot number, rotor outer diameter, air-gap length, permanent magnet material, thickness, and pole arc. The no-load and full-load performance of the HSPMM is investigated in this paper by using 2-D finite element method (FEM). In addition, the power losses in the HSPMM including core loss, winding loss, rotor eddy current loss, and air friction loss are predicted. Based on the analysis, a prototype motor is manufactured and experimentally tested to verify the machine design.

A novel data reduction technique for single slanted hot-wire measurements used to study incompressible compressor tip leakage flows

The single slanted hot-wire technique has been used extensively as a method for measuring three velocity components in turbomachinery applications. The cross-flow orientation of probes with respect to the mean flow in rotating machinery results in detrimental prong interference effects when using multi-wire probes. As a result, the single slanted hot-wire technique is often preferred. Typical data reduction techniques solve a set of nonlinear equations determined by curve fits to calibration data. A new method is proposed which utilizes a look-up table method applied to a simulated triple-wire sensor with application to turbomachinery environments having subsonic, incompressible flows. Specific discussion regarding corrections for temperature and density changes present in a multistage compressor application is included, and additional consideration is given to the experimental error which accompanies each data reduction process. Hot-wire data collected from a three-stage research compressor with two rotor tip clearances are used to compare the look-up table technique with the traditional nonlinear equation method. The look-up table approach yields velocity errors of less than 5 % for test conditions deviating by more than 20 °C from calibration conditions (on par with the nonlinear solver method), while requiring less than 10 % of the computational processing time.

Transient Analysis of 220 kW Solid Oxide Fuel Cell-Gas Turbine Hybrid System Using Computational Fluid Dynamics Results

A better understanding of turbulent unsteady flows in gas turbine systems is a necessary step toward a breakthrough in compressor applications for hybrid fuel cell gas turbine (FC-GT) systems. In this study, compressor stall/surge analysis for a 220 kW hybrid solid oxide FC-GT system is performed for the two different compressor design configurations of a single-stage and a multi-stage compressor. Control methods have been previously developed at National Fuel Cell Research Center (NFCRC) for this system. These control strategies can prevent the operation of hybrid SOFC-GT near the stall/surge limit line; however, computational fluid dynamics (CFD) tools can provide a better understandig of flow distribution and instabilities near the surge limit of operation. The results show that using a multi-stage compressor is preferred over a single-stage compressor for the 220kW SOFC-GT topping cycle design due to the enhanced ability to sustain flow through the compressor during dynamic operation.

Tribological interactions of advanced polymeric coatings with polyalkylene glycol lubricant and r1234yf refrigerant

We report on the tribological performance of an aromatic thermosetting polyester (ATSP) blended with polytetrafluroethylene (PTFE) as a coating material for air-conditioning compressor applications. Tribological experiments were conducted in the presence of environmentally friendly r1234yf refrigerant and polyalkyleneglycol (PAG) lubricant, to compare state-or-the-art polymeric coatings with ATSP/PTFE. Results showed better performance for ATSP/PTFE, compared to PTFE-based and Fluorocarbon- based coatings under both dry and boundary lubricated sliding conditions. Significant reduction of 69% in friction was obtained with the inclusion of PAG lubricant, suggesting a synergistic combination for ATSP/PTFE and PAG/r1234yf. Morphological evolution via scanning electron microscopy revealed surface cracks and voids for PTFE/MoS2, responsible for negative interactions under lubricated condition, which was not the case for ATSP/PTFE coating.

Compressor application for extending production life cycle in mature fields

Compressor application for extending production life cycle in mature fields

Motor Conversion for Reduced Energy Consumption: Compressor Applications Use More Energy Than Applications with Newer Technologies

Significant energy savings can be achieved by converting inefficient direct-driven rotary vane compressor applications to belt-driven applications.

Wear Mechanisms of Gray Cast Iron in the Presence of Environmentally Friendly Hydrofluoroolefin-Based Refrigerant and the Effect of Tribofilm Formation

Hydrofluoroolefin-based refrigerant (2,3,3,3-tetrafluoropropene, namely, HFO-1234yf), which has been developed as an environmentally friendly refrigerant, is proposed as a direct replacement solution in automotive air-conditioning compressor applications. In the present work, the wear mechanisms of this refrigerant using gray cast iron interfaces were investigated under a wide range of operating conditions. A critical velocity was measured from scuffing type experiments, where beyond that maximum interfacial loads did not change significantly with sliding velocity, suggesting a mechanical rubbing-type wear mechanism. Below the critical velocity, scuffing loads decreased almost linearly with sliding velocities. Wear type experiments identified two different wear mechanisms, namely, oxygen-dominating and fluorine-dominating wear, depending on sliding velocities and normal loads. Oxygen-dominating wear mechanism prevailed under low sliding velocities and normal loads. In contrast, fluorine-dominating wear was predominant under moderate sliding velocities and low or moderate loads. The formation of protective tribofilms and their effect on the wear mechanism was used to construct a wear map.

Riblet Application in Compressors: Toward Efficient Blade Design

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step toward more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number (LRN) conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5 × 105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 deg. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” was used for the optimization process. The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5 × 105–9.0 × 105. Furthermore, the measurements were carried out at a low turbulence level of 0.8% and at a high turbulence level of 4%, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study, riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating techniques, were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets (CRs) have a width of 50 μm. The wake measurements were performed using a three-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.

Experimental evaluation of MPC-based anti-surge and process control for electric driven centrifugal gas compressors

The present work concerns model predictive control (MPC) of centrifugal gas compressors and describes the development of an MPC application for the tasks of anti-surge and process control. More specifically, the MPC formulation focuses on the question of how the transient manipulation of driver torque can be used to improve the performance of anti-surge and process control. For the purpose of testing and validating the proposed control algorithm, an experimental compressor test rig is presented, which is designed to mimic a typical centrifugal compressor application in the oil and gas industry. Modeling and parameter identification of the experimental setup is followed by the realization of the MPC solution on an embedded system to comply with the stringent real-time requirements for anti-surge control. Testing is performed with experiments using suction and discharge side disturbances, which are created by rapid valve closures. For comparison the same tests are repeated with conventional control approaches. The test results indicate improvements in maintaining the distance to surge by up to 11%, while at the same time reducing the process control settling time by up to 50%.

Design and validation of new cavity profiles for diaphragm stress reduction in a diaphragm compressor

The application of diaphragm compressors is severely limited by the low reliability and short life of diaphragms. The cavity profile has considerable influence on a diaphragm's stress level and therefore on its fatigue life. This experimental and theoretical analysis of the traditional cavity profile (as defined by a single-parameter generatrix) indicated that the short life of diaphragms may be caused by the superposition of peak radial stress and additional stress due to the discharge holes in the central region that occur when the diaphragm clings to the cavity surface. Therefore, two new kinds of cavity profiles are proposed to decrease the diaphragm's radial and total stress. The new cavity profiles based on different generatrices were designed in an attempt to reduce the peak radial stress in the central region. These cavities were manufactured to experimentally validate the designs. Experiments were carried out under various design conditions to investigate the radial stress distribution in the diaphragms. The reductions of radial stress on the diaphragms in the new cavities were compared with stress levels found in the traditional design. Although their cavity volumes and radii were all the same, the radial stress levels on diaphragms in the cavities designed by the new generatrices were less than those found in the traditionally designed cavity. The greatest decline in radial stress on the diaphragms in the cavities based on new generatrices was 13.8%. With the additional stress taken into account, the decline in radial stress in the diaphragm's central region reached as high as 19.6%.

An Investigation on the Pin Bearings’ Optimization of a Hermetic Reciprocating Compressor

A hermetic reciprocating compressor is the most energy consuming component of the refrigerators. Therefore performance improvement studies of the compressor play an important role to reduce overall energy consumption of the refrigerators. Design of bearings is one of the major study areas influencing reciprocating compressor performance.In this study crank pin and piston pin bearings in hermetic compressor applications are investigated and optimized. The effect of operating conditions, bearing offset between crank pin and piston pin, bearing clearance and bearing location along the shaft on the friction loss were investigated and optimal bearing designs were developed.Efficiency measurements of the compressor showed that the improved crank pin and piston pin bearing designs provide up to 3.8% increase in the COP as a result of reduction in mechanical loss that is significantly influenced by the length of the bearings, bearing location along the shaft and operating conditions.