Compressor Losses Research Articles

Performance Analysis of an Irreversible Regenerative Brayton Cycle Based on Ecological Optimization Criterion

An ecological optimization along with a detailed parametric analysis of an irreversible regenerative Brayton cycle with finite heat capacity of external reservoirs have been carried out. The external irreversibilities due to finite temperature difference and internal irreversibilities due to fluid friction losses in compressor / turbine, regenerative heat loss, pressure loss are included in the analysis. Ecological function is thermodynamically optimized which is defined as the power output minus the product of environment temperature and entropy generation rate. A detailed analysis shows that the ecological function and corresponding power output / thermal efficiency can be maximized with judicious selection of parameters such as efficiency of turbine and compressor, effectiveness of various heat exchangers, heat source inlet temperature, pressure drop recovery coefficients and heat capacitance rate of the working fluid. It is found that the regenerative effectiveness is more prominent for maximum ecological function and corresponding thermal efficiency while cold side effectiveness is dominant factor for corresponding power output. It is also found that the effect of turbine efficiency (ηt) is more than the compressor efficiency (ηc) on the thermodynamic performance of an irreversible regenerative Brayton heat engine cycle. The model analyzed in this paper gives lower values of various performance parameters as expected and replicates the results of an irreversible regenerative Brayton cycle model discussed in the literature at pressure recovery coefficients of α1=α2=1.

Control of Corner Separation to Enhance Stability in a Linear Compressor Cascade by Boundary Layer Suction

Certificating characteristics of stall and surge is an important work for engine airworthiness. Requirements and instructions of these characteristics are issued under CCAR 33.65. For stator cascade, the flow structure of corner separation region is complex. The separation can lead to highly loss in compressors and even cause corner stall and deterioration on cascade performance. This paper studied boundary layer suction on the suction surface and end wall to control the corner separation and eliminate corner stall to enhance the stability of the compressor. A total of six slot arrangements were investigated by CFD method. The results showed that using boundary layer suction can reduce passage total pressure loss and extend available attack angle of the cascade. Furthermore, through the analysis of the control effects, two groups of combination suctions are proposed to get better control effects.

Blade Tips - Clearance and Its Control

This article focuses on studying blade tip clearance phenomena. It is important to realize that to be freely turning, a blade (or a cantilevered stator) must have a clearance gap between its tip and the engine casing (or hub). Such clearances introduce aerodynamic losses, decreasing gas turbine efficiency. Tip leakage losses in compressors can be significant and have been reviewed by the experts. During transient operations, gas turbine blade tip clearances will change based on blade/disk centrifugal loads and the different response times of engine parts to thermally induced expansions and contractions. Designers have perfected active clearance control (ACC) systems to deal with these transient conditions. ACC uses cool or hot gas path and fan air at appropriate times during transients to control the rate of expansion or contraction of internal parts adjacent to the gas path and outer casings. The research shows that continued enhancement of blade tip clearance management systems over a range of engine operating conditions has brought and will bring about gains in gas turbine efficiency.

Friction Loss and Wear in a Meso Scale Wankel Compressor

In a meso scale Wankel compressor, the surface-to-volume ratio and the contact surfaces with friction are larger compared with conventional scale Wankel compressor. The analysis of friction loss is highly important for the design of a meso scale Wankel compressor. In this paper, we comprehensively analyze seven kinds of friction losses of a meso scale Wankel compressor. The rationality of the friction losses equations is verified by the friction loss and wear experiments that are based on a Wankel compressor prototype (the dimension of prototype is about 40 × 50 × 24 mm). The two greatest contribution of total friction loss are from the friction loss between the seal apex and internal surface of the cylinder and that among the end face of the eccentric shaft, end faces of the rotor, and endplates to total friction loss. The most sensitive parameter is eccentric distance. The relative error between the simulation and experimental results is relatively small when motor speed lies within the common range of the compressor.

A model for parameter estimation of multistage centrifugal compressor and compressor performance analysis using genetic algorithm

A model for performance prediction of multistage centrifugal compressor is proposed. The model allows the users to predict the compressor performance, e.g. pressure ratio, efficiency and losses using the compressor geometric information and speed by a stage stacking calculation based on the characteristics of each stage. To develop the compressor elemental stage characteristics, the compressor losses, such as incidence losses and friction losses, are mathematically modeled. For a composite systems, for instance a gas turbine power plant, the performance of the multistage centrifugal compressor can be evaluated. Since some important parameters of the compressor model, e.g., the slip factor σ, shock loss coefficient ζ and reference diameter D1, are hard to be determined by empirical laws, a genetic algorithm (GA) is used to solve the parameter estimation problem of the proposed model, and in turn the compressor performance analysis and parameters study are performed. The surge line for the multistage centrifugal compressor can also be determined from the simulation results. Furthermore, the model presented here provides a valuable tool for evaluating the multistage centrifugal compressor performance as a function of various operation parameters.

Finite-time exergoeconomic optimal performance for an irreversible gas turbine closed-cycle cogeneration plant

Finite-time exergoeconomic performance of an irreversible constant temperature heat reservoir gas turbine closed-cycle cogeneration plant with heat resistance losses in heat exchangers and compression and expansion losses in compressors and turbines is investigated. Heat conductance allocations among hot-, cold- and consumer-side heat exchangers and pressure ratio of the compressor are optimized by taking the maximum profit rate as an objective. There exist a sole group of optimal heat conductance allocations among the three heat exchangers, an optimal pressure ratio of the compressor and an optimal consumer-side temperature, which leads to the maximum dimensionless profit rate.

나노 윤활유를 이용한 스크롤 압축기 스러스트 베어링의 윤활특성 평가

This paper presents the friction and anti-wear characteristics of nano-oil with a mixture of a refrigerant oil and carbon nano-particles in the thrust slide-bearing of scroll compressors. Frictional loss in the thrust slide-bearing occupies a large part of total mechanical loss in scroll compressors. The characteristics of friction and anti-wear using nano-oil is evaluated using the thrust bearing experimental apparatus for measuring friction surface temperature and the coefficient of friction at the thrust slide-bearing as a function of normal loads up to 4,000 N and rotating speed up to 3,200 rpm. It is found that the coefficient of friction increases with decreasing rotating speed and normal force. The friction coefficient of carbon nano-oil is 0.023, while that of pure oil is 0.03 under the conditions of refrigerant gas R-22 at the pressure of 5 bars. It is believed that carbon nano-particles can be coated on the friction surfaces and the interaction of nano-particles between surfaces can be improved the lubrication in the friction surfaces. Carbon nano-oil enhances the characteristics of the anti-wear and friction at the thrust slide-bearing of scroll compressors.

Exergetic analysis of transcritical CO 2 residential air-conditioning system based on experimental data

The experimental system for the transcritical CO 2 residential air-conditioning with an internal heat exchanger was built. The effects of working conditions on system performance were experimentally studied. Based on the experimental dada, the second law analysis on the transcritical CO 2 system was performed. The effects of working conditions on the total exergetic efficiency of the system were investigated. The results show that in the studied parameter ranges, the exergetic efficiency of the system increases with the increases of gas cooler side air inlet temperature, gas cooler side air inlet velocity and evaporating temperature. And it will decrease with the increases of evaporator side air inlet temperature and velocity. Then, a complete exergetic analysis was performed for the entire CO 2 transcritical cycle including compressor, gas cooler, expansion valve, evaporator and internal heat exchanger under different working conditions. The average exergy loss in gas cooler is the highest one under all working conditions which is about 30.7% of the total exergy loss in the system. The second is the average exergy loss in expansion valve which is about 24.9% of the total exergy loss, followed by the exergy losses in evaporator and compressor, which account for 21.9% and 19.5%, respectively. The exergy loss in internal heat exchanger is the lowest one which is only about 3.0%. So in the optimization design of the transcritical CO 2 residential air-conditioning system more attentions should be paid to the gas cooler and expansion valve.

Power density analysis of an endoreversible, closed, constant-temperature heat reservoir, intercooled regenerative Brayton cycle

In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as objective for performance analysis of an endoreversible, closed, intercooled regenerated Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite-time thermodynamics or entropy generation minimization. The analytical formulae about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers, the intercooler and the regenerator. The intercooling pressure ratio is optimized for dimensionless power density. The effects of effectivenesses of the intercooler and the regenerator on the optimal dimensionless power density and its corresponding efficiency are analyzed by detailed numerical examples. The obtained results are compared with those results obtained by using the maximum power criterion, including the cycle efficiencies, the normalized maximum specific volumes and the normalized maximum specific volume differences at two design objectives. The advantages and disadvantages of maximum power density design are obtained via the comparison of the main parameters of cycle at the maximum power and maximum power density conditions. The effects of turbine and compressor losses on the cycle performance are analyzed. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.

Numerical investigation of a high-subsonic axial-flow compressor rotor with non-axisymmetric hub endwall

The major source of loss in modern compressors is the secondary loss. Non-axisymmetric endwall profile contouring is now a well established design methodology in axial flow turbines. However, flow development in axial compressors is differ from turbines, the effects of non-axisymmetric endwall to axial compressors requires flow analysis in detail. This paper presents both experimental and numerical data to deal with the application of a non-axisymmetric hub endwall in a high-subsonic axial-flow compressor. The aims of the experiment here were to make sure the numerically obtained flow fields is the physical mechanism responsible for the improvement in efficiency, due to the non-axisymmetric hub endwall. The computational results were first compared with available measured data of axisymmetric hub endwall. The results agreed well with the experimental data for estimation of the global performance. The coupled flow of the compressor rotor with non-axisymmetric hub endwall was simulated by a state-of-the-art multi-block flow solver. The non-axisymmetric hub endwall was designed for a subsonic compressor rotor with the help of sine and cosine functions. This type of non-axisymmetric hub endwall was found to have a significant improvement in efficiency of 0.45% approximately and a slightly increase for the total pressure ratio. The fundamental mechanisms of non-axisymmetric hub endwall and their effects on the subsonic axial-flow compressor endwall flow field were analyzed in detail. It is concluded that the non-axisymmetric endwall profiling, though not optimum, can mitigate the secondary flow in the vicinity of the hub endwall, resulting in the improvement of aerodynamic performance of the compressor rotor.

평균반경해석법을 이용한 축류압축기 성능해석 프로그램 개발

Axial-flow compressor is one of the most important parts of gas turbine units with axial turbine and combustor. Therefore, precise prediction of performance is very important for development of new compressor or modification of existing one. Meanline analysis is a simple, fast and powerful method for performance prediction of axial-flow compressors with different geometries. So, Meanline analysis is frequently used in preliminary design stage and performance analysis for given geometry data. Much correlations for meanline analysis have been developed theoretically and experimentally for estimating various types of losses and flow deviation angle for long time. In present study, meanline analysis program was developed to estimate compressor losses, incidence angles, deviation angles, stall and surge conditions with many correlations. Performance prediction of one stage axial compressors is conducted with this meanline analysis program. The comparison between experimental and numerical results show a good agreement. This meanline analysis program can be used for various types of single stage axial-flow compressors with different geometries, as well as multistage axial-flow compressors.

揺動ピストン形ロータリ圧縮機の損失に関する研究 : 機械摩擦損失の解析(流体工学,流体機械)

揺動ピストン形ロータリ圧縮機の損失に関する研究 : 機械摩擦損失の解析(流体工学,流体機械)

Performance analysis of a series of hermetic reciprocating compressors working with R290 (propane) and R407C

In this paper, a series of compressors with different capacities and geometries working with propane as refrigerant are analyzed in terms of the compressor model developed by [E. Navarro, E. Granryd, J.F. Urchueguía, J.M. Corberán, A phenomenological model for analyzing reciprocating compressors, International Journal of Refrigeration, in this issue, doi:10.1016/j.irefrig.2007.02.006]. The relative influence of the diverse compressor losses is estimated as a function of the operating conditions. In addition, a comparison study between propane and R407C was carried out for one compressor and the observed differences were analyzed in terms of the compressor model. This study was also useful to verify the model's goodness with the aim of predicting the compressor performance with an untested refrigerant.

Dynamic centrifugal compressor model for system simulation

A dynamic model of a centrifugal compressor capable of system simulation in the virtual test bed (VTB) computational environment is presented. The model is based on first principles, i.e. the dynamic performance including the losses is determined from the compressor geometry and not from the experimentally determined characteristic performance curves. In this study, the compressor losses, such as incidence and friction losses, etc., are mathematically modeled for developing compressor characteristics. For easy implementation in the VTB platform, the non-linear governing equations are discretized in resistive companion (RC) form. The developed simulation model can be applied to virtually any centrifugal compressor. By interfacing with a composite system, such as a Brayton cycle gas turbine, or a fuel cell, the compressor dynamic performance can be evaluated. The surge line for the compressor can also be determined from the simulation results. Furthermore, the model presented here provides a valuable tool for evaluating the system performance as a function of various operating parameters.

New integrated scheme of the closed gas-turbine cycle with synthesis gas production

New integrated scheme of the closed gas-turbine cycle with synthesis gas production was proposed. A comparative exergy analysis of the traditional gas-fired power generation cycle and proposed integrated gas-turbine cycle with synthesis gas production was carried out. The exergy losses in compressors and turbines are evaluated by using intrinsic coefficients. It has been shown that the integration of power generation and synthesis gas production technologies is an effective method to increase the electric energy generation by 9–12% or reduce methane consumption in its conversion into synthesis gas by 18–23%. Such integration is especially favourable if synthesis gas production is considered at initial stage of liquid synthetic fuels producing.

Wake Recovery Performance Benefit in a High-Speed Axial Compressor

Abstract Rotor wakes are an important source of loss in axial compressors. The decay rate of a rotor wake is largely due to both mixing (results in loss) and stretching (no loss accrual). Thus, the actual loss associated with rotor wake decay will vary in proportion to the amounts of mixing and stretching involved. This wake stretching process, referred to by Smith (1996) as recovery, is reversible and for a 2-D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. It will be shown that for the rotor/stator spacing typical of core compressors, wake stretching is the dominant wake decay process within the stator with viscous mixing playing only a secondary role. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated alone and in a stage configuration at near peak efficiency and near stall operating conditions. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model and laser anemometer measurements indicate that rotor wake straining (stretching) is the primary decay process in the stator passage. Some implications of these results on compressor stage design are discussed.

An experimental analysis of cycling in an automotive air conditioning system

In the majority of automotive air conditioning systems, the compressor continuously cycles on and off to meet the steady-state cooling requirements of the passenger compartment. Since the compressor is a belt-driven accessory device coupled to the engine, its cycling rate is directly related to the vehicle speed. The refrigeration system’s losses increase with increasing vehicle speed and thus with increasing compressor cycling. This paper identifies and quantifies individual losses in an automotive vapor-compression refrigeration system during compressor cycling. The second law of thermodynamics, in particular, nondimensional entropy generation, is used to quantify the thermodynamic losses of the refrigeration system’s individual components under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A passenger vehicle containing a cycling-clutch orifice-tube vapor–compression refrigeration system was instrumented to measure refrigerant temperature and pressure, and air temperature and relative humidity. Data were collected under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A thermodynamic analysis is presented to determine the refrigeration system’s performance. This analysis shows that the performance of the system degrades with increasing vehicle speed. Thermodynamic losses increase 18% as the vehicle speed changes from idle to 48.3 kph (30 mph) and increase 5% as the vehicle speed changes from 48.3 kph (30 mph) to 96.6 kph (60 mph). The compressor cycling rate increases with increasing vehicle speed, thus increasing the refrigeration system’s losses. The component with the greatest increase in thermodynamic losses as a result of compressor cycling is the compressor itself. Compressor cycling reduces the compressor’s isentropic efficiency, and thus the system’s thermodynamic performance. The individual component losses of the refrigeration system are quantified. The redistribution of these losses is also given as a function of increasing vehicle speed (i.e. increasing compressor cycling). At 96.6 kph (60 mph), the thermodynamic losses, based on the ratio of entropy generation to entropic load, are 0.22, 0.10, 0.07, and 0.02 in the compressor, the condenser, the evaporator-accumulator, and the orifice tube, respectively. The compressor losses dominated the overall system performance. The overall system efficiency could be significantly improved by increasing the compressor’s efficiency. The compressor’s efficiency could be improved by reducing or eliminating cycling, such as could be accomplished by using a variable capacity compressor or by not directly coupling the compressor to the engine. Another way to increase the compressor’s volumetric efficiency during cycling would be to reduce the compressor operating range. This could be accomplished by using two compressors such as is done in two-stage cascade refrigeration systems.

A Study on the Leakage Analysis of Scroll Compressor with Thermal Deformation Considered

In general, it is known that the portion of leakage loss is more than 20 % of total loss in scroll compressor. So far many studies have been done to improve the leakage problem and volumetric efficiency. In order to do this it is necessary that the leakage is exactly evaluated for conventional scroll model. Almost all studies that have been done were assumed that the clearance remains constant while operating. But in actual operating conditions, scroll wrap is deformed due to elevated refrigerant gas temperature. And this makes the leakage clearance change, so the leakage mass flow and the volumetric efficiency are also changed. In this study we assumed the steady state operating condition and obtain the average temperature and convection heat transfer coefficient in terms of involute angle. With these results, using finite element method we analyzed the heat transfer of scroll wrap, then did thermal deformation analysis. Then we obtain the leakage clearance and do the leakage and volumetric efficiency analysis. Compared with undeformed feature, we examine the effect of the thermal deformation on the leakage. The results say that the leakage mass flow for the case of considering thermal deformation is less than that for the unconsidered one, and this means that the leakage clearance is reduced due to thermal deformation.

The Effects Of Thermal Gradients On The Performance of Axial Compressors

The effects of thermal gradients and hot streaks on the durability and performance of high-pressure turbine airfoils have received considerable attention during the last decade. Compressor flow fields can also experience large temperature gradients when the machine is throttled from a high-rotation speed to a significantly lower rotation speed. In the current investigation, an unsteady, quasi-three-dimensional Navier-Stokes analysis has been used to investigate the physics of thermal gradients in a compressor rotor, typical of rotors used in the high-pressure compressors of commercial jet engines. Simulations have been performed for a wide range of operating conditions, and for different thermal gradients. The predicted results indicate that the thermal gradients can increase the losses in compressors.

Advanced Compressor Loss Correlations, Part II:Experimental Verifications

Reliable efficiency calculation of high‐subsonic and transonic compressor stages requires a detailed and accurate prediction of the flow field within these stages. Despite the tremendous progress in turbomachinery computational fluid mechanics, the compressor designer still uses different loss correlations to estimate the total pressure losses and thus the efficiency of the compressor stage. The new shock loss model and the modified diffusion factor, developed in Part I, were implemented into a loss calculation procedure. In this part, correlations for total pressure loss, profile loss, and secondary loss coefficients are presented, using the available experimental data. Based on the profile loss coefficients, correlations were also established for boundary layer momentum thickness. These correlations allow the compressor designer to accurately estimate the blade losses and therefore the stage efficiency.