Centrifugal Compressors During Fast Transients

2010 ◽  
Author(s):  
Matthew Blieske ◽  
Augusto Garcia Hernandez ◽  
Rainer Kurz ◽  
Klaus Brun
Keyword(s):  
Steady State ◽  
Flow Speed ◽  
Operating Conditions ◽  
Fast Transients ◽  
Rapid Transients ◽  
Relationship Of ◽  
The Impact ◽  
Flow Head ◽  
Stationary Heat Transfer ◽  
Transient And Steady State

Transient studies for compressor systems allow the prediction of the compressor system behavior during fast transients such as they occur during emergency shutdowns. For the system simulations, the compressor behavior is assumed to be quasi steady state. This means in particular that the steady state compressor flow-head-efficiency-speed map remains valid. During well instrumented emergency shutdown tests conducted on a centrifugal compressor system under realistic operating conditions, data showing the head-flow-speed relationship of the rapidly decelerating compressor was taken. This data is compared to steady state head-flow relationships taken at a number of speeds. This allows to determine the relative deviation between the transient and steady state head-flow-relationships, and thus answers the question of the validity of steady state assumptions during rapid transients. The impact of the fast transients on efficiency and consumed power, which can be derived from the speed decay of the system, as well as the impact of non-stationary heat transfer are also evaluated and reported.

Centrifugal Compressors During Fast Transients

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Matthew Blieske ◽  
Rainer Kurz ◽  
Augusto Garcia-Hernandez ◽  
Klaus Brun
Keyword(s):  
Steady State ◽  
Flow Speed ◽  
Operating Conditions ◽  
Nonstationary Heat Transfer ◽  
Fast Transients ◽  
Rapid Transients ◽  
Relationship Of ◽  
The Impact ◽  
Flow Head

Transient studies for compressor systems allow the prediction of the compressor system behavior during fast transients such as they occur during emergency shutdowns. For the system simulations, the compressor behavior is assumed to be quasi-steady-state. This means in particular that the steady-state compressor flow-head-efficiency-speed map remains valid. During well instrumented emergency shutdown tests conducted on a centrifugal compressor system under realistic operating conditions, data showing the head-flow-speed relationship of the rapidly decelerating compressor were taken. These data are compared with steady-state head-flow relationships taken at a number of speeds. This allows the determination of the relative deviation between the transient and steady-state head-flow-relationships and thus answers the question of the validity of steady-state assumptions during rapid transients. The impact of the fast transients on efficiency and consumed power, which can be derived from the speed decay of the system, as well as the impact of nonstationary heat transfer are also evaluated and reported.

scholarly journals Relationship of transient and steady-state auditory evoked fields

1993 ◽  
Vol 88 (5) ◽  
pp. 389-396 ◽  
Author(s):  
C. Pantev ◽  
T. Elbert ◽  
S. Makeig ◽  
S. Hampson ◽  
C. Eulitz ◽  
...  
Keyword(s):  
Steady State ◽  
Auditory Evoked Fields ◽  
Evoked Fields ◽  
Relationship Of ◽  
Transient And Steady State

scholarly journals Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions

2019 ◽  
Vol 9 (21) ◽  
pp. 4610 ◽  
Author(s):  
Dario Di Maio ◽  
Carlo Beatrice ◽  
Valentina Fraioli ◽  
Pierpaolo Napolitano ◽  
Stefano Golini ◽  
...  
Keyword(s):  
Steady State ◽  
Natural Gas ◽  
Catalytic Converter ◽  
Operating Conditions ◽  
Oxygen Storage ◽  
Continuous Control ◽  
Engine Exhaust ◽  
Compressed Natural Gas ◽  
The Impact ◽  
Three Way Catalyst

The main objective of the present research activity was to investigate the effect of very fast composition transitions of the engine exhaust typical in real-world driving operating conditions, as fuel cutoff phases or engine misfire, on the aftertreatment devices, which are generally very sensitive to these changes. This phenomenon is particularly evident when dealing with engines powered by natural gas, which requires the use of a three-way catalyst (TWC). Indeed, some deviations from the stoichiometric lambda value can interfere with the catalytic converter efficiency. In this work, a numerical “quasi-steady” model was developed to simulate the chemical and transport phenomena of a specific TWC for a compressed natural gas (CNG) heavy-duty engine. A dedicated experimental campaign was performed in order to evaluate the catalyst response to a defined λ variation pattern of the engine exhaust stream, thus providing the data necessary for the numerical model validation. Tests were carried out to reproduce oxygen storage phenomena that make catalyst behavior different from the classic steady-state operating conditions. A surface reaction kinetic mechanism concerning CH4, CO, H2, oxidation and NO reduction has been appropriately calibrated at different λ values with a step-by-step procedure, both in steady-state conditions of the engine work plan and during transient conditions, through cyclical and consecutive transitions of variable frequency between rich and lean phases. The activity also includes a proper calibration of the reactions involving cerium inside the catalyst in order to reproduce oxygen storage and release dynamics. Sensitivity analysis and continuous control of the reaction rate allowed evaluating the impact of each of them on the exhaust composition in several operating conditions. The proposed model predicts tailpipe conversion/formation of the main chemical species, starting from experimental engine-out data, and provides a useful tool to evaluate the catalyst’s performance.

Formaldehyde Formation in Large Bore Engines Part 2: Factors Affecting Measured CH2O

1999 ◽  
Vol 122 (4) ◽  
pp. 611-616 ◽  
Author(s):  
Daniel B. Olsen ◽  
Charles E. Mitchell
Keyword(s):  
Natural Gas ◽  
Air Pollutant ◽  
Operating Conditions ◽  
Factors Affecting ◽  
Natural Gas Engines ◽  
Spark Timing ◽  
Wide Range ◽  
Hazardous Air Pollutant ◽  
Relationship Of ◽  
The Impact

Current research shows that the only hazardous air pollutant of significance emitted from large bore natural gas engines is formaldehyde CH2O. A literature review on formaldehyde formation is presented focusing on the interpretation of published test data and its applicability to large bore natural gas engines. The relationship of formaldehyde emissions to that of other pollutants is described. Formaldehyde is seen to have a strong correlation to total hydrocarbon (THC) level in the exhaust. It is observed that the ratio of formaldehyde to THC concentration is roughly 1.0–2.5 percent for a very wide range of large bore engines and operating conditions. The impact of engine operating parameters, load, rpm, spark timing, and equivalence ratio, on formaldehyde emissions is also evaluated. [S0742-4795(00)01004-8]

Transient and Steady State Vibration Analysis of a Wavy Thrust Bearing

2005 ◽  
Vol 128 (1) ◽  
pp. 139-145 ◽  
Author(s):  
H. Zhao ◽  
F. K. Choy ◽  
M. J. Braun
Keyword(s):  
Steady State ◽  
Vibration Analysis ◽  
Thrust Bearing ◽  
Numerical Procedure ◽  
Operating Conditions ◽  
System Stability ◽  
Thrust Bearings ◽  
External Perturbations ◽  
Vibration Signature ◽  
Transient And Steady State

This paper describes a numerical procedure for analyzing the dynamics of transient and steady state vibrations in a wavy thrust bearing. The major effects of the wavy geometry and the operating parameters on the dynamic characteristics of the bearing had been discussed in a previous paper; the present paper thus concentrates on examining the relationships between the development of the transient and steady state vibrations when operating conditions are parametrically varied. Special attention is given to the development of steady state vibrations from initial transients with comparisons and consequences to the overall system stability. Numerical based vibration signature analysis procedures are then used to identify and quantify the transient vibrations. The conclusions provide general indicators for designing wavy thrust bearings that are less susceptible to transients induced by external perturbations.

scholarly journals Experimental investigation energy balance and distribution of a turbocharged GDI engine fuelled with ethanol and gasoline blend under transient and steady-state operating conditions

2020 ◽  
Vol 24 (1 Part A) ◽  
pp. 243-257 ◽  
Author(s):  
Xiongbo Duan ◽  
Yiqun Liu ◽  
Xianjie Zhou ◽  
Peng Zou ◽  
Jingping Liu
Keyword(s):  
Experimental Investigation ◽  
Steady State ◽  
Thermal Efficiency ◽  
Cfd Simulation ◽  
Design Procedure ◽  
Operating Conditions ◽  
Fuel Injector ◽  
Gdi Engine ◽  
Rotating Injector ◽  
Transient And Steady State

Improving the performance and reducing emissions in a Diesel engine is the single most objective in current research. Various methods of approach have been studied and presented in literature. A novel but not so pursued study is on the performance of a rotating diesel injector. To date, there has been very little study by implementing a rotating injector. Studies have shown an improvement on the performance of an engine, but with a complicated external rotating mechanism. In the present research, a novel self-rotating fuel injector is designed and developed that is expected to improve the performance without the need for a complicated rotating mechanism. The design procedure, CFD simulation along with 3- D printing of a prototype is presented. Numerical modelling and simulation are performed to study the combustion characteristics of the rotating injector viz-a-viz a standard static injector. Comparison based on heat release, efficiency, and emissions are presented. While the proposed 9-hole injector had slight loss in thermal efficiency, the modified 5-hole had a slight increase in thermal efficiency when compared to the static baseline readings. The NOx reduced by 13% and CO increased by 14% compared baseline emissions for the 5-hole version.

Thermal Assessment of Cooling System Incorporating Heat Sink and Embedded Heat Pipes for Testing High Power Microelectronics

2005 ◽  
Author(s):  
Victor Adrian Chiriac ◽  
Tien-Yu Tom Lee
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Pipes ◽  
Optimal Operation ◽  
Operating Conditions ◽  
Peak Temperature ◽  
Testing System ◽  
The Impact

A numerical study was conducted to model the transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, copper inserts and a leaded package dissipating large amounts of power over short time durations. The system is optimized by choosing appropriate heat sink/fan structure for the efficient operation of the device under constant powering. The intent of the study is to provide a better understanding and prediction of a transient powering scenario at high powering levels, while evaluating the impact of alternative cooling fan/heat pipe designs on the thermal performance of the testing system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is ~95°C, with the corresponding Rja thermal resistance ~0.58°C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (the end temperature reduces by ~16%). The temperature drop between peak and end for each cycle is ~80.2°C, while the average power per transient cycle is ~31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of ~98°C. Applying the superposition principle to the steady state value and 40.1°C fluctuation, the maximum transient temperature after a large number of cycles will not exceed ~138.1°C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum and minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are investigated; using a combination of numerical and analytical methods, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. The comparison between measurement and simulation shows good agreement.

Facing the Challenges in CFD Modelling of Multistage Axial Compressors

2017 ◽  
Author(s):  
Lorenzo Cozzi ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Pio Astrua ◽  
...  
Keyword(s):  
Steady State ◽  
Axial Compressor ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Cfd Modelling ◽  
Main Research ◽  
Axial Compressors ◽  
Rotor Stator Interaction ◽  
The Impact

Multistage axial compressors have always been a great challenge for designers since the flow within these kind of machines, subjected to severe diffusion, is usually characterized by complex and widely developed 3D structures, especially next to the endwalls. The development of reliable numerical tools capable of providing an accurate prediction of the overall machine performance is one of the main research focus areas in the multistage axial compressor field. This paper is intended to present the strategy used to run numerical simulations on compressors achieved by the collaboration between the University of Florence and Ansaldo Energia. All peculiar aspects of the numerical setup are introduced, such as rotor/stator tip clearance modelling, simplified shroud leakage model, gas and turbulence models. Special attention is payed to the mixing planes adopted for steady-state computations because this is a crucial aspect of modern heavy-duty transonic multistage axial compressors. In fact, these machines are characterized by small inter-row axial gaps and transonic flow in front stages, which both may affect non-reflectiveness and fluxes conservation across mixing planes. Moreover, the high stage count may lead to conservation issues of the main flow properties form inlet to outlet boundaries. Finally, the likely occurrence of partspan flow reversal in the endwall regions affects the robustness of non-reflecting mixing plane models. The numerical setup has been validated on an existing machine produced and experimentally tested by Ansaldo Energia. In order to evaluate the impact on performance prediction of the mixing planes introduced in the steady-state computation, un-steady simulations of the whole compressor have been performed at different operating conditions. These calculations have been carried out both at the compressor design point and close to the surge-line to evaluate the effect of rotor/stator interaction along the compressor working line.

Thermal Modeling of HRSG Transient Behavior in Combined Cycle Power Plants

2006 ◽  
Author(s):  
Sepehr Sanaye ◽  
Moein Rezazadeh ◽  
Jalaleddin Oladi ◽  
Gholam Hossein Sadeghpoor ◽  
Farid Bashiri ◽  
...  
Keyword(s):  
Steady State ◽  
Power Plants ◽  
Cold Start ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Master Program ◽  
Load Change ◽  
Start Up ◽  
Program Software ◽  
Transient And Steady State

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.

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