Steady-state Performance Model Research Articles

A computationally efficient and high-fidelity 1D steady-state performance model for PEM fuel cells

The performance of a proton exchange membrane (PEM) fuel cell is determined by many factors, including operating conditions, component specifications, and system design, making it challenging to predict its performance over a wide range of operating conditions. Existing fuel cell models can be complex and computationally demanding or may be over-simplified by neglecting many transport phenomena. Therefore, a high-fidelity and computationally efficient model is urgently needed for the model-based control of fuel cells. In this study, semi-implicit multi-physics numerical models have been established, taking the mass, momentum, reactants, liquid water, membrane water, electrons, ions, and energy in all fuel cell components into account. The developed 1D model is of high fidelity by incorporating the two-phase flow, non-isothermal effect, and convection, and is still computationally efficient. These models are validated against data from an auto manufacturer with good agreements, and the computing efficiency is evaluated on a modest laptop computer. The modeling results suggest that the two-phase flow model exhibits better prediction accuracy than the single-phase flow model when reactants are fully humidified, while under low humidity conditions, the two models present equivalent performance as liquid water does not exist in the fuel cell components. The results also suggest that the maximum convective/diffusive ratio of H2, O2, and vapor mass fluxes can be 12%, 5.3%, and 35%, respectively, which are ignored in most diffusion-dominant models. The developed models are computationally efficient, requiring only 0.56 s and 0.26 s to simulate a steady-state operation of fuel cells for the two- and single-phase flow models, respectively. This implies that the developed models are suitable for the control of PEM fuel cells.

Simulation of packed bed reactors for naphtha reforming unit

The study focused on the performance evaluation of catalytic naphtha reforming unit via a packed bed reactors arranged in series. Three series arranged packed bed naphtha reforming reactors were developed and simulated using Aspen hysys software and steady state performance models of the packed bed naphtha reforming reactor were developed through the application of the principle of conservation of mass and energy to predict both the yields of theses reactors, their dimensions in terms of length, diameter, height, volume and temperature effects or progressions along the reactors’ length respectively. Three main reaction paths were considered in this research study that include the conversion of naphthenes to aromatics, naphthenes to paraffins and hydrocracking of paraffins. The developed performance models yielded first order ordinary differential equations which were solved using Runge-Kutta fourth order ODE45 solver. The packed bed reactor operating conditions of temperature and pressure are between 4800C and 5200C and 2atm respectively with ninety percent (90%) conversion. The simulated reactor performance model for the three reactors yielded 29.7 m3, 40.78 m3 and 52.33 m3 for reactor volume, catalyst bed height of 11m, 12.98 m, 16 m, and reactor’s diameter of 1.85 m, 2 m and 2.04 m respectively.

The Effect of Physical Faults on a Three-Shaft Gas Turbine Performance at Full- and Part-Load Operation.

A gas path analysis approach of dynamic modelling was used to examine the gas turbine performance. This study presents an investigation of the effect of physical faults on the performance of a three-shaft gas turbine at full-load and part-load operation. A nonlinear steady state performance model was developed and validated. The datasheet from the engine manufacturer was used to gather the input and validation data. Some engineering judgement and optimization were used. Following validation of the engine performance model with the engine manufacturer data using physical fault and component health parameter relationships, physical faults were implanted into the performance model to evaluate the performance characteristics of the gas turbine at degradation state at full- and part-load operation. The impact of erosion and fouling on the gas turbine output parameters, component measurement parameters, and the impact of degraded components on another primary component of the engine have been investigated. The simulation results show that the deviation in the output parameters and component isentropic efficiency due to compressor fouling and erosion is linear with the load variation, but it is almost nonlinear for the downstream components. The results are discussed following the plots.

Aircraft Performance Model Calibration and Validation for General Aviation Safety Analysis

Performance models facilitate a wide range of safety analyses in aviation. In an ideal scenario, the performance models would show inherently good agreement with the true performance of the aircraft. However, in reality, this is rarely the case: either owing to underlying simplifications or due to the limited fidelity of applicable tools or data. In such cases, calibration is required to fine-tune the behavior of the performance models. For point-mass steady-state performance models, challenges arise due to the fact that there is no obvious, unique metric or flight condition at which to assess the accuracy of the model predictions, as well as because a large number of model parameters may potentially influence model accuracy. This work presents a two-level approach to aircraft performance model calibration. The first level consists of using manufacturer-developed performance manuals for calibration, whereas the second level provides additional refinement when flight data are available. The performance models considered in this work consist of aerodynamic and propulsion models (performance curves) that are capable of predicting the nondimensional lift, drag, thrust, and torque at any given point in time. The framework is demonstrated on two representative general aviation aircraft. The demonstrated approach results in models that can predict critical energy-based safety metrics with improved accuracy for use in retrospective safety analyses.

Gas turbine gas path diagnosis under transient operating conditions: A steady state performance model based local optimization approach

To improve gas turbine reliability and availability and prolong service life while reducing operation and maintenance costs, many gas path diagnostic methods based on steady state or quasi-steady state have been obtained, but no complete scientific system of gas-path diagnosis has been formed yet. Nowadays the operation of gas turbines needs to be more flexible in grid support mode, and the service life will be consumed faster than that during base load steady-state /quasi-steady-state operation under transient conditions. Therefore, it is urgent to solve the problem of optimal identification of component health parameters under transient conditions. Aiming at above problem, a novel gas path diagnostic method is proposed. Firstly, an equivalent cooling flow processing method is proposed for thermodynamic modeling for gas path diagnostic purpose. Secondly, a steady state performance model based diagnostic scheme under transient conditions based on local optimization algorithm is proposed. At last the diagnostic performance with Newton-Raphson algorithm and Kalman filter algorithm as local optimization algorithm is comparatively analyzed. The case studies have showed that the proposed diagnostic method can be effectively utilized to detect both component gradual failure and abrupt fault quantitatively and the former has better real-time performance and diagnostic accuracy under transient conditions.

Dynamic and steady state performance model of fire tube boilers with different turn boxes

The market for fire tube boilers is increasingly demanding custom designs from the manufacturers. For these new designs, a comprehensive thermal model is needed. In this article, both a steady state and dynamic thermal model is developed based on the plug flow furnace model with general experimental correlations. The steady state model allows optimizing (i.e. safely downsizing) boiler designs. This model has been verified with measurement reports. The dynamic model is used to estimate the peak load capability of a boiler. In the presented case, the fire tube boiler can produce up to 2.5 times the nominal steam flow rate for a period of 10 min. Special attention has been paid to the turn boxes and their specific placement, which other models in literature neglect. The efficiency penalty of a non-submerged turn box can reach up to 12% but can be reduced significantly by insulation. Turn boxes also affect peak load capability. If the total length of the boiler is constant, submerging the turn box has a positive effect on the peak load capability. This effect is mostly attributed to the increased water volume. Finally, the article includes a comparison between the plug flow furnace model the ε-NTU method and the ε-NTU method with inclusion of radiation to model the tube passes. The ε-NTU method with inclusion of radiation allows to significantly reduce the necessary number of control volumes without reduction in the model accuracy.

Effect of passing clouds on the dynamic performance of a CSP tower receiver with molten salt heat storage

The present paper explores the off-design performance of a CSP tower receiver due to the passage of clouds over the solar field. A quasi steady-state performance model is considered in the first part of the paper, accounting for the optical performance of the solar field and receiver only, yielding the expected incoming heat flux distribution on the aperture plane of the receiver and without further considerations about the thermal performance of the receiver itself. The twofold aim of this analysis is to identify the type of cloud that brings about the worst operating conditions of the receiver and to define an aiming strategy that produces the most homogeneous distribution of the incoming heat flux, this being a indirect metric of reduced thermal stress on this component. It is observed that larger clouds have a more negative impact on the heat flux distribution whereas the effect of smaller clouds is easily compensated for by other uncovered areas of the field. Large differences in performance arise when considering different aiming strategies, what leads to the selection of one of these as the optimum one given that it manages to evenly distribute the heat flux over the receiver surface. This limits the number and intensity of hot spots without affecting the overall power production. The optimum strategy is based on pointing the heliostats towards different aiming spots strategically located on the receiver surface, depending on the distance between tower and heliostat.The second part of the paper presents an in-house code developed to study the transient thermal performance of the receiver. The outcome of this second analysis confirms the results of the previous optical study: the selected optimum strategy leads to a 1% higher efficiency of the receiver. Also, the temperature distribution of the larger shadows is more harmful than when several smaller clouds pass over the solar field, both for the larger temperature gradients in the receiver and for the production of molten salts. This is also confirmed in the last part of the paper where different patterns of combined cloud passages are explored in regards to the charge/discharge process of the thermal energy storage system.

Modeling of steady-state performance of skid-steering for high-speed tracked vehicles

This paper presents a high-fidelity, general, and modular method for lateral dynamics simulation of high-speed tracked vehicle. Based on classic terramechanics, a novel nonlinear track terrain model is derived. The track terrain model meets the needs of longitudinal and steering motions, comprehensive track slips, and modular modeling for tracked vehicles with various configurations. The proposed lateral dynamics model is in reasonably agreement with the available experimental data. Using the lateral dynamics model, the main factors (normal pressure distribution, position of gravity center, and ratio of track-ground contact length and tread L/B) effecting the steady state characteristics of skid steering are discussed. The normal pressure distribution is idealized as trapezoid and dual trapezoid distribution to reflect same common driving situation. The under-steer parameter is introduced in this paper to quantitatively evaluate the steady-state characteristics of skid steering for tracked vehicle. The results show that the ratio of theoretical speed difference and average speed of both side tracks Δu/u as the steering input is more suitable for the high-speed tracked vehicle. The vehicle with dual trapezoid normal pressure distribution slightly tending to localize in the middle of track or with slightly rearward position of gravity center has better handling stability characteristics.

Jet Engine Gas Path Analysis Based on Takeoff Performance Snapshots

Current engine condition monitoring (ECM) systems for jet engines include the analysis of on-wing gas path data using steady-state performance models. Such data, which are also referred to as performance snapshots, usually are taken during cruise flight and during takeoff. Using steady-state analysis, it is assumed that these snapshots have been taken under stabilized operating conditions. However, this assumption is reasonable only for cruise snapshots. During takeoff, jet engines operate in highly transient conditions with significant heat transfer occurring between the fluid and the engine structure. Hence, steady-state analysis of takeoff snapshots is subject to high uncertainty. Because of this, takeoff snapshots are not used for performance analysis in current ECM systems. We quantify the analysis uncertainty by transient simulation of a generic takeoff maneuver using a performance model of a medium size two-shaft turbofan engine with high bypass ratio. Taking into account the influence of the preceding operating regimes on the transient heat transfer effects, this takeoff maneuver is extended backward in time to cover the aircraft turnaround as well as the end of the last flight mission. We present a hybrid approach for thermal calculation of both the fired engine and the shutdown engine. The simulation results show that takeoff derate, ambient temperature, taxi-out (XO) duration and the duration of the preceding aircraft turnaround have a major influence on the transient effects occurring during takeoff. The analysis uncertainty caused by the transient effects is significant. Based on the simulation results, we propose a method for correction of takeoff snapshots to steady-state operating conditions. Furthermore, we show that the simultaneous analysis of cruise and corrected takeoff snapshots leads to significant improvements in observability.

Theory and Modeling of Fuel Cells: Extravaganza to Panacea?

<i>Theory and Modeling of Fuel Cells: Extravaganza to Panacea?</i>

Navigating environmental, economic, and technological trade-offs in the design and operation of submerged anaerobic membrane bioreactors (AnMBRs)

Anaerobic membrane bioreactors (AnMBRs) enable energy recovery from wastewater while simultaneously achieving high levels of treatment. The objective of this study was to elucidate how detailed design and operational decisions of submerged AnMBRs influence the technological, environmental, and economic sustainability of the system across its life cycle. Specific design and operational decisions evaluated included: solids retention time (SRT), mixed liquor suspended solids (MLSS) concentration, sludge recycling ratio (r), flux (J), and specific gas demand per membrane area (SGD). The possibility of methane recovery (both as biogas and as soluble methane in reactor effluent) and bioenergy production, nutrient recovery, and final destination of the sludge (land application, landfill, or incineration) were also evaluated. The implications of these design and operational decisions were characterized by leveraging a quantitative sustainable design (QSD) framework which integrated steady-state performance modeling across seasonal temperatures (using pilot-scale experimental data and the simulating software DESASS), life cycle cost (LCC) analysis, and life cycle assessment (LCA). Sensitivity and uncertainty analyses were used to characterize the relative importance of individual design decisions, and to navigate trade-offs across environmental, economic, and technological criteria. Based on this analysis, there are design and operational conditions under which submerged AnMBRs could be net energy positive and contribute to the pursuit of carbon negative wastewater treatment.

Modeling the Energy Yield Enhancement From a Wind Turbine at a Deep Offshore Low Wind Site Through Combined Power and Thermocline Energy Production

This paper presents steady-state performance modeling and analysis of a novel wind powered system that concurrently exploits thermocline thermal energy through deep sea water extraction in conjunction with offshore wind energy for combined power and thermal energy production. A single offshore wind turbine rotor directly coupled to a large positive displacement pump is modeled to supply deep sea water at high pressure to a land-based plant, the latter consisting of a hydro-electric generator coupled to a heat exchanger. The steady-state power-wind speed characteristics for the system are derived from a numerical thermofluid model. The latter integrates the hydraulic characteristics of the wind turbine-pump combination and a numerical code to simulate the heat gained/lost by deep sea water as it flows through a pipeline to shore. The model was applied to a hypothetical megawatt-scale wind turbine installed at a deep offshore low wind site in the vicinity of the Central Mediterranean island of Malta. One year of wind speed and ambient measurements were used in conjunction with marine thermocline data to estimate the time series electricity and thermal energy yields. The total energy yield from the system was found to be significantly higher than that from a conventional offshore wind turbine generator (OWTG) that only produces electricity. It could be shown that at sites having less energetic wind behavior and high ambient temperatures as a result of a hotter climate, the cooling energy component that can be delivered from such a system is relatively high even at periods of low wind speeds.

SIMULINK를 이용한 2-스풀 분리형 배기방식 터보팬 엔진의 구성품 성능맵 생성 및 성능모사에 관한 연구

본 연구에서는 중형 항공기의 추진 기관인 2 스풀 분리-배기 형식 터보팬 엔진 (BR715-56)의 성능 해석을 수행하기 위하여 상용코드인 MATLAB/SIMULINK를 이용하여 성능모델을 구성하였으며 유량 및 일 조합에 새로운 조합 서브시스템 블록을 새로이 개발하였다. 성능 모사는 먼저 팬, 고압압축기, 고압터빈, 저압터빈 구성품 성능 맵들을 축척방법을 이용하여 유사성능 맵들로 부터 생성하였고, 다음은 탈설계점 성능 해석을 할 수 있도록 구성품들 간 유량과 일 조합이 이루어 질수 있도록 하였다. 제안된 SIMULINK 성능모델은 정상 및 동적 모사와 사용자 편의의 장점을 가지고 있으며, 다양한 작동 조건들에서 개발된 프로그램을 이용한 탈설계점 해석 결과들이 GASTURB에 의한 해석 결과들과 잘 일치함이 확인 되었다. In this work, a steady-state performance modeling and off-design performance analysis of the 2-spool separate-flow turbofan engine named (BR715-56) which is a power plant for the narrow body commercial aircraft is carried out for engine performance behaviors investigation and condition monitoring using a commercial code MATLAB/SIMULINK. Firstly, the engine component maps of fan, high pressure compressor, high pressure turbine and low pressure turbine are generated from similar component maps using the scaling method, and then the off-design performance simulation model is constructed by the mass flow matching and the work matching between components. The model is developed using SIMULINK, which has advantages of easy steady-stare and dynamic modelling and user friendly interface function. It is found that the off-design performance analysis results using the proposed model are well agreed with the performance analysis results by GASTURB at various operating conditions.

A General Matrix Approach to Model Steady-State Performance of Cross-Flow Heat Exchangers

A steady-state performance model of multirow multipass cross-flow tubular heat exchangers is developed. The proposed matrix approach uses the concepts of local effectiveness, energy balance, and number of transfer units (NTU) applied to every pass/row in the cross-flow heat exchanger to predict thermal performance. The method can predict the total effectiveness of assemblies of heat exchangers. Several circuiting configurations, such as overall counter-cross-flow, overall parallel cross-flow, and fluids in parallel in one of the streams, were considered. Predictions of the steady heat transfer performance of selected multirow multipass cross-flow heat exchangers are obtained by applying the general matrix approach. The heat exchanger geometries selected for the comparative study represent common cross-flow heat exchanger configurations used in industry. For these heat exchangers the overall heat exchanger effectiveness values were computed for various capacity rate ratios and NTU values. The validity of the matrix approach was then verified by comparing the resulting predictions with those obtained using the P-NTU approach and the Domingos method for the selected complex cross-flow heat exchanger configurations.

Modeling Stream Communications in Component-based Applications

Component technology is a promising approach to develop Grid applications, allowing to design very complex applications by hierarchical composition of basic components. Nevertheless, component applications on Grids have complex deployment models. Performance-sensitive decisions should be taken by automatic tools, matching developer knowledge about component performance with QoS requirements on the applications, in order to find deployment plans that satisfy a Service Level Agreement (SLA). This paper presents a steady-state performance model for component-based applications with stream communication semantics. The model strictly adheres to the hierarchical nature of component-based applications, and is of practical use in launch-time decisions.

A Techno-Economic Analysis of a Proposed 1.5 MW Wind Turbine with a Hydrostatic Drive Train

This paper presents a techno-economic feasibility study for a proposed 1.5 MW wind turbine utilizing a continuously variable ratio hydrostatic drive train between the rotor and the generator. The estimated cost of energy is compared to that of a conventional wind turbine of equivalent rated power. The annual energy production is estimated for the hydrostatic turbine using an assumed wind speed distribution and a turbine power curve resulting from a steady state performance model of the turbine. The initial capital cost of the turbine is estimated using cost models developed for various components unique to the hydrostatic turbine as well as economic parameters and models developed by the National Renewable Energy Lab (NREL) in the WindPACT advanced wind turbine drive train study. The resulting cost of energy, along with various performance characteristics of interest, are presented and compared to those of the WindPACT baseline turbine intended to represent a conventional utility scale wind turbine.

Steady-State and Transient Performance Modeling of Smart UAV Propulsion System Using SIMULINK

Because an aircraft gas turbine operates under various flight conditions that change with altitude, flight velocity, and ambient temperature, the performance estimation that considers the flight conditions must be known before developing or operating the gas turbine. More so, for the unmanned aerial vehicle (UAV) where the engine is activated by an onboard engine controller in emergencies, the precise performance model including the estimated steady-state and transient performance data should be provided to the engine control system and the engine health monitoring system. In this study, a graphic user interface (GUI) type steady-state and transient performance simulation model of the PW206C turboshaft engine that was adopted for use in the Smart UAV was developed using SIMULINK for the performance analysis. For the simulation model, first the component maps including the compressor, gas generator turbine, and power turbine were inversely generated from the manufacturer’s limited performance deck data by the hybrid method. For the work and mass flow matching between components of the steady-state simulation, the state-flow library of SIMULINK was applied. The proposed steady-state performance model can simulate off-design point performance at various flight conditions and part loads, and in order to evaluate the steady-state performance model their simulation results were compared with the manufacturer’s performance deck data. According to comparison results, it was confirmed that the steady-state model agreed well with the deck data within 3% in all flight envelopes. In the transient performance simulation model, the continuity of mass flow (CMF) method was used, and the rotational speed change was calculated by integrating the excess torque due to the transient fuel flow change using the Runge–Kutta method. In this transient performance simulation, the turbine overshoot was predicted.

Technical and economic performance analysis for a microturbine in combined heat and power generation

This paper focuses on a single-shaft microturbine in combined heat and power generation. In the application, the microturbine is operated by the heat demand and it replaces purchased electricity and produced heat in an existing boiler. The objective of the study is to analyze the effect of recuperation and different load control methods on the overall economy of the operation. The control parameters include the turbine inlet temperature and the rotational speed of the shaft. As a basis for the analysis, a steady-state performance model using realistic component descriptions has been constructed for the microturbine. The economy of the operation is determined by combining the performance model with the economy model developed for the engine. The economy model uses the net present value from investing in the microturbine as a criterion. As a result, the conditions for the cost-effective operation of the engine are determined. In addition to the analysis of general validity, the developed models are applied to a case with given profiles for heat and power demand. The size range with the highest economic potential is determined for the microturbine options. For the selected size, the maximum costs that can be allowed for the investment are determined. Apart from the microturbine specifications and case-specific heat and power demand, the results are strongly dependent on the economic parameters. The sensitivity of the results against the energy prices is presented.

Gas Turbine Engine and Sensor Fault Diagnosis Using Optimization Techniques

A diagnostic system is described for performance analysis of gas turbine engine components and sensors. The system estimates the performance parameters expressing the fault condition of the engine components in the presence of measurement noise and biases. The measurement uncertainty is supposed to affect even the parameters setting the operating condition of the engine. Estimation is performed through bptimization of an objective function by means of an ad hoc genetic algorithm. The genetic algorithm uses an accurate nonlinear steady-state performance model of the engine. The only statistical assumption required by the technique concerns the measurement noise and the maximum allowed number of faulty sensors and engine components, which is enclosed as a constraint. The technique has been thoroughly tested with the model of a low bypass ratio turbofan, and the results show the high level of accuracy achieved.

Distributed steady state nonlinear modeling of turboalternators

This paper presents an alternate approach for modeling of steady state performance of large turboalternators including the effects of magnetic saturation. To avoid the superposition limitations of the conventional d-q approach, a sectoral model of a pole of the machine is developed and solved iteratively. The computational effort is orders of magnitude less than for a finite element solution. Results from the proposed model are compared with those from a conventional d-q model and with measurements made for a wide range of load conditions on a 588-MVA turbogenerator.