Field Outlet Research Articles

Constraint Optimal Model-Based Disturbance Predictive and Rejection Control Method of a Parabolic Trough Solar Field

The control of the field outlet temperature of a parabolic trough solar field (PTSF) is crucial for the safe and efficient operation of the solar power system but with the difficulties arising from the multiple disturbances and constraints imposed on the variables. To this end, this paper proposes a constraint optimal model-based disturbance predictive and rejection control method with a disturbance prediction part. In this method, the steady-state target sequence is dynamically corrected in the presence of constraints, the lumped disturbance, and its future dynamics predicted by the least-squares support vector machine. In addition, a maximum controlled allowable set is constructed in real time to transform an infinite number of constraint inequalities into finite ones with the integration of the corrected steady-state target sequence. On this basis, an equivalent quadratic programming constrained optimization problem is constructed and solved by the dual-mode control law. The simulation results demonstrate the setpoint tracking and disturbance rejection performance of our design under the premise of constraint satisfaction.

Usage of Artificial Intelligence for Prediction of CSP Plant Parameters

Artificial intelligence offers the opportunity to use the large amounts of data from commercial CSP power plants to supplement the experience of operations personnel through accurate predictions to optimize predictive maintenance and operations management. As a constant high outlet temperature of the solar field even under fluctuating environmental conditions is a relevant factor for the efficiency of commercial CSP power plants, the focus of this work is on the prediction of solar field outlet temperature. The analysis of this work is based on operating data of the commercial CSP power plant Andasol III in Spain with a temporal resolution of 5 minutes over a period of 5 consecutive years. To optimize the prediction, the three models random forest, feed forward artificial neural network – also known as multiple layer perceptron (MLP) – and long short-term memory (LSTM) network were compared in their performance and optimized separately by means of hyperparameter variation. The best results were achieved with the LSTM model with a mean absolute error of 6.78 K averaged over the prediction period of one year. By using AI models, future deviating outlet temperatures can be predicted at an early stage. These predictions offer the possibility to keep the outlet temperature more constant by predictive adjustment of the mass flow and thus increase the efficiency of the solar field and the whole CSP plant.

Thermal Analysis of Parabolic and Fresnel Linear Solar Collectors Using Compressed Gases as Heat Transfer Fluid in CSP Plants

This study introduces the use of compressed air as a heat transfer fluid in small-scale, concentrated linear solar collector technology, evaluating its possible advantages over traditional fluids. This work assumes the adoption of readily available components for both linear parabolic trough and Fresnel collectors and the coupling of the solar field with Brayton cycles for power generation. The aim is to provide a theoretical analysis of the applicability of this novel solar plant configuration for small-scale electricity generation. Firstly, a lumped thermal model was developed in a MatLab® (v. 2023a) environment to assess the thermal performance of a PT collector with an evacuated receiver tube. This model was then modified to describe the performance of a Fresnel collector. The resulting optical–thermal model was validated through literature data and appears to provide realistic estimates of temperature distribution along the entire collector length, including both the receiver tube surface and the Fresnel collector’s secondary concentrator. The analysis shows a high thermal efficiency for both Fresnel and parabolic collectors, with average values above 0.9 (in different wind conditions). Th5s study also shows that the glass covering of the Fresnel evacuated receiver, under the conditions considered (solar field outlet temperature: 550 °C), reaches significant temperatures (above 300 °C). Furthermore, due to the presence of the secondary reflector, the temperature difference between the upper and the lower part of the glass envelope can be very high, well above 100 °C in the final part of the collector string. Differently, in the case of PTs, this temperature difference is quite limited (below 30 °C).

Design of a Parabolic Trough Collector Solar Field for a Pilot CO2 Capture Plant from Natural Gas Combined Cycle Power Plant Flue Gas.

A parabolic trough collector solar field was designed to supply the heat needed to regenerate the CO2-rich monoethanolamine in a solar-assisted carbon capture system. Process design modeling was performed for 90% of the CO2 removal from 1% of the flue gas produced by a 255 MWe natural gas combined cycle power plant. Calculations with and without 24 h of thermal energy storage by increasing the solar collector size needed and providing a buffer vessel to store hot heat transfer fluid were performed. A dynamic analysis of the solar field using the hourly solar forecast was performed to investigate how heat transfer fluid mass flow changes during January and June to maintain the desired parabolic solar field outlet temperature needed for CO2 reboiler operation. The calculations provided here present an explicit method to calculate relevant solar field design parameters that can be scaled up and used in solar energy-assisted gas capture processes.

Analysis of a solar driven ORC-absorption based CCHP system from a novel exergy approach

The present study comprehensively analyses the thermodynamic performance of a zero-emissions solar driven trigeneration system using a numerical approach. The analysis is conducted from both the First and Second law of Thermodynamics viewpoints, employing a novel and coherent exergy approach. Solar parabolic trough collectors (SPTCs) provide the heat input to an organic Rankine cycle (ORC) system, while a single-effect H2O/LiBr absorption heat pump is coupled in cascade to the ORC. The proposed ORC layout is based on a single-pressure regenerated, recuperated and superheated cycle. There is divergence of opinion among researchers regarding key aspects of the exergy analysis of trigeneration systems. Therefore, this study proposes the definition of the dead state conditions for each subsystem individually, taking into account their specific constraints. Unlike temperature, specific dead state conditions for pressure and composition are defined separately. An energy-exergy parametric approach is conducted to evaluate the effects of different system parameters on the system performance. The system is also optimized following single and multi-objective approaches with different criteria. The optimum system achieve an energy efficiency of 152.4%, an exergy efficiency of 21.1%, and an electrical-exergy efficiency of 17.5%. The electricity, cooling and heating productions are 82.1 kW, 200.4 kW and 471.7 kW, respectively. The SPTCs are identified as the main source of exergy destruction, responsible for 73% of inlet exergy is destructed. In addition, the systeḿs performance is shown to be sensitive to the variations in the solar field outlet temperature and in the ORC condensation temperature. Consequently, controlling these parameters could be effectively utilized for regulating power generation as well as cooling and heating production.

Adaptive control mechanism of shock wave/boundary layer interaction induced by the secondary recirculation jet with outlet backpressure

The increased and unstable flow field backpressure will cause problems such as the non-starting of the inlet tract, and the widespread shock wave/boundary layer interaction (SWBLI) phenomena in the supersonic flow field exacerbates these problems. Hence, a powerful flow control system is required. In this paper, backpressure is introduced at the flow field outlet, and the effect of different backpressure ratios on the flow field is explored. An adaptive control scheme is also developed by using the optimized secondary flow recirculation configuration. The three-dimensional implicit Reynolds Averaged Navier–Stokes equations are utilized for numerical simulation of the flow field. The results show that the adaptive control of the secondary recirculation jet has a positive control effect on the SWBLI of the flow field when backpressure is applied. Moreover, the adaptive control mechanism under the backpressure condition is analyzed, which is applicable to different backpressure flow fields with Mach numbers between 2.5 and 3.5.

Stable data‐driven Koopman predictive control: Concentrated solar collector field case study

AbstractNon‐linearity is an inherent feature of practical systems. Although there have been significant advances in the control of nonlinear systems, the proposed methods often require considerable computational resources or rely on local linearization around equilibrium points. The Koopman operator is an infinite‐dimensional linear operator that fully captures a system's non‐linear dynamics. However, one of the major problems is identifying a Koopman finite dimensional linear model for a nonlinear system. Initiated by the Willems’ fundamental Lemma, a class of data‐driven control methods has been developed for linear systems without the need to identify the system's matrices. Motivated by these two ideas, a data‐driven Koopman‐based predictive control scheme for non‐linear systems is proposed for unknown disturbed non‐linear systems utilising a finite‐length dataset. Then, considering the uncertainty in the Koopman state variables, a robust data‐driven Koopman predictive control structure is presented. Also, the results led to the design of a data‐driven Koopman predictive control strategy with terminal components to ensure the closed‐loop stability of nonlinear systems. The proposed scheme is tested on the distributed‐parameter model of the ACUREX solar collector field (located at Almería, Spain) to regulate the field outlet temperature around a desired value. Finally, simulation results show the effectiveness of the proposed approach.

Spatially Resolved Heterogeneous Electrocatalyst Degradation in Polymer Electrolyte Fuel Cells Subjected to Accelerated Aging Conditions

This work quantifies in-plane spatial heterogeneity (polymer electrolyte fuel cell cathode inlet vs outlet) in Pt particle size growth and distribution as a function of nitrogen (N2) flow rate during a square-wave accelerated stress test (AST). The average Pt particle sizes for membrane electrode assemblies (MEAs) subjected to N2 flow rates ranging from 4–16 sccm cm−2 are in the range 9–10.5 nm at the end-of-life (EOL) with similar electrochemically active surface area (ECSA) loss (∼65%). However, Pt particle size at EOL exhibits spatial heterogeneity: greater Pt particle size growth occurs near the flow field outlet than the inlet. The spatial heterogeneity for a fully-humidified N2 flow is believed to originate from non-uniform humidification (outlet is more humidified than the inlet) across the cell for a co-flow arrangement. A first-order rate model for ECSA loss predicts linear increase of the rate constant with N2 flow rate. The polarization losses of the aged MEAs over a wide range of operating conditions increase with N2 flow rate. From the results of this work, for holistically assessing durability of Pt catalysts in fuel cells at high humidity conditions, it is recommended to include purge gas flow rate as a stressor during an AST.

On the reliability of individual economic rationality measurements

A contemporary research agenda in behavioral economics and neuroeconomics aims to identify individual differences and (neuro)psychological correlates of rationality. This research has been widely received in important interdisciplinary and field outlets. However, the psychometric reliability of such measurements of rationality has been presumed without enough methodological scrutiny. Drawing from multiple original and published datasets (in total over 1,600 participants), we unequivocally show that contemporary measurements of rationality have moderate to poor reliability according to common standards. Further analyses of the variance components, as well as a allowing participants to revise previous choices, suggest that this is driven by low between-subject variance rather than high measurement error. As has been argued previously for other behavioral measurements, this poses a challenge to the predominant correlational research designs and the search for sociodemographic or neural predictors. While our results draw a sobering picture of the prospects of contemporary measurements of rationality, they are not necessarily surprising from a theoretical perspective, which we outline in our discussion.

Plant morphology and distribution control runoff and erosion in semi-arid environments

Understanding of the effects of vegetation patches and their distribution on soil erosion is important for ecological restoration in semi-arid environments. In this study, six multidimensional morphology metrics and expectations were applied to analyze the effects of plant morphology and distribution on runoff and sediment in two dominant plant species, Artemisia sacrorum Ledeb (AS) and Spiraea pubescensTurcz (SP), at micro-plots (60 cm × 60 cm plots) and field-plots (3 m × 10 m field-plots) in the Loess Plateau of China. The results indicated that, at micro-plot scale, the morphological heterogeneity of the two isolated shrubs (AS and SP) could be identified by spherical cap surface area of canopy and plant volume, which also lead to the isolated SP to have stronger ability to control runoff and erosion than the isolated AS. At field-plot scale, spherical cap surface area of canopy expectation (32.01 ± 1.99 m2) and plant volume expectation (4.06 ± 0.38 m3) of SP field-plots was significantly larger than those of the AS field-plots (15.85 ± 2.46 m2 and 1.10 ± 0.21 m3 respectively) in the potential contributing runoff area (2 m area form the field outlet). These differences result in SP field-plot to have more effective ability to retain runoff and to trap sediment than AS field-plot. The high-dimensional morphology metrics and expectations could determine the role of plant hydrological functions in controlling runoff and sediment at multiple spatial scales. This knowledge improves our understanding of the roles that plant morphology and distribution have on the runoff and erosion from different vegetated plots, and offers a new route to explaining plant morphology and distribution as controls on soil erosion in water-limited ecosystem.

A Dynamic Optimization Tool to Size and Operate Solar Thermal District Heating Networks Production Plants

The aim of the ISORC/OPTIMISER project is to increase and improve the use of solar thermal energy in district heating networks. One of the main tasks of the project is to develop an optimization tool for the sizing and operation of a solar district heating network. This is the first optimization tool using an open-source interface (Julia, JuMP) and solver (Ipopt) to solve nonlinear problems. This paper presents the multi-period optimization problem which is implemented to consider the dynamic variations in a year, represented by four typical days, with an hourly resolution. The optimum is calculated for a total duration of 20 years. First, this paper presents the modeling of the different components of a solar district heating network production plant: district network demand, storage and three sources, i.e., a fossil (gas) and two renewable (solar and biomass) sources. In order to avoid prohibitive computational time, the modeling of sources and storage has to be fairly simple. The multi-period optimization problem was formulated. The chosen objective function is economic: The provided economic model is accurate and use nonlinear equations. Finally the formulated problem is a nonlinear Programming problem. Optimization of the studied case exhibits consistent operating profiles and design. A comparison is made of different types of storage connection at the production site, highlighting the relevance of placing the storage at the solar field outlet. The optimum configuration supplies 49% of demand using solar energy, achieving a renewable rate of 69% in combination with the biomass boiler.

Re-distributing the field outlets for irrigation networks within the new growth cities: The Central District of Kerbala city as example

Generally, the rivers in both the natural and lined form use the open-section system to carry water, either for distribution or conveyance purposes. With time and depreciation effect, this system needs to be change or modify to become more indirectly suitable with growth of cities, and specially with transformation of land use from agricultural to residential. The present paper aims to reach a proper decision to re-distribute the field outlets for a part of AliHneidiyah river in Karbala city, Republic of Iraq, for the distance between stations (0+000) and (4+000), to choose between keeping up the current number of outlets or reduce them to a certain, actually used one. For this study, the cadastral maps were used as a reference to determine the agricultural areas served by the river during its route within the study area, and geographic information system to monitor the change in the nature of these areas represented by gradual transformation from agricultural to residential purpose, by using of satellite images for four different years, 2002, 2007, 2013, and 2016. The results of this study showed a great reduction in the agricultural areas on both sides of the chosen length of river route by a percentage of 88%, which leads to change location and specifications of the remain, actually used outlets. In addition, use the whole section for conveyance purposes to protect the water quality. This study showed that the geographic information system is a good and helpful technique for evaluation and make decisions of water related subjects.

Numerical Calculations on Liquid-Metal Magnetohydrodynamic Flow in Magnetic Field Inlet Region and Outlet Region

Numerical calculations have been performed on liquid-metal magnetohydrodynamic flows through a rectangular channel in the magnetic field inlet region and magnetic field outlet region. The conservation equations of fluid mass and fluid momentum and the Poisson equation for electrical potential have been solved numerically. The numerical calculations have been carried out for Hartmann (Ha) numbers up to the order of 10 000 and a rectangular channel with electrically conducting channel walls. Attention is focused on pressure drops along the flow channel in the magnetic field inlet region and outlet region. The loss coefficients ζ can be represented by for both the magnetic field inlet region and outlet region, where k is a coefficient, and Ha, Re, and β are the Hartmann number, the Reynolds number, and the channel aspect ratio, respectively. The coefficient k depends on the gradient of applied magnetic field in the magnetic field inlet region and outlet region. However, the coefficient k does not change with the Ha number, the Re number, the wall conductivity number, and the aspect ratio very much.

Full-day dynamic characteristics analysis of a solar aided coal-fired power plant in fuel saving mode

Solar aided (coal-fired) power generation (SAPG) technology has been rapidly developed over the last few years for its fewer coal consumption rate than the original coal-fired power plant and the lower initial investment than the solar alone thermal power generation. However, due to the frequent variation of meteorological conditions, the operation behaviors of the SAPG plant are ever-changing. In this paper, according to the transient models of SAPG plant, the continuous operation behaviors of a 330 MW SAPG system in a full day are studied. The coupling and decoupling times of the solar field are optimized, and variations of oil and feed water parameters in the solar field during the coupling and decoupling processes are discussed. Besides, some dynamic thermal performances of the SAPG system are studied under the control strategy of maintaining the solar field outlet heat transfer fluid (HTF) temperature constant when the direct normal irradiance (DNI) varies. The research results indicate that during a whole day, the main operating parameters of the SAPG system can operate within the safety ranges, and the system power generation almost keeps 330 MW constant, both the solar output power and the carbon dioxide emission reductions are 207.7 MWh and 186.7t/day, respectively.

Thermodynamic and economic analysis of a micro-combined polygeneration system coupled with solar energy and fuels for distributed applications

A novel micro-combined polygeneration system based on solar energy and fuels is designed with aim to simultaneously satisfy energy demands of electricity, heating and cooling in distributed areas. Integration solar radiation with conventional natural gas-fired power systems is conceived to eliminate existing disadvantages of low efficiency and high cost for fuel-only and solar-only plants. Thermodynamic and economic analyses are evaluated to explore performance of proposed systems with three working fluids. Energetic and exergic efficiencies are individually 0.839 and 0.4536, 0.8721 and 0.5852, and 0.8656 and 0.5825 for N2-, He- and Ar-based micro-combined systems under specified power capacity of 100 kW. Solar collector field, compressor, turbine and combustion chamber exhibit four largest exergy destruction, followed orderly by heat exchanger, generator, condenser, evaporator, throttling valve and pump. Preliminary economic analysis indicates that levelized electricity costs of N2-, He- and Ar-based micro-combined systems are 0.112, 0.103 and 0.101 $ kWh−1 with corresponding payback periods of 4.563, 5.090 and 5.138 years. Parametric analysis reveals that five operating parameters (compression ratio, turbine inlet temperature, solar collector field outlet temperature, generator outlet temperature and split ratio) exert noticeable influence on thermal efficiency of micro-combined systems. In conclusion, proposed micro-combined polygeneration system achieves efficient conversation of thermal energy into electricity, heating and cooling at a rational energy utilization for distributed areas.

A novel three-dimensional flow field design and experimental research for proton exchange membrane fuel cells

As an indispensable part of proton exchange membrane fuel cells (PEMFCs), flow field plays a vital role in cell performance especially at high current density. Plenty of works have been done on flow fields, and baffled flow fields become research hotspots in recent years. However, owing to the processing difficulty of these types of flow fields, the vast majority of previous works just stay in the simulation level and very little experimental data can be found. In this work, a series of three-dimensional flow fields (3DFFs) with trapezoid-shaped baffles are designed and machined. Polarization curves of the designed flow fields under various operation conditions are experimentally recorded and it’s no doubt that the designed flow fields can improve cell performance obviously owing to their enhanced oxygen transport and water management. The relation between transport ability and inclination angle was studied detailedly through electrochemical impedance spectroscopy (EIS), limiting current density, polarization curves and pressure drops. The results indicates that the flow field with small inclination angle is more suitable for the scenarios with high water content, such as high relative humidity, low stoichiometric ratio, high operating pressure, and etc. On the contrary, the flow field with big inclination angle is more appropriate for low water content cases. What’s more, pressure drops from cathode inlet to outlet of different flow fields are tested and the results show that the designed flow fields increase little parasitic power compared with the conventional parallel flow field (CPFF), which further proves that the designed flow fields are fit for PEMFCs.

Adaptive UKF-based model predictive control of a Fresnel collector field

One of the ways to improve the efficiency of solar energy plants is by using advanced control and optimization algorithms. In particular, model predictive control strategies have been applied successfully in their control.The control objective of this kind of plant is to regulate the solar field outlet temperature around a desired set-point. Due to the highly nonlinear dynamics of these plants, a simple linear controller with fixed parameters is not able to cope with the changing dynamics and the multiple disturbance sources affecting the field.In this paper, an adaptative model predictive control strategy is designed for a Fresnel collector field belonging to the solar cooling plant installed at the Escuela Superior de Ingenieros in Sevilla. The controller changes the linear model used to predict the future evolution of the system with respect to the operating point.Since only the inlet and outlet temperatures of the heat transfer fluid are measurable, the intermediate temperatures have to be estimated. An unscented Kalman filter is used as a state estimator. It estimates metal-fluid temperature profiles and effective solar radiation.Simulation results are provided comparing the proposed strategy with a PID + feedforward series controller showing better performance. The controller is also compared to a gain scheduling generalized predictive controller (GS-GPC) which has previously been tested at the actual plant with a very good performance. The proposed strategy outperforms these two strategies.Furthermore, two real tests are presented. These tests show that the proposed controller achieves adequate set-point tracking in spite of strong disturbances.

Adaptive incremental state space MPC for collector defocusing of a parabolic trough plant

Commercial solar plants produce energy around a nominal operating point in which the solar field outlet temperature is high and close to the thermal limit of the heat transfer fluid. The main control of the temperature is carried out by means of the fluid flow-rate that circulates through the solar field. Defocusing the collectors is normally used as a safety mechanism to avoid exceeding the thermal limit. However, in situations in which the flow is saturated, the control of defocusing the collectors becomes of vital importance and is the system in charge of controlling the solar field outlet temperature.The paper presents an Adaptive State Space Model Predictive Control strategy with an incremental formulation to control the fourth and third collector defocus angles for field outlet temperature set-point tracking at the nominal operation point, avoiding the Heat Transfer Fluid temperature from exceeding the manufacturer thermal limit (oil degradation). The state space description uses an Unscented Kalman Filter for estimating the non-measurable states. A 50 MW parabolic solar trough plant nonlinear model has been used to design and validate the strategy. Simulation results are presented showing the advantages of using the proposed strategy.

Dynamic modeling and behavior of parabolic trough concentrated solar power system under cloudy conditions

As a promising application of solar energy, parabolic trough concentrating solar power with indirect thermal energy storage has been widely used in concentrating solar power plants constructed in China. The dynamic modeling and behavior of the power plants were important for achieving fast start-up and shut down and to overcome weather disturbances. This study investigated the dynamic characteristics of a 50 MW parabolic trough concentrating solar power plant with indirect thermal energy storage. Simplified cloud disturbances were simulated to obtain the dynamic characteristics of a power block coupled with solar field and thermal energy storage. Simulation results indicated that the thermal inertia of solar field is an order of magnitude larger than that of power block and thermal energy storage subsystems, and the heat transfer fluid temperature at the solar field outlet fluctuates within a narrow range at rated value under the control scheme of solar field. The disturbances caused by heat transfer fluid temperature fluctuation were reduced by thermal energy storage operation. To minimize the generation load fluctuation under thick-cloud condition, the thermal energy stored in solar field could be used to moderate the fluctuation caused by the start-up of thermal energy storage discharging exchanger.

Numerical studies of effect of interdigitated flow field outlet channel width on PEM fuel cell performance

As an extremely important component, flow field plays an important role in a proton exchange membrane (PEM) fuel cell. In this study, a two-dimensional model of interdigitated flow field was developed to simulate the effect of outlet channel width on PEM fuel cell performance using COMSOL Multiphysics, and the simulated results coincided accurately with the experimental results. From the results, the PEM fuel cell performance with narrower outlet channel width was better than that with conventional outlet channel width, since the molarity distribution of oxygen in the porous medium and the electrolyte current density distribution at the membrane cross section were more uniform, and the drainage capacity was stronger. The simulated results have certain reference significance for the design and optimization of interdigitated flow field.