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See detailCharge-sensitive methods for the off-design performance characterization of organic Rankine cycle (ORC) power systems
Dickes, Rémi ULiege

Doctoral thesis (2019)

The organic Rankine cycle (ORC) is among the most suited technologies to convert low-grade and low-capacity heat sources into useful work. For many reasons - including predictive control, optimal sizing ... [more ▼]

The organic Rankine cycle (ORC) is among the most suited technologies to convert low-grade and low-capacity heat sources into useful work. For many reasons - including predictive control, optimal sizing or performance forecast - a proper understanding and characterization of the ORC behaviour under off-design conditions is of significant interest. In order to avoid any intrinsic state assumption, predictive models must account for both fundamental conversation laws of hermodynamics, namely the conservation of energy and the conservation of mass. Besides of modelling the energy transfers, a true off-design model must account for the constant amount of working fluid in the system and simulate its distribution among the different components. Although well-known for HVAC systems, such charge-sensitive considerations are quasi absent for the ORC technology and existing models have never been completely validated. The goal intended by this PhD thesis is to fill this gap. To begin this work, experiments are conducted to assess the fluid distribution and the impact of the charge on a real system operation. To this end, a 2 kWe ORC test rig is constructed and tested over wide range of conditions. Besides of standard thermohydraulic sensors, the fluid charge distribution is measured on-line by bending load cells and infrared imaging techniques. Following a complete experimental campaign (which includes more than 300 steady-state points), a dual reconciliation method is applied on the raw measurements to obtain a reference dataset. An extensive study of the experimental data is then conducted. Among many results, the important contribution of the heat exchangers in the charge inventory is highlighted, so as the impact of oil circulation on the ORC performance rating. Following this experimental study, a complete modelling library is developed to replicate and extrapolate the system off-design behaviour. The intended goal is to create a true performance simulator, i.e. a predictive tool able to estimate the ORC behaviour based solely on its boundary environment (without state assumption, i.e. accounting for the charge distribution in the system). In a first step, a miscibility model of R245fa/POE oil is developed to account for the presence of the lubricant in the ORC operation. Afterwards, the modelling of each system component is conducted, with a particular focus on the heat exchangers and their charge estimation. Then a global ORC model is constructed by coupling the various components sub-models accordingly to a robust resolution scheme. The ORC model predictions are ultimately confronted to the experimental measurements, both in terms of thermodynamics and charge inventory predictions, and a good fit is demonstrated for all the model outputs. Finally, the utility of such a charge- and lubricant-sensitive ORC model is highlighted for different tasks. Considering the experimental test rig as case study, the off-design modelling tool is employed (i) to fully characterize the ORC response under off-design conditions, (ii) to prevent operating conditions where pump cavitation is likely to occur, (iii) to build optimal performance mappings for full- and part-load operations, and, finally, (iv) to optimally select the charge of working fluid and to accordingly size the liquid receiver. [less ▲]

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See detailInfrared imaging of a multi-zone condenser for heat transfer coefficients assessment
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Lemort, Vincent ULiege

in Proceedings of ECOS 2019 (2019, June)

Although crucial for simulations, a proper identification of the convective heat transfer coefficients in multi-zone heat exchangers is a challenging task. While well instrumented thermal systems permit ... [more ▼]

Although crucial for simulations, a proper identification of the convective heat transfer coefficients in multi-zone heat exchangers is a challenging task. While well instrumented thermal systems permit to accurately record the energy balance in such components, the sole knowledge of the global heat transfer rate is not enough to reliably assess these coefficients. In this work, it is proposed to use the zones spatial distribution (i.e. the spatial fraction occupied by the liquid phase, the vapour phase and/or the two-phase regions) as a second identification criteria. An air-cooled condenser into which flows R245fa is considered as case study and a dedicated infrared imaging method is presented to assess the spatial distribution of its different phases. These new data, combined with standard heat transfer rate measurements, are exploited to identify the best heat transfer correlations pre-selected from the scientific literature. In order to further improve the model predictions, the original heat transfer correlations are ultimately adjusted so as to best fit both the global heat transfer rate and the zones distribution data. [less ▲]

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See detailSteady-state and dynamic validation of a parabolic trough collector model using the ThermoCycle Modelica library
Desideri, Adriano ULiege; Dickes, Rémi ULiege; Bonilla, Javier et al

in Solar Energy (2018), 174

Small-capacity (<200 kWel) concentrated solar power plants has been recognized as a promising technology for micro power applications. In particular, parabolic trough collectors have been identified as ... [more ▼]

Small-capacity (<200 kWel) concentrated solar power plants has been recognized as a promising technology for micro power applications. In particular, parabolic trough collectors have been identified as the most promising focusing technology. In this context, physics-based dynamic model of parabolic trough constitutes a significant tool for the further development of the technology, allowing to evaluate and optimize response times during transients, or to implement and test innovative control strategies. In this contribution, the dynamic model of a parabolic trough line based on the ThermoCycle Modelica library is validated against steady-state and transient experimental results from the parabolic trough test loop available at the Plataforma Solar de Almería, Spain. The simulation results are in good agreement with the measurements, both in steady-state and in transient conditions. The validated model is readily usable to investigate demanding dynamics-based problems for low capacity solar power systems. [less ▲]

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See detailOnline Measurement Of The Working Fluid Mass Repartition In A Small-Scale Organic Rankine Cycle Power System
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Quoilin, Sylvain ULiege et al

in Proceedings of Purdue 2018 (2018, July 12)

This paper presents an experimental investigation of the working fluid charge repartition in a 2kWe ORC (organic Rankine cycle) test bench. To this end, an online measurement apparatus is built and fully ... [more ▼]

This paper presents an experimental investigation of the working fluid charge repartition in a 2kWe ORC (organic Rankine cycle) test bench. To this end, an online measurement apparatus is built and fully calibrated to evaluate the charge enclosed in the three heat exchangers and the liquid receiver of the ORC unit. By changing all the system boundary conditions (including the charge enclosed in the test rig), an experimental database of 304 steady-state points is gathered and post-treated. The charge inventories obtained by online measurements demonstrate promising results on average but experience high uncertainties when considering each point individually (i.e. the uncertainty on the global inventory is around ± 2.5 kg for a total charge of 31.2 kg). Deviations of the evaporator mass measurements are identified at high temperature of the heat source and discussed in details. A reconciliation method is applied to the raw measurements in order to retrieve consistent charge inventories while accounting for the different sources of uncertainty. Ultimately, the paper analyses the impact of increasing the charge in the ORC and how this parameter influences the thermodynamic state of the system. [less ▲]

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See detailExperimental performance of a field of parabolic trough collectors for small-scale power generation
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Thiebaut, Jérémie et al

in Proceedings of ECOS 2018 (2018, June 23)

The present work investigates the solar field performance of a pilot system installed at the University of Liège in Belgium. The system includes eight parabolic trough collectors connected in series (66m² ... [more ▼]

The present work investigates the solar field performance of a pilot system installed at the University of Liège in Belgium. The system includes eight parabolic trough collectors connected in series (66m² in total) and is aimed for small-scale power generation (2kWe) at low-temperature operation (150°C max.). The paper describes the test facility and presents experimental data gathered under various operating conditions. After posttreatment, the measurements are used to calibrate a deterministic model of the solar collectors. This model is used to better estimate the various sources of losses during the solar energy conversion and to investigate potential means of performance improvements. While the collection efficiency recorded experimentally does not exceed 30%, it is shown that an improvement of the tracking could raise this value to 65% and thus meet the design expectations. [less ▲]

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See detailExperimental validation of heat transport modeling in large solar thermal plant.
Sartor, Kevin ULiege; Dickes, Rémi ULiege; Resimont, Thibaut ULiege et al

Scientific conference (2018, June)

Solar thermal plants are often considered as a convenient and environmental-friendly way to supply heat to buildings or low temperature industrial processes. Some modelling techniques are required to ... [more ▼]

Solar thermal plants are often considered as a convenient and environmental-friendly way to supply heat to buildings or low temperature industrial processes. Some modelling techniques are required to assess the dynamic behaviour of solar thermal plants in order to control them correctly. This aspect is reinforced while large plants are considered. Indeed some atmospheric conditions as local clouds could have significant influence on the outlet temperature of the solar field. A common modelling approach to assess the heat transport in pipes is the one-dimensional finite volume method. However previous work shows limitations in the assessment of the temperatures and in the computational time require simulating large pipe networks. In this contribution, a previous alternative method developed and validated in a district heating network is used and extended to a solar thermal plant considering the thermal solar gain and the inertia of the pipes. The present contribution intends to experimentally validate this model on an existing solar plant facility available at the Plataforma Solar de Almeria in Spain. [less ▲]

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See detailCharge-sensitive modelling of organic Rankine cycle power systems for off-design performance simulation
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Guillaume, Ludovic ULiege et al

in Applied Energy (2018), 212

This paper focuses on a charge-sensitive model to characterize the off-design performance of low-capacity organic Rankine cycle (ORC) power systems. The goal is to develop a reliable steady-state model ... [more ▼]

This paper focuses on a charge-sensitive model to characterize the off-design performance of low-capacity organic Rankine cycle (ORC) power systems. The goal is to develop a reliable steady-state model that only uses the system boundary conditions (i.e. the supply heat source/heat sink conditions, the mechanical components rotational speeds, the ambient temperature and the total charge of working fluid) in order to predict the ORC performance. To this end, sub-models are developed to simulate each component and they are assembled to model the entire closed-loop system. A dedicated solver architecture is proposed to ensure high-robustness for charge-sensitive simulations. This work emphasizes the complexity of the heat exchangers modelling. It demonstrates how state-of-the-art correlations may be used to identify the convective heat transfer coefficients and how the modelling of the charge helps to assess their reliability. In order to compute the fluid density in two-phase conditions, five different void fraction models are investigated. A 2 kWe unit is used as case study and the charge-sensitive ORC model is validated by comparison to experimental measurements. Using this ORC model, the mean percent errors related to the thermal power predictions in the heat exchangers are lower than 2%. Regarding the mechanical powers in the pump/expander and the net thermal efficiency of the system, these errors are lower than 11.5% and 11.6%, respectively. [less ▲]

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See detailExperimental investigation and optimal performance assessment of four volumetric expanders (scroll, screw, piston and roots) tested in a small-scale organic Rankine cycle system
Dumont, Olivier ULiege; Parthoens, Antoine ULiege; Dickes, Rémi ULiege et al

in Energy (2018)

The aim of this paper is to facilitate the selection of the expander for a small-scale organic Rankine cyclebased on an experimental comparison of a piston, a screw, a scroll and a roots expander. First ... [more ▼]

The aim of this paper is to facilitate the selection of the expander for a small-scale organic Rankine cyclebased on an experimental comparison of a piston, a screw, a scroll and a roots expander. First, based on aliterature review, a comparison between these four technologies of volumetric expansion machines isperformed. Afterward, four displacement expanders [2e4 kW] are tested on two similar small-scale ORCunit withfluid R245fa. The maximum effective isentropic efficiencies measured are 53% for the pistonexpander and the screw expander, 76% for the variable-speed scroll and 48% for the roots machine.However, these performances do not reflect the highest efficiencies achievable by each expander: thetest-rig presents experimental limitations in terms of massflow rate and pressure drop (among others)that restricts the achievable operating conditions. The calibration of semi-empirical models based on themeasurements allows to overcome this issue and to predict the isentropic efficiency in optimal condi-tions despite the limitations of the test-rigs. Based on experimental results, extrapolated prediction ofthe semi-empirical model and practical considerations, some guidelines are drawn to help the reader toselect properly a volumetric expander. [less ▲]

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See detailTechnical and economic optimization of subcritical, wet expansion and transcritical Organic Rankine Cycle (ORC) systems coupled with a biogas power plant
Dumont, Olivier ULiege; Dickes, Rémi ULiege; De Rosa, M. et al

in Energy Conversion and Management (2018), 157

Generally, >40% of the useful energy (cooling engine and exhaust gases) are wasted by a biogas power plant through the cooling radiator and the exhaust gases. An efficient way to convert this waste heat ... [more ▼]

Generally, >40% of the useful energy (cooling engine and exhaust gases) are wasted by a biogas power plant through the cooling radiator and the exhaust gases. An efficient way to convert this waste heat into work and eventually electricity is the use of an organic Rankine cycle (ORC) power system. Over the last few years, different architectures have been widely investigated (subcritical, wet expansion and trans-critical). Despite the promising performances, realistic economic and technical constraints, also related to the application, are required for a meaningful comparison between ORC technologies and architectures. Starting from the limited literature available, the aim of the present paper is to provide a methodology to compare sub-critical, trans-critical and wet expansion cycles and different types of expanders (both volumetric and turbomachinery) from both technical and economic point of view, which represent one of the main novel aspects of the present work. In particular, the paper focuses on the thermo-economic optimization of an ORC waste heat recovery unit for a 500 kWe biogas power plant located in a detailed regional market, which was not investigated yet. By means of a genetic algorithm, the adopted methodology optimizes a given economic criteria (Pay-Back Period, Net Present Value, Profitability Index and Internal Rate of Return) while respecting technical constraints (expander limitations) and thermodynamic constraints (positive pinch points in heat exchangers, etc.). The results show that optimal ORC solutions with a potential of energy savings up to 600 MWh a year and with a pay-back period lower than 3 years are achievable in the regional market analysed. © 2017 Elsevier Ltd [less ▲]

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See detailPerformance correlations for characterizing the optimal off-design operation of an ORC power system
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Quoilin, Sylvain ULiege et al

in Energy Procedia (2017), 129

The goal of this work is to develop a set of simple correlations in order to characterize the optimal off-design performance of an ORC power system. To this end, a 2kWe ORC test rig is investigated as ... [more ▼]

The goal of this work is to develop a set of simple correlations in order to characterize the optimal off-design performance of an ORC power system. To this end, a 2kWe ORC test rig is investigated as case study and a validated off-design model is used to assess the highest net power generation achievable by the system over its complete range of operating conditions. The off-design model employed is charge-sensitive (i.e. it imposes the total mass of refrigerant in the system) which permits to predict the ORC state (i.e. its pressures, temperatures, mass flow rates, subcooling, etc.) based on the system boundary conditions only. Since such modelling approach and optimization process are time-consuming, a set of simple analytical equations is developed so as to easily predict the optimal performance of the ORC systems. [less ▲]

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See detailEffects of void fraction and heat transfer correlations in a charge-sensitive ORC model – a comparison with experimental data
Dickes, Rémi ULiege; Guillaume, Ludovic ULiege; Dumont, Olivier ULiege et al

in Proceedings of ECOS 2017 (2017, July 02)

In order to properly evaluate the off-design performance of an ORC unit, it is important to use simulation tools that minimize the number of assumptions regarding the system state. To avoid imposing the ... [more ▼]

In order to properly evaluate the off-design performance of an ORC unit, it is important to use simulation tools that minimize the number of assumptions regarding the system state. To avoid imposing the condenser subcooling (or any other equivalent state variable), the ORC model should account for the mass repartition of working fluid through the unit in function of the operating conditions. Among the various components constituting ORC power systems, the proper modelling of the mass of working fluid enclosed in the heat exchangers is of primary importance. The goal of this work is to develop such a reliable charge-sensitive ORC model. To this end, a 2kWe recuperative ORC system is used as case study and experimental measurements are used as reference dataset. The ORC system features two brazed plate heat exchangers and one fin coil condenser. For these three heat exchangers, a large set of empirical correlations is investigated in order to evaluate both the fluids void fractions and their convective heat transfer coefficients. By comparing the models predictions with the experimental data, the study highlights the limitations of existing correlations and investigates three different correction methods to improve them. Ultimately, the analysis compares nine models of brazed plate heat exchangers, two models of condenser, three correction methods for improving the heat transfer correlations and four void fraction methods. Accounting for every combination possible, 288 different models of the ORC are compared for predicting both the heat exchangers thermal performance and the total mass enclosed in the ORC unit. Out of this study, the best modelling approach is identified and details of its charge inventory predictions are presented. [less ▲]

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See detailModelling of organic Rankine cycle power systems in off-design conditions: an experimentally-validated comparative study
Dickes, Rémi ULiege; Dumont, Olivier ULiege; Daccord, Rémi et al

in Energy (2017), 123

Because of environmental issues and the depletion of fossil fuels, the world energy sector is undergoing many changes toward increased sustainability. Among the many fields of research and development ... [more ▼]

Because of environmental issues and the depletion of fossil fuels, the world energy sector is undergoing many changes toward increased sustainability. Among the many fields of research and development, power generation from low-grade heat sources is gaining interest and the organic Rankine cycle (ORC) is seen as one of the most promising technologies for such applications. In this paper, it is proposed to perform an experimentally-validated comparison of different modelling methods for the off-design simulation of ORC-based power systems. To this end, three types of modelling paradigms (namely a constant-efficiency method, a polynomial-based method and a semi-empirical method) are compared both in terms of their fitting and extrapolation capabilities. Post-processed measurements gathered on two experimental ORC facilities are used as reference for the models calibration and evaluation. The study is first applied at a component level (i.e. each component is analysed individually) and then extended to the characterization of the entire organic Rankine cycle power systems. Benefits and limi- tations of each modelling method are discussed. The results show that semi-empirical models are the most reliable for simulating the off-design working conditions of ORC systems, while constant-efficiency and polynomial-based models are both demonstrating lack of accuracy and/or robustness. [less ▲]

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See detailExperimental investigation of four volumetric expanders
Dumont, Olivier ULiege; Dickes, Rémi ULiege; Lemort, Vincent ULiege

in Energy Procedia (2017)

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See detailThermo-economic optimization during preliminary design phase of organic Rankine cycle systems for waste heat recovery from exhaust and recirculated gases of heavy duty trucks
Guillaume, Ludovic ULiege; Legros, Arnaud; Dickes, Rémi ULiege et al

in IMechE (Ed.) Vehicle Thermal Management Systems conference (2017)

Waste heat recovery (WHR) Organic Rankine Cycle (ORC) system is a very promising technology for reducing fuel consumption and consequently the CO2 emissions of future heavy-duty trucks (HDT). Nonetheless ... [more ▼]

Waste heat recovery (WHR) Organic Rankine Cycle (ORC) system is a very promising technology for reducing fuel consumption and consequently the CO2 emissions of future heavy-duty trucks (HDT). Nonetheless, the adoption of this technology in the automotive domain requires specific R&D activities going from the system definition to the on-board integration. This study focuses on the preliminary design phase of ORC systems recovering the heat wasted from two of the sources available on a HDT: the exhaust and recirculated gases. From these heat sources and their combinations, 6 possible architectures are identified. On the other hand, 4 volumetric expansion machine technologies are considered (scroll, screw, piston and vane Expanders). At the end, 24 topologies are therefore modelled considering the main components (Pump, Heat exchangers, Expansion machines). A three-step optimization method is proposed to identify the most promising system. First, the most suitable conditions are identified for the design of the ORC systems using a simple model of volumetric expansion machine. In a second step, the design phase, using more detailed models for the expansion machines, a thermos-economic optimization is performed. Finally, in a third step, the output power of the latter system models is maximized in off-design conditions, optimizing the evaporating pressure and the overheating degree. [less ▲]

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See detailChapter 16 - Solar thermal powered Organic Rankine Cycles
Orosz, Matthew; Dickes, Rémi ULiege

in Macchi, Ennio; Astolfi, Marco (Eds.) Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications (2016)

Reference chapter about solar-based organic Rankine cycle power systems published in the book "Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications"

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See detailORCmKit: an open-source library for organic Rankine cycle modelling and analysis
Dickes, Rémi ULiege; Ziviani, Davide; van den Broek, Martjin et al

in Proceedings of ECOS 2016 (2016, June 20)

As for many other technologies, modelling and simulation of organic Rankine cycles (ORCs) are crucial for design, optimization and control purposes. However, model development is often time consuming and ... [more ▼]

As for many other technologies, modelling and simulation of organic Rankine cycles (ORCs) are crucial for design, optimization and control purposes. However, model development is often time consuming and the scientific community lacks of open-access tools to study ORC systems. For these reasons, researchers from the universities of Liège and Ghent in Belgium gathered their knowledge and created “ORC modelling Kit” (ORCmKit), an open-source library dedicated to the steady-state simulation and analysis of organic Rankine cycles. Both component-level and cycle-level models are provided and different ORC architectures can be simulated. For each of the main component of ORC systems, different models are available with increasing complexity which allows a wide range of modelling possibilities. In order to remain general and accessible to as many people as possible, three widely used programming languages are covered within ORCmKit, i.e. Matlab, Python and EES (Engineering Equation Solver). Besides source codes, ORCmKit also includes calibration tools for empirical and semi-empirical models as well as a complete documentation for ease of use. [less ▲]

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See detailOrganic Rankine cycle modelling and the ORCmKit library: analysis of R1234ze(Z) as drop-in replacement of R245fa for low-grade waste heat recovery
Ziviani, Davide; Dickes, Rémi ULiege; Quoilin, Sylvain ULiege et al

in Proceedings of ECOS 2016 (2016, June 20)

Due to the wide interest in organic Rankine cycles (ORCs) as a sustainable technology and the importance of numerical analyses and optimization procedures while considering such systems, we created a ... [more ▼]

Due to the wide interest in organic Rankine cycles (ORCs) as a sustainable technology and the importance of numerical analyses and optimization procedures while considering such systems, we created a dedicated open-source library named “ORC modelling Kit” (ORCmKit). The comprehensive library includes single com-ponents and overall models for subcritical, transcritical and supercritical ORCs. Three main programming environments are currently supported: Matlab, Python and EES (Engineering Equation Solver). A detailed steady-state cycle model of a small-scale regenerative ORC with a single-screw expander is used to evalu-ate the performance influence of R1234ze(Z) as a drop-in replacement of R245fa currently used in the instal-lation. The ORC system is used to recover low-grade waste heat with a temperature range between 90°C and 120°C. A thermal oil heater is used to simulate the heat source. A parametric study is carried out to in-vestigate the performance of the system throughout the range of interest in order to optimize the ORC with R1234ze(Z). [less ▲]

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See detailSolar-based ORC systems
Dickes, Rémi ULiege

Conference (2016, May 20)

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