1,098 research outputs found
Dynamic Modeling of Organic Rankine Cycle Power Systems
No full textNew promising applications of organic Rankine cycle (ORC) technology, e.g., concentrated solar power, automotive heat recovery and off-grid distributed electricity generation, demand for more dynamic operation of ORC systems. Accurate physically-based dynamic modeling plays an important role in the development of such systems, both during the preliminary design as an aid for configuration and equipment selection, and for
control design and optimization purposes. A software library of modular reusable dynamic models of ORC components has been developed in the MODELICA language and is documented in the paper. The model of an exemplary ORC system, namely the 150
kW e Tri-O-Gen ORC turbogenerator is validated using few carefully conceived experiments. The simulations are able to reproduce steady-state and dynamic measurements of
key variables, both in nominal and in off-design operating conditions. The validation of the library opens doors to control-related studies, and to the development of more challenging dynamic applications of ORC power plants
Notes on the evolution of cemetery areas in Italy
No full textRecent changing in funerary architecture in Ital
The flexible asymmetric shock tube (FAST): A Ludwieg tube facility for wave propagation measurements in high-temperature vapours of organic fluids
No full textThis paper describes the commissioning of the flexible asymmetric shock tube (FAST), a novel Ludwieg tube-type facility designed and built at Delft University of Technology, together with the results of preliminary experiments. The FAST is conceived to measure the velocity of waves propagating in dense vapours of organic fluids, in the so-called non-ideal compressible fluid dynamics (NICFD) regime, and can operate at pressures and temperatures as high as 21 bar and 400 ?C, respectively. The set-up is equipped with a special fast-opening valve, separating the high-pressure charge tube from the low-pressure plenum. When the valve is opened, a wave propagates into the charge tube. The wave speed is measured using a time-of-flight technique employing four pressure transducers placed at known distances from each other. The first tests led to the following results: (1) the leakage rate of 5×10?4mbarl s?1 for subatmospheric and 5×10?2mbarl s?1 for a superatmospheric pressure is compatible with the purpose of the conceived experiments, (2) the process start-up time of the valve has been found to be between 2.1 and 9.0 ms, (3) preliminary rarefaction wave experiments in the dense vapour of siloxane D6 (dodecamethylcyclohexasiloxane, an organic fluid) were successfully accomplished up to temperatures of 300?C, and (4) a method for the estimation of the speed of sound from wave propagation experiments is proposed. Results are found to be within 2.1 % of accurate model predictions for various gases. The method is then applied to estimate the speed of sound of D6 in the NICFD regime.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin
Working Fluid Design for Organic Rankine Cycle (ORC) Systems
No full textThe Organic Rankine Cycle is an energy conversion cycle similar to the conventional Rankine cycle which runs on a working fluid other than water. The selection of a working fluid is a critical part of designing an Organic Rankine Cycle (ORC) system. The number of fluid types actually used in commercial ORC power plants do not justify the number of fluid selection studies present in scientific literature. Hence the objective of this work is to develop a tool which simultaneously optimizes the energy conversion process and selects the optimum working fluid for a given heat source. It is based on a framework that uses a continuous-molecular targeting approach which allows for an integrated working fluid and system design. The process is modeled in Cycle Tempo, a modern graphical tool for thermodynamic analysis and optimization of systems for the production of electricity, heat and refrigeration. The system is simultaneously optimized with the pure component parameters of PCP-SAFT equation of state using a state-of-the-art optimization suite. The working fluid is selected by comparison of the pure component parameters of the PCP-SAFT equation of state with real fluids. A preliminary turbine model implemented directs the tool to generate suitable fluids for practically realistic systems. The tool has been tested for a waste heat recovery system for heavy-duty truck engines based on an ORC turbogenerator. The choice of working fluid is restricted to only the siloxane class which not only adheres to the technical, environmental, and toxicological requirements typical of the automotive sector but also allows for the implementation of a preliminary radial turbine model, whose shaft can be lubricated by the working fluid itself. The turbine has been modeled by applying the methodology of using non-dimensional parameters. Future work will be devoted to implement detailed component models and extending the scope of fluid selection to other organic fluid classes.Energy TechnologyProcess and EnergyMechanical, Maritime and Materials Engineerin
Working fluid design for organic rankine cycle systems (ORC)
No full textThe Organic Rankine Cycle is an energy conversion cycle similar to the conventional Rankine cycle which runs on a working fluid other than water. The selection of a working fluid is a critical part of designing an Organic Rankine Cycle (ORC) system. The number of fluid types actually used in commercial ORC power plants do not justify the number of fluid selection studies present in scientific literature. Hence the objective of this work is to develop a tool which simultaneously optimizes the energy conversion process and selects the optimum working fluid for a given heat source. It is based on a framework that uses a continuous-molecular targeting approach which allows for an integrated working fluid and system design. The process is modeled in Cycle Tempo, a modern graphical tool for thermodynamic analysis and optimization of systems for the production of electricity, heat and refrigeration. The system is simultaneously optimized with the pure component parameters of PCP-SAFT equation of state using a state-of-the-art optimization suite. The working fluid is selected by comparison of the pure component parameters of the PCP-SAFT equation of state with real fluids. A preliminary turbine model implemented directs the tool to generate suitable fluids for practically realistic systems. The tool has been tested for a waste heat recovery system for heavy-duty truck engines based on an ORC turbogenerator. The choice of working fluid is restricted to only the siloxane class which not only adheres to the technical, environmental, and toxicological requirements typical of the automotive sector but also allows for the implementation of a preliminary radial turbine model, whose shaft can be lubricated by the working fluid itself. The turbine has been modeled by applying the methodology of using non-dimensional parameters. Future work will be devoted to implement detailed component models and extending the scope of fluid selection to other organic fluid classes.Energy TechnologyProcess & EnergyMechanical, Maritime and Materials Engineerin
Experimental Observation of Non-Ideal Compressible Fluid Dynamics: with Application in Organic Rankine Cycle Power Systems
No full textFlight Performance and PropulsionEnergy Technolog
Collective Entrainment and Confinement Amplify Transport by Schooling Microswimmers
No full textMicroswimmers can serve as cargo carriers that move deep inside complex flow networks. When a school collectively entrains the surrounding fluid, their transport capacity can be enhanced. This effect is quantified with good agreement between experiments with self-propelled droplets and a confined Brinkman squirmer model. The volume of liquid entrained can be much larger than the droplet itself, amplifying the effective cargo capacity over an order of magnitude, even for dilute schools. Hence, biological and engineered swimmers can efficiently transport materials into confined environments
Wave Speed Measurements in Non-Ideal Compressible Flows Using the Flexible Asymmetric Shock Tube (FAST)
No full textNon-ideal compressible fluid dynamics (NICFD) are defined as compressible fluid flows occurring in the dense vapour, dense vapour-liquid equilibrium or supercritical thermodynamic region. This type of flow can occur in expanders of organic Rankine cycle power plants. In order to study NICFD, a Ludwieg tube-type facility has been designed and constructed at Delft University of Technology. A large variety of fluids can be employed in the facility, but for this study D6 siloxane is chosen as working fluid due to its high thermal stability and the possibility of encountering non-classical gasdynamic phenomena. This compound belongs to the siloxane class, which are also used as working fluids in ORC power systems. Gasdynamic experiments within the NICFD region are presented from which the wave speed and speed of sound can be inferred using the time-of-flight technique. These data can be used to improve and validate thermodynamic models
Stereoscopic PIV on a delta wing in supersonic flow
No full textEver since the 1950s delta wings are being used as an efficient planform for supersonic flight. Over time extensive research on the aerodynamics of this type of wings has been performed using many different measurement techniques. Due to technical difficulties, measurements on delta wings in a supersonic flow are still scarce and often limited to qualitative data only. The addition of PIV as a diagnostic tool in aerodynamics opened doors for new measurements. Nowadays PIV is a well-established non-intrusive measurement method that is being applied in large scale subsonic industrial facilities on a regular basis and in research facilities in all flow regimes. Stereoscopic PIV measurements on delta wings are done previously in sub- and transonic flow, and one 2C-PIV experiment has been done on a delta wing in supersonic flow at moderate angle of attack. The motivation of the current investigation is to perform stereo-PIV measurements around a sharp-edged delta wing in a supersonic flow at high angle of attack using the latest advances in PIV. Furthermore an extension is made to a similar setup in the industrial facility of DNW-SST on the EUROSUP model. The flow around a delta wing is succesfully described at different Mach numbers and for several angles of attack. A spanwise scan using individual measurement planes in streamwise orientation has been made, which are combined to construct a mean flow field in the complete volume. The response of the tracer particles is measured by an oblique shock test, from which the slip velocity with respect to the flow and the drift from the flow path, due to their inertia, is determined. Schlieren, shadowgraphy and oil flow visualisation are applied to give additional information on the flow. Several flow features have been measured by PIV. As expected a vortex is present on the leeward surface of the wing. Due to the large deflection of the flow on the windward surface, a detached shock is present before the leading edge extending to the expansion side of the wing. Attached to the vortex an inboard shock wave has been measured. Furthermore the flow field appeared to be conical, i.e. the flow variables are constant on rays emerging from the apex. A similar stereo-PIV setup has been succesfully applied in the industrial supersonic facility SST at DNW using a high-repetition acquisition system including a model sliding mechanism to increase data production. However, due to the large size of the seeding particles in this campaign, the data generated in this tunnel remains questionable, and a thorough investigation on the seeding production is necessary to acquire reliable PIV data in this facility.AerodynamicsAerospace Engineerin
Anomalous current transients in organic field-effect transistors
No full textHere we study the origin of the gate bias-stress effect in organic p-type transistors. Based on water-mediated exchange between holes in the semiconductor and protons in the gate dielectric, we predict anomalous current transients for a non-constant gate bias, while ensuring accumulation. When applying a strongly negative gate bias followed by a less negative bias a back-transfer of protons to holes and an increase of the current is expected. We verify this counterintuitive behavior experimentally and can quantitatively model the transients with the same parameters as used to describe the threshold voltage shift
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